The Influence of Footwear on Running Mechanics, Impact, and Plantar Loading in Habitual Rearfoot Strikers

Abstract

Running overuse injuries are related to the magnitude of impact forces and shocks, loading rates, and the distribution of forces underfoot. Minimalist shoes and barefoot running might reduce or eliminate running impacts by encouraging softer landings. However, reduced cushioning could increase plantar loading and some runners may not alter their habitual running mechanics to account for less cushioning. PURPOSE: To examine the acute effects of a cushioned neutral shoe (CN), minimal shoes (MN), and neoprene socks (BF) on running mechanics, impact, and plantar pressure. METHODS: Forty habitual rearfoot strikers ran on an instrumented treadmill while 3D kinematics, ground reactions forces (GRF), tibial accelerations (TA), and plantar pressure were recorded. Variables examined included: foot and knee angle at contact, vertical GRF loading rate (VLR), the isolated impact component of vertical GRF (IP), and the magnitude of peak positive to negative TA. Peak plantar pressure was compared for the forefoot (FFP), midfoot (MFP), and rearfoot (RFP). Differences were compared with a RMANOVA and post hoc t-tests (α=0.05). RESULTS: With less cushioning the foot was less dorsiflexed at contact BF 8.6±5.3° < MN 11.30±5.0 ° < CN 16.0±4.4° (p<0.01). The knee was more extended at contact in CN 13.3±6.6° than MN 14.8±5.9° and BF 15.2±5.8° (p<0.001). VLR was less in CN 670±212 N/kg/s compared to MN 980±268 N/kg/s and BF 975±371 N/kg/s (p<0.001) as was IP 4.1±16 N/kg vs 6.8±2.6 N/kg & 6.7±3.2 N/kg (p<0.001). TA was lower in CN 9.4±4.2 g than BF 12.6±6.7 g and MN 11.4±5.5 g (p<0.01). FFP increased with less cushioning: CN 330±70 kPa < MN 430±87 kPa < BF 561±76 kPa (p<0.001). MFP was less in CN 144±35 kPa compared to MN 212±58 kPa and BF 224±108 kPa (p<0.05). RFP was lower in CN 253±52 kPa vs MN 272±81 kPa and BF 396±170 kPa (p<0.001). CONCLUSION: Less cushioning resulted in a more compliant configuration of the limb at ground contact, which agrees with previous research. However, the CN shoe reduced VLR, IP, and TA compared to MN and BF despite a more extended knee and dorsiflexed foot. Lower peak plantar pressures in CN suggest that cushioning better distributes plantar forces of a less compliant limb particularly in the rearfoot. These results highlight the importance of both cushioning and mechanics on injury related variables.