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Gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise
Accepted Manuscript Title: Gas Exchange Kinetics Following Concentric-Eccentric Isokinetic Arm and Leg Exercise Authors: U. Drescher, S. Mookerjee, A. Steegmanns, A. Knicker, U. Hoffmann PII: DOI: Reference:
S1569-9048(16)30301-9 http://dx.doi.org/doi:10.1016/j.resp.2017.02.003 RESPNB 2766
To appear in:
Respiratory Physiology & Neurobiology
Received date: Revised date: Accepted date:
30-11-2016 8-2-2017 9-2-2017
Please cite this article as: Drescher, U., Mookerjee, S., Steegmanns, A., Knicker, A., Hoffmann, U., Gas Exchange Kinetics Following ConcentricEccentric Isokinetic Arm and Leg Exercise.Respiratory Physiology and Neurobiology http://dx.doi.org/10.1016/j.resp.2017.02.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gas Exchange Kinetics Following Concentric-Eccentric Isokinetic Arm and Leg Exercise Drescher, U.a, Mookerjee, S.b, Steegmanns, A.a, Knicker, A.c, Hoffmann, U.a
a
Institute of Physiology and Anatomy, Am Sportpark Müngersdorf 6, German Sport University Cologne, Cologne, 50933, Germany.
b
Department of Exercise Science, 400 E.2nd St, Bloomsburg University, Bloomsburg, PA 17815, USA.
c
Institute of Movement and Neuroscience, Am Sportpark Müngersdorf 6, German Sport University Cologne, Cologne, 50933, Germany.
Correspondence: Uwe Drescher German Sport University Institute of Physiology and Anatomy Am Sportpark Müngersdorf 6 50933 Cologne Germany Tel: +49 (0)221 4982 6761 E-Mail: [email protected]
Highlights
High intensity, combined concentric-eccentric isokinetic arm and leg exercise was performed to determine the time course of cardio-respiratory kinetics – with focus on pulmonary gas exchange and arteriovenous oxygen content difference (avDO2) – immediately in the recovery phases. The time to attain the avDO2-peak seems to be different between arm and leg exercise. Significant differences in the kinetics responses could be identified between 60 deg·s-1 and 150 deg·s-1 for isokinetic speed, and between oxygen uptake and carbon dioxide output (V’CO2) as well as between V’CO2 and ventilation.
ABSTRACT Purpose: To evaluate the effects of exercise velocity (60, 150, 240 deg·s-1) and muscle mass (arm vs leg) on changes in gas exchange and arterio-venous oxygen content difference (avDO2) following high-intensity concentric-eccentric isokinetic exercise.
Methods: Fourteen subjects (26.9±3.1 years) performed a 3x20-repetition isokinetic exercise protocol. Recovery beat-to-beat cardiac output (CO) and breath-by-breath gas exchange were recorded to determine post-exercise half-time (t1/2) for oxygen uptake (V’O2pulm), carbon dioxide output (V’CO2pulm), and ventilation (V’E).
Results: Significant differences of the t1/2 values were identified between 60 and 150 deg·s-1. Significant differences in the t1/2 values were observed between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E. The time to attain the first avDO2-peak showed significant differences between arm and leg exercise.
Conclusions: The present study illustrates, that V’O2pulm kinetics are distorted due to non-linear CO dynamics. Therefore, it has to be taken into account, that V’O2pulm may not be a valuable surrogate for muscular oxygen uptake kinetics in the recovery phases.
Keywords Oxygen uptake kinetics, skeletal muscle, resistance exercise, recovery phase
List of specific abbreviations avDO2
[L·L-1]
Arterio-venous oxygen content difference
CO
[L·min-1]
Cardiac output
CO0
[L·min-1]
Average of the first 5 s of CO during recovery
HR
[min-1]
Heart rate
SV
[ml]
Stroke volume
t1/2
[s]
Half-times: time to reach 50% from maximum to rest
tmax
[s]
Time to attain the 1st avDO2-peak
V’CO2pulm
[L·min-1]
Pulmonary carbon dioxide output
V’E
[L·min-1]
Ventilation
V’O2pulm
[L·min-1]
Pulmonary oxygen uptake
virtV’O2
[L·min-1]
Virtual pulmonary oxygen uptake
1. Introduction The greater oxygen uptake elicited by arm exercise versus leg exercise has been attributed to relatively smaller muscle mass, greater isometric component, and torso stabilization. Despite similarities in cardiac output (CO) during upper and lower body exercise, the hemodynamic responses, however, are quiet varied. Further, the relatively greater surface area to mass ratio in the arms coupled with a reduced skeletal muscle pump effect from the lower body could reduce the venous return (Toner et al. 1990; Miles et al. 1984). The resultant greater total peripheral resistance and afterload during upper body exercise may also influence the oxygen uptake kinetics (Miles et al. 1989). During exercise, the regulation of skeletal muscle perfusion becomes important to supply the exercising muscles with oxygen (Delp and Laughlin 1998). Therefore, perfusion and CO distribution are important exercisedependent parameters that influence muscular performance during and following exercise. The kinetics of the cardio pulmonary responses of both upper (e.g. arm) and lower (e.g. leg) body segments during and following resistance exercise training are of importance for an understanding of the associated regulatory mechanisms as well as for individual fitness assessments. One the one hand, this is of interest for those engaged in predominantly upper body tasks such as canoeing or swimming (Sanada et al. 2005), individuals with spinal cord injuries (Myers 2005), as well as those involved in industrial, military or space flight operations (Sawka 1989; Sawka and Pandolf 1991; Cowell et al. 2002). On the other hand, various lower body activities such as sprinting (Wilkerson et al. 2004; Dupont et al. 2010), running (Dupont et al. 2005), cycling (Tordi et al. 2003) and numerous resistance training exercises (Millet et al. 2002) actively involve the upper body. In this regard, since these skills and events are performed at varying movement velocities (e.g. Billat et al. 2000) during both training and competition, this is another factor that must be taken into account.
Normally, resistance exercise training is focused on the development of maximal muscle force output which, in turn, is associated with changes in single motor unit firing rate, firing rate synchronization, increased double discharges, and cortical excitability (e. g. Griffin and Cafarelli 2005). Resistance exercise training sessions are characterized by brief, intermittent sets and exercise combinations typically lasting a few minutes. Thus, it would be of interest to focus on the aspects of pulmonary gas exchange kinetics immediately (i.e. 120 seconds post-exercise) following high intensity resistance exercise. The utilization of varied exercise modes (i.e. upper versus lower body exercise) as well as movement velocities will also enable a clearer understanding of the effects of these variables on pulmonary gas exchange kinetics. High intensity resistance exercise is characterized by various ventilatory behaviors such as hyperventilation, Valsalva, apnea. These modifications result in significant alterations in tidal breathing and gas exchange at the mouth, which complicates the measurement of pulmonary oxygen uptake (V’O2pulm). Additionally, intra-thoracic and intra-abdominal pressure changes during vigorous exercise (Sharpey-Schafer 1953; Lee et al. 1954), alter venous return and consequently CO, delaying and distorting the pulmonary gas exchange (e.g. oxygen uptake). But post-exercise breathing patterns will normalize and attain relatively greater stability. Therefore, indirect inferences about muscular metabolism can be derived more reliably from the recovery gas exchange kinetics. During high intensity resistance exercise the corresponding isometric component (even during so-called dynamic exercise) results in occlusion of vascular beds in the contracting muscle producing a transient ischemic effect (Barcroft and Millen, 1939; Barnes, 1980; Sjøgaard et al. 1988). This may enhance anaerobiosis resulting in the accumulation of associated metabolites. At the cessation of exercise these metabolites would enter the greater circulation and may influence pulmonary gas exchange kinetics. The magnitude of these effects could be influenced
by exercise intensity. In this context, the influences of muscle mass and movement velocity on the pulmonary and cardio-dynamic parameters are important. During high-intensity exercise accurate assessment of pulmonary gas exchange, as a proxy of muscle oxygen uptake, needs to be approached with caution, due to the aforementioned issues. However, the immediate post-exercise assessment of cardiopulmonary variables provides for relatively greater stable recording conditions since distorted breathing maneuvers (e.g. apnea, Valsalva, etc.) will be significantly diminished. In this regard, usually faster oxygen uptake kinetics are associated with higher maximal oxygen uptake values (Chilibeck et al. 1996). Accelerated pulmonary gas exchange can therefore be associated with improved V’O2pulm and increased pulmonary carbon dioxide output (V’CO2pulm) mediated by increased ventilatory drive. In the analysis of V’O2pulm, sparse attention has been given to the additional influences of CO and arterio-venous difference of oxygen content (avDO2). However, the avDO2 measured by V’O2pulm and CO may be used as a surrogate of the synchronization of muscle perfusion and muscular oxygen demand. Further, avDO2 can give important information about the time delay of the arrival of venous blood volume between exercising muscles and the lungs. V’O2pulm kinetics will be influenced on the one hand by the time delay of the venous return and its stored oxygen as well as the perfusion of the lungs. This impedes an unambiguous conclusion on the muscular oxygen uptake kinetics following the onset of recovery. Therefore, the purpose of this study was to - (1) determine the time course of cardio-respiratory kinetics – focusing on pulmonary gas exchange and avDO2 – immediately after high intensity, combined concentric-eccentric isokinetic exercise; (2) assess the influence of isokinetic velocity and muscle mass on cardio-respiratory kinetics following high intensity, combined concentriceccentric isokinetic exercise.
2. Methods 2.1 Subjects Written informed consent was obtained from 14 healthy, male subjects: age 26.9 ± 3.1 years; height 181.8 ± 9.6 cm; weight 81.2 ± 9 kg; BMI 24.6 ± 1.8 kg/m2 (mean ± SD) to participate in the study. The study was approved by the Ethics Committee of the German Sport University Cologne in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. 2.2 Isokinetic Strength Testing Three sets of twenty maximal voluntary concentric-eccentric contractions were performed (Fig. 1) on an IsoMed 2000 Isokinetic dynamometer (D&R Ferstl GmbH, Hemau, Germany), at 60 deg·s-1, 150 deg·s-1, and 240 deg·s-1 in a randomized order. The leg exercises consisted of single leg knee extensions / flexions with a range of motion (ROM) of 90° and the arm exercises consisted of single arm elbow flexions / extensions with a ROM of also 90°. During each test gas exchange (V’O2pulm, V’CO2pulm, V’E) was measured breath-by-breath (ZAN 680, ZAN Meßgeräte GmbH, Oberthulba, Germany), heart rate (HR; by R-R interval from electrocardiography), stroke volume (SV; by impedance cardiography; see Fortin et al. 2006 for details) and blood pressure (finger plethysmography) continuously beat-to-beat (Task Force® Monitor, CNSystems Medizintechnik AG, Graz, Austria). The ZAN 680 device was calibrated with oxygen and carbon dioxide with known concentrations before each test was performed. For the beat-to-beat measurement of continuous blood pressure the device was calibrated by oscillatory measures before each test was started and the subject was seated on the exercise device in the resting condition and upright position. The left hand and arm were fixed on an armrest to avoid movements of the hand and fingers to preserve good signal quality of the
continuous blood pressure measurement. Ambient conditions (temperature, humidity, pressure) were kept constant for all tests. << Fig. 1 >> Recovery (120 s) breath-by-breath gas exchange data were recorded to determine postexercise half-time (t1/2) for V’O2pulm, V’CO2pulm, and V’E, denoted as the time taken to reach 50% from maximum to rest. All parameters were time aligned and interpolated for 1 s intervals. avDO2 was determined by the quotient between V’O2pulm and CO (Eq. 1); CO was derived as the product of HR and SV. avDO2(t) = V’O2pulm(t) / CO(t)
(Equation 1)
For pulmonary oxygen uptake a virtual pulmonary oxygen uptake (virtV’O2; Eq. 2) was calculated assuming no change of CO after the onset of recovery. virtV’O2(t) = V’O2pulm(t) · CO0 /CO(t)
(Equation 2)
For this purpose CO0 was calculated as the average of the first 5 s of recovery to avoid artifacts from muscle contraction on ICG measurements for the SV assessment. 2.4 Statistical analyses Three-way repeated measures analysis of variance (ANOVA) was used to determine the effect of Parameter (V’O2pulm, V’CO2pulm, V’E), Speed (60 deg·s-1, 150 deg·s-1, 240 deg·s-1) and Limb (arm, leg) on t1/2 values. Differences between the peaks (amplitude) and the time to attain the peaks (tmax) of avDO2 were analyzed via a two-way repeated measures ANOVA with factors Limb and Speed. The alpha level was set to 0.05 for statistical significance. For all statistical analyses SPSS 23 was applied.
3. Results 3.1 Cardio-respiratory responses Fig. 2 displays the pulmonary and cardio dynamic responses following concentric-eccentric isokinetic arm and leg exercise. The time course of V’O2pulm, V’CO2pulm, V’E and avDO2 displays a steep increase within the first 10 seconds of recovery. The V’O2pulm and avDO2 at 150 deg·s-1and 240 deg·s-1 velocities following leg exercise, exhibit a pronounced secondary hyperventilation around 20 seconds into recovery. V’E declines steeply followed by a slower phase to recovery. VirtV’O2 displays a similar relative temporal course as the real measured V’O2pulm. The absolute values of virtV’O2 are a bit higher than the measured V’O2pulm for both arm and leg exercise. CO following leg exercise (peak values ~ 12.5 L · min-1) displays higher perfusion rates than arm exercise (peak values ~11.0 L · min-1). Interestingly, for arm exercise in the 60 deg·s-1 condition, CO values are clearly below the other two exercise speeds within the first 60 seconds. Although we did not measure muscle metabolites or lactate, the large increases in V’ E are consistent with previous reports. In our experiments, respiratory exchange ratio (RER) exceeded 1.0 for all tests post-exercise. << Fig. 2a-2l >> For pulmonary avDO2 the first peak was identified in 82 of 84 cases. Amplitudes tmax values are summarized in Tab. 1. Both factors Limb and Speed, as well as the interactions showed no significant differences (p > 0.05 each) between the amplitudes of the first peaks in the avDO2 curves. In contrast, the two-way repeated measures ANOVA showed a significant factor Limb (p < 0.05) for tmax of avDO2 (arm: 7.2 ± 3.5s, leg: 9.9 ± 4.1s); for the factor Speed and interaction no differences could be identified (p > 0.05) for tmax of avDO2. A second avDO2-peak was
identified in 47 of 84 cases. Since there was no systematic pattern of distribution of these second avDO2-waveforms across the testing conditions, no further analyses were conducted. << Tab. 1 >> 3.2 Dynamics analysis Applying a three-way repeated measures ANOVA with factors Parameter, Speed and Limb significant influences on t1/2 were found for the factors Parameter and Speed (p < 0.05; Tab. 2). The factor Limb and all interactions were not significant (p > 0.05). Post-Hoc Bonferroni pairwise comparisons reveal significant differences of t1/2 between 60 deg·s-1 (37.1 ± 7.5s) and 150 deg·s1
(49.4 ± 6.6s; p < 0.05), but not between 60 deg·s-1 and 240 deg·s-1 (47.9 ± 7.1s) as well as
between 150 deg·s-1 and 240 deg·s-1 (p > 0.05). << Tab. 2 >> For the factor Parameter significant differences on t1/2 were identified between V’O2pulm (42.1 ± 5.0s) and V’CO2pulm (52.0 ± 7.2s; p < 0.05) and between V’CO2pulm and V’E (40.4 ± 7.6s; p < 0.05), but not between V’O2pulm and V’E (p > 0.05).
4. Discussion To our knowledge no studies have previously looked upon pulmonary gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise in the early phase of recovery. Therefore, the aim of this study was to describe and analyze the effects of high intensity, combined concentric-eccentric isokinetic exercise on pulmonary (e.g. V’O2pulm, V’CO2pulm, V’E) and cardio-dynamic (e.g. avDO2) parameters, influenced by isokinetic velocity and involved muscle mass during the recovery phase. The major findings are:
1) For the time to attain the 1st avDO2-peak (tmax) significant differences were observed between arm and leg exercise in the recovery phase. 2) Significant differences of the t1/2 values between 60 deg·s-1 and 150 deg·s-1 were identified for factor Speed in the recovery phase. 3) For factor Parameter significant differences in the t1/2 values were identified between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E in the recovery phase. 4) No significant differences for the t1/2 values were noticed for factor Limb (arm vs. leg) in the recovery phase. 4. 1 Methodological aspects Most studies have utilized mono or double exponential models for data fitting of the cardiorespiratory and muscle parameters (Haseler et al. 1999, Özyener et al. 2001, Ferreira et al. 2005, Ferreira et al. 2006, Harper et al. 2008, Lai et al. 2008). In the present study we opted not to utilize those specific model applications because our results indicate that the responses of the cardio-dynamic parameters in the recovery phase demonstrate more complex temporal profiles than mono or double exponential models can sufficiently represent. Therefore, and for reasons of simplicity we calculated the t1/2 values of the parameters of interest, which do not rely on any specific model assumptions, to highlight possible differences in the kinetics responses by means of these values. Also, previous analyses of exercise onset or recovery phases typically utilize leg or arm ergometers with constant work rate increments or phases for on- and off-kinetics analysis. Our testing protocol included maximal voluntary contractions throughout the eccentric-concentric phases of arm and leg exercise. This has to be taken into account in the following discussions, because there are differences across the study designs (e. g. exercise intensities, exercise modes) which do impede a one-to-one comparison.
4. 2 Pulmonary and cardio-dynamic responses 4.2.1 Temporal profiles The temporal profiles show a clear first peak of V’O2pulm, V’CO2pulm, V’E and avDO2 within the first 10 s of the recovery phase for both arm and leg exercise and across all movement velocities. In addition, a second peak can be seen in V’O2pulm for 150 and 240 deg·s-1, in V’CO2pulm for 240 deg·s-1 and in avDO2 for all three movement velocities, but for leg exercise only. Most likely, the concentric-eccentric isokinetic exercise mode increases the consumption of oxygen due to a very high oxygen requirement at muscular level and simultaneously by restriction of blood flow to the exercising muscles due to the isometric component (Sjøgaard et al. 1988), which will result in a greater avDO2 during exercise in the leg than in the arm muscles. At the onset of recovery, the 1st avDO2 peak is caused by the arrival of oxygen desaturated blood from the muscle to the lungs. This delay results from the occlusion of venous blood flow during muscle activity. The time between the offset in exercise and changes in the avDO 2 can be used to gauge transport time delays between the muscular and pulmonary sites. In the comparison between arm and leg exercise the amount of avDO2 accumulated during the concentric-eccentric arm exercise phase is less than the amount during concentric-eccentric leg, so that the 2nd peak for arm exercise cannot be observed clearly, which may represent an imbalance between perfusion and aerobic metabolism during recovery. The smaller 2nd peak in avDO2 could be due to significant differences between involved skeletal arm and leg muscle masses. For Caucasian men, Gallagher et al. (1997) determined the total appendicular skeletal muscles masses of arms and legs as 7.2 ± 1.5 kg and 21.1 ± 2.8 kg, respectively, which implies a leg-to-arm ratio of about 2.93. Therefore, it can be assumed that maximal voluntary concentric-eccentric isokinetic contractions produce definite differences between arm and leg exercise in the cardio-respiratory responses.
Kustrup et al. (2009) showed that following high-intensity knee extension exercise the blood transit time from exercising muscles to the lungs lasts about 6-7 seconds after 10 and 30 seconds respectively, and about 11 seconds after 1 minute in recovery. These values are close to our tmax values (see Tab. 1) which range from 7.1 ± 4.3s (arm; 60 deg·s-1) to 11.0 ± 6.7s (leg; 150 deg·s-1). Assuming, that the venous transit way is shorter for arm than for leg exercise, the tmax values seem to be coherent. Additionally, Kustrup et al. (2009) mentioned that V’O2pulm kinetics does not reflect muscular oxygen uptake kinetics in the recovery phase. This is consistent with Haseler et al. (1999) indicating that differences in the kinetics responses of phosphocreatine kinetics could not be limited to metabolic issues but rather to variations in oxygen availability. With the present results we cannot derive a certain conclusion about the muscular metabolism at cellular level. However, the temporal profiles of V’O2pulm, avDO2 and CO suppose, that cardio-respiratory kinetics have to be taken with caution for an estimation of oxidative metabolism at muscular and cellular level following high-intensity exercise in the recovery phase; this is due to the time-delaying and distortive effects of perfusion and venous return. 4.2.2 Dynamics – Half-time (t1/2) values The observed effect of Velocity on the t1/2 values were only significantly different between 60 deg·s-1 and 150 deg·s-1. Assuming, that the velocity of 60 deg·s-1 provoke high demands on the exercising muscles which is accompanied by an increased motor-unit recruitment and therefore a greater activation of muscle fibers, may result in faster aerobic metabolism responses indicated by faster oxygen uptake kinetics. Furthermore, the isometric component during the muscle contractions may be more prevalent during the 60 deg·s-1 condition than during the other two velocities, because the velocity of 60 deg·s-1 is sufficiently slow to produce high resistances and muscle forces on the arm or leg lever. Based on this line of reasoning there
should be a significant difference between 60 deg·s-1 and 240 deg·s-1 for the t1/2 values. However, this is not the case and could possibly be explained by altered interactions of muscle contraction components (e.g. isotonic, isometric, auxotonic) across the exercise velocities. This issue cannot be resolved because dynamic force measurements were not performed, as this was not the main focus of this study. For the factor Parameter significant differences were observed in t1/2 between V’O2pulm (42.1 ± 6.7 s) and V’CO2pulm (52.0 ± 13.7 s) and between V’CO2pulm and V’E (40.4 ± 15.5 s). The typical order of the kinetics responses during exercise can be characterized as followed: HR as the fastest parameter, followed by muscular oxygen uptake (depends on the oxidative fitness level), V’O2pulm, V’CO2pulm and V’E (Drescher 2012). In this regard, in the present study V’E appears to be speeded up in recovery. The mechanism behind this observation may be related to the fact that in the high-intensity exercise phase, carbon dioxide is accumulated in the venous blood. This elicits augmented breathing impulses after exercise cessation, resulting in higher V’E to remove carbon dioxide and to maintain the pH-value of the blood. Our results imply that V’E is decoupled from V’O2pulm after the initial first 10 seconds of recovery for leg exercise due to different temporal profiles. Even the typical ranking of kinetics with V’O2pulm exhibiting the fastest change and V’E as the slowest parameter during moderate dynamic leg exercise (Drescher 2012), cannot be supported in general here. For factor Limb (arm vs. leg) no significant differences for the t1/2-values could be identified. Hence, we conclude, that both arm and leg muscles involved in the concentric-eccentric isokinetic exercise phases generate similar responses in their dynamics, resulting in no differences between the two limbs. 4.3 Limitations
The present study aimed to compare the cardio-respiratory kinetics following isokinetic arm and leg exercise utilizing non-invasive measurements. Therefore we are not able to discuss muscle capillary blood flow, muscle oxygen uptake kinetics, blood gas analysis, and muscle creatine phosphate kinetics. It has also to be taken into account that the so-called skeletal muscle pump also influences the cardio-dynamic responses (Gallagher et al. 1997). However, we did not determine the skeletal muscle and limb masses, and did not perform gravity corrections before isokinetic testing (Aagaard et al. 1995). However, for the comparisons between arm vs. leg exercise in relation to the three different movement velocities we established comparable conditions in the study design for the data analysis, so that the results presented here are internally consistent. Direct comparisons to other studies should be made with caution due to varying study designs as mentioned in the discussion. 4.4 Conclusion The present study determined and compared the kinetics responses of V’O2pulm, V’CO2pulm, V’E and avDO2 between concentric-eccentric isokinetic arm and leg exercise across 60 deg·s-1, 150 deg·s-1 and 240 deg·s-1, respectively. In conclusion, the results reveal that (a) for the time to attain the first avDO2-peak (tmax) significant differences were observed between arm and leg exercise, (b) significant differences of the t1/2 values between 60 deg·s-1 and 150 deg·s-1 were identified for factor Speed, (c) significant differences in the t1/2 values were identified between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E, and (d) no significant differences for the t1/2 values were noticed for factor Limb (arm vs. leg).
The results of the present study illustrate, that V’O2pulm kinetics are distorted due to timedelayed and sluggish venous return dynamics in the recovery phases. These distortions can be observed by the 1st peak in avDO2, which imply the arrival of the bulk oxygen desaturated blood from the exercising muscles after cessation of exercise. Therefore, it has to be taken into account, that during early recovery phases, V’O2pulm kinetics may not be a valuable indicator or surrogate for the assessment of muscular oxygen uptake kinetics – the origin parameter of interest for oxidative metabolism (mitochondria). For a better evaluation of aerobic exercise performance, future investigations should employ practical circulatory models (Barstow and Molé 1987; Barstow et al. 1990; Eßfeld et al. 1991; Cochrane and Hughson 1992; Lai et al. 2006; Lai et al. 2007; Zhou et al. 2007; Zhou et al. 2008; Zhou et al. 2009; Wagner 2011; Benson et al. 2013; Hoffmann et al. 2013; Drescher et al. 2015; Hoffmann et al. 2016; Drescher et al. 2016; Koschate et al. 2016a; Koschate et al. 2016b) that account for the distortive effects of venous return on pulmonary gas exchange measurements. Previous assessments comparing venous blood volume of exercising musculature (e.g. arms versus legs) and the lungs, can explain the venous transit times between these two tissue sites (Hoffmann et al. 2013; Drescher et al. 2015). Subsequently, the incorporation of this previously estimated venous volume into isokinetic concentric-eccentric exercise protocols, similar to the one employed in this study will facilitate a more accurate estimation of recovery muscle oxygen uptake off-kinetics. This will enable the estimation of a hypothesized peak oxygen uptake value for both muscle and pulmonary sites at the start of the cessation of exercise using the recovery data as demonstrated by Chaverri et al. (2016) for swimming. Lastly, these procedures could be applied in other sport and exercise situations (e.g. swimming and water polo) where the measurement of real-time gas exchange may not be feasible, or at best, impractical.
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Figure and table legends Fig. 1 Illustration of the test protocol with exercise and recovery phases (A). Following concentriceccentric isokinetic arm and leg exercise the parameters of interest were interpolated in 1s-Intervals in the recovery phases (B) and averaged for further analysis (C).
Fig. 2 Recovery data (mean ± SE) of concentric-eccentric isokinetic arm and leg exercise of pulmonary oxygen uptake (V’O2pulm; 2a, 2b), virtual oxygen uptake (virtV’O2; 2c, 2d), carbon dioxide output (V’CO2pulm; 2e, 2f), ventilation (V’E; 2g, 2h), cardiac output (CO; 2I, 2j), and arterio-venous oxygen content difference (avDO2; 2k, 2l) across the different exercise velocities (60 deg·s-1, 150 deg·s-1, 240 deg·s-1).
Tab. 1 Amplitudes and times to attain the first avDO2-peak (tmax) for both concentric-eccentric isokinetic arm and leg exercise across the speed conditions.
Tab. 2 Half-time data (t1/2; mean ± SD) of concentric-eccentric isokinetic arm and leg exercise of pulmonary oxygen uptake (V’O2pulm), carbon dioxide output (V’CO2pulm) and ventilation (V’E) across the different exercise velocities (60 deg·s-1, 150 deg·s-1, 240 deg·s-1).
Figures Fig. 1
Fig. 2a
Fig. 2b
Fig. 2c
Fig. 2d
Fig. 2e
Fig. 2f
Fig. 2g
Fig. 2h
Fig. 2i
Fig. 2j
Fig. 2k
Fig. 2k
Tables Tab. 1
Exercise speed [deg·s-1] Significance 60
150
240
Arm
188 ± 51
169 ± 35
173 ± 31
[mL/L]
Leg
174 ± 33
165 ± 28
180 ± 40
Factor Limb: n.s. Factor Speed: n.s. Interactions: n.s.
tmax
Arm
7.1 ± 4.3
7.3 ± 4.2
6.5 ± 3.2
Leg
8.2 ± 4.1
11.0 ± 6.7
9.8 ± 5.3
Factor Limb: p<0.05 Factor Speed: n.s. Interactions: n.s.
Amplitude
[s]
Tab. 2
Exercise speed [deg·s-1] Significance
_O2pulm [s]
_CO2pulm [s]
_E [s]
60
150
240
Arm
32.8 ± 13.8
45.0 ± 12.8
43.9 ± 9.0
Leg
38.5 ± 11.6
45.5 ± 7.1
46.8 ± 12.7
Arm
35.2 ± 19.0
56.7 ± 16.7
54.2 ± 14.8
Leg
46.6 ± 22.4
58.8 ± 16.2
60.3 ± 24.6
Arm
29.9 ± 20.4
42.3 ± 20.9
43.0 ± 25.6
Leg
39.8 ± 26.6
48.1 ± 22.3
39.1 ± 26.5
a) Significant difference between 60 deg·s-1 and 150 deg·s-1, p < 0.05 b) Significant difference between _O2pulm and _CO2pulm, p < 0.05 c) Significant difference between _CO2pulm and _E, p < 0.05
Factor Limb: n.s. Factor Speed (a): p<0.05 Factor Parameter (b, c): p<0.05 Interactions: n.s.
S1569-9048(16)30301-9 http://dx.doi.org/doi:10.1016/j.resp.2017.02.003 RESPNB 2766
To appear in:
Respiratory Physiology & Neurobiology
Received date: Revised date: Accepted date:
30-11-2016 8-2-2017 9-2-2017
Please cite this article as: Drescher, U., Mookerjee, S., Steegmanns, A., Knicker, A., Hoffmann, U., Gas Exchange Kinetics Following ConcentricEccentric Isokinetic Arm and Leg Exercise.Respiratory Physiology and Neurobiology http://dx.doi.org/10.1016/j.resp.2017.02.003 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Gas Exchange Kinetics Following Concentric-Eccentric Isokinetic Arm and Leg Exercise Drescher, U.a, Mookerjee, S.b, Steegmanns, A.a, Knicker, A.c, Hoffmann, U.a
a
Institute of Physiology and Anatomy, Am Sportpark Müngersdorf 6, German Sport University Cologne, Cologne, 50933, Germany.
b
Department of Exercise Science, 400 E.2nd St, Bloomsburg University, Bloomsburg, PA 17815, USA.
c
Institute of Movement and Neuroscience, Am Sportpark Müngersdorf 6, German Sport University Cologne, Cologne, 50933, Germany.
Correspondence: Uwe Drescher German Sport University Institute of Physiology and Anatomy Am Sportpark Müngersdorf 6 50933 Cologne Germany Tel: +49 (0)221 4982 6761 E-Mail: [email protected]
Highlights
High intensity, combined concentric-eccentric isokinetic arm and leg exercise was performed to determine the time course of cardio-respiratory kinetics – with focus on pulmonary gas exchange and arteriovenous oxygen content difference (avDO2) – immediately in the recovery phases. The time to attain the avDO2-peak seems to be different between arm and leg exercise. Significant differences in the kinetics responses could be identified between 60 deg·s-1 and 150 deg·s-1 for isokinetic speed, and between oxygen uptake and carbon dioxide output (V’CO2) as well as between V’CO2 and ventilation.
ABSTRACT Purpose: To evaluate the effects of exercise velocity (60, 150, 240 deg·s-1) and muscle mass (arm vs leg) on changes in gas exchange and arterio-venous oxygen content difference (avDO2) following high-intensity concentric-eccentric isokinetic exercise.
Methods: Fourteen subjects (26.9±3.1 years) performed a 3x20-repetition isokinetic exercise protocol. Recovery beat-to-beat cardiac output (CO) and breath-by-breath gas exchange were recorded to determine post-exercise half-time (t1/2) for oxygen uptake (V’O2pulm), carbon dioxide output (V’CO2pulm), and ventilation (V’E).
Results: Significant differences of the t1/2 values were identified between 60 and 150 deg·s-1. Significant differences in the t1/2 values were observed between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E. The time to attain the first avDO2-peak showed significant differences between arm and leg exercise.
Conclusions: The present study illustrates, that V’O2pulm kinetics are distorted due to non-linear CO dynamics. Therefore, it has to be taken into account, that V’O2pulm may not be a valuable surrogate for muscular oxygen uptake kinetics in the recovery phases.
Keywords Oxygen uptake kinetics, skeletal muscle, resistance exercise, recovery phase
List of specific abbreviations avDO2
[L·L-1]
Arterio-venous oxygen content difference
CO
[L·min-1]
Cardiac output
CO0
[L·min-1]
Average of the first 5 s of CO during recovery
HR
[min-1]
Heart rate
SV
[ml]
Stroke volume
t1/2
[s]
Half-times: time to reach 50% from maximum to rest
tmax
[s]
Time to attain the 1st avDO2-peak
V’CO2pulm
[L·min-1]
Pulmonary carbon dioxide output
V’E
[L·min-1]
Ventilation
V’O2pulm
[L·min-1]
Pulmonary oxygen uptake
virtV’O2
[L·min-1]
Virtual pulmonary oxygen uptake
1. Introduction The greater oxygen uptake elicited by arm exercise versus leg exercise has been attributed to relatively smaller muscle mass, greater isometric component, and torso stabilization. Despite similarities in cardiac output (CO) during upper and lower body exercise, the hemodynamic responses, however, are quiet varied. Further, the relatively greater surface area to mass ratio in the arms coupled with a reduced skeletal muscle pump effect from the lower body could reduce the venous return (Toner et al. 1990; Miles et al. 1984). The resultant greater total peripheral resistance and afterload during upper body exercise may also influence the oxygen uptake kinetics (Miles et al. 1989). During exercise, the regulation of skeletal muscle perfusion becomes important to supply the exercising muscles with oxygen (Delp and Laughlin 1998). Therefore, perfusion and CO distribution are important exercisedependent parameters that influence muscular performance during and following exercise. The kinetics of the cardio pulmonary responses of both upper (e.g. arm) and lower (e.g. leg) body segments during and following resistance exercise training are of importance for an understanding of the associated regulatory mechanisms as well as for individual fitness assessments. One the one hand, this is of interest for those engaged in predominantly upper body tasks such as canoeing or swimming (Sanada et al. 2005), individuals with spinal cord injuries (Myers 2005), as well as those involved in industrial, military or space flight operations (Sawka 1989; Sawka and Pandolf 1991; Cowell et al. 2002). On the other hand, various lower body activities such as sprinting (Wilkerson et al. 2004; Dupont et al. 2010), running (Dupont et al. 2005), cycling (Tordi et al. 2003) and numerous resistance training exercises (Millet et al. 2002) actively involve the upper body. In this regard, since these skills and events are performed at varying movement velocities (e.g. Billat et al. 2000) during both training and competition, this is another factor that must be taken into account.
Normally, resistance exercise training is focused on the development of maximal muscle force output which, in turn, is associated with changes in single motor unit firing rate, firing rate synchronization, increased double discharges, and cortical excitability (e. g. Griffin and Cafarelli 2005). Resistance exercise training sessions are characterized by brief, intermittent sets and exercise combinations typically lasting a few minutes. Thus, it would be of interest to focus on the aspects of pulmonary gas exchange kinetics immediately (i.e. 120 seconds post-exercise) following high intensity resistance exercise. The utilization of varied exercise modes (i.e. upper versus lower body exercise) as well as movement velocities will also enable a clearer understanding of the effects of these variables on pulmonary gas exchange kinetics. High intensity resistance exercise is characterized by various ventilatory behaviors such as hyperventilation, Valsalva, apnea. These modifications result in significant alterations in tidal breathing and gas exchange at the mouth, which complicates the measurement of pulmonary oxygen uptake (V’O2pulm). Additionally, intra-thoracic and intra-abdominal pressure changes during vigorous exercise (Sharpey-Schafer 1953; Lee et al. 1954), alter venous return and consequently CO, delaying and distorting the pulmonary gas exchange (e.g. oxygen uptake). But post-exercise breathing patterns will normalize and attain relatively greater stability. Therefore, indirect inferences about muscular metabolism can be derived more reliably from the recovery gas exchange kinetics. During high intensity resistance exercise the corresponding isometric component (even during so-called dynamic exercise) results in occlusion of vascular beds in the contracting muscle producing a transient ischemic effect (Barcroft and Millen, 1939; Barnes, 1980; Sjøgaard et al. 1988). This may enhance anaerobiosis resulting in the accumulation of associated metabolites. At the cessation of exercise these metabolites would enter the greater circulation and may influence pulmonary gas exchange kinetics. The magnitude of these effects could be influenced
by exercise intensity. In this context, the influences of muscle mass and movement velocity on the pulmonary and cardio-dynamic parameters are important. During high-intensity exercise accurate assessment of pulmonary gas exchange, as a proxy of muscle oxygen uptake, needs to be approached with caution, due to the aforementioned issues. However, the immediate post-exercise assessment of cardiopulmonary variables provides for relatively greater stable recording conditions since distorted breathing maneuvers (e.g. apnea, Valsalva, etc.) will be significantly diminished. In this regard, usually faster oxygen uptake kinetics are associated with higher maximal oxygen uptake values (Chilibeck et al. 1996). Accelerated pulmonary gas exchange can therefore be associated with improved V’O2pulm and increased pulmonary carbon dioxide output (V’CO2pulm) mediated by increased ventilatory drive. In the analysis of V’O2pulm, sparse attention has been given to the additional influences of CO and arterio-venous difference of oxygen content (avDO2). However, the avDO2 measured by V’O2pulm and CO may be used as a surrogate of the synchronization of muscle perfusion and muscular oxygen demand. Further, avDO2 can give important information about the time delay of the arrival of venous blood volume between exercising muscles and the lungs. V’O2pulm kinetics will be influenced on the one hand by the time delay of the venous return and its stored oxygen as well as the perfusion of the lungs. This impedes an unambiguous conclusion on the muscular oxygen uptake kinetics following the onset of recovery. Therefore, the purpose of this study was to - (1) determine the time course of cardio-respiratory kinetics – focusing on pulmonary gas exchange and avDO2 – immediately after high intensity, combined concentric-eccentric isokinetic exercise; (2) assess the influence of isokinetic velocity and muscle mass on cardio-respiratory kinetics following high intensity, combined concentriceccentric isokinetic exercise.
2. Methods 2.1 Subjects Written informed consent was obtained from 14 healthy, male subjects: age 26.9 ± 3.1 years; height 181.8 ± 9.6 cm; weight 81.2 ± 9 kg; BMI 24.6 ± 1.8 kg/m2 (mean ± SD) to participate in the study. The study was approved by the Ethics Committee of the German Sport University Cologne in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. 2.2 Isokinetic Strength Testing Three sets of twenty maximal voluntary concentric-eccentric contractions were performed (Fig. 1) on an IsoMed 2000 Isokinetic dynamometer (D&R Ferstl GmbH, Hemau, Germany), at 60 deg·s-1, 150 deg·s-1, and 240 deg·s-1 in a randomized order. The leg exercises consisted of single leg knee extensions / flexions with a range of motion (ROM) of 90° and the arm exercises consisted of single arm elbow flexions / extensions with a ROM of also 90°. During each test gas exchange (V’O2pulm, V’CO2pulm, V’E) was measured breath-by-breath (ZAN 680, ZAN Meßgeräte GmbH, Oberthulba, Germany), heart rate (HR; by R-R interval from electrocardiography), stroke volume (SV; by impedance cardiography; see Fortin et al. 2006 for details) and blood pressure (finger plethysmography) continuously beat-to-beat (Task Force® Monitor, CNSystems Medizintechnik AG, Graz, Austria). The ZAN 680 device was calibrated with oxygen and carbon dioxide with known concentrations before each test was performed. For the beat-to-beat measurement of continuous blood pressure the device was calibrated by oscillatory measures before each test was started and the subject was seated on the exercise device in the resting condition and upright position. The left hand and arm were fixed on an armrest to avoid movements of the hand and fingers to preserve good signal quality of the
continuous blood pressure measurement. Ambient conditions (temperature, humidity, pressure) were kept constant for all tests. << Fig. 1 >> Recovery (120 s) breath-by-breath gas exchange data were recorded to determine postexercise half-time (t1/2) for V’O2pulm, V’CO2pulm, and V’E, denoted as the time taken to reach 50% from maximum to rest. All parameters were time aligned and interpolated for 1 s intervals. avDO2 was determined by the quotient between V’O2pulm and CO (Eq. 1); CO was derived as the product of HR and SV. avDO2(t) = V’O2pulm(t) / CO(t)
(Equation 1)
For pulmonary oxygen uptake a virtual pulmonary oxygen uptake (virtV’O2; Eq. 2) was calculated assuming no change of CO after the onset of recovery. virtV’O2(t) = V’O2pulm(t) · CO0 /CO(t)
(Equation 2)
For this purpose CO0 was calculated as the average of the first 5 s of recovery to avoid artifacts from muscle contraction on ICG measurements for the SV assessment. 2.4 Statistical analyses Three-way repeated measures analysis of variance (ANOVA) was used to determine the effect of Parameter (V’O2pulm, V’CO2pulm, V’E), Speed (60 deg·s-1, 150 deg·s-1, 240 deg·s-1) and Limb (arm, leg) on t1/2 values. Differences between the peaks (amplitude) and the time to attain the peaks (tmax) of avDO2 were analyzed via a two-way repeated measures ANOVA with factors Limb and Speed. The alpha level was set to 0.05 for statistical significance. For all statistical analyses SPSS 23 was applied.
3. Results 3.1 Cardio-respiratory responses Fig. 2 displays the pulmonary and cardio dynamic responses following concentric-eccentric isokinetic arm and leg exercise. The time course of V’O2pulm, V’CO2pulm, V’E and avDO2 displays a steep increase within the first 10 seconds of recovery. The V’O2pulm and avDO2 at 150 deg·s-1and 240 deg·s-1 velocities following leg exercise, exhibit a pronounced secondary hyperventilation around 20 seconds into recovery. V’E declines steeply followed by a slower phase to recovery. VirtV’O2 displays a similar relative temporal course as the real measured V’O2pulm. The absolute values of virtV’O2 are a bit higher than the measured V’O2pulm for both arm and leg exercise. CO following leg exercise (peak values ~ 12.5 L · min-1) displays higher perfusion rates than arm exercise (peak values ~11.0 L · min-1). Interestingly, for arm exercise in the 60 deg·s-1 condition, CO values are clearly below the other two exercise speeds within the first 60 seconds. Although we did not measure muscle metabolites or lactate, the large increases in V’ E are consistent with previous reports. In our experiments, respiratory exchange ratio (RER) exceeded 1.0 for all tests post-exercise. << Fig. 2a-2l >> For pulmonary avDO2 the first peak was identified in 82 of 84 cases. Amplitudes tmax values are summarized in Tab. 1. Both factors Limb and Speed, as well as the interactions showed no significant differences (p > 0.05 each) between the amplitudes of the first peaks in the avDO2 curves. In contrast, the two-way repeated measures ANOVA showed a significant factor Limb (p < 0.05) for tmax of avDO2 (arm: 7.2 ± 3.5s, leg: 9.9 ± 4.1s); for the factor Speed and interaction no differences could be identified (p > 0.05) for tmax of avDO2. A second avDO2-peak was
identified in 47 of 84 cases. Since there was no systematic pattern of distribution of these second avDO2-waveforms across the testing conditions, no further analyses were conducted. << Tab. 1 >> 3.2 Dynamics analysis Applying a three-way repeated measures ANOVA with factors Parameter, Speed and Limb significant influences on t1/2 were found for the factors Parameter and Speed (p < 0.05; Tab. 2). The factor Limb and all interactions were not significant (p > 0.05). Post-Hoc Bonferroni pairwise comparisons reveal significant differences of t1/2 between 60 deg·s-1 (37.1 ± 7.5s) and 150 deg·s1
(49.4 ± 6.6s; p < 0.05), but not between 60 deg·s-1 and 240 deg·s-1 (47.9 ± 7.1s) as well as
between 150 deg·s-1 and 240 deg·s-1 (p > 0.05). << Tab. 2 >> For the factor Parameter significant differences on t1/2 were identified between V’O2pulm (42.1 ± 5.0s) and V’CO2pulm (52.0 ± 7.2s; p < 0.05) and between V’CO2pulm and V’E (40.4 ± 7.6s; p < 0.05), but not between V’O2pulm and V’E (p > 0.05).
4. Discussion To our knowledge no studies have previously looked upon pulmonary gas exchange kinetics following concentric-eccentric isokinetic arm and leg exercise in the early phase of recovery. Therefore, the aim of this study was to describe and analyze the effects of high intensity, combined concentric-eccentric isokinetic exercise on pulmonary (e.g. V’O2pulm, V’CO2pulm, V’E) and cardio-dynamic (e.g. avDO2) parameters, influenced by isokinetic velocity and involved muscle mass during the recovery phase. The major findings are:
1) For the time to attain the 1st avDO2-peak (tmax) significant differences were observed between arm and leg exercise in the recovery phase. 2) Significant differences of the t1/2 values between 60 deg·s-1 and 150 deg·s-1 were identified for factor Speed in the recovery phase. 3) For factor Parameter significant differences in the t1/2 values were identified between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E in the recovery phase. 4) No significant differences for the t1/2 values were noticed for factor Limb (arm vs. leg) in the recovery phase. 4. 1 Methodological aspects Most studies have utilized mono or double exponential models for data fitting of the cardiorespiratory and muscle parameters (Haseler et al. 1999, Özyener et al. 2001, Ferreira et al. 2005, Ferreira et al. 2006, Harper et al. 2008, Lai et al. 2008). In the present study we opted not to utilize those specific model applications because our results indicate that the responses of the cardio-dynamic parameters in the recovery phase demonstrate more complex temporal profiles than mono or double exponential models can sufficiently represent. Therefore, and for reasons of simplicity we calculated the t1/2 values of the parameters of interest, which do not rely on any specific model assumptions, to highlight possible differences in the kinetics responses by means of these values. Also, previous analyses of exercise onset or recovery phases typically utilize leg or arm ergometers with constant work rate increments or phases for on- and off-kinetics analysis. Our testing protocol included maximal voluntary contractions throughout the eccentric-concentric phases of arm and leg exercise. This has to be taken into account in the following discussions, because there are differences across the study designs (e. g. exercise intensities, exercise modes) which do impede a one-to-one comparison.
4. 2 Pulmonary and cardio-dynamic responses 4.2.1 Temporal profiles The temporal profiles show a clear first peak of V’O2pulm, V’CO2pulm, V’E and avDO2 within the first 10 s of the recovery phase for both arm and leg exercise and across all movement velocities. In addition, a second peak can be seen in V’O2pulm for 150 and 240 deg·s-1, in V’CO2pulm for 240 deg·s-1 and in avDO2 for all three movement velocities, but for leg exercise only. Most likely, the concentric-eccentric isokinetic exercise mode increases the consumption of oxygen due to a very high oxygen requirement at muscular level and simultaneously by restriction of blood flow to the exercising muscles due to the isometric component (Sjøgaard et al. 1988), which will result in a greater avDO2 during exercise in the leg than in the arm muscles. At the onset of recovery, the 1st avDO2 peak is caused by the arrival of oxygen desaturated blood from the muscle to the lungs. This delay results from the occlusion of venous blood flow during muscle activity. The time between the offset in exercise and changes in the avDO 2 can be used to gauge transport time delays between the muscular and pulmonary sites. In the comparison between arm and leg exercise the amount of avDO2 accumulated during the concentric-eccentric arm exercise phase is less than the amount during concentric-eccentric leg, so that the 2nd peak for arm exercise cannot be observed clearly, which may represent an imbalance between perfusion and aerobic metabolism during recovery. The smaller 2nd peak in avDO2 could be due to significant differences between involved skeletal arm and leg muscle masses. For Caucasian men, Gallagher et al. (1997) determined the total appendicular skeletal muscles masses of arms and legs as 7.2 ± 1.5 kg and 21.1 ± 2.8 kg, respectively, which implies a leg-to-arm ratio of about 2.93. Therefore, it can be assumed that maximal voluntary concentric-eccentric isokinetic contractions produce definite differences between arm and leg exercise in the cardio-respiratory responses.
Kustrup et al. (2009) showed that following high-intensity knee extension exercise the blood transit time from exercising muscles to the lungs lasts about 6-7 seconds after 10 and 30 seconds respectively, and about 11 seconds after 1 minute in recovery. These values are close to our tmax values (see Tab. 1) which range from 7.1 ± 4.3s (arm; 60 deg·s-1) to 11.0 ± 6.7s (leg; 150 deg·s-1). Assuming, that the venous transit way is shorter for arm than for leg exercise, the tmax values seem to be coherent. Additionally, Kustrup et al. (2009) mentioned that V’O2pulm kinetics does not reflect muscular oxygen uptake kinetics in the recovery phase. This is consistent with Haseler et al. (1999) indicating that differences in the kinetics responses of phosphocreatine kinetics could not be limited to metabolic issues but rather to variations in oxygen availability. With the present results we cannot derive a certain conclusion about the muscular metabolism at cellular level. However, the temporal profiles of V’O2pulm, avDO2 and CO suppose, that cardio-respiratory kinetics have to be taken with caution for an estimation of oxidative metabolism at muscular and cellular level following high-intensity exercise in the recovery phase; this is due to the time-delaying and distortive effects of perfusion and venous return. 4.2.2 Dynamics – Half-time (t1/2) values The observed effect of Velocity on the t1/2 values were only significantly different between 60 deg·s-1 and 150 deg·s-1. Assuming, that the velocity of 60 deg·s-1 provoke high demands on the exercising muscles which is accompanied by an increased motor-unit recruitment and therefore a greater activation of muscle fibers, may result in faster aerobic metabolism responses indicated by faster oxygen uptake kinetics. Furthermore, the isometric component during the muscle contractions may be more prevalent during the 60 deg·s-1 condition than during the other two velocities, because the velocity of 60 deg·s-1 is sufficiently slow to produce high resistances and muscle forces on the arm or leg lever. Based on this line of reasoning there
should be a significant difference between 60 deg·s-1 and 240 deg·s-1 for the t1/2 values. However, this is not the case and could possibly be explained by altered interactions of muscle contraction components (e.g. isotonic, isometric, auxotonic) across the exercise velocities. This issue cannot be resolved because dynamic force measurements were not performed, as this was not the main focus of this study. For the factor Parameter significant differences were observed in t1/2 between V’O2pulm (42.1 ± 6.7 s) and V’CO2pulm (52.0 ± 13.7 s) and between V’CO2pulm and V’E (40.4 ± 15.5 s). The typical order of the kinetics responses during exercise can be characterized as followed: HR as the fastest parameter, followed by muscular oxygen uptake (depends on the oxidative fitness level), V’O2pulm, V’CO2pulm and V’E (Drescher 2012). In this regard, in the present study V’E appears to be speeded up in recovery. The mechanism behind this observation may be related to the fact that in the high-intensity exercise phase, carbon dioxide is accumulated in the venous blood. This elicits augmented breathing impulses after exercise cessation, resulting in higher V’E to remove carbon dioxide and to maintain the pH-value of the blood. Our results imply that V’E is decoupled from V’O2pulm after the initial first 10 seconds of recovery for leg exercise due to different temporal profiles. Even the typical ranking of kinetics with V’O2pulm exhibiting the fastest change and V’E as the slowest parameter during moderate dynamic leg exercise (Drescher 2012), cannot be supported in general here. For factor Limb (arm vs. leg) no significant differences for the t1/2-values could be identified. Hence, we conclude, that both arm and leg muscles involved in the concentric-eccentric isokinetic exercise phases generate similar responses in their dynamics, resulting in no differences between the two limbs. 4.3 Limitations
The present study aimed to compare the cardio-respiratory kinetics following isokinetic arm and leg exercise utilizing non-invasive measurements. Therefore we are not able to discuss muscle capillary blood flow, muscle oxygen uptake kinetics, blood gas analysis, and muscle creatine phosphate kinetics. It has also to be taken into account that the so-called skeletal muscle pump also influences the cardio-dynamic responses (Gallagher et al. 1997). However, we did not determine the skeletal muscle and limb masses, and did not perform gravity corrections before isokinetic testing (Aagaard et al. 1995). However, for the comparisons between arm vs. leg exercise in relation to the three different movement velocities we established comparable conditions in the study design for the data analysis, so that the results presented here are internally consistent. Direct comparisons to other studies should be made with caution due to varying study designs as mentioned in the discussion. 4.4 Conclusion The present study determined and compared the kinetics responses of V’O2pulm, V’CO2pulm, V’E and avDO2 between concentric-eccentric isokinetic arm and leg exercise across 60 deg·s-1, 150 deg·s-1 and 240 deg·s-1, respectively. In conclusion, the results reveal that (a) for the time to attain the first avDO2-peak (tmax) significant differences were observed between arm and leg exercise, (b) significant differences of the t1/2 values between 60 deg·s-1 and 150 deg·s-1 were identified for factor Speed, (c) significant differences in the t1/2 values were identified between V’O2pulm and V’CO2pulm and between V’CO2pulm and V’E, and (d) no significant differences for the t1/2 values were noticed for factor Limb (arm vs. leg).
The results of the present study illustrate, that V’O2pulm kinetics are distorted due to timedelayed and sluggish venous return dynamics in the recovery phases. These distortions can be observed by the 1st peak in avDO2, which imply the arrival of the bulk oxygen desaturated blood from the exercising muscles after cessation of exercise. Therefore, it has to be taken into account, that during early recovery phases, V’O2pulm kinetics may not be a valuable indicator or surrogate for the assessment of muscular oxygen uptake kinetics – the origin parameter of interest for oxidative metabolism (mitochondria). For a better evaluation of aerobic exercise performance, future investigations should employ practical circulatory models (Barstow and Molé 1987; Barstow et al. 1990; Eßfeld et al. 1991; Cochrane and Hughson 1992; Lai et al. 2006; Lai et al. 2007; Zhou et al. 2007; Zhou et al. 2008; Zhou et al. 2009; Wagner 2011; Benson et al. 2013; Hoffmann et al. 2013; Drescher et al. 2015; Hoffmann et al. 2016; Drescher et al. 2016; Koschate et al. 2016a; Koschate et al. 2016b) that account for the distortive effects of venous return on pulmonary gas exchange measurements. Previous assessments comparing venous blood volume of exercising musculature (e.g. arms versus legs) and the lungs, can explain the venous transit times between these two tissue sites (Hoffmann et al. 2013; Drescher et al. 2015). Subsequently, the incorporation of this previously estimated venous volume into isokinetic concentric-eccentric exercise protocols, similar to the one employed in this study will facilitate a more accurate estimation of recovery muscle oxygen uptake off-kinetics. This will enable the estimation of a hypothesized peak oxygen uptake value for both muscle and pulmonary sites at the start of the cessation of exercise using the recovery data as demonstrated by Chaverri et al. (2016) for swimming. Lastly, these procedures could be applied in other sport and exercise situations (e.g. swimming and water polo) where the measurement of real-time gas exchange may not be feasible, or at best, impractical.
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Figure and table legends Fig. 1 Illustration of the test protocol with exercise and recovery phases (A). Following concentriceccentric isokinetic arm and leg exercise the parameters of interest were interpolated in 1s-Intervals in the recovery phases (B) and averaged for further analysis (C).
Fig. 2 Recovery data (mean ± SE) of concentric-eccentric isokinetic arm and leg exercise of pulmonary oxygen uptake (V’O2pulm; 2a, 2b), virtual oxygen uptake (virtV’O2; 2c, 2d), carbon dioxide output (V’CO2pulm; 2e, 2f), ventilation (V’E; 2g, 2h), cardiac output (CO; 2I, 2j), and arterio-venous oxygen content difference (avDO2; 2k, 2l) across the different exercise velocities (60 deg·s-1, 150 deg·s-1, 240 deg·s-1).
Tab. 1 Amplitudes and times to attain the first avDO2-peak (tmax) for both concentric-eccentric isokinetic arm and leg exercise across the speed conditions.
Tab. 2 Half-time data (t1/2; mean ± SD) of concentric-eccentric isokinetic arm and leg exercise of pulmonary oxygen uptake (V’O2pulm), carbon dioxide output (V’CO2pulm) and ventilation (V’E) across the different exercise velocities (60 deg·s-1, 150 deg·s-1, 240 deg·s-1).
Figures Fig. 1
Fig. 2a
Fig. 2b
Fig. 2c
Fig. 2d
Fig. 2e
Fig. 2f
Fig. 2g
Fig. 2h
Fig. 2i
Fig. 2j
Fig. 2k
Fig. 2k
Tables Tab. 1
Exercise speed [deg·s-1] Significance 60
150
240
Arm
188 ± 51
169 ± 35
173 ± 31
[mL/L]
Leg
174 ± 33
165 ± 28
180 ± 40
Factor Limb: n.s. Factor Speed: n.s. Interactions: n.s.
tmax
Arm
7.1 ± 4.3
7.3 ± 4.2
6.5 ± 3.2
Leg
8.2 ± 4.1
11.0 ± 6.7
9.8 ± 5.3
Factor Limb: p<0.05 Factor Speed: n.s. Interactions: n.s.
Amplitude
[s]
Tab. 2
Exercise speed [deg·s-1] Significance
_O2pulm [s]
_CO2pulm [s]
_E [s]
60
150
240
Arm
32.8 ± 13.8
45.0 ± 12.8
43.9 ± 9.0
Leg
38.5 ± 11.6
45.5 ± 7.1
46.8 ± 12.7
Arm
35.2 ± 19.0
56.7 ± 16.7
54.2 ± 14.8
Leg
46.6 ± 22.4
58.8 ± 16.2
60.3 ± 24.6
Arm
29.9 ± 20.4
42.3 ± 20.9
43.0 ± 25.6
Leg
39.8 ± 26.6
48.1 ± 22.3
39.1 ± 26.5
a) Significant difference between 60 deg·s-1 and 150 deg·s-1, p < 0.05 b) Significant difference between _O2pulm and _CO2pulm, p < 0.05 c) Significant difference between _CO2pulm and _E, p < 0.05
Factor Limb: n.s. Factor Speed (a): p<0.05 Factor Parameter (b, c): p<0.05 Interactions: n.s.