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Rehabilitation Physiology Lab

Recent Publications


Perini R, S. Milesi, NM Fisher, DR Pendergast, A Veicsteinas. Heart rate variability during dynamic exercise in elderly males and females. Eur J Appl Physiol 82(1-2):8-15, 2000 .

It has been proposed that cardiac control is altered in the elderly. Power spectral analysis of heart rate variability (HRV) was performed on 12 male and 11 female elderly subjects (mean age 74 years) while at rest in supine and sitting positions, and at steady states during 5 min of exercise (35-95% peak oxygen consumption, VO2peak). There were no differences in power, measured as a percentage of the total of the high frequency peak (HF, centered at about 0.25 Hz; 13% in males vs 12% in females), low frequency peak (LF, centered at 0.09 Hz; 25% in males and 22% in females), and very low frequency component (VLF, at 0.03 Hz; 66^ in males and 69% in females) between body positions at rest. There was no difference in spectral power between male and female subjects. Total power decreased as a function of oxygen consumption during exercise, LF% did not change up to about 14 ml x kg(-1) x min(-1) (40% and 80% VO2peak in males and females, respectively), then decreased towards minimal values in both genders. HF% power and central frequency increased linearly with metabolic demand, reaching higher values in male subjects than in female subjects at VO2peak, while VLF% remained unchanged. Thus, the power spectra components of HRV did not reflect the changes in autonomic activity that occur at increasing exercise intensities, confirming previous findings in young subjects, and indicated similar responses in both genders.

Horvath PJ, CK Eagen, NM Fisher, JJ Leddy and DR Pendergast. The effects of varying dietary fat on performance and metabolism in trained male and female runners. J Am College Nutrition 19(1):52-60, 2000.

Low dietary fat intake has become the diet of choice for many athletes. Recent studies in animals and humans suggest that a high fat diet may increase VO2max and endurance. We studied the effects of a low, medium and high fat diet on performance and metabolism in runners. Twelve male and 13 female runners (42 miles/week) ate diets of 16% and 31% fat for four weeks. Six males and six females increased their fat intakes to 44%. All diets were designed to be isocaloric. Endurance and VO2max were tested at the end of each diet. Plasma levels of lactate, pyruvate glucose, glycerol, and triglycerides were measured before and after the VO2max and endurance runs. Free fatty acids were measured during the VO2max and endurance runs. Runners on the low fat diet ate 19% fewer calories than on the medium or high fat diets. Body weight, percent body fat (males=71 kg and 16%; females=57 kg and 19%), VO2max and anaerobic power were not affected by the level of dietary fat. Endurance time increased from the low fat to medium fat diet by 14%. No differences were seen in plasma lactate, glucose, glycerol, triglycerides and fatty acids when comparing the low versus the medium fat diet. Subjects who increased dietary fat to 44% had higher plasma pyruvate (46%) and lower lactate levels (39%) after the endurance run. These results suggest that runners on a low fat diet consume fewer calories and have reduced endurance performance than on a medium or high fat diet. A high fat diet, providing sufficient total calories, does not compromise anaerobic power.