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1.
Abstract

Respiratory muscle fatigue has been reported following short bouts of high-intensity exercise, and prolonged, moderate-intensity exercise, as evidenced by decrements in inspiratory and expiratory mouth pressures. However, links to functionally relevant outcomes such as breathing effort have been lacking. The present study examined dyspnoea and leg fatigue during a treadmill marathon in nine experienced runners. Maximal inspiratory and expiratory pressure, peak inspiratory and expiratory flow, forced vital capacity, and forced expiratory volume in one second were assessed before, immediately after, and four and 24 hours after a marathon. During the run, leg effort was rated higher than respiratory effort from 18 through 42 km (P < 0.05). Immediately after the marathon, there were significant decreases in maximal inspiratory pressure and peak inspiratory flow (from 118 ± 20 cm H2O and 6.3 ± 1.4 litres · s?1 to 100 ± 22 cm H2O and 4.9 ± 1.5 litres · s?1 respectively; P < 0.01), while expiratory function remained unchanged. Leg maximum voluntary contraction force was significantly lower post-marathon. Breathing effort correlated significantly with leg fatigue (r = 0.69), but not inspiratory muscle fatigue. Our results confirm that prolonged moderate-intensity exercise induces inspiratory muscle fatigue. Furthermore, they suggest that the relative intensity of inspiratory muscle work during exercise makes some contribution to leg fatigue.  相似文献   

2.
Inspiratory muscle fatigue may occur in as little as 6 min during high-intensity spontaneously breathing exercise. The aims of this study were to determine whether inspiratory muscle fatigue occurs during swimming exercise and whether inspiratory muscle strength differs between the supine and standing body positions. Seven competitive swimmers were recruited to perform a single 200 m front-crawl swim, corresponding to 90-95% of race pace. Inspiratory muscle strength was measured at residual volume using a hand-held mouth pressure meter that measured maximal inspiratory pressure in the upright and supine positions. At baseline, maximal inspiratory pressure in the supine position was significantly lower than maximal inspiratory pressure in the upright position (112 +/- 20.4 and 133 +/- 16.7 cmH2O, respectively; P < or = 0.01). Post-exercise maximal inspiratory pressure in the supine position (80 +/- 15.7 cmH2O) was significantly lower than baseline maximal inspiratory pressure in the supine position (P < or = 0.01). The results indicate that a single 200 m front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue in less than 2.7 min. Furthermore, although diaphragm muscle length is optimized when supine, our results indicate that the force output of the diaphragm and inspiratory accessory muscles is greater when upright than when supine.  相似文献   

3.
The effect of inspiratory muscle training for 10 min twice a day for 27.5 days was evaluated in 20 human subjects, of whom 10 formed a training group and 10 a sham training group. The maximal oxygen uptake (VO2 max), maximal ventilation, breathing frequency during maximal exercise and the distance run in 12 min on a track were determined in addition to resting peak expiratory flow, forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), with alveolar oxygen tension (pAO2) during maximal exercise being calculated. Inspiratory muscle training increased maximal inspiratory pressure from 93 (range 38-118) to 110 (65-165) mmHg in the training group (P less than 0.0005), but did not affect VO2 max, ventilation during maximal exercise, peak expiratory flow, FEV1 or FVC. However, breathing frequency during maximal exercise decreased slightly from 56 (44-87) to 53 (38-84) breaths min-1 (P less than 0.05) in the training group only; but the calculated pAO2 did not increase from the pre-training value of 126 (116-132) mmHg. The maximal distance run during 12 min increased similarly in the training and sham training groups by 8% (3-12%) and 6% (2-12%), respectively (P less than 0.01). The results of this study show that inspiratory muscle training resulting in a 32% (0-85%) increase in maximal inspiratory pressure does not change FEV1, FVC, peak expiratory flow, VO2 max or work capacity.  相似文献   

4.
We evaluated the effects of specific inspiratory muscle training on simulated time-trial performance in trained cyclists. Using a double-blind, placebo-controlled design, 16 male cyclists (VO2max = 64 +/- 2 ml x kg(-1) x min(-1); mean +/- s(x)) were assigned at random to either an experimental (pressure-threshold inspiratory muscle training) or sham-training control (placebo) group. Pulmonary function, maximum dynamic inspiratory muscle function and the physiological and perceptual responses to maximal incremental cycling were assessed. Simulated time-trial performance (20 and 40 km) was quantified as the time to complete pre-set amounts of work. Pulmonary function was unchanged after the intervention, but dynamic inspiratory muscle function improved in the inspiratory muscle training group (P < or = 0.05). After the intervention, the inspiratory muscle training group experienced a reduction in the perception of respiratory and peripheral effort (Borg CR10: 16 +/- 4% and 18 +/- 4% respectively; compared with placebo, P < or = 0.01) and completed the simulated 20 and 40 km time-trials faster than the placebo group [66 +/- 30 and 115 +/- 38 s (3.8 +/- 1.7% and 4.6 +/- 1.9%) faster respectively; P = 0.025 and 0.009]. These results support evidence that specific inspiratory muscle training attenuates the perceptual response to maximal incremental exercise. Furthermore, they provide evidence of performance enhancements in competitive cyclists after inspiratory muscle training.  相似文献   

5.
Pulmonary diffusing capacity (DICO), together with spirometric variables, arterial oxygen tension (paO2) and cardiac output were determined before and at intervals after maximal arm cranking, treadmill running and ergometer rowing. Independent of the type of exercise, D1CO increased immediately post-exercise from a median 13.6 (range 7.3-16.3) to 15.1 (9.3-19.6) mmol min-1 kPa-1 (P < 0.01). However, it decreased to 11.6 (6.9-15.5) mmol min-1 kPa-1 (P < 0.01) after 24 h with cardiac output and paO2 at resting values, and D1CO normalized after 20 h. Thoracic electrical impedance at 2.5 and 100 kHz increased slightly post-exercise, indicating a decrease in thoracic fluid balance, and there were no echocardiographic signs of left ventricular failure at the time of the decrease in D1CO. Also, active muscle (limb) circumference and volume, and an increase in haematocrit from 43.8 (38.0-47.0) to 47.1 (42.7-49.8) (P < 0.01), had normalized at the time of the decrease in D1CO. Vital capacity, forced vital capacity, forced expiratory volume in 1 s, peak and peak mid-expiratory flows did not change. However, total lung capacity increased from 6.8 (5.0-7.6) to 7.0 (5.1-7.8) litres (P < 0.05) immediately after exercise and remained elevated at 6.9 (5.1-8.7) litres (P < 0.05) when a decrease in D1CO was noted. The results demonstrate that independent of the type of maximal exercise, an approximate 15% reduction in D1CO takes place 2-3 h post-exercise, which normalizes during the following day of recovery.  相似文献   

6.
The aim of this study was to examine the acute effects of prolonged static stretching (SS) on running economy. Ten male runners (VO2(peak) 60.1 +/- 7.3 ml x kg(-1) x min(-1)) performed 10 min of treadmill running at 70% VO2(peak) before and after SS and no stretching interventions. For the stretching intervention, each leg was stretched unilaterally for 40 s with each of eight different exercises and this was repeated three times. Respiratory gas exchange was measured throughout the running exercise with an automated gas analysis system. On a separate day, participants were tested for sit and reach range of motion, isometric strength and countermovement jump height before and after SS. The oxygen uptake, minute ventilation, energy expenditure, respiratory exchange ratio and heart rate responses to running were unaffected by the stretching intervention. This was despite a significant effect of SS on neuromuscular function (sit and reach range of motion, +2.7 +/- 0.6 cm; isometric strength, -5.6% +/- 3.4%; countermovement jump height -5.5% +/- 3.4%; all P < 0.05). The results suggest that prolonged SS does not influence running economy despite changes in neuromuscular function.  相似文献   

7.
A well-documented observation after eccentric exercise is a reduction in maximal voluntary force. However, little is known about the ability to maintain maximal isometric force or generate and maintain dynamic peak power. These aspects of muscle function were studied in seven participants (5 males, 2 females). Knee extensor isometric strength and rate of fatigue were assessed by a sustained 60 s maximal voluntary contraction at 80 degrees and 40 degrees knee flexion, corresponding to an optimal and a shortened muscle length, respectively. Dynamic peak power and rate of fatigue were assessed during a 30 s Wingate cycle test. Plasma creatine kinase was measured from a fingertip blood sample. These variables were measured before, 1 h after and 1, 2, 3 and 7 days after 100 repetitions of the eccentric phase of the barbell squat exercise (10 sets x 10 reps at 80% concentric one-repetition maximum). Eccentric exercise resulted in elevations in creatine kinase activity above baseline (274+/-109 U x l(-1); mean +/- s(x)) after 1 h (506+/-116 U x l(-1), P < 0.05) and 1 day (808+/-117 U x l(-1), P < 0.05). Isometric strength was reduced (P < 0.05) for 7 days (35% at 1 h, 5% at day 7) and the rate of fatigue was lower (P < 0.05) for 3 days at 80 degrees and for 1 day at 40 degrees. Wingate peak power was reduced to a lesser extent (P < 0.05) than isometric strength at 1 h (13%) and, although the time course of recovery was equal, the two variables differed in their pattern of recovery. Eccentrically exercised muscle was characterized by an inability to generate high force and power, but an improved ability to maintain force and power. Such functional outcomes are consistent with the proposition that type II fibres are selectively recruited or damaged during eccentric exercise.  相似文献   

8.
Inspiratory muscle fatigue may occur in as little as 6 min during high-intensity spontaneously breathing exercise. The aims of this study were to determine whether inspiratory muscle fatigue occurs during swimming exercise and whether inspiratory muscle strength differs between the supine and standing body positions. Seven competitive swimmers were recruited to perform a single 200 m front-crawl swim, corresponding to 90-95% of race pace. Inspiratory muscle strength was measured at residual volume using a hand-held mouth pressure meter that measured maximal inspiratory pressure in the upright and supine positions. At baseline, maximal inspiratory pressure in the supine position was significantly lower than maximal inspiratory pressure in the upright position (112±20.4 and 133±16.7 cmH2O, respectively; P?0.01). Post-exercise maximal inspiratory pressure in the supine position (80±15.7 cmH2O) was significantly lower than baseline maximal inspiratory pressure in the supine position (P?0.01). The results indicate that a single 200 m front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue in less than 2.7 min. Furthermore, although diaphragm muscle length is optimized when supine, our results indicate that the force output of the diaphragm and inspiratory accessory muscles is greater when upright than when supine.  相似文献   

9.
Carbohydrate ingestion before and during endurance exercise delays the onset of fatigue (reduced power output). Therefore, endurance athletes are recommended to ingest diets high in carbohydrate (70% of total energy) during competition and training. However, increasing the availability of plasma free fatty acids has been shown to slow the rate of muscle and liver glycogen depletion by promoting the utilization of fat. Ingested fat, in the form of long-chain (C 16-22 ) triacylglycerols, is largely unavailable during acute exercise, but medium-chain (C 8-10 ) triacylglycerols are rapidly absorbed and oxidized. We have shown that the ingestion of medium-chain triacylglycerols in combination with carbohydrate spares muscle carbohydrate stores during 2 h of submaximal (< 70% VO 2 peak) cycling exercise, and improves 40 km time-trial performance. These data suggest that by combining carbohydrate and medium-chain triacylglycerols as a pre-exercise supplement and as a nutritional supplement during exercise, fat oxidation will be enhanced, and endogenous carbohydrate will be spared. We have also examined the chronic metabolic adaptations and effects on substrate utilization and endurance performance when athletes ingest a diet that is high in fat (> 70% by energy). Dietary fat adaptation for a period of at least 2-4 weeks has resulted in a nearly two-fold increase in resistance to fatigue during prolonged, low- to moderate-intensity cycling (< 70% VO 2 peak). Moreover, preliminary studies suggest that mean cycling 20 km time-trial performance following prolonged submaximal exercise is enhanced by 80 s after dietary fat adaptation and 3 days of carbohydrate loading. Thus the relative contribution of fuel substrate to prolonged endurance activity may be modified by training, pre-exercise feeding, habitual diet, or by artificially altering the hormonal milieu or the availability of circulating fuels. The time course and dose-response of these effects on maximizing the oxidative contribution of fat for exercise metabolism and in exercise performance have not been systematically studied during moderate- to high-intensity exercise in humans.  相似文献   

10.
The respiratory time and flow profile at volitional exercise termination   总被引：1，自引：0，他引：1  
In this study, we examine the effect of exercise on the time and flow characteristics of the respiratory cycle profile at the point of volitional exercise termination. Eight males (mean age 29 years, s = 10; body mass 74 kg, s = 7; height 1.75 m, s = 0.04) undertook a cycle test to volitional exhaustion on a cycle ergometer, which allowed peak oxygen uptake (VO(2peak)) to be measured (mean 51 ml x kg(-1) x min(-1), s = 7). At a later date, two sub-maximal tests to volitional exhaustion were completed in a random order at 76% (s = 6) and 86% VO(2peak) (s = 7). As expected, the magnitude of the respiratory flow and time characteristics varied with the three exercise intensities, as did the point of exercise termination and terminal ventilation rates, which varied from 7 to 27 min and 112 to 132 litres x min(-1) respectively. More importantly, however, at exercise termination some of the characteristics were similar, particularly the breathing frequency (at termination 49 breaths x min(-1)), the ratio between inspiration and total breath time (0.5), and the later occurrence of peak inspiratory flow (0.24-0.48 s). The coincident unity of these time and flow profile characteristics at exercise termination illustrates how the integration of timing and flow during breathing influence exercise capacity in non-elite athletes.  相似文献   

11.
Abstract

Pulmonary diffusing capacity (Dlco), together with spirometric variables, arterial oxygen tension (paO2) and cardiac output were determined before and at intervals after maximal arm cranking, treadmill running and erogmeter rowing. Independent of the type of exercise, Dlco increased immediately post‐exercise from a median 13.6 (range 7.3–16.3) to 15.1 (9.3–19.6) mmol min‐1 kPa‐1 (P <0.01). However, it decreased to 11.6 (6.9–15.5) mmol min‐1 kPa‐1 (P <0.01) after 24 h with cardiac output and paO2 at resting values, and Dlco normalized after 20 h. Thoracic electrical impedance at 2.5 and 100 kHz increased slightly post‐exercise, indicating a decrease in thoracic fluid balance, and there were no echocardiographic signs of left ventricular failure at the time of the decrease in Dlco. Also, active muscle (limb) circumference and volume, and an increase in haematocrit from 43.8 (38.0–47.0) to 47.1 (42.7–49.8) (P <0.01), had normalized at the time of the decrease in Dlco. Vital capacity, forced vital capacity, forced expiratory volume in 1 s, peak and peak mid‐expiratory flows did not change. However, total lung capacity increased from 6.8 (5.0–7.6) to 7.0 (5.1–7.8) litres (P <0.05) immediately after exercise and remained elevated at 6.9 (5.1–8.7) litres (P <0.05) when a decrease in Dlco was noted. The results demonstrate that independent of the type of maximal exercise, an approximate 15% reduction in Dlco takes place 2–3 h post‐exercise, which normalizes during the following day of recovery.  相似文献   

12.
Fatigue represents a reduction in the capability of muscle to generate force. The aim of the present study was to establish the effects of exercise that simulates the work rate of competitive soccer players on the strength of the knee extensors and knee flexors. Thirteen amateur soccer players (age 23.3+/-3.9 years, height 1.78+/-0.05 m, body mass 74.8+/-3.6 kg; mean+/-s) were tested during the 2000-2001 soccer season. Muscle strength of the quadriceps and hamstrings was measured on an isokinetic dynamometer. A 90 min soccer-specific intermittent exercise protocol, incorporating a 15 min half-time intermission, was developed to provide fatiguing exercise corresponding in work rate to a game of soccer. The exercise protocol, performed on a programmable motorized treadmill, consisted of the different intensities observed during soccer match-play (e.g. walking, jogging, running, sprinting). Muscle strength was assessed before exercise, at half-time and immediately after exercise. A repeated-measures analysis of variance showed significant reductions (P < 0.001) in peak torque for both the quadriceps and hamstrings at all angular velocities (concentric: 1.05, 2.09, 5.23 rad x s(-1); eccentric: 2.09 rad x s(-1)). The peak torque of the knee extensors (KE) and knee flexors (KF) was greater before exercise [KE: 232+/-37, 182+/-34, 129+/-27, 219+/-41 N x m at 1.05, 2.09 and 5.23 rad x s(-1) (concentric) and 2.09 rad x s(-1) (eccentric), respectively; KF: 126+/-20, 112+/-19, 101+/-16, 137+/-23 N x m] than at half-time (KE: 209+/-45, 177+/-35, 125+/-36, 214+/-43 N x m; KF: 114+/-31, 102+/-20, 92+/-15, 125+/-25 N x m) and greater at half-time than after exercise (KE: 196+/-43, 167+/-35, 118+/-24, 204+/-43 N x m; KF: 104+/-25, 95+/-21, 87+/-13, 114+/-27 N x m). For the hamstrings:quadriceps ratio, significant changes were found (P < 0.05) for both legs, the ratio being greater before than after exercise. For fast:slow speed and left:right ratios, no significant changes were found. We conclude that there is a progressive reduction in muscle strength that applies across a range of functional characteristics during exercise that mimics the work rate in soccer.  相似文献   

13.
Abstract

Congestive heart failure (CHF) patients experience reduced muscle fatigue resistance and exercise capacity. The aim of this study was to assess whether skeletal muscle in CHF patients has a normal training response compared to healthy subjects. We compared the effect of one-legged knee extensor (1-KE) endurance training in CHF patients (n=10), patients with coronary artery disease (CAD, n=9) and healthy subjects (n=13). The training response was evaluated by comparing trained leg and control leg after the training period. The fall in peak torque during 75 maximal 1-KE isokinetic contractions revealed that CHF patients were less fatigue resistant than healthy subjects in the control leg, but not in the trained leg. Peak power and peak oxygen uptake during dynamic 1-KE exercise was ~10–16% higher in trained leg than control leg. This training response was not significant different between groups. Muscle biopsies of vastus lateralis showed that fibre type composition was not different between trained leg and control leg. Capillary density was 6.5% higher in trained leg than control leg when all groups were pooled. In conclusion, the more fatigable skeletal muscle of CHF patients responds equally to endurance training compared to skeletal muscle of CAD patients and healthy subjects.  相似文献   

14.
Purpose: Skeletal muscle damage occurs following high-intensity or unaccustomed exercise; however, it is difficult to monitor damage to the respiratory muscles, particularly in humans. The aim of this study was to use clinical measures to investigate the presence of skeletal muscle damage in the inspiratory muscles. Methods: Ten healthy subjects underwent 60 minutes of voluntary inspiratory threshold loading (ITL) at 70% of maximal inspiratory pressure. Maximal inspiratory and expiratory mouth pressures, delayed onset muscle soreness on a visual analogue scale and plasma creatine kinase were measured prior to ITL, and at repeated time points after ITL (4, 24 and 48 hours post-ITL). Results: Delayed onset muscle soreness was present in all subjects 24 hours following ITL (intensity = 22 ± 6 mm; significantly higher than baseline p = 0.02). Muscle soreness was reported primarily in the anterior neck region, and was correlated to the amount of work done by the inspiratory muscles during ITL (r = 0.72, p = 0.02). However, no significant change was observed in maximal inspiratory or expiratory pressures or creatine kinase. Conclusions: These findings suggest that an intense bout of ITL results in muscle soreness primarily in the accessory muscles of inspiration, however, may be insufficient to cause significant muscle damage in healthy adults.Key Words: delayed onset muscle soreness, respiratory muscles, skeletal muscle damage  相似文献   

15.
This study was performed to determine the influence of single and repetitive exercise on nitric oxide (NO) concentration in the lung. Exhaled NO concentration (FE(NO)) was measured during a constant-flow exhalation manoeuvre (170 ml x s(-1), against a 10 cmH2O resistance) in healthy individuals (a) during and after a 100-min square-wave exercise of between 25 and 60% of maximal power output (n = 18) and (b) before and after five successive prolonged exercises (90-120 min, 75-85% of maximal heart rate) separated by 48 or 24 h (n = 8). The FE(NO0.170) was decreased during and after the 100-min exercise test (mean +/- s(x): 58.5 +/- 3.7% and 76.7 +/- 5.2% of resting value at 90 min of exercise and 15 min post-exercise, respectively; P < 0.05). The five successive exercise sessions induced a similar post-exercise FE(NO0.170) decrement (73.1 +/- 2.9% of resting value 15 min post-exercise), while basal FE(NO0.170) values were not different between the five sessions (P > 0.05). These results suggest that prolonged exercise induces a reduction in NO concentration within the lung that lasts for several minutes after the end of exercise. However, repetitive exercises (at least every 24 h) allow complete NO recovery from one session to another. The implication of such a decrease in NO availability within the lung remains to be clarified.  相似文献   

16.
Ad libitum fluid intakes and thermoregulatory responses were compared in eight female marathon runners during a 30 km treadmill run at individual best marathon race pace (range = 2.45-4.07 m x s(-1)) under three wet bulb globe temperature conditions (25 degrees C, 17 degrees C and 12 degrees C, corresponding to hot, moderate and cool conditions, respectively). Rectal temperature, mean skin temperature and heart rate were recorded at 10 min intervals and expired air was collected every 5 km during exercise. Simulated water stations were also provided at 5 km intervals with voluntary fluid intake being recorded. Blood was drawn before and after exercise for the determination of plasma volume changes and osmolarity. Ad libitum fluid intakes in the hot trial (0.70+/-0.31 l x h(-1); mean+/-s) were greater (P< 0.05) than in the cool (0.47+/-0.13 l x h(-1)) but not the moderate (0.54+/-0.26 l x h(-1)) trial. Each volume replaced 63%, 68% and 73% of total sweat losses in each condition, respectively, and kept dehydration below approximately 3% of body mass. After the initial 30 min of exercise, rectal temperature was maintained well below 39 degrees C for > 2 h of continuous running. The results demonstrate that the thermoregulatory responses of female distance runners to exercise in variable, but compensable, weather conditions is well maintained when ad libitum fluid intakes replace approximately 60-70% of sweat losses.  相似文献   

17.
We evaluated the effects of specific inspiratory muscle training on simulated time-trial performance in trained cyclists. Using a double-blind, placebo-controlled design, 16 male cyclists (VO 2max = 64 - 2 ml·kg -1 ·min -1 ; mean - sx ¥ ) were assigned at random to either an experimental (pressure-threshold inspiratory muscle training) or sham-training control (placebo) group. Pulmonary function, maximum dynamic inspiratory muscle function and the physiological and perceptual responses to maximal incremental cycling were assessed. Simulated time-trial performance (20 and 40 km) was quantified as the time to complete pre-set amounts of work. Pulmonary function was unchanged after the intervention, but dynamic inspiratory muscle function improved in the inspiratory muscle training group ( P h 0.05). After the intervention, the inspiratory muscle training group experienced a reduction in the perception of respiratory and peripheral effort (Borg CR10: 16 - 4% and 18 - 4% respectively; compared with placebo, P h 0.01) and completed the simulated 20 and 40 km time-trials faster than the placebo group [66 - 30 and 115 - 38 s (3.8 - 1.7% and 4.6 - 1.9%) faster respectively; P = 0.025 and 0.009]. These results support evidence that specific inspiratory muscle training attenuates the perceptual response to maximal incremental exercise. Furthermore, they provide evidence of performance enhancements in competitive cyclists after inspiratory muscle training.  相似文献   

18.
Nine participants performed two bouts of a step exercise, during which the quadriceps muscle of one leg acted eccentrically. Before and after the exercise, isokinetic torque was measured over a range of knee angles to determine the optimum angle for torque. Immediately after the first bout of exercise, the quadriceps showed a significant (P < 0.05) shift of 15.6 +/- 1.4 degrees (mean +/-sx) of its optimum angle in the direction of longer lengths, suggesting the presence of damage. A drop in peak torque, together with delayed soreness and swelling, confirmed that damage to muscle fibres had occurred. After the second bout of exercise, 8 days later, the shift in optimum angle was 10.4 +/- 1.0 degrees, which was significantly less than after the first bout (P < 0.05). Other indicators of damage were also reduced. In addition, the muscle exhibited a sustained shift in optimum angle (3.4 +/- 0.9 degrees), suggesting that some adaptation had taken place after the first bout of exercise. We conclude that muscles like the quadriceps can show evidence of damage after a specific programme of eccentric exercise, followed by an adaptation response. This is despite the fact that the quadriceps routinely undergoes eccentric contractions in everyday activities.  相似文献   

19.
The jump performance of ten youth soccer players (mean age 15.8 years, s= 0.4) was assessed before and after 42 min of soccer-specific exercise performed on a non-motorized treadmill. A squat, countermovement, and drop jump were performed on a force platform and simultaneously surface EMG activity of four lower limb muscles was collected. Jump height deteriorated across all conditions with mean reductions of - 1.4 cm (s = 1.6; P < 0.05), - 3.0 cm (s = 2.9; P < 0.05), and -2.3 cm (s = 1.7; P < 0.01) in the squat, countermovement, and drop jump respectively. The impact force in the drop jump was the only force variable to show a significant change with fatigue (P < 0.05). Following the prolonged exercise, reductions in total muscle activity were non-significant for the squat jump, approached significance for the counter-ovement jump (P = 0.07), and achieved significance for the drop jump (P < 0.05). The results showed that completing soccer-specific exercise reduced performance in all jump tasks. Reductions in muscle activity were greatest for the drop jump, suggesting an influence of muscle stretch and loading on reduced muscle activity when fatigued.  相似文献   

20.
A high ambient temperature reduces the capacity to perform prolonged exercise. Total carbohydrate oxidation is less, and thus glycogen depletion is not limiting. Fluid ingestion in the heat should, therefore, focus on maintenance of hydration status rather than on substrate provision. Six healthy males cycled to exhaustion at 60% of maximum oxygen consumption (VO2max) with no drink, ingestion of a 15% carbohydrate-electrolyte drink (1.45+/-0.29 litres) or ingestion of a 2% carbohydrate-electrolyte drink (3.12+/-0.47 litres). The ambient temperature was 30.2+/-0.6 degrees C (mean +/- s), with a relative humidity of 71+/-1% and an air speed of approximately 0.7 m x s(-1) on all trials. Weighted mean skin temperature, rectal temperature and heart rate were recorded and venous samples drawn for determination of plasma volume changes, blood metabolites, serum electrolytes and osmolality. Expired gas was collected to estimate rates of fuel oxidation. Exercise capacity was significantly (P < 0.05) different in all trials. The median (range) time to exhaustion was 70.9 min (39.4-97.4 min) in the no-drink trial, 84.0 min (62.7-145 min) in the 15% carbohydrate trial and 118 min (82.6-168 min) in the 2% carbohydrate trial. The 15% carbohydrate drink resulted in significantly (P < 0.05) elevated blood glucose and total carbohydrate oxidation compared with the no-drink trial. The 2% carbohydrate drink restored plasma volume to pre-exercise values by the end of exercise. No differences were observed in other thermoregulatory or cardiorespiratory responses between trials. These results suggest that fluid replacement with a large volume of a dilute carbohydrate drink is beneficial during exercise in the heat, but the precise mechanisms for the improved exercise capacity are unclear.  相似文献   

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