Maximal Intermittent Exercise Research Articles

Delayed neuromuscular fatigue recovery unveils reduced fatigue tolerance in elderly following maximal intermittent exercise.

The aim of the study was to assess the impact of aging on neuromuscular fatigue and recovery. Ten young (23.08 ± 1.43years) and older (61.19 ± 1.80years) males performed an intermittent maximal isometric exercise with the knee extensors followed by 27min of recovery. Maximal voluntary contraction (MVC), total work (W'), voluntary activation (VA), potentiated resting twitch (Ptw), and electromyography (EMG) were recorded and then analyzed. Peripheral and central fatigue following exercise were lower in old compared to young (- 29.99% vs. - 42.68% and - 14.55 vs. - 20.02%; P < 0.05, respectively). Despite old performing 50% less work, RMS/Mmax reduction was similar between old and young (- 26.46% vs. - 29.93%; P > 0.05, respectively). During the recovery period, our results showed that recovery of the MVC was impaired for old (14.93% for old vs. 30.66% for young) and still incomplete until 27min.VA increased significantly compared to post exercise after 1min only for young (P = 0.001), potentially affecting the recovery pattern of MVC during the early phase due to their significant correlation (r2 = 0.58, P = 0.01). Peripheral fatigue recovery was also lower for old (11.18% vs. 18.72%; P < 0.001), and both groups failed to recover their baseline value (both P < 0.005). The lower peripheral and central fatigue observed in elderly following exercise appears for the first instance as a fatigue resistance. However, the delayed neuromuscular recovery reveals instead a reduced fatigue tolerance reflecting age-related alteration within contractile properties and/or within central nervous system.

THE EFFECTS OF CREATINE SUPPLEMENTATION ON SINGLE AND INTERMITTENT ANAEROBIC EXERCISES AND BODY COMPOSITION DURING REDUCED TRAINING IN SOCCER PLAYERS

Abstract: BACKGROUNDː Several studies have examined the effects of creatine supplementation in adult athletes in season or pre-season preparation. However, few studies have examined the effects of creatine supplementation in adolescent soccer players during reduced training in an off-season. OBJECTIVE: The aim of the study was to examine the effects of short-term creatine monohydrate supplementation on the anaerobic performance and body composition in adolescent soccer players during reduced training in an off-season. METHODSː Using a double-blind experiment design, 16 soccer players (aged 18.0 ± 0.8 yr) were randomly assigned to 5 days of either 20 g . day-1 creatine monohydrate (Cr) or placebo supplementation. One day before and a day after the supplementation, participants completed squat and countermovement jumps (SJ, CMJ), 10-m running sprint, 6-s single cycling sprint (CST), an intermittent anaerobic test on a bicycle ergometer (10 x 6s, IAnTBE) and measurement of body composition. RESULTSː Cr supplementation had no significant effect (p &gt; .05) on any performance test. However, effect size values indicated medium or small clinical significance in SJ (d = 0.59), CST (6-s power, d = 0.50; peak power, d = 0.48) and IAnTBE (best peak power, d = 0.44; post-exercise blood lactate concentration, d = - 0.59; fatigue index, d = - 0.28 ). Relative to the placebo, Cr supplementation resulted in a significant increase in body weight (BW) (p = .015). CONCLUSIONSː The results of the study suggest that short-term Cr supplementation administered to adolescent soccer players during their off-season significantly increase body weight and could have small/medium clinical significance effect on improve lower-body maximal anaerobic power output and power output recovery during maximal intermittent exercise. The study also confirms that Cr supplementation is safe and without side effects for adolescent athletes.

Intermittent Maximal Exercise Improves Attentional Performance Only in Physically Active Students

Regular physical activity participation seems to be linked to brain metabolism and to be one factor responsible for different effects of high intensity exercise on cognition. Due to this, we investigated the effect of an intermittent maximal exercise intervention on a neuropsychological test requiring sustained and selective attention in a group of low and high physically active subjects. Forty six healthy students (age: M = 23.11, SD = 2.60 years) performed in a cross-over design an intermittent incremental exercise until they reached their maximal heart rate (HR Max; intervention condition) or rested for the same duration (control condition) followed by the administration of the d2-test. A significant interaction between physical activity participation level and exercise effect on cognitive performance emerged, with only the more physically active participants improving the performance in the cognitive test after the intervention. These data extend the current knowledge base by showing that a higher participation rate in physical activity may lead to neurobiological adaptations that facilitate selected cognitive processes (i.e., attention) after high exercise intensities.

Mechanism of ATP loss in nonoxidative contracting muscle

The transition from rest to intense exercise is a challenge to cellular energetics ([11][1], [13][2], [15][3]). The metabolic fuels, i.e., the sources of ATP to sustain muscular contraction, are creatine phosphate and glycogen. Two anaerobic metabolic paths, leading to ATP generation, are catalyzed

Training Effects on Endurance Capacity in Maximal Intermittent Exercise: Comparison Between Continuous and Interval Training

The purpose of this study was to examine the effects of 2 different training regimens, continuous (CT) and interval (IT), on endurance capacity in maximal intermittent exercise. Eighteen lacrosse players were divided into CT (n = 6), IT (n = 6), and nontraining (n = 6) groups. Both training groups trained for 3 days per week for 15 weeks using bicycle ergometers. Continuous training performed continuous aerobic training for 20-25 minutes, and IT performed high-intensity pedaling comprising 10 sets of 10-second maximal pedaling with 20-second recovery periods. Maximal anaerobic power, maximal oxygen uptake (V(O2max)), and intermittent power output were measured before and after the training period. The intermittent exercise test consisted of a set of ten 10-second maximal sprints with 40-second intervals. Maximal anaerobic power significantly increased in IT (p <or= 0.05), whereas V(O2max) increased in both training groups (p <or= 0.05). In the intermittent exercise test, the average of the total mean power output (1-10 sets) increased in both training groups (p <or= 0.05); however, the mean power output in the last stage (8-10 sets) and fatigability improved only in IT. Consequently, continuous aerobic training reduced lactate production and increased the mean power output, but there was little effect on high-power endurance capacity in maximal intermittent exercise. In contrast, although lactate production did not decrease, IT improved fatigability and mean power output in the last stage. These results indicated that the endurance capacities for maximal intermittent and continuous exercises were not identical. Ball game players should therefore improve their endurance capacity with high-intensity intermittent exercise, and it is insufficient to assess their capacity with only V(O2max) or continuous exercise tests.

High-Intensity Training Improves Plasma Glucose and Acid-Base Regulation During Intermittent Maximal Exercise in Type 1 Diabetes

In individuals without diabetes, high-intensity exercise (HIE) training may reduce (1) the characteristic postexercise rise in plasma glucose with HIE (2–4) and reduces (5,6) the marked acid-base balance perturbations (5–8). In type 1 diabetes, continuous HIE induces sustained hyperglycemia (9,10), while very brief intermittent HIE may reduce hyperglycemia (11). Acid-base disturbances during exercise may be heightened in type 1 diabetes (12–14). Effects of HIE training on glycemia and acid-base balance during intermittent HIE in type 1 diabetes are unknown; thus, despite the potential clinical importance of such exercise, there is no evidence on which to base patient guidelines. The aim of the present study was thus to investigate the effects of HIE training on glycemia and acid-base regulation during intermittent HIE in type 1 diabetes. Eight subjects with type 1 diabetes (duration of diabetes 7.1 ± 4.0 years) and seven subjects without diabetes (control group), all of whom were healthy and took no medications (other than insulin in type 1 diabetic subjects), consented to participate. The study was approved by the human ethics committees of The University of Sydney and the South Sydney West Area Health Service. Control subjects closely matched those with diabetes for age (type 1 diabetes 25 ± 4 years and control 25 ± 4 years), BMI (25.4 ± 3.2 and 23.8 ± 5.0 kg/m2, respectively), and V o2peak (42.7 ± 12.2 and 43.7 ± 6.2 ml · kg−1 · min−1), as detailed in a related study that reported effects of sprint training on muscle sodium-potassium ATPase and on plasma potassium during maximal exercise (15). Testing was conducted after overnight fasting. Type 1 diabetic subjects delayed their morning insulin. Subjects completed four 30-s maximal exercise bouts (EB1–4) (each separated by …

Effect of creatine supplementation on phosphocreatine resynthesis, inorganic phosphate accumulation and pH during intermittent maximal exercise

In this study, we examined the effect of creatine ingestion on muscle power output, muscle phosphocreatine resynthesis, inorganic phosphate and pH during repeated brief bouts of maximal exercise. Nine healthy males performed maximal plantar flexion before and after creatine ingestion (20 g ·day -1 for 6 days). The experimental protocol consisted of five 8 s bouts (bouts 1-5) interspersed with 30 s recovery, followed by bouts 6 (8 s) and 7 (16 s) separated by 1 and 2 min, respectively. Muscle phosphocreatine, inorganic phosphate and pH were estimated every 16 s by 31 P magnetic resonance spectroscopy. After creatine ingestion, muscle power output increased by ~5% ( P ≪ 0.05) from bouts 3 to 7 and muscle phosphocreatine resynthesis increased ( P ≪ 0.05) during 10 min recovery. The higher phosphocreatine concentration observed after only 30 s of recovery was accompanied by lower inorganic phosphate accumulation and higher pH. Strong correlations were found between exercise power restoration and the corresponding pre-exercise phosphocreatine and inorganic phosphate concentrations and muscle pH after creatine ingestion. The better maintenance of muscle power output observed after creatine ingestion was attributed to a higher rate of phosphocreatine resynthesis, lower accumulation of inorganic phosphate and higher pH.

Creatine loading and resting skeletal muscle phosphocreatine flux: a saturation-transfer NMR study.

31P saturation-transfer nuclear magnetic resonance spectroscopy was used to study skeletal muscle phosphocreatine (PCr) flux in healthy male volunteers. Data analysis included consideration of effects from incomplete saturation and radiofrequency spillover. Spectra were recorded from the resting gastrocnemius muscle before and after 6 days of creatine monohydrate (Cr-H2O) intake (20 g/day). Parallel to an improved muscle performance during maximal intermittent exercise following Cr-H2O supplementation, the concentration of PCr increased (P=0.01) by 23% (34.9+/-2.8 mmol/l vs. 28.6+/-2.7 mmol/l), whereas other metabolites were unaffected (inorganic phosphate: 4.3+/-1.4 mmol/l, free intracellular Mg(2+): 1.1+/-0.7 mmol/l, cytosolic pH: 7.04+/-0.02). Forward and reverse fluxes through the creatine kinase (CK) reaction did not change significantly from their baseline levels (v(for): 11.8+/-5.4 mmol/l per second vs. 15.3+/-6.8 mmol/l per second, (v(rev): 9.5+/-3.4 mmol/l per second vs. 10.9+/-3.7 mmol/l per second). The rate of PCr resynthesis in resting muscle is not limited by the CK reaction, which is near equilibrium. Consequently, the post-load increase in total creatine has no effect on the unidirectional CK reaction rates.

VALIDITY OF INTERMITTENT ENDURANCE INDICATORS FOR RUGBY FOOTBALL PLAYERS

The purpose of this study was to examine the validity of indicators evaluating intermittent endurance with high power output required in rugby football games. Eleven collegiate rugby football players performed an incremental exercise test into exhaustion on a cycle ergometer to determine VO2max, VO2AT and VO2 at the respiratory compensation point (RCP). The subjects also performed an intermittent exercise test on the cycle ergometer, consisting of twenty 5-s maximal effort exercise with 20-s recovery periods and the power output (W/kg) was measured. The absolute power decline and its rate (%decline) were calculated by dividing the average power output from the 9th to the 20th trials by that of the first trial. Correlations of VO2max, VO2AT and VO2RCP to the power output were higher (p < .05) in the middle and the last phases during the intermittent exercise test, while no significant correlations were observed the beginning phase. These results indicate that not only the aerobic energy supply system but also muscle metabolic and buffering capacity contribute to the maximal intermittent exercise with high intensity. Moderate correlation coefficients were found between RCP-% VO2max and decline (r = 0.69), and 0.67 for VO2RCP with %decline, 0.66 for RCP-%VO2max with %decline. Consequently, it is inferred that the RCP indicators (VO2RCP, RCP-%VO2max) are valid to measure the intermittent endurance with high power output requiring in the maximal intermittent exercise with high intensity in rugby games.

The effect of creatine monohydrate loading on maximal intermittent exercise and sport-specific strength in well trained power-lifters

The effect of creatine loading on the performance of sedentary and recreationally active individuals has been well documented, but research on well trained individuals is still lacking. In this double-blind study the effect of creatine monohydrate loading (9g/day) on maximal intermittent isokinetic exercise and sport-specific strength in 13 well trained power-lifters was ascertained. Both before and after supplementation the creatine (n=8) and placebo (n=5) groups performed three sets of maximal unilateral knee extensions on an isokinetic dynamometer interspaced with 60s rest periods. This was followed up the next day by a maximal deadlift strength feat performed in a gymnasium. Values for peak torque, average power, total work and work output during the first five sample repetitions in the creatine group increased significantly and in a relatively constant fashion in all subjects (correlation coefficients ranged between 0.84 and 0.92) after five supplementation days. There was also a significant ( p = 0.010) increase in the deadlift lifting volume after six days of creatine supplementation. Findings from this study suggest that nine grams of creatine monohydrate per day for five and six days respectively, improves maximal intermittent isokinetic power output and sport-specific strength in well trained power-lifters.

Regulation of skeletal muscle glycogen phosphorylase and PDH during maximal intermittent exercise.

The time course for the activation of glycogen phosphorylase (Phos) and pyruvate dehydrogenase (PDH) and their allosteric regulators was determined in human skeletal muscle during repeated bouts of maximal exercise. Six subjects completed three 30-s bouts of maximal isokinetic cycling separated by 4-min recovery periods. Muscle biopsies were taken at rest and at 6, 15, and 30 s of exercise during bouts 1 and 3. Phos was rapidly activated within the first 6 s of bout 1 from 12% at rest to 47% at 6 s. The activation of PDH increased from 14% at rest to 48% at 6 s and 95% at 15 s of bout 1. Phos reverted back to basal values at the end of the first bout, whereas PDH remained fully activated. In contrast, in the third bout, PDH was 42% at rest and was activated more rapidly and was nearly completely activated by 6 s, whereas Phos remained at basal levels (range 14-20%). Lactate accumulation was marked in the first bout and increased progressively from 2.7 to 76.1 mmol/kg dry wt with no further increase in bout 3. Glycogen utilization was also marked in the first bout and was negligible in bout 3. The rapid activation of Phos and slower activation of PDH in bout 1 was probably due to Ca(2+) release from the sarcoplasmic reticulum. Lactate accumulation appeared to be due to an imbalance of the relative activities of Phos and PDH. The increase in H(+) concentration may have served to reduce pyruvate production by inhibiting Phos transformation and may have simultaneously activated PDH in the third bout such that there was a better matching between pyruvate production and oxidation and minimal lactate accumulation. As each bout progressed and with successive bouts, there was a decreasing ability to stimulate substrate phosphorylation through phosphocreatine hydrolysis and glycolysis and a shift toward greater reliance on oxidative phosphorylation.

EFFECT OF ORAL CREATINE AND CAFFEINE ON MUSCLE PHOSPHOCREATINE RESYNTHESIS IN COMPETITIVE SWIMMERS

1283 The purpose of this investigation was to examine the effects of creatine (Cr) + caffeine (Ca) on the resynthesis of muscle phosphocreatine and on performance characteristics associated with swimming. Six highly trained female swimmers were randomly selected and tested for baseline measurements prior to supplementation. Each subject consumed Cr(0.4 g/kg/d) for 5d + a gelatin placebo (200 mg/d) for the final 3d. Following a brief washout period each subject consumed Cr(0.4 g/kg/d) for 5d + Ca(200 mg/d) for the final 3d (Treatment: randomized, double blind). 31P NMRs of the forearm flexors and a maximal intermittent exercise fatigue test of a wrist curl were performed. The exercise test consisted of 3×30s maximal wrist curls on a 3min rest interval. Also, a 6×8s tethered resistance swim to measure force generated and a 6×50y repeat swim on a 3min rest interval to measure performance time were also conducted. Muscle PCr resynthesis was not changed across the treatment conditions. Total force produced was increased by Cr + Ca (P<0.05) but was not changed by Cr alone. Performance time was significantly faster after Cr(P<0.05), but was not altered following Cr + Ca. The data show that Cr supplementation markedly improves swim performance when a 3min recovery is provided between repeat swims. Conversely, Cr + Ca significantly improved force generation when a 30s recovery is provided between repeat swims. Finally, 31P NMRs is not an appropriate measuring device for PCr resynthesis. These results await further confirmation in a subsequent study utilizing a larger number of subjects.

The Relationship Between Aerobic Fitness and Both Power Output and Subsequent Recovery During Maximal intermittent Exercise

The primary aim of the study was to establish a link between aerobic adaptation and both the recovery from maximal short duration exercise, and the ability to maintain power output in a subsequent bout. The question as to whether the aerobic adaptations facilitating recovery are centrally or peripherally located was also examined. Male university level rugby and soccer players (n=20) volunteered for the study. Mean (SD) age, mass and maximal oxygen uptake (VO2 max) was 21.9 (1.8) years, 84.7 (12.7) kg and 52.7 (6.9) ml x kg(-1) x min(-1) respectively. Subjects completed six 15s maximal intensity sprints (90s active recovery) on a Monark friction braked cycle ergometer. A significant relationship (r=-.49, P=0.03) was obtained between VO2 max (mL x kg(-1) x min(-1)) and the percent drop-off in mean power in bouts 5 and 6 compared with bout 1. A correlation of r=-.62 (P=0.002) was obtained between VO2 max (mL x kg(-1) x min(-1)) and the percent drop off in peak power in bouts 5 and 6 compared with bout 1. A significant correlation was obtained between arterial venous oxygen difference and the drop in mean power (r=-.54, P=0.02) but not with the drop in peak power (r=-.22, P=.36). There was no significant relationship between cardiac output and the drop in mean power (r=-.16, P=.51) or the drop in peak power (r=-.02, P=.94). Percent drop-off in oxygen consumption, when compared with the first, in the second (RVO2(30-60)), third (RVO2(60-90)), fourth (RVO2(90-120)) and fifth (RVO2(120-150)) 30s time periods of recovery following the intermittent protocol was calculated. Correlations between VO2 max (ml x kg(-1) x min(-1)) and these variables were (r=.51, P=-0.03), (r=.44, P=0.06), (r=.63, P=-0.003) and (r=.6, P=0.007) respectively. Consequently it was concluded that maximal oxygen uptake particularly the peripheral component, is an important determinant of the ability to perform intermittent exercise of this nature and to recover between bouts.

Capillary blood lactate concentrations during intermittent all-out exercise

The average maximal peak torques of the knee extensor and knee flexor muscles were measured during one, two or three series of 20 maximal contractions at an angular velocity of pi rad s -1 . After the first series, a 10 min rest was allowed before the second series of contractions. In one case only was a third series of contractions performed. Various sequences of contractions of the dominant and contralateral limbs were tested. Capillary blood lactate concentration ([LA] cap ) was determined in the blood samples taken from an earlobe during each recovery. The difference between peak capillary blood lactate concentration and the concentration that would have occurred without any previous contraction (delta[LA] cap ) was taken as the index of metabolic comparison between the exercise bouts. The mechanical power output during the first series of contractions was similar to that in the second and third series, but the lactate elevation was significantly higher in the first series. The discrepancy between the constancy of the power output and the decrease in lactate elevation was even more evident if delta[LA] cap was calculated as the difference between peak capillary blood lactate concentration and the value measured immediately before the second or third series. The decrease in lactate elevation was not affected by the change of the contracting limb from the first to the second series. In conclusion, the capillary blood lactate concentration profile during intermittent maximal exercise cannot be considered a suitable technique for evaluating lactate production. Each series lasted about 20 s.

ACTIVATION RATE OF GLYCOGEN PHOSPHORYLASE AND PYRUVATE DEHYDROGENASE IN HUMAN SKELETAL MUSCLE DURING INTENSE EXERCISE 588

The purpose of this study was to determine the time course for the transformation of glycogen phosphorylase and pyruvate dehydrogenase (PDH) during the first and third bouts of maximal intermittent exercise. Six subjects completed three 30-s bouts of maximal isokinetic cycling at 100 rpm, each separated by 4 min of rest. Biopsies of the vastus lateralis were taken before, and at 6s, 15s and 30s of bouts 1 and 3. Total work in bout 1 was 18.4±0.5 kJ, and decreased to 13.7±1.0 kJ in bout 3. Prior to bout 1, PDH was 14.2±0.1% activated, increased to 48.4±0.1% at 6s, and was totally activated by 15s. The mole fraction of active phosphorylase (PHOS a) was 9.9±2.2% at rest, increased to 46.8±5.3% and 47.4±6.4% at 6s and 15s, respectively, and by 30s, decreased to 21.8±4.2%. Prior to bout 3, PDH was 41.7±0.1% activated; by 6s it was 100% activated. PHOS a fraction increased from 10.5±2.7% to 14.7±2.7% and 20.5±1.6% at 6s and 15s, respectively, and was partially inactivated to 16.2±5.7% at 30s. Glycogen utilization was 127.0±35.1 and 15.1±10.2 mmol/kg dw in bouts 1 and 3, respectively. Lactate increased from 2.7±0.4 to 76.1±7.4 mmol/kg dw in bout 1 and from 97.7±16.7 to 107.1±15.3 mmol/kg dw in bout 3. In bout 1, the rapid transformation to PHOS a was associated with rapid increases in glycogenolysis and a large accumulation of lactate due to the delayed activation of PDH. However, in bout 3 the small change in PHOS a resulted in a lower rate of glycogenolysis and the rapid activation of PDH resulted in a greater oxidation of pyruvate and hence less lactate accumulation.

Sodium Bicarbonate Ingestion, Muscle Metabolism and Performance during Intermittent Maximal Exercise

Sodium Bicarbonate Ingestion, Muscle Metabolism and Performance during Intermittent Maximal Exercise

Human muscle metabolism during intermittent maximal exercise

Eight male subjects volunteered to take part in this study. The exercise protocol consisted of ten 6-s maximal sprints with 30 s of recovery between each sprint on a cycle ergometer. Needle biopsy samples were taken from the vastus lateralis muscle before and after the first sprint and 10 s before and immediately after the tenth sprint. The energy required to sustain the high mean power output (MPO) that was generated over the first 6-s sprint (870.0 +/- 159.2 W) was provided by an equal contribution from phosphocreatine (PCr) degradation and anaerobic glycolysis. Indeed, within the first 6-s bout of maximal exercise PCr concentration had fallen by 57% and muscle lactate concentration had increased to 28.6 mmol/kg dry wt, confirming significant glycolytic activity. However, in the tenth sprint there was no change in muscle lactate concentration even though MPO was reduced only to 73% of that generated in the first sprint. This reduced glycogenolysis occurred despite the high plasma epinephrine concentration of 5.1 +/- 1.5 nmol/l after sprint 9. In face of a considerable reduction in the contribution of anaerobic glycogenolysis to ATP production, it was suggested that, during the last sprint, power output was supported by energy that was mainly derived from PCr degradation and an increased aerobic metabolism.

Physiological responses to maximal intermittent exercise: Differences between endurance‐trained runners and games players

Six games players (GP) and six endurance-trained runners (ET) completed a standardized multiple sprint test on a non-motorized treadmill consisting of ten 6-s all-out sprints with 30-s recovery periods. Running speed, power output and oxygen uptake were determined during the test and blood samples were taken for the determination of blood lactate and pH. Games players tended to produce a higher peak power output (GP vs ET: 839 +/- 114 vs 777 +/- 89 W, N.S.) and higher peak speed (GP vs ET: 7.03 +/- 0.3 vs 6.71 +/- 0.3 m s-1, N.S.), but had a greater decrement in mean power output than endurance-trained runners (GP vs ET: 29.3 +/- 8.1% vs 14.2 +/- 11.1%, P less than 0.05). Blood lactate after the test was higher for the games players (GP vs ET: 15.2 +/- 1.9 vs 12.4 +/- 1.7 mM, P less than 0.05), but the decrease in pH was similar for both groups (GP vs ET: 0.31 +/- 0.08 vs 0.28 +/- 0.08, N.S.). Strong correlations were found between peak blood lactate and peak speed (r = 0.90, P less than 0.01) and between peak blood lactate and peak power fatigue (r = 0.92, P less than 0.01). The average increase in oxygen uptake above pre-exercise levels during the sprint test was greater for endurance-trained athletes than for the games players (ET vs GP: 35.0 +/- 2.2 vs 29.6 +/- 3.0 ml kg-1 min-1, P less than 0.05), corresponding to an average oxygen uptake per sprint (6-s sprint and 24 s of subsequent recovery) of 67.5 +/- 2.9% and 63.0 +/- 4.5% VO2 max respectively (N.S.). A modest relationship existed between the average increase in oxygen uptake above pre-exercise values during the sprint test and mean speed fatigue (r = -0.68, P less than 0.05). Thus, the greater decrement in performance for the games players may be related to higher glycolytic rates as reflected by higher lactate concentrations and to their lower oxygen uptake during the course of the 10 sprints.

The hormonal responses to repetitive brief maximal exercise in humans

The responses of nine men and nine women to brief repetitive maximal exercise have been studied. The exercise involved a 6-s sprint on a non-motorised treadmill repeated 10 times with 30 s recovery between each sprint. The total work done during the ten sprints was 37,693 +/- 3,956 J by the men and 26,555 +/- 4,589 J by the women (M greater than F, P less than 0.01). This difference in performance was not associated with higher blood lactate concentrations in the men (13.96 +/- 1.70 mmol.l-1) than the women (13.09 +/- 3.04 mmol.l-1). An 18-fold increase in plasma adrenaline (AD) occurred with the peak concentration observed after five sprints. The peak AD concentration in the men was larger than that seen in the women (9.2 +/- 7.3 and 3.7 +/- 2.4 nmol.l-1 respectively, P less than 0.05). The maximum noradrenaline (NA) concentration occurred after ten sprints in the men (31.6 +/- 10.9 nmol.l-1) and after five sprints in the women (27.4 +/- 20.8 nmol.l-1). Plasma cardiodilatin (CDN) and atrial natriuretic peptide (ANP) concentrations were elevated in response to the exercise. The peak ANP concentration occurred immediately post-exercise and the response of the women (10.8 +/- 4.5 pmol.l-1) was greater than that of the men (5.1 +/- 2.6 pmol.l-1, P less than 0.05). The peak CDN concentrations were 163 +/- 61 pmol.l-1 for the women and 135 +/- 61 pmol.l-1 for the men. No increases in calcitonin gene related peptide (CGRP) were detected in response to the exercise. These results indicate differences between men and women in performance and hormonal responses. There was no evidence for a role of CGRP in the control of the cardiovascular system after brief intermittent maximal exercise.

Muscle power and metabolism in maximal intermittent exercise.

Muscle power and the associated metabolic changes in muscle were investigated in eight male human subjects who performed four 30-s bouts of maximal isokinetic cycling at 100 rpm, with 4-min recovery intervals. In the first bout peak power and total work were (mean +/- SE) 1,626 +/- 102 W and 20.83 +/- 1.18 kJ, respectively; muscle glycogen decreased by 18.2 mmol/kg wet wt, lactate increased to 28.9 +/- 2.7 mmol/kg, and there were up to 10-fold increases in glycolytic intermediates. External power and work decreased by 20% in both the second and third exercise periods, but no further change occurred in the fourth bout. Muscle glycogen decreased by an additional 14.8 mmol/kg after the second exercise and thereafter remained constant. Muscle adenosine triphosphate (ATP) was reduced by 40% from resting after each exercise period; creatine phosphate (CP) decreased successively to less than 5% of resting; in the recovery periods ATP and CP increased to 76 and 95% of initial resting levels, respectively. Venous plasma glycerol increased linearly to 485% of resting; free fatty acids did not change. Changes in muscle glycogen, lactate, and glycolytic intermediates suggested rate limitation at phosphofructokinase during the first and second exercise periods, and phosphorylase in the third and fourth exercise periods. Despite minimal glycolytic flux in the third and fourth exercise periods, subjects generated 1,000 W peak power and sustained 400 W for 30 s, 60% of the values recorded in the first exercise period.(ABSTRACT TRUNCATED AT 250 WORDS)