beta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors.

The leucine metabolite, beta-hydroxy-beta-methylbutyrate (HMB) enhances the effects of exercise on muscle size and strength. Although several reports in animals and humans indicate that HMB is safe, quantitative safety data in humans have not been reported definitively. The objective of this work was to summarize safety data collected in nine studies in which humans were fed 3 g HMB/d. The studies were from 3 to 8 wk in duration, included both males and females, young and old, exercising or nonexercising. Organ and tissue function was assessed by blood chemistry and hematology; subtle effects on emotional perception were measured with an emotional profile test (Circumplex), and tolerance of HMB was assessed with a battery of 32 health-related questions. HMB did not adversely affect any surrogate marker of tissue health and function. The Circumplex emotion profile indicated that HMB significantly decreased (improved) one indicator of negative mood (Unactivated Unpleasant Affect category, P < 0.05). No untoward effects of HMB were indicated. Compared with the placebo, HMB supplementation resulted in a net decrease in total cholesterol (5.8%, P < 0.03), a decrease in LDL cholesterol (7.3%, P < 0.01) and a decrease in systolic blood pressure (4.4 mm Hg, P < 0.05). These effects of HMB on surrogate markers of cardiovascular health could result in a decrease in the risk of heart attack and stroke. In conclusion, the objective data collected across nine experiments indicate that HMB can be taken safely as an ergogenic aid for exercise and that objective measures of health and perception of well-being are generally enhanced.

Effect of L-carnitine supplementation on muscle and blood carnitine content and lactate accumulation during high-intensity sprint cycling.

This study examined the effects of 14 days of L-carnitine supplementation on muscle and blood carnitine fractions, and muscle and blood lactate concentrations, during high-intensity sprint cycling exercise. Eight subjects performed three experimental trials: control I (CON I, Day 0), control II (CON II, Day 14), and L-carnitine (L-CN, Day 28). Each trial consisted of a 4-min ride at 90% VO2max, followed by a rest period of 20 min, and then five repeated 1-min rides at 115% VO2max (2 min rest between each). Following CON II, all subjects began dietary supplementation of L-carnitine for a period of 14 days (4 g/day). Plasma total acid soluble and free carnitine concentrations were significantly higher (p < .05) at all time points following supplementation. L-carnitine supplementation had no significant effect on muscle carnitine content and thus could not alter lactate accumulation during exercise.

The effects of L-carnitine supplementation on performance during interval swimming.

To examine the effects of L-carnitine supplementation on short high-intensity exercise, twenty male collegiate swimmers completed two trials separated by seven days. Each trial consisted of five 91.4 m (100 yd) swims with a two minute rest interval between each bout. Following the first trial subjects were evenly and randomly assigned to either an L-carnitine (LC) group or a placebo (PL) group. The LC group ingested 2 grams L-carnitine in a citrus drink twice daily for 7 days, while the PL group received only the citrus drink during the same time period. Performance times were recorded for each repeat during both trials. Blood samples (5 ml) were obtained from an antecubital vein 1 minute following the interval set. Blood pH, base excess (BE), lactate (LA), carnitine and carnitine fractions were measured. Total serum carnitine was significantly (p < 0.05) elevated (75.9 +/- 2.0 vs. 106.4 +/- 3.5 mumol.l-1) in the LC group following treatment, while the PL group was unchanged (79.5 +/- 2.8 vs. 77.6 +/- 5.3 mumol.l-1). Free and short-chain serum carnitine fractions were also increased (p < 0.05) in the LC group, but were not altered in the PL group. No differences in performance times were observed between trials or between groups. Blood pH, LA and BE revealed a similar response in both groups during each trial. Despite the elevation in serum L-carnitine and carnitine fractions, these results indicate that L-carnitine supplementation does not provide an ergogenic benefit during repeated bouts of high-intensity anaerobic exercise in highly trained swimmers.

Effect of fat emulsion infusion and fat feeding on muscle glycogen utilization during cycle exercise.

Elevated plasma fatty acids have been shown to spare muscle glycogen during exercise. However, on the basis of recent findings, the saturation of fatty acids may influence this response. The purpose of this study was to determine whether saturated or unsaturated fatty acids affected muscle glycogenolysis to varying degrees during cycle exercise. Five healthy men completed three 60-min cycle ergometer trials (EX) at approximately 70% maximal O2 uptake (VO2max). Triglyceride levels were elevated by a fat feeding (FF) composed of 90% saturated fatty acids (heavy whipping cream, 90 g) or by the infusion of Intralipid (IL; Clintec Nutrition; 45 ml/h of 20% IL, 9.0 g), which was 85% unsaturated. A control trial (CON) consisted of a light breakfast (43 g carbohydrate and 1 g fat). Heparin (2,000 U) was administered 15 min before EX in FF and IL trials, resulting in one- and threefold increases in free fatty acid (FFA) levels in IL and FF, respectively. Pre-EX muscle glycogen did not differ. The utilization of muscle glycogen during 60 min of EX was less (P < 0.05) during the FF (60.0 +/- 5.2 mmol/kg wet wt) and IL (58.6 +/- 6.2 mmol/kg wet wt) compared with CON (81.8 +/- 7.5 mmol/kg wet wt). There was no difference between FF and IL in the amount of glycogen utilized. Serum triglyceride levels were greater (P < 0.05) at preheparin in FF (1.58 +/- 0.37 mmol/l) and IL (0.98 +/- 0.13 mmol/l) compared with CON (0.47 +/- 0.14 mmol/l).(ABSTRACT TRUNCATED AT 250 WORDS)