The effects of creatine supplementation on thermoregulation and isokinetic muscular performance following acute (3-day) supplementation.

AIM: The purpose of this investigation was to determine the effects of 3 d of creatine supplementation on thermoregulation and isokinetic muscular performance. METHODS: Fourteen males performed two exercise bouts following 3 d of creatine supplementation and placebo. Subjects exercised for 60 min at 60-65% of VO2max in the heat followed by isokinetic muscular performance at 60, 180, and 300°·s(-1). Dependent variables for pre- and postexercise included nude body weight, urine specific gravity, and serum creatinine levels. Total body water, extracellular water and intracellular water were measured pre-exercise. Core temperature was assessed every 5 min during exercise. Peak torque and Fatigue Index were used to assess isokinetic muscular performance. RESULTS: Core temperature increased during the run for both conditions. Total body water and extracellular water were significantly greater (P<0.05) following creatine supplementation. No significant difference (P>0.05) was found between conditions for intracellular water, nude body weight, urine specific gravity, and serum creatinine. Pre-exercise scores for urine specific gravity and serum creatinine were significantly less (P<0.05) versus post-exercise. No significant differences (P>0.05) were found in peak torque values or Fatigue Index between conditions for each velocity. A significant (P<0.05) overall velocity effect was found for both flexion and extension. As velocity increased, mean peak torque values decreased. CONCLUSION: Three d of creatine supplementation does not affect thermoregulation during submaximal exercise in the heat and is not enough to elicit an ergogenic effect for isokinetic muscle performance following endurance activity.

Effects of oral creatine and resistance training on myosin heavy chain expression.

PURPOSE: This study examined 12 wk of creatine (Cr) supplementation and heavy resistance training on muscle strength and myosin heavy chain (MHC) isoform mRNA and protein expression. METHODS: Twenty-two untrained male subjects were randomly assigned to either a control (CON), placebo (PLC), or Cr (CRT) group in a double-blind fashion. Muscle biopsies were obtained before and after 12 wk of heavy resistance training. PLC and CRT trained thrice weekly using three sets of 6-8 repetitions at 85-90% 1-RM on the leg press, knee extension, and knee curl exercises. CRT ingested 6 g.d-1 of Cr for 12 wk, whereas PLC consumed the equal concentration of placebo. RESULTS: There were no significant differences for percent body fat (P > 0.05). However, for total body mass, fat-free mass, thigh volume, muscle strength, and myofibrillar protein, CRT and PLC exhibited significant increases after training when compared to CON (P < 0.05), whereas CRT was also significantly greater than PLC (P < 0.05). For Type I, IIa, and IIx MHC mRNA expression, CRT was significantly greater than CON and PLC, whereas PLC was greater than CON (P < 0.05). For MHC protein expression, CRT was significantly greater than CON and PLC for Type I and IIx (P < 0.05) but was equal to PLC for IIa. CONCLUSION: Long-term Cr supplementation increases muscle strength and size, possibly as a result of increased MHC synthesis.

Decongestant effects on hemodynamics at rest, exercise, and recovery from exercise during--6 degrees of head down tilt.

HYPOTHESIS: Ten males were studied to examine the effects of a decongestant, pseudoephedrine hydrochloride, on rest, exercise, and recovery from exercise during -6 degrees of head down tilt (HDT). METHODS: Subjects were positioned in the HDT for a total of 6 hr: 2 hr 45 min rest, 30 min exercise, and 2 hr 45 min recovery. Sessions were identical except for the ingestion of a drug or placebo. Variables evaluated during rest, exercise, and recovery conditions were: systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR), stroke volume (SV), cardiac output (Q), pulse pressure (PP), mean arterial pressure (MAP), total peripheral resistance (TPR), and forearm blood flow (FBF). RESULTS: During rest PP at 120 min was less than resting baseline, and MAP increased throughout rest. There was a treatment effect for SBP which increased up to 90 min from resting baseline for the placebo treatment only. Normal changes were found with exercise, with all variables increasing above baseline except for TPR which decreased. DBP showed no change during exercise. During the recovery condition for the drug treatment HR decreased, while SBP increased from 30 min. In addition, DBP and MAP were higher for the placebo at 30 min and higher for the drug at 90 min. CONCLUSION: The results show that ingestion of the sympathomimetic agent pseudoephedrine hydrochloride has no significant effects on the cardiovascular system during simulated microgravity.

The effect of submaximal exercise on recovery hemodynamics and thermoregulation in men and women.

Five women and 5 men were studied to examine the effects of submaximal exercise on thermoregulatory and hemodynamic variables during recovery in two environments: (a) control (C), 22 degrees C, 33% rh; and (b) hot humid (H), 32 degrees C. The participants exercised on a cycle ergometer at 60% of peak oxygen consumption for 35 min prior to 90 min of seated recovery. Sessions were identical, except for environment. Variables evaluated (p < .05) were: core temperature (TR), mean skin temperature (Ts), sweat rate (SR), heart rate (HR), stroke index (SI), cardiac index (CI), forearm blood flow (FBF), systolic blood pressure (SBP), and diastolic blood pressure (DBP). Men and women exhibited similar patterns of TR, Ts, and SR in both environments. Ts and SR (collapsed means for gender) were higher in the H than in the C. DBP was higher in men than in women throughout recovery in both environments. With combined means for gender, HR was higher in the H than in the C. CI, SI, FBF, and SBP were similar in both environments and returned to baseline within 15 min into recovery. These data suggest that heat dissipation during extended recovery was accomplished with similar contributions of cutaneous vasodilation and sweating in M and F. Furthermore, the moderate exercise level did not influence hemodynamics beyond 15 min of recovery in either environment.

Anterior tibial translation in collegiate athletes with normal anterior cruciate ligament integrity.

OBJECTIVE: To examine differences in anterior tibial translation (ATT) among sports, sex, and leg dominance in collegiate athletes with normal anterior cruciate ligament integrity. DESIGN AND SETTING: Subjects from various athletic teams were measured for ATT in right and left knees. SUBJECTS: Sixty subjects were measured for ATT with a KT-1000 knee arthrometer. MEASUREMENTS: Statistical analyses were computed for each sex and included a 2 x 3 x 4 mixed-factorial analysis of variance (ANOVA) for anterior cruciate ligament displacement, right and left sides, and force and sport. A 2 x 2 x 3 mixed-factorial ANOVA was computed to compare means for sex and force. A 2 x 3 mixed-factorial ANOVA was computed to compare sex differences across 3 forces. RESULTS: For males and females, no significant interactions were found among leg, force, and sport for mean ATT, for leg and sport or leg and force, or for translation values between dominant and nondominant legs. Males had a significant interaction for force and sport, and a significant difference was found for side of body, since the right side had less translation than the left side. Females had greater ATT than males at all forces. CONCLUSIONS: Sex differences exist for ATT, and differences in ATT exist among sports for both sexes. Differences between the right and left sides of the body should be expected when making comparisons of ligamentous laxity.