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Kevin R. Short and K. Sreekumaran Nair

Loss of muscle mass, strength, and oxidative capacity accompanies normal aging in humans. The mechanisms responsible for these changes remain to be clearly defined. Muscle protein mass and function depend on protein turnover. Synthesis rate of the major muscle contractile protein, myosin heavy chain (MHC), and transcript levels of fast MHC isoforms decrease in association with strength reductions, while mitochondrial protein synthesis rate declines in parallel with activities of mitochondrial enzymes and maximal oxidative capacity (V̇O2max). Resistance exercise training increases the synthesis rate of MHC and transcript levels of the slow MHC isoform in older humans, along with increasing muscle strength. The relationship between the synthesis of muscle proteins, and muscle size and function, with aging and exercise training are discussed in this review.

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Kevin R. Short, Melinda Sheffield-Moore and David L. Costill

This investigation was undertaken to determine whether consuming several small feedings of preexercise carbohydrate (CHO), rather than a single bolus, would affect blood glucose and insulin responses during rest and exercise. Eight trained cyclists ingested 22.5,45, or 75 total g maltodextrin and dextrose dissolved in 473 ml of water or an equal volume of placebo (PL). Drinks were divided into four portions and consumed at 15-min intervals in the hour before a 120-min ride at 66% VO2max. Serum glucose values were elevated by the CHO feedings at rest and fell significantly below baseline and PL at 15 min of exercise. However, glucose concentrations were similar in each of the CHO trials. Insulin concentrations also increased rapidly during rest, then fell sharply at the onset of exercise. The findings demonstrate that CHO consumed within an hour before exercise, even when taken in several small feedings, can produce transient hypoglycemia near the onset of exercise. Additionally, the magnitude of the response appears to be unrelated to either the amount of CHO ingested or the insulin response.

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Kevin R. Short, April M. Teague, Jake C. Klein, Elizabeth Malm-Buatsi and Dominic Frimberger

Purpose:

Whole body or leg exercise before a meal can increase insulin sensitivity, but it is unclear whether the same can occur with upper body exercise since a smaller muscle mass is activated. We measured the impact of a single session of handcycle exercise on glucose tolerance and insulin sensitivity.

Methods:

Nonambulatory (Non-Amb) adolescents with spina bifida or cerebral palsy (4F/3M), or ambulatory peers (Control, 4F/7M) completed 2 glucose tolerance tests on separate days, preceded by either rest or a 35-min bout of moderate-to-vigorous intermittent handcycle exercise.

Results:

The Non-Amb group had higher body fat (mean ± SD: 38 ± 12%, Control: 24 ± 9, p = .041) but similar VO2peak (17.7 ± 6.1 ml/kg/min, Control: 21.1 ± 7.9). Fasting glucose and insulin were normal for all participants. Compared with the rest trial, exercise resulted in a reduction in glucose area under the curve (11%, p = .008) without a significant group x trial interaction and no difference in the magnitude of change between groups. Insulin sensitivity was increased 16% (p = .028) by exercise in the Control group but was not significantly changed in the Non-Amb group.

Conclusion:

A single bout of handcycle exercise improves glucose tolerance in adolescents with and without mobility limitations and could therefore help maintain or improve metabolic health.