8 Week Exercise Protocol and Minimalist Shoes Walking Effect on Lower Leg Muscle Size

Abstract

Transitioning to minimalist shoes (MS) is desired by many runners. However, there are concerns about transitioning safely. Pre-transition exercises or low intensity training may facilitate this transition. PURPOSE: The purpose of this preliminary study was to investigate muscle size change after either 8 weeks of walking in MS or 8 weeks of following an exercise protocol. The muscles of interest in the lower leg were the tibialis anterior (TA), tibialis posterior (TP) and flexor digitorum longus (FDL). METHODS: 28 runners (22.6±2.6 yr, 174.4±10.3 cm, 70.0±13.0 kg) continued to run their usual weekly amount and were randomly assigned to a control group (n=7), MS walking group (n=7, progressively increase walking from 2500 steps in MS to 7000 steps/day at 8 weeks), or an exercise group (n=14, 8 weeks of progressive foot muscle exercises). Videos of the TA, TP and FDL were taken starting from a relaxed state to a contracted state and back to the relaxed state via B-mode ultrasound imaging using a 10 MHz linear probe (GE LogiqP6). Videos for the FDL were taken at a point 50% distal from the medial knee joint line to the inferior tip of the medial malleolus with the probe held perpendicular to the shaft of the leg. For the TP and TA the probe was held at a point 30% from the knee joint line to the inferior tip of the lateral malleolus. To obtain videos of the TA and TP, each participant was instructed to invert their foot. For the videos of the FDL, participants were instructed to flex their toes. Videos of the contraction cycle for the TA, TP, and FDL were recorded. 2 separate still-shots of the muscles at rest were saved from the recorded videos to make size measurements. Repeated measures ANCOVA with the respective baseline muscle size as covariate was run. RESULTS: There was a significant main effect for time for all muscles (p<0.02), and a significant group by time interaction (p<0.05) for the change in muscle size for the FDL and TP. The mean and SD for the muscles were TA: 2.5±0.3 cm, TP: 1.8±0.25 cm, FDL: 1.7±0.36 cm2. CONCLUSION: The data from this preliminary study appear to support the idea that walking in MS or performing foot intrinsic strengthening exercises may increase the size of some lower leg muscles. It is unknown if this increase in muscles size will alter the potential risks associated with a transition to minimalist shoe running.