The purpose of this study was to determine if there is a difference between the way in which aerobically trained and untrained women metabolize fats and carbohydrates at rest in response to either a high-fat or high-carbohydrate meal. Subjects, 6 per group, were fed a high CHO meal (2068 kJ, 76% CHO. 23% fat, 5% protein) and a high fat meal (2093 kJ, 21% CHO, 72% fat, 8% protein) in counterbalanced order. Resting metabolic rate (RMR) was measured every half-hour for 5 hours. RMR was similar between groups. Training status had no overall effect on postprandial metabolic rate or total energy expenditure. The high fat meal resulted in no significant differences in RMR or respiratory exchange ratio (RER) between groups. However, after ingesting a high CHO meal, trained subjects had a peak in metabolism at minute 60, not evident in the untrained subjects. In addition, postprandial RER from minutes 120-300 were lower and fat use was greater after the high CHO meal for the trained subjects. These results suggest that aerobically trained women have an accelerated CHO uptake and overall lower CHO oxidation following the ingestion of a high CHO meal.
Victoria L. Bowden and Robert G. McMurray
Dawn M. Maffucci and Robert G. McMurray
The purpose of this study was to compare the effect a 6-hr versus 3-hr prefeeding regimen on exercise performance. The subjects were 8 active women (21.4 ± 0.9 years, 60.4±2.4 kg, 19.9 ± 1.3% body fat. and 165.6±2.1 cm). All women completed 2 exercise trials (separated by 3—6d) on a treadmill where they ran at moderate intensity for 30 min with 30-s sprints at 5-min intervals, followed directly by increasing incrementally the grade until volitional fatigue was achieved. The exercise trials were performed 3 hr and 6 hr after consuming 40 ± 3 kJ/kg meal. Time to exhaustion was 0.75 min shorter (p = .0001) for the 6-H trials compared to the 3-H trials. There were no significant differences in submaximal or peak oxygen uptake, heart rate, or rating of perceived exertion (p > .05). The 6-H trials compared to the 3-H trials resulted in .05 lower RERs (p = .0002), and a 2 mmol lower blood lactate at exhaustion (p = .012). Blood glucose levels and cortisol responses to exercise were similar between trials (p > .05). However, both resting and post exercise insulin levels were lower during 6-H trials. It was concluded that performance of moderate- to high-intensity exercise lasting 35—40 min is improved by consuming a moderately-high carbohydrate. low fat, low protein meal 3-hr before exercise compared to a similar meal consumed 6 hr prior to exercise. Thus, athletes should not skip meals before competition or training sessions.
Daniela A. Rubin, Robert G. McMurray, Joanne S. Harrell, Barbara W. Carlson, and Shrikant Bangdiwala
The purpose of this project was to determine the accuracy in lipids measurement and risk factor classification using Reflotron, Cholestech, and Ektachem DT-60 dry-chemistry analyzers. Plasma and capillary venous blood from fasting subjects (n = 47) were analyzed for total cholesterol (TC), high density lipoprotein (HDL-C), and triglycerides (TG) using these analyzers and a CDC certified laboratory. Accuracy was evaluated by comparing the results of each portable analyzer against the CDC reference method. One-way ANOVAs were performed for TC, HDL-C, and TG between all portable analyzers and the reference method. Chi-square was used for risk classification (2001 NIH Guidelines). Compared to the reference method, the Ektachem and Reflotron provided significantly lower values for TC (p < .05). In addition, the Cholestech and Ektachem values for HDL-C were higher than the CDC (p < .05). The Reflotron and Cholestech provided higher values of TG than the CDC (p < .05). Chi-squares analyses for risk classification were not significant (p > .45) between analyzers. According to these results, the Ektachem and Cholestech analyzers met the current NCEP III guidelines for accuracy in measurement of TC, while only Ektachem met guidelines for TG. All 3 analyzers provided a good overall risk classification; however, values of HDL-C should be only used for screening purposes.
Mitch D. VanBruggen, Anthony C. Hackney, Robert G. McMurray, and Kristin S. Ondrak
The effect of exercise intensity on the tracking of serum and salivary cortisol responses was examined in 12 endurance-trained males (maximal oxygen uptake [VO2max] = 58.2 ± 6.4 mL/kg/min).
Subjects rested for 30 min (control) and exercised on a cycle ergometer for 30 min at 40% (low), 60% (moderate), and 80% (high intensity) of VO2max on separate days. Serum and saliva samples were collected pretrial, immediately posttrial, and 30 min into the recovery period from each trial.
Cortisol responses increased significantly for both serum (40.4%; P = .001) and saliva (170.6%; P = .007) only in response to high-intensity exercise. Peak saliva cortisol occurred at 30 min of recovery, whereas peak serum was at the immediate posttrial sampling time point. The association between serum and saliva cortisol across all trials was examined using concordance correlation (R c) analysis, which accounts for repeated measures. The overall correlation between serum and saliva cortisol levels in all matched samples was significant (R c = 0.728; P = .001). The scatter plot revealed that salivary cortisol responses tracked closely to those of serum at lower concentrations, but not as well at higher concentrations.
Findings suggest salivary measurements of cortisol closely mirror those in the serum and that peak salivary concentrations do not occur until at least 30 min into the recovery from intense exercise.