Effects of age and mode of exercise on power output profiles during repeated sprints

The aim of this study was to compare power output profiles during repeated cycling and running sprints in children and adults. On two separate visits, 12 boys [11.7 (0.5) years] and 13 men [22.1 (2.9) years] performed ten consecutive 10-s sprints interspersed with 15-s recovery intervals on a non-motorised treadmill and cycle ergometer. Peak (PPO) and mean (MPO) power outputs were measured during each sprint. Capillary fingertip blood samples were drawn at rest and 3 min after the final sprint to measure lactate accumulation ([La]). PPO and MPO decreased significantly more in adults compared to children over the ten sprints irrespective of the mode of exercise (P<0.001). PPO decreased by a similar amount during running and cycling in children (–17.7 versus –14.3%, P>0.05, respectively) and adults (–43.3 versus –40.0%, P>0.05, respectively). In contrast, MPO decreased significantly more during running compared to cycling both in children (–28.9 versus –18.7%, P<0.05) and adults (–47.0 versus –36.7%, P<0.05). The greater decrease in MPO during running compared to cycling was accompanied in children by significantly higher [La] values (7.7 versus 4.1 mmol l^–1, P<0.001). In adults, blood lactate accumulation tended to be higher during running than cycling (12.7 versus 10.8 mmol l^–1, P=0.06). To conclude, adults displayed a greater decrement in power output compared to children over the ten repeated running and cycling sprints. Furthermore, children and adults experienced greater fatigue during running compared to cycling. This last result may be attributed to additional muscle recruitment during sprint running.     

Effects of hyperthermia on the metabolic responses to repeated high-intensity exercise

In this study, we investigated the metabolic and performance responses to hyperthermia during high-intensity exercise. Seven males completed two 30-s cycle sprints (SpI and SpII) at an environmental temperature of 20.6 (0.3) °C [mean (SD)] with 4 min recovery between sprints. A hot or control treatment preceded the sprint exercise. For the hot trial, subjects were immersed up to the neck in hot water [43°C for 16.0 (3.2) min] prior to entering an environmental chamber [44.2 (0.8)°C for 30.7 (7.1) min]. For the control trial, subjects were seated in an empty bath (15 min) and thereafter in a normal environment [20.2 (0.6)°C for 29.0 (1.9) min]. Subjects core temperature prior to exercise was 38.1 (0.3)°C in the hot trial and 37.1 (0.3)°C in the control trial. Mean power output (MPO) was significantly higher in the hot condition for SpI [683 (130) W hot vs 646 (119) W control (P<0.025)]. Peak power output (PPO) tended to be higher in the hot trial compared with the control trial for SpI [1057 (260) W hot vs 990 (245) W control (P=0.03, NS)]. These differences in power output were a consequence of a faster pedal cadence in the hot trial (P<0.025). There were no differences in sprint performance in SpII in the hot trial compared to the control trial; however, MPO was significantly reduced from SpI to SpII in the hot condition but not in the control condition (P<0.025). Plasma ammonia was higher in the hot trial at 2 min post-SpI [169 (65) mol l^-1 hot vs 70 (26) mol l^-1 control (P<0.01)], immediately and at 2 min post-SpII [231 (76) mol l^-1 hot vs 147 (72) mol l^-1 control (P<0.01)]. Blood lactate was higher in the hot trial compared with the control trial at 5 min post-SpII (P<0.025). The results of this study suggest that an elevation in core body temperature by 1°C can improve performance during an initial bout of high-intensity cycle exercise but has no further beneficial effect on subsequent power production following a 4-min recovery period.     

Faster oxygen uptake kinetics during recovery is related to better repeated sprinting ability

This study was designed to test the hypothesis that subjects having faster oxygen uptake (VO₂) kinetics during off-transients to exercises of severe intensity would obtain the smallest decrement score during a repeated sprint test. Twelve male soccer players completed a graded test, two severe-intensity exercises, followed by 6 min of passive recovery, and a repeated sprint test, consisting of seven 30-m sprints alternating with 20 s of active recovery. The relative decrease in score during the repeated sprint test was positively correlated with time constants of the primary phase for the VO₂ off-kinetics (r = 0.85; p < 0.001) and negatively correlated with the VO₂ peak (r = −0.83; p < 0.001). These results strengthen the link found between VO₂ kinetics and the ability to maintain sprint performance during repeated sprints.     

Effects of menstrual phase on performance and recovery in intense intermittent activity

Game sport and training require repeated high intensity bursts. This study examined differences between high intensity, intermittent work in two phases of the menstrual cycle. Six physically active young women (age 19–29) performed 10 6-s sprints on a cycle ergometer in both the mid-follicular (FP) (days 6–10) and late-luteal phases (LP) (days 20–24) of the menstrual cycle. Work, power, oxygen intake parameters, and capillarized blood lactate were measured. Data are analyzed using the Friedman and Wilcoxon matched pairs tests. There was no difference between menstrual phases in peak 6-s power (6.8(0.6) W kg⁻¹ in FP, 6.9(0.6) W kg⁻¹ in LP), the drop off in work (1.2(3.5) J kg⁻¹ in FP and 1.0(2.7) J kg⁻¹ in LP), or in the sprint (23.7 (1.5) mL kg⁻¹ min⁻¹ in LP and 24.3(2.4) mL kg⁻¹ min⁻¹ in FP). Capillarized blood lactate was also similar in both phases of the menstrual cycle both at 1 min (9.2 (2.7) mmol L⁻¹ in FP, 9.2 (3.1) mmol L⁻¹) and at 3 min (9.0 (2.2) mmol L⁻¹ in FP, 9.2 (2.2) mmol L⁻¹ in LP). However, the average 6-s work was greater in the LP (39.3 (3.4) J kg⁻¹) than during the FP (38.3 (3.1) J kg⁻¹) (P=0.023). The recovery was also greater in the LP than the FP (26.3 (2.4) mL kg⁻¹ min⁻¹ in LP, 25.0 (2.6) mL kg⁻¹ min⁻¹ in FP, P=0.023). Average work over a series of sprints and the consumed between sprints may be slightly greater during the LP than the FP of the menstrual cycle.     

Fatigue in repeated-sprint exercise is related to muscle power factors and reduced neuromuscular activity

The purpose of this study was (1) to determine the relationship between each individual’s anaerobic power reserve (APR) [i.e., the difference between the maximum anaerobic (P _ana) and aerobic power (P _aer)] and fatigability during repeated-sprint exercise and (2) to examine the acute effects of repeated sprints on neuromuscular activity, as evidenced by changes in the surface electromyogram (EMG) signals. Eight healthy males carried out tests to determine P _ana (defined as the highest power output attained during a 6-s cycling sprint), P _aer (defined as the highest power output achieved during a progressive, discontinuous cycling test to failure) and a repeated cycling sprint test (10 × 6-s max sprints with 30 s rest). Peak power output (PPO) and mean power output (MPO) were calculated for each maximal 6-s cycling bout. Root mean square (RMS) was utilized to quantify EMG activity from the vastus lateralis (VL) muscle of the right leg. Over the ten sprints, PPO and MPO decreased by 24.6 and 28.3% from the maximal value (i.e., sprint 1), respectively. Fatigue index during repeated sprints was significantly correlated with APR (R = 0.87; P < 0.05). RMS values decreased over the ten sprints by 14.6% (±6.3%). There was a strong linear relationship (R ² = 0.97; P < 0.05) between the changes in MPO and EMG RMS from the vastus lateralis muscle during the ten sprints. The individual advantage in fatigue-resistance when performing a repeated sprint task was related with a lower anaerobic power reserve. Additionally, a suboptimal net motor unit activity might also impair the ability to repeatedly generate maximum power outputs.     

Ammonia and lactate in the blood after short-term sprint exercise

Summary Nine well-trained subjects performed 15-, 30-and 45-s bouts of sprint exercise using a cycle ergometer. There was a significant difference in the mean power between a 15-s sprint (706.0 W, SD 32.5) and a 30-s sprint (627.0 W, SD 27.8;P<0.01). The mean power of the 30-s sprint was higher than that of the 45-s sprint (554.7 W, SD 29.8;P<0.01). Blood ammonia and lactate were measured at rest, immediately after warming-up, and 2.5, 5, 7.5, 10, 12.5 min after each sprint. The peak blood ammonia content was 133.8 mol·1^–1, SD 33.5,- for the 15-s sprint, 130.2 ol·1^–1, SD 44.9, for the 30-s sprint, and 120.8 mol ·1^–1, SD 24.6, for the 45-s sprint. Peak blood lactates after the 15-, 30- and 45-s sprints were 8.1 mmol · 1^–1, SD 1.7, 11.2 mmol · 1^–1, SD 2.4, and 14.7 mmol ·1^–1, SD 2.1, respectively. There was a significant linear relationship between peak blood ammonia and lactate in the 15-s (r, 0.709;P< 0.05), 30-s (r, 0.797;P<0.05) and 45-s (r, 0.696;P<0.05) sprints. Though the peak blood lactate content increased significantly with increasing duration of the sprints (P<0.01), no significant difference was found in peak blood ammonia content among the 15-, 30- and 45-s sprints. These results suggest that the peak value of ammonia in the blood appears in sprints within 15-s and that the blood ammonia level is linked to the lactate in the blood.     

Influence of resistive load on power output and fatigue during intermittent sprint cycling exercise in children

This study examined the effects of two resistive loads on fatigue during repeated sprints in children. Twelve 11.8 (0.2) year old boys performed a force–velocity test to determine the load (Fopt) corresponding to the optimal pedal rate. On two separate occasions, ten 6-s sprints interspersed with 24-s recovery intervals were performed on a friction-loaded cycle ergometer, against a load equal to Fopt or 50%Fopt. Although mean power output (MPO) was higher in the Fopt [397 (24) and 356 (19) W, P < 0.01], the decline in MPO over the 10 sprints was similar in Fopt [8.8 (1.9) %] and 50%Fopt [9.0 (2.4) %]. In contrast, peak power (PPO) was not different in sprint 1 between the two conditions [459 (24) and 460 (28) W], but was decreased only in 50%Fopt [11.4 (3.2) %, P < 0.01], while it was maintained in the Fopt despite the higher total work during each sprint. Fatigue within each sprint (percent drop from peak to end power output) was also higher in the 50%Fopt compared with the Fopt [32 (2.5) vs. 10 (1.6) %, P < 0.01]. Peak and mean pedal rate in Fopt condition were close to the optimum (Vopt), while a large part of the sprint time in 50%Fopt was spent far from Vopt. The present study shows that sprinting against Fopt reduces fatigue within and between repeated short sprints in children. It is suggested that fatigue during repeated sprints is modified when pedal rate is not close to Vopt, according to the parabolic power versus pedal rate relationship.     

Effect of 6 weeks of sprint training on growth hormone responses to sprinting

This study examined the effect of 6 weeks of prescribed sprint training on the human growth hormone (hGH) response to cycle ergometer sprinting. Sixteen male subjects were randomly assigned to a training (n=8) or a control (n=8) group. Each subject completed two main trials, consisting of two all-out 30-s cycle-ergometer sprints separated by 60 min of passive recovery, once before, and once after a 6-week training period. The training group completed three supervised sprint-training sessions per week in addition to their normal activity, whilst control subjects continued with their normal activity. In the training group, peak and mean power increased post-training by 6% (P<0.05) and 5% (P<0.05), respectively. Post-exercise blood pH did not change following training, but the highest post-exercise blood lactate concentrations were greater [highest measured value: 13.3 (1.0) vs 15.0 (1.1) mmol l^–1], with lower blood lactate concentrations for the remainder of the recovery period (P<0.05). Post-exercise plasma ammonia concentrations were lower after training [mean highest measured value: 184.1 (9.8) vs 139.0 (11.7) mol l^–1, P<0.05]. Resting serum hGH concentrations did not change following training, but the peak values measured post-exercise decreased by over 40% in the training group [10.3 (3.1) vs 5.8 (2.5) g l^–1, P<0.05], and mean integrated serum hGH concentrations were 55% lower after training [567 (158) vs 256 (121) min g l^–1, P<0.05]. The hGH response to the second sprint was attenuated similarly before and after training. This study showed that 6 weeks of combined speed- and speed-endurance training blunted the human growth hormone response to sprint exercise, despite an improvement in sprint performance.     

Effect of in- versus out-of-water recovery on repeated swimming sprint performance

The aim of this study was to compare the effect of passive in- (IN) versus out-of-(OUT) water recovery on performance during repeated maximal sprint swimming. Nine well-trained male swimmers (21 ± 3.5 years) performed six repeated maximal 50-m sprints (RS), departing every 2 min, interspersed with either IN or OUT recovery. Best (RS_b) and mean (RS_m) RS times, percentage speed decrement (%Dec) and between-sprint heart rate recovery (HRR_80s) were calculated for both conditions. Blood lactate was measured after the third ([La]_b S3) and sixth sprints (post [La]_b). Rating of perceived recovery level (REC) and exertion (RPE) were collected before and after each sprint. Repeated sprint performance was significantly lower in the OUT condition (i.e., for RS_m, P = 0.02, +1.3%, 90% CI −0.7, 3.2%). OUT was also associated with poorer HRR_80s (P < 0.001, −23%, 90% CI −34, −10%) and higher [La]_b S3 (P < 0.01, +13%, 90% CI −1, 29%). Post [La]_b, however, was similar (P = 0.44, +1%, 90% CI −7, 10%). RPE and REC were not significantly different between the two conditions (all P > 0.43). To conclude, present results confirm the beneficial effect of the IN condition on repeated swim sprint performance, but also suggest that the OUT recovery modality could be an effective training practice for eliciting a low intramuscular energy status.     

Rapid recovery of power output in females

The purpose of the present study was to examine whether the magnitude of the changes in the concentration of muscle metabolites influences the recovery of power output following short-term maximal intensity cycle exercise performed at different average pedalling rates. In part A of the study eight female subjects performed four trials on a cycle ergometer. Two trials involved maximal sprints of 30- and 6-s duration separated by a very short (2–3 s) recovery period. Average pedal rate during the first 30-s sprint was manipulated by employing resistances of either 7.5 or 10.1% of body weight; the second sprint always being performed against 7.5% BW. In two further trials subjects performed only a single 30-s sprint against the two resistances with pre- and post-exercise muscle biopsies and blood samples being taken. Peak power in the second sprint was significantly higher (442 ± 31W vs. 402 ± 33W; P < 0.05) following prior exercise against the greater resistance during which average pedal rate was lower (≈ 26%; P < 0.01) compared with the lesser resistance. However, despite this the muscle metabolite responses to the first sprint were similar (ΔPCr (7.5 vs. 10.1% applied resistance) –55 vs. –59 mmol kg dry muscle^?1: ΔLactate + 104 vs. +107 mmol kg dry muscle^?1: both P > 0.05). In part B of the study six female subjects performed 19 trials in which the recovery interval between a maximal 30-s sprint (where average pedalling rate was manipulated in a manner similar to part A) and a 6-s sprint ranged from 0 to 300 s. The rate of restoration of power output was influenced by the average pedal rate in sprint 1 only for recovery durations of up to 3 s. These findings suggest that the recovery of power is not exclusively determined by muscle metabolites, in particular PCr, when the recovery duration is very short (≤ 3 s). As it has been previously shown that the pattern of muscle activation influences ionic balance it is speculated that ionic factors may be very important in the early and rapid recovery of power.     

Hormonal and metabolic response to three types of exercise of equal duration and external work output

Summary Five normal men, aged 20–30 years, participated in three types of exercise (I, II, III) of equal duration (20 min) and total external work output (120–180 kJ) separated by ten days of rest. Exercises consisted of seven sets of squats with barbells on the shoulders (I; Maximal Power Output _max=600−900 W), continuous cycling at 50 rev · min⁻¹ (II; _max=100−150 W) and seven bouts of intermittent cycling at 70 rev · min⁻¹ (III; _max=300−450 W). Plasma cortisol, glucagon and lactate increased significantly (P<0.05) during the exercise and recovery periods of the anaerobic, intermittent exercise (I and III) but not in the continuous, aerobic exercise (II). No consistent significant changes were found in plasma glucose. Plasma insulin levels decreased only during exercise II. The highest increase in cortisol and glucagon was not associated with the highest , , _max or HR; however it was associated with the anaerobic component of exercise (lactic acid). It is suggested that in exercises of equal duration and total external work output, the continuous, aerobic exercise (II) led to lowest levels of glucogenic hormones.     

No acute effects of short-term creatine supplementation on muscle properties and sprint performance

In a double-blind, placebo, controlled study, we investigated the acute effects of short-term oral creatine supplementation (20 g · day⁻¹ for 6 days) on muscle activation, fatigue and recovery of the m. quadriceps femoris during electrical stimulation, and on maximal performance during sprint cycling. The quadriceps muscles of 23 well-trained rowers were stimulated at different frequencies (10, 20, 50, 100, 150 and 200 Hz). Furthermore, 40 repetitive, electrically stimulated (duration 220 ms, stimulation frequency 150 Hz) concentric contractions were imposed at a constant angular velocity of 180° · s⁻¹ over a range of 50° (from 90 to 140° knee angle), each extension/flexion cycle lasting 1200 ms. To determine recovery, torque was measured at 20, 50, 80, 120, 180 and 300 s after the last contraction. In addition, two maximal 30-s sprints were performed on a cycle ergometer with 4 min rest in between. Following short-term creatine supplementation, body mass [mean (SEM)] increased (P < 0.05) from 85.7 (2.7) kg to 87.3 (2.9) kg. Creatine supplementation had no effect on maximal voluntary isometric torque and muscle activation, or on fatigue and recovery of dynamic exercise. There was also no significant effect on peak power, time to peak power and work to peak power, or total work during both sprints on the cycle ergometer. It was concluded that short-term oral creatine supplementation resulted in increased body mass, but did not enhance muscle performance or maximal output during sprint cycling. Accepted: 16 March 2000     

Power output and muscle metabolism during and following recovery from 10 and 20 s of maximal sprint exercise in humans

On two separate days eight male subjects performed a 10- or 20-s cycle ergometer sprint (randomized order) followed, after 2 min of recovery, by a 30-s sprint. Muscle biopsies were obtained from the vastus lateralis at rest, immediately after the first sprint and after the 2 min of recovery on both occasions.The anaerobic ATP turnover during the initial 10 s of sprint 1 was 129 ± 12 mmol kg dry weight^?1 and decreased to 63 ± 10 mmol kg dry weight^?1 between the 10th and 20th s of sprint 1. This was a result of a 300% decrease in the rate of phosphocreatine breakdown and a 35% decrease in the glycolytic rate. Despite this 51% reduction in anaerobic ATP turnover, the mean power between 10 and 20 s of sprint 1 was reduced by only 28%. During the same period, oxygen uptake increased from 1.30 ± 0.15 to 2.40 ± 0.23 L min^?1, which partially compensated for the decreased anaerobic metabolism. Muscle pH decreased from 7.06 ± 0.02 at rest to 6.94 ± 0.02 after 10 s and 6.82 ± 0.03 after 20 s of sprinting (for all changes P < 0.01). Muscle pH did not change following a 2-min recovery period after both the 10- and 20-s sprints, but phosphocreatine was resynthesized to 86 ± 3 and 76 ± 3% of the resting value, respectively (n.s. 10- vs. 20-s sprint). Following 2 min of recovery after the 10-s sprint subjects were able to reproduce peak but not mean power. Restoration of both mean and peak power following the 20-s sprint was 88% of sprint 1, and was lower compared with that after the 10-s sprint (P < 0.01). Total work during the second 30-s sprint after the 10- and the 20-s sprint was 19.3 ± 0.6 and 17.8 ± 0.5 kJ, respectively (P < 0.01). As oxygen uptake was the same during the 30-s sprints (2.95 ± 0.15 and 3.02 ± 0.16 L min^?1), and [Phosphocreatine] before the sprint was similar, the lower work may be related to a reduced glycolytic ATP regeneration as a result of the higher muscle acidosis.     

Influence of different rest intervals during active or passive recovery on repeated sprint swimming performance

The purpose of this study was to investigate the effect of active or passive recovery after two different rest intervals on performance during repeated bouts of maximal swimming exercise. Sixteen swimmers (eight males and eight females) performed four trials in a counterbalanced order. Eight repetitions of 25-m sprints (8×25 m), with a rest interval of 45 or 120 s, followed by a 50-m sprint test 6 min later, were performed in each trial. The 45 or 120-s interval was either active (A45 and A120) or passive (P45 and P120). The intensity of the active recovery corresponded to 60% of the individual best 100-m velocity. Performance time was recorded using an official competition timing system. The first 25-m sprint was comparable across trials (P>0.05), but performance was decreased after the second sprint during active compared to passive recovery, irrespective of the interval duration (P<0.05). The 50-m sprint time was 2.4% better in the P120 and A120 compared to the A45 and P45 trials (P<0.05). After completing the 8×25 m, blood lactate was decreased with active recovery when the interval period was 120 s (P120 vs A120, P<0.05). Blood lactate concentration at the start as well as 5 min after the 50-m sprint was lower in the A120 and A45 compared to the P120 and P45 trials respectively (P<0.05). Plasma glycerol was not different between trials (P>0.05), whereas plasma ammonia was higher in the A45 compared to the P120 trial (P<0.05). The interval period separating short-duration sprints may therefore alter performance when subsequent maximum exertion is applied. For sustained sprinting ability, passive recovery is advised during repeated swimming sprints of short duration.     

The influence of muscle metabolic characteristics on physical performance

Summary This study describes the influence of muscle fiber type composition, enzyme activities and capillary supply on muscle strength, local muscle endurance or aerobic power and capacity. Muscle biopsies were obtained from m. vastus lateralis in thirteen physically active men. Histochemical staining procedures were applied to assess the percentage of fast twitch (FT) fibers, muscle fiber area, and capillary density. Also, the activity of citrate synthase (CS), creatine kinase (CK), hexokinase (HK), lactate dehydrogenase (LDH), and phosphofructokinase (PFK) were analysed using fluorometrical assays. Peak torque at ‘low’ and ‘high’ angular velocities was measured during leg extension. Similarly, muscle fatigue (e. g. peak torque decline) and recovery from a short-term exercise task were measured during maximal, voluntary consecutive leg extensions. Aerobic power ( ) and aerobic capacity (e.g. onset of blood lactate concentration; OBLA), as defined by a blood lactate concentration of 4 mol · l⁻¹ were measured during cycling. Peak torque at a high angular velocity was positively correlated with % FT area (p<0.001). Fatigue and recovery were correlated with LDH · CS⁻¹ (p<0.001). W_OBLA was best correlated with PFK and PFK · CS⁻¹ (p<0.001). Hence, muscle strength was partly determined by fiber type composition whereas local muscle endurance, recovery and aerobic capacity reflect mainly capillary supply and the activity of key enzymes involved in aerobic and anaerobic metabolism.     

The influence of acetaminophen on repeated sprint cycling performance

Introduction

The aim of this study was to investigate the effect of acetaminophen on repeated sprint cycling performance.

Methods

Nine recreationally active male participants completed a graded exercise test, a familiarisation set of Wingate Anaerobic Tests (WAnTs) and two experimental sets of WAnTs (8 × 30 s sprints, 2 min active rest intervals). In the experimental WAnTs, participants ingested either 1.5 g acetaminophen or a placebo in a double-blind, randomised, crossover design. During the WAnT trials, participants provided ratings of perceived pain 20 s into each sprint. Mean and peak power output and heart rate were recorded immediately following each sprint, and percentage decrement in mean power output was subsequently calculated.

Results

Participants cycled at a significantly greater mean power output over the course of 8 WAnTs (p < 0.05) following the ingestion of acetaminophen (391 ± 74 vs. 372 ± 90 W), due to a significantly greater mean power output during sprints 6, 7 and 8 (p < 0.05). Percentage decrements in mean power output were also significantly reduced (p < 0.05) following acetaminophen ingestion (17 ± 14 vs. 24 ± 17 %). No significant differences in peak power output, perceived pain or heart rate were observed between conditions.

Conclusion

Acetaminophen may have improved performance through the reduction of pain for a given work rate, thereby enabling participants to exercise closer to a true physiological limit. These results suggest that exercise may be regulated by pain perception, and that an increased pain tolerance can improve exercise performance.     

Performance for short intermittent runs: active recovery vs. passive recovery

The purpose of this study was to compare the effects of active vs. passive recovery on the time to exhaustion for intermittent runs (15 s) at supramaximal velocity (120% of maximal aerobic speed). Twelve male subjects performed a graded test, an intermittent run to exhaustion with active recovery (50% of maximal aerobic speed) and an intermittent run to exhaustion with passive recovery. Results showed that intermittent runs to exhaustion with passive recovery [745 (171) s] allowed subjects to run for a significantly longer (p<0.001) time than intermittent runs to exhaustion with active recovery [445 (79) s]. These results could be explained by a significantly higher (p<0.001) energy requirement for intermittent runs with active recovery [59.9 (9.6) ml·kg⁻¹·min⁻¹] than for intermittent runs with passive recovery [48.9 (6.9) ml·kg⁻¹·min⁻¹]. It could be also hypothesized that the energy required to run during short active recovery would result in less oxygen being available to reload myoglobin and haemoglobin, to remove lactate concentrations and to resynthesize the phosphocreatine. Consequently, for intermittent runs with short recovery periods, passive recovery will induce a longer time to exhaustion than active recovery.     

Aerobic and anaerobic contribution to Wingate test performance in sprint and middle-distance runners

We investigated the aerobic and anaerobic contributions to performance during the Wingate test in sprint and middle-distance runners and whether they were related to the peak aerobic and anaerobic performances determined by two commonly used tests: the force-velocity test and an incremental aerobic exercise test. A group of 14 male competitive runners participated: 7 sprinters, aged 20.7 (SEM 1.3) years, competing in 50, 100 and 200-m events and 7 middle-distance runners, aged 20.0 (SEM 1.0) years, competing in 800, 1,000 and 1,500 m-events. The oxygen uptake ( ) was recorded breath-by-breath during the test (30 s) and during the first 20 s of recovery. Blood samples for venous plasma lactate concentrations were drawn at rest before the start of the test and during the 20-min recovery period. During the Wingate test mean power ( ) was determined and three values of mechanical efficiency, one individual and two arbitrary, 16% and 25%, were used to calculate the contributions of work by aerobic ( _{aer,ind,16%,25%}) and anaerobic ( _{an,ind,16%,25%}) processes. Peak anaerobic power ( _an,peak) was estimated by the force-velocity test and maximal aerobic energy expenditure ( _aer,peak) was determined during an incremental aerobic exercise test. During the Wingate test, the middle-distance runners had a significantly greater than the sprinters (P < 0.001), who had significantly greater venous plasma lactate concentrations (P < 0.001). Moreover, _{aer,ind,16%,25%} were also significantly higher (P < 0.05) in the middle-distance runners [ _aer,ind 45 (SEM 4) % vs 28 (SEM 2) %; _aer,16% 30 (SEM 3) % vs 19 (SEM 2) %; _aer,25% 46 (SEM 3) % vs 29 (SEM 2)%]; _{an,ind,16%,25%} in the sprint runners (P < 0.05) [ _an,ind 72 (SEM 3) % vs 55 (SEM 4) %; _an,16% 81 (SEM 2) % vs 70 (SEM 3) %; _an,25% 71 (SEM 2) % vs 54 (SEM 3) %]. The _aer,ind/ _aer,peak and × _an,ind/ _an,peak ratios, however, were not significantly different between the two groups of athletes. These results would indicate that the sprinters and middle-distance runners used preferentially a metabolic system according to their speciality. Nevertheless, under the conditions of its experiment, they seemed to rely on the same percentage of both peak anaerobic and peak aerobic performance for a given exercise task.     

Evidence for neuromuscular fatigue during high-intensity cycling in warm, humid conditions

The purpose of this study was to examine and describe the neuromuscular changes associated with fatigue using a self-paced cycling protocol of 60-min duration, under warm, humid conditions. Eleven subjects [mean (SE) age 21.8 (0.8) years; height 174.9 (3.0) cm; body mass 74.8 (2.7) kg; maximum oxygen consumption 50.3 (1.8) ml · kg · min⁻¹] performed one 60-min self-paced cycling time trial punctuated with six 1-min “all out” sprints at 10-min intervals, while 4 subjects repeated the trial for the purpose of determining reproducibility. Power output, integrated electromyographic signal (IEMG), and mean percentile frequency shifts (MPFS) were recorded at the mid-point of each sprint. There were no differences between trials for EMG variables, distance cycled, mean heart rate, and subjective rating of perceived exertion for the subjects who repeated the trial (n=4). The results from the repeated trials suggest that neuromuscular responses to self-paced cycling are reproducible between trials. The mean heart rate for the 11 subjects was 163.6 (0.71) beats · min⁻¹. Values for power output and IEMG expressed as a percentage of that recorded for the initial sprint decreased during sprints 2–5, with normalised values being 94%, 91%, 87% and 87%, respectively, and 71%, 71%, 73%, and 77%, respectively. However, during the final sprint normalised power output and IEMG increased to 94% and 90% of initial values, respectively. MPFS displayed an increase with time; however, this was not significant (P=0.06). The main finding of this investigation is the ability of subjects to return power output to near initial values during the final of six maximal effort sprints that were included as part of a self-paced cycling protocol. This appears to be due to a combination of changes in neuromuscular recruitment, central or peripheral control systems, or the EMG signal itself. Further investigations in which changes in multiple physiological systems are assessed systematically are required so that the underlying mechanisms related to the development of fatigue during normal dynamic movements such as cycling can be more clearly delineated. Accepted: 25 September 2000     

Longitudinal associations between anaerobic threshold and distance running performance

Summary Longitudinal alterations in anaerobic threshold (AT) and distance running performance were assessed three times within a 4-month period of intensive training, using 20 male, trained middle-distance runners (19–23 yr). A major effect of the high intensity regular intensive training together with 60- to 90-min AT level running training (2d ·wk ⁻¹) was a significant increase in the amount of O₂ uptake corresponding to AT ( AT; ml O₂ · min⁻¹ · kg⁻¹) and in maximal oxygen uptake ( ; ml O₂ · min⁻¹ · kg⁻¹). Both AT and showed significant correlations (r=−0.69 to −0.92 andr=−0.60 to −0.85, respectively) with the 10,000 m run time in every test. However, further analyses of the data indicate that increasing AT (r=−0.63,P<0.05) rather than (r=−0.15) could result in improving the 10,000 m race performance to a larger extent, and that the absolute amount of change (δ) in the 10,000 m run time is best accounted for by a combination of δ AT and δ5,000 m run time. Our data suggest that, among runners not previously trained over long distances, training-induced alterations in AT in response to regular intensive training together with AT level running training may contribute significantly to the enhancement of AT and endurance running performance, probably together with an increase in muscle respiratory capacity. This study was supported by Grant 59780141 from the Scientific Research Fund of the Ministry of Education, Science, and Culture, Japan