Effects of load and gradient on energy cost of running

Abstract

This study quantified the interaction of electromyography (EMG) obtained from the vastus lateralis and metabolic energy cost of running (Cr; mL· [mass+load]-1· meter-1), an index of running economy, during submaximal treadmill running. Experiments were conducted with and without load on the back on a motor-driven treadmill on the downhill, level and uphill slopes. The obtained EMG was full-wave rectified and integrated (iEMG). The iEMG was divided into eccentric (ECC) and concentric (CON) phases with a foot sensor and a knee-joint goniometer. The ratio of ECC to CON (ECC/CON ratio) was regarded as the muscle elastic capacity during running on each slope. The Cr was determined as the ratio of the 2-min steady-state V̇ O2 to the running speed. We found a significant decrease in the Cr when carrying the load at all slopes. The ECC/CON ratio was significantly higher in the load condition at the downhill and level slopes, but not at the uphill slope. A significant gradient difference was observed in the Cr (down uphill). Thus, an alteration of Cr by the gradient and load was almost consistent with that of the ECC/CON ratio. The ECC/CON ratio, but not the rotative torque (T) functioning around the center of body mass, significantly correlated with Cr (r=-0.41, p<0.05). These results indicated that the ECC/CON ratio, rather than T, contributed to one of the energy-saving mechanisms during running with load.