Abdominal muscle contraction thickness and function after specific and general exercises: A randomized controlled trial in chronic low back pain patients

Manual Therapy 15 (2010) 482e489

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Original article

Abdominal muscle contraction thickness and function after specific and general exercises: A randomized controlled trial in chronic low back pain patients Ottar Vasseljen*, Anne Margrethe Fladmark Department of Public Health and General Practice, Faculty of Medicine, Norwegian University of Science and Technology (NTNU), Medisinsk teknisk forskningssenter, 7489 Trondheim, Norway

a r t i c l e i n f o

a b s t r a c t

Article history: Received 26 October 2009 Received in revised form 26 April 2010 Accepted 28 April 2010

The aim of this study was to assess changes in deep abdominal muscle function after 8 weeks of exercise in chronic low back pain patients. Patients (n ¼ 109) were randomized to specific ultrasound guided, sling or general exercises. Contraction thickness ratio in transversus abdominis (TrA), obliquus internus (OI) and externus (OE), and TrA lateral slide were assessed during the abdominal drawing-in maneuver by b-mode ultrasound. Changes in abdominal muscle function were also regressed on changes in pain. Only modest effects in deep abdominal muscle function were observed, mainly due to reduced activation of OI (contraction thickness ratio: 1.42e1.22, p ¼ 0.01) and reduced TrA lateral slide (1.26e1.01 cm, p ¼ 0.02) in the ultrasound group on the left side. Reduced pain was associated with increased TrA and reduced OI contraction ratio (R2 ¼ 0.18). It is concluded that 6e8 treatments with specific or general exercises for chronic low back patients attained only marginal changes in contraction thickness and slide in deep abdominal muscles, and could only to a limited extent account for reductions in pain. Ó 2010 Elsevier Ltd. All rights reserved.

Keywords: Exercise LBP Abdominal muscles Thickness

1. Introduction Changes in the deep abdominal muscles, such as delayed onset (Hodges and Richardson, 1996; Hodges, 2001) and changes in muscle thickness and slide (Ferreira et al., 2004; Hides et al., 2008; Kiesel et al., 2008) have been associated with low back pain (LBP). The changes may be markers of motor control dysfunction, normal adaptation to pain or both. There is a need for research investigating if tailored exercises can normalize motor control dysfunction in the deep abdominal muscles. The abdominal drawing-in maneuver (ADIM) was introduced to volitionally activate the transversus abdominis (TrA) to correct impairments in motor control (Richardson et al., 1999; Urquhart et al., 2005b). This has led to widespread use of stability exercises in LBP rehabilitation. The purpose of the ADIM is to voluntary activate TrA thickening and lateral slide while obliquus internus (OI) and externus (OE) should remain relatively unchanged (Richardson et al., 1999; Teyhen et al., 2007a). Isolated control of TrA was perceived as a necessary first step in normalizing motor control deficits and thereby, presumably, reducing pain and recurrence of symptoms. There is some evidence that ADIM exercises may reduce onset deficits and pain (Tsao and Hodges, 2007,

* Corresponding author. Tel.: þ47 73598876; fax: þ47 73597577. E-mail address: [email protected] (O. Vasseljen). 1356-689X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.math.2010.04.004

2008). However, it seems logical that the ADIM should also influence abdominal muscle contraction thickness and slide. This has only been investigated in experimentally induced pain which caused reduced contraction thickness ratio in TrA during ADIM (Kiesel et al., 2008). The effect of ADIM exercises on contraction thickness and slide has not been investigated in an interventional study, and there is no knowledge of whether specifically designed low load ADIM exercises are more successful than high load specific exercises or general exercises to correct contraction dysfunction in the deep abdominal muscles. The purpose of this study was to assess changes in deep abdominal muscle function during ADIM in terms of contraction thickness ratios and muscle slide, as recorded by ultrasound imaging. Three exercise modes for patients with chronic LBP were investigated; low (ADIM) and high load specific exercises and general exercises. A second aim was to investigate associations between changes in pain and changes in muscle contraction functions during the intervention period. 2. Methods 2.1. Subjects Subjects with LBP were recruited from local medical practitioners and through advertisement. Men and women at age 18e60 years with non-specific chronic LBP (>12 weeks) and pain at

O. Vasseljen, A.M. Fladmark / Manual Therapy 15 (2010) 482e489

presentation between 2 and 8 on an 11-point Numeric Rating Scale (NRS 0e10) were included. Exclusion criteria were prior spinal surgery, radiating pain below the knee, other chronic pain, neurological or rheumatic diagnosis, ongoing insurance case, sick-leave due to LPB for more than a year at presentation, pregnancy, and insufficient comprehension of Norwegian language. The study was approved by the Regional Ethics Committee and is a sub-study of a registered clinical trial (clinicaltrials.gov: NCT00201513). Participants gave signed consent after receiving verbal and written information about the study. 2.2. Design Subjects in this RCT study were randomly assigned to either low load ultrasound guided ADIM exercises, high load sling exercises or general exercises. Block randomization with a random sequence of permuted blocks of variable sizes from 3 to 9 was used and administered by an independent project secretary. Eleven subjects were excluded before randomization; hence 109 persons were randomized to treatment. Subjects progressed through the trial is outlined in Fig. 1. 2.3. Ultrasound recordings

483

2.4. Procedures and outcome measures Ultrasound recordings during ADIM test contractions were performed with the subject in supine hook-lying position on a couch and with the examiner sitting to the right side of the subject (Whittaker, 2007; Teyhen et al., 2007b). Instructions were given to perform the ADIM by pulling the lower abdomen in toward the spine at end of normal expiration (Richardson et al., 1999; Urquhart et al., 2005b; Teyhen et al., 2007b; Koppenhaver et al., 2009a). The following instruction preceded the contraction; “breath in, breath out, do not breath in, gently and slowly draw your lower abdomen in toward the spine”. The ADIM contraction was held for 5e10 s and performed four times; the first two with ultrasound recordings on the left side and the last two on the right. US video loops capturing ADIM test contractions were stored for later measurements using a Matlab adapted software. Onscreen caliper measurements of muscle thickness in TrA, OI and OE were done by drawing the caliper perpendicular inside the hyperechoic region between adjacent fascial borders (Fig. 2). Thickness measurements were made 1 and 2 cm lateral to the v-shaped medial border of TrA, except for OE which was measured only at 1 cm. Resting thickness was measured in relaxed state at end of exhalation and contraction thickness at

A Vivid 7 ultrasound scanner with a M12L linear transducer set to 10 MHz was used for recordings in b-mode (GE-Vingmed Ultrasound, Horten, Norway). The transducer was placed halfway between the 11th costal cartilage and the iliac crest (Richardson et al., 1999; Hodges et al., 2003b; Teyhen et al., 2007b). It was further oriented in a slightly oblique angle approximating the muscle fiber direction of TrA (Urquhart et al., 2005a) and adjusted so that all three lateral abdominal muscle layers (TrA, OI, OE) were visible on the screen. The final transducer location was adjusted so the v-shaped midline border of TrA appeared toward one side of the image display (Fig. 2A).

Recruited, n = 120 11 - Excluded 7 - inclusion criteria failure 1 - declined participation 3 - other reasons Pre test n = 109

Pre-test

Randomization

A US guided n = 36

B Sling exercise n = 36

C General exercise n = 37

Intervention period 8 weeks Post-test A n = 30

B n = 29

C n = 26

6 Lost to post-test 3 illness 1 withdrew 1 moved 1 tech. US error

7 Lost to post-test 3 illness 3 withdrew 1 tech. US error

11 Lost to post-test 8 withdrew 2 illness 1 no reason

Fig. 1. Flow of participants through the study.

Fig. 2. Thickness measurements were obtained at rest (A) and full contraction (B) during the abdominal drawing-in maneuver (ADIM). Thickness measurements were obtained 1 cm (1) and 2 cm (5) lateral from were the transversus abdominis converge medially. Thickness was measured at two locations in transversus abdominis (2, 6), obliquus internus (3, 7) and one location in obliquus externus (4). The distance (cm) of lateral slide for the transversus abdominis (TrAS) from rest to full contraction during ADIM was recorded (B). TrAS and thickness measures in locations 2, 3 and 4 were used for analysis.

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maximal lateral slide of TrA during the ADIM holding period. Contraction thickness ratio was calculated by dividing muscle thickness at maximal contraction on muscle thickness at rest. TrA lateral slide distance (cm) was measured from the v-shaped border at rest and then scrolling the US video to obtain the distance of maximum lateral slide (Fig. 2B). The highest ratio or slide value of two repeated contractions at each site was used for analyses. Ultrasound measurements were done before (pre-test) and after (post-test) the intervention period by the same researcher. Pre-test assessment was done before randomization and post-test 8e10 weeks after the pre-test. Ultrasound measurements of thickness and slide were performed by a person blind to group allocation. 2.5. Interventions The ultrasound guided exercise group (US) represented the low load specific exercise group. ADIM exercises were performed in supine hook-lying position under real-time b-mode ultrasound guidance. Tactile and verbal feedback of proper TrA contractions were provided if needed (Richardson et al., 1999). The treatment goal was to attain gentle TrA contractions in isolation from other abdominal muscles with bilateral symmetrical activation (Richardson et al., 1999). When optimal ADIM was attained (isolated TrA contraction), pelvic floor and multifidus co-contraction was included. Toward the end of the intervention period the subjects were encouraged to implement the ADIM into activities of daily living. A physical therapist with several years experience in ADIM and ultrasound imaging was in charge of the intervention. Written instruction to carry out the ADIM exercise at home was provided, and subjects encouraged to perform 10 pain free contractions 2e3 times per day, holding each contraction for 10 s.

The sling exercise group (sling) represented the high load specific exercise group. Sling exercises for the lumbopelvic area were performed using the Redcord TrainerÓ (Redcord AS, Norway). The system has been described previously by Stuge et al. (2004, 2006) although applied somewhat differently than in this study. With emphasis on controlling the lumbar spine in a neutral position the subjects performed pain free exercises in closed kinetic chain and under increasing loads (Fig. 3). The overall goal was to improve muscle strength and neuromuscular control. Elastic ropes attached to the band supporting the pelvis were used to ease the load and help subjects maintain a neutral spine position at all times, and for exercises to progress without pain. Exercise progression was achieved by gradually reducing the elasticity of the ropes or increasing the distance (torque) to the distal band. Participants were tested in the slings for muscle weakness in a preset number of stabilizing exercises. When weakness, pain, fatigue or asymmetry was identified, this position served as starting point for training and further progression. The number of repetitions/sets was individually adjusted according to pain and fatigue. All training sessions were guided by a physical therapist that was trained in the concept. No instructions on ADIM were given in this group. The general exercise group (general) performed general trunk exercises under guidance of a physical therapist at a fitness center. The participants were given instructions in trunk, leg and back muscle strengthening exercises. The exercises included sit-ups, push-ups, back rotation, leg press, and pull downs. Number of repetitions/sets and progression of exercises were individually adjusted. There was no specific emphasis on trunk stabilizing exercises in this group. All groups had one treatment session per week for 8 weeks. The US and sling exercise groups exercised under individual guidance for 40e60 min. The general exercise group exercised for 1 h and

Fig. 3. Examples of sling exercises with firm ropes supporting the distal leg(s) and elastic ropes supporting the pelvis. The purpose of the elastic ropes was to assist the subject raise the pelvis to neutral lumbar spine position. The neutral position was kept until it could no longer be maintained. Load was progressively increased by giving less support for the pelvis (increasing the elasticity of the pelvic ropes), increasing the lever arm distance (attachment of the firm ropes), increasing the range of lower extremity movements or by removing distal support for one leg. Exercises were done in prone, supine and side-lying.

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under guidance until the exercises were performed correctly. One physical therapist was in charge for each treatment arm. Subjects were asked to refrain from other organized training in the intervention period, but were allowed to carry out ordinary physical activities such as cycling, walking, swimming, and skiing. An information booklet with general information on LBP was given to all participants. 2.6. Statistical analysis To be included in the analyses participants had to complete 6 exercise sessions or more. Complete case analyses were used. Depending on data distribution, one-way ANOVA or KruskaleWallis tests were used to analyze overall group differences, and post-hoc tests carried out with bivariate statistics (e.g. t-test). Change in muscle function was calculated by subtracting pre- from post-test scores and analyzed with ANCOVA with group as factor, change score as response and pre-test scores as covariate, i.e. controlling for baseline group differences (Vickers and Altman, 2001). Post-hoc multiple comparison tests were performed with the TuckeyeKramer test. To study relationships between changes in muscle function and pain (0e10, NRS), the subjects were sorted in equal thirds based on change in current pain (pre- minus post-test) and, for second order sorting; strongest pain during last 4 weeks at post-test. Robust multiple regression using Huber’s correction method (constant ¼ 1.345), which seeks to reduce the influence of outliers (ncss.com; manual III for description), was used to regress change in pain on change in muscle contraction thickness ratios and slide, averaged for left and right side. All comparisons were performed two-tailed and the level of significance set to P  0.05. Statistical analyses were performed with Number Cruncher Statistical System (NCSS 2007, Utah, USA). The study was part of a larger project. Sample size was calculated to detect between group differences in feed-forward activity in TrA (manuscript in preparation).

485

months to 39 years, with 80% of the subjects reporting symptom debut 3 or more years ago and 73% reporting continuous pain since the first episode. Numbers and reasons for drop-outs are given in Fig. 1. Lost data were due to suboptimal image quality, technical difficulties, and drop-outs. There was no significant difference in resting thickness or lateral slide at pre- and post-test for neither women nor men (Table 2). Increase in contraction thickness during ADIM at baseline varied from 76 to 92% in TrA, from 22 to 42% in OI, from 6 to 25% in OE, and TrA lateral slide varied from 0.76 to 1.32 cm depending on side and group (Table 3). No group differences were found on the left side at pre-test, while on the right side, TrA lateral slide was lower in the US (0.76 cm) compared to the sling group (1.05 cm), p ¼ 0.01, and OE contraction ratio was higher in the general exercise (1.25) compared to the US group (1.06), p ¼ 0.03. Side differences were found in the US group (OI ratio; p ¼ 0.02 and TrA lateral slide; p < 0.01) and the general exercise group (TrA lateral glide; p ¼ 0.02). 3.2. Intervention effects

3. Results

Differences between groups in muscle function from pre- to post-test were analyzed adjusted for age and muscle function at pre-test for the outcome variable. Overall group differences were found in left OI contraction ratio (p ¼ 0.04) and left TrA lateral slide (p ¼ 0.03), mainly due to reduced OI ratio (1.42e1.22, p ¼ 0.01) and TrA lateral slide in the US group (1.26e1.01, p ¼ 0.02), (Table 3). No significant changes were found on the right side. Data in Table 3 are presented graphically as mean change scores (95% CI) adjusted for pre-test values in Fig. 4. Negative values indicate contraction values were lower at post compared to pre-test. Overall, small changes were observed. Reduced (mean;  95% CI) left OI contraction ratio was seen in the US (0.16; 0.12) compared to the sling group (0.04; 0.12), p ¼ 0.02. The reduction in left TrA lateral slide in the US group (0.26; 0.18) was significantly greater than in the sling (0.02; 0.18) and general exercise groups (0.10; 0.19), p < 0.05. Visually, between group differences were relatively similar on the left and right side.

3.1. Baseline (pre-test)

3.3. Pain associations

Participants’ characteristics were similar in the three intervention groups except for age. Subjects in the general exercise group were on average 7 years younger than subjects in the sling group, p < 0.01 (Table 1). Participants were characterized by modest pain at baseline but reported fairly high levels of “worst pain” during the past 4 weeks (Table 1). Time since first episode of LBP ranged from 6

Subjects were split in three pain groups (thirds) irrespective of intervention group and based on change in pain from pre- to posttest (Fig. 5). The third with the highest pain reduction had a mean reduction of 3.48 cm (95% CI; 3.04e3.92, n ¼ 29), the middle group 1.34 cm (95% CI; 1.13e1.56, n ¼ 29) and the lowest group 1.21 cm (95% CI; 1.76 to 0.66, n ¼ 29). Fig. 5 indicates that increase in TrA contraction thickness ratio was associated with greater pain reduction (ns). Change in pain was thus regressed on change in abdominal muscle thickness ratios and slide in a multiple regression model (Table 4). Increased TrA and reduced OI contraction thickness ratios contributed significantly to the model which explained 18% of the variance in pain. To verify if these associations were also present at baseline, baseline scores of current pain and

Table 1 Characteristics of participants in the three intervention groups and pain at baseline. Pain was assessed by a 0e10 numeric rating scale (NRS; 0e10). Data are mean (SD) unless otherwise denoted.

Gender M/F (n) Age, yrs. BMI, kg/m2 LBP, yrs. since first episodea NRS, pain at test day NRS, worst pain last 4 wks

Ultrasound guided Sling exercise (n ¼ 36) (n ¼ 36)

General exercise p (n ¼ 37)

7/29 40.9 (11.5) 24.9 (3.1) 6 (2e19)

13/23 43.4 (10.2) 24.9 (3.1) 9 (2e15)

13/24 36 (10.3) 24.3 (2.8) 6 (3.5e11.5)

0.22 0.01b 0.61 0.86

3.3 (1.3)

3.6 (1.7)

3.3 (1.9)

0.71

6.3 (2.0)

6.4 (2.3)

6.2 (2.0)

0.93

BMI; body mass index. a Median (IQR; interquartile range). b Difference between sling and general exercise groups.

Table 2 Muscle thickness (mm) at rest and TrA lateral slide (mm) during the ADIM in men and women at pre- and post-test. Data are in mean (SD). Men (n ¼ 33)

TrA OI OE TrA lateral slide

Women (n ¼ 76)

Pre-test

Post-test

Pre-test

Post-test

3.1 8.1 4.8 11.1

3.2 7.9 4.5 10.1

2.7 6.6 4.2 9.5

2.6 6.8 4.2 9.0

(0.6) (1.5) (1.8) (3.9)

(0.6) (1.9) (1.6) (5.2)

(0.6) (1.3) (1.2) (4.1)

(0.5) (1.3) (1.1) (4.0)

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Table 3 Muscle contraction thickness ratio during ADIM in the right and left TrA, OI and OE muscles, and TrA lateral slide (cm) at baseline (T1) and after intervention (T2) for the three intervention groups: Ultrasound guided exercise (Ul), sling exercise (Sling) and general exercise (Gen). Mean (95% CI) values are given and n represents the number of subjects with valid data on both tests, i.e. complete case analysis. Group

Right

Ul Sling Gen Ul Sling Gen Ul Sling Gen Ul Sling Gen

1.89 1.92 1.85 1.22 1.35 1.29 1.06 1.08 1.25 0.76 1.05 0.96

Within group

T1 TrA, ratio

OI, ratio

OE, ratio

Lat. slide TrA, cm

T2 (1.59e2.18) (1.70e2.14) (1.59e2.11) (1.12e1.32) (1.24e1.46) (1.18e1.40) (0.94e1.17) (0.99e1.16) (1.11e1.39) (0.60e0.93) (0.89e1.22) (0.77e1.14)

*

y y *y y *

1.62 1.86 1.70 1.21 1.34 1.24 1.09 1.16 1.18 0.81 0.98 1.05

(1.46e1.78) (1.65e2.07) (1.50e1.90) (1.10e1.31) (1.25e1.43) (1.16e1.32) (1.00e1.18) (1.06e1.26) (1.01e1.35) (0.62e0.99) (0.77e1.18) (0.78e1.31)

Left

p

n

T1

0.10 0.71 0.28 0.83 0.85 0.26 0.57 0.08 0.43 0.70 0.50 0.48

24 25 23 25 26 23 22 25 15 25 26 24

1.88 1.76 1.80 1.42 1.34 1.35 1.08 1.06 1.10 1.26 1.32 1.24

Between groupsa

Within group T2 (1.67e2.10) (1.55e1.96) (1.56e2.05) (1.29e1.54) * (1.23e1.46) (1.24e1.47) (0.98e1.18) (0.96e1.15) (1.01e1.19) (1.03e1.49) * (1.09e1.55) (1.08e1.40) *

1.77 2.00 1.81 1.22 1.40 1.30 1.12 1.10 1.16 1.01 1.31 1.35

(1.62e1.91) (1.74e2.27) (1.60e2.03) (1.15e1.29) (1.25e1.55) (1.15e1.45) (1.03e1.21) (1.00e1.20) (1.06e1.26) (0.81e1.21) (1.07e1.56) (1.14e1.57)

p

n

Right p

Left p

0.37 0.14 0.94 0.01 0.35 0.55 0.48 0.40 0.34 0.02 0.98 0.29

23 26 22 22 24 22 19 23 21 25 27 23

0.19

0.29

0.22

0.04

0.76

0.50

0.58

0.03

Significant muscular asymmetry (side difference) within group at the same test (T1 or T2) is marked with an asterisk (*). Significant between group differences in muscle function within the same test (T1 or T2) are indicated by (y). a ANCOVA; group difference in change (T2eT1) adjusted for baseline value (T1) and age.

worst pain over last 4 weeks were regressed on the same measures but no associations were found. 4. Discussion Changes in deep abdominal muscle contraction thickness and slide during ADIM were assessed after 8 weeks with either specific US guided exercises, sling exercises or general exercises in chronic LBP patients. Small changes were observed and the significant findings were mainly due to reduced activation on the left side and reduced asymmetry in the US group. Regardless of group, reduced pain was weak but significantly associated with an increase in TrA and a decrease in OI contraction thickness ratios over the intervention period. Reduced abdominal muscle contraction thickness is reported in cross-sectional studies of chronic LBP patients compared to healthy subjects during the ADIM (Critchley and Coutts, 2002), during lower limb tasks (Ferreira et al., 2004), and in studies with experimentally induced pain (Kiesel et al., 2008). However, the current study represents the first large scale interventional trial investigating changes in abdominal muscle contraction thickness and slide. Deep abdominal muscles and particularly TrA are proposed to contribute to segmental stiffness in the lumbar spine (Hodges et al., 2003a), possibly by tensioning the thoracolumbar fascia and increasing the intra-abdominal pressure (Cresswell et al., 1992; Hodges et al., 2005; Barker et al., 2006; Hides et al., 2006). Some evidence supports this position (Hodges et al., 2003a; Hides et al., 2006; McCook et al., 2009), while it has been disputed by advocates of more forceful bracing exercises (Grenier and McGill, 2007; Vera-Garcia et al., 2007). There are however consistent reports of motor control changes in TrA and OI (Hodges, 2001; van Dieen et al., 2003; Ferreira et al., 2004; Kiesel et al., 2008), most likely reflecting neuromuscular adaptation to pain, e.g. Hodges (2008). Causal relationship between pain and muscle activity has been studied in experimental pain trials only, while firm evidence requires studies of healthy individuals followed prospectively until pain appears. Inference cannot be made from experimental pain studies to longstanding chronic LBP. Some knowledge of relationship between pain and muscle activity can be gained from interventional studies like ours. The regression model in our study suggests weak associations between change in abdominal muscle activity and change in pain over an 8-week intervention period. The general exercise group served as control for the specific exercise groups since good evidence exists for exercises in chronic

LBP (Hayden et al., 2005; Henchoz and Kai-Lik, 2008). Evidence favoring specific over general exercises for chronic LBP is however marginal (Ferreira et al., 2006; Rackwitz et al., 2006), which is supported by the small differences in deep abdominal muscle function between specific and general exercises in this study. The reduced OI contraction thickness in the US group may represent a clinically relevant finding as increased OI muscle activity with increasing load is reported in LBP relative to healthy subjects (Hides et al., 2009). On the other hand, reduced TrA lateral slide on one side in the US group is contrary to what is expected based on previous observations of reduced slide in LBP patients compared to healthy subjects (Hides et al., 2009). We cannot rule out that these findings are influenced by regression toward the mean (at least for OI; Table 3) or type I error due to multiple comparisons. The current study showed that alterations in deep abdominal muscle contraction thickness and slide explained merely 18% of the pain variation, meaning 82% of the variation must be explained by other factors. The association between reduced pain and increased TrA and decreased OI contraction thickness ratios complies with the objectives for ADIM exercises. However, the results should be replicated due to the modest explained variance (R2 ¼ 0.18). In this study, sling exercises were marginally better for increasing TrA contraction ratio while ADIM exercises with feedback (US group) were better for reducing activity in OI. If 6e8 treatments is sufficient to observe muscular effects depend on whether the exercises are intended for muscular hypertrophy or neuromuscular adaptation. The emphasis on low level contractions and isolated control of TrA in ADIM favors the latter. Muscle hypertrophy is typically found after 8e12 weeks of intensive strength training (Danneels et al., 2001; Seynnes et al., 2007). Early changes in contraction force observed within days to a few weeks after initiating training are mainly due to increased central drive and neural adaptation (Narici et al., 1989; Enoka, 1997; Seynnes et al., 2007). Although the intervention period in the current study was potentially sufficient to induce neuromuscular adaptations, we cannot exclude that a longer intervention period would produce different effects. Ultrasound imaging is found reliable and valid for measuring deep abdominal muscle structures (Hides et al., 2006; Kiesel et al., 2007; Mannion et al., 2008; Koppenhaver et al., 2009a). The transducer location in this study was similar to previous studies; detailed by Teyhen et al. (2007b). The abdominal muscle resting thickness values (Table 2) are similar to healthy persons (Bunce et al., 2002; Hodges et al., 2003b; Hides et al., 2007; Koppenhaver

O. Vasseljen, A.M. Fladmark / Manual Therapy 15 (2010) 482e489

OE

TrA lateral slide

US guided

Sling

General

Contraction ratio (Post-Pre)

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

OI

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

Contraction ratio (Post-Pre)

Contraction ratio (Post-Pre)

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

TrA

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

Contraction ratio (Post-Pre)

Contraction ratio (Post-Pre)

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

Left

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

Lateral slide, cm (Post-Pre)

Contraction ratio (Post-Pre)

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

Lateral slide, cm (Post-Pre)

Right

487

0.5 0.4 0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 -0.4 -0.5

TrA

OI p=0.02

OE

TrA lateral slide p=0.01 p=0.04

US guided

Sling

General

Fig. 4. Change in contraction thickness ratio in transversus abdominis (TrA), obliquus internus (OI), and obliquus externus (OE) muscles, and change in lateral slide of TrA during ADIM for the three intervention groups. Change was calculated by subtracting pre-test from post-test scores, i.e. negative values mean that thickness ratio or lateral slide values were reduced after the intervention period, and vice versa. The left column of figures represents the right abdominal muscles and the right column the left abdominal muscles. Dashed lines illustrate zero (no change). Data are mean change (95% CI); T2eT1.

et al., 2009a) and LBP subjects (Mannion et al., 2008; Koppenhaver et al., 2009a). TrA ratio values during ADIM in comparable studies are reported in the range from 1.5 to 2.1 in LBP patients (Kiesel et al., 2007; Teyhen et al., 2008; Koppenhaver et al., 2009a), similar to the ratios in the current study (1.76e1.92; Table 3). TrA lateral slide are mainly reported by one group (Hides et al., 2006, 2007, 2008, 2009). Elite cricketers with LBP had reduced TrA lateral slide during ADIM (0.54 cm) compared to healthy controls (Hides et al., 2008). This is considerably lower than observed in the current study (1.11 cm in males at baseline). The difference may be explained by higher levels of pain in the former study (5.8 vs z3.4

on 0e10 scales), that the cricketers had to perform ADIM while in the MRI scanner, or it may reflect reduced muscle activity in deep abdominal muscles in athletes. Values for TrA lateral slide in our study were nevertheless lower compared to healthy subjects in the study by Hides et al. (2008). Certain limitations apply to this study. Ultrasound may have insufficient sensitivity to small changes in muscle activity. The smallest detectable change in muscle thickness and slide corresponded to a change in EMG recorded muscle activity proportional to 17% (TrA thickness), 22% (OI thickness) and 12% (TrA slide) of MVC (Hodges et al., 2003b), meaning muscle activity changes

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TrA 0.4 0.2 0.0 -0.2 -0.4

Highest

Middle

OI 0.4 0.2 0.0 -0.2 -0.4

Lowest

Highest

OE 0.4 0.2 0.0 -0.2 -0.4

Highest

Middle

Lowest

TrA lateral slide Change (cm T2 - cm T1)

Change (ratio T2 - ratio T1)

Change (ratio T2 - ratio T1)

Change (ratio T2 - ratio T1)

488

Middle

Lowest

0.4 0.2 0.0 -0.2 -0.4

Highest

Middle

Lowest

Pain reduction

Pain reduction

Fig. 5. Change in contraction thickness ratio in TrA, OI and OE, and in TrA lateral slide (cm) relative to change in pain from pre- to post-test. Subjects are partitioned in equal thirds according to the size of pain reduction from pre- to post-test. Only subjects with valid data on both tests are included (n ¼ 86). Data are mean change (95% CI); T2eT1.

below this magnitude may go undetected by ultrasound measures of thickness and slide. A 20% reduced TrA contraction thickness in LBP patients compared to healthy controls was found during ADIM in a recent study by Teyhen et al. (2009). This might thus represent a clinical important effect and is also above measurement error which has been reported to 17% in a study investigating reliability for change in TrA thickness (Kiesel et al., 2007). With 25 subjects in each group, the trial had 80% post-hoc power to detect a 20% change in contraction thickness ratio. Applying a 20% change to our data for TrA contraction thickness ratio (Table 3) would mean an improvement from 1.85 at pre-test to 2.22, which is clearly above the reported change. However, post-hoc power calculations are not recommended (Walters, 2009), and we cannot exclude that the study was slightly underpowered. OE should remain unchanged under execution of the ADIM. Contraction thickness measurement of OE was included in this study to verify this. The validity of contraction thickness Table 4 (A) Regression of change in pain on change in abdominal muscle contraction thickness (TrA, OI and OE) or TrA lateral slide from pre- to post-test, and (B) ANOVA table corresponding to the regression model. A Variable

Beta (b)

SE (b)

t

p

Constant Change in TrA ratio Change in OI ratio Change in OE ratio Change TrA lat. slide

1.011 1.165 2.322 0.747 0.249

0.211 0.398 0.883 0.815 0.582

2.92 2.63 0.92 0.43

0.0046 0.01 0.36 0.67

measurements in OE has however been questioned due to low or inconsistent association between thickness measurements and EMG activity during ADIM (John and Beith, 2007; Koppenhaver et al., 2009b). The fact that ADIM served as basis for outcome measures while also used as training in the US group did not appear to favor the outcome in this group. Greater effects cannot be ruled out if subjects are subdivided based on performance on the ADIM. The lack of a healthy control group is of less concern given the marginal and equal effects in all groups. It is possible that changes occurred in other muscles or motor control properties not included in this study, such as onset of muscle activity or in automatic activation during more functional tasks, and our study did not explore possible long term benefits. Further explorations will include muscle onset and effects of psychological variables, e.g. fear of avoidance, in these groups. In conclusion, 6e8 treatments with low load ultrasound guided abdominal drawing-in maneuver, high load sling exercises or general exercises for chronic low back patients attained only marginal changes in contraction thickness and slide in deep abdominal muscles, and could only to a limited extend account for reductions of pain. Regardless of group, reduced pain was weakly but significantly associated with increased TrA and decreased OI contraction thickness ratios over the intervention period. Acknowledgments

B Source of variation

DF

R2

SS

MS

F

p

Regression model Change in TrA ratio Change in OI ratio Change in OE ratio Change TrA lat. slide Residual Total

4 1 1 1 1 71 75

0.18 0.10 0.08 0.01 0.00

44.71 23.97 19.38 2.36 0.51 199.12 243.83

11.18 23.97 19.38 2.36 0.51 2.80 3.25

3.99 8.55 6.91 0.84 0.18

0.0057 0.0046 0.01 0.36 0.67

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