Differential response of muscle phosphocreatine to creatine supplementation in young and old subjects.

This study compared the effects of short-term creatine supplementation on muscle phosphocreatine, blood and urine creatine levels, and urine creatinine levels in elderly and young subjects. Eight young (24 +/- 1.4 years) and seven old (70 +/- 2.9 years) men ingested creatine (20 g day-1) for 5 days. Baseline muscle phosphocreatine measurements were taken pre- and post-supplementation using nuclear magnetic resonance spectroscopy (NMR). On the first day of supplementation subjects had blood samples taken immediately before and hourly for 5 h following ingestion of 5 g of creatine, and a pharmacokinetic analysis of plasma creatine levels was conducted. Twenty-four hour urine collections were conducted for 2 days prior to the supplementation period and for 5 days during supplementation. Old subjects had significantly higher baseline plasma creatine levels than young subjects (68.5 +/- 12.5 vs. 34.9 +/- 4.7 micromol L-1; P < 0.02). There were no significant differences between groups in plasma creatine pharmacokinetic parameters (i.e. area under the curve, elimination rate constant, absorption rate constant, time to maximum concentration, and maximum concentration) following the 5 g oral creatine bolus. Urine creatine, assessed pre and on 5 days of supplementation, increased (P < 0.001), with no difference between groups. Urine creatinine did not change as a result of creatine supplementation. Young subjects showed a significantly greater increase in muscle phosphocreatine compared with old subjects, and post-supplementation muscle phosphocreatine levels were greater in young subjects (young 27.6 +/- 0.5; old 25.7 +/- 0.8 mmol kg-1 ww) (P=0.02). There were no differences in blood or urine creatine between groups in response to supplementation, but old subjects had a relatively small increase (young 35% vs. old 7%) in muscle phosphocreatine after supplementation.

The effects of creatine supplementation on exercise-induced muscle damage.

This investigation evaluated the effects of oral creatine (Cr) supplementation on markers of exercise-induced muscle damage following high-force eccentric exercise in subjects randomly administered Cr or placebo (P) in a double-blind fashion. When injected, exogenous phosphocreatine has been shown to stabilize the muscle membrane in cardiac tissue and enhance recovery of strength and power following injury. Twenty-three men aged 18-36 years ingested either 20 g of Cr or P for 5 days. Criterion measures were maximal isometric force of the elbow flexors (MIF), range of motion (ROM) about the elbow, mid and distal arm circumference (CIR; to assess swelling), soreness with movement and palpation (SOR), and blood levels of creatine kinase (CK) and lactate dehydrogenase (LDH). Following the supplementation period, subjects performed 50 maximal eccentric contractions of the elbow flexors. Criterion measures were assessed pre-exercise, immediately postexercise, and for 5 days after exercise. Both groups experienced a significant loss of MIF and ROM (time effect, p < 0.05). There was a significant increase in CIR of the mid and distal biceps, SOR with movement and palpation, CK, and LDH (time effect, p < 0.05), indicating that there was significant muscle damage. However, there were no significant differences in any of the criterion measures between groups (group x time interaction term, p > 0.05). The pattern of change over the 6 days, in response to the eccentric exercise, was nearly identical between groups. These data suggest that 5 days of Cr supplementation does not reduce indirect markers of muscle damage or enhance recovery from high-force eccentric exercise.

Acute creatine supplementation in older men.

The hypothesis of this study was that short term creatine (Cr) ingestion in older individuals would increase body mass and exercise performance, as has been shown in younger subjects. Seventeen males 60-78 years old were randomly placed into two groups, Cr and placebo (P), and supplemented in double-blind fashion for 5 days. Subjects ingested either 5 g of Cr plus 1 g of sucrose 4x per day or 6 g of a sucrose placebo 4x per day. Isometric strength of the elbow flexors was assessed using a modified preacher bench attached to a strain gauge. Isokinetic exercise performance was assessed using an intermittent fatigue test of the knee extensors. Subjects performed 3 sets of 30 repetitions with 60 sec rest between sets. There was a small (0.5 kg) but statistically significant increase in body mass (p < 0.05) in the Cr group after supplementation. There was a significant overall interaction between groups in isokinetic performance from pre to post supplementation (group x time x set, p < 0.05). However, analysis of the groups separately revealed that the subjects in the Cr group demonstrated a small non-significant increase in isokinetic performance while subjects in the P group demonstrated a small non-significant performance decrement. There was no significant difference in isometric strength between groups from pre to post supplementation. These data suggest that acute oral Cr supplementation does not increase isometric strength and only produces small increases in isokinetic performance and body mass in men over the age of 60.

Nutritional supplements to increase muscle mass.

Although nutritional supplements purported to increase muscle mass are widely available at health food stores, gyms, by mail order, and over the Internet, many of these supplements have little or no data to support their claims. This article reviews the theory and research behind popular nutritional supplements commonly marketed as muscle mass builders. Included are the minerals chromium, vanadyl sulfate, and boron, the steroid hormone dehydroepiandrosterone (DHEA), beta-methyl-hydroxy-beta-methylbutyrate (HMB), creatine, protein supplements, and amino acids. Research has shown that chromium vanadyl sulfate, and boron do not appear to be effective in increasing lean body mass. The few studies examining DHEA have not supported the claim of increased muscle gain. Preliminary work on HMB supports an anticatabolic effect, but only one human study is currently available. Many studies reported increased body mass and several have reported increased lean body mass following creatine ingestion. This weight gain is most likely water retention in muscle but could also be due to some new muscle protein. Although athletes have a greater protein requirement than sedentary individuals, this is easily obtained through the diet, negating the use of protein supplements. Studies on amino acids have not supported their claim to increase growth hormone or insulin secretion. Nutritional supplements can be marketed without FDA approval of safety or effectiveness. Athletes who choose to ingest these supplements should be concerned with unsubstantiated claims, questionable quality control, and safety of long-term use.

Effects of 30 days of creatine ingestion in older men.

In this investigation we evaluated the effects of oral creatine (Cr) supplementation on body composition, strength of the elbow flexors, and fatigue of the knee extensors in 20 males aged 60-82 years who were randomly administered Cr or placebo (P) in a double-blind fashion. Subjects ingested either 20 g of Cr or P for 10 days, followed by either 4 g of Cr or P, respectively, for 20 days. Tests were conducted pre-supplementation and following 10 and 30 days of supplementation. Leg fatigue was determined using an isokinetic dynamometer; subjects performed 5 sets of 30 maximal voluntary contractions at 180 degrees x s(-1), with 1 min of recovery between sets. The strength of the elbow flexors was assessed using a modified preacher bench attached to a strain gauge. There was a significant interaction (P < 0.05; group x time) in leg fatigue following supplementation. However, this interaction appears to have resulted from a combination of the improved fatigue score by the Cr-supplemented group and the decreased fatigue score by the P-supplemented group, because when the simple main effects were analyzed for the groups individually, there was no significant difference over time for either of the groups. There were no significant differences in body mass, body density, or fat-free mass as assessed by hydrostatic weighing, or strength between the Cr-supplemented or P-supplemented groups. These data suggest that 30 days of Cr-supplementation may have a beneficial effect on reducing muscle fatigue in men over the age of 60 years, but it does not affect body composition or strength.