Duty factor and stride frequency as (potential) load magnitude determinants of slow, female runners’ habitual running pattern

Running is one of the most popular leisure activities due to its low costs, easy accessibility and associated health benefits. Most of the runners are recreational runners who run at (very) slow speeds. Unfortunately, half of these runners develop a running related injury (RRI). These injuries are predominantly determined by the load that is exerted on the body. Whereas the internal load exerted on tissue level is difficult to quantify, external forces and kinematics are not. As such, ground reaction forces (GRFs) and joint moments are often used as operational measure to provide insights in this internal loading. Running style spatiotemporal defined by duty factor (DF; the product of contact time with stride frequency) and stride frequency (SF) determines the external loading that a runner experiences. Given that recreational runners show a high interindividual variation in DF and SF, establishing the relationship between these parameters themselves but also with external and internal load measures provide deeper understanding of how running style can be used to identify runners’ with a higher risk for the development of a RRI.