Intrinsic and Extrinsic Muscle Function in Rearfoot Strikers During Barefoot and Shod Treadmill Running

Abstract

Barefoot/minimalist running is theorized to cause an increase in the activity of intrinsic and extrinsic foot muscles. Although studies have shown an increase in the activity of extrinsic foot muscles during barefoot running very little data exists documenting the effects of barefoot running on intrinsic foot muscles. PURPOSE: To compare the activity of select extrinsic and intrinsic muscles during barefoot and shod running in rearfoot strikers. METHODS: A convenience sample of 21 recreational runners were assigned to run both shod and barefoot in a random order. Electrodes were placed on the subjects’ dominant lower extremity over the peroneus longus (PL), tibialis anterior (TA), and abductor halluces (AH) muscles. Subjects participated in a treadmill running protocol consisting of running at 8.0 and 9.7 kph while lower extremity kinematics and electromyographic (EMG) activity of the muscles were recorded using an 8 camera motion analysis system in both footwear conditions. The EMG data were filtered with a fourth order, band pass filter with 10 and 350 Hz cutoffs. Using a 250 ms window, the root mean square (RMS) of the filtered data was obtained. The RMS was normalized to the peak EMG activity of the 8.0 kmh barefoot trials. Using the marker displacement data, the stance phases of the amplitude normalized 9.7 kmh trials were extracted. The average RMS value of the PL, TA, and AH during the stance phase of these trials were obtained and grouped according to running speed and muscle. A two factor, fixed effects ANOVA model was used to determine the effect of footwear condition and muscle on the mean RMS values. RESULTS: The mean (± 1 S.E.) amplitude normalize RMS value during the barefoot condition for the TA, PL, and AH was 50 (± 4.7), 109 (± 17.9), and 123 (± 18.4) percent, respectively. During the shod condition the mean (± 1 S.E.) amplitude normalize RMS value for the TA, PL, and AH was 52 (± 6.1), 103 (± 17.3), and 130 (± 16.8). A significant effect was noted only for muscle (p < .001). Both the PL and the AH exhibited significantly greater activity than the TA in both the shod and barefoot conditions. A significant effect of footwear condition was not present (p = .923). CONCLUSIONS: In rearfoot strikers, footwear does not appear to affect the EMG activity of the TA, PL, or AH.