The mechanisms behind these improvements in running performance, running economy, and running speed continued to be studied by researchers. In general these positive adaptations can be summarized into three main areas.

1. Muscle fiber type – strength training has been shown to prolong the time required before an athlete must recruit their fast twitch or type II muscle fibers. Thus becoming more efficient through longer utilization of their slow twitch or type I fibers. In addition, authors have found an improvement in the oxygen utilization and fatigue resistant subtype of type II fibers (Aagaard et al. Scan J Med Sci Sports. 2011).

2. Improvements in rate of force development – heavy strength training, especially eccentric focused strength training, consistently has been shown to improve the speed at which a muscle develops force. RFD is a critical component of sports performance and running economy allowing a runner to move more quickly through their running gait.

3. Improvements in tendon stiffness – strength training improves the elastic quality of our muscle’s tendons improving their ability to store and release energy. This mechanism reduces our muscle’s required effort during gait conserving valuable fuel and oxygen. For example, researchers have estimated runners would burn 1/3 more oxygen and fuel if they were without these evolutionary adaptation.

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