Effects of caffeine on repeated sprint ability, reactive agility time, sleep and next day performance.

AIM: This study assessed the effects of caffeine on repeated sprint ability (RSA), reactive agility time (RAT), sleep and next day exercise performance. METHODS: Ten moderately trained male athletes (single-blind, randomized, crossover design) ingested either caffeine (6 mg.kg-1 bm) or placebo 1 h before exercise. Trials were performed on the same day one week apart. Performance measures included a RAT test (10 trials¥10.2 m, separated by 30 s), followed by 7 min of active recovery and then a RSA test (five sets of 6¥20 m sprints with 25 or 60 s of recovery). The RSA was then followed by 5 min of active recovery and another RAT. That night, participants wore a wrist sleep actigraph to bed. Next day, participants repeated the RAT and the first set of the RSA tests. RESULTS: Significant improvements were demonstrated after caffeine ingestion compared to placebo for the combined total time of each set (TT; combined sets 1, 3, 5; 58.947±1.88 vs. 59.683±2.54 s, respectively; P=0.05), best sprint time (BT; next day performance; 3.176±0.10 vs. 3.230±0.12 s, respectively, P=0.01), and % decrement (combined sets 2, 4; 2.866±1.24 vs. 3.801±1.69 s, respectively; P=0.02). Moderate to strong effect sizes were found for % decrement for set 2 (Cohen's d=-0.82; 1.312±0.65 vs. 2.110±1.20 s for caffeine and placebo conditions, respectively) and for sets 2 and 4 combined (Cohen's d=-0.63; 2.866±1.24 vs. 3.801±1.69 for caffeine and placebo conditions, respectively). No significant differences were found for RAT or for sleep measures (P>0.05). CONCLUSION: Caffeine improved RSA, including next day performance, but had little effect on RAT or sleep parameters.

Generic versus small-sided game training in soccer.

The aim of this study was to compare 7 weeks of soccer-specific small-sided game (SSG) and mixed generic fitness training, on selected physiological, perceptual and performance variables. Twenty-five elite youth players were randomly allocated to either a SSG (coach selected) or generic training group (GTG), in a randomised, parallel matched-group design. In addition to normal training, each group completed two fitness training sessions per week of equal duration. Players completed a V O (2 max) treadmill test, Multistage Fitness Test (MSFT), Yo-Yo Intermittent Recovery Test Level 1 (YYIRTL1), 12x20 m test of repeated-sprint ability (RSA) and 20-m sprint test pre and post training. Training heart rate, perceived training intensity and perceptual fatigue measures were recorded throughout the training period. There were no differences in training heart rate or perceptual well-being measures. However, the GTG did perceive their training to be more intense than SSG. There were no changes in either group for V O (2 max), MSFT, RSA or sprint performance. However, there were improvements in YYIRTL1 performance for both groups over time, but not between groups. The results show that both types of training are equally effective at improving pre-season YYIRTL1 performance, despite GTG being perceived to be more intense.

Anaerobic ATP production and accumulated O2 deficit in cyclists.

Anaerobic ATP production in skeletal muscle and the accumulated oxygen deficit (O2D) incurred during an exhaustive cycle bout (duration = 173 +/- 24 s; intensity = 112 +/- 3% VO2peak), were determined in 10 male cyclists (mean +/- SD: VO2peak = 69.8 +/- 4.2 ml.kg-1.min-1). Anaerobic ATP production (mmol.kg-1 d.w.) was determined from changes in lactate, phosphocreatine, ATP, and ADP in vastus lateralis. Muscle buffer value and the activities of glycogen phosphorylase (PHOS), phosphofructokinase and citrate synthase (CS) were also determined. The anaerobic ATP production determined from measured muscle metabolites was 202.7 +/- 46.9 mmol.kg-1 d.w. and was correlated (P < or = 0.05) with muscle buffer value (r = 0.81), PHOS (r = 0.69) and the ratio of PHOS to CS activity (r = 0.77). The O2D was 55.2 +/- 10.3 ml O2 Eq.kg-1, but was not correlated (P > 0.05) with anaerobic ATP production (r = -0.38), buffer value (r = -0.50) or PHOS (r = -0.39). These latter findings could be explained by error in measuring the O2D and/or muscle anaerobic ATP production in well-trained cyclists.

Methodological effects on the VO2-power regression and the accumulated O2 deficit.

The VO2-power regression and O2 demand predicted for a supra-VO2peak intensity (i.e., 432 W) were determined in seven well-trained male cyclists (mean +/- SD: VO2peak = 5.29 +/- 0.51 l.min-1), using five incremental exercise protocols. These protocols were either continuous (CON) or discontinuous (DISCON), and comprised five to eight work bouts ranging in intensity between 40% and 85% VO2peak; the work bouts differed in duration (4-15 min), and the VO2 was measured during the 4th minute (CON4, DISCON4), from min 4 to 6 (DISCON6), 8 to 10 (DISCON10), or 13 to 15 (DISCON15) of each work bout. The y-intercepts of the VO2-power regressions were not different (P > 0.05), whereas the slope was higher (P < or = 0.01) when determined using DISCON10 (12.7 +/- 0.9 ml.min-1.W-1) and DISCON15 (12.5 +/- 0.9 ml.min-1.W-1) compared with DISCON6 (12.2 +/- 1.0 ml.min-1.W-1), DISCON4 (11.6 +/- 1.1 ml.min-1.W-1) or CON4 (11.9 +/- 0.7 ml.min-1.W-1). The O2 demand (at 432 W) was also higher (P < or = 0.01) for DISCON10 (6.05 +/- 0.29 l.min-1) and DISCON15 (6.05 +/- 0.28 l.min-1) compared with DISCON6 (5.88 +/- 0.31 l.min-1), DISCON4 (5.70 +/- 0.31 l.min-1) and CON4 (5.82 +/- 0.25 l.min-1). This demonstrates that the O2 demand predicted for high power outputs depends on the incremental protocol used.

The Y-intercept of the maximal work-duration regression and field tests of anaerobic capacity in cyclists.

The purpose of the present study was to provide initial data upon which field tests of anaerobic capacity for cyclists might be developed, by examining the relationships between the y-intercept of the maximal work-duration regression (Y-int) and cycle performance variables in fifteen well-trained male cyclists (mass = 73.3 +/- 8.6 kg; VO2peak = 4.93 +/- 0.70 l.min-1). The Y-int was determined from three maximal supra-VO2peak cycle bouts varying in duration from 195 to 369 s. Each cyclist performed two performance tests: 1) an all-out cycle sprint over 1000 m (AOS) during which the accumulated time over intervals of 125 m (e.g., AOS125, AOS250, etc. was recorded; 2) a 2-by-2000 m ride from which an "anaerobic distance" (Anl) was determined as the product of anaerobic speed (i.e. average speed during a second, maximal 2000 m time-trial minus the average speed during a 20 km time-trial) and time taken to complete the maximal 2000 m ride. The frontal area (FA) of each cyclist and common values for air density, work efficiency and the drag coefficient were used to estimate the energy equivalent of Anl. The Y-int was 20.0 +/- 9.4 kJ or 278 +/- 128 J.kg-1. The Y-int (J.FA-1) was correlated (p < or = 0.05) with AOS250 (r = -0.50), AOS375 (r = -0.53) and AOS625 (r = -0.50) which were 21.5 +/- 1.1 s, 30.1 +/- 1.3 s and 47.5 +/- 1.9 s long, respectively. The Y-int (kJ) was also correlated with AOS375 (r = -0.51), but Y-int (kJ) was not correlated with a performance variable lasting longer than approximately 30 s. The energy equivalent of Anl (91.5 +/- 26.0 kJ) was similar to the energy equivalent for Y-int (90.9 +/- 43 kJ), although these two variables were not significantly correlated. However, given the potential sources of variance in determining both of these variables, their quantitative similarity provides limited evidence supporting the use of Anl to estimate anaerobic capacity. The results also support the use of an all-out sprint performance lasting between 20-30 s to best reflect anaerobic work capacity in cyclists.

The oxygen uptake-power regression in cyclists and untrained men: implications for the accumulated oxygen deficit.

The regression of oxygen uptake (VO2) on power output and the O2 demand predicted for suprapeak oxygen uptake (VO2peak) exercise (power output = 432 W) were compared in ten male cyclists [C, mean VO2peak = 67.9 (SD 4.2) ml.kg-1.min-1] and nine active, yet untrained men [UT, mean VO2peak = 54.1 (SD 6.5) ml.kg-1.min-1]. The VO2-power regression was determined using a continuous incremental cycle test (CON4), performed twice, which comprised several 4-min exercise periods progressing in intensity from approximately 40%-85% VO2peak. Minute ventilation (VE), heart rate (HR), respiratory exchange ratio (R), blood lactate concentration ([la-]b) and rectal temperature (Tre) were measured at rest and during CON4. The slope of the VO2-power regression was greater (P < or = 0.05) in C [12.4 (SD 0.7) ml.min-1.W-1] compared to UT [11.7 (SD 0.4) ml.min-1.W-1]; as a result, the O2 demand (at 432 W) was also higher (P < or = 0.05) in C [5.97 (SD 0.23) l.min-1] than UT [5.70 (SD 0.15) l.min-1]. Exercise R and [la-]b were lower (P < or = 0.05) in C in comparison to UT at all power outputs, whereas VE and HR were relatively lower (P < or = 0.05) in C at power outputs approximating 180 W, 220 W and 270 W. Differences in fat metabolism estimated over the first three power outputs accounted for approximately 19% of the difference in VO2-power slopes between the groups and up to 46% of the difference in VO2 at a given intensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Y-intercept of the maximal work-duration relationship and anaerobic capacity in cyclists.

The degree to which the y-intercept (Y-int) of the linear regression of maximal work output on exercise duration represented anaerobic capacity was determined in ten well-trained male cyclists [peak oxygen uptake (VO2peak) = 69.8 (SD 4.2) ml.kg-1.min-1]. Each cyclist performed three exhausting cycle sessions on separate occasions; the mean exercise durations were 312, 243 and 141 s for the low (approximately 104% VO2peak), medium (approximately 108% VO2peak) and high (approximately 113% VO2peak) intensities respectively, and Y-int (kilojoules; joules per kilogram) was derived from the regression of work output on exercise duration. The muscle anaerobic adenosine 5'-triphosphate (ATP) yield (sigma ATP) and anaerobic capacity (AC) were estimated from changes in metabolites in the vastus lateralis muscle and blood lactate concentration during the high intensity cycling session. The activities of glycogen phosphorylase, phosphofructokinase and citrate synthase, as well as muscle buffer value (in vitro beta) were also determined. The Y-int (kilojoules) was positively correlated (P < or = 0.05) with AC (r = 0.73), sigma ATP (r = 0.70) and in vitro beta (r = 0.71); similar correlations (P < or = 0.05) were observed for Y-int (joules per kilogram). The Y-int was not correlated (P > 0.05) with any enzyme activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of mesomorphy on hyperthermia during exercise in a warm, humid environment.

The hyperthermic response to exercise in a warm (30 degrees C), humid (80% relative humidity) environment was obtained for 27 men who exhibited a wide range of body physique in terms of the mesomorphy component of somatotype. Increase in tympanic temperature (Yty) was significantly dependent on mesomorphy rating (X) according to the regression equation Yty = -0.390 + 0.088X. Increase in rectal temperature (Yre) was also significantly dependent on mesomorphy rating according to the equation Yre = -0.100 + 0.066X. The hyperthermic response was significantly correlated with other measures of physique, including ectomorphy, surface area/weight ratio, and body weight, but was not correlated with fatness or fitness. The results support the generalization that during exercise in a warm, humid environment individual differences in heat strain can be highly dependent on physique, especially if fitness and fatness are similar. In this context, mesomorphy appears to provide the optimum description of physique variation. Individuals with a mesomorphy rating greater than 7 warrant designation as being at high risk for heat intolerance during exercise in environments that significantly impair the rate of body heat loss.