Effectiveness of antenatal care on weight of infants attending underfive clinic

The present study examined whether a six-week resistance training program would influence the critical power (CP) function, time to exhaustion (TE) at CP and/or peak oxygen uptake (VO2 peak). The CP function is believed to provide an index of endurance ability (CP given by the slope), and anaerobic work capacity (the y-intercept). Eight healthy, untrained males undertook lower-body resistance training (90 min/day, 3-4 times/wk) for six weeks; eight controls refrained from resistance or endurance training for the same period. Before and immediately following the training period, subjects completed three trials to determine their CP function, a test of VO2 peak, a one-repetition maximum (1-RM) leg press test and TE at their CP. Training significantly increased both 1-RM leg press (28.6%, P < 0.05) and the y-intercept (34.9%, P < 0.05) while no changes in CP, VO2 peak or TE (p > 0.05) were found. Changes in the y-intercept following resistance training were negatively correlated with changes in the CP (r = -0.94, p < 0.05, N = 8). The present data show that the y-intercept of the CP function is sensitive to, and modified by, six weeks of resistance training. Given that resistance training had no significant influence on CP, TE at CP or VO2 peak, the present study has also shown that six weeks of resistance training will not alter indices of endurance ability. The negative relationship between changes in the y-intercept and CP exposes a potential limitation of the linear CP function when evaluating changes in endurance ability following an intervention which significantly alters the y-intercept.     

Physical factors influencing the oviposition of Lutzomyia migonei (Diptera: Psychodidae) in laboratory conditions

Anthropometric and demographic characteristics are important determinants of exercise performance in healthy subjects, but their influence has not yet been studied in severe chronic heart failure, although peak oxygen uptake is frequently assessed in such patients for prognostic purposes. The aim of the present analysis was to examine the association between peak oxygen uptake and age, gender, and measures of body size in patients with severe chronic heart failure. We selected 122 (99 male) adult heart transplant candidates who were able to perform a bicycle ergometer test with respiratory gas analysis until voluntary fatigue. Peak oxygen uptake was higher in male than in female patients, both before and after adjustment for weight. In single regression analysis on the total study population, peak oxygen uptake was positively related to weight and to height, but inversely to age (r = 0.59 (P < 0.001), 0.42 (P < 0.001), and -0.33 (P < 0.001), respectively). Multiple stepwise regression analysis identified weight (P < 0.001), age (P < 0.001), and gender (P < 0.01) as independent determinants of peak oxygen uptake (cumulative R2 = 0.45). Similar to the findings in healthy subjects, peak oxygen uptake of patients with severe chronic heart failure is influenced by anthropometric and demographic characteristics.     

Muscle performance and enzymatic adaptations to sprint interval training

Our purpose was to examine the effects of sprint interval training on muscle glycolytic and oxidative enzyme activity and exercise performance. Twelve healthy men (22 +/- 2 yr of age) underwent intense interval training on a cycle ergometer for 7 wk. Training consisted of 30-s maximum sprint efforts (Wingate protocol) interspersed by 2-4 min of recovery, performed three times per week. The program began with four intervals with 4 min of recovery per session in week 1 and progressed to 10 intervals with 2.5 min of recovery per session by week 7. Peak power output and total work over repeated maximal 30-s efforts and maximal oxygen consumption (VO2 max) were measured before and after the training program. Needle biopsies were taken from vastus lateralis of nine subjects before and after the program and assayed for the maximal activity of hexokinase, total glycogen phosphorylase, phosphofructokinase, lactate dehydrogenase, citrate synthase, succinate dehydrogenase, malate dehydrogenase, and 3-hydroxyacyl-CoA dehydrogenase. The training program resulted in significant increases in peak power output, total work over 30 s, and VO2 max. Maximal enzyme activity of hexokinase, phosphofructokinase, citrate synthase, succinate dehydrogenase, and malate dehydrogenase was also significantly (P < 0.05) higher after training. It was concluded that relatively brief but intense sprint training can result in an increase in both glycolytic and oxidative enzyme activity, maximum short-term power output, and VO2 max.     

Contribution of phosphocreatine and aerobic metabolism to energy supply during repeated sprint exercise

This study examined the contribution of phosphocreatine (PCr) and aerobic metabolism during repeated bouts of sprint exercise. Eight male subjects performed two cycle ergometer sprints separated by 4 min of recovery during two separate main trials. Sprint 1 lasted 30 s during both main trials, whereas sprint 2 lasted either 10 or 30 s. Muscle biopsies were obtained at rest, immediately after the first 30-s sprint, after 3.8 min of recovery, and after the second 10- and 30-s sprints. At the end of sprint 1, PCr was 16.9 +/- 1.4% of the resting value, and muscle pH dropped to 6.69 +/- 0.02. After 3.8 min of recovery, muscle pH remained unchanged (6.80 +/- 0.03), but PCr was resynthesized to 78.7 +/- 3.3% of the resting value. PCr during sprint 2 was almost completely utilized in the first 10 s and remained unchanged thereafter. High correlations were found between the percentage of PCr resynthesis and the percentage recovery of power output and pedaling speed during the initial 10 s of sprint 2 (r = 0.84, P < 0.05 and r = 0.91, P < 0.01). The anaerobic ATP turnover, as calculated from changes in ATP, PCr, and lactate, was 235 +/- 9 mmol/kg dry muscle during the first sprint but was decreased to 139 +/- 7 mmol/kg dry muscle during the second 30-s sprint, mainly as a result of a approximately 45% decrease in glycolysis. Despite this approximately 41% reduction in anaerobic energy, the total work done during the second 30-s sprint was reduced by only approximately 18%. This mismatch between anaerobic energy release and power output during sprint 2 was partly compensated for by an increased contribution of aerobic metabolism, as calculated from the increase in oxygen uptake during sprint 2 (2.68 +/- 0.10 vs. 3.17 +/- 0.13 l/min; sprint 1 vs. sprint 2; P < 0.01). These data suggest that aerobic metabolism provides a significant part (approximately 49%) of the energy during the second sprint, whereas PCr availability is important for high power output during the initial 10 s.     

Optimal velocity for maximal power production in non-isokinetic cycling is related to muscle fibre type composition

To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W.kg-1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power. expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.     

Carbohydrate drinks delay fatigue during intermittent, high-intensity cycling in active men and women

The effects of ingesting carbohydrate drinks on fatigue during intermittent, high-intensity cycling in men and women were determined. Physically active but untrained women (n = 7) and men (n = 9) completed one practice trial and two experimental sessions separated by 1 week. Sessions consisted of repeated 1-min cycling bouts on a bicycle ergometer at 120-130% VO2max separated by 3 min rest until fatigue. Carbohydrate (CHO) or placebo (P) beverages (4 ml.kg body weight-1) were ingested immediately before exercise (18% CHO) and every 20 min during exercise (6% CHO). Plasma glucose and insulin were higher, RPE for the legs was lower, and time to fatigue was longer in CHO than P. Men's and women's responses were not different for any variable measured. These data suggest a beneficial role of CHO drinks on performance of intermittent, high-intensity exercise in men and women.     

Effect of acetazolamide on sodium and potassium absorption in the sheep forestomach

The purpose of the present study was to determine whether the linear relationship between CO2 output (VCO2) and pulmonary ventilation (VE) is altered during incremental cycling performed after exercise-induced metabolic acidosis. Ten untrained, female subjects performed two incremental cycling tests (15 W x min(-1) up to 165 W) on separate days. One incremental exercise test was conducted without prior exercise, whereas the other test was preceded by a 1-min bout of maximal cycling. The ventilatory equivalent for O2 (VE/VO2) was only elevated above control values at 15-60 W during incremental cycling performed after high-intensity exercise. In contrast, the ventilatory equivalent for CO2 (VE/VCO2) was significantly increased above control levels at nearly every work stage of incremental work (all except 165 W). Hyperventilation relative to VCO2 was confirmed by the significantly lower end-tidal CO2 tension (P(ET)CO2) obtained throughout the incremental cycling that was performed after high-intensity exercise (except at 165 W). VE and VCO2 were significantly correlated under both treatment conditions (r > 0.99; P < 0.001). Moreover, both the slope and y-intercept of the linear regression were found to be significantly elevated during the incremental cycling performed after high-intensity cycling compared to control conditions (P < 0.01). The increase in the slope of the VE-VCO2 relationship during incremental exercise performed under these conditions does not represent an uncoupling of VE from VCO2, but could be accounted for by the significantly lower P(ET)CO2 observed during exercise.     

Relationship between nitric oxide and prostaglandins in carrageenin pleurisy

PURPOSE: To examine the effects of repeated bouts of exercise on the blood lactate [HLa]-ratings of perceived exertion (RPE) relation. METHODS: Six moderately trained males were studied on two occasions: a sequential exercise bouts day (SEB: 1000 h, 1130 h, and 1300 h) and a delayed exercise bouts day (DEB: 1000 h, 1400 h, and 1800 h). Each of the three exercise bouts within a given condition were 30 min in duration at the power output (PO) associated with 70% of VO2peak on a cycle ergometer. A standardized meal was provided at 0600 h. VO2, PO, HR, and RER were recorded every min during exercise and blood [HLa] and RPE were measured every 5 min during exercise. RESULTS: A 2 x 3 analysis of variance with repeated measures revealed that blood [HLa] decreased significantly with each repeated exercise bout (X +/- SEM: bout 1: SEB = 3.5 (0.3), DEB = 3.8 (0.4); bout 2: SEB = 2.6 (0.3), DEB = 2.8 (0.3); bout 3: SEB = 2.0 (0.2), DEB = 2.1 (0.4); mM). No differences were observed in the blood [HLa] response to repeated bouts of exercise between SEB and DEB. RPE-peripheral (legs, RPE-L) was higher during bout 3 compared with bout 1 (P <0.05) (bout 1: SEB = 11.8 (0.8), DEB = 12.3 (0.2); bout 2: SEB = 12.3 (0.5), DEB = 13.3 (0.4); bout 3: SEB = 13.5 (0.8), DEB = 14.0 (0.7); RPE-central (chest and breathing, RPE-C) was not affected by repeated bouts of exercise, whereas RPE-Overall (RPE-O) was higher during bout 3 compared with bouts 1 and 2 (P < 0.05) (bout 1: SEB = 12.5 (0.2), DEB = 12.3 (0.4); bout 2: SEB = 12.8 (0.4), DEB = 12.7 (0.4); bout 3: SEB = 13.7 (0.7), DEB = 13.2 (0.3)). No interaction for RPE x condition was observed. HR increased with repeated bouts of exercise with HR during exercise bout 3 being higher than HR during exercise bout 1 (164 vs. 156 bpm, P < 0.05). There was also a strong trend for HR during exercise bout 3 to be higher than HR during exercise bout 2 (P < 0.06). A trend for a reduction in VO2 with repeated exercise was observed (P < 0.07), with the reduction apparently related to the SEB condition (P < 0.12 for VO2 x condition). PO and kcal.min-1 were not affected by repeated bouts of exercise. RER decreased significantly with each repeated bout of exercise (from RER = 0.96 to RER = 0.89, P < 0.05) with no difference observed between SEB and DEB. CONCLUSIONS: We conclude that the blood [HLa]-RPE relation is altered by repeated bouts of exercise and that this alteration does not appear to be affected by recovery time between exercise bouts (up to 3.5 h of recovery). These data suggest that, after the first exercise bout, RPE should not be used to produce a specific blood [HLa] on subsequent exercise bouts.     

Metabolic profile of high intensity intermittent exercises

To evaluate the magnitude of the stress on the aerobic and the anaerobic energy release systems during high intensity bicycle training, two commonly used protocols (IE1 and IE2) were examined during bicycling. IE1 consisted of one set of 6-7 bouts of 20-s exercise at an intensity of approximately 170% of the subject's maximal oxygen uptake (VO2max) with a 10-s rest between each bout. IE2 involved one set of 4-5 bouts of 30-s exercise at an intensity of approximately 200% of the subject's VO2max and a 2-min rest between each bout. The accumulated oxygen deficit of IE1 (69 +/- 8 ml.kg-1, mean +/- SD) was significantly higher than that of IE2 (46 +/- 12 ml.kg-1, N = 9, p < 0.01). The accumulated oxygen deficit of IE1 was not significantly different from the maximal accumulated oxygen deficit (the anaerobic capacity) of the subjects (69 +/- 10 ml.kg-1), whereas the corresponding value for IE2 was less than the subjects' maximal accumulated oxygen deficit (P < 0.01). The peak oxygen uptake during the last 10 s of the IE1 (55 +/- 6 ml.kg-1.min-1) was not significantly less than the VO2max of the subjects (57 +/- 6 ml.kg-1.min-1). The peak oxygen uptake during the last 10 s of IE2 (47 +/- 8 ml.kg-1.min-1) was lower than the VO2max (P < 0.01). In conclusion, this study showed that intermittent exercise defined by the IE1 protocol may tax both the anaerobic and aerobic energy releasing systems almost maximally.     

Cardiovascular responses to treadmill and cycle ergometer exercise in children and adults

This study was conducted to determine whether submaximal cardiovascular responses at a given rate of work are different in children and adults, and, if different, what mechanisms are involved and whether the differences are exercise-modality dependent. A total of 24 children, 7 to 9 yr old, and 24 adults, 18 to 26 yr old (12 males and 12 females in each group), participated in both submaximal and maximal exercise tests on both the treadmill and cycle ergometer. With the use of regression analysis, it was determined that cardiac output (Q) was significantly lower (P 相似文献   

Changes in gas exchange kinetics with training in patients with spinal cord injury

We examined the ability of patients with spinal cord injury to undergo adaptations to chronic exercise training (cycle ergometry) invoked by functional electrical stimulation (FES) of the legs. Nine such patients performed incremental and constant work rate exercise before and after exercise training. Exercise sessions averaged 2.1 +/- 0.4/wk, and consisted of 30 min/session of continuous FES recumbent cycling with increasing work rate as tolerated. Peak VO2 and peak work rate significantly improved with training. Peak VO2 was significantly correlated with peak heart rate both before and after training (r = 0.97 pre and 0.85 post, P < 0.01 for both). The time course of the VO2, VCO2 and VE responses to constant-load exercise (unloaded cycling) and in recovery (mean response time MRT) were very long prior to training, and became significantly faster following training. However, there was no correlation between percentage improvement in either MRTon or MRToff for VO2 and the percentage increase in peak VO2. Exercise tolerance in these patients with spinal cord injury appears to be a direct function of the ability to increase heart rate. Further, exercise training can elicit significant improvements in both exercise tolerance and in gas exchange kinetics, even when performed only twice per week. However, these improvements may be accomplished by different mechanisms.     

Expanded blood volumes contribute to the increased cardiovascular performance of endurance-trained older men

To determine whether expanded intravascular volumes contribute to the older athlete's higher exercise stroke volume and maximal oxygen consumption (VO2 max), we measured peak upright cycle ergometry cardiac volumes (99mTc ventriculography) and plasma (125I-labeled albumin) and red cell (NaCr51) volumes in 7 endurance-trained and 12 age-matched lean sedentary men. The athletes had approximately 40% higher VO2 max values than did the sedentary men and larger relative plasma (46 vs. 38 ml/kg), red cell (30 vs. 26 ml/kg), and total blood volumes (76 vs. 64 ml/kg) (all P < 0.05). Athletes had larger peak cycle ergometer exercise stroke volume indexes (75 vs. 57 ml/m2, P < 0.05) and 17% larger end-diastolic volume indexes. In the total group, VO2 max correlated with plasma, red cell, and total blood volumes (r = 0.61-0.70, P < 0.01). Peak exercise stroke volume was correlated directly with the blood volume variables (r = 0.59-0.67, P < 0.01). Multiple regression analyses showed that fat-free mass and plasma or total blood volume, but not red cell volume, were independent determinants of VO2 max and peak exercise stroke volume. Plasma and total blood volumes correlated with the stroke volume and end-diastolic volume changes from rest to peak exercise. This suggests that expanded intravascular volumes, particularly plasma and total blood volumes, contribute to the higher peak exercise left ventricular end-diastolic volume, stroke volume, and cardiac output and hence the higher VO2 max in master athletes by eliciting both chronic volume overload and increased utilization of the Frank-Starling effect during exercise.     

Exercise-induced anxiolysis: a test of the "time out" hypothesis in high anxious females

PURPOSE: One purpose was to test the hypothesis that anxiety reductions following exercise are caused by a "time out" from daily cares and worries, and the second purpose was to document the magnitude of the change in state anxiety after exercise in high trait anxious females. METHODS: Anxious women (N = 14) completed four randomly ordered conditions: Exercise Only, 20 min of cycling (40% of VO2peak) followed by 20 min of recovery; Study Only, 40 min of studying while sitting on a cycle ergometer; Exercise/Study, 20 min of cycling (40% of VO2peak) while studying followed by 20 min of studying while sitting on the cycle ergometer; and Control, sitting quietly on an ergometer for 40 min. RESULTS: State anxiety was assessed before and after each condition. State anxiety was reduced following the Exercise Only condition (mean raw change score +/- 95% confidence interval (CI) of 4.3 +/- 3.5; t = 2.3, P = 0.04, d = 0.52). The 95% CI did not include zero after adjusting for precondition anxiety scores (adjusted change +/- 95% CI of 3.3 +/- 3.2). CONCLUSIONS: Because the reduction in state anxiety following exercise was blocked in the Exercise/Study condition (t = -0.05, P = 0.97, d = 0.01) and the associated CIs included zero (unadjusted 0.1 +/- 3.4, adjusted 0.8 +/- 3.2), the findings support the hypothesis that anxiety reductions following exercise occur because exercise affords individuals a time out from daily worries.     

Metabolic efficiency during arm and leg exercise at the same relative intensities

This study was conducted to compare gross efficiency (GE), net efficiency (NE), work efficiency (WE), and delta efficiency (DE) between arm crank and cycle exercise at the same relative intensities. Eight college-aged males underwent two experimental trials presented in a randomized counterbalanced order. During each trial subjects performed three intermittent 7-min exercise bouts separated by 10-min rest intervals on an arm or semirecumbent leg ergometer. The power outputs for the three bouts of arm crank or cycle exercise corresponded to 50, 60, and 70% of the mode-specific VO2peak. GE, NE, and WE were determined as the ratio of Kcal.min-1 equivalent of power output to Kcal.min-1 of total energy expended, energy expended above rest and energy expended above unloaded exercise, respectively. DE was determined as the ratio of the increment of Kcal.min-1 of power output above the previous lower intensity to the increment of kcal.min-1 of total energy expended above the previous lower intensity. GE and NE did not differ between arm crank and cycle exercises. However, WE was lower (P < 0.05) during arm crank than cycle exercise at 50, 60, and 70% VO2peak. DE was also lower (P < 0.05) during arm crank than cycle exercise at delta 50-60 and at delta 60-70% VO2peak. It is concluded metabolic efficiency as determined by work and delta efficiency indices was lower during arm crank compared with cycle exercise at the same relative intensities. These findings add to the understanding of the difference in metabolic efficiency between upper and lower body exercise.     

Exercise duration and mood state: How much is enough to feel better?

The effects of exercise duration on mood state were examined. In a repeated-measures design, the Profile of Mood States inventory (D. M. McNair, M. Lorr, & L. F. Droppleman, 1971) was administered before and after 1 quiet resting trial and 3 exercise trials of 10, 20, and 30 min on a bicycle ergometer. Heart rate levels were controlled at 60% of the participant's estimated V02max level. An overall analysis of variance found improved levels of vigor with reduced levels of confusion, fatigue, and total negative mood. Planned analyses revealed that the improvements in vigor, fatigue, and total mood occurred after 10 min of exercise, with progressive improvements in confusion over 20 min and with no additional improvement over longer periods. These results complement current recommendations, which suggest that to experience positive fitness and health benefits, healthy adults should participate in a total of 30 min of moderate physical exercise daily, accumulated in short bouts throughout the day. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of physical training on exercise-induced hyperkalemia in chronic heart failure. Relation with ventilation and catecholamines

BACKGROUND: The exercise-induced rise in arterial potassium concentration ([K+]a) may contribute to exercise hyperpnea and could play a role in exertional fatigue. This study was designed to determine whether the exercise-induced rise in [K+]a is altered in patients with chronic heart failure (CHF) and whether physical training affects K+ homeostasis. METHODS AND RESULTS: We evaluated 10 subjects with CHF (ejection fraction, 23 +/- 3.9%) and 10 subjects with normal left ventricular function (NLVF) who had undergone previous coronary artery graft surgery (ejection fraction, 63 +/- 8.6%). Subjects performed an incremental cycle ergometer exercise test before and after a physical training or detraining program. Changes in [K+]a and ventilation (VE) during exercise were closely related in both groups. Subjects with CHF did less absolute work and had reduced maximal oxygen consumption (VO2max) compared with subjects with NLVF (P < .01). Exercise-induced rises in [K+]a, VE, norepinephrine, lactate, and heart rate were greater at matched absolute work rates in subjects with CHF than in subjects with NLVF (P < .01). However, when the rise in [K+]a was plotted against percentage of VO2max to match for relative submaximal effort, there were no differences between the two groups. Physical training resulted in reduced exercise-induced hyperkalemia at matched submaximal work rates in both groups (P < .01) despite no associated change in the concentration of arterial catecholamines. At maximal exercise when trained, peak increases in [K+]a were unaltered, but peak concentrations of catecholamines were raised (P < .05). The decrease in VE at submaximal work rates after training was not significant with this incremental exercise protocol, but both groups had an increased peak VE when trained (P < .01). CONCLUSIONS: Exercise-induced rises in [K+]a, catecholamines, and VE are greater at submaximal work rates in subjects with CHF than in subjects with NLVF. Physical training reduces the exercise-induced rise in [K+]a but does not significantly decrease VE during submaximal exercise with this incremental cycle ergometry protocol. The reduction in exercise-induced hyperkalemia after training is not the result of altered concentrations of arterial catecholamines. The pathophysiological significance of the increased exercise-induced hyperkalemia in CHF and the mechanisms of improved K+ homeostasis with training have yet to be established.     

Effects of exercise and estrogen therapy on lipid profiles of postmenopausal women

PURPOSE: We compared the effects of aerobic exercise training on lipid and lipoprotein levels in 18 postmenopausal women who were (N = 8) or were not (N = 10) receiving estrogen replacement therapy (ERT). METHODS: Each group was tested for lipids, diet recall and VO2max before and after a 12 wk exercise program, consisting of 30-50 min of an aerobic activity at 75-85% of VO2max, 3-4 sessions per week. RESULTS: Both groups increased VO2max by 8% and neither group changed their diet. The ERT group had higher levels of triglycerides and lower levels of low density lipoprotein (LDL-C) (P < 0.01) before training. There were no mean group changes in any of the lipid variables with training. However, individual changes in LDL-C and Total Cholesterol (TC) were strongly related to baseline weight in the nonestrogen group (r = 109.91, r = -0.82) but not in ERT (r = -0.30, r = -0.51). Subsequently, all subjects were redivided into two groups based on BMI (< or = 27 or > or = 27) regardless of ERT status. TC decreased significantly (P < 0.05) in the < or = 27 BMI group. CONCLUSIONS: Exercise training had little effect on the lipid profiles of the ERT and the nonestrogen groups, but body weight seems to be a modulating factor. Heavier subjects did not respond as favorably to 12 wk of exercise training as postmenopausal women with less body mass, regardless of the presence of exogenous estrogen.     

Muscle function during brief maximal exercise: accurate measurements on a friction-loaded cycle ergometer

A friction loaded cycle ergometer was instrumented with a strain gauge and an incremental encoder to obtain accurate measurement of human mechanical work output during the acceleration phase of a cycling sprint. This device was used to characterise muscle function in a group of 15 well-trained male subjects, asked to perform six short maximal sprints on the cycle against a constant friction load. Friction loads were successively set at 0.25, 0.35, 0.45, 0.55, 0.65 and 0.75 N.kg-1 body mass. Since the sprints were performed from a standing start, and since the acceleration was not restricted, the greatest attention was paid to the measurement of the acceleration balancing load due to flywheel inertia. Instantaneous pedalling velocity (v) and power output (P) were calculated each 5 ms and then averaged over each downstroke period so that each pedal downstroke provided a combination of v, force and P. Since an 8-s acceleration phase was composed of about 21 to 34 pedal downstrokes, this many v-P combinations were obtained amounting to 137-180 v-P combinations for all six friction loads in one individual, over the widest functional range of pedalling velocities (17-214 rpm). Thus, the individual's muscle function was characterised by the v-P relationships obtained during the six acceleration phases of the six sprints. An important finding of the present study was a strong linear relationship between individual optimal velocity (vopt) and individual maximal power output (Pmax) (n = 15, r = 0.95, P < 0.001) which has never been observed before. Since vopt has been demonstrated to be related to human fibre type composition both vopt, Pmax and their inter-relationship could represent a major feature in characterising muscle function in maximal unrestricted exercise. It is suggested that the present method is well suited to such analyses.     

Compartmental analysis of colonic transit reveals abnormalities in constipated patients with normal transit

Previous studies had concluded that the treadmill velocity-endurance time hyperbolic relationship for runs could be accuratly approached with a regression at condition that bouts of exercise duration were included between 2 and 12 min. This regression allows to calculate the critical speed (CS) defined as the slope of the regression of work (distance) on time to exhaustion, the anaerobic running capacity (ARC) being the intercept of this line (Monod & Scherrer, 1965). The purpose of this investigation was to give practical indication concerning the choice of the velocities in reference to the maximal aerobic speed (MAS i.e. the minimum speed which elicits VO2max). Subjects were fourteen elite male long-distance runners (27 +/- 3 years old; VO2max = 74.9 +/- 2.9 ml.kg-1.min-1, MAS = 22.4 +/- 0.8 km.h-1, CS = 19.3 +/- 0.7 km.h-1 and 86.2 +/- 1.5% MAS). tlim 100 values (321 +/- 83 s) were negatively correlated with MAS (r = -0.538, p < 0.05) and with CS (km.h-1) (r = -0.644, p < 0.01). tlim 90 (1015 +/- 266 s) was positively correlated with CS when expressed in % MAS (r = 0.645, p < 0.01) and not when expressed in km.h-1 (r = -0.095, P > 0.05). tlim 105 (176 +/- 40 s) only was correlated with ARC (r = 0.526, p < 0.05). These data demonstrate that running time to exhaustion at 100 and 105% of MAS in a homogeneous elite male long-distance runners group is inversely related to MAS. Moreover, tlim 90 is positively correlated with CS (%MAS) but neither with tlim 100 and 105 nor with maximal aerobic speed. So from a practical point of view, the velocities chosen to determine the critical speed, would be closed to the maximal aerobic speed (time to exhaustion around 6 min), taking into account that the tlim 105 is correlated with the anaerobic capacity, whereas tlim 90 is correlated with the critical speed.     

Caffeine, performance, and metabolism during repeated Wingate exercise tests

Investigations examining the ergogenic and metabolic influence of caffeine during short-term high-intensity exercise are few in number and have produced inconsistent results. This study examined the effects of caffeine on repeated bouts of high-intensity exercise in recreationally active men. Subjects (n = 9) completed four 30-s Wingate (WG) sprints with 4 min of rest between each exercise bout on two separate occasions. One hour before exercise, either placebo (P1; dextrose) or caffeine (Caf; 6 mg/kg) capsules were ingested. Caf ingestion did not have any effect on power output (peak or average) in the first two WG tests and had a negative effect in the latter two exercise bouts. Plasma epinephrine concentration was significantly increased 60 min after Caf ingestion compared with P1; however, this treatment effect disappeared once exercise began. Caf ingestion had no significant effect on blood lactate, O2 consumption, or aerobic contribution at any time during the protocol. After the second Wingate test, plasma NH3 concentration increased significantly from the previous WG test and was significantly higher in the Caf trial compared with P1. These data demonstrate no ergogenic effect of caffeine on power output during repeated bouts of short-term, intense exercise. Furthermore, there was no indication of increased anaerobic metabolism after Caf ingestion with the exception of an increase in NH3 concentration.