Oxygen consumption and energy expenditure of level versus downhill running

<b>Objective</b>\ud \ud - The purpose of this study was to assess and compare submaximal oxygen consumption (VO2) and energy expenditure (kJ) while running at 0, -1.8, -3.6, and -5.4% grades for three individually selected running speeds (9.4 + 0.79, 10.3 + 0.74, 11.3 + 0.73 km.h-1).\ud \ud <b>Experimental Design</b>\ud \ud - Subjects completed the four grade conditions in random order via a modified Latin squares design at three self-selected submaximal running speeds for each condition.\ud \ud <b>Participants</b>\ud \ud - Thirteen (5 females and 8 males) recreational (< 35 km.wk-1) runners (age: 27.7 +/- 4.3 yrs) volunteered for the study.\ud \ud <b>Measures</b>\ud \ud - Two-way repeated measures ANOVA (Grade x Speed) was used to analyze steady-state VO2 and kJ expenditure. Stepwise linear multiple regression was used to develop an equation for predicting VO2 for running at recreational speeds on moderately negative grades.\ud \ud <b>Results</b>\ud \ud - VO2 and kJ mean values were significantly different between all speed and % grade comparisons. Compared to level grade, the average reductions in VO2 and kJ expenditure ranged from approximately 9% at a grade of -1.8% to 22% at a grade of -5.4%. The relationship between VO2 and % grade for each running speed was linear.\ud \ud <b>Conclusions</b>\ud \ud - For a given speed, running at a modest negative grade can significantly decrease VO2 and kJ expenditure compared to level running. The following regression equation can be used to estimate VO2 (ml.kg-1.min-1) for running at recreational speeds on slight downhills: VO2 = 6.8192 + 0.1313 (speed in m.min-1) + 1.2367 (% grade)