High-intensity running and plantar-flexor fatigability and plantar-pressure distribution in adolescent runners

Abstract

Context: Fatigue-induced alterations in foot mechanics may lead to structural overload and injury. Objectives: To investigate how a high-intensity running exercise to exhaustion modifies ankle plantar-flexor and dorsiflexor strength and fatigability, as well as plantar-pressure distribution in adolescent runners. Design: Controlled laboratory study. Setting: Academy research laboratory. Patients or Other Participants: Eleven male adolescent distance runners (age 1/4 16.9 6 2.0 years, height 1/4 170.6 6 10.9 cm, mass 1/4 54.6 6 8.6 kg) were tested. Intervention(s): All participants performed an exhausting run on a treadmill. An isokinetic plantar-flexor and dorsiflexor maximal-strength test and a fatigue test were performed before and after the exhausting run. Plantar-pressure distribution was assessed at the beginning and end of the exhausting run. Main Outcome Measure(s): We recorded plantar-flexor and dorsiflexor peak torques and calculated the fatigue index. Plantar-pressure measurements were recorded 1 minute after the start of the run and before exhaustion. Plantar variables (ie, mean area, contact time, mean pressure, relative load) were determined for 9 selected regions. Results: Isokinetic peak torques were similar before and after the run in both muscle groups, whereas the fatigue index increased in plantar flexion (28.1%; P 1/4 .01) but not in dorsiflexion. For the whole foot, mean pressure decreased from 1 minute to the end (3.4%; P 1/4 .003); however, mean area (9.5%; P 1/4 .005) and relative load (7.2%; P 1/4 .009) increased under the medial midfoot, and contact time increased under the central forefoot (8.3%; P 1/4 .01) and the lesser toes (8.9%; P 1/4 .008). Conclusions: Fatigue resistance in the plantar flexors declined after a high-intensity running bout performed by adolescent male distance runners. This phenomenon was associated with increased loading under the medial arch in the fatigued state but without any excessive pronation.