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Petra Stiegler, S. Andrew Sparks, and Adam Cunliffe

Maximizing postprandial energy expenditure and fat oxidation could be of clinical relevance for the treatment of obesity. This study investigated the effect of prior exercise on energy expenditure and substrate utilization after meals containing varying amounts of macronutrients. Eight lean (11.6% ± 4.0% body fat, M ± SD) and 12 obese (35.9% ± 5.3% body fat) men were randomly assigned to a protein (43% protein, 30% carbohydrate) or a carbohydrate (10% protein, 63% carbohydrate) meal. The metabolic responses to the meals were investigated during 2 trials, when meals were ingested after a resting period (D) or cycling exercise (Ex+D; 65% of oxygen consumption reserve, 200 kcal). Energy expenditure, substrate utilization, and glucose and insulin responses were measured for 4 hr during the postprandial phase. Although postprandial energy expenditure was not affected by prior exercise, the total amount of fat oxidized was higher during Ex+D than during D (170.8 ± 60.1 g vs. 137.8 ± 50.8 g, p < .05), and, accordingly, the use of carbohydrate as substrate was decreased (136.4 ± 45.2 g vs. 164.0 ± 42.9 g, p < .05). After the protein meal fat-oxidation rates were higher than after carbohydrate intake (p < .05), an effect independent of prior exercise. Plasma insulin tended to be lower during Ex+D (p = .072) and after the protein meal (p = .066). No statistically significant change in postprandial blood glucose was induced by prior exercise. Exercising before meal consumption can result in a marked increase in fat oxidation, which is independent of the type of meal consumed.

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Gulshanara Begum, Adam Cunliffe, and Michael Leveritt

High-intensity exercise leads to reductions in muscle substrates (ATP, PCr, and glycogen) and a subsequent accumulation of metabolites (ADP, Pi, H+, and Mg2+) with a possible increase in free radical production. These factors independently and collectively have deleterious effects on muscle, with significant repercussions on high-intensity performance or training sessions. The effect of carnosine on overcoming muscle fatigue appears to be related to its ability to buffer the increased H+ concentration following high-intensity work. Carnosine, however, has other roles such as an antioxidant, a metal chelator, a Ca2+ and enzyme regulator, an inhibitor of protein glycosylation and protein-protein cross-linking. To date, only 1 study has investigated the effects of carnosine supplementation (not in pure form) on exercise performance in human subjects and found no improvement in repetitive high-intensity work. Much data has come from in vitro work on animal skeletal muscle fibers or other components of muscle contractile mechanisms. Thus further research needs to be carried out on humans to provide additional understanding on the effects of carnosine in vivo.