The sympathetic nervous system contributes to resting metabolic rate (RMR) via beta-adrenergic receptor (beta-AR) stimulation of energy metabolism. RMR and beta-AR support of RMR are greater in habitually exercising compared with sedentary older adults possibly due to greater energy flux (magnitude of energy intake and energy expenditure during energy balance). In 10 older adults regularly performing aerobic endurance exercise (mean +/- se, 66 +/- 1 yr) compared with baseline, a reduction in energy flux (via abstention of exercise and proportional reduction in dietary intake) decreased (P < 0.05) energy expenditure (7746 +/- 440 vs. 9630 +/- 662 kJ.d(-1)), caloric intake (7808 +/- 431 vs. 9433 +/- 528 kJ.d(-1)), RMR (5192 +/- 167 vs. 5401 +/- 209 kJ.d(-1)), and skeletal muscle sympathetic nervous system activity (36 +/- 2 vs. 42 +/- 2 bursts.min(-1)). Significant beta-AR support of RMR was observed at baseline (167 +/- 42 kJ.d(-1)) but not during reduced energy flux. The change in RMR from baseline to reduced energy flux was related to the corresponding change in beta-AR support of RMR (r = 0.77, P = 0.009). No changes were observed in seven time controls (69 +/- 3 yr) who maintained energy flux. High energy flux is a key mechanism contributing to the elevated RMR and beta-AR support of RMR in habitually exercising older adults. Maintenance of high energy flux via regular exercise may be an effective strategy for maintaining energy expenditure and preventing age-associated obesity.

This study investigated whether different beverage carbohydrate concentration and osmolality would provoke gastrointestinal (GI) discomfort during intermittent, high-intensity exercise. Thirty-six adult and adolescent athletes were tested on separate days in a double-blind, randomized trial of 6 % and 8 % carbohydrate-electrolytes (CHO-E) beverages during four 12-min quarters (Q) of circuit training that included intermittent sprints, lateral hops, shuttle runs, and vertical jumps. GI discomfort and fatigue surveys were completed before the first Q and immediately after each Q. All ratings of GI discomfort were modest throughout the study. The cumulative index for GI discomfort, however, was greater for the 8 % CHO-E beverage than for the 6 % CHO-E beverage at Q3 and Q4 (P < 0.05). Averaging across all 4 quarters, the 8 % CHO-E treatment produced significantly higher mean ratings of stomach upset and side ache. In conclusion, higher CHO concentration and osmolality in an ingested beverage provokes stomach upset and side ache.

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The authors measured 24-h fluid-turnover (FTO) rate during 6 d of preseason training in U.S. college football players. Players, training (T, n = 9, full gear and contact drills) and reference (R, n = 4, conditioning without gear or contact), ingested a deuterium oxide (D(2)O) dose and provided urine samples every 24 h for analysis of D(2)O. During one approximately 2.3-h practice (wet-bulb globe temperature 24.6 degrees C), body-mass change, urine production, and voluntary fluid intake were measured to calculate gross sweat loss (GSL). Average FTO was 10.3 +/- 2.2 L/d for T and 7.0 +/- 1.0 L/d for R. GSL was 3.4 +/- 1.5 L for T and 1.7 +/- 1.3 for R (P > 0.05). By Day 6, body mass decreased significantly in T (-2.4 +/- 1.3 kg, P < 0.05) but not in R (0.38 +/- 0.95 kg). With preseason training under moderate environmental stress, football players had high FTO and sweat rates, which might have contributed to a loss of body mass during preseason football training.

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