Positive joint work redistribution in running: the role of plantar flexor fatigue and the effect of advanced footwear technology

Over the course of a near-maximal effort 10 km run, positive mechanical work decreases at the ankle and increases at the knee. Although plantar flexor fatigue is believed to be responsible for the proximal shift in mechanical work generation, this has yet to be confirmed experimentally. PurposeTo 1) determine the effect of plantar flexor fatigue on lower limb positive joint work during running and 2) determine the effect of running shoes on this relationship. MethodsTrained male runners (n = 12) were analyzed over two 30 s runs at their 10 km race pace, without and with local plantar flexor fatigue induced via a calf-raise protocol to a level commensurate with that accumulated over an exhaustive run ([~]24% reduction in peak torque). Both the unfatigued and fatigued runs were performed in a traditional shoe and in advanced footwear technology on an instrumented treadmill while three-dimensional motion capture and ground reaction force data were collected. ResultsPlantar flexor fatigue led to a redistribution of joint work, with lower positive ankle work (p < 0.001), greater positive knee work (p = 0.001), and similar positive hip work (p = 0. 550) in the fatigued run as compared to the unfatigued run. The relative positive joint contributions shifted proximally with fatigue (ankle - 4%, knee +3%); however, this shift was not influenced by shoe condition (p > 0.05). ConclusionPlantar flexor fatigue contributes to the proximal redistribution of positive joint work during running. However, the adoption of a suboptimal gait strategy appears to occur regardless of whether a runner wears a traditional shoe or advanced running footwear technology.