Muscle Activation and Limb Kinematics During Running on Sloped Surfaces

Mechanical energy requirements are different when running up or down a slope relative to level ground. Work must be done when running up the hill and work must be done on the runner when descending. Muscles that do work would generate more force which would be reflected in the EMG activity of the muscle. When work is done on the muscle, the EMG activity may be reduced as the energy is absorbed by connective and muscle tissue combined. PURPOSE: Comparing kinematics and EMG recordings of the lower limb may provide insight as to the control of running on sloped surfaces. METHODS: Thirteen recreational runners (7 male, 6 female), ran on a treadmill on five sloped surfaces (+10°, +5°, 0°, -5°, -10°). Sagittal plane motion was recorded via video and ankle, knee and hip angles were determined. Surface EMG recordings were made of the gastrocnemius, soleus, tibialis anterior, vastus medialis, and semitendinosus in synchrony with the video recordings. The EMG signal was integrated and rectified, and the total magnitude of muscle activity for each 5% of stance determined. An ANOVA with repeated measures was used to assess the presence of differences in ankle, knee, and hip range of motion during stance and total EMG activation of each muscle between the three conditions (alpha = 0.05). RESULTS: Total muscle activiation increased when running up the slope for the gastrocnemius, vastus medialis, rectus femoris and semitendinosus (P<0.05), but were not different when running down hill. Both the ankle and hip extended more when running up hill compared to running down hill (Ankle ROM: inc=52°, dec=32°; Hip ROM: inc=32°, dec=25°), while the knee was opposite (Knee ROM: inc=28°, dec=34°). CONCLUSIONS: Gastrocnemius activity was greater with increased ankle plantar flexion when running up the slope. Similarly, the activation of semitendinosus increased with increased hip extension on the incline. Vastus medialis and rectus femoris increased activity when running up a slope perhaps to stabilize the knee since ROM was lower relative to the downhill condition. Muscle activation during downhill running was similar to level running.