Purpose: To determine the effect of manipulating foot longitudinal arch motion with different-stiffness foot orthoses on running economy (RE) in runners with flat-arched feet and if changes in arch deformation and recoil were associated with changes in RE.
Methods: Twenty-three recreational distance runners performed 5-minute submaximal treadmill runs at 12 km·h-1, in the following 3 conditions in a randomized order: (1) footwear only, (2) flexible orthoses (reduced arch thickness), and (3) standard orthoses. The RE (submaximal steady-state oxygen consumption [VO2submax]) and sagittal arch range of motion were compared among conditions using a repeated-measures analysis of variance and effect sizes (Cohen d). Pearson correlation coefficients were used to determine the association between the change in the sagittal arch range of motion and VO2submax.
Results: Compared with standard orthoses, the mean VO2submax was significantly lower in both the flexible orthoses (-0.8 mL·kg-1·min-1, P < .001, d = 0.35) and footwear-only conditions (-1.2 mL·kg-1·min-1, P < .001, d = 0.49). The change in VO2submax between the flexible orthoses and footwear-only conditions was significantly positively correlated with the change in sagittal arch range of motion (r = .591, P = .005).
Conclusion: Conventional foot orthoses were associated with poorer RE compared with flexible orthoses and footwear alone. Changes in arch deformation were positively correlated to changes in oxygen consumption, indicating that foot orthoses that limit arch deformation and recoil degrade RE. Foot orthoses that facilitate energy storage and release in the foot longitudinal arch may be advisable for athletes prescribed these devices for clinical purposes to maintain optimal running performance.
Keywords: athlete; biomechanics; energy; footwear; performance.