The purpose of this investigation was to examine the effects of diet on muscle triglyceride and endurance performance. Seven endurance-trained men completed a 120-min cycling bout at 65% of maximal oxygen uptake. Each subject then ingested an isocaloric high-carbohydrate (Hi-CHO; 83% of energy) or a high-fat (Hi-Fat; 68% of energy) diet for the ensuing 12 h. After a 12-h overnight fast, a 1,600-kJ self-paced cycling bout was completed. Muscle triglyceride measured before (33.0 +/- 2.3 vs. 37.0 +/- 2.1 mmol/kg dry wt) and after (30.9 +/- 2.4 vs. 32.8 +/- 1.6 mmol/kg dry wt) the 120-min cycling bout was not different between the Hi-CHO and Hi-Fat trials, respectively. After the 24-h dietary-fasting period, muscle triglyceride was significantly higher for the Hi-Fat (44.7 +/- 2.4 mmol/kg dry wt) vs. the Hi-CHO (27.5 +/- 2.1 mmol/kg dry wt) trial. Furthermore, self-paced cycling time was significantly greater for the Hi-Fat (139.3 +/- 7.1 min) compared with the Hi-CHO (117.1 +/- 3.2 min) trial. These data demonstrate that there was not a significant difference in muscle triglyceride concentration before and after a prolonged moderate-intensity cycling bout. Nevertheless, a high-fat diet increased muscle triglyceride concentration and reduced self-paced cycling performance 24 h after the exercise compared with a high-carbohydrate diet.

We compared the accuracy of two physical activity recall questionnaires and a motion detector in 45- to 84-yr-old women ( n = 35) and men ( n = 32), using doubly labeled water (DLW) in conjunction with indirect calorimetry as the criterion measure. Subjects were administered the Yale Physical Activity Survey (YPAS) and Minnesota Leisure Time Physical Activity Questionnaire (LTA). Physical activity energy expenditure was determined over a 10-day period by using a Caltrac uniaxial accelerometer and DLW in conjunction with indirect calorimetry. In older women, Minnesota LTA (386 ± 228 kcal/day) and Caltrac (379 ± 162 kcal/day) underestimated physical activity by ∼55% compared with DLW (873 ± 244 kcal/day). No difference was observed between daily physical activity measured by the YPAS (863 ± 447 kcal/day) and DLW in older women. In older men, Minnesota LTA (459 ± 288 kcal/day) and Caltrac (554 ± 242 kcal/day) underestimated daily physical activity by ∼50–60% compared with DLW (1,211 ± 429 kcal/day). No difference was found between physical activity measured by the YPAS (1,107 ± 612 kcal/day) and DLW in older men. Despite no difference in mean physical activity levels between YPAS and DLW in women and men, Bland and Altman ( Lancet 1: 307–310, 1986) analyses demonstrated poor concordance between DLW and YPAS (i.e., limits of agreement = −1,310–1,518 kcal/day). Our data suggest that the Minnesota LTA recall and Caltrac uniaxial accelerometer may significantly underestimate free-living daily physical activity energy expenditure in older women and men. Although the YPAS compares favorably with DLW on a group basis, its use as a proxy measure of individual daily physical activity energy expenditure may be limited in older women and men.

In weight-stable subjects, MI resulted in no change in ISGD, and the improvement in ISGD with HI was completely reliant on improvements in nonoxidative glucose disposal.

The purpose of this investigation was to determine the effect of caffeine ingestion on work output at various levels of perceived exertion during 30 min of isokinetie variable-resistance cycling exercise. Ten subjects completed six trials 1 hr after consuming either 6 mg · kg−1caffeine (3 trials) or a placebo (3 trials). During each trial the subjects cycled at what they perceived to be a rating of 9 on the Borg rating of perceived exertion scale for the first 10 min, a rating of 12 for the next 10 min, and a rating of 15 for the final 10 min. Total work performed during the caffeine trials averaged 277.8 ± 26.1 kJ, whereas the mean total work during the placebo trials was 246.7 ± 21.5 kJ (p< .05). Blood glycerol and free fatty acid levels increased over time to a significantly greater degree in the caffeine trials than in the placebo trials (p< .05). However, there were no significant differences between conditions in respiratory exchange ratio. These data suggest that caffeine may play an ergogenic role in exercise performance by altering both neural perception of effort and substrate availability.

A high-carbohydrate diet consumed ad libitum, with no attempt at energy restriction or change in energy intake, results in losses of body weight and body fat in older men and women.