Effects of creatine supplementation on performance and training adaptations

Creatine has become a popular nutritional supplement among athletes. Recent research has also suggested that there may be a number of potential therapeutic uses of creatine. This paper reviews the available research that has examined the potential ergogenic value of creatine supplementation on exercise performance and training adaptations. Review of the literature indicates that over 500 research studies have evaluated the effects of creatine supplementation on muscle physiology and/or exercise capacity in healthy, trained, and various diseased populations. Short-term creatine supplementation (e.g. 20 g/day for 5–7 days) has typically been reported to increase total creatine content by 10–30% and phosphocreatine stores by 10–40%. Of the approximately 300 studies that have evaluated the potential ergogenic value of creatine supplementation, about 70% of these studies report statistically significant results while remaining studies generally report non-significant gains in performance. No study reports a statistically significant ergolytic effect. For example, short-term creatine supplementation has been reported to improve maximal power/strength (5–15%), work performed during sets of maximal effort muscle contractions (5–15%), single-effort sprint performance (1–5%), and work performed during repetitive sprint performance (5–15%). Moreover, creatine supplementation during training has been reported to promote significantly greater gains in strength, fat free mass, and performance primarily of high intensity exercise tasks. Although not all studies report significant results, the preponderance of scientific evidence indicates that creatine supplementation appears to be a generally effective nutritional ergogenic aid for a variety of exercise tasks in a number of athletic and clinical populations.     

Effects of creatine supplementation and resistance training on muscle strength and weightlifting performance

Creatine monohydrate has become the supplement of choice for many athletes striving to improve sports performance. Recent data indicate that athletes may not be using creatine as a sports performance booster per se but instead use creatine chronically as a training aid to augment intense resistance training workouts. Although several studies have evaluated the combined effects of creatine supplementation and resistance training on muscle strength and weightlifting performance, these data have not been analyzed collectively. The purpose of this review is to evaluate the effects of creatine supplementation on muscle strength and weightlifting performance when ingested concomitant with resistance training. The effects of gender, interindividual variability, training status, and possible mechanisms of action are discussed. Of the 22 studies reviewed, the average increase in muscle strength (1, 3, or 10 repetition maximum [RM]) following creatine supplementation plus resistance training was 8% greater than the average increase in muscle strength following placebo ingestion during resistance training (20 vs. 12%). Similarly, the average increase in weightlifting performance (maximal repetitions at a given percent of maximal strength) following creatine supplementation plus resistance training was 14% greater than the average increase in weightlifting performance following placebo ingestion during resistance training (26 vs. 12%). The increase in bench press 1RM ranged from 3 to 45%, and the improvement in weightlifting performance in the bench press ranged from 16 to 43%. Thus there is substantial evidence to indicate that creatine supplementation during resistance training is more effective at increasing muscle strength and weightlifting performance than resistance training alone, although the response is highly variable.     

Effects of short-term GH supplementation and treadmill exercise training on physical performance and skeletal muscle apoptosis in old rats

We have investigated the regulation of translation during the period of rapid liver growth that occurs at the end of gestation in the rat. This work was based on our prior observation that fetal hepatocyte proliferation is resistant to the inhibitory effects of rapamycin, an inhibitor of the mammalian target of rapamycin (mTOR), a nutrient-sensing kinase that controls ribosome biogenesis and protein translation. We hypothesized that translation control in late-gestation fetal liver differs from that in adult liver. We first examined the ability of rapamycin to inhibit the translation of mRNAs encoding ribosomal proteins. Consistent with the effect of rapamycin on proliferation, the activation of adult liver 5'-terminal oligopyrimidine tracts (5'-TOP) translation that occurred during refeeding after food deprivation was sensitive to rapamycin. Fetal liver 5'-TOP translation was insensitive. We went on to examine the eukaryotic initiation factor (eIF) 4F cap-binding complex that controls global protein synthesis. The molecular weights of the multiple eIF4G1 isoforms present in fetal and adult liver eIF4F complexes differed. In addition, fetal liver expressed the eIF4A1 form of the eIF4A helicase, whereas adult liver contained eIF4A1 and eIF4A2. Rapamycin administration before refeeding in adult rats inhibited formation of the preinitiation complex to a much greater degree than rapamycin administration to fetal rats in situ. We conclude that there are major structural and functional differences in translation control between late-gestation fetal and adult liver. These differences may confer differential sensitivity to the growth inhibitory effects of rapamycin.     

Effects of exercise training on thermoregulatory responses and blood volume in older men.

We assessed the effects of aerobic and/or resistance training on thermoregulatory responses in older men and analyzed the results in relation to the changes in peak oxygen consumption rate (VO(2 peak)) and blood volume (BV). Twenty-three older men [age, 64 +/- 1 (SE) yr; VO(2 peak), 32.7 +/- 1.1 ml. kg(-1). min(-1)] were divided into three training regimens for 18 wk: control (C; n = 7), aerobic training (AT; n = 8), and resistance training (RT; n = 8). Subjects in C were allowed to perform walking of ~10,000 steps/day, 6-7 days/wk. Subjects in AT exercised on a cycle ergometer at 50-80% VO(2 peak) for 60 min/day, 3 days/wk, in addition to the walking. Subjects in RT performed a resistance exercise, including knee extension and flexion at 60-80% of one repetition maximum, two to three sets of eight repetitions per day, 3 days/wk, in addition to the walking. After 18 wk of training, VO(2 peak) increased by 5.2 +/- 3.4% in C (P > 0.07), 20.0 +/- 2.5% in AT (P < 0.0001), and 9.7 +/- 5.1% in RT (P < 0.003), but BV remained unchanged in all trials. In addition, the esophageal temperature (T(es)) thresholds for forearm skin vasodilation and sweating, determined during 30-min exercise of 60% VO(2 peak) at 30 degrees C, decreased in AT (P < 0.02) and RT (P < 0.02) but not in C (P > 0.2). In contrast, the slopes of forearm skin vascular conductance/T(es) and sweat rate/T(es) remained unchanged in all trials, but both increased in subjects with increased BV irrespective of trials with significant correlations between the changes in the slopes and BV (P < 0.005 and P < 0.0005, respectively). Thus aerobic and/or resistance training in older men increased VO(2 peak) and lowered T(es) thresholds for forearm skin vasodilation and sweating but did not increase BV. Furthermore, the sensitivity of the increase in skin vasodilation and sweating at a given increase in T(es) was more associated with BV than with VO(2 peak).     

Myogenic gene expression at rest and after a bout of resistance exercise in young (18-30 yr) and old (80-89 yr) women.

The purpose of this study was to investigate mRNA expression of several key skeletal muscle myogenic controllers; myogenic differentiation factor (MyoD), muscle regulatory factor 4 (MRF4), myogenic factor 5 (Myf5), myogenin, myostatin, and myocyte enhancer factor 2 (MEF2) at rest and 4 h after a single bout of resistance exercise (RE) in young and old women. Eight young women (YW; 23 +/- 2 yr, 67 +/- 5 kg) and six old women (OW; 85 +/- 1 yr, 67 +/- 4 kg) performed 3 sets of 10 repetitions of bilateral knee extensions at 70% of one repetition maximum. Muscle biopsies were taken from the vastus lateralis before and 4 h after RE. Using real-time RT PCR, mRNA from the muscle samples was amplified and normalized to GAPDH. At rest, OW expressed higher (P < 0.05) levels of MyoD, MRF4, Myf5, myogenin, and myostatin compared with YW. In response to RE, there was a main time effect (P < 0.05) for the YW and OW combined in the upregulation of MyoD (2.0-fold) and MRF4 (1.4-fold) and in the downregulation of myostatin (2.2-fold). There was a trend (P = 0.08) for time x age interaction in MRF4. These data show that old women express higher myogenic mRNA levels at rest. The higher resting myogenic mRNA levels in old women may reflect an attempt to preserve muscle mass and function. When challenged with RE, old women appear to respond in a similar manner as young women.     

Effect of creatine supplementation on sprint exercise performance and muscle metabolism

The aim of thepresent study was to examine the effect of creatine supplementation(CrS) on sprint exercise performance and skeletal muscle anaerobicmetabolism during and after sprint exercise. Eight active, untrainedmen performed a 20-s maximal sprint on an air-braked cycle ergometerafter 5 days of CrS [30 g creatine (Cr) + 30 g dextrose perday] or placebo (30 g dextrose per day). The trials wereseparated by 4 wk, and a double-blind crossover design was used. Muscleand blood samples were obtained at rest, immediately after exercise,and after 2 min of passive recovery. CrS increased the muscle total Crcontent (9.5 ± 2.0%, P < 0.05, mean ± SE); however, 20-s sprint performance was not improved byCrS. Similarly, the magnitude of the degradation or accumulation ofmuscle (e.g., adenine nucleotides, phosphocreatine, inosine 5'-monophosphate, lactate, and glycogen) and plasma metabolites (e.g., lactate, hypoxanthine, and ammonia/ammonium) were also unaffected by CrS during exercise or recovery. These data demonstrated that CrS increased muscle total Cr content, but the increase did notinduce an improved sprint exercise performance or alterations inanaerobic muscle metabolism.

     

Effects of resistance exercise with and without creatine supplementation on gene expression and cell signaling in human skeletal muscle.

To test the hypothesis that creatine supplementation would enhance the anabolic responses of muscle cell signaling and gene expression to exercise, we studied nine subjects who received either creatine or a placebo (maltodextrin) for 5 days in a double-blind fashion before undergoing muscle biopsies: at rest, immediately after exercise (10 x 10 repetitions of one-leg extension at 80% 1 repetition maximum), and 24 and 72 h later (all in the morning after fasting overnight). Creatine supplementation decreased the phosphorylation state of protein kinase B (PKB) on Thr308 at rest by 60% (P < 0.05) and that of eukaryotic initiation factor 4E-binding protein on Thr37/46 (4E-BP1) by 30% 24 h postexercise (P < 0.05). Creatine increased mRNA for collagen 1 (alpha(1)), glucose transporter-4 (GLUT-4), and myosin heavy chain I at rest by 250%, 45%, and 80%, respectively, and myosin heavy chain IIA (MHCIIA) mRNA immediately after exercise by 70% (all P < 0.05). Immediately after exercise, and independent of creatine, mRNA for muscle atrophy F-box (MAFbx), MHCIIA, peroxisome proliferator-activated receptor gamma coactivator-1alpha, and interleukin-6 were upregulated (60-350%; P < 0.05); the phosphorylation state of p38 both in the sarcoplasm and nucleus were increased (12- and 25-fold, respectively; both P < 0.05). Concurrently, the phosphorylation states of PKB (Thr308) and 4E-BP1 (Thr37/46) were decreased by 50% and 75%, respectively (P < 0.05). Twenty-four hours postexercise, MAFbx, myostatin, and GLUT-4 mRNA expression decreased below preexercise values (-35 to -50%; P < 0.05); calpain 1 mRNA increased 70% 72 h postexercise (P < 0.05) and at no other time. In conclusion, 5 days of creatine supplementation do not enhance anabolic signaling but increase the expression of certain targeted genes.     

Effect of creatine supplementation on oxygen uptake kinetics during submaximal cycle exercise.

The purpose of this study was to test the effect of oral creatine (Cr) supplementation on pulmonary oxygen uptake (VO(2)) kinetics during moderate [below ventilatory threshold (VT)] and heavy (above VT) submaximal cycle exercise. Nine subjects (7 men; means +/- SD: age 28 +/- 3 yr, body mass 73.2 +/- 5.6 kg, maximal VO(2) 46.4 +/- 8.0 ml. kg(-1). min(-1)) volunteered to participate in this study. Subjects performed transitions of 6-min duration from unloaded cycling to moderate (80% VT; 8-12 repeats) and heavy exercise (50% change; i.e., halfway between VT and maximal VO(2); 4-6 repeats), both in the control condition and after Cr loading, in a crossover design. The Cr loading regimen involved oral consumption of 20 g/day of Cr monohydrate for 5 days, followed by a maintenance dose of 5 g/day thereafter. VO(2) was measured breath by breath and modeled by using two (moderate) or three (heavy) exponential terms. For moderate exercise, there were no differences in the parameters of the VO(2) kinetic response between control and Cr-loaded conditions. For heavy exercise, the time-based parameters of the VO(2) response were unchanged, but the amplitude of the primary component was significantly reduced with Cr loading (means +/- SE: control 2.00 +/- 0.12 l/min; Cr loaded 1.92 +/- 0.10 l/min; P < 0.05) as was the end-exercise VO(2) (control 2.19 +/- 0.13 l/min; Cr loaded 2.12 +/- 0.14 l/min; P < 0.05). The magnitude of the reduction in submaximal VO(2) with Cr loading was significantly correlated with the percentage of type II fibers in the vastus lateralis (r = 0.87; P < 0.01; n = 7), indicating that the effect might be related to changes in motor unit recruitment patterns or the volume of muscle activated.     

Muscle quality. II. Effects of strength training in 65-to 75-yr-old men and women

To determine theeffects of strength training (ST) on muscle quality (MQ,strength/muscle volume of the trained muscle group), 12 healthy oldermen (69 ± 3 yr, range 65-75 yr) and 11 healthy older women (68 ± 3 yr, range 65-73 yr) were studied before and after aunilateral leg ST program. After a warm-up set, four sets ofheavy-resistance knee extensor ST exercise were performed 3 days/wk for9 wk on the Keiser K-300 leg extension machine. The men exhibitedgreater absolute increases in the knee extension one-repetition maximum(1-RM) strength test (75 ± 2 and 94 ± 3 kg before andafter training, respectively) and in quadriceps muscle volume measuredby magnetic resonance imaging (1,753 ± 44 and 1,955 ± 43 cm³) than the women (42 ± 2 and 55 ± 3 kg for the 1-RM test and 1,125 ± 53 vs.1,261 ± 65 cm³ forquadriceps muscle volume before and after training, respectively, inwomen; both P < 0.05). However,percent increases were similar for men and women in the 1-RM test (27 and 29% for men and women, respectively), muscle volume (12% forboth), and MQ (14 and 16% for men and women, respectively).Significant increases in MQ were observed in both groups in the trainedleg (both P < 0.05) and in the 1-RMtest for the untrained leg (both P < 0.05), but no significant differences were observed between groups,suggesting neuromuscular adaptations in both gender groups. Thus,although older men appear to have a greater capacity for absolutestrength and muscle mass gains than older women in response to ST, the relative contribution of neuromuscular and hypertrophic factors to theincrease in strength appears to be similar between genders.

     

Effects of depletion exercise and light training on muscle glycogen supercompensation in men

Supercompensated muscle glycogen can be achieved by using several carbohydrate (CHO)-loading protocols. This study compared the effectiveness of two "modified" CHO-loading protocols. Additionally, we determined the effect of light cycle training on muscle glycogen. Subjects completed a depletion (D, n = 15) or nondepletion (ND, n = 10) CHO-loading protocol. After a 2-day adaptation period in a metabolic ward, the D group performed a 120-min cycle exercise at 65% peak oxygen uptake (VO2 peak) followed by 1-min sprints at 120% VO2 peak to exhaustion. The ND group performed only 20-min cycle exercise at 65% VO2 peak. For the next 6 days, both groups ate the same high-CHO diets and performed 20-min daily cycle exercise at 65% VO2 peak followed by a CHO beverage (105 g of CHO). Muscle glycogen concentrations of the vastus lateralis were measured daily with 13C magnetic resonance spectroscopy. On the morning of day 5, muscle glycogen concentrations had increased 1.45 (D) and 1.24 (ND) times baseline (P < 0.001) but did not differ significantly between groups. However, on day 7, muscle glycogen of the D group was significantly greater (p < 0.01) than that of the ND group (130 +/- 7 vs. 104 +/- 5 mmol/l). Daily cycle exercise decreased muscle glycogen by 10 +/- 2 (D) and 14 +/- 5 mmol/l (ND), but muscle glycogen was equal to or greater than preexercise values 24 h later. In conclusion, a CHO-loading protocol that begins with a glycogen-depleting exercise results in significantly greater muscle glycogen that persists longer than a CHO-loading protocol using only an exercise taper. Daily exercise at 65% VO2 peak for 20 min can be performed throughout the CHO-loading protocol without negatively affecting muscle glycogen supercompensation.     

不同步数的健步走对男性中老年人健身的效果

目的：基于运动生理生化技术手段,对不同步数的健步走在男性中老年人健身中的干预效果进行科学分析,以期为全民健身的开展提供更多理论依据。方法：募集的80名中老年受试者分成3组：健步走运动A组（30名、平均年龄56.26 ±3.68岁）、健步走运动B组（30名、平均年龄57.65 ±4.78岁）、对照组C组（20名、平均年龄55.73 ±4.18岁）;健步走运动A组在整个实验过程中每天运动步数控制在10 000~12 000步,共计16周;健步走运动B组在前10周内每天运动步数控制在10 000~12 000步,后6周控制在14 000~15 000步/天;对照组保持原先正常的生活状态和运动习惯。分别在试验开始前、第10周、第16周结束后对研究对象进行各个指标的测试。测试指标主要包括收缩压、舒张压、心率、肺活量、时间肺活量、总胆固醇、甘油三酯、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇等。结果：两个运动组在10周、16周后收缩压、舒张压、血清总胆固醇、甘油三酯较试验前明显下降（P<0.05,P<0.01）,肺活量、血清高密度脂蛋白胆固醇较试验前明显升高（P<0.05,P<0.01）,且运动B组在16周后舒张压（P<0.05）、时间肺活量（P<0.05）、血清甘油三酯（P<0.05）、高密度脂蛋白胆固醇（P<0.05）改变幅度明显大于运动A组16周后值。结论：每天万步走运动可有效地改善男性中老年血压、肺活量、血清甘油三酯、总胆固醇、高密度脂蛋白胆固醇等指标,且运动10周以后适当增加步数可进一步提高改善幅度。     

Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training

Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) ( approximately 10 g . day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects.     

Aerobic power and insulin action improve in response to endurance exercise training in healthy 77-87 yr olds.

Previous studies have demonstrated that frail octogenarians have an attenuated capacity for cardiovascular adaptations to endurance exercise training. In the present study, we determined the magnitude of cardiovascular and metabolic adaptations to high-intensity endurance exercise training in healthy, nonfrail elderly subjects. Ten subjects [8 men, 2 women, 80.3 yr (SD2.5)] completed 10-12 mo (108 exercise sessions) of a supervised endurance exercise training program consisting of 2.5 sessions/wk (SD 0.2), 58 min/session (SD 6), at an intensity of 83% (SD 5) of peak heart rate. Primary outcomes were maximal attainable aerobic power [peak aerobic capacity (Vo(2peak))]; serum lipids, oral glucose tolerance, and insulin action during a hyperglycemic clamp; body composition by dual-energy X-ray absorptiometry, and energy expenditure using doubly labeled water and indirect calorimetry. The training program resulted in an increase in Vo(2peak) of 15% (SD 7) [22.9 (SD 3.3) to 26.2 ml.kg(-1).min(-1) (SD 4.0); P < 0.0001]. Favorable lipid changes included reductions in total cholesterol (-8%; P = 0.002) and LDL cholesterol (-10%; P = 0.003), with no significant change in HDL cholesterol or triglycerides. Insulin action improved, as evidenced by a 29% increase in glucose disposal rate relative to insulin concentration during the hyperglycemic clamp. Fat mass decreased by 1.8 kg (SD 1.4) (P = 0.003); lean mass did not change. Total energy expenditure increased by 400 kcal/day because of an increase in physical activity. No change occurred in resting metabolism. In summary, healthy nonfrail octogenarians can adapt to high-intensity endurance exercise training with improvements in aerobic power, insulin action, and serum lipid and lipoprotein risk factors for coronary heart disease; however, the adaptations in aerobic power and insulin action are attenuated compared with middle-aged individuals.     

The effects of creatine supplementation on high-intensity exercise performance in elite performers

The aim of this research was to determine whether creatine supplementation at a dose of 20 g · day⁻¹, given in 4 × 6-g doses (5 g creatine monohydrate and 1 g glucose) for 5 days, was effective in improving kayak ergometer performances of different durations. Sixteen male subjects with the following characteristics [mean (SEM)]: age 21 (1.2) years, height 170.2 (1.7) cm, weight 75.3 (2.3) kg, Σ8 skinfolds 59.3 (2.6) mm, and maximal oxygen consumption 67.1 ± (4.3) ml · kg · min⁻¹, undertook three maximal kayak ergometer tests of 90, 150 and 300 s duration on a wind-braked kayak ergometer (CON). Two groups were then randomly formed, with one group taking the supplement (SUP) while the other took a placebo (PLAC). No pre-test differences existed between the SUP and the PLAC groups in any of the variables measured. After supplementation each group then repeated the same kayak ergometer tests as performed previously and after a 4-week “washout period” the groups took either the PLAC or SUP for another 5 days and then completed the final tests. The SUP group completed significantly more work than either the CON or PLAC groups in all of the tests (90 s, P < 0.01; 150 s, P < 0.001; 300 s, P < 0.05). Body mass remained stable throughout the test period in both the CON and PLAC groups, but both were significantly less than the SUP body mass of 77.3 (1.0) kg (P < 0.01). The results of this work indicate that creatine supplementation can significantly increase the amount of work accomplished during kayak ergometer performance at durations ranging from 90 to 300 s. Accepted: 8 January 1998     

Effect of creatine supplementation on cycle ergometer exercise in a hyperthermic environment

In order to examine thermoregulatory response to creatine (CR) supplementation, competitive male cyclists and triathletes (n = 7, VO2max = 50.6 +/- 0.8 ml x kg(-1) x min(-1)) completed three 1-hour hyperthermic (ambient temperature = 38.7 +/- 1.0 degrees C, relative humidity = 33 +/- 4%) exercise sessions at 181 +/- 12 W (50% of Wmax, approximately 66% of VO2max). Subjects completed a baseline (BL) session, then 2 sessions following 5 days of CR (20 g x d(-1)) and placebo (PL, 20 g x d(-1)) administered in a double-blind counterbalanced crossover manner with > or = 28-day washout. Pre-exercise BL, CR, and PL body mass were unchanged, with similar decreases in postexercise mass among the three conditions. Tympanic temperature, heart rate, systolic blood pressure, perceived exertion, and lactate, cortisol, and aldosterone concentrations increased similarly during BL, CR, and PL exercise. A greater (p = 0.013) estimated decrease in plasma volume occurred following BL (-16.5 +/- 2.0%) and PL (-17.6 +/- 1.7%) exercise compared to CR (-13.5 +/- 2.1%). Creatine supplementation reduces plasma volume loss during 1 hour of hyperthermic exercise but does not appear to otherwise change thermoregulatory response to hyperthermic exercise.     

Effects of eight weeks of caffeine supplementation and endurance training on aerobic fitness and body composition

The purpose of this study was to examine the effects of daily administration of a supplement that contained caffeine in conjunction with 8 weeks of aerobic training on VO(2)peak, time to running exhaustion at 90% VO(2)peak, body weight, and body composition. Thirty-six college students (14 men and 22 women; mean +/- SD, age 22.4 +/- 2.9 years) volunteered for this investigation and were randomized into either a placebo (n = 18) or supplement group (n = 18). The subjects ingested 1 dose (3 pills = 201 mg of caffeine) of the placebo or supplement per day during the study period. In addition, the subjects performed treadmill running for 45 minutes at 75% of the heart rate at VO(2)peak, three times per week for 8 weeks. All subjects were tested pretraining and posttraining for VO(2)peak, time to running exhaustion (TRE) at 90% VO(2)peak, body weight (BW), percentage body fat (%FAT), fat weight (FW), and fat-free weight (FFW). The results indicated that there were equivalent training-induced increases (p < 0.05) in VO(2)peak and TRE for the supplement and placebo groups, but no changes (p > 0.05) in BW, %FAT, FW, or FFW for either group. These findings indicated that chronic use of the caffeine-containing supplement in the present study, in conjunction with aerobic training, provided no ergogenic effects as measured by VO(2)peak and TRE, and the supplement was of no benefit for altering body weight or body composition.     

Effect of low-dose, short-duration creatine supplementation on anaerobic exercise performance

To examine the efficacy of a low-dose, short-duration creatine monohydrate supplement, 40 physically active men were randomly assigned to either a placebo or creatine supplementation group (6 g of creatine monohydrate per day). Testing occurred before and at the end of 6 days of supplementation. During each testing session, subjects performed three 15-second Wingate anaerobic power tests. No significant (p > 0.05) group or time differences were observed in body mass, peak power, mean power, or total work. In addition, no significant (p > 0.05) differences were observed in peak power, mean power, or total work. However, the change in the rate of fatigue of total work was significantly (p < 0.05) lower in the creatine supplementation group than in the placebo group, indicating a reduced fatigue rate in subjects supplementing with creatine compared with the placebo. Although the results of this study demonstrated reduced fatigue rates in patients during high-intensity sprint intervals, further research is necessary in examining the efficacy of low-dose, short-term creatine supplementation.     

Effects of exercise training on alpha-motoneurons.

Evidence is presented that one locus of adaptation in the "neural adaptations to training" is at the level of the alpha-motoneurons. With increased voluntary activity, these neurons show evidence of dendrite restructuring, increased protein synthesis, increased axon transport of proteins, enhanced neuromuscular transmission dynamics, and changes in electrophysiological properties. The latter include hyperpolarization of the resting membrane potential and voltage threshold, increased rate of action potential development, and increased amplitude of the afterhyperpolarization following the action potential. Many of these changes demonstrate intensity-related adaptations and are in the opposite direction under conditions in which chronic activity is reduced. A five-compartment model of rat motoneurons that innervate fast and slow muscle fibers (termed "fast" and "slow" motoneurons in this paper), including 10 active ion conductances, was used to attempt to reproduce exercise training-induced adaptations in electrophysiological properties. The results suggest that adaptations in alpha-motoneurons with exercise training may involve alterations in ion conductances, which may, in turn, include changes in the gene expression of the ion channel subunits, which underlie these conductances. Interestingly, the acute neuromodulatory effects of monoamines on motoneuron properties, which would be a factor during acute exercise as these monoaminergic systems are activated, appear to be in the opposite direction to changes measured in endurance-trained motoneurons that are at rest. It may be that regular increases in motoneuronal excitability during exercise via these monoaminergic systems in fact render the motoneurons less excitable when at rest. More research is required to establish the relationships between exercise training, resting and exercise motoneuron excitability, ion channel modulation, and the effects of neuromodulators.