Biomedical subjects

P Hespel

Publications and source records attributed to P Hespel.

At least 19 recordsLinked to original sources

PubMed2006

Fiber type-specific muscle glycogen sparing due to carbohydrate intake before and during exercise.

The effect of carbohydrate intake before and during exercise on muscle glycogen content was investigated. According to a randomized crossover study design, eight young healthy volunteers (n = 8) participated in two experimental sessions with an interval of 3 wk. In each session subjects performed 2 h of constant-load bicycle exercise ( approximately 75% maximal oxygen uptake). On one occasion (CHO), they received carbohydrates before ( approximately 150 g) and during (1 g.kg body weight(-1).h(-1)) exercise. On the other occasion they exercised after an overnight fast (F). Fiber type-specific relative glycogen content was determined by periodic acid Schiff staining combined with immunofluorescence in needle biopsies from the vastus lateralis muscle before and immediately after exercise. Preexercise glycogen content was higher in type IIa fibers [9.1 +/- 1 x 10(-2) optical density (OD)/microm(2)] than in type I fibers (8.0 +/- 1 x 10(-2) OD/microm(2); P < 0.0001). Type IIa fiber glycogen content decreased during F from 9.6 +/- 1 x 10(-2) OD/microm(2) to 4.5 +/- 1 x 10(-2) OD/microm(2) (P = 0.001), but it did not significantly change during CHO (P = 0.29). Conversely, in type I fibers during CHO and F the exercise bout decreased glycogen content to the same degree. We conclude that the combination of carbohydrate intake both before and during moderate- to high-intensity endurance exercise results in glycogen sparing in type IIa muscle fibers.

Adult↗

PubMed2006

Dietary supplements for football.

Physical training and competition in football markedly increase the need for macro- and micronutrient intake. This requirement can generally be met by dietary management without the need for dietary supplements. In fact, the efficacy of most supplements available on the market is unproven. In addition, players must be cautious of inadequate product labelling and supplement impurities that may cause a positive drug test. Nonetheless, a number of dietary supplements may beneficially affect football performance. A high endurance capacity is a prerequisite for optimal match performance, particularly if extra time is played. In this context, the potential of low-dose caffeine ingestion (2 - 5 mg . kg body mass(-1)) to enhance endurance performance is well established. However, in the case of football, care must be taken not to overdose because visual information processing might be impaired. Scoring and preventing goals as a rule requires production of high power output. Dietary creatine supplementation (loading dose: 15 - 20 g . day(-1), 4 - 5 days; maintenance dose: 2 - 5 g g . day(-1)) has been found to increase muscle power output, especially during intermittent sprint exercises. Furthermore, creatine intake can augment muscle adaptations to resistance training. Team success and performance also depend on player availability, and thus injury prevention and health maintenance. Glucosamine or chondroitin may be useful in the treatment of joint pain and osteoarthritis, but there is no evidence to support the view that the administration of these supplements will be preventative. Ephedra-containing weight-loss cocktails should certainly be avoided due to reported adverse health effects and positive doping outcomes. Finally, the efficacy of antioxidant or vitamin C intake in excess of the normal recommended dietary dose is equivocal. Responses to dietary supplements can vary substantially between individuals, and therefore the ingestion of any supplement must be assessed in training before being used in competition. It is recommended that dietary supplements are only used based on the advice of a qualified sports nutrition professional.

Dietary Supplements↗

PubMed2005

Exercise in the fasted state facilitates fibre type-specific intramyocellular lipid breakdown and stimulates glycogen resynthesis in humans.

The effects were compared of exercise in the fasted state and exercise with a high rate of carbohydrate intake on intramyocellular triglyceride (IMTG) and glycogen content of human muscle. Using a randomized crossover study design, nine young healthy volunteers participated in two experimental sessions with an interval of 3 weeks. In each session subjects performed 2 h of constant-load bicycle exercise ( approximately 75% ), followed by 4 h of controlled recovery. On one occasion they exercised after an overnight fast (F), and on the other (CHO) they received carbohydrates before ( approximately 150 g) and during (1 g (kg bw)(-1) h(-1)) exercise. In both conditions, subjects ingested 5 g carbohydrates per kg body weight during recovery. Fibre type-specific relative IMTG content was determined by Oil red O staining in needle biopsies from m. vastus lateralis before, immediately after and 4 h after exercise. During F but not during CHO, the exercise bout decreased IMTG content in type I fibres from 18 +/- 2% to 6 +/- 2% (P = 0.007) area lipid staining. Conversely, during recovery, IMTG in type I fibres decreased from 15 +/- 2% to 10 +/- 2% in CHO, but did not change in F. Neither exercise nor recovery changed IMTG in type IIa fibres in any experimental condition. Exercise-induced net glycogen breakdown was similar in F and CHO. However, compared with CHO (11.0 +/- 7.8 mmol kg(-1) h(-1)), mean rate of postexercise muscle glycogen resynthesis was 3-fold greater in F (32.9 +/- 2.7 mmol kg(-1) h(-1), P = 0.01). Furthermore, oral glucose loading during recovery increased plasma insulin markedly more in F (+46.80 microU ml(-1)) than in CHO (+14.63 microU ml(-1), P = 0.02). We conclude that IMTG breakdown during prolonged submaximal exercise in the fasted state takes place predominantly in type I fibres and that this breakdown is prevented in the CHO-fed state. Furthermore, facilitated glucose-induced insulin secretion may contribute to enhanced muscle glycogen resynthesis following exercise in the fasted state.

Adult↗

PubMed2005

Effect of exercise-induced dehydration on lactate parameters during incremental exercise.

Cyclists often use heart rate limits or power output zones, obtained from lactate parameters during incremental exercise testing, to control training intensity. However, the relationship between heart rate or power output, and blood lactate can be changed by several factors including dehydration. Therefore, in the current study we investigated the impact of exercise-induced dehydration on lactate parameters during graded exercise. Nine triathletes completed two test sessions in random order, with a 1-week interval. Each session consisted of 2 graded cycling tests to exhaustion (pretest, posttest), interspersed by a 2-h endurance exercise bout. In one session the cyclists received adequate fluid replacement (EH, 1350 ml . h (-1)) whilst in the other session dehydration was not prevented (DH, 225 ml . h (-1)). Subjects received equal amounts of carbohydrates (150 g) during either condition. The 4-mmol lactate threshold (OBLA) and the d (max) lactate threshold (TH-Dm) were calculated from the power : lactate curves. Weight loss was 0.5 +/- 0.3 kg in EH versus 2.5 +/- 0.2 kg in DH (p < 0.05). Heart rate (HR) at TH-Dm remained unchanged in all test occasions. Conversely, HR at OBLA increased by approximately 10 beats . min (-1) from the pretest to the posttest (p < 0.05), in both EH and DH. Compared to the pretest, in the posttest power output at TH-Dm was reduced (minus approximately 12 %, p < 0.05) in DH, but not in EH. Gross mechanical efficiency at TH-Dm was 20.7 +/- 1 % in the pretest in EH and was not different from the pretest value in DH (21.4 +/- 0.7 %, n.s.). Gross efficiency decreased in the posttest in DH (18.4 +/- 0.6 %, p < 0.05), but not in EH (20.2 +/- 0.8 %, n.s.). It is concluded that heart rate rather than power output should be used to monitor training load in cyclists exercising in environmental conditions predisposing to dehydration. Furthermore, in the latter condition, adequate rehydration is essential to preserve optimal mechanical efficiency.

Adult↗

PubMed2004

Effects of air ventilation during stationary exercise testing.

The impact of air ventilation on performance and physiological responses during stationary exercise in the laboratory was studied. Fourteen well-trained cyclists performed three exercise tests on a cycle ergometer, each separated by a 1-week interval. The first test was a graded test to determine the power output corresponding with the 4-mmol l(-1) lactate level. Tests 2 and 3 were 30-min constant-load tests at a power output corresponding with this 4-mmol l(-1) lactate threshold. One constant-load test was performed in the absence (NAV), whilst the other was performed in the presence (AV) of air ventilation (3 m s(-1)). During the constant-load tests, heart rate, tympanic temperature, blood lactate concentration and oxygen uptake (VO2) were measured at 10-min intervals and at the end of the test. Differences between the two test conditions were evaluated using paired t-tests. During NAV, 12 subjects interrupted the test due to premature exhaustion (exercise duration <30 min), versus only seven in AV ( P<0.05). At the end of the test tympanic temperature was 35.9 (0.2) degrees C in AV and was higher in NAV [36.7 (0.2) degrees C, P<0.05]. Exercise heart rate increased at a faster rate during NAV [+2.2 (0.3) beats min(-1)] than during AV [+1.5 (0.2) beats min(-1), P<0.05]. Blood lactate concentration and VO2 were similar between conditions. Air ventilation is essential to prevent an upward shift in the lactate:heart rate as well as the power output:heart rate relationship during laboratory exercise testing and indoor exercise training.

Adaptation, Physiological↗

PubMed2004

Correlations between lactate and ventilatory thresholds and the maximal lactate steady state in elite cyclists.

We investigated the validity of different lactate and ventilatory threshold methods, to estimate heart rate and power output corresponding with the maximal lactate steady-state (MLSS) in elite cyclists. Elite cyclists (n = 21; 21 +/- 0.4 y; VO2peak, 5.4 +/- 0.2 l x min (-1)) performed either one (n = 10) or two (n = 11) maximal graded exercise tests, as well as two to three 30-min constant-load tests to determine MLSS, on their personal race bicycle which was mounted on an ergometer. Initial workload for the graded tests was 100 Watt and was increased by either 5 % of body mass (in Watt) with every 30 s (T30 s), or 60 % of body mass (in Watt) with every 6 min (T6min). MLSS was defined as the highest constant workload during which lactate increased no more than 1 mmol x l (-1) from min 10 to 30. In T30 s and T6 min the 4 mmol (TH-La4), the Conconi (TH-Con) and dmax (TH-Dm) lactate threshold were determined. The dmax lactate threshold was defined as the point that yields the maximal distance from the lactate curve to the line formed by the lowest and highest lactate values of the curve. In T30 s also ventilatory (TH-Ve) and Vslope (TH-Vs) thresholds were calculated. Time to exhaustion was 36 +/- 1 min for T30 s versus 39 +/- 1 min for T6 min. None of the threshold measures in T30 s, except TH-Vs (r2 = 0.77 for heart rate) correlated with either MLSS heart rate or power output. During T6 min, power output at TH-Dm was closely correlated with MLSS power (r2=0.72). Low correlations were found between MLSS heart rate and heart rate measured at TH-Dm (r2=0.46) and TH-La4 (r2=0.25), respectively, during T6 min. It is concluded that it is not possible to precisely predict heart rate or power output corresponding with MLSS in elite cyclists, from a single graded exercise test causing exhaustion within 35-40 min. The validity of MLSS predicted from an incremental test must be verified by a 30-min constant-load test.

Adult↗

PubMed2003

Creatine supplementation in Huntington's disease: a placebo-controlled pilot trial.

OBJECTIVE: To evaluate the effect of creatine (Cr) supplementation (5 g/day) in Huntington's disease (HD). METHODS: A 1-year double-blind placebo-controlled study was performed in 41 patients with HD (stage I through III). At baseline and after 6 and 12 months, the functional, neuromuscular, and cognitive status of the patients was assessed by a test battery that consisted of 1) the Unified Huntington's Disease Rating Scale (UHDRS), 2) an exercise test on an isokinetic dynamometer to assess strength of the elbow flexor muscles, 3) a maximal exercise test on a bicycle ergometer to evaluate cardiorespiratory fitness, and 4) a test to assess bimanual coordination ability. Following the baseline measurements, the subjects were assigned to either a creatine (n = 26) or a placebo group (n = 15). RESULTS: Scores on the functional checklist of the UHDRS (p < 0.05), maximal static torque (p < 0.05), and peak oxygen uptake (p < 0.05) decreased from the start to the end of the study, independent of the treatment received. Cognitive functioning, bimanual coordination ability, and general motor function (total motor scale, UHDRS) did not change from baseline to 1 year in either group. CONCLUSION: One year of Cr intake, at a rate that can improve muscle functional capacity in healthy subjects and patients with neuromuscular disease (5 g/day), did not improve functional, neuromuscular, and cognitive status in patients with stage I to III HD.

Cognition↗

PubMed2003

Prediction of sprint triathlon performance from laboratory tests.

This study investigated whether sprint triathlon performance can be adequately predicted from laboratory tests. Ten triathletes [mean (SEM), age 21.8 (0.3) years, height 179 (2) cm, body mass 67.5 (2.5) kg] performed two graded maximal exercise test in random order, either on their own bicycle which was mounted on an ergometer or on a treadmill, to determine their peak oxygen consumption ( VO(2)peak). Furthermore, they participated in two to three 30-min constant-load tests in both swimming, cycling and running to establish their maximal lactate steady state (MLSS) in each exercise mode. Swim tests were performed in a 25-m swimming pool (water temperature 27 degrees C). During each test heart rate (HR), power output (PO) or running/swimming speed and blood lactate concentration (BLC) were recorded at regular intervals. Oxygen uptake ( VO(2)) was continuously measured during the graded tests. Two weeks after the laboratory tests all subjects competed in a triathlon race (500 m swim, 20-km bike, 5-km run) [1 h 4 min 45 s (1 min 38 s)]. Peak HR was 7 beats.min(-1) lower in the graded cycle test than in the treadmill test ( p<0.05) at similar peak BLC (approximately 10 mmol.l(-1)) and VO(2)peak (approximately 5 L.min(-1)). High correlations were found between VO(2)peak during cycling ( r=-0.71, p<0.05) or running ( r=-0.69, p<0.05) and triathlon performance. Stepwise multiple regression analysis showed that running speed and swimming speed at MLSS, together with BLC in running at MLSS, yielded the best prediction of performance [1 h 5 min 18 s (1 min 49 s)]. Thus, our data indicate that exercise tests aimed to determine MLSS in running and swimming allow for a precise estimation of sprint triathlon performance.

Adult↗

PubMed2003

[The effects of physical exercise on the immune system].

Physical exercise has numerous effects on the human body, including the immune system. After strenuous exercise, athletes pass through a period of impaired immune resistance. During this period, athletes are theoretically more susceptible to upper respiratory tract infections, although a causal relation has never been demonstrated. Moderate exercise seems to have a beneficial effect on the immune function, which could protect against upper respiratory tract infections. Exercise has effects on both the humoral and the cellular immune system. Doping products, except glucocorticoids, only have modest effects on the immune system, although erythropoietin may, in rare cases, cause severe side-effects. Glutamine and vitamin C could, hypothetically, prevent the negative effects of strenuous exercise on the immune function, but further studies are needed to demonstrate and explain these effects.

Antibody Formation↗

PubMed2003

Effects of oral creatine-pyruvate supplementation in cycling performance.

A double-blind study was performed to evaluate the effects of oral creatine-pyruvate administration on exercise performance in well-trained cyclists. Endurance and intermittent sprint performance were evaluated before (pretest) and after (posttest) one week of creatine-pyruvate intake (Cr(pyr), 2 x 3.5 g x d-1, n = 7) or placebo (PL, n = 7). Subjects first performed a 1-hour time trial during which the workload could be adjusted at 5-min intervals. Immediately they did five 10-sec sprints interspersed by 2-min rest intervals. Tests were performed on an individual race bicycle that was mounted on an ergometer. Steady-state power production on average was about 235-245 W, which corresponded to blood lactate concentrations of 4-5 mmol x l -1 and heart rate in the range of 160-170 beats x min -1. Power outputs as well as blood lactate levels and heart rates were similar between Cr(pyr) and PL at all times. Total work performed during the 1-h trial was 872 +/- 44 KJ in PL versus 891 +/- 51 KJ in CR pyr. During the intermittent sprint test power peaked at about 800-1000 watt within 2-3 sec, decreasing by 15-20 % towards the end of each sprint. Peak and mean power outputs were similar between groups at all times. Peak lactate concentrations after the final sprint were approximately 11 mmol x l -1 in both groups during both the pretest and the posttest. It is concluded that one week of creatine-pyruvate supplementation at a rate of 7 g x d -1 does not beneficially impact on either endurance capacity or intermittent sprint performance in cyclists.

Bicycling↗

PubMed2002

Unimanual and bimanual voluntary movement in Huntington's disease.

Unimanual and bimanual cyclical forearm movements were studied in 15 Huntington's disease (HD) patients and 15 healthy, gender- and age-matched controls. Whereas the unimanual task was only performed at maximal speed, the bimanual movements were performed according to the in-phase and anti-phase mode at different cycling frequencies. The HD patients also performed the tasks after 12 months of follow-up. Findings revealed that maximal cycling frequency during unimanual movement was significantly lower in HD patients as compared with controls. In addition, measures of relative phasing established that bimanual cyclical movements were performed with lower accuracy and higher variability in HD patients. The differential variability between both groups was magnified by increasing the cycling frequency and coordinative complexity whereas only coordinative complexity differentially affected the accuracy of relative phasing. The obtained performance measures were found to be significantly correlated with disease duration (unimanual) and with the score on the total motor scale, the Mini-Mental State Examination and the Stroop Interference Test (uni- and bimanual). After 12 months, maximal cycling frequency of unimanual elbow flexion-extension was significantly decreased in HD patients whereas the quality of the in-phase and anti-phase movement patterns remained stable.

Adult↗

PubMed2002

Opposite actions of caffeine and creatine on muscle relaxation time in humans.

The effect of creatine and caffeine supplementation on muscle torque generation and relaxation was investigated in healthy male volunteers. Maximal torque (T(max)), contraction time (CT) from 0.25 to 0.75 of T(max), and relaxation time (RT) from 0.75 to 0.25 of T(max) were measured during an exercise test consisting of 30 intermittent contractions of musculus quadriceps (2 s stimulation, 2 s rest) that were induced by electrical stimulation. According to a double-blind randomized crossover design, subjects (n = 10) performed the exercise test before (pretest) and after (posttest) creatine supplementation (Cr, 4 x 5 g/day, 4 days), short-term caffeine intake (Caf, 5 mg x kg(-1) x day(-1), 3 days), creatine supplementation + short-term caffeine intake (Cr+Caf), acute caffeine intake (ACaf, 5 mg/kg) or placebo. Compared with placebo, Cr shortened RT by approximately 5% (P < 0.05). Conversely, Caf increased RT (+ approximately 10%, P < 0.05), in particular as RT increased because of fatigue. RT was not significantly changed by either Cr+Caf or ACaf. T(max) and CT were similar during all experimental conditions. Initial T(max) was approximately 20% of voluntary maximal isometric contraction force, which was not different between treatments. It is concluded that Caf intake (3 days) prolongs muscle RT and by this action overrides the shortening of RT due to creatine supplementation.

Adult↗

PubMed2001

Oral creatine supplementation facilitates the rehabilitation of disuse atrophy and alters the expression of muscle myogenic factors in humans.

1. We investigated the effect of oral creatine supplementation during leg immobilization and rehabilitation on muscle volume and function, and on myogenic transcription factor expression in human subjects. 2. A double-blind trial was performed in young healthy volunteers (n = 22). A cast was used to immobilize the right leg for 2 weeks. Thereafter the subjects participated in a knee-extension rehabilitation programme (3 sessions x week(-1), 10 weeks). Half of the subjects received creatine monohydrate (CR; from 20 g down to 5 g daily), whilst the others ingested placebo (P; maltodextrin). 3. Before and after immobilization, and after 3 and 10 weeks of rehabilitation training, the cross-sectional area (CSA) of the quadriceps muscle was assessed by NMR imaging. In addition, an isokinetic dynamometer was used to measure maximal knee-extension power (Wmax), and needle biopsy samples taken from the vastus lateralis muscle were examined to asses expression of the myogenic transcription factors MyoD, myogenin, Myf5, and MRF4, and muscle fibre diameters. 4. Immobilization decreased quadriceps muscle CSA (approximately 10 %) and Wmax (approximately 25 %) by the same magnitude in both groups. During rehabilitation, CSA and Wmax recovered at a faster rate in CR than in P (P < 0.05 for both parameters). Immobilization changed myogenic factor protein expression in neither P nor CR. However, after rehabilitation myogenin protein expression was increased in P but not in CR (P < 0.05), whilst MRF4 protein expression was increased in CR but not in P (P < 0.05). In addition, the change in MRF4 expression was correlated with the change in mean muscle fibre diameter (r = 0.73, P < 0.05). 5. It is concluded that oral creatine supplementation stimulates muscle hypertrophy during rehabilitative strength training. This effect may be mediated by a creatine-induced change in MRF4 and myogenin expression.

Adenosine Triphosphate↗

PubMed2001

Effect of creatine supplementation on creatine and glycogen content in rat skeletal muscle.

The effects of high dose creatine feeding (5 g kg(-1) BW day(-1), 5 days) on creatine content, glucose transport, and glycogen accumulation in white gastrocnemius, red gastrocnemius and soleus muscles of the rat was investigated. Isolated rat hindquarters of creatine fed and control rats were perfused with a standard medium containing either insulin alone (0, 100 or 20 000 microU mL(-1)) or in combination with creatine (2 or 10 mmol L(-1)). Furthermore, plasma insulin concentration was measured in normal rats during creatine feeding, as well as in anaesthetized rats during intravenous creatine infusion. Five days of creatine feeding increased (P < 0.05) total creatine content in soleus (+ 20%) but not in red gastrocnemius (+15%, n.s.) and white gastrocnemius (+ 10%, n.s.). In parallel, glycogen content was markedly elevated (P < 0.05) in soleus (+ 40%), less (P < 0.05) in red gastrocnemius (+ 15%), and not in white gastrocnemius (+ 10%, n.s.). Glucose transport rate, muscle GLUT-4 content, glycogen synthase activity in perfused muscles and glycogen synthesis rate were not significantly altered by creatine feeding in either muscle type. Furthermore, high dose creatine feeding raised (P < 0.05) plasma creatine concentration fivefold but did not alter circulating insulin level. It is concluded that short-term high dose creatine feeding enhances creatine disposal and glycogen storage in rat skeletal muscle. However, the creatine and glycogen response to creatine supplementation is markedly greater in oxidative than in glycolytic muscles.

Animals↗

PubMed2001

Creatine loading does not impact on stroke performance in tennis.

The effect of acute creatine supplementation on stroke quality was investigated during simulated match play. Well-trained tennis players reported to the test center on two occasions. On each occasion they performed the Leuven Tennis Performance Test (LTPT) and a 70 m shuttle run (SHR). During 5 days prior to each test session they received in random order and according to a double-blind cross-over study design either oral creatine supplements (4 x 5 g per day) or placebo. The two experimental periods were separated by a 5-week washout period. Stroke quality was evaluated during the LTPT by means of registration of error rate and measurement of ball velocity and precision of lateral and longitudinal ball placement. Compared with placebo, creatine supplementation did not significantly impact on either power or precision of first and second services, baseline strokes in neutral and defensive rallies, and volleys. Shuttle run time was 19.87 +/- 0.30 sec during placebo versus 19.85 +/- 0.27 sec during creatine treatment. Acute creatine supplementation does not enhance stroke performance or sprint power in match-like conditions in elite tennis players.

Adult↗

PubMed2001

Short-term creatine supplementation does not alter the hormonal response to resistance training.

PURPOSE: In this study, the effect of short-term creatine supplementation on the growth hormone, testosterone, and cortisol response to heavy resistance training was investigated. METHODS: According to a double-blind crossover study design, 11 healthy young male volunteers underwent a 1-h standardized heavy resistance training session (3 series of 10RM; 12 exercises), both before (pretest) and after (posttest) 5 d of either placebo (P, maltodextrine) or creatine (CR; 20 g.d-1, 5 d) supplementation. A 5-wk washout period separated the treatments. Thirty minutes before each training session, CR subjects ingested 10 g of creatine monohydrate (CR) while P subjects received placebo. Venous blood was sampled before, immediately after, and 30 and 60 min after the training session. RESULTS: The exercise-induced increase (P < 0.05) of serum growth hormone was not altered by acute creatine intake and was similar in P and CR. The weight training session, either or not in conjunction with acute or chronic creatine intake, did not significantly impact on serum testosterone. However, serum cortisol during recovery tended to be higher in CR than in P. CONCLUSION: It is concluded that short-term creatine supplementation does not alter the responses of growth hormone, testosterone, and cortisol to a single bout of heavy resistance training.

Administration, Oral↗

PubMed2001

Creatine supplementation: exploring the role of the creatine kinase/phosphocreatine system in human muscle.

The effect of oral creatine supplementation on high-intensity exercise performance has been extensively studied over the past ten years and its ergogenic potential in young healthy subjects is now well documented. Recently, research has shifted from performance evaluation towards elucidating the mechanisms underlying enhanced muscle functional capacity after creatine supplementation. In this review, we attempt to summarise recent advances in the understanding of potential mechanisms of action of creatine supplementation at the level of skeletal muscle cells. By increasing intracellular creatine content, oral creatine ingestion conceivably stimulates operation of the creatine kinase (CK)/phosphocreatine (PCr) system, which in turn facilitates muscle relaxation. Furthermore, evidence is accumulating to suggest that creatine supplementation can beneficially impact on muscle protein and glycogen synthesis. Thus, muscle hypertrophy and glycogen supercompensation are candidate factors to explain the ergogenic potential of creatine ingestion. Additional issues discussed in this review are the fibre-type specificity of muscle creatine metabolism, the identification of responders versus non-responders to creatine intake, and the scientific background concerning potential side effects of creatine supplementation.

Creatine↗

PubMed2001

No effects of oral ribose supplementation on repeated maximal exercise and de novo ATP resynthesis.

A double-blind randomized study was performed to evaluate the effect of oral ribose supplementation on repeated maximal exercise and ATP recovery after intermittent maximal muscle contractions. Muscle power output was measured during dynamic knee extensions with the right leg on an isokinetic dynamometer before (pretest) and after (posttest) a 6-day training period in conjunction with ribose (R, 4 doses/day at 4 g/dose, n = 10) or placebo (P, n = 9) intake. The exercise protocol consisted of two bouts (A and B) of maximal contractions, separated by 15 s of rest. Bouts A and B consisted of 15 series of 12 contractions each, separated by a 60-min rest period. During the training period, the subjects performed the same exercise protocol twice per day, with 3-5 h of rest between exercise sessions. Blood samples were collected before and after bouts A and B and 24 h after bout B. Knee-extension power outputs were approximately 10% higher in the posttest than in the pretest but were similar between P and R for all contraction series. The exercise increased blood lactate and plasma ammonia concentrations (P < 0.05), with no significant differences between P and R at any time. After a 6-wk washout period, in a subgroup of subjects (n = 8), needle-biopsy samples were taken from the vastus lateralis before, immediately after, and 24 h after an exercise bout similar to the pretest. ATP and total adenine nucleotide content were decreased by approximately 25 and 20% immediately after and 24 h after exercise in P and R. Oral ribose supplementation with 4-g doses four times a day does not beneficially impact on postexercise muscle ATP recovery and maximal intermittent exercise performance.

Adenine Nucleotides↗