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Electrically Induced Resistance Training in Individuals With Motor Complete Spinal Cord Injury
Archives of Physical Medicine and Rehabilitation journal homepage: www.archives-pmr.org Archives of Physical Medicine and Rehabilitation 2013;94:2166-73
ORIGINAL ARTICLE
Electrically Induced Resistance Training in Individuals With Motor Complete Spinal Cord Injury Terence E. Ryan, PhD,a Jared T. Brizendine, MS,a Deborah Backus, DPT, PhD,b Kevin K. McCully, PhDa From the aDepartment of Kinesiology, University of Georgia, Athens, GA; and bCrawford Research Institute, Shepherd Center, Atlanta, GA.
Abstract Objective: To examine the effects of 16 weeks of electrically induced resistance training on insulin resistance and glucose tolerance, and changes in muscle size, composition, and metabolism in paralyzed muscle. Design: Pre-post intervention. Setting: University-based trial. Participants: Participants (NZ14; 11 men and 3 women) with chronic (>2y post spinal cord injury), motor complete spinal cord injury. Intervention: Home-based electrically induced resistance exercise training twice weekly for 16 weeks. Main Outcome Measures: Plasma glucose and insulin throughout a standard clinical oral glucose tolerance test, thigh muscle and fat mass via dual-energy x-ray absorptiometry, quadriceps and hamstrings muscle size and composition via magnetic resonance imaging, and muscle oxidative metabolism using phosphorus magnetic resonance spectroscopy. Results: Muscle mass increased in all participants (mean SD, 39%27%; range, 5%e84%). The mean change SD in intramuscular fat was 3%22%. Phosphocreatine mean recovery time constants SD were 10224 and 7718 seconds before and after electrical stimulation-induced resistance training, respectively (P<.05). There was no improvement in fasting blood glucose levels, homeostatic model assessment calculated insulin resistance, 2-hour insulin, or 2-hour glucose. Conclusions: Sixteen weeks of electrical stimulation-induced resistance training increased muscle mass, but did not reduce intramuscular fat. Similarly, factors associated with insulin resistance or glucose tolerance did not improve with training. We did find a 25% improvement in mitochondrial function, as measured by phosphocreatine recovery rates. Larger improvements in mitochondrial function may translate into improved glucose tolerance and insulin resistance. Archives of Physical Medicine and Rehabilitation 2013;94:2166-73 ª 2013 by the American Congress of Rehabilitation Medicine
Spinal cord injury (SCI) currently affects approximately 250,000 individuals in the U.S.,1 with around 10,000 new cases each year. With advances in science and medicine, the life expectancy after SCI is nearly identical to individuals without SCI.1 Mortality from cardiovascular disease is the leading cause of death in individuals with SCI and occurs at a much higher rate than able-bodied individuals, such that mortality from conditions, such as coronary artery disease, is more likely to occur prematurely in individuals with SCI.2,3 Prevalence of symptomatic cardiovascular disease is 30% to 50% in the SCI population compared with 5% to
Supported by the National Institutes of Health (grant no. R01-HD-039676-11). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.
10% prevalence in the able-bodied population.3,4 Risk factors for cardiovascular disease, namely hyperlipidemia, metabolic syndrome, and diabetes mellitus, are also more common in the SCI population.3 Dyslipidemia also occurs as rapidly as a year after injury, and severity is linked to duration of injury and is seen among a wide range of body mass index scores.2 The prevalence of metabolic syndrome and diabetes mellitus is 23% and 22%, respectively, in SCI populations, more than twice as high as the prevalence for these 2 conditions in the able-bodied population.5 Increased mortality from cardiovascular and metabolic diseases in the SCI population is because of a multitude of physiological alterations after injury.6 After paralysis, skeletal muscle atrophy occurs rapidly, and the muscle cross-sectional area can be as low as 30% to 50% compared with able-bodied controls.7,8 Furthermore, skeletal muscle atrophy has also been
0003-9993/13/$36 - see front matter ª 2013 by the American Congress of Rehabilitation Medicine http://dx.doi.org/10.1016/j.apmr.2013.06.016
Neuromuscular electrical stimulation resistance training in SCI linked with increasing intramuscular fat (IMF) levels in SCI.8,9 Atrophy and increased IMF are both associated with glucose intolerance9,10 and diabetes mellitus/metabolic syndrome,11 dyslipidemia,10 cardiovascular disease,12 and osteoporosis.13 Many of these factors are influenced by the lack of physical activity, both because of paralysis and a lack of opportunities to engage in physical activity. Neuromuscular electrical stimulation (NMES), particularly resistance exercise training (RET), effectively induces skeletal muscle hypertrophy in participants with chronic SCI, with increases in muscle volume from 39% to 75%.14,15 RET using NMES in paralyzed musculature may result in increased levels of metabolically active muscle tissue, which can aid in postprandial glucose removal, thus reducing the risk of diabetes. Furthermore, NMES training may decrease fatty infiltration of IMF16 and could improve the reduced muscle oxidative capacity found in individuals with SCI.17 NMES could potentially represent a cost-effective means of reducing the health care cost associated with SCI by reducing risk factors associated with chronic diseases. Ragnarsson18 provides a comprehensive review of the literature regarding electrical stimulation therapies in SCI. The purpose of this study was to examine the effects of 16 weeks of NMES-induced RET of the knee extensors on oral glucose tolerance, lipid profiles, muscle cross-sectional area and IMF, and skeletal muscle oxidative capacity in individuals with chronic SCI. We hypothesized that RET would increase the muscle cross-sectional area and decrease IMF and would improve oral glucose tolerance, lipid profiles, and skeletal muscle oxidative capacity.
Methods Participants Fourteen participants (11 men, 3 women) with chronic, motor complete SCI were tested in this study. Participants were required to be at least 2 years post injury and between 18 and 65 years of age. Participants were recruited from the Shepherd Center (Atlanta, GA) and the local community (Athens, GA and surrounding counties). This study was conducted with the approval of the Institutional Review Boards at the University of Georgia (Athens,
List of abbreviations: DXA FES HOMA HOMA-IR HOMA-%B HOMA-%S IMF MRI NMES OGTT PCr RET SCI
dual-energy x-ray absorptiometry functional electrical stimulation homeostatic model assessment homeostatic model assessment calculated insulin resistance homeostatic model assessment calculated beta-cell function homeostatic model assessment calculated insulin sensitivity intramuscular fat magnetic resonance imaging neuromuscular electrical stimulation oral glucose tolerance test phosphocreatine resistance exercise training spinal cord injury
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2167 GA) and the Shepherd Center (Atlanta, GA), and all participants gave written, informed consent before testing.
Study design A pretest/posttest experimental design was implemented for this study. Inclusion criteria were as follows: traumatic SCI 2 years post injury, between the ages of 18 and 65 years, motor complete SCI C4-T12 level, with International Standards for the Neurological Classification of SCI impairment grades A or B19 (no motor function below the level of injury), and normative range of motion in the knee and hip joints. We did not assess participants for lower motor neuron damage. If participants responded to the electrical stimulation (ie, had visible muscle contractions), we considered them eligible for the study. Study measures included oral glucose tolerance testing (OGTT), fasting glucose, insulin, and lipid profiles, dual-energy x-ray absorptiometry (DXA), and magnetic resonance imaging (MRI), if given clearance for magnetic resonance safety. Study measurements were performed 1 week prior to the intervention and within 1 week of termination of NMES training in the same order.
RET protocol using surface NMES Participants performed RET of the knee extensor muscles twice weekly for 16 weeks. RET was performed in each participant’s home with phone monitoring by 1 of the investigators during each training session. Four sets of 10 knee extensions were performed using NMES. Legs were alternated after 10 repetitions, and training sets were separated by approximately 2 minutes. Ankle weights were used to increase the training stimulus. Increments of w0.9kg were added when 2 sessions of 40 full extensions were completed. Failure to obtain 40 full extensions resulted in the maintenance of the current load until 40 full extensions (0 of flexion) were achieved. For the first 4 sessions, no weight was added to minimize exercise-induced skeletal muscle injury.20 Two electrodesa (7.612.7cm) were placed proximally over the vastus lateralis and distally over the vastus medialis. Electrodes were replaced every 2 weeks. A Theratouch Mini 2.0 NMES unita was placed in the participant’s home and set for the following parameters: 35Hz and 250/50ms pulse duration/interval. NMES current was increased gradually over approximately 5 seconds until a full leg extension (0 flexion) was achieved, followed by a gradual (w5s) decrease in current. NMES current amplitudes varied between participants (70e200mA). However, for each participant, the current amplitude of electrical stimulation was monitored for each repetition to ensure that the increase in weight lifted was a result of muscle adaptations, not increased electrical stimulation current amplitudes.
Study measurements Oral glucose tolerance and metabolic testing After an overnight fast for 10 to 12 hours, participants were admitted to the Multi-Specialty Clinic of the Shepherd Center (Atlanta, GA) at 9:00 AM. Blood draws of approximately 5mL were obtained by the same registered nurse using standard venipuncture procedures. A standard 75-g glucose drink was then administered, and blood was drawn at 0 minutes before the
2168 glucose drink and at 30, 60, 90, and 120 minutes after consumption of the glucose drink. All blood samples were centrifuged, separated, and frozen at 20 C and then sent to LabCorp (Birmingham, AL) for analysis. The plasma concentrations of triglycerides, cholesterol, low-density lipoprotein, high-density lipoprotein, glucose, insulin, and hemoglobin A1C were determined using commercially available assays. The plasma insulin concentration was measured using a commercially available radioimmunoassay kit.b Quantitative estimates of insulin resistance were obtained using the homeostatic model assessment (HOMA).21 HOMA-calculated insulin sensitivity (HOMA-%S), beta-cell function (HOMA-%B), and insulin resistance (HOMA-IR) were calculated from the fasting plasma glucose and insulin values using a downloadable calculator (available at: https://www.dtu.ox.ac.uk/homacalculator/index. php). The values of insulin resistance were log-transformed to normalize for parametric analyses. All metabolic measurements were performed 1 week before and after the intervention. DXA and magnetic resonance imaging/magnetic resonance spectroscopy testing Dual-energy x-ray absorptiometry: Lower limb composition was measured by DXA.c Regions of interest were manually drawn for both legs with the proximal endpoint being the bottom edge of the ischium bone and the distal endpoint being the tibiofemoral joint. Magnetic resonance imaging: Participants were tested in a 3-T whole-body magnet (Signa HDxd) in the Bio-Imaging Researcher Center at the University of Georgia. T1-weighted anatomic images of both thighs were acquired with a knee volume coil using a fast gradient-recalled echo sequence (parameters: repetition time/echo time Z700/8.1ms, flip angle Z90, echo-train length Z3, number of excitations Z3, field of view Z2020cm, slice thickness Z1cm, gap thickness Z1cm, number of slices Z18, and acquired matrix Z256256 [reconstructed 512512]). Two participants could not be cleared for magnetic resonance testing in the 3-T environment because of a lack of record of metallic implants. These 2 participants were tested in a 1.5-T whole-body magnet (Signa Excited) at the Shepherd Hospital (Atlanta, GA). T1-weighted images of both thighs were acquired using the whole-body transmit/receive coil using a gradient-recalled echo pulse sequence (parameters: repetition time/echo time Z400/15ms, flip angle Z90, field of view Z4646cm, slice thickness Z1cm, gap thickness Z1cm, number of slices Z48, acquired matrix Z256256 [reconstructed 512512]). Images were exported and analyzed offline using Image J software.e Regions of interest were manually drawn around the quadriceps and hamstrings muscle groups and the femur bone (both cortical bone and marrow). A histogram of all pixels and signal intensities within the region of interest was produced. To differentiate between skeletal muscle and fat in the histogram, a midpoint between skeletal muscle and fat was chosen corresponding to the average signal intensity of pure skeletal muscle pixels. Percent fat was calculated using values of skeletal muscle and fat pixels from the histogram. The cortical bone and marrow area of the femur were used as an internal reference to ensure accurate pre-post comparisons of images. A subset of 4 images from each participant was analyzed for IMF levels in the vastus lateralis muscle. A region of interest was carefully drawn to exclude any IMF, and a histogram was used to estimate percent IMF, as previously described.
T.E. Ryan et al Phosphorus magnetic resonance spectroscopy measurements of muscle oxidative capacity Eight participants (6 men, 2 women) underwent phosphorus magnetic resonance spectroscopy measurements of skeletal muscle oxidative capacity using the kinetics of phosphocreatine (PCr) recovery, as previously described,17 before and after completion of NMES RET. To summarize, participants were placed into a 3-T clinical magnetic resonance scanner with a commercially available dual 1H/31P surface coil (31P coil dimensions: 13cm2; 1H coil dimensions: 20cm2), and manual shimming was performed on the proton signal. One minute of electrical stimulation (4Hz) was applied to the vastus lateralis muscle using 4 aluminum foil electrodes to deplete PCr.
Statistical analysis Data are presented as mean SD. Repeated-measures analysis of variance was used to determine the effects of RET on oral glucose tolerance, lipid profiles, skeletal muscle cross-sectional area and IMF, and mitochondrial function. When appropriate, a Bonferroni post hoc test for multiple comparisons was performed. Statistical analyses were performed using SPSS version 19.0.f The relation between the 2 variables was analyzed by a least-squares regression analysis. Significance was accepted at P<.05.
Results Resistance exercise training All participants completed the RET without any adverse events. Physical and clinical characteristics of all 14 participants are shown in table 1. All participants were able to increase the weight lifted and/or the number of repetitions performed throughout the training period. Training progression for all participants is shown in table 2.
Oral glucose tolerance and lipid profiles The participants had a wide range of glucose tolerance and insulin sensitivity. Two participants (P3 and P6) were classified as diabetic according to plasma glucose concentrations at the end of the OGTT (>200mg/dL). Using the HOMA2 calculations, 6 additional participants (P2, P8, P11, P12, P13, and P14) were characterized as insulin resistant using HOMA-%B and HOMA-% S values. There was no improvement in fasting blood glucose levels with RET (F1,13Z2.349; PZ.149; h2Z.153) or blood glucose levels at 120 minutes during the OGTT (F1,13Z1.31; PZ.273; h2Z.092). Similarly, we found no changes in the HOMA-IR with RET (F1,13Z.078; PZ.785; h2Z.006) for the entire group. However, both participants with diabetes (P3 and P6) showed improved insulin sensitivity (HOMA-%S and HOMA-IR) with NMES resistance training. Four of the 6 participants (P8, P11, P12, and P13) with insulin resistance showed improved insulin sensitivity (HOMA-%S and HOMA-IR) after NMES resistance training. Individual changes in glucose and insulin status are shown in appendix 1. Three participants had hyperlipidemia prior to beginning RET. RET did not improve low-density lipoprotein (F1,13Z2.446; PZ.142; h2Z.158) or triglyceride levels (F1,13Z1.226; PZ.288; h2Z.086). High-density lipoprotein www.archives-pmr.org
Neuromuscular electrical stimulation resistance training in SCI Table 1
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Physical and clinical characteristics of participants
Participants
Height (cm)
Weight (kg)
Age (y)
Level of Injury
Duration of Injury (y)
Sex (M/F)
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 Mean SD
187.9 180.3 185.4 177.8 172.7 195.6 190.5 185.4 175.3 187.9 187.9 175.3 175.2 167.6 181.88.0
78.9 97.7 106.8 61.4 75.0 105.9 86.2 122.5 82.5 76.2 87.8 86.2 72.7 95.7 88.216.1
28 33 47 35 44 45 44 44 57 26 44 28 28 32 26.74.7
T7 T3 T3 T6 T5 C4-6 T7 T1 T1 T5-7 T3 T3 T6 C6 NA
6.8 2.0 3.8 3.1 9.9 2.3 8.6 22.4 5.4 5.9 21.8 4.9 6.3 5.1 7.76.5
M M M M M M M M M M M F F F 11M/3F
Abbreviations: F, female; M, male; NA, not applicable.
was significantly greater after RET (F1,13Z6.955; PZ.021; h2Z.349). Total cholesterol was not significantly improved after RET (F1,13Z4.292; PZ.059; h2Z.248). Results for blood testing are shown in table 3.
thigh area increased approximately 10%15% after RET (F1,13Z6.682; PZ.024; h2Z.358). Bone mineral density of the femur bone was not different after RET (F1,13Z.738; PZ.407; h2Z.058).
Dual-energy x-ray absorptiometry
Magnetic resonance imaging
Thigh composition was measured before and after RET using DXA. Fat tissue (in grams) was not different after RET (F1,13Z.246; PZ.629; h2Z.02). The percentage fat (measured by DXA) in the thighs was also unchanged with RET (pre vs post, 39%9% vs 38%9%, respectively). Lean tissue of the
Representative pre- and posttraining images from a man and woman are shown in figure 1. Quadriceps and hamstring muscle groups were analyzed for muscle and fat composition. Quadriceps muscle volume (average of both legs) was increased by 39%27% (range, 5%e84%) (pre vs post, 618343 vs 815399cm3) (F1,13Z27.228; P<.001; h2Z.694). Both legs responded similarly to training. There was a slight increase in
Table 2
Resistance training progression for all participants First Training Session Repetitions
Last Training Session
Weight
Repetitions
Table 3
All SCI Subjects (NZ14)
Weight
Right Left Right Left Right Left Right Left Participants Leg Leg Leg Leg Leg Leg Leg Leg P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14
30 40 40 40 40 40 40 14 22 25 40 4 20 40
40 40 40 40 40 40 40 11 17 20 40 4 20 40
0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0
40 40 40 40 40 40 40 40 40 40 40 40 40 40
40 40 40 40 40 40 40 40 40 40 40 40 40 40
20 16 0 10 20 14 12 10 10 12 14 2 20 20
20 16 0 10 20 14 12 10 10 12 14 0 20 20
NOTE. Weight represents the added resistance of ankle weights, but does not account for the weight of the lower leg and foot.
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Metabolic characteristics pre- and post-RET
Variable 2
BMI (kg/m ) Fasting glucose (mg/dL) Ha1C HOMA-IR HOMA-%B HOMA-%S Triglycerides (mg/dL) Total cholesterol (mg/dL) LDL (mg/dL) HDL (mg/dL) C/H ratio OGTT: 120-min glucose (mg/dL)
Pretraining
Posttraining
P
26.74.7 89.019.0 5.71.4 1.61.4 125.068.0 136.0112.0 137.183.5 183.939.8 114.136.3 42.315.3 4.81.8 119.377.4
26.44.2 93.025.0 5.91.5 1.51.7 111.078.0 143.089.0 125.264.5 177.044.0 106.138.5 45.915.3 4.21.8 134.786.0
.701 .157 .875 .728 .169 .652 .358 .048* .105 .023* .427 .412
NOTE. Values presented as mean SD or as otherwise indicated. Abbreviations: BMI, body mass index; C/H, total cholesterol/HDL cholesterol ratio; Ha1C, hemoglobin A1C; HDL, high-density lipoprotein; LDL, low-density lipoprotein. * P<.05 using repeated-measures analysis of variance.
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Fig 3 Relation between the NMES training-induced change in the quadriceps muscle cross-sectional area and the change in HOMA-IR for all participants. Abbreviation: CSA, cross-sectional area. Fig 1 Representative T1-weighted axial MRI images of a man before (A) and after (B) RET. Images from a woman before (C) and after RET (D) are also shown. Manually drawn regions of interest are shown in blue. The quadriceps muscle cross-sectional area for each image was also calculated (A Z40.6cm2, B Z53.9cm2, C Z45.8cm2, D Z61.5cm2).
hamstring muscle volume (7%15%), but this was not statistically significant (F1,13Z4.113; PZ.065; h2Z.255). There was also no change in absolute fat volume for either the quadriceps (pre vs post, 11463 vs 11362cm3, respectively) (F1,13Z.064; PZ.805; h2Z.005) or hamstrings muscles (F1,13Z.159; PZ.697; h2Z.013). Relative changes in muscle and fat volumes for both the quadriceps and hamstring muscle groups are shown in figure 2. We found no relation between the
Fig 2 Relative changes in quadriceps and hamstrings muscle and IMF volume as a result of RET. Error bars represent SDs.
magnitude of muscle hypertrophy and improvements in glucose or insulin status (fig 3).
Phosphorus magnetic resonance spectroscopy measurements of mitochondrial function Eight participants underwent pre- and posttraining measurements of PCr recovery kinetics. Time constants for the recovery of PCr after electrical stimulation were 10224 and 7718 seconds before and after RET, respectively. This represents an approximate 25% improvement in skeletal muscle oxidative capacity, which was statistically significant (F1,7Z10.493; PZ.014; h2Z.60). Pre- and posttraining PCr time constants for the 8 participants are shown in figure 4. We did not observe
Fig 4 PCr recovery time constants for all participants (closed diamonds) before and after RET. The dotted line represents the mean value for PCr recovery time constants from the vastus lateralis muscle of able-bodied participants from a previous study.17 Abbreviation: AB, able-bodied.
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Neuromuscular electrical stimulation resistance training in SCI a statistically significant relation between the PCr recovery time constant and baseline glucose or insulin status in these 8 participants.
Discussion In this study, we found no improvements in HOMA-IR, fasting blood glucose, or 120-minute blood glucose level after 4 months of RET. Obesity, type II diabetes, and cardiovascular diseases are more prevalent in the SCI population than the non-SCI population.12,22 Electrical stimulation therapies may result in contractile activity-induced adaptations in paralyzed skeletal muscle that may translate into health and wellness benefits. Previous studies have suggested that NMES exercise training programs improve glucose and insulin status in people with SCI. Mahoney et al23 used a similar RET protocol and glucose tolerance measurements in 4 participants (1 additional participant was missing data). The authors reported a trend toward improvements in plasma glucose levels (PZ.074) after RET. The results of the present study do not substantiate the previous study and suggest that RET of the quadriceps muscles alone does not improve glucose tolerance in participants with motor complete SCI. Both studies used similar 4-month duration electrical stimulation weight training protocols that resulted in similar increases in muscle size (30%e40%). The current study had a larger sample size, included both men and women, and included more participants with impaired glucose tolerance or insulin action prior to NMES training. Gorgey et al24 also reported improvements in glucose area under the curve after a similar RET protocol, but this training was in combination with a dietary intervention. The study by Gorgey et al,24 similar to the current study, also reported no change in HOMA-IR in response to RET. Other studies used more elaborate electrical stimulation training protocols. Functional electrical stimulation (FES) cycling training for 8 weeks reduced glucose levels at the 2-hour mark of an OGTT in people with motor complete SCI.25 In the study by Jeon et al,25 3 of the 7 participants underwent more invasive testing via a hyperglycemic clamp technique, which also showed improved insulin sensitivity. More recently, an FESrowing exercise program resulted in improvements in the HOMA-IR after 12 weeks of exercise training in 6 participants with paraplegia.26 However, FES cycling uses tetanic contractions that involve a combination of resistance and endurance exercise stimuli. FES cycling also activates the gluteal and hamstring muscle groups in addition to the quadriceps that were trained in the current study. Improvements in glucose and insulin status are likely linked to the volume of activated musculature and the intensity of the exercise program,27 which may have been greater in these FES-induced exercise training protocols than the NMES training in the current study. In the FES-cycling/rowing studies, the participants were also exercising 3 days per week compared with the 2 days per week in the current study25,26; thus, exercise dosing may have an effect. Further investigation is required. The 16 week electrically induced resistance training program used in this study did result in significant hypertrophy of the quadriceps muscle group, similar to previous resistance training protocols. The 39% increase in quadriceps muscle size was similar to increases reported by Mahoney23 (w38%), Gorgey24 (w35%), Gorgey16 (w43%), and colleagues. In the
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2171 current study, we had a wide range of hypertrophy responses to the RET (5%e84% increase in quadriceps cross-sectional area). Interestingly, we found no relation between the magnitude of size increase with training and changes in insulin or glucose levels. We also found no relation between initial insulin or glucose status and the amount of muscle size increase. We did find some evidence of hypertrophy in the knee flexors (w7%), although we aimed the RET to the knee extensor muscle group. Visible inspection of some participants during training suggested that the level of current used was enough to activate some of the hamstring muscle groups. Electrical stimulation training programs that activate more musculature (knee flexors, hip extensors, plantarflexors, etc) may provide greater improvements in oral glucose tolerance and lipid profiles. Of interest, some of the participants had visible muscle contractions, but they were very weak and able to perform only a few electrically stimulated leg lifts at the start of the study. All participants improved their strength and performance, as indicated by increases in the weight lifted and/ or the number of completed leg extensions. We used considerable caution when increasing the load, in order to minimize the risks for musculoskeletal injuries and the effects of exercise-induced muscle injury. No weight was used during the first 2 weeks of training, even if the participant was capable of lifting heavier loads. We also did not increase the weight throughout the 16 weeks of training until 2 to 3 sessions were successfully completed; when the load was increased, it was done by increments of only w0.9kg. We also found no changes in IMF levels (in absolute area/ volume) after RET. In contrast, in a case report by Gorgey and Shepherd,16 12 weeks of RET decreased the IMF cross-sectional area by >50%. Gorgey et al24 also reported relative decreases in the percentage of IMF after RET, but it is unclear if these changes were because of muscle hypertrophy or a decrease of IMF. IMF has been strongly linked with glucose intolerance in chronic SCI9; therefore, training that effectively reduces IMF could be beneficial. This is the first study, to our knowledge, that reports changes in in vivo skeletal muscle mitochondrial capacity after electrically induced RET in individuals with chronic SCI. Previous studies have examined skeletal muscle mitochondrial capacity using phosphorus magnetic resonance spectroscopy and reported that people with SCI have approximately one half to one third the mitochondrial function of healthy able-bodied individuals.17 In this study, skeletal muscle mitochondrial function improved approximately 25% after 16 weeks of RET. Although RET is not commonly associated with improvements in mitochondrial capacity, the decreased initial mitochondrial capacity provides a large dynamic range for improvements, even with RET. Endurance exercise should provide a larger stimulus for improvements in mitochondrial function.28-30 For example, Martin et al31 found that 6 months of endurance training via electrical stimulation resulted in approximately a 2-fold increase in succinate dehydrogenase activity in participants with SCI. Similarly, Kjaer et al32 reported a 2-fold increase in citrate synthase of the vastus lateralis after 3 months of electrical stimulation cycling in individuals with SCI. These results are similar to those reported by Crameri,33 Rochester,34 and colleagues. In contrast, training-induced changes in mitochondrial capacity can be 70% to 100% in able-bodied individuals.35,36 Thus, the changes in this study, although
We thank Hui-Ju Young, MS, and Melissa Erickson, MS, for their assistance with data collection and participant recruitment.
269.7 15.7 35.5 206.9 268.8 191.7 147.4 66.7 261.0 150.0 87.7 104.9 176.5 27.2 143.5089.80
HOMA-IR HOMA-%S HOMA-%B
59.9 317.9 68.5 73.5 58.4 23.5 73.2 171.9 79.3 71.4 160.1 122.7 73.5 203.3 111.2078.10 2.1 52.3 19.7 3.8 2 3.6 5.2 12.1 3.1 5.1 9.3 7.6 4.4 28.9 11.4014.00
Fasting Plasma Insulin Fasting Plasma Glucose HOMA-IR HOMA-%S HOMA-%B Fasting Plasma Insulin
NOTE. HOMA calculations were made using a freely downloadable calculator (https://www.dtu.ox.ac.uk/homacalculator/index.php). * Participants that are classified with type II diabetes mellitus prior to beginning NMES training. y Participants classified as glucose intolerant/insulin resistant prior to beginning NMES training.
Acknowledgements
84 91 136 70 66 119 91 82 65 89 88 83 91 85 88.0019.00
Terence E. Ryan, PhD, University of Georgia, 330 River Rd, Athens, GA 30602. E-mail address: [email protected].
P1 P2 P3* P4 P5 P6* P7 P8y P9 P10 P11y P12y P13y P14 Mean SD
Corresponding author
Fasting Plasma Glucose
Cell respiration; Electric stimulation; Paralysis; Rehabilitation
Participants
Keywords
Pretraining
a. Richmar, 4120 S Creek Rd, Chattanooga, TN 37406. b. LabCorp, 1801 First Ave, Birmingham, AL 35233. c. iDXA; GE Medical Systems Lunar, 3030 Ohmeda Dr, Madison, WI 53718. d. GE Healthcare Institute, N16W22419 Watertown Rd, Waukesha, WI 53186. e. Image J; http://rsbweb.nih.gov/ij/index.html. f. IBM, 1 New Orchard Rd, Armonk, NY 10504.
All participant data for glucose and insulin status pre- and post-NMES training
Suppliers
Appendix 1
Sixteen weeks of electrically induced RET in individuals with SCI resulted in no changes in glucose tolerance or insulin action. This was despite a 39% increase in quadriceps muscle volume and a 25% improvement in skeletal muscle mitochondrial function. Future studies should aim to optimize electrical stimulation training for improving health in individuals with SCI. Health benefits from electrical stimulation training may require more than a primarily resistance training stimulus, or resistance training of more muscle mass.
82 95 151 81 83 140 90 78 73 90 74 79 85 97 92.0023.00
Posttraining
Conclusions
0.4 3.9 4.1 0.4 0.3 1.4 1.0 2.3 0.3 0.4 1.6 1.3 1.2 3.7 1.591.38
This study, as with many others, had a relatively small sample size (NZ14). Small sample sizes are very common when dealing with clinical populations, especially SCI. Because of the sample size, statistical comparisons between participants with differing glucose and insulin statuses were certainly underpowered. Nonetheless, the sample size in this study is larger than previous studies.22,23 Another limitation was the methods for assessing glucose tolerance and insulin sensitivity. Insulin/glucose clamp techniques may have provided a more sensitive measurement of glucose/insulin sensitivity, but are more technically challenging than the OGTT. We used standard clinical measures, such as the OGTT, fasting plasma glucose and insulin, and HOMA-IR, because of their relatively low cost and ease of use. It is possible that more sensitive methodologies, such as euglycemic-hyperinsulinemic clamps, could detect an effect of RET.
267.9 25.4 24.4 282.4 287.6 70.3 102.3 44.2 288.9 263.8 63.5 74.6 83.7 27.1 136.10112.20
Study limitations
57.0 243.8 112.4 82.7 93.3 67.1 91.6 204.9 96.3 50.7 136.8 139.0 105.2 268.6 124.9068.00
statistically significant, might be relatively small in magnitude compared with those reported in able-bodied individuals.
0.4 6.4 2.8 0.5 0.4 0.5 0.7 1.5 0.4 0.7 1.1 1.0 0.6 3.7 1.481.72
T.E. Ryan et al
2.0 31.6 29.9 2.0 2.0 10.3 7.5 18.2 2.0 2.8 12.3 10.6 9.2 30.1 12.2011.00
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Neuromuscular electrical stimulation resistance training in SCI
References 1. Devivo MJ. Epidemiology of traumatic spinal cord injury: trends and future implications. Spinal Cord 2012;50:365-72. 2. Flank P, Wahman K, Levi R, Fahlstrom M. Prevalence of risk factors for cardiovascular disease stratified by body mass index categories in patients with wheelchair-dependent paraplegia after spinal cord injury. J Rehabil Med 2012;44:440-3. 3. Myers J, Lee M, Kiratli J. Cardiovascular disease in spinal cord injury: an overview of prevalence, risk, evaluation, and management. Am J Phys Med Rehabil 2007;86:142-52. 4. van den Berg ME, Castellote JM, de Pedro-Cuesta J, MahilloFernandez I. Survival after spinal cord injury: a systematic review. J Neurotrauma 2010;27:1517-28. 5. LaVela SL, Weaver FM, Goldstein B, et al. Diabetes mellitus in individuals with spinal cord injury or disorder. J Spinal Cord Med 2006;29:387-95. 6. Soden RJ, Walsh J, Middleton JW, Craven ML, Rutkowski SB, Yeo JD. Causes of death after spinal cord injury. Spinal Cord 2000;38:604-10. 7. Castro MJ, Apple DF, Hillegass EA, Dudley GA. Influence of complete spinal cord injury on skeletal muscle cross-sectional area within the first 6 months of injury. Eur J Appl Physiol 1999;80:373-8. 8. Gorgey AS, Dudley GA. Skeletal muscle atrophy and increased intramuscular fat after incomplete spinal cord injury. Spinal Cord 2007;45:304-9. 9. Elder CP, Apple DF, Bickel CS, Meyer RA, Dudley GA. Intramuscular fat and glucose tolerance after spinal cord injuryea cross-sectional study. Spinal Cord 2004;42:711-6. 10. Bauman WA, Spungen AM. Carbohydrate and lipid metabolism in chronic spinal cord injury. J Spinal Cord Med 2001;24:266-77. 11. Bauman WA, Adkins RH, Spungen AM, Waters RL. The effect of residual neurological deficit on oral glucose tolerance in persons with chronic spinal cord injury. Spinal Cord 1999;37:765-71. 12. Bauman WA, Spungen AM. Coronary heart disease in individuals with spinal cord injury: assessment of risk factors. Spinal Cord 2008;46:466-76. 13. Garland DE, Stewart CA, Adkins RH, et al. Osteoporosis after spinal cord injury. J Orthop Res 1992;10:371-8. 14. Dudley GA, Castro MJ, Rogers S, Apple DF Jr. A simple means of increasing muscle size after spinal cord injury: a pilot study. Eur J Appl Physiol Occup Physiol 1999;80:394-6. 15. Bickel CS, Slade JM, Haddad F, Adams GR, Dudley GA. Acute molecular responses of skeletal muscle to resistance exercise in able-bodied and spinal cord-injured subjects. J Appl Physiol 2003;94: 2255-62. 16. Gorgey AS, Shepherd C. Skeletal muscle hypertrophy and decreased intramuscular fat after unilateral resistance training in spinal cord injury: case report. J Spinal Cord Med 2010;33:90-5. 17. McCully KK, Mulcahy TK, Ryan TE, Zhao Q. Skeletal muscle metabolism in individuals with spinal cord injury. J Appl Physiol 2011;111:143-8. 18. Ragnarsson KT. Functional electrical stimulation after spinal cord injury: current use, therapeutic effects and future directions. Spinal Cord 2008;46:255-74. 19. Kirshblum SC, Burns SP, Biering-Sorensen F, et al. International standards for neurological classification of spinal cord injury (revised 2011). J Spinal Cord Med 2011;34:535-46.
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2173 20. Bickel CS, Slade JM, Dudley GA. Long-term spinal cord injury increases susceptibility to isometric contraction-induced muscle injury. Eur J Appl Physiol 2004;91:308-13. 21. Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985;28:412-9. 22. Gater DR Jr. Obesity after spinal cord injury. Phys Med Rehabil Clin N Am 2007;18:333-51, vii. 23. Mahoney ET, Bickel CS, Elder C, et al. Changes in skeletal muscle size and glucose tolerance with electrically stimulated resistance training in subjects with chronic spinal cord injury. Arch Phys Med Rehabil 2005;86:1502-4. 24. Gorgey AS, Mather KJ, Cupp HR, Gater DR. Effects of resistance training on adiposity and metabolism after spinal cord injury. Med Sci Sport Exer 2012;44:165-74. 25. Jeon JY, Weiss CB, Steadward RD, et al. Improved glucose tolerance and insulin sensitivity after electrical stimulation-assisted cycling in people with spinal cord injury. Spinal Cord 2002;40:110-7. 26. Jeon JY, Hettinga D, Steadward RD, Wheeler GD, Bell G, Harber V. Reduced plasma glucose and leptin after 12 weeks of functional electrical stimulation-rowing exercise training in spinal cord injury patients. Arch Phys Med Rehabil 2010;91:1957-9. 27. Mohr T, Dela F, Handberg A, Biering-Sorensen F, Galbo H, Kjaer M. Insulin action and long-term electrically induced training in individuals with spinal cord injuries. Med Sci Sports Exerc 2001; 33:1247-52. 28. McCully KK, Boden BP, Tuchler M, Fountain MR, Chance B. Wrist flexor muscles of elite rowers measured with magnetic resonance spectroscopy. J Appl Physiol 1989;67:926-32. 29. Mccully KK, Kakihira H, Vandenborne K, Kentbraun J. Noninvasive measurements of activity-induced changes in muscle metabolism. J Biomech 1991;24:153-61. 30. Larsen RG, Callahan DM, Foulis SA, Kent-Braun JA. In vivo oxidative capacity varies with muscle and training status in young adults. J Appl Physiol 2009;107:873-9. 31. Martin TP, Stein RB, Hoeppner PH, Reid DC. Influence of electricalstimulation on the morphological and metabolic properties of paralyzed muscle. J Appl Physiol 1992;72:1401-6. 32. Kjaer M, Mohr T, Biering-Sorensen F, Bangsbo J. Muscle enzyme adaptation to training and tapering-off in spinal-cord-injured humans. Eur J Appl Physiol 2001;84:482-6. 33. Crameri RM, Weston A, Climstein M, Davis GM, Sutton JR. Effects of electrical stimulation-induced leg training on skeletal muscle adaptability in spinal cord injury. Scand J Med Sci Sports 2002;12: 316-22. 34. Rochester L, Barron MJ, Chandler CS, Sutton RA, Miller S, Johnson MA. Influence of electrical stimulation of the tibialis anterior muscle in paraplegic subjects. 2. Morphological and histochemical properties. Paraplegia 1995;33:514-22. 35. Gollnick PD, Armstrong RB, Saltin B, Saubert CW 4th, Sembrowich WL, Shepherd RE. Effect of training on enzyme activity and fiber composition of human skeletal muscle. J Appl Physiol 1973;34:107-11. 36. Holloszy JO, Coyle EF. Adaptations of skeletal muscle to endurance exercise and their metabolic consequences. J Appl Physiol 1984;56: 831-8.
ORIGINAL ARTICLE
Electrically Induced Resistance Training in Individuals With Motor Complete Spinal Cord Injury Terence E. Ryan, PhD,a Jared T. Brizendine, MS,a Deborah Backus, DPT, PhD,b Kevin K. McCully, PhDa From the aDepartment of Kinesiology, University of Georgia, Athens, GA; and bCrawford Research Institute, Shepherd Center, Atlanta, GA.
Abstract Objective: To examine the effects of 16 weeks of electrically induced resistance training on insulin resistance and glucose tolerance, and changes in muscle size, composition, and metabolism in paralyzed muscle. Design: Pre-post intervention. Setting: University-based trial. Participants: Participants (NZ14; 11 men and 3 women) with chronic (>2y post spinal cord injury), motor complete spinal cord injury. Intervention: Home-based electrically induced resistance exercise training twice weekly for 16 weeks. Main Outcome Measures: Plasma glucose and insulin throughout a standard clinical oral glucose tolerance test, thigh muscle and fat mass via dual-energy x-ray absorptiometry, quadriceps and hamstrings muscle size and composition via magnetic resonance imaging, and muscle oxidative metabolism using phosphorus magnetic resonance spectroscopy. Results: Muscle mass increased in all participants (mean SD, 39%27%; range, 5%e84%). The mean change SD in intramuscular fat was 3%22%. Phosphocreatine mean recovery time constants SD were 10224 and 7718 seconds before and after electrical stimulation-induced resistance training, respectively (P<.05). There was no improvement in fasting blood glucose levels, homeostatic model assessment calculated insulin resistance, 2-hour insulin, or 2-hour glucose. Conclusions: Sixteen weeks of electrical stimulation-induced resistance training increased muscle mass, but did not reduce intramuscular fat. Similarly, factors associated with insulin resistance or glucose tolerance did not improve with training. We did find a 25% improvement in mitochondrial function, as measured by phosphocreatine recovery rates. Larger improvements in mitochondrial function may translate into improved glucose tolerance and insulin resistance. Archives of Physical Medicine and Rehabilitation 2013;94:2166-73 ª 2013 by the American Congress of Rehabilitation Medicine
Spinal cord injury (SCI) currently affects approximately 250,000 individuals in the U.S.,1 with around 10,000 new cases each year. With advances in science and medicine, the life expectancy after SCI is nearly identical to individuals without SCI.1 Mortality from cardiovascular disease is the leading cause of death in individuals with SCI and occurs at a much higher rate than able-bodied individuals, such that mortality from conditions, such as coronary artery disease, is more likely to occur prematurely in individuals with SCI.2,3 Prevalence of symptomatic cardiovascular disease is 30% to 50% in the SCI population compared with 5% to
Supported by the National Institutes of Health (grant no. R01-HD-039676-11). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated.
10% prevalence in the able-bodied population.3,4 Risk factors for cardiovascular disease, namely hyperlipidemia, metabolic syndrome, and diabetes mellitus, are also more common in the SCI population.3 Dyslipidemia also occurs as rapidly as a year after injury, and severity is linked to duration of injury and is seen among a wide range of body mass index scores.2 The prevalence of metabolic syndrome and diabetes mellitus is 23% and 22%, respectively, in SCI populations, more than twice as high as the prevalence for these 2 conditions in the able-bodied population.5 Increased mortality from cardiovascular and metabolic diseases in the SCI population is because of a multitude of physiological alterations after injury.6 After paralysis, skeletal muscle atrophy occurs rapidly, and the muscle cross-sectional area can be as low as 30% to 50% compared with able-bodied controls.7,8 Furthermore, skeletal muscle atrophy has also been
0003-9993/13/$36 - see front matter ª 2013 by the American Congress of Rehabilitation Medicine http://dx.doi.org/10.1016/j.apmr.2013.06.016
Neuromuscular electrical stimulation resistance training in SCI linked with increasing intramuscular fat (IMF) levels in SCI.8,9 Atrophy and increased IMF are both associated with glucose intolerance9,10 and diabetes mellitus/metabolic syndrome,11 dyslipidemia,10 cardiovascular disease,12 and osteoporosis.13 Many of these factors are influenced by the lack of physical activity, both because of paralysis and a lack of opportunities to engage in physical activity. Neuromuscular electrical stimulation (NMES), particularly resistance exercise training (RET), effectively induces skeletal muscle hypertrophy in participants with chronic SCI, with increases in muscle volume from 39% to 75%.14,15 RET using NMES in paralyzed musculature may result in increased levels of metabolically active muscle tissue, which can aid in postprandial glucose removal, thus reducing the risk of diabetes. Furthermore, NMES training may decrease fatty infiltration of IMF16 and could improve the reduced muscle oxidative capacity found in individuals with SCI.17 NMES could potentially represent a cost-effective means of reducing the health care cost associated with SCI by reducing risk factors associated with chronic diseases. Ragnarsson18 provides a comprehensive review of the literature regarding electrical stimulation therapies in SCI. The purpose of this study was to examine the effects of 16 weeks of NMES-induced RET of the knee extensors on oral glucose tolerance, lipid profiles, muscle cross-sectional area and IMF, and skeletal muscle oxidative capacity in individuals with chronic SCI. We hypothesized that RET would increase the muscle cross-sectional area and decrease IMF and would improve oral glucose tolerance, lipid profiles, and skeletal muscle oxidative capacity.
Methods Participants Fourteen participants (11 men, 3 women) with chronic, motor complete SCI were tested in this study. Participants were required to be at least 2 years post injury and between 18 and 65 years of age. Participants were recruited from the Shepherd Center (Atlanta, GA) and the local community (Athens, GA and surrounding counties). This study was conducted with the approval of the Institutional Review Boards at the University of Georgia (Athens,
List of abbreviations: DXA FES HOMA HOMA-IR HOMA-%B HOMA-%S IMF MRI NMES OGTT PCr RET SCI
dual-energy x-ray absorptiometry functional electrical stimulation homeostatic model assessment homeostatic model assessment calculated insulin resistance homeostatic model assessment calculated beta-cell function homeostatic model assessment calculated insulin sensitivity intramuscular fat magnetic resonance imaging neuromuscular electrical stimulation oral glucose tolerance test phosphocreatine resistance exercise training spinal cord injury
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2167 GA) and the Shepherd Center (Atlanta, GA), and all participants gave written, informed consent before testing.
Study design A pretest/posttest experimental design was implemented for this study. Inclusion criteria were as follows: traumatic SCI 2 years post injury, between the ages of 18 and 65 years, motor complete SCI C4-T12 level, with International Standards for the Neurological Classification of SCI impairment grades A or B19 (no motor function below the level of injury), and normative range of motion in the knee and hip joints. We did not assess participants for lower motor neuron damage. If participants responded to the electrical stimulation (ie, had visible muscle contractions), we considered them eligible for the study. Study measures included oral glucose tolerance testing (OGTT), fasting glucose, insulin, and lipid profiles, dual-energy x-ray absorptiometry (DXA), and magnetic resonance imaging (MRI), if given clearance for magnetic resonance safety. Study measurements were performed 1 week prior to the intervention and within 1 week of termination of NMES training in the same order.
RET protocol using surface NMES Participants performed RET of the knee extensor muscles twice weekly for 16 weeks. RET was performed in each participant’s home with phone monitoring by 1 of the investigators during each training session. Four sets of 10 knee extensions were performed using NMES. Legs were alternated after 10 repetitions, and training sets were separated by approximately 2 minutes. Ankle weights were used to increase the training stimulus. Increments of w0.9kg were added when 2 sessions of 40 full extensions were completed. Failure to obtain 40 full extensions resulted in the maintenance of the current load until 40 full extensions (0 of flexion) were achieved. For the first 4 sessions, no weight was added to minimize exercise-induced skeletal muscle injury.20 Two electrodesa (7.612.7cm) were placed proximally over the vastus lateralis and distally over the vastus medialis. Electrodes were replaced every 2 weeks. A Theratouch Mini 2.0 NMES unita was placed in the participant’s home and set for the following parameters: 35Hz and 250/50ms pulse duration/interval. NMES current was increased gradually over approximately 5 seconds until a full leg extension (0 flexion) was achieved, followed by a gradual (w5s) decrease in current. NMES current amplitudes varied between participants (70e200mA). However, for each participant, the current amplitude of electrical stimulation was monitored for each repetition to ensure that the increase in weight lifted was a result of muscle adaptations, not increased electrical stimulation current amplitudes.
Study measurements Oral glucose tolerance and metabolic testing After an overnight fast for 10 to 12 hours, participants were admitted to the Multi-Specialty Clinic of the Shepherd Center (Atlanta, GA) at 9:00 AM. Blood draws of approximately 5mL were obtained by the same registered nurse using standard venipuncture procedures. A standard 75-g glucose drink was then administered, and blood was drawn at 0 minutes before the
2168 glucose drink and at 30, 60, 90, and 120 minutes after consumption of the glucose drink. All blood samples were centrifuged, separated, and frozen at 20 C and then sent to LabCorp (Birmingham, AL) for analysis. The plasma concentrations of triglycerides, cholesterol, low-density lipoprotein, high-density lipoprotein, glucose, insulin, and hemoglobin A1C were determined using commercially available assays. The plasma insulin concentration was measured using a commercially available radioimmunoassay kit.b Quantitative estimates of insulin resistance were obtained using the homeostatic model assessment (HOMA).21 HOMA-calculated insulin sensitivity (HOMA-%S), beta-cell function (HOMA-%B), and insulin resistance (HOMA-IR) were calculated from the fasting plasma glucose and insulin values using a downloadable calculator (available at: https://www.dtu.ox.ac.uk/homacalculator/index. php). The values of insulin resistance were log-transformed to normalize for parametric analyses. All metabolic measurements were performed 1 week before and after the intervention. DXA and magnetic resonance imaging/magnetic resonance spectroscopy testing Dual-energy x-ray absorptiometry: Lower limb composition was measured by DXA.c Regions of interest were manually drawn for both legs with the proximal endpoint being the bottom edge of the ischium bone and the distal endpoint being the tibiofemoral joint. Magnetic resonance imaging: Participants were tested in a 3-T whole-body magnet (Signa HDxd) in the Bio-Imaging Researcher Center at the University of Georgia. T1-weighted anatomic images of both thighs were acquired with a knee volume coil using a fast gradient-recalled echo sequence (parameters: repetition time/echo time Z700/8.1ms, flip angle Z90, echo-train length Z3, number of excitations Z3, field of view Z2020cm, slice thickness Z1cm, gap thickness Z1cm, number of slices Z18, and acquired matrix Z256256 [reconstructed 512512]). Two participants could not be cleared for magnetic resonance testing in the 3-T environment because of a lack of record of metallic implants. These 2 participants were tested in a 1.5-T whole-body magnet (Signa Excited) at the Shepherd Hospital (Atlanta, GA). T1-weighted images of both thighs were acquired using the whole-body transmit/receive coil using a gradient-recalled echo pulse sequence (parameters: repetition time/echo time Z400/15ms, flip angle Z90, field of view Z4646cm, slice thickness Z1cm, gap thickness Z1cm, number of slices Z48, acquired matrix Z256256 [reconstructed 512512]). Images were exported and analyzed offline using Image J software.e Regions of interest were manually drawn around the quadriceps and hamstrings muscle groups and the femur bone (both cortical bone and marrow). A histogram of all pixels and signal intensities within the region of interest was produced. To differentiate between skeletal muscle and fat in the histogram, a midpoint between skeletal muscle and fat was chosen corresponding to the average signal intensity of pure skeletal muscle pixels. Percent fat was calculated using values of skeletal muscle and fat pixels from the histogram. The cortical bone and marrow area of the femur were used as an internal reference to ensure accurate pre-post comparisons of images. A subset of 4 images from each participant was analyzed for IMF levels in the vastus lateralis muscle. A region of interest was carefully drawn to exclude any IMF, and a histogram was used to estimate percent IMF, as previously described.
T.E. Ryan et al Phosphorus magnetic resonance spectroscopy measurements of muscle oxidative capacity Eight participants (6 men, 2 women) underwent phosphorus magnetic resonance spectroscopy measurements of skeletal muscle oxidative capacity using the kinetics of phosphocreatine (PCr) recovery, as previously described,17 before and after completion of NMES RET. To summarize, participants were placed into a 3-T clinical magnetic resonance scanner with a commercially available dual 1H/31P surface coil (31P coil dimensions: 13cm2; 1H coil dimensions: 20cm2), and manual shimming was performed on the proton signal. One minute of electrical stimulation (4Hz) was applied to the vastus lateralis muscle using 4 aluminum foil electrodes to deplete PCr.
Statistical analysis Data are presented as mean SD. Repeated-measures analysis of variance was used to determine the effects of RET on oral glucose tolerance, lipid profiles, skeletal muscle cross-sectional area and IMF, and mitochondrial function. When appropriate, a Bonferroni post hoc test for multiple comparisons was performed. Statistical analyses were performed using SPSS version 19.0.f The relation between the 2 variables was analyzed by a least-squares regression analysis. Significance was accepted at P<.05.
Results Resistance exercise training All participants completed the RET without any adverse events. Physical and clinical characteristics of all 14 participants are shown in table 1. All participants were able to increase the weight lifted and/or the number of repetitions performed throughout the training period. Training progression for all participants is shown in table 2.
Oral glucose tolerance and lipid profiles The participants had a wide range of glucose tolerance and insulin sensitivity. Two participants (P3 and P6) were classified as diabetic according to plasma glucose concentrations at the end of the OGTT (>200mg/dL). Using the HOMA2 calculations, 6 additional participants (P2, P8, P11, P12, P13, and P14) were characterized as insulin resistant using HOMA-%B and HOMA-% S values. There was no improvement in fasting blood glucose levels with RET (F1,13Z2.349; PZ.149; h2Z.153) or blood glucose levels at 120 minutes during the OGTT (F1,13Z1.31; PZ.273; h2Z.092). Similarly, we found no changes in the HOMA-IR with RET (F1,13Z.078; PZ.785; h2Z.006) for the entire group. However, both participants with diabetes (P3 and P6) showed improved insulin sensitivity (HOMA-%S and HOMA-IR) with NMES resistance training. Four of the 6 participants (P8, P11, P12, and P13) with insulin resistance showed improved insulin sensitivity (HOMA-%S and HOMA-IR) after NMES resistance training. Individual changes in glucose and insulin status are shown in appendix 1. Three participants had hyperlipidemia prior to beginning RET. RET did not improve low-density lipoprotein (F1,13Z2.446; PZ.142; h2Z.158) or triglyceride levels (F1,13Z1.226; PZ.288; h2Z.086). High-density lipoprotein www.archives-pmr.org
Neuromuscular electrical stimulation resistance training in SCI Table 1
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Physical and clinical characteristics of participants
Participants
Height (cm)
Weight (kg)
Age (y)
Level of Injury
Duration of Injury (y)
Sex (M/F)
P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 Mean SD
187.9 180.3 185.4 177.8 172.7 195.6 190.5 185.4 175.3 187.9 187.9 175.3 175.2 167.6 181.88.0
78.9 97.7 106.8 61.4 75.0 105.9 86.2 122.5 82.5 76.2 87.8 86.2 72.7 95.7 88.216.1
28 33 47 35 44 45 44 44 57 26 44 28 28 32 26.74.7
T7 T3 T3 T6 T5 C4-6 T7 T1 T1 T5-7 T3 T3 T6 C6 NA
6.8 2.0 3.8 3.1 9.9 2.3 8.6 22.4 5.4 5.9 21.8 4.9 6.3 5.1 7.76.5
M M M M M M M M M M M F F F 11M/3F
Abbreviations: F, female; M, male; NA, not applicable.
was significantly greater after RET (F1,13Z6.955; PZ.021; h2Z.349). Total cholesterol was not significantly improved after RET (F1,13Z4.292; PZ.059; h2Z.248). Results for blood testing are shown in table 3.
thigh area increased approximately 10%15% after RET (F1,13Z6.682; PZ.024; h2Z.358). Bone mineral density of the femur bone was not different after RET (F1,13Z.738; PZ.407; h2Z.058).
Dual-energy x-ray absorptiometry
Magnetic resonance imaging
Thigh composition was measured before and after RET using DXA. Fat tissue (in grams) was not different after RET (F1,13Z.246; PZ.629; h2Z.02). The percentage fat (measured by DXA) in the thighs was also unchanged with RET (pre vs post, 39%9% vs 38%9%, respectively). Lean tissue of the
Representative pre- and posttraining images from a man and woman are shown in figure 1. Quadriceps and hamstring muscle groups were analyzed for muscle and fat composition. Quadriceps muscle volume (average of both legs) was increased by 39%27% (range, 5%e84%) (pre vs post, 618343 vs 815399cm3) (F1,13Z27.228; P<.001; h2Z.694). Both legs responded similarly to training. There was a slight increase in
Table 2
Resistance training progression for all participants First Training Session Repetitions
Last Training Session
Weight
Repetitions
Table 3
All SCI Subjects (NZ14)
Weight
Right Left Right Left Right Left Right Left Participants Leg Leg Leg Leg Leg Leg Leg Leg P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14
30 40 40 40 40 40 40 14 22 25 40 4 20 40
40 40 40 40 40 40 40 11 17 20 40 4 20 40
0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0
40 40 40 40 40 40 40 40 40 40 40 40 40 40
40 40 40 40 40 40 40 40 40 40 40 40 40 40
20 16 0 10 20 14 12 10 10 12 14 2 20 20
20 16 0 10 20 14 12 10 10 12 14 0 20 20
NOTE. Weight represents the added resistance of ankle weights, but does not account for the weight of the lower leg and foot.
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Metabolic characteristics pre- and post-RET
Variable 2
BMI (kg/m ) Fasting glucose (mg/dL) Ha1C HOMA-IR HOMA-%B HOMA-%S Triglycerides (mg/dL) Total cholesterol (mg/dL) LDL (mg/dL) HDL (mg/dL) C/H ratio OGTT: 120-min glucose (mg/dL)
Pretraining
Posttraining
P
26.74.7 89.019.0 5.71.4 1.61.4 125.068.0 136.0112.0 137.183.5 183.939.8 114.136.3 42.315.3 4.81.8 119.377.4
26.44.2 93.025.0 5.91.5 1.51.7 111.078.0 143.089.0 125.264.5 177.044.0 106.138.5 45.915.3 4.21.8 134.786.0
.701 .157 .875 .728 .169 .652 .358 .048* .105 .023* .427 .412
NOTE. Values presented as mean SD or as otherwise indicated. Abbreviations: BMI, body mass index; C/H, total cholesterol/HDL cholesterol ratio; Ha1C, hemoglobin A1C; HDL, high-density lipoprotein; LDL, low-density lipoprotein. * P<.05 using repeated-measures analysis of variance.
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T.E. Ryan et al
Fig 3 Relation between the NMES training-induced change in the quadriceps muscle cross-sectional area and the change in HOMA-IR for all participants. Abbreviation: CSA, cross-sectional area. Fig 1 Representative T1-weighted axial MRI images of a man before (A) and after (B) RET. Images from a woman before (C) and after RET (D) are also shown. Manually drawn regions of interest are shown in blue. The quadriceps muscle cross-sectional area for each image was also calculated (A Z40.6cm2, B Z53.9cm2, C Z45.8cm2, D Z61.5cm2).
hamstring muscle volume (7%15%), but this was not statistically significant (F1,13Z4.113; PZ.065; h2Z.255). There was also no change in absolute fat volume for either the quadriceps (pre vs post, 11463 vs 11362cm3, respectively) (F1,13Z.064; PZ.805; h2Z.005) or hamstrings muscles (F1,13Z.159; PZ.697; h2Z.013). Relative changes in muscle and fat volumes for both the quadriceps and hamstring muscle groups are shown in figure 2. We found no relation between the
Fig 2 Relative changes in quadriceps and hamstrings muscle and IMF volume as a result of RET. Error bars represent SDs.
magnitude of muscle hypertrophy and improvements in glucose or insulin status (fig 3).
Phosphorus magnetic resonance spectroscopy measurements of mitochondrial function Eight participants underwent pre- and posttraining measurements of PCr recovery kinetics. Time constants for the recovery of PCr after electrical stimulation were 10224 and 7718 seconds before and after RET, respectively. This represents an approximate 25% improvement in skeletal muscle oxidative capacity, which was statistically significant (F1,7Z10.493; PZ.014; h2Z.60). Pre- and posttraining PCr time constants for the 8 participants are shown in figure 4. We did not observe
Fig 4 PCr recovery time constants for all participants (closed diamonds) before and after RET. The dotted line represents the mean value for PCr recovery time constants from the vastus lateralis muscle of able-bodied participants from a previous study.17 Abbreviation: AB, able-bodied.
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Neuromuscular electrical stimulation resistance training in SCI a statistically significant relation between the PCr recovery time constant and baseline glucose or insulin status in these 8 participants.
Discussion In this study, we found no improvements in HOMA-IR, fasting blood glucose, or 120-minute blood glucose level after 4 months of RET. Obesity, type II diabetes, and cardiovascular diseases are more prevalent in the SCI population than the non-SCI population.12,22 Electrical stimulation therapies may result in contractile activity-induced adaptations in paralyzed skeletal muscle that may translate into health and wellness benefits. Previous studies have suggested that NMES exercise training programs improve glucose and insulin status in people with SCI. Mahoney et al23 used a similar RET protocol and glucose tolerance measurements in 4 participants (1 additional participant was missing data). The authors reported a trend toward improvements in plasma glucose levels (PZ.074) after RET. The results of the present study do not substantiate the previous study and suggest that RET of the quadriceps muscles alone does not improve glucose tolerance in participants with motor complete SCI. Both studies used similar 4-month duration electrical stimulation weight training protocols that resulted in similar increases in muscle size (30%e40%). The current study had a larger sample size, included both men and women, and included more participants with impaired glucose tolerance or insulin action prior to NMES training. Gorgey et al24 also reported improvements in glucose area under the curve after a similar RET protocol, but this training was in combination with a dietary intervention. The study by Gorgey et al,24 similar to the current study, also reported no change in HOMA-IR in response to RET. Other studies used more elaborate electrical stimulation training protocols. Functional electrical stimulation (FES) cycling training for 8 weeks reduced glucose levels at the 2-hour mark of an OGTT in people with motor complete SCI.25 In the study by Jeon et al,25 3 of the 7 participants underwent more invasive testing via a hyperglycemic clamp technique, which also showed improved insulin sensitivity. More recently, an FESrowing exercise program resulted in improvements in the HOMA-IR after 12 weeks of exercise training in 6 participants with paraplegia.26 However, FES cycling uses tetanic contractions that involve a combination of resistance and endurance exercise stimuli. FES cycling also activates the gluteal and hamstring muscle groups in addition to the quadriceps that were trained in the current study. Improvements in glucose and insulin status are likely linked to the volume of activated musculature and the intensity of the exercise program,27 which may have been greater in these FES-induced exercise training protocols than the NMES training in the current study. In the FES-cycling/rowing studies, the participants were also exercising 3 days per week compared with the 2 days per week in the current study25,26; thus, exercise dosing may have an effect. Further investigation is required. The 16 week electrically induced resistance training program used in this study did result in significant hypertrophy of the quadriceps muscle group, similar to previous resistance training protocols. The 39% increase in quadriceps muscle size was similar to increases reported by Mahoney23 (w38%), Gorgey24 (w35%), Gorgey16 (w43%), and colleagues. In the
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2171 current study, we had a wide range of hypertrophy responses to the RET (5%e84% increase in quadriceps cross-sectional area). Interestingly, we found no relation between the magnitude of size increase with training and changes in insulin or glucose levels. We also found no relation between initial insulin or glucose status and the amount of muscle size increase. We did find some evidence of hypertrophy in the knee flexors (w7%), although we aimed the RET to the knee extensor muscle group. Visible inspection of some participants during training suggested that the level of current used was enough to activate some of the hamstring muscle groups. Electrical stimulation training programs that activate more musculature (knee flexors, hip extensors, plantarflexors, etc) may provide greater improvements in oral glucose tolerance and lipid profiles. Of interest, some of the participants had visible muscle contractions, but they were very weak and able to perform only a few electrically stimulated leg lifts at the start of the study. All participants improved their strength and performance, as indicated by increases in the weight lifted and/ or the number of completed leg extensions. We used considerable caution when increasing the load, in order to minimize the risks for musculoskeletal injuries and the effects of exercise-induced muscle injury. No weight was used during the first 2 weeks of training, even if the participant was capable of lifting heavier loads. We also did not increase the weight throughout the 16 weeks of training until 2 to 3 sessions were successfully completed; when the load was increased, it was done by increments of only w0.9kg. We also found no changes in IMF levels (in absolute area/ volume) after RET. In contrast, in a case report by Gorgey and Shepherd,16 12 weeks of RET decreased the IMF cross-sectional area by >50%. Gorgey et al24 also reported relative decreases in the percentage of IMF after RET, but it is unclear if these changes were because of muscle hypertrophy or a decrease of IMF. IMF has been strongly linked with glucose intolerance in chronic SCI9; therefore, training that effectively reduces IMF could be beneficial. This is the first study, to our knowledge, that reports changes in in vivo skeletal muscle mitochondrial capacity after electrically induced RET in individuals with chronic SCI. Previous studies have examined skeletal muscle mitochondrial capacity using phosphorus magnetic resonance spectroscopy and reported that people with SCI have approximately one half to one third the mitochondrial function of healthy able-bodied individuals.17 In this study, skeletal muscle mitochondrial function improved approximately 25% after 16 weeks of RET. Although RET is not commonly associated with improvements in mitochondrial capacity, the decreased initial mitochondrial capacity provides a large dynamic range for improvements, even with RET. Endurance exercise should provide a larger stimulus for improvements in mitochondrial function.28-30 For example, Martin et al31 found that 6 months of endurance training via electrical stimulation resulted in approximately a 2-fold increase in succinate dehydrogenase activity in participants with SCI. Similarly, Kjaer et al32 reported a 2-fold increase in citrate synthase of the vastus lateralis after 3 months of electrical stimulation cycling in individuals with SCI. These results are similar to those reported by Crameri,33 Rochester,34 and colleagues. In contrast, training-induced changes in mitochondrial capacity can be 70% to 100% in able-bodied individuals.35,36 Thus, the changes in this study, although
We thank Hui-Ju Young, MS, and Melissa Erickson, MS, for their assistance with data collection and participant recruitment.
269.7 15.7 35.5 206.9 268.8 191.7 147.4 66.7 261.0 150.0 87.7 104.9 176.5 27.2 143.5089.80
HOMA-IR HOMA-%S HOMA-%B
59.9 317.9 68.5 73.5 58.4 23.5 73.2 171.9 79.3 71.4 160.1 122.7 73.5 203.3 111.2078.10 2.1 52.3 19.7 3.8 2 3.6 5.2 12.1 3.1 5.1 9.3 7.6 4.4 28.9 11.4014.00
Fasting Plasma Insulin Fasting Plasma Glucose HOMA-IR HOMA-%S HOMA-%B Fasting Plasma Insulin
NOTE. HOMA calculations were made using a freely downloadable calculator (https://www.dtu.ox.ac.uk/homacalculator/index.php). * Participants that are classified with type II diabetes mellitus prior to beginning NMES training. y Participants classified as glucose intolerant/insulin resistant prior to beginning NMES training.
Acknowledgements
84 91 136 70 66 119 91 82 65 89 88 83 91 85 88.0019.00
Terence E. Ryan, PhD, University of Georgia, 330 River Rd, Athens, GA 30602. E-mail address: [email protected].
P1 P2 P3* P4 P5 P6* P7 P8y P9 P10 P11y P12y P13y P14 Mean SD
Corresponding author
Fasting Plasma Glucose
Cell respiration; Electric stimulation; Paralysis; Rehabilitation
Participants
Keywords
Pretraining
a. Richmar, 4120 S Creek Rd, Chattanooga, TN 37406. b. LabCorp, 1801 First Ave, Birmingham, AL 35233. c. iDXA; GE Medical Systems Lunar, 3030 Ohmeda Dr, Madison, WI 53718. d. GE Healthcare Institute, N16W22419 Watertown Rd, Waukesha, WI 53186. e. Image J; http://rsbweb.nih.gov/ij/index.html. f. IBM, 1 New Orchard Rd, Armonk, NY 10504.
All participant data for glucose and insulin status pre- and post-NMES training
Suppliers
Appendix 1
Sixteen weeks of electrically induced RET in individuals with SCI resulted in no changes in glucose tolerance or insulin action. This was despite a 39% increase in quadriceps muscle volume and a 25% improvement in skeletal muscle mitochondrial function. Future studies should aim to optimize electrical stimulation training for improving health in individuals with SCI. Health benefits from electrical stimulation training may require more than a primarily resistance training stimulus, or resistance training of more muscle mass.
82 95 151 81 83 140 90 78 73 90 74 79 85 97 92.0023.00
Posttraining
Conclusions
0.4 3.9 4.1 0.4 0.3 1.4 1.0 2.3 0.3 0.4 1.6 1.3 1.2 3.7 1.591.38
This study, as with many others, had a relatively small sample size (NZ14). Small sample sizes are very common when dealing with clinical populations, especially SCI. Because of the sample size, statistical comparisons between participants with differing glucose and insulin statuses were certainly underpowered. Nonetheless, the sample size in this study is larger than previous studies.22,23 Another limitation was the methods for assessing glucose tolerance and insulin sensitivity. Insulin/glucose clamp techniques may have provided a more sensitive measurement of glucose/insulin sensitivity, but are more technically challenging than the OGTT. We used standard clinical measures, such as the OGTT, fasting plasma glucose and insulin, and HOMA-IR, because of their relatively low cost and ease of use. It is possible that more sensitive methodologies, such as euglycemic-hyperinsulinemic clamps, could detect an effect of RET.
267.9 25.4 24.4 282.4 287.6 70.3 102.3 44.2 288.9 263.8 63.5 74.6 83.7 27.1 136.10112.20
Study limitations
57.0 243.8 112.4 82.7 93.3 67.1 91.6 204.9 96.3 50.7 136.8 139.0 105.2 268.6 124.9068.00
statistically significant, might be relatively small in magnitude compared with those reported in able-bodied individuals.
0.4 6.4 2.8 0.5 0.4 0.5 0.7 1.5 0.4 0.7 1.1 1.0 0.6 3.7 1.481.72
T.E. Ryan et al
2.0 31.6 29.9 2.0 2.0 10.3 7.5 18.2 2.0 2.8 12.3 10.6 9.2 30.1 12.2011.00
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Neuromuscular electrical stimulation resistance training in SCI
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