High energy flux mediates the tonically augmented beta-adrenergic support of resting metabolic rate in habitually exercising older adults.

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.

Hyperthermia and maximal oxygen uptake in men and women.

To compare the effect of hyperthermia on maximal oxygen uptake (VO2max) in men and women, VO2max was measured in 11 male and 11 female runners under seven conditions involving various ambient temperatures (Ta at 50% RH) and preheating designed to manipulate the esophageal (Tes) and mean skin (Tsk) temperatures at VO2max. The conditions were: 25 degrees C, no preheating (control); 25, 35, 40, and 45 degrees C, with exercise-induced preheating by a 20-min walk at approximately 33% of control VO2max; 45 degrees C, no preheating; and 45 degrees C, with passive preheating during which Tes and Tsk were increased to the same degree as at the end of the 20-min walk at 45 degrees C. Compared to VO2max (l x min(-1)) in the control condition (4.52+/-0.46 in men, 3.01+/-0.45 in women), VO2max in men and women was reduced with exercise-induced or passive preheating and increased Ta, approximately 4% at 35 degrees C, approximately 9% at 40 degrees C and approximately 18% at 45 degrees C. Percentage reductions (7-36%) in physical performance (treadmill test time to exhaustion) were strongly related to reductions in VO2max (r=0.82-0.84). The effects of hyperthermia on VO2max and physical performance in men and women were almost identical. We conclude that men and women do not differ in their thermal responses to maximal exercise, or in the relationship of hyperthermia to reductions in VO2max and physical performance at high temperature. Data are reported as mean (SD) unless otherwise stated.

Cooling vest worn during active warm-up improves 5-km run performance in the heat.

We investigated whether a cooling vest worn during an active warm-up enhances 5-km run time in the heat. Seventeen competitive runners (9 men, maximal oxygen uptake = 66.7 +/- 5.9 ml x kg(-1) x min(-1); 8 women, maximal oxygen uptake = 58.0 +/- 3.2 ml x kg(-1) x min(-1)) completed two simulated 5-km runs on a treadmill after a 38-min active warm-up during which they wore either a T-shirt (C) or a vest filled with ice (V) in a hot, humid environment (32 degrees C, 50% relative humidity). Wearing the cooling vest during warm-up significantly (P < 0.05) blunted increases in body temperature, heart rate (HR), and perception of thermal discomfort during warm-up compared with control. At the start of the 5-km run, esophageal, rectal, mean skin, and mean body temperatures averaged 0.3, 0.2, 1.8, and 0.4 degrees C lower; HR averaged 11 beats/min lower; and perception of thermal discomfort (5-point scale) averaged 0.6 point lower in V than C. Most of these differences were eliminated during the first 3.2 km of the run, and these variables were not different at the end. The 5-km run time was significantly lower (P < 0.05) by 13 s in V than C, with a faster pace most evident during the last two-thirds of the run. We conclude that a cooling vest worn during active warm-up by track athletes enhances 5-km run performance in the heat. Reduced thermal and cardiovascular strain and perception of thermal discomfort in the early portion of the run appear to permit a faster pace later in the run.

Effects of prior exercise on postprandial lipemia: a quantitative review.

The purpose of this report is to synthesize the results from studies examining the effect of exercise on postprandial lipemia to summarize the existing data and provide direction for future research. A quantitative review of the literature was performed using meta-analytic methods to quantify the effect sizes. Moderator analyses were performed to examine features of the studies that could potentially influence the effect of exercise on postprandial lipemia. Thirty-eight effects from 555 people were retrieved from 29 studies. The mean weighted effect was moderate as indicated by Cohen's d (d = -0.57; 95% confidence interval [CI], -0.71 to -0.43), indicating that people who perform exercise before meal ingestion exhibit a 0.5 standard deviation reduction in the postprandial triglyceride (TG) response relative to persons in comparison groups. There was no significant effect of study design, gender, age, type of meal ingested, exercise intensity, exercise duration, or timing of exercise on the postprandial response (P >.05). There was, however, significant variation in the effect sizes, for women for exercise performed within 24 hours of meal ingestion, and for exercise performed more than 24 hours before meal ingestion (P <.01). For studies that reported the energy expenditure of exercise, there was a significant relationship between effect size and energy expenditure (r = -.62, P =.02). Results from this quantitative review of the literature suggest that exercise has a moderate effect on the postprandial lipemic response and that the energy expenditure of prior exercise may play a role in the magnitude of this effect. Other factors that may affect the response remain to be clarified.

Effect of resistance exercise on postprandial lipemia.

The purpose of this study was to examine the effect of resistance exercise on postprandial lipemia. Fourteen young men and women participated in each of three treatments: 1) control (Con), 2) resistance exercise (RE), and 3) aerobic exercise (AE) estimated to have an energy expenditure (EE) equal that for RE. Each trial consisted of performing a treatment on day 1 and ingesting a fat-tolerance test meal 16 h later (day 2). Resting metabolic rate and fat oxidation were measured at baseline and at 3 and 6 h postprandial on day 2. Blood was collected at baseline and at 0.5, 1, 2, 3, 4, 5, and 6 h after meal ingestion. RE and AE were similar in EE [1.7 +/- 0.1 vs. 1.6 +/- 0.1 (SE) MJ, respectively], as measured by using the Cosmed K4b(2). Baseline triglycerides (TG) were significantly lower after RE than after Con (19%) and AE (21%). Furthermore, the area under the postprandial response curve for TG, adjusted for baseline differences, was significantly lower after RE than after Con (14%) and AE (18%). Resting fat oxidation was significantly greater after RE than after Con (21%) and AE (28%). These results indicate that resistance exercise lowers baseline and postprandial TG, and increases resting fat oxidation, 16 h after exercise.