The Effects of Heel Spring on Lower Limb Muscular Activity and Running Economy

Objective: Running economy (RE) is a performance variable for distance runners. It can be affected by parameters such as equipment, running technique and surface. It has been shown that substantial mechanical energy will return by shoe integrated and that energy could be stored in the Muscle Tendon Units (MTU). The purpose was to investigate the influence of three difference heel positions induced by insoles on lower limb muscular activity and VO₂ and RE (performance variable) changes during steady state running. It was hypothesized that with decreasing heel spring a linear increase in RE would be observed.
Methods: Fifteen healthy trained male runners were tested on a treadmill submaximal pace while surface electromyography (EMG) from nine muscles of leg and thigh, the VO₂ by spirometry and kinematics by 2D video camera was measured. Subjects had to run in three insoles Up Heel (UH) (14 mm heel spring), Flat insole/Heel (FH) and negative spring (DH) (Down Heel) (forefoot 5 mm higher). Data were analyzed with a repeated- measures ANOVA for significant differences between shoe insoles (p<0.05).
Results: Ankle kinematics was systematically altered in response to the inserts (expected) by VO₂ and running economy was not changed. It was shown that not all subject followed the implied changes so when looking at 10 responders a higher activity for Tibialis Anterior (TA) was shown.
Conclusion: It was concluded that heel spring potentially changes energy exchange in the triceps-surae while changes in muscle coordination may compensate for these improvements.  RE is related to many factors such as running style and individually properties.