An orphan nuclear receptor activated by pregnanes defines a novel steroid signaling pathway

PURPOSE: To determine the effects of 28 d of creatine supplementation during training on body composition, strength, sprint performance, and hematological profiles. METHODS: In a double-blind and randomized manner, 25 NCAA division IA football players were matched-paired and assigned to supplement their diet for 28 d during resistance/agility training (8 h x wk[-1]) with a Phosphagen HP (Experimental and Applied Sciences, Golden, CO) placebo (P) containing 99 g x d(-1) of glucose, 3 g x d(-1) of taurine, 1.1 g x d(-1) of disodium phosphate, and 1.2 g x d(-1) of potassium phosphate (P) or Phosphagen HP containing the P with 15.75 g x d(-1) of HPCE pure creatine monohydrate (HP). Before and after supplementation, fasting blood samples were obtained; total body weight, total body water, and body composition were determined; subjects performed a maximal repetition test on the isotonic bench press, squat, and power clean; and subjects performed a cycle ergometer sprint test (12 x 6-s sprints with 30-s rest recovery). RESULTS: Hematological parameters remained within normal clinical limits for active individuals with no side effects reported. Total body weight significantly increased (P < 0.05) in the HP group (P 0.85 +/- 2.2; HP 2.42 +/- 1.4 kg) while no differences were observed in the percentage of total body water. DEXA scanned body mass (P 0.77 +/- 1.8; HP 2.22 +/- 1.5 kg) and fat/bone-free mass (P 1.33 +/- 1.1; HP 2.43 +/- 1.4 kg) were significantly increased in the HP group. Gains in bench press lifting volume (P -5 +/- 134; HP 225 +/- 246 kg), the sum of bench press, squat, and power clean lifting volume (P 1,105 +/- 429; HP 1,558 +/- 645 kg), and total work performed during the first five 6-s sprints was significantly greater in the HP group. CONCLUSION: The addition of creatine to the glucose/taurine/electrolyte supplement promoted greater gains in fat/bone-free mass, isotonic lifting volume, and sprint performance during intense resistance/agility training.     

Effect of sodium bicarbonate ingestion on exhaustive resistance exercise performance

Six weight trained males were studied prior to, during, and in recovery from exhaustive resistance exercise, 105 min after ingesting 300 mg.kg-1 of either a placebo or NaHCO3. The exercise test consisted of four sets of 12 repetitions with a fifth set to volitional fatigue on a Universal leg press machine at a resistance equaling approximately 70% of the subjects 1-repetition maximum. Arterialized venous blood was analyzed for lactate concentration, blood gas, and acid-base parameters. The ingestion of NaHCO3 produced a significant increase in resting pH (7.39 to 7.46), HCO3- (22.9 to 28.3 mEq.l-1), and oxygenated base excess (-1.3 to 4.4 mEq.l-1). With the completion of each exercise set, a progressive decline in the acid-base status of both groups was observed (pH set 1-5: NaHCO3, 7.40 to 7.31; placebo, 7.34 to 7.25; HCO3- set 1-5: NaHCO3, 25.3 to 17.9; placebo, 21.7 to 15.3 mEq.l-1; base excess set 1-5: NaHCO3, 3.7 to -7.1; placebo, -1.4 to -10.7 mEq.l-1); however, the NaHCO3 condition was significantly more alkaline than the placebo condition. Blood lactate concentration [La] progressively increased with the completion of each exercise set ([La] set 1-5: NaHCO3, 1.37 to 11.15; placebo, 1.31 to 9.81 mM); but were not significantly different between treatments. Repetitions performed in the final exercise set were not significantly different between groups (NaHCO3: 19.6 +/- 1.6, placebo: 18.2 +/- 1.1 repetitions).(ABSTRACT TRUNCATED AT 250 WORDS)     

Prognostic factors for musculoskeletal sickness absence and return to work among welders and metal workers

The effect of creatine loading on endurance capacity and sprint performance was investigated in elite cyclists according to a double-blind cross-over study design. Subjects (n = 12) underwent on 3 occasions and separated by 5 week wash-out periods, a 2 h 30 min standardized endurance protocol on their own race bicycle, which was mounted on an electromagnetically braked roller-system, whereupon they cycled to exhaustion at their predetermined 4 mmol lactate threshold. Immediately thereafter they performed 5 maximal 10 second sprints, separated by 2 min recovery intervals, on a Monark bicycle ergometer at 6 kg resistance on the flywheel. Before the exercise test, subjects were either creatine loaded (C: 25 g creatine monohydrate/day, 5 days) or were creatine loaded plus ingested creatine during the exercise test (CC: 5 g/h), or received placebo (P). Compared with P, C but not CC increased (p<0.05) peak and mean sprint power output by 8-9% for all 5 sprints. Endurance time to exhaustion was not affected by either C or CC. It is concluded that creatine loading improves intermittent sprint capacity at the end of endurance exercise to fatigue. This ergogenic action is counteracted by high dose creatine intake during exercise.     

Creatine supplementation and exercise performance: an update

Creatine, a natural nutrient found in animal foods, is alleged to be an effective nutritional ergogenic aid to enhance sport or exercise performance. Research suggests that oral creatine monohydrate supplementation may increase total muscle creatine [TCr], including both free creatine [FCr] and phosphocreatine [PCr]. Some, but not all, studies suggest that creatine supplementation may enhance performance in high-intensity, short-term exercise tasks that are dependent primarily on PCr (i.e., < 30 seconds), particularly laboratory tests involving repeated exercise bouts with limited recovery time between repetitions; additional corroborative research is needed regarding its ergogenic potential in actual field exercise performance tasks dependent on PCr. Creatine supplementation has not consistently been shown to enhance performance in exercise tasks dependent on anaerobic glycolysis, but additional laboratory and field research is merited. Additionally, creatine supplementation has not been shown to enhance performance in exercise tasks dependent on aerobic glycolysis, but additional research is warranted, particularly on the effect of chronic supplementation as an aid to training for improvement in competitive performance. Short-term creatine supplementation appears to increase body mass in males, although the initial increase is most likely water. Chronic creatine supplementation, in conjunction with physical training involving resistance exercise, may increase lean body mass. However, confirmatory research data are needed. Creatine supplementation up to 8 weeks has not been associated with major health risks, but the safety of more prolonged creatine supplementation has not been established. Creatine is currently legal and its use by athletes is not construed as doping.     

Stimulation of insulin release and potentiation of the insulinotropic action of antidiabetic agents by 1,2,3-tri(methylsuccinyl)glycerol ester in anaesthetized rats

The study was designed to investigate the effect of creatine monohydrate ingestion (20 g daily for 5 days) on performance in 45 s maximal continuous jumping and in all-out treadmill running at 20 km x h(-1), (inclination 5 degrees, duration approximately 60s). The participants were qualified sprinters and jumpers. The effect of creatine was compared with placebo in a double-blind design. Creatine (Cr) supplementation led to a significant enhancement of performance capacity in the jumping test by 7% during the first 15 s and by 12% during the second 15 s of the exercise. The positive effect of Cr supplementation was not observed in the last third of the continuous jumping exercise, when the contribution of anaerobic metabolism was decreasing. The time of intensive running up to exhaustion improved by 13%. The results show that Cr supplementation helps to prolong the time during which the maximal rate of power output could be maintained.     

The breast cancer screening controversy and the National Institutes of Health Consensus Development Conference on Breast Cancer Screening for Women Ages 40-49

PURPOSE: Unaccustomed exercise is associated with an elevated plasma creatine kinase (CK), myofibrillar inflammation, and delayed onset muscle soreness (DOMS). Nonsteroidal antiinflammatory drugs (NSAID) may attenuate DOMS and indirect indices of inflammation in humans. METHODS: We studied the effects of an NSAID (naproxen sodium (500 mg, 2 times a day for 48 h)) taken before and after resistance exercise in eight healthy, moderately trained men in a randomized, double-blind trial. The exercise consisted of unilateral knee concentric/eccentric weight lifting with 6 sets x 10 repetitions at 80-85% of the 1 repetition maximal contraction. Muscle biopsies of each vastus lateralis (EX = exercised/REST = control) were taken 24 h after exercise for immunohistochemical staining of inflammatory cells (leukocyte common antigen). At 24 and 48 h postexercise, we also determined DOMS, plasma CK activity, and knee extensor muscle torque. RESULTS: Exercise resulted in an increased CK activity at +24 and +48 h (vs preexercise: P < 0.01), with no treatment effect. There were no treatment effects for any of the measured variables except for a return of voluntary knee extension torque to baseline by +48 h postexercise for NSAID treatment (P < 0.05). CONCLUSIONS: NSAID administration did not alter CK rise, muscle force deficit at 24 h postexercise, nor perceived muscle pain. In addition, the increased CK at 24 h postexercise was not associated with an acute myofibrillar inflammatory cell infiltrate in moderately trained men after resistance exercise.     

Hormonal responses to consecutive days of heavy-resistance exercise with or without nutritional supplementation

Nine resistance-trained men consumed either a protein-carbohydrate supplement or placebo for 1 wk in a crossover design separated by 7 days. The last 3 days of each treatment, subjects performed resistance exercise. The supplement was consumed 2 h before and immediately after the workout, and blood was obtained before and after exercise (0, 15, 30, 45, and 60 min postexercise). Lactate, growth hormone, and testosterone were significantly (P 相似文献   

Effect of glucose supplement timing on protein metabolism after resistance training

We determined the effect of the timing of glucose supplementation on fractional muscle protein synthetic rate (FSR), urinary urea excretion, and whole body and myofibrillar protein degradation after resistance exercise. Eight healthy men performed unilateral knee extensor exercise (8 sets/approximately 10 repetitions/approximately 85% of 1 single maximal repetition). They received a carbohydrate (CHO) supplement (1 g/kg) or placebo (Pl) immediately (t = 0 h) and 1 h (t = +1 h) postexercise. FSR was determined for exercised (Ex) and control (Con) limbs by incremental L-[1-13C]leucine enrichment into the vastus lateralis over approximately 10 h postexercise. Insulin was greater (P < 0.01) at 0.5, 0.75, 1.25, 1.5, 1.75, and 2 h, and glucose was greater (P < 0.05) at 0.5 and 0.75 h for CHO compared with Pl condition. FSR was 36.1% greater in the CHO/Ex leg than in the CHO/Con leg (P = not significant) and 6.3% greater in the Pl/Ex leg than in the Pl/Con leg (P = not significant). 3-Methylhistidine excretion was lower in the CHO (110.43 +/- 3.62 mumol/g creatinine) than P1 condition (120.14 +/- 5.82, P < 0.05) as was urinary urea nitrogen (8.60 +/- 0.66 vs. 12.28 +/- 1.84 g/g creatinine, P < 0.05). This suggests that CHO supplementation (1 g/kg) immediately and 1 h after resistance exercise can decrease myofibrillar protein breakdown and urinary urea excretion, resulting in a more positive body protein balance.     

State anxiety and ambulatory blood pressure following resistance exercise in females

The purpose of this investigation was to examine state anxiety and blood pressure responses during ambulatory recovery from resistance exercise. Fourteen females completed three separate bouts of resistance exercise in which the sets (N = 3), repetitions (N = 10), exercise type (knee extension, knee flexion, arm pull down, chest press, shoulder press, and abdominal curl), and time (30 min) were held constant, but the intensity was manipulated to equal 40%, 60%, and 80% of the 10-repetition maximum for each exercise. Immediately before as well as 1, 15, 30, 45, 60, 75, 90, 105, and 120 min following the cessation of exercise blood pressure and heart rate were assessed. State anxiety assessments were initiated immediately following blood pressure measurements. The subjects were ambulatory during the post-exercise period, and information about body posture during the cardiovascular assessments was obtained. MANOVAs, ANOVAs, and Tukey tests revealed that post-exercise state anxiety levels were reduced compared with pre-exercise values from 90 to 120 min following exercise. Systolic blood pressure was elevated at 1 and 15 min following the 80% intensity condition, and at 1 min following the 60% intensity condition. It is concluded that during ambulatory recovery from resistance exercise: 1) reductions in state anxiety are realized; and 2) systolic blood pressure, in contrast to what has been shown to occur following aerobic exercise, is not reduced.     

Skeletal muscle fiber type, resistance training, and strength-related performance

The research goal was to attempt to clarify the consequences of increased strength on performance at submaximal exercise intensities. Eight subjects (4 males, 4 females) completed a 3-d.wk-1, 16-wk resistance training regimen. After training, upper (bench press, BP) and lower (parallel squat, PS) extremity strength were increased by 23% and 37%, respectively. Performance at the same absolute work rates as before training was increased by 30-159% following training depending on intensity and type of exercise. Performance at the same relative work rates (80%, 60%, 40%) remained unchanged by the training for both exercises. Prior to training, PS repetitions at 40% were correlated (r = 0.69, P < 0.05) with the percentage of slow-twitch (ST) fibers in the vastus lateralis muscle. There were similar relationships at 40% (r = 0.73) and at 60% (r = 0.83) for the PS exercise after training. However, the resistance program did not result in greater relative submaximal performance in individuals with a higher percentage of ST fibers. We conclude that strength improvement of up to 40% does not produce a strength-related performance deficit, when training and testing procedures are identical. Yet, these data do not rule out the potential of a strength-related repetition performance deficit. When subjects were equally divided by strength levels, those tested at the highest absolute resistance had significantly lower bench press repetition performance at 60% and 40% of the 1-RM than the subjects tested at the lowest absolute resistance.     

Effect of fluid ingestion on muscle metabolism during prolonged exercise

Five trained men were studied during 2 h of cycling exercise at 67% peak oxygen uptake at 20-22 degrees C to examine the effect of fluid ingestion on muscle metabolism. On one occasion, the subjects completed this exercise without fluid ingestion (NF) while on the other they ingested a volume of distilled deionized water that prevented loss of body mass (FR). No differences in oxygen uptake during exercise were observed between the two trials. Heart rate was lower (P < 0.01) throughout exercise when fluid was ingested, and rectal temperature after 2 h of exercise was lower (38.0 +/- 0.2 and 38.6 +/- 0.2 degrees C for FR and NF, respectively; P < 0.01), as was muscle (vastus lateralis) temperature (38.5 +/- 0.4 and 39.1 +/- 0.5 degrees C for FR and NF, respectively; P < 0.05). Resting muscle ATP, creatine phosphate, creatine, glycogen, and lactate levels were similar in the two trials, as were the postexercise ATP, creatine phosphate, and creatine levels. In contrast, muscle glycogen was higher (P < 0.05) and muscle lactate was lower (P < 0.05) after 2 h of exercise in FR compared with NF. Net muscle glycogen utilization during exercise was reduced by 16% when fluid was ingested (318 +/- 46 and 380 +/- 53 mmol/kg dry weight for FR and NF, respectively; P < 0.05). These results indicate that fluid ingestion reduces muscle glycogen use during prolonged exercise, which may account, in part, for the improved performance previously observed with fluid ingestion.     

Effect of postexercise carbohydrate supplementation on muscle glycogen repletion in trained sled dogs

OBJECTIVE: To evaluate the effect of immediate postexercise carbohydrate supplementation on muscle glycogen (MG) repletion during the first 4 hours of recovery in sled dogs. ANIMALS: 24 Alaskan Huskies. PROCEDURE: Dogs were assigned to 1 of 3 treatment groups, and a muscle biopsy specimen was obtained 1 hour before and immediately (group A) or 4 hours (groups B and C) after a 30-km run. Immediately after exercise, dogs in group A and group C were given water; dogs in group B were given a glucose polymer solution (1.5 g/kg of body weight) in water. RESULTS: At 4 hours after exercise, MG concentration was significantly greater in group-B than in group-C dogs; the value in group-C dogs was not different from the value in group-A dogs immediately after exercise. Assuming similar rates of glycogen depletion between treatment groups, during the first 4 hours of recovery, group-B dogs replaced 49% of the glycogen used during exercise. Plasma glucose concentration was significantly greater in group-B than in group-A and group-C dogs at 100 minutes after exercise. CONCLUSIONS: Immediate postexercise carbohydrate supplementation in sled dogs leads to increased glucose concentration, which in turn promotes more rapid rate of MG repletion in the first 4 hours of recovery than is observed in dogs not given supplements. CLINICAL RELEVANCE: For dogs running in multiple heats on a single day or over several consecutive days, immediate postexercise carbohydrate supplementation may promote more rapid and complete recovery between bouts of exercise.     

Effects of cross-training on markers of insulin resistance/hyperinsulinemia

This study examined, through a randomized controlled trial, the effects of cross-training (combined resistance and endurance exercise) on markers of insulin resistance, (e.g., dyslipidemia, intra-abdominal obesity, hyperinsulinemia, and hypertension), body composition, and performance in hyperinsulinemic individuals. Sedentary adult males characterized as hyperinsulinemic (fasting insulin > 2 OuU.mL-1), randomly assigned to two groups (N = 8 each), completed 14 wk of training at 3 d.wk-1. An endurance-only (E) group performed both continuous cycle exercise and walking (30 min each at 60-70% heart rate reserve). A cross-training (C) group performed both endurance and resistance exercise (8 exercises, 4 sets/exercise, 8-12 repetitions/set) in a single session. Both E and C groups demonstrated similar increases in VO2max (25% and 27%) while only C demonstrated an increase in 1 RM bench press (19%) and leg press (25%). The changes induced by C training were significantly greater than those from E training alone in percent fat (6.9 +/- 1.3 vs 1.4 +/- 1.4), insulin concentration (8.5 +/- 2.7 vs 3.0 +/- 1.3 uU.mL-1), glucose levels (11.1 +/- 2.9 vs 5.9 +/- 2.6 mg.dL-1), HDL-C levels (5.1 +/- 1.3 vs 2.9 +/- 1.6 mg.dL-1), triglyceride concentration (43.8 +/- 13.6 mg.dL-1), and systolic blood pressure (14.6 +/- 5.5 vs 8.3 +/- 6.8 mm Hg). Results indicate that the addition of resistance training to an endurance training program will induce significantly greater differences in markers of insulin resistance and body composition in individuals with hyperinsulinemia than endurance training alone.     

Creatine supplementation and age influence muscle metabolism during exercise

Young [n = 5, 30 +/- 5 (SD) yr] and middle-aged (n = 4, 58 +/- 4 yr) men and women performed single-leg knee-extension exercise inside a whole body magnetic resonance system. Two trials were performed 7 days apart and consisted of two 2-min bouts and a third bout continued to exhaustion, all separated by 3 min of recovery. 31P spectra were used to determine pH and relative concentrations of Pi, phosphocreatine (PCr), and beta-ATP every 10 s. The subjects consumed 0.3 g . kg-1 . day-1 of a placebo (trial 1) or creatine (trial 2) for 5 days before each trial. During the placebo trial, the middle-aged group had a lower resting PCr compared with the young group (35.0 +/- 5.2 vs. 39.5 +/- 5.1 mmol/kg, P < 0.05) and a lower mean initial PCr resynthesis rate (18.1 +/- 3.5 vs. 23.2 +/- 6.0 mmol . kg-1 . min-1, P < 0.05). After creatine supplementation, resting PCr increased 15% (P < 0.05) in the young group and 30% (P < 0.05) in the middle-aged group to 45.7 +/- 7.5 vs. 45.7 +/- 5.5 mmol/kg, respectively. Mean initial PCr resynthesis rate also increased in the middle-aged group (P < 0.05) to a level not different from the young group (24.3 +/- 3.8 vs. 24.2 +/- 3.2 mmol . kg-1 . min-1). Time to exhaustion was increased in both groups combined after creatine supplementation (118 +/- 34 vs. 154 +/- 70 s, P < 0.05). In conclusion, creatine supplementation has a greater effect on PCr availability and resynthesis rate in middle-aged compared with younger persons.     

Effect of systemic versus topical nonsteroidal anti-inflammatory drugs on postexercise jaw-muscle soreness: a placebo-controlled study

Certain types of jaw-muscle pain may be managed with pharmacologic treatment. This study evaluated the effect of topical and systemic nonsteroidal anti-inflammatory drugs on acute postexercise jaw-muscle soreness. Ten men without temporomandibular disorders performed six 5-minute bouts of submaximal eccentric jaw exercise. The outcome variables were pressure pain thresholds and pain tolerance thresholds at the masseter muscles, and maximum voluntary occlusal force. Surface electromyography from the masseter muscles was used to assess the development of muscle fatigue during the exercise period. Three treatment modalities were tested in a placebo-controlled, double-blind approach: (A) placebo gel and placebo tablets; (B) nonsteroidal anti-inflammatory drug gel (2 g, 5% ibuprofen) and placebo tablets; and (C) placebo gel and nonsteroidal anti-inflammatory drug tablets (400 mg ibuprofen). The subjects used their medication 3 times a day for 3 days in the postexercise period. In the exercise period, the mean power frequency of the electromyography signal, pressure pain threshold, pain tolerance threshold, and maximum voluntary occlusal force decreased significantly (analysis of variance, P < .01). In the postexercise period, the effect of treatment on pressure pain thresholds was significant (F[2,9] = 4.41, P = .02). On day 3, treatment with topical nonsteroidal anti-inflammatory drugs was associated with significantly higher pressure pain thresholds as compared to treatment with systemic nonsteroidal anti-inflammatory drugs (P < .05) and placebo (P < .05). Treatment effects on pain tolerance thresholds and on maximum voluntary occlusal force were nonsignificant. The results demonstrated that repeated eccentric jaw exercise caused muscle fatigue and low levels of postexercise pain and soreness. Topical nonsteroidal anti-inflammatory drugs seem to have some advantages over systemic nonsteroidal anti-inflammatory drugs for management of exercise-induced jaw-muscle pain.     

Responses of IGF-I to endogenous increases in growth hormone after heavy-resistance exercise

The purpose of this study was to examine the effects of a heavy-resistance exercise protocol known to dramatically elevate immunoreactive growth hormone (GH) on circulating insulin-like growth factor I (IGF-I) after the exercise stimulus. Seven men (23.1 +/- 2.4 yr) volunteered to participate in this study. Each subject was asked to perform an eight-station heavy-resistance exercise protocol consisting of 3 sets of 10 repetition maximum resistances with 1-min rest between sets and exercises followed by a recovery day. In addition, a control day followed a nonexercise day to provide baseline data. Pre- and postexercise (0, 15, and 30 min) blood samples were obtained and analyzed for lactate, creatinine kinase, GH, and IGF-I. Postexercise values for lactate and GH were significantly (P < 0.05) elevated above preexercise and resting baseline values. The highest mean GH concentration after the heavy-resistance exercise protocol was 23.8 +/- 11.8 micrograms/l, observed at the immediate postexercise time point. Significant increases in creatine kinase were observed after the exercise protocol and during the recovery day. No significant relationships were observed between creatine kinase and IGF-I concentrations. No significant changes in serum IGF-I concentrations were observed with acute exercise or between the recovery and control days. Thus, these data demonstrate that a high-intensity bout of heavy-resistance exercise that increases circulating GH did not appear to affect IGF-I concentrations over a 24-h recovery period in recreationally strength-trained and healthy young men.     

Effects of different heavy-resistance exercise protocols on plasma beta-endorphin concentrations

To examine the changes of plasma beta-endorphin (beta-EP) concentrations in response to various heavy-resistance exercise protocols, eight healthy male subjects randomly performed each of six heavy-resistance exercise protocols, which consisted of identically ordered exercises carefully designed to control for the repetition maximum (RM) resistance (5 vs. 10 RM), rest period length (1 vs. 3 min), and total work (joules). Plasma beta-EP, ammonia, whole blood lactate and serum cortisol, creatine kinase, urea, and creatinine were determined preexercise, midexercise, immediately postexercise, and at various time points after the exercise session (5 min-48 h), depending on the specific blood variable examined. Only the high total work-exercise protocol [1 min rest, 10 RM load (H10/1)] demonstrated significant increases in plasma beta-EP and serum cortisol at midexercise and 0, 5, and 15 min postexercise. Increases in lactate were observed after all protocols, but the largest increases were observed after the H10/1 protocol. Within the H10/1 protocol, lactate concentrations were correlated (r = 0.82, P < 0.05) with plasma beta-EP concentrations. Cortisol increases were significantly correlated (r = 0.84) with 24-h peak creatine kinase values. The primary finding of this investigation was that beta-EP responds differently to various heavy-resistance exercise protocols. In heavy-resistance exercise, it appears that the duration of the force production and the length of the rest periods between sets are key exercise variables that influence increases in plasma beta-EP and serum cortisol concentrations. Furthermore the H10/1 protocol's significant challenge to the acid-base status of the blood, due to marked increases in whole blood lactate, may be associated with mechanisms modulating peripheral blood concentrations of beta-EP and cortisol.     

Effects of creatine supplementation on repetitive sprint performance and body composition in competitive swimmers

In a double-blind and randomized manner, 18 male and female junior competitive swimmers supplemented their diets with 21 g.day-1 of creatine monohydrate (Cr) or a maltodextrin placebo (P) for 9 days during training. Prior to and following supplementation, subjects performed three 100-m freestyle sprint swims (long course) with 60 s rest/recovery between heats. In addition, subjects performed three 20-s arm ergometer maximal-effort sprint tests in the prone position with 60 s rest/recovery between sprint tests. Significant differences were observed among swim times, with Cr subjects swimming significantly faster than P subjects following supplementation in Heat 1 and significantly decreasing swim time in the second 100-m sprint. There was also some evidence that cumulative time to perform the three 100-m swims was decreased in the Cr group. Results indicate that 9 days of Cr supplementation during swim training may provide some ergogenic value to competitive junior swimmers during repetitive sprint performance.     

Postexercise potentiation of the H-reflex in humans

Post-muscle activation effects on segmental reflexes reveal divergent results dependent upon the manner in which the muscle is activated. Electrically activating triceps surae invokes a potentiation of the Achilles' tendon reflex and the soleus (S) H-reflex termed posttetanic potentiation. In contrast, brief volitional activation produces a subsequent potentiation of tendon reflexes, whereas H-reflexes become depressed. PURPOSE: The present investigation explored the effect of an intense bout of volitional resistance exercise on the S and lateral gastrocnemius (LG) H-reflexes to determine if a potentiation of the H-reflex could be induced with physiological stimuli. METHODS: LG and S H-reflexes were obtained from 10 college age men and women before and after a vigorous bout (eight sets of 10 repetitions) of concentric-eccentric triceps surae exercise. RESULTS: Every subject displayed an initial depression of the LG (P < 0.01) and S H-reflex (P < 0.05) immediately postexercise, consistent with postactivation depression. As a group, there was a significant (P > 0.01) potentiation of the LG H/M ratio following the depression. Five of 10 subjects demonstrated this potentiation, which often lasted 10 min postexercise. The other five subjects displayed a longer and more profound early depression followed by a return to control levels. CONCLUSION: The data suggest that at least two overlapping processes are occurring, a brief depression followed by or superimposed over a longer lasting potentiation. Possible neural mechanisms and implications to strength training are discussed.     

Caffeine counteracts the ergogenic action of muscle creatine loading

This study aimed to compare the effects of oral creatine (Cr) supplementation with creatine supplementation in combination with caffeine (Cr+C) on muscle phosphocreatine (PCr) level and performance in healthy male volunteers (n = 9). Before and after 6 days of placebo, Cr (0.5 g x kg-1 x day-1), or Cr (0.5 g x kg-1 x day-1) + C (5 mg x kg-1 x day-1) supplementation, 31P-nuclear magnetic resonance spectroscopy of the gastrocnemius muscle and a maximal intermittent exercise fatigue test of the knee extensors on an isokinetic dynamometer were performed. The exercise consisted of three consecutive maximal isometric contractions and three interval series of 90, 80, and 50 maximal voluntary contractions performed with a rest interval of 2 min between the series. Muscle ATP concentration remained constant over the three experimental conditions. Cr and Cr+C increased (P < 0.05) muscle PCr concentration by 4-6%. Dynamic torque production, however, was increased by 10-23% (P < 0.05) by Cr but was not changed by Cr+C. Torque improvement during Cr was most prominent immediately after the 2-min rest between the exercise bouts. The data show that Cr supplementation elevates muscle PCr concentration and markedly improves performance during intense intermittent exercise. This ergogenic effect, however, is completely eliminated by caffeine intake.