The mechanical determinants of energetic cost in backward running

Thesis (M.S.)--Humboldt State University, Kinesiology: Exercise Science/Wellness Management, 2009The purpose of this experimental study was to investigate the determinants of energetic cost of backward running and determine if backward running is metabolically more expensive than forward running as a result of using faster stride frequencies and/or reduced effective mechanical advantage. Twelve adults (six females and six males) ran forward and backward on a treadmill at a speed of 2.24 m/s (5 mph). Researchers examined the effect of stride frequency on metabolic cost and kinematics as subjects performed three seven minute running trials: one forward at preferred stride frequency, one backward at preferred stride frequency and one forward at a prescribed stride frequency matched to the backward stride frequency. Metabolic cost was determined using indirect calorimetry and lower limbs kinematics were measured using 3-D motion capture (Vicon, Centennial, CO). A 2X2 ANOVA revealed that at preferred stride frequencies, backward running elicits a 27.81% ?? 0.86 higher metabolic cost compared to forward running. Moreover, when using the same stride frequency, backward running still had a 25% ?? 0.82 greater metabolic cost compared to forward running. During backward running, average knee flexion increases 11.93% ??4.15 and stance time decreases 22.23% ?? 4.18 compared to forward running. Multivariate regression analysis revealed that average stance phase knee flexion can predict 54% of the variance in metabolic cost of running and stance time can predict 13% of the variance in metabolic cost of running. Thus, a decrease in effective mechanical advantage of the knee extensor muscles and reduced stance time are the primary determinants of the greater metabolic cost of backward running