M. J. Williams

Effects of exercise intensity on 24-h energy expenditure and substrate oxidation

The purpose of this study was to determine: 1) the reliability of 24-h respiratory calorimetry measurements, and 2) the effects of low- versus high-intensity exercise on energy expenditure (EE) and substrate oxidation over a 24-h period. Eight women (age 28 +/- 4.3 yr) were measured for body composition, maximal oxygen consumption while cycling, and EE in three, 24-h calorimeter tests, with identical work output but differing intensity during a 60-min exercise session. Low-intensity (LI) exercise involved continuous cycling at 50% VO2max; whereas high-intensity (HI) exercise involved interval cycling (2 min exercise/recovery) at 100% VO2max. Subjects were randomly assigned to the first two tests at LI or HI, with the third test at the alternate intensity. No differences in EE or respiratory quotient (RQ) during rest, sleep, exercise, or over the 24 h were found between the first two tests (C.V. = 6.0%), demonstrating the reliability of the measurements. The HI protocol elicited significantly higher EE than LI during rest, exercise, and over 24 h, whereas sleeping EE approached significance. No significant differences in RQ during rest, sleep, or over 24 h were found, but 24-h lipid and carbohydrate oxidation were similar in the two protocols. The HI exercise RQ was significantly higher than LI. These findings demonstrated higher 24-h EE in the HI than LI protocol, but similar 24-h substrate oxidation rates.

INTRA-ABDOMINAL ADIPOSE TISSUE CUT-POINTS RELATED TO ELEVATED CARDIOVASCULAR RISK IN WOMEN.: 1034

Intra-abdominal adipose tissue (IAF) seems to be the primary fat depot putting individuals at risk for cardiovascular disease (CVD). The purpose of this study was to determine IAF cut-points for identifying CVD risk in pre- and post-menopausal women. Age ranged from 18 to 77 y and percentage fat ranged from 9 to 48%. Computed tomography (CT), IAF, DEXA determined regional fat and blood lipid profiles were obtained on 220 Caucasian women. Students t-tests were run to determine differences between pre- and post-menopausal women. Receiver-operating characteristic (ROC) analysis was used to develop IAF cut-points associated with elevated CVD risk. Post-menopausal women had higher percentage fat, greater proportion IAF and higher CVD risk. Menopausal status was not consistently independently related to CVD risk after adjusting for IAF, but IAF was after adjusting for menopausal status. The same cut-points for CVD risk were found with both 4- and 6-CVD risk factor analysis and for both pre- and post-menopausal as well as pooled data. 4-CVD risk factor analysis comprised cholesterol (C), HDL-C, systolic blood pressure and diastolic blood pressure. 6-CVD risk factor analysis comprised the 4-CVD risk factors plus triglycerides and cholesterol : HDL-C ratio. ROC L positive values indicate levels of IAF above which metabolic disturbances will be increased and were determined to be 110 cm2. ROC L negative values indicate levels of IAF below which CVD risk will not be affected and were determined to be 40 cm2. False positives were 3% and false negatives were 9%. ANOVA comparing women with IAF cross-sections less than 40 cm2, between 40 and 110 cm2 and more than 110 cm2 demonstrate large differences in CVD risk profile. It is suggested women who have IAF values above 110 cm2 are in jeopardy of possessing elevated CVD risk.