Redistribution of mechanical work at the knee and ankle joints during fast running in minimalist shoes

Context: Minimalist shoes have been suggested as a way to alter running biomechanics to improve running performance and reduce injuries. However, to date, researchers have only considered the effect of minimalist shoes at slow running speeds. Objective: To determine if runners change foot-strike pattern and alter the distribution of mechanical work at the knee and ankle joints when running at a fast speed in minimalist shoes compared with conventional running shoes. Design: Crossover study. Setting: Research laboratory. Patients or Other Participants: Twenty-six trained runners (age = 30.0 ± 7.9 years [age range, 18-40 years], height = 1.79 ± 0.06 m, mass = 75.3 ± 8.2 kg, weekly training distance = 27 ± 15 km) who ran with a habitual rearfoot foot-strike pattern and had no experience running in minimalist shoes. Intervention(s): Participants completed overground running trials at 18 km/h in minimalist and conventional shoes. Main Outcome Measure(s): Sagittal-plane kinematics and joint work at the knee and ankle joints were computed using 3-dimensional kinematic and ground reaction force data. Footstrike pattern was classified as rearfoot, midfoot, or forefoot strike based on strike index and ankle angle at initial contact. Results: We observed no difference in foot-strike classification between shoes (χ²₁ = 2.29, P =.13). Ankle angle at initial contact was less (2.468 versus 7.43°; t₂₅ = 3.34, P =.003) and strike index was greater (35.97% versus 29.04%; t₂₅ = 2.38, P =.03) when running in minimalist shoes compared with conventional shoes. We observed greater negative (52.87 J versus 42.46 J; t₂₄ = 2.29, P =.03) and positive work (68.91 J versus 59.08 J; t₂₄ = 2.65, P=.01) at the ankle but less negative (59.01 J versus 67.02 J; t₂₄ = 2.25, P =.03) and positive work (40.37 J versus 47.09 J; t₂₄ = 2.11, P =.046) at the knee with minimalist shoes compared with conventional shoes. Conclusions: Running in minimalist shoes at a fast speed caused a redistribution of work from the knee to the ankle joint. This finding suggests that runners changing from conventional to minimalist shoes for short-distance races could be at an increased risk of ankle and calf injuries but a reduced risk of knee injuries.