Effects Of Gradient Variations On Physiological Responses To A 30-minute Run

Abstract

PURPOSE: This study was designed to test the hypothesis that when subjects engaged in DHR at different gradients, the extent of their physiological and biomechanical responses would be related to the gradient at which DHR took place. METHODS: Forty-eight untrained men (21.5±0.5 years) were randomly assigned into 0%, -5%, -11%, and -16% groups (n=12 per group), and then performed a 30-minute run at gradients of 0%, -5%, -11%, and -16%, respectively, at the intensity of 70% of their pre-determined VO2max. VO2, minute ventilation (VE), heart rate (HR), and rating of perceived exertion (RPE) were measured at 5, 10, 15, 20, 25 and 30 minutes, respectively, during each run. Blood lactate (LA) concentration was assessed by fingertip blood sample at 3 minutes after each run. Stride length, stride frequency, and range of motion for the ankle, knee and hip joints at 5, 10, 15, 20, 25 and 30 minutes, respectively, during each run were analyzed using high-speed (120Hz) video images. A two-way mixed-design ANOVA was used to determine the differences of physiological and biomechanical parameters among the groups. RESULTS: Elevations of VO2, VE, and HR during running for the -11% and -16% groups were significantly greater than for the -5% and 0% groups (p<.05). However, the changes in these measures showed no significant difference (p>.05) between the 0% and -5% groups, or the -11% and -16% groups. As for RPE, LA, and biomechanical parameters, no significant differences (p>.05) among the groups were observed. CONCLUSION: These findings suggest that the steeper the gradient, the greater the increases in VO2, VE and HR. This may be due to the fact that at a steeper downhill gradient (-16%), the quadriceps femoris muscle lengthens to a greater extent than at lower (-5%, -11%) and level gradients. Further studies are warranted to understand the mechanisms underlying the different extents of physiological responses at different gradients of running.