Mechanical output about the ankle joint in isokinetic plantar flexion and jumping

The purpose of this study was to compare for a group of ten subjects the mechanical output about the ankle during isokinetic plantar flexion with that during one-legged vertical jumps. For evaluation of the mechanical output the plantar flexion moment of force was related to the angular velocity of plantar flexion. The relationship for isokinetic plantar flexion was obtained using an isokinetic dynamometer; that for plantar flexion in jumping was obtained by combining kinematics and ground reaction forces. It was found that, at any given angular velocity of plantar flexion above 1 rad.s-1, the subjects produced much larger moments during jumping than during isokinetic plantar flexion. In order to explain the observed differences in mechanical output about the ankle, a model was used to simulate isokinetic plantar flexion and plantar flexion during jumping. The model represented both m. soleus and m. gastrocnemius as a complex composed of elastic tissue in series with muscle fibers. The force of the muscle fibers depended on fiber length, shortening velocity (Vfibers), and active state. The input variables of the model were histories of shortening velocities of the complexes, determined from kinematics, and active state. Among the output variables were Vfibers and plantar flexion moment. The simulation results were very similar to the experimental findings. According to the simulation results there are two reasons why at the same angular velocity of plantar flexion larger moments were produced during jumping than during isokinetic plantar flexion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between the slow component of oxygen uptake and the potential reduction in maximal power output during constant-load exercise.

BACKGROUND: The purpose of the present study was to examine the relationship between the slow component of oxygen uptake (VO2) and muscle fiber fatigue. Maximal power output (MPO) was used as an index of muscle fiber fatigue. METHODS: Two constant exercises were carried out at exercise intensities of 40% and 80% of maximal oxygen uptake (VO2max). Each exercise was repeated three times, once for the measurement for VO2, and the other two times for MPO testing, at 3 and 6 minutes after work output. RESULTS: Reproducibility of MPO at rest was assessed by correlation coefficient. Its value was 0.933. At 40% VO2max, MPO did not significantly decrease from the resting value. At 80% VO2max, MPO significantly decreased by 129+/-77 watts at 3 min and by 178+/-108 watts at 6 min. The VO2 kinetic at 40% VO2 was well described by a monoexponential function with a time constant of 0.432 min. However, at 80% VO2max, a slow component of the form of a linear drift superimposed on a monoexponential function with an essentially equal time constant (0.469 min) was unambiguously detected. This slow component was significantly related to the decrease in MPO (r=0.567). CONCLUSIONS: The present results suggested that the fatigue of muscle fibers may be one of the factors that produce the slow component of VO2 during high intensity exercise.     

Attainment of maximal exercise criteria in boys and men

BACKGROUND: This study tested the hypothesis that the occurrence of a VO(2) plateau at maximal exercise would be greater in men versus boys. Secondary indicators of maximal effort also were examined. METHODS: Sixteen boys (10.7+/-0.6 yrs) and 21 men (22.5+/-2.0 yrs) performed a graded exercise test on a treadmill at a constant speed of 8.04 km x hr(-1) with 2.5% increments in elevation. The men also performed a second test at 11.26 km x hr(-1) with similar increases in slope. RESULTS: At 8.04 km x hr(-1) , VO(2) max was 52.3+/-6.0 and 52.5+/-5.1 ml x kg(-1) x min(-1) in boys and men, respectively (p>0.05). In the men, VO(2) max (53.3+/-5.4 ml x kg(-1) x min(-1) ) was higher (p<0.05) in the faster protocol. The percentage of men achieving the criterion was nearly double the percentage of boys (23.8 vs 12.5%), although the difference was not significant. Age-specific criteria heart rate (HR) and respiratory exchange ratio (RER) were achieved in a similar manner; however, more men (100%) than boys (86.7%) achieved an age-specific blood lactate (BLa) criterion (p<0.05). Plateau achievement increased to 33.0% in the 11.26 km x hr(-1) protocol, but was not significantly different from 8.04 km x hr(-1). HR, RER and BLa criteria achievement were comparable. CONCLUSIONS: Maturation may influence the achievement of a plateau and BLa criteria, but not age-specific criteria for RER or HR.     

Caffeine, maximal power output and fatigue.

The purpose of this investigation was to determine the effects of caffeine ingestion on maximal power output and fatigue during short term, high intensity exercise. Nine adult males performed 15 s maximal exercise bouts 60 min after ingestion of caffeine (7 mg.kg-1) or placebo. Exercise bouts were carried out on a modified cycle ergometer which allowed power output to be computed for each one-half pedal stroke via microcomputer. Peak power output under caffeine conditions was not significantly different from that obtained following placebo ingestion. Similarly, time to peak power, total work, power fatigue index and power fatigue rate did not differ significantly between caffeine and placebo conditions. These results suggest that caffeine ingestion does not increase one's maximal ability to generate power. Further, caffeine does not alter the rate or magnitude of fatigue during high intensity, dynamic exercise.     

Neural control of force output during maximal and submaximal exercise

A common belief in exercise physiology is that fatigue during exercise is caused by changes in skeletal muscle metabolism. This 'peripheral' fatigue results either from substrate depletion during submaximal exercise or metabolite accumulation during maximal exercise in the exercising muscles. However, if substrate depletion alone caused fatigue, intracellular ATP levels would decrease and lead to rigor and cellular death. Alternatively, metabolite accumulation would prevent any increase in exercise intensity near the end of exercise. At present, neither of these effects has been shown to occur, which suggests that fatigue may be controlled by changes in efferent neural command, generally described as 'central' fatigue. In this review, we examine neural efferent command mechanisms involved in fatigue, including the concepts of muscle wisdom during short term maximal activity, and muscle unit rotation and teleoanticipation during submaximal endurance activity. We propose that neural strategies exist to maintain muscle reserve, and inhibit exercise activity before any irreparable damage to muscles and organs occurs. The finding that symptoms of fatigue occur in the nonexercising state in individuals with chronic fatigue syndrome indicates that fatigue is probably not a physiological entity, but rather a sensory manifestation of these neural regulatory mechanisms.     

Difference in breathing strategies during exercise between trained elderly men and women

This study compared the ventilatory responses and exercise tidal flow-volume (Vt) loops during exercise in order to analyze the influence of gender on breathing strategy in a fit aging population. Sixteen trained elderly men (63.0+/-2.9 years) and eight peer women (62.3 +/- 5.5 years) performed an incremental test on a cycle ergometer. At 90% maximal oxygen consumption (VO2max), the women presented a significantly higher expiratory flow limitation (EFL) than the men (38 +/- 10 vs 17 +/- 8% of Vt, respectively) (P<0.01) and a lower value of expiratory reserve volume relative to forced vital capacity (FVC) compared with the men (16.8 +/- 5.3% vs 23.0 +/- 5.2%, respectively) (P<0.05). Inspiratory reserve volume relative to FVC was significantly higher in women than men at 50% (P<0.05), 70% (P<0.01) and 90%VO2max (25.2 +/- 5.4% vs 12.2 +/- 4.2%, respectively, at 90%VO2max) (P<0.01). Mechanical ventilatory constraints occurred in trained elderly men and women. However, different breathing strategies were observed relative to gender. A significantly higher EFL was measured in women, whereas men rather presented a dynamic hyperinflation. This specific breathing strategy measured in trained elderly women would induce lower ventilatory efficiency than in peer men.     

Decreased foot inversion force and increased plantar surface after maximal incremental running exercise

Formulating the hypothesis that a maximal running exercise could induce fatigue of some foot muscles, we searched for electromyographic (EMG) signs of fatigue in the tibialis anterior (TA), peroneus longus (PL), and gastrocnemius medialis (GM) muscles. We also searched for post-exercise alterations of the stationary upright standing in normal-arched feet subjects.Healthy subjects performed a maximal running exercise. Surface EMGs of the TA, PL, and GM muscles were analysed during maximal dynamic efforts. Before and after the running bout, we measured the evoked compound muscle potential (M-wave) in TA, the maximal force into inversion (MIF), and the repartition of the plantar and barycentre surfaces with a computerised stationary platform.During maximal running exercise, the median frequency of the EMG spectra declined in TA while it remained stable in the PL and GM muscles. After the exercise, MIF decreased, and both the rearfoot plantar surface and the barycentre surface increased.We concluded that a maximal running bout elicits EMG signs of fatigue, though only in the TA muscle. It also elicits post-exercise changes in the foot position during stationary upright standing which indicates a foot eversion. These data solely concern a maximal running test and they can not be extrapolated to walking or running at a low speed.     

How the ankle joint angle alters the antagonist and agonist torques during maximal efforts in dorsi- and plantar flexion

The aim of this study was to assess, via an EMG bio-feedback method, the ankle joint angle effect on the agonist and antagonist torques in plantar- (PF) and dorsi-flexion (DF). The isometric PF and DF maximal voluntary contractions (MVCs) torques were measured simultaneously with surface EMG activity of triceps surae (TS) and tibialis anterior (TA) muscles in 12 young adults (mean age 27) at five different ankle joint angles. Our results showed that: (i) The coactivation level does not properly reflect the mechanical effect of the antagonist muscle, (ii) TS antagonist torque significantly altered the DF MVC-angle relationship, whereas TA antagonist torque did not influence this MVC-angle relationship in PF. The alteration of the MVC with angular position was due, in part, to the coactivation phenomenon in DF, but not in PF. Thenceforth, when investigating the torque at the ankle joint, it is necessary to take into account both agonist and antagonist torque modifications with ankle joint angle.     

Non-random fluctuations in power output during self-paced exercise

Objectives

To analyse the power output measured during a self‐paced 20‐km cycling time trial, during which power output was free to vary, in order to assess the level and characteristics of the variability in power output that occurred during the exercise bout.

Methods

Eleven well‐trained cyclists performed a 20‐km cycling time trial, during which power output was sampled every 200 m. Power spectrum analysis was performed on the power output data, and a fractal dimension was calculated for each trial using the Higuchi method.

Results

In all subjects, power output was maintained throughout the trial until the final kilometre, when it increased significantly, indicating the presence of a global pacing strategy. The power spectrum revealed the presence of 1/f‐like scaling of power output and multiple frequency peaks during each trial, with the values of the frequency peaks changing over the course of the trial. The fractal dimension (D‐score) was similar for all subjects over the 20‐km trial and ranged between 1.5 and 1.9.

Conclusions

The presence of an end spurt in all subjects, 1/f‐like scaling and multiple frequency peaks in the power output data indicate that the measured oscillations in power output during cycling exercise activity may not be system noise, but may rather be associated with system control mechanisms that are similar in different individuals.     

Optimal loading for maximal power output during lower-body resistance exercises

PURPOSE: The influence of various loads on power output in the jump squat (JS), squat (S), and power clean (PC) was examined to determine the load that maximizes power output in each lift. METHODS: Twelve Division I male athletes participated in four testing sessions. The first session involved performing one-repetition maximums (1RM) in the S and PC, followed by three randomized testing sessions involving either the JS, S, or PC. Peak force, velocity, and power were calculated across loads of 0, 12, 27, 42, 56, 71, and 85% of each subject's 1RM in the JS and S and at 10% intervals from 30 to 90% of each subject's 1RM in the PC. RESULTS: The optimal load for the JS was 0% of 1RM; absolute peak power was significantly lower from the optimal load at 42, 56, 71, and 85% of 1RM (P < or = 0.05), whereas peak power relative to body mass was significantly lower at 27% of 1RM in addition to 42, 56, 71, and 85% of 1RM. Peak power in the S was maximized at 56% of 1RM; however, power was not significantly different across the loading spectrum. The optimal load in the PC occurred at 80% of 1RM. Relative peak power at 80% of 1RM was significantly different from the 30 and 40% of 1RM. CONCLUSION: This investigation indicates that the optimal load for maximal power output occurs at various percentages of 1RM in the JS, S, and PC.     

Comparative anaerobic power of men and women

The purpose of this study was to determine the differences in anaerobic power (AnP) between men and women and the contribution of anthropometric variables in accounting for these differences. There were 18 female and 19 male subjects who performed the 30-s Wingate test where power outputs in watts are expressed as mean power (MP, the mean for 30 s) and peak power (PP, the highest 5-s interval). Thigh volume (TV), lean body mass (LBM) and body weight (BW) were used as anthropometric variables. Absolute AnP of men was 35% and 40% higher (p less than 0.001) than that of women for PP and MP, respectively. These differences decreased to 10% and 17% for PP and MP when expressed relative to kg LBM. Anthropometric variables explained less than 50% of the variation in PP and MP for men, while in women, TV accounted for 66% and 71% of the variation in PP and MP, respectively. When the data were combined, TV, BW, and LBM explained 48%, 74%, and 79% of variation in MP and 53%, 71%, and 76% in PP, respectively. These data show that gender differences in indices of AnP are similar to those reported for muscular strength and aerobic power. Additionally, a larger portion of the between gender variation compared to the within gender variation in AnP can be accounted for by anthropometric variables.     

Left ventricular dynamics during early recovery from maximal exercise in boys and men

A transient increase in left ventricular emptying has been reported in adults during the early recovery from submaximal upright exercise. PURPOSE: To investigate whether this "overshoot" occurs also after maximal exercise, and whether it is an age-related phenomenon. METHODS: Ten healthy young men (mean age: 22.5 +/- 1.5 yr) and 17 healthy prepubertal boys (11.5 +/- 0.8 yr) performed an upright cycle test until exhaustion. Respiratory gas exchange, heart rate, left ventricular dimensions (two-dimensional echocardiography method) as well as blood pressures (manual sphygmomanometry) were assessed and systemic vascular resistances were calculated at rest, during the final minute of the test, and during a 10-min recovery period. RESULTS: An improvement of cardiac emptying, characterized by a decrease in left ventricular end-systolic diameter, was observed in adults only. Moreover, during the first minute of recovery, a larger decrease in heart rate -21.8 +/- 7.6% and -13.7 +/- 6.3 beat.min, respectively, in children and adults, P < 0.01) and a larger increase in systemic vascular resistance (+24.1 +/- 18.2% and +6.4 +/- 12.6%, P < 0.05) were observed in the boys rather than in the adults. CONCLUSION: Our results suggest that a higher increase in cardiac afterload and a more prominent decrease in heart rate may be responsible in part for the absence of cardiac overshoot in children.     

Relationship between vertical jump and maximal power output of legs and arms: Effects of ethnicity and sport

The hypothesis that ethnicity and sport practice influence the relationship between maximal power in cycling (P_max) and countermovement jump (CMJ) has been studied by relating CMJ and P_max in two groups (volleyball players, VB, and physical education students, PES) including subjects with Caucasian (67 C) or West African (39 WA) origins. Maximal power of the arms (P_max Arms) was also measured. A two‐way analysis of variance (groups × ethnicity) showed significant effects of both factors upon CMJ, which was higher in WA and VB, P = 0.002 and P < 0.001, respectively. Within WA, CMJ was significantly higher in VB (0.732 ± 0.057 m) than in PES (0.661 ± 0.082 m), although there was no difference in P_max (14.7 ± 1.7 vs 14.7 ± 1.9 W/kg). CMJ was significantly higher in WA (0.69 ± 0.08 vs 0.65 ± 0.09 m in C, P = 0.002) without significant interethnic difference in P_max (14.7 ± 1.8 in WA, and 14.8 ± 1.9 W/kg in C). The CMJ–P_max relationships were different in C and WA (P = 0.003). Therefore, CMJ predicted from P_max would be underestimated in WA. The same difference was observed for the relationship between CMJ and P_max Arms. These results were confirmed by the comparison with previous P_max–CMJ relationship in the literature, collected in Caucasian and African subjects with the same protocols.     

Effect of 6 d of exercise training on responses to maximal and sub-maximal exercise in middle-aged men

Nine sedentary men (53 +/- 3 yr) were studied before and after 6 d of endurance exercise training to determine the effects on maximal oxygen uptake (VO2max), and on the heart rate, blood pressure, and metabolic responses to a standard bout of steady-state sub-maximal exercise. The subjects exercised approximately 1 h.d-1 at about 68% of VO2max. The 6-d protocol elicited no improvement in VO2max (2.50 +/- 0.14 before vs 2.58 +/- 0.15 l.min-1 after training). Heart rates were significantly lower by 5 to 8 b.min-1, systolic blood pressures were reduced by 16 to 19 mm Hg, and blood lactate concentrations were 25 to 35% less at the same exercise intensities (60, 70, and 80% of VO2max) after 6 d of exercise. Rate pressure product was about 15% lower at the same exercise intensity after 6 d of training (P less than 0.05). The respiratory exchange ratio during submaximal exercise was 0.02 to 0.04 units lower (P less than 0.05; P less than 0.01) after 6 d of exercise, indicating a shift in substrate utilization favoring fat oxidation. These findings suggest that short-term endurance training can induce heart rate, blood pressure, and metabolic adaptations to sub-maximal exercise before there is a significant increase in VO2max in sedentary, middle-aged men who are capable of vigorous exercise.