Physiological responses of women during lifting exercise

Summary Physiological responses were measured in 7 women subjects who lifted boxes weighing 6.8, 15.9 or 22.7 kg from the floor to a height of 60 cm. After training and establishing the O₂ max, the boxes were lifted for 1 h at 30, 50, and 60% O₂ max. The changes in heart rate, O₂, the integrated EMG during lifting and the loss of isometric hand-grip endurance after lifting were used to assess the development of fatigue. There was no evidence of fatigue at 30% O₂ max but fatigue did exist in some conditions at 50% and in all conditions at 60% O₂ max. It is suggested that fatigue is unlikely to occur while lifting boxes up to 15.9 kg weight at 35–40% O₂ max, i.e., at rates of lifting varying from 5 to 7 times per min.     

Physiological responses to maximal intensity intermittent exercise

Summary Physiological responses to repeated bouts of short duration maximal-intensity exercise were evaluated. Seven male subjects performed three exercise protocols, on separate days, with either 15 (S₁₅), 30 (S₃₀) or 40 (S₄₀) m sprints repeated every 30 s. Plasma hypoxanthine (HX) and uric acid (UA), and blood lactate concentrations were evaluated pre- and postexercise. Oxygen uptake was measured immediately after the last sprint in each protocol. Sprint times were recorded to analyse changes in performance over the trials. Mean plasma concentrations of HX and UA increased during S₃₀ and S₄₀ (P<0.05), HX increasing from 2.9 (SEM 1.0) and 4.1 (SEM 0.9), to 25.4 (SEM 7.8) and 42.7 (SEM 7.5) µmol · l^–1, and UA from 372.8 (SEM 19) and 382.8 (SEM 26), to 458.7 (SEM 40) and 534.6 (SEM 37) µmol · l^–1, respectively. Postexercise blood lactate concentrations were higher than pretest values in all three protocols (P<0.05), increasing to 6.8 (SEM 1.5), 13.9 (SEM 1.7) and 16.8 (SEM 1.1) mmol · l^–1 in S₁₅, S₃₀ and S₄₀, respectively. There was no significant difference between oxygen uptake immediately after S₃₀ [3.2 (SEM 0.1) l · min^–1] and S₄₀ [3.3 (SEM 0.4) l · min^–1], but a lower value [2.6 (SEM 0.1) l · min^–1] was found after S₁₅ (P<0.05). The time of the last sprint [2.63 (SEM 0.04) s] in S₁₅ was not significantly different from that of the first [2.62 (SEM 0.02) s]. However, in S₃₀ and S₄₀ sprint times increased from 4.46 (SEM 0.04) and 5.61 (SEM 0.07) s (first) to 4.66 (SEM 0.05) and 6.19 (SEM 0.09) s (last), respectively (P<0.05). These data showed that with a fixed 30-s intervening rest period, physiological and performance responses to repeated sprints were markedly influenced by sprint distance. While 15-m-sprints could be repeated every 30 s without decreases in performance, 40-m sprint times increased after the third sprint (P<0.05) and this exercise pattern was associated with a net loss to the adenine nucleotide pool.     

Cardiopulmonary responses to combined rhythmic and isometric exercise in humans

Summary A rhythmic (R) and an isometric (I) exercise were performed separately and in combination to assess their additive effects on arterial systolic (P _as) and diastolic (P _ad) blood pressures, heart rate (f _c), and minute ventilation (V _I). The isometric effort consisted of a 40% maximal voluntary handgrip contraction (MVC) performed for a duration of 80% of a previously determined 40% MVC fatiguing effort. The R effort consisted of a 13-min cycle effort at 75% maximum oxygen consumption (VO_2maX). For the combined efforts, I was performed starting simultaneously with or ending simultaneously with R. Data on nine subjects yield statistically significant evidence (P<0.05) that the effects of I and R are not additive for the following three cases: (1)P _as when I and R are ended simultaneously (I alone=4.9, SEM 0.5 kPa increase; R alone=no significant change from steady state; I+R=1.2, SEM 0.4 kPa increase), (2)P _ad when I and R are started simultaneously (I alone=4.1, SEM 0.4 kPa increase; R alone=0.7, SEM 0.3 kPa decrease; I+R=1.9, SEM 0.4 kPa increase), and (3)P _ad when I and R are ended simultaneously (I alone=4.1, SEM 0.4 kPa increase; R alone=0.3, SEM 0.5 kPa decrease; I+R=0.8, SEM 0.3 kPa increase). For all other variables and cases, there is not sufficient evidence to conclude that the effects of I and R are not additive. We conclude that R and I exercises do not invariably produce strictly additive cardiopulmonary responses. When R and I exercises are started simultaneously, however,P _as,f _c, andV _I are additive. Finally, cardiopulmonary responses to I efforts superimposed on steady-state 75%VO_2max R efforts suggest that cardiopulmonary controls already established during R efforts attenuate responses to the I effort.     

Effects of prolonged cycle ergometer exercise on maximal muscle power and oxygen uptake in humans

Summary The mechanical power (W_tot, W·kg^–1) developed during ten revolutions of all-out periods of cycle ergometer exercise (4–9 s) was measured every 5–6 min in six subjects from rest or from a baseline of constant aerobic exercise [50%–80% of maximal oxygen uptake (VO_2max)] of 20–40 min duration. The oxygen uptake [VO₂ (W·kg^–1, 1 ml O₂ = 20.9 J)] and venous blood lactate concentration ([la]_b, mM) were also measured every 15 s and 2 min, respectively. During the first all-out period, W_tot decreased linearly with the intensity of the priming exercise (W_tot = 11.9–0.25·VO₂). After the first all-out period (i greater than 5–6 min), and if the exercise intensity was less than 60% VO_2max, W_tot, VO₂ and [la]_b remained constant until the end of the exercise. For exercise intensities greater than 60% VO_2max, VO₂ and [la]_b showed continuous upward drifts and W_tot continued decreasing. Under these conditions, the rate of decrease of W_tot was linearly related to the rate of increase of V [(d W_tot/dt) (W·kg^–1·s^–1) = 5.0·10^–5 –0.20·(d VO₂/dt) (W·kg^–1·s^–1)] and this was linearly related to the rate of increase of [la]_b [(d VO₂/dt) (W·kg^–1·s^–1) = 2.310^–4 + 5.910^–5·(d [la]_b/dt) (mM·s^–1)]. These findings would suggest that the decrease of W_tot during the first all-out period was due to the decay of phosphocreatine concentration in the exercising muscles occurring at the onset of exercise and the slow drifts of VO₂ (upwards) and of W_tot (downwards) during intense exercise at constant W_tot could be attributed to the continuous accumulation of lactate in the blood (and in the working muscles).     

Influence of two pedalling rate conditions on mechanical output and physiological responses during all-out intermittent exercise

The purpose of this study was to investigate the effect of two cycling velocities on power output and concomitant metabolic and cardiorespiratory responses to repeated all-out exercises. Mean power output (P _m), total work (W _tot), total oxygen consumption (VO_2tot) and blood lactate accumulation (Δ[La]_b) were evaluated in 13 male subjects who performed two series of twelve 5-s bouts of sprint cycling. Recovery periods of 45-s were allowed between trials. One series was executed at optimal velocity (V _opt: velocity for greatest power) and the other one at 50% V _opt (0.5V _opt). Velocities obtained in these conditions were V_opt=116.6 (4.7) rpm; 0.5V_opt=60.6 (4.9) rpm. After a phase of adaptation in oxygen uptake in the first part of the series, the data from the 6th to the 12th sprint were as follows: P _m, 924.6 (73.9) versus 689.2 (61.8) W; W _tot, 29.95 (4.14) versus 22.04 (3.17) kJ; VO_2tot, 12.80 (1.36) versus 10.58 (1.37) l; Δ[La]_b, 2.72 (1.22) versus 0.64 (0.79) mmol.l⁻¹, respectively (P<0.001). Both W _tot and VO_2tot were consistently higher at optimal velocity (+21 and +35.8%, respectively). The present findings demonstrate that during intermittent short-term all-out exercise requiring maximal activation, the energy turnover is not necessarily maximal. It depends on muscle contraction velocity. The increase, lower than expected, in metabolic response from 0.5V _opt to V _opt suggests also that mechanical efficiency is higher at V _opt. Electronic Publication     

膝屈伸肌群等速肌力训练改善膝骨性关节炎患者步态的效果分析

目的探讨膝屈伸肌群等速肌力训练改善膝骨性关节炎(KOA)患者步态的效果。方法采用前瞻性研究方法,为保证研究的安全性和科学性,选择2013年2月~2015年10月在我院诊治的KOA患者98例,根据入院顺序分为观察组与对照组各49例,两组都给予玻璃酸钠关节腔内注射和关节松动治疗,对照组给予积极康复训练,观察组给予膝屈伸肌群等速肌力训练,治疗观察时间都为4周。结果观察组与对照组的疗效优良率分别为93.9%和75.5%,观察组明显高于对照组(0.05)。治疗后观察组与对照组的Lysholm膝关节功能评分分别为(86.33±11.31)分和(75.84±10.71)分,都明显高于治疗前的(56.24±12.55)分和(56.24±11.12)分,组内与组间对比差异都有统计学意义(0.05)。观察组治疗后的屈肌PT与AOPT值分别为(21.87±3.67)N·m和(99.23±11.48)°,而对照组分别为(18.34±4.11)N·m和(89.02±10.45)°,都明显高于治疗前(0.05),且组间对比差异有统计学意义(0.05)。两组在治疗期间都无严重并发症,但观察组的恶心、呕吐、腹痛、腹胀等并发症发生率明显少于对照组(0.05)。结论膝屈伸肌群等速肌力训练在KOA患者中的应用能显著缓解疼痛、增强膝关节功能,具有很好的安全性,从而促进步态改善,具有重要的推广价值。     

Electrically evoked isometric and isokinetic properties of the triceps surae in young male subjects

Summary The relationship between electrically evoked isometric and isokinetic properties of the triceps surae have been studied in 11 healthy male subjects. The results showed that the time to peak tension (TPT) and half relaxation time (1/2 RT) of the maximal twitch were 110±11 ms and 82±11 ms respectively, and the peak rates of rise of contraction (P ₅₀, P ₂₀₀) and relaxation (P _R50, P _R200) at 50 and 200 Hz were 0.36±0.07, 0.48±0.08 and 1.27±0.33, 1.25±0.27% Po ms^–1 respectively. The decline in force during a fatigue test was significantly (P<0.02) associated with the decrease in maximal relaxation rate (r=0.79). The TPT was significantly (P<0.05) and inversely related to P ₅₀ and P ₂₀₀. The mean angle specific torque-velocity relationship for the 11 subjects was adequately described by the empirical exponential equation of the form: V=16.5 (e ^–p/30.8–e ^–84.3/30.8) where V=velocity (rads s^–1) P=torque (Nm). The only significant association found between the isometric and isokinetic properties of the muscle was between P _R200 and the torque expressed at a given velocity of 4 rads s^–1. This lack of association between the two variables is difficult to explain with certainty but it is suggested that it may be due to the differential effects of Ca²⁺ release and uptake and cross-bridge turnover rate in the two situations.     

The effect of muscle contraction velocity on cardiorespiratory responses to repetitive isokinetic exercise in humans

We investigated the effect of muscle contraction velocity on cardiorespiratory responses during exercise. Eight males (23 +/- 2 years, 175 +/- 5 cm, 64 +/- 6 kg, mean +/- SD) performed 3-min repetitive one-leg extension exercises at various angular velocities (30, 60, 120, and 240 deg/s) with a controlled relaxation interval, relatively constant (duty cycle = 1:1, A trial) and absolutely constant (relaxation time = 0.75 s, B trial) at a total work of 2,100-2,400 J in an isokinetic mode, using a Cybex II dynamometer. We measured heart rate (HR), mean blood pressure (MAP), minute ventilation (Vdot;E), and oxygen uptake (Vdot;O(2)) during the exercise. The angular velocity significantly affected the increase in HR, MAP, Vdot;E, and Vdot;O(2) at the end of exercise from resting in both A and B trials (e.g., MAP: 12 +/- 2, 10 +/- 2, 11 +/- 2, and 18 +/- 2 mmHg in the A trial). The result suggests that muscle contraction velocity affects cardiorespiratory responses during repetitive isokinetic exercise.     

Effects of moderate hyperoxia on oxygen consumption during submaximal and maximal exercise

The present study examined the effect of hyperoxia on oxygen uptake (V˙O₂) and on maximal oxygen uptake (V˙O_2max) during incremental exercise (IE) and constant work rate exercise (CWRE). Ten subjects performed IE on a bicycle ergometer under normoxic and hyperoxic conditions (30% oxygen). They also performed four 12-min bouts of CWRE at 40, 55, 70 and 85% of normoxic V˙O_2max (ex1, ex2, ex3 and ex4, respectively) in normoxia and in hyperoxia. V˙O_2max was significantly improved by 15.0 (15.2)% under hyperoxia, while performance (maximum workload, W _max) was improved by only +4.5 (3.0)%. During IE, the slope of the linear regression relating V˙O₂ to work rate was significantly steeper in hyperoxia than in normoxia [10.80 (0.88) vs 10.06 (0.66) ml·min^–1·W^–1]. During CWRE, we found a higher V˙O₂ at ex1, ex2, ex3 and ex4, and a higher V˙O₂ slow component at ex4 under hyperoxia. We have shown that breathing hyperoxic gas increases V˙O_2max, but to an extent that is difficult to explain by an increase in oxygen supply alone. Changes in metabolic response, fibre type recruitment and V˙O₂ of non-exercising tissue could explain the additional V˙O₂ for a given submaximal work rate under hyperoxia. Electronic Publication     

Aerobic exercise performance correlates with post-ischemic flow-mediated dilation of the brachial artery in young healthy men

In older healthy men, aerobic exercise capacity is related to postischemic flow-mediated dilation of the brachial artery (FMD), but corresponding data in a younger population is not available. In addition, whether submaximal aerobic exercise performance also correlates with this kind of vasomotor reactivity is not known. Therefore, in 15 nonsmoking young healthy men [age 27 (5) years; body mass index: 24 (2) kg/m²; mean (SD)] with different levels of ordinary physical activity, but not performing upper-extremity training, we measured FMD at 1 min after reactive hyperemia, and pulmonary oxygen uptake (O₂) at ventilatory anaerobic threshold (O₂AT) and at peak effort (peak O₂) during an incremental exercise on a treadmill. In our participants, FMD was 9.1 (3.4)%, O₂AT was 40.72 (5.92) ml/kg per min, and peak O₂ was 52.95 (8.13) ml/kg per min. Using bivariate Pearsons correlation, and in separate multivariate regression analyses, O₂AT and peak VO₂ showed a significant and reasonably good correlation with FMD (r=0.84, P<0.001 and r=0.77, P=0.001, respectively), independent of age, body mass index and serum total cholesterol (=0.77, P<0.001, R² of the overall model=0.79 and =0.70, P<0.005, R² of the overall model=0.69, respectively). Our data provide evidence suggesting that in young healthy men a higher submaximal and maximal aerobic exercise performance is associated with a greater FMD of peripheral conduit arteries.     

Measurement of directional force and power during human submaximal and maximal isokinetic exercise

An isokinetic cycle ergometer has been developed to measure power output generated over a wide range of constant velocities. The ergometer system has two operating modes and it can be instantly switched from one to another. In its conventional mode the cycle ergometer is connected to a conventional electrically braked cycle ergometer so that the subjects can perform submaximal steady-state exercise. For maximal power measurements the system can be instantly switched to an isokinetic control mechanism which allows a constant pedalling rate to be set in the range of 23–180 rev·min^–1. In both operating modes the forces generated on the pedals are monitored by strain gauges mounted inside the pedals. This enables information to be obtained regarding the direction of forces generated at the foot-pedal interface. The output from the strain-gauges was A-D converted and stored along with data giving pedal and crank position. Data was sampled 150 times in each revolution of the crank. Force data are usually analysed for maximal peak power (highest instantaneous power generated during each revolution), mean power (power generated over a complete revolution), extension and flexion power (power generated during leg extension and leg flexion respectively). This system allows characterisation of the relationship between maximal leg power and pedalling rate, both under control and exercise-induced potentiation and fatigue conditions. Thus it is possible for example to quantify instantly the magnitude of fatigue induced by preceding dynamic exercise of a given duration, intensity or contraction velocity.     

Effects of isokinetic training of the knee extensors on high-intensity exercise performance and skeletal muscle buffering

Twenty-three subjects isokinetically trained the right and left quadriceps femoris, three times per week for 16 weeks; one group (n=13) trained at an angular velocity of 4.19 rad · s^–1 and a second group (n=10), at 1.05 rad · s^–1. A control group (n=10) performed no training. Isometric endurance time at 60% quadriceps maximum voluntary contraction (MVC), mean power output and work done (W) during all-out cycling, and the muscle buffer value (B) and carnosine concentration of biopsy samples from the vastus lateralis, were all assessed before and after training. The two training groups did not differ significantly from each other in their training response to any of these variables (P < 0.05). No significant difference in either 60% MVC endurance time or impulse [(endurance time × force) at 60% MVC] was observed for any group after the 16 week period (P > 0.05). However, the post-training increase (9%) in W during high-intensity cycling was greater in the training group than in the control group (P=0.04). NeitherB nor carnosine concentration showed any significant change following training (P=0.56 andP=0.37, respectively). It is concluded that 16 weeks of isokinetic training of the knee extensors enables subjects to do more work during high-intensity cycling. Although the precise adaptations responsible for the improved performance have yet to be identified, they are unlikely to include an increase inB.     

Cardiovascular responses to sustained maximal isometric contractions of the finger flexors

Summary This study investigated cardiovascular responses to 2 min sustained submaximal (20% MVC) and maximal (100% MVC) voluntary isometric contractions of the finger flexors in healthy young women. Cardiovascular variables investigated were: heart rate (f _c), mean arterial pressure ( _a), and stroke volume (SV). Doppler echocardiography was used to estimate SV from measures of aortic diameter (AD) and time-velocity integrals. Preliminary studies indicated that AD did not change significantly after 2 min sustained 100% MVC. Therefore, pre-exercise AD values were used to calculate SV before, during and after exercise. During the 2-min 100% MVC period, f _c and _aincreased significantly during the first 30 s of contraction. f _c then remained constant during the remainder of the 2-min contraction period, while _acontinued to rise. SV did not change significantly during the 100% MVC task but increased significantly during recovery from sustained 100% MVC. The data suggest that the magnitude of cardiovascular responses to isometric exercise is dependent on the specific task performed, and that there is a different pattern of response for f _c, _a, and SV during 20% and 100% MVC tasks. Unlike f _c and _a, SV did not change significantly during isometric exercise, but increased significantly after sustained 100% MVC.     

Cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise

In occupational work, continuous repetitive and isometric actions performed with the upper extremity primarily cause local muscle strain and musculoskeletal disorders. They may also have some adverse effects on the cardiorespiratory system, particularly, through the elevation of blood pressure. The aim of the present study was to compare peak cardiorespiratory responses to fatiguing dynamic and isometric hand-grip exercise. The subjects were 21 untrained healthy men aged 24–45 years. The dynamic hand-grip exercise (DHGE) was performed using the left hand-grip muscles at the 57 (SD 4)% level of each individual's maximal voluntary contraction (MVC) with a frequency of 51 (SD 4) grips · min^−l. The isometric hand-grip exercise (IHGE) was done using the right hand at 46 (SD 3)% of the MVC. The endurance time, ventilatory gas exchange, heart rate (HR) and blood pressure were mea- sured during both kinds of exercise. The mean endurance times for DHGE and IHGE were different, 170 (SD 62) and 99 (SD 27) s, respectively (P < 0.001). During DHGE the mean peak values of the breathing frequency [20 (SD 6) breaths · min⁻¹] and tidal volume [0.89 (SD 0.34) l] differed significantly (P < 0.01) from peak values obtained during IHGE [15 (SD 5) breaths · min⁻¹, and 1.14 (SD 0.32) l, respectively]. The corresponding peak oxygen consumptions, pulmonary ventilations, HR and systolic blood pressures did not differ, and were 0.51 (SD 0.06) and 0.46 (SD 0.11) l · min⁻¹, 17.1 (SD 3.0) and 16.7 (SD 4.7) l · min⁻¹, 103 (SD 18) and 102 (SD 17) beats · min⁻¹, and 156 (SD 17) and 161 (SD 17) mmHg, respectively. The endurance times of both DHGE and IHGE were short (<240 s). The results indicate that the peak responses for the ventilatory gas exchange, HR and blood pressure were similar during fatiguing DHGE and IHGE, whereas the breathing patterns differed significantly between the two types of exercise. The present findings emphasize the importance of following ergonomic design principles in occupational settings which aim to reduce the output of force, particularly in tasks requiring isometric and/or one-sided repetitive muscle actions. Accepted: 16 February 2000     

Fatigability during repetitive maximal knee extensions in 14-year-old boys

The isokinetic forces, during 50 repeated maximal knee extensions with a constant velocity of 3.14 rad · s^–1, and muscle cross-sectional area (CSA) of the quadriceps femoris muscles were measured for boys aged 14 years (n = 26) and young adult men (n = 26). As representative scores in the maximal session, the mean values of force ( ) of every five consecutive and all trials were calculated. The CSA was measured by using a B-mode ultrasound technique at the midpoint of the thigh length (l _t). The average values of at the 1st–5th contractions were 193 (SEM 12) N for the boys and 303 (SEM 13) N for the young adults. The average decline of with 50 contractions, expressed as a percentage of the value in the 1st–5th trial, was higher in the young adults than in the boys: for the young adults was reduced by 48 (SEM 2.9)%, for the boys by 36 (SEM 3.1)%. The of every five consecutive and all trials were significantly correlated to the product of CSA andl _t (CSA ·l _t) in separate groups: for the boysr = 0.762–0.894 (P < 0.01), for the young adultsr = 0.598–0.837 (P < 0.01). In a trial range between the 1st–5th and 11th–15th contractions, the young adults showed significantly higher values in the ratio of to CSA ·l _t ( · CSA^–1 ·l _t) than the boys. However, the difference between groups of the ratio on and after the 16th–20th trial and for all trials became insignificant. Thus, at least for 50 maximal repeated knee extensions, the 14-year-old boys were inferior to the young adults in their ability to produce force during the earlier sessions even when the difference in muscle size was allowed for. The inferiority in the boys might be attributed to a lower reliance on glycolysis as pointed out in previous biochemical studies.     

Lowered cutaneous sensitivity to nonpainful electrical stimulation during isometric exercise in humans

Summary The effect of isometric exercise on cutaneous sensitivity to nonpainful electric stimulation was studied in human subjects. The exercises consisted of brief (duration: 1–10 s) palmar flexions of the hand or foot against varying loads (10–30% of the maximal force). A visual go cue was used to indicate the start and end of the exercise. Isometric hand exercise produced a load-dependent increase of electrotactile thresholds of the fingers. The threshold elevation was rapidly attenuated with prolonged duration of the exercise. The hand exercise-induced threshold elevation was of equal magnitude in the glabrous and hairy skin of the fingers. Thresholds were not changed for the hand contralateral to the exercising hand. Passive static pressure of the hand did not produce threshold changes, whereas activation of afferent inhibition by a vibrotactile stimulus (100 Hz, 0.1 mm) did produce a significant threshold elevation. Exerciseinduced threshold elevation was also significant immediately prior to the EMG response of the arm but not at the time of the visual go signal, or before it. The threshold increase found during the EMG response was not significantly stronger than that found prior to the EMG response. These results suggest that isometric exercise load-dependently produces a phasic, rapidly attenuating increase in cutaneous tactile thresholds in the exercising limb but not multisegmentally. Corollary efferent barrage from motor to sensory structures of the brain could be underlying the threshold changes produced by isometric exercise, whereas afferent inhibitory mechanisms seem to have only a minor role.     

Sex difference in force generation capacity during repeated maximal knee extensions

The force generation capacity, during 50 repeated maximal knee extensions with a constant velocity of 3.14 rad · s^–1, and cross-sectional area (CSA) of the quadriceps femoris muscles were determined for untrained women (n = 36) and men (n = 27) aged from 18 to 25 years. As force scores in the maximal repetitions, the mean values of force ( ) of every 5 consecutive and all trials and the percentage of decline of (%D) with 50 contractions were calculated. The CSA was measured by using a B-mode ultrasound technique at the midpoint of the thigh length. The decreased from 303 (SEM 13) N at the 1st–5th trial to 155 (SEM 9) N at the 46th–50th trial for the men, and from 202 (SEM 9) N to 94 (SEM 4) N for the women. The of every 5 consecutive and all trials were significantly correlated to muscle CSA: for the men r = 0.552–0.872 (P < 0.01) and for the women r = 0.609–0.857 (P < 0.01). The men showed significantly higher at every 5 consecutive trials than the women even when calculated per unit muscle CSA ( ·CSA^–1). There were significant correlations between %D and ·CSA^–1 at the 1st–5th trial: r = 0.538 (P < 0.01) for the men and r = 0.631 (P < 0.01) for the women, respectively. The average values of %D were almost the same in both sexes: for the men 48 (SEM 3) % and for the women 52 (SEM 2) %, respectively. However, an ANCOVA calculation on %D, using ·CSA^–1 the 1st–5th trial as the covariate, indicated that the women had significantly higher %D than the men. Thus, the force output during the maximal repetitions was significantly correlated to the CSA of quadriceps femoris in both sexes. The force output was lower in the women than in the men even when the difference in the muscle CSA was allowed for. The women had higher %D than the men when force output per unit muscle CSA during the initial 5 repetitions was compared.     

Gas exchange responses to continuous incremental cycle ergometry exercise in primary pulmonary hypertension in humans

In patients suffering from primary pulmonary hypertension (PPH), a raised pulmonary vascular resistance may limit the ability to increase pulmonary blood flow as work rate increases. We hypothesised that oxygen uptake (V˙O₂) may not rise appropriately with increasing work rate during incremental cardiopulmonary exercise tests. Nine PPH patients and nine normal subjects performed symptom-limited maximal continuous incremental cycle ergometry exercise. Mean peak V˙O₂ [1.00 (SD 0.22) compared to 2.58 (SD 0.64) l · min⁻¹] and mean V˙O₂ at lactic acidosis threshold [LAT, 0.73 (SD 0.17) compared to 1.46 (SD 0.21 · l) ml · min⁻¹] were much lower in patients than in normal subjects (both P < 0.01, two-way ANOVA with Tukey test). The mean rate of change of V˙O₂ with increasing work rate above the LAT [5.9 (SD 2.1) compared to 9.4 (SD 1.3) ml · min⁻¹ · W⁻¹, P < 0.01)] was also much lower in patients than in normal subjects [apparent δ efficiency 60.3 (SD 38.8)% in patients compared to 31.0 (SD 4.9)% in normal subjects]. The patients displayed lower mean values of end-tidal partial pressure of carbon dioxide than the normal subjects at peak exercise [29.7 (SD 6.8) compared to 42.4 (SD 5.8) mmHg, P < 0.01] and mean oxyhaemoglobin saturation [89.1 (SD 4.1) compared to 93.6 (SD 1.8)%, P < 0.05]. Mean ventilatory equivalents for CO₂ [49.3 (SD 11.4) compared to 35.0 (SD 7.3), P < 0.05] and O₂ [44.2 (SD 10.7) compared to 29.9 (SD 5.1), P < 0.05] were greater in patients than normal subjects. The sub-normal slopes for the V˙O₂-work-rate relationship above the LAT indicated severe impairment of the circulatory response to exercise in patients with PPH. The ventilatory abnormalities in PPH suggested that the lung had become an inefficient gas exchange organ because of impaired perfusion of the ventilated lung. Accepted: 17 April 2000     

Mechanomyographic and electromyographic time and frequency domain responses during submaximal to maximal isokinetic muscle actions of the biceps brachii

The purpose of this investigation was to determine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) versus torque relationships during isokinetic muscle actions of the biceps brachii. Twelve adults [mean (SD) age, 22.2 (2.7) years] performed submaximal to maximal isokinetic muscle actions of the dominant forearm flexors. Following determination of isokinetic peak torque (PT), the subjects randomly performed submaximal muscle actions in 20% increments from 20% to 80% PT. Polynomial regression analyses indicated linear increases in both MMG (r²=0.984) and EMG (r²=0.988) amplitude to 100% PT. There were no significant (P>0.05) relationships, however, for MMG and EMG MPF versus isokinetic torque. The results demonstrated similar responses for MMG and EMG in both the time and frequency domains. These findings suggested that simultaneous examination of MMG and EMG amplitude and MPF may be useful for describing the unique motor control strategies that modulate dynamic torque production. Furthermore, the results indicated that dynamic muscle actions can be used when applying techniques that require a linear EMG amplitude versus torque relationship.     

Time-of-day effect on nonthermal control of sweating response to maintained static exercise in humans

To investigate the influence of nonthermal factors in the time-of-day effect on the sweating response to maintained static exercise, eight healthy male subjects performed handgrip exercise at 20%, 35% and 50% maximal voluntary contraction (MVC) for 60 s at 0600 hours (morning) and at 1800 hours (evening). Oesophageal temperature (T _oes) before the experiment showed a diurnal rhythm [mean (SEM)] [36.3 (0.1) (morning) compared to 36.8 (0.1) °C (evening), P<0.01]. Experiments were conducted with subjects in a state of mild hyperthermia during which the mean skin temperature (T _sk) was kept constant at 35.5–36.5 °C using a water-perfused suit to activate sudomotor responses. The T _oes and mean T _sk remained stable during the pre-exercise, handgrip exercise and recovery periods. The response in sweating rate (ΔSR) on the chest and forearm to handgrip exercise increased significantly with increasing exercise intensity in both the morning and evening tests (P<0.05). The ΔSR on the palm did not change significantly with increasing exercise intensity in the morning test (P>0.1). During handgrip exercise at 50% MVC only, ΔSR on the chest, forearm and palm in the evening was significantly higher than in the morning (P<0.05). On the other hand, mean arterial blood pressure and the rating of perceived exertion during 50% MVC handgrip exercise were not significantly different between the morning and evening (P>0.1). These results indicate the presence of a time-of-day effect on nonthermal control of the sweating response to isometric handgrip exercise, and that this effect is dependent on exercise intensity. Electronic Publication