Reduced oxygen cost of running is related to alignment of the resultant GRF and leg axis vector: A pilot study

 Purpose: This pilot study investigated whether a ten-week running programme (10wkRP), which reduced the oxygen cost of running, affected resultant ground reaction force (GRF), leg axis alignment, joint moment characteristics and gear ratios. Methods: Ten novice, female runners completed a 10wkRP. Running kinematics and kinetics, in addition to oxygen consumption (VO2) " during steady-state running, were recorded pre- and post-10wkRP. Results: VO2 decreased (8%) from pre-10wkRP to post-10wkRP. There was a better alignment of the resultant GRF and leg axis at peak propulsion post-10wkRP compared to pre-10wkRP (10.8 ± 4.9 vs. 1.6 ± 1.2°), as the resultant GRF vector was applied 7 ± 0.6° (p=0.008) more horizontally. There were shorter external ankle moment arms (24%) and smaller knee extensor moments (23%) at peak braking post-10wkRP. The change in VO2 was associated with the change in alignment of the resultant GRF and leg axis (rs = 0.88, p=0.003). Conclusion: As runners became more economical they exhibited a more aligned resultant GRF vector and leg axis at peak propulsion. This appears to be a self-optimisation strategy that may improve performance. Additionally, changes to external ankle moment arms indicated beneficial low gear ratios were achieved at the time of peak braking force.