Skeletal muscle in running.

"skeletal muscle may provide a fundamentally different mechanical function during running than during activities such as swimming,flying, or jumping. These activities require muscle contractions that produce mechanical work at high rates to overcome drag,produce lift, or accelerate the body. Because running requires negligible work against drag and the average mechanical energy of the body is constant over time (at a steady speed on level ground), the demands of support may be met most economically by muscles that produce force while minimizing mechanical work."- Roberts et al

Muscular Force in Running Turkeys:
The Economy of Minimizing Work
Thomas J. Roberts,* Richard L. Marsh, Peter G. Weyand,
C. Richard Taylor