Eriksud, O., Moltubakk, M. M, & Smith, G. A. (2007). Flexibility and stiffness interactions influence running economy. ACSM Annual Meeting New Orleans, Presentation Number, 820.

"Running economy is the submaximal oxygen uptake at a given speed and has been found to vary considerably for any group of runners. Both flexibility and leg stiffness have been associated with running economy. A stiffer system is perhaps more effective in returning energy stored elastically as part of the stretch-shortening cycles of running, but increased range of motion (ROM) may enhance a runner's stride length capability. The interaction of these factors influencing running economy are poorly understood".

This study determined the effect of leg stiffness and joint ranges of motion in the lower extremity on running economy. Ss (N = 26) completed range of motion, running economy, and VO2max testing. Measures of ankle and hip flexibility were obtained using standard hand-held goniometer measurement procedures. VO2max was measured with a standard protocol from which running speeds corresponding to 60, 70, and 80% of maximum velocity were obtained. Running economy measures at these speeds were recorded during the 5-7th minute of an eight- minute bout.

Significant negative correlations of ankle range of motion to oxygen uptake at the common speeds and vertical stiffness were found. While vertical stiffness and hamstring flexibility were negatively correlated, neither was related to economy. Step time was positively related to VO2 at the common speeds.

Implication. Running economy was not related to vertical stiffness or hip ranges of motion, but was clearly influenced by ankle flexibility/stiffness.

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