ABSTRACT
PURPOSE: This study quantified the metabolic demands (oxygen uptake (VÌO 2 )), power output adjustments, changes in the VÌO 2 /power output ratio, and perceptual responses (rating of perceived exertion (RPE)) during constant heart rate (HR) exercise performed within the vigorous intensity range (77%-95% HR peak ). METHODS: Twelve women (mean ± SD age, 22 ± 4 yr) performed a graded exercise test to exhaustion to determine peak parameters, and three randomly ordered, constant HR trials to exhaustion or for 60 min at the lower (HR L = 77% HR peak ), middle (HR M = 86% HR peak ), and higher (HR H = 95% HR peak ) end of the vigorous intensity range. Time course of changes and patterns of responses were examined for VÌO 2 , power output, VÌO 2 /power output, and RPE for the composite and for each subject. RESULTS: Across the HR L (time to exhaustion ( Tlim ) = 56.3 ± 9.9 min), HR M (51.8 ± 13.5 min), and HR H (27.2 ± 17.7 min) trials, VÌO 2 and power output decreased quadratically ( P < 0.05) relative to the initial value from 10% to 100% of Tlim , whereas the VÌO 2 /power output increased quadratically from 20% to 100% Tlim , and RPE increased linearly from 50% to 100% Tlim . The VÌO 2 and RPE, collapsed across time, for HR L (54.3% ± 3.3% VÌO 2peak , 11 ± 1.5 RPE) were lower than HR M (64.9% ± 4.5% VÌO 2peak , 14 ± 1.7 RPE), and both were lower than HR H (80.1% ± 4.1% VÌO 2peak , 17 ± 1.4 RPE). None of the 12 subjects at HR L , 6 at HR M , and 7 at HR H were within the vigorous VÌO 2 range. CONCLUSIONS: The HR L was not sufficient to meet the desired metabolic intensity for vigorous exercise, whereas the middle to higher end of the range elicited a VÌO 2 within the prescribed range of only ~50%-60% of the subjects. This study indicated that exercise held constant at a percentage of HR peak cannot consistently be used to prescribe a desired metabolic stimulus.
Subject(s)
Exercise , Oxygen Consumption , Humans , Female , Adolescent , Young Adult , Adult , Heart Rate/physiology , Oxygen Consumption/physiology , Exercise/physiology , Exercise Test , Physical Exertion/physiologyABSTRACT
The objectives of this study are threefold: 1) to assess whether 7 days of oral glutamine (GLN) supplementation reduces exercise-induced intestinal permeability; 2) whether supplementation prevents the proinflammatory response; and 3) whether these changes are associated with upregulation of the heat shock response. On separate occasions, eight human subjects participated in baseline testing and in GLN and placebo (PLA) supplementation trials, followed by a 60-min treadmill run. Intestinal permeability was higher in the PLA trial compared with baseline and GLN trials (0.0604 ± 0.047 vs. 0.0218 ± 0.008 and 0.0272 ± 0.007, respectively; P < 0.05). IκBα expression in peripheral blood mononuclear cells was higher 240 min after exercise in the GLN trial compared with the PLA trial (1.411 ± 0.523 vs. 0.9839 ± 0.343, respectively; P < 0.05). In vitro using the intestinal epithelial cell line Caco-2, we measured effects of GLN supplementation (0, 4, and 6 mM) on heat-induced (37° or 41.8°C) heat shock protein 70 (HSP70), heat shock factor-1 (HSF-1), and occludin expression. HSF-1 and HSP70 levels increased in 6 mM supplementation at 41°C compared with 0 mM at 41°C (1.785 ± 0.495 vs. 0.6681 ± 0.290, and 1.973 ± 0.325 vs. 1.133 ± 0.129, respectively; P < 0.05). Occludin levels increased after 4 mM supplementation at 41°C and 6 mM at 41°C compared with 0 mM at 41°C (1.236 ± 0.219 and 1.849 ± 0.564 vs. 0.7434 ± 0.027, respectively; P < 0.001). GLN supplementation prevented exercise-induced permeability, possibly through HSF-1 activation.