Physiological and biomechanical differences between wheelchair-dependent and able-bodied subjects during wheelchair ergometry

Summary The purpose of this study was to compare the physiological and biomechanical responses of wheelchair-dependent persons (WCD) to able-bodied persons (AB) during manual wheelchair ergometry. Five WCD and five AB performed a discontinuous wheelchair ergometer test starting at 12.8 W at 30 rev·min^–1 (57 m·min^–1) with increments of 7.0 W at 6-min intervals. Biomechanical data were collected 3.5 min into each stage followed by the collection of physiological data. After the fifth stage, peak oxygen consumption was determined by having the subject work against a resistance of 14.7–19.6 N at 30 rev · min^–1. The WCD had significantly higher net mechanical efficiency at 26.7, 33.6 and 40.6 W in comparison to the AB. The WCD had significantly greater shoulder extension at the point of initial wheel contact as measured by the shoulder angle, while the AB had significantly greater shoulder range of motion at all work rates in comparison to the WCD. The results demonstrate that a significant physiological difference exists in the manner by which WCD and AB accomplish wheelchair ergometry. The biomechanical differences between AB and WCD were found to be a prominent factor contributing to the higher mechanical efficiency of WCD over AB. It was concluded that basic physiological and biomechanical differences exist between WCD and AB in manual wheelchair locomotion and that these differences are important considerations to the interpretation of data in wheelchair ergometry studies.     

Physiological responses to asynchronous and synchronous arm-cranking exercise

The purpose of this study was to examine mechanical efficiency (ME) and physiological responses during asynchronous (the pedal arms oriented in opposing directions) arm-cranking exercise (AACE) and compare these responses to those obtained during synchronous (the pedal arms oriented in the same direction) arm-cranking exercise (SACE). Ten male subjects participated in the study and performed two exercise tests, one AACE and the other SACE in counter-balanced order. Each test consisted of submaximal (30, 60 and 90 W) and maximal exercise. At 30 W, gross ME was significantly lower during SACE compared to AACF, whereas at 60 W and 90 W no differences between the two types of exercise could be observed. We found that at lower power output levels the flywheel mass and its moment of inertia may have induced more body movements for compensation, which may have been more pronounced during SACE than during AACE. At higher levels of power output this flywheel mass-effect was less, which explained the lack of differences in ME at these levels. Physiological responses to maximal AACE or SACE exercise were not significantly different. The results indicated that there were no differences in physiological responses to AACE and SACE exercise at higher exercise intensities. However, at lower levels of power output ME seemed to decrease, most likely as a result of the flywheel-mass effect, which was more pronounced during SACE.     

The effects of arm crank training on the physiological responses to silbmaximal wheelchair ergometry

Summary The purpose of this investigation was to examine the cardiovascular and metabolic effects of a 5 wk arm crank (AC) training program on submaximal wheelchair (WC) ergometry in ablebodied women. The 6 subjects in the training group (TG) and 4 in the control group (CG) performed a 10 min WC exercise prior to and following the training period at a power output (PO) that elicited 70% of the pre-training peak oxygen uptake ( ). Steady state , heart rate (HR), cardiac output and stroke volume (V _s) were measured. Resting and post-exercise blood lactate concentrations (LA) were measured, the difference was recorded as net LA. The TG exercised on the AC 3 d · wk^–1 at a PO that elicited 85% of each subject's recorded peak HR. Each session consisted of four 4 min exercise bouts preceded by a 2 min warm-up and interspersed with 2 min rest periods. After training, the TG had a significantly (p<0.05) lower HR, largerV _s and lower LA in response to the WC exercise. and were not significantly altered. The results demonstrate that the AC exercise program used in this study produced a physiological training effect which was observed during submaximal WC exercise of an intensity frequently encountered during daily WC ambulation. It appears that short-term, moderate intensity AC training offers an adequate stimulus to reduce the stress imposed by wheelchair locomotion.     

The effect of exercise-induced muscle damage on perceived exertion and cycling endurance performance

This study evaluated the effects of exercise-induced muscle damage (EIMD) on fixed-load cycling and 5-min time-trial performance. Seven recreational athletes performed two submaximal fixed-load exercise bouts followed by a 5-min time-trial before, 48 and 168 h following 100 counter-movement jumps. Measurements of heart rate, RER and blood lactate concentration remained unchanged during the fixed-load bouts following jumping exercise. However, and increased (P < 0.05) at 48 h. RPE values were higher at 48 h as were the ratio of RPE:HR and RPE: (P < 0.05). In the time-trial, mean peak power output, mean power output, distance covered and post exercise blood lactate were lower at 48 h (P < 0.05). RPE remained unchanged between trials. These findings indicate that the ventilatory equivalent for oxygen and perceived exertion at submaximal work rates are increased 48 h following eccentric exercise. Furthermore, EIMD increases perceived exertion and impairs performance during a 5-min all-out effort.     

Hypotension following mild bouts of resistance exercise and submaximal dynamic exercise

Our purposes were (1) to examine resting arterial blood pressure following an acute bout of resistance exercise and submaximal dynamic exercise, (2) to examine the effects of these exercises on the plasma concentrations of atrial natriuretic peptide ([ANP]), and (3) to evaluate the potential relationship between [ANP] and post-exercise blood pressure. Thirteen males [24.3 ± (2.4) years] performed 15 min of unilateral leg press exercise (65% of their one-repetition maximum) and, 1 week later, ≈15 min of cycle ergometry (at 65% of their maximum oxygen consumption). Intra-arterial pressure was monitored during exercise and for 1 h post-exercise. Arterial blood was drawn at rest, during exercise and at intervals up to 60 min post-exercise for analysis of haematocrit and [αANP]. No differences occurred in blood pressure between trials, but significant decrements occurred following exercise in both trials. Systolic pressure was ≈20 mmHg lower than before exercise after 10 min, and mean pressure was ≈7 mmHg lower from 30 min onwards. Only slight (non-significant) elevations in [αANP] were detected immediately following exercise, with the concentrations declining to pre-exercise values by 5 min post-exercise. We conclude that post-exercise hypotension occurs following acute bouts of either resistance or submaximal dynamic exercise and, in this investigation, that this decreased blood pressure was not directly related to the release of αANP. Accepted: 29 July 1998     

The entrainment of ventilation frequency to exercise rhythm

Summary To investigate whether ventilation frequency could be entrained to a sub-harmonic of the exercise rhythm, 19 experimentally naive male volunteers were tested during steady state bicycle ergometry and arm cranking under conditions of constant applied workload. Each exercise was performed at two separate ventilatory loads, one within the linear range and the other in the curvilinear range of ventilatory response to exercise. A preferred exercise rhythm was initially adopted (4 min.) followed by forced incremented and decremented rhythm changes each lasting 3 min during a 12 min exercise period. Ventilation, pedal pulse train and heart rate were sampled at 17 Hz on a PDP 11/23 computer. Ratios of limb frequency to dominant respiratory frequency were determined following Fourier analysis of these signals. Data that lay within ±0.05 of an integer and half-integer ratio were accepted as indices of entrainment, provided that the observed entrained scores were statistically significant. Ventilation frequency showed a clear, but intermittent tendency to entrain with limb frequency. This tendency was greater during bicycle ergometry, possibly as a consequence of task familiarisation, although both exercise entrainments were independent of workload. No difference between preferred versus varied exercise rhythm was evident, but more entrainment (p<0.01) was observed during a decremental change in exercise rhythm. These responses do not appear to support an appreciable role for limb-based afferents in the control of entrainment. The results of this study provide evidence that exercise rhythm has some regulatory role in the control of breathing during moderate rhythmical laboratory-based exercise ergometry.     

The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol · 1−1 lactate level

This study examined lactate concentration during incremental and submaximal treadmill exercise at work rates corresponding to 4 mmol· 1^–1 lactate concentration, determined by fingertip (OBLAI) and venous blood (OBLA2). Initially, eight subjects performed a 4-min incremental exercise test until exhaustion. On two other occasions, seven of the subjects undertook submaximal exercise tests (30 min) at work rates corresponding to OBLA1 and OBLA2. Blood was simultaneously obtained from both sites at rest and at the end of each exercise stage during the incremental exercise, and at 5, 10, 20 and 30 min during the submaximal exercise and 5 min into recovery. Fingertip blood lactate concentrations were significantly higher (P<0.05) than venous blood at rest, throughout the incremental exercise, consistently during exercise at OBLA1 and OBLA2, and into recovery. Data also revealed an exercise intensity-dependent lactate difference between the two sampling sites during both exercise protocols. Exercise at OBLA1 did not result in a progressive increase in lactate level nor exhaustion, and the lactate value at the end of 30 min corresponded to the predetermined value. However, exercise at OBLA2 resulted in a significantly higher (P<0.05) lactate level than OBLA1, the lactate concentration at the end of 30 min was substantially higher than the predetermined value (P<0.05) and exhaustion was evident. It is concluded that the lactate concentration value during incremental and submaximal exercise (at 4 mmol·l^–1 OBLA) is dependent on the blood sampling site. This finding should be considered in studies concerned with the determination of OBLA.     

TSH,T3, rT3 and fT4 in maximal and submaximal physical exercise

Summary The response of various thyroid hormone parameters to maximal physical exercise (MPE) was investigated in 14 medium and long distance runners and 13 divers. The effect of submaximal long time physical exercise (SMPE) was examined in seven divers. The TSH-level decreases significantly during MPE and slightly rises again after the end of the exercise. In SMPE, however, TSH continuously rises until 15 min after the end of the exercise. The T₃ level rises significantly in MPE and falls below the initial value 15 min after the exercise finishes, during SMPE it remains practically unchanged and slightly decreases after the finish. In MPE, the rT₃ level does not change and slightly decreases after termination, while the fT₄ level continuously decreases from the beginning till 15 min after the exercise period. The latter two parameters do not show any change in SMPE. As possible reasons for the changes of TSH levels a decrease (MPE) or an increase (SMPE) of pituitary secretion might play a role. Furthermore, in MPE the rise in T₃ level might be related to hemoconcentration, and the decrease in fT₄ level to an elevated cellular utilization.     

Optoelectronic plethysmography compared to spirometry during maximal exercise

The purpose of this study was to compare simultaneous measurements of tidal volume (Vt) by optoelectronic plethysmography (OEP) and spirometry during a maximal cycling exercise test to quantify possible differences between methods.     

Lactate concentration differences in plasma,whole blood,capillary finger blood and erythrocytes during submaximal graded exercise in humans

Summary The aim of the study was to investigate the distribution of lactate in plasma, whole blood, erythrocytes, and capillary finger blood, before and during submaximal exercise. Ten healthy male subjects performed submaximal graded cycle ergometer exercise for 20–25 min. Venous blood samples and capillary finger blood samples were taken before exercise and every 5th min during exercise for lactate determination. The plasma lactate concentration was significantly higher (P<0.001, approximately 50%) than in the erythrocytes. This difference was not altered by the venous blood lactate concentration or exercise intensity. A significant difference (P<0.01) in lactate concentration was also found between capillary whole blood and venous whole blood. It was concluded that direct comparisons between lactate in capillary finger blood, venous whole blood and plasma could not be made.The study was performed at the Department of Clinical Physiology, University Hospital, S-75185 Uppsala, Sweden     

Effect of submaximal exercise at low temperatures on pulmonary function in healthy young men

Summary In order to understand more fully the effect on pulmonary function of whole body exposure to cold during submaximal exercise, we measured pulmonary function indices in ten healthy male students and ten healthy male forestry workers of similar age following submaximal treadmill walking at different temperatures in a climatic chamber. After measuring the maximal aerobic capacity with a cycle ergometer test, the subjects had to walk on four separate occasions in the climatic chamber at an intensity of 70%–75% of their individual maximal heart rate; the first at normal room temperature and then randomly, either at 0°C or at −20°C, and vice versa. The duration of each walk was 8 min. Finally, each subject had to walk in the chamber at −20° C for 17 min. Flow volume spirometry was performed at room temperature 1, 5, 10, and 20 min after exercise and the values were compared to baseline values taken prior to the last walking test. There were only minor changes in pulmonary function indices following exercise at different temperatures. Only one student showed a reduction of over 15% in peak expiratory flow rate after an 8-min walk at −20° C. It seems that submaximal exercise of short duration, even at a temperature as low as −20° C, does not impair pulmonary function in healthy young men.     

Effect of a pulsating anti-gravity suit on peak exercise performance in individual with spinal cord injuries

The aim of this study was to examine effects of a pulsating pressure anti-gravity suit on the peak values of oxygen uptake (V˙O₂) and power during maximal arm exercise in spinal-cord-injured (SCI) individuals. Five well-trained SCI men (with lesions at levels between T6 and L1) and seven well-trained able-bodied men (ABC) performed two incremental (10 W · min⁻¹) arm-cranking tests. During one test the pressure in the anti-G suit pulsated between 4.7 kPa (35 mmHg) and 9.3 kPa (70 mmHg) every 2 s (PPG+), during the other test (PPG−) all the subjects wore the anti-G suit in a deflated state. Tests were performed in a counter-balanced order. Peak V˙O₂ in SCI was 1 ml · kg⁻¹ · min⁻¹ lower during PPG+ compared to PPG− (P = 0.05). Peak power and peak heart rate were not significantly different during PPG+ compared to PPG−. These results would suggest that no increase in work capacity can be obtained with a pulsating pressure anti-gravity suit in either SCI or ABC. Accepted: 1 September 1998     

Measurements of cardiac output in maximum exercise. Application of an acetylene rebreathing method to arm and leg exercise

Summary An acetylene rebreathing technique suitable for the measurement of cardiac output in maximum exercise is described; results have a coefficient of variation of 2.9–3.6%, and show good agreement with observations made by other methods during arm and leg work. Gas samples are analysed by gas chromatograph, using silica gel and molecular sieve/glass columns. Recirculation of the foreign gas is avoided by collection of the final gas sample after 7 sec of rebreathing. Allowance is also made for other systematic errors, including the dead space of the sampling needles and solution of gas in the lung parenchyma.Arm work has a similar oxygen cost to leg work if extraneous movements are avoided; however, the maximal attainable oxygen intake is less in arm exercise (28% in 5 young men). The heart rate in sub-maximum effort is 36–39 beats/min greater for arm work; however, the maximum heart rate is unchanged. The cardiac stroke volume is 25% smaller for both sub-maximum and maximum arm work, while the arterio-venous oxygen difference is slightly greater than in leg work.Both stroke volume and arterio-venous difference increase somewhat between 60 and 100% of aerobic power, but the main burden of increasing oxygen transport is accepted by the increase in heart rate.     

Accuracy of internal dynamics models in limb movements depends on stability

This study investigated the ability to use an internal model of the environmental dynamics when the dynamics were predictable but unstable. Subjects performed goal-directed movements using a robot manipulandum while counteracting a force field, which created instability by assisting the movement in proportion to hand velocity. Subjects performance was better on the last trial than on the first trial in the force field for all four movement directions tested: out, in, right and left. Subjects adapted to the force field primarily by increasing muscle co-contraction, compared to null field movements, during all phases of movement. This co-contraction generally declined for both the deceleration and stabilization phases during the course of the first 25 movements in each direction, but tended not to decrease significantly thereafter. Catch trials at the end of the learning period suggested that increased viscoelastic impedance due to muscle co-contraction was used to counteract the force field. Only in the case of outward movements were aftereffects observed that were consistent with formation of an accurate internal model of the force field dynamics. Stabilization of the hand for outward movements required less muscle co-contraction than for movements in other directions due to stability conferred by the geometry of the arm. The results suggest that the accuracy of an internal model depends critically on the stability of the coupled dynamics of the limb and the environment.     

Endurance training slows down the kinetics of heart rate increase in the transition from moderate to heavier submaximal exercise intensities

Summary To find out whether endurance training influences the kinetics of the increases in heart rate (f _c) during exercise driven by the sympathetic nervous system, the changes in the rate off _c adjustment to step increments in exercise intensities from 100 to 150 W were followed in seven healthy, previously sedentary men, subjected to 10-week training. The training programme consisted of 30-min cycle exercise at 50%–70% of maximal oxygen uptake ( O_2max) three times a week. Every week during the first 5 weeks of training, and then after the 10th week the subjects underwent the submaximal three-stage exercise test (50, 100 and 150 W) with continuousf _c recording. At the completion of the training programme, the subjects' O_2max had increased significantly(39.2 ml·min^–1·kg^–1, SD 4.7 vs 46 ml·min^–1·kg^–1, SD 5.6) and the steady-statef _c at rest and at all submaximal intensities were significantly reduced. The greatest decrease in steady-statef _c was found at 150 W (146 beats·min^–1, SD 10 vs 169 beats·min^–1, SD 9) but the difference between the steady-statef _c at 150 W and that at 100 W (f _c) did not decrease significantly (26 beats·min^–1, SD 7 vs 32 beats·min^–1, SD 6). The time constant () of thef _c increase from the steady-state at 100 W to steady-state at 150 W increased during training from 99.4 s, SD 6.6 to 123.7 s, SD 22.7 (P<0.01) and the acceleration index (A=0.63·f _c·^–1) decreased from 0.20 beats·min^–1·s^–1, SD 0.05 to 0.14 beats·min^–1·s^–1, SD 0.04 (P<0.02). The major part of the changes in and A occurred during the first 4 weeks of training. It was concluded that heart acceleration following incremental exercise intensities slowed down in the early phase of endurance training, most probably due to diminished sympathetic activation.     

Changes in isometric function following rhythmic exercise

Summary Seven male subjects exercised for 1, 3, 10 and 20 min on a cycle ergometer at 20, 60 and 80% , and then held to fatigue a sustained contraction of the quadriceps at 40% maximal voluntary contraction in order to determine what influence various levels of dynamic exercise would have on isometric function of the same group of muscles. Muscle temperature was measured before and within 15 s of the completion of the cycling to determine whether changes in muscle temperature might influence the subsequent isometric perormance. Isometric endurance was shorter as the severity of the cycling increased beyond 20% , and as the duration of cycling increased up to 10 min. There were discrete linear relationships between muscle temperature and isometric endurance associated with cycling at 60% and 80% . There was a direct inverse relationship between quadriceps strength after cycling and muscle temperature, yet a significant reduction in strength occurred only after cycling at 80% . These results suggest that the encroachment on endurance and strength are controlled by different mechanisms. The heart rates during the isometric contractions were dependent on the preceding rhythmic exercise and decreased after exercise at 60 or 80% . In contrast, the blood pressure always increased during the isometric contractions, reaching similar values at the point of fatigue, regardless of the severity of the previous rhythmic exercise. These data provide additional evidence that separate mechanisms control changes in heart rate and blood pressure.     

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.     

Factors in maximal power production and in exercise endurance relative to maximal power

Summary The relationship of muscle fiber type and mass to maximal power production and the maintenance of power (endurance time to exhaustion) at 36%, 55%, and 73% of maximal power was investigated in 18 untrained but physically active men. Power output was determined at constant pedalling rate (60 rev · min^–1) on a cycle ergometer instrumented with force transducers and interfaced with a computer. Maximal power was determined for each subject as the highest one-revolution average power. Fat-free mass was determined by hydrostatic weighing, fat-free thigh volume by water displacement and skinfold measurement, and percent age and area of type 11 fibers from biopsy specimens taken from the vastus lateralis. Maximal power averaged 771 ± 149 W with a range of 527–1125 W. No significant correlations were found among percentage of type II fibers, relative area of type II fibers, or fat-free thigh volume and maximal power or endurance times to exhaustion at any percentage of maximal power. Weak but significant relationships were found for fat free mass with both maximal power (r=0.57) and endurance time at 73% of maximal power (r= -0.47). These results show maximal power to be more dependent on factors related to body size than muscle-fiber characteristics. The low correlations for so many of the relationships, however, suggest that individuals employ either different combinations of these factors or utilize other strategies for the generation of high power.Human subjects participated in these studies after giving their free and informed voluntary consent. Investigators adhered to AR 70-25 and USAMRDC regulation 70-25 on Use of Volunteers in Research.The views, opinions, and/or findings contained in this report are those of the author(s) and should not be construed as an official Department of the Army position, policy, or decision, unless so designated by other official documentation.     

Critical power test for ramp exercise

The critical power test for cycle ergometry has been criticised as providing an overestimate of the real value of the critical power. Part of the blame may rest in the practical problem associated with getting reliable measurements of longer endurance times when power settings are not much above the critical power. However, by adjusting the incremental slope of ramp exercises, exhaustion brought about by high power and in a reasonably short time can be ensured, so avoiding this practical problem. This communication presents the theory and methods required to obtain estimates of both anaerobic work capacity and critical power from several ramp tests conducted to exhaustion. The method is illustrated with published laboratory data collected from exercising subjects.