Perturbing Stride Frequency Has No Effect On Average Muscle Activity

Abstract

Running is a popular and widely used mode of exercise in the world today. Preferred stride frequency (PSF) is the stride frequency (SF) a runner selects for a given speed. Changes in SF may influence metabolic costs while running (Meardon & Derrick, 2009, MSSE, 41, 512-513), but it is not clear if muscle activity is minimized at PSF compared to running with other SFs. PURPOSE: To determine if muscle activity is minimized while running at PSF. METHODS: 10 healthy participants (24.7±3.8 years; M=7, F=3) ran on a treadmill at PSF-15%, PSF-10%, PSF-5%, PSF, PSF+5%, PSF+10%, PSF+15%. Conditions were randomized for each subject to account for task adaptation. Treadmill running speed was determined initially by each participant instructing the tester to increase or decrease the speed until felt like a speed representative of a 30-minute run. During preferred running condition, PSF was calculated by visually identifying the time to complete 20 strides. Target SFs were then calculated for all other conditions. Participants ran for 5-minutes at each condition with 1-minute rest between conditions. SF was controlled by having the participants match foot strikes to the beat of a metronome set to each desired SF for 15 sec of every minute. Data were collected 4 times throughout each trial for 30s every minute of the condition. The first collection was used for this analysis. EMG sample rate was 2000Hz from the Rectus Femoris (RF), Biceps Femoris (BF), Tibialis Anterior (TA), and Gastrocnemius (GA). Average and root mean squared (RMS) EMG data were analyzed via repeated-measures ANOVA (α=0.05). Data were normalized to %PSF to assess minimization. RESULTS: PSF RMS EMG were not minimized in any muscle across all SF conditions. Average EMG for BF (F(1.24, 11.19) = 7.32, p>0.05, ηp2 = 0.45) and GA (F(1.49, 1.71) = 21.38, p>0.05, ηp2 = 0.70) were both influenced by SF, but PSF EMG were not minimized for either of those muscles. Normalized EMG for BF were 103.90±27.02%, 90.83±26.02%, 98.37±16.19%,104.20±29.61%, 103.42±42.59%, 109.48±48.37% and for GA were 112.73±25.02%, 90.77±24.90%, 95.33±27.33%, 108.35±36.24%, 90.89±19.40%, 106.68±20.33% for PSF -15%, -10%, -5%, +5%, +10%, +15% respectively. CONCLUSION: Muscle activity was not minimized while running at PSF compared across all conditions. Supported by NIH INBRE P20 GM103440 Grant