Differences in Joint Kinematics and Ground Reaction Forces between Preferred and Fixed Running Speeds

Abstract

Gait analysis studies typically use a standardized absolute speed with a usual deviation range of ±5%. However, this predetermined speed may not be within an individual's range of preferred speeds. Diverging from a preferred gait pattern may lead to significant kinematic modifications in order to perform the task. These alterations in gait at certain speeds may increase inter-subject variability to a point where significant differences between groups or conditions cannot be detected. PURPOSE: To determine the extent to which individuals can deviate from preferred speed before differences in kinematics and external forces emerge and to determine the difference between subjects who ran at the same absolute speed. METHODS: 3 males and 4 females ran on an instrumented treadmill at 0%, ±5%, ±10%, and ±15% of their preferred speed. 3D kinematic data and ground reaction force (GRF) were collected at 240 Hz and 1200 Hz respectively for 30s after 3-4 min of running. Peak joint angles (PJA) and range of motion (ROM) were calculated for the hip, knee, and ankle. Effect sizes (ES) were calculated to determine the differences in kinematics and GRF from the preferred speed (ES > 0.8 = large; ES > 0.5 = moderate). RESULTS: A moderate to large ES (0.5-0.9) was found for many kinematic and GRF variables between each condition and the preferred speed. ES did not systematically increase with deviation from the preferred speed. The largest differences were found for the hip PJA and ROM. ES was larger when calculated for each subject individually. Large to moderate differences in joint kinematics and GRF were found when comparing subjects who ran at the same absolute speed (ES>0.5). Similar differences where found when comparing subjects running at their preferred speed (ES>0.5). CONCLUSION: Speed had a significant effect on PJA, ROM, and GRF. Large ES (>0.8) for the +5% and -5% speed conditions suggest a ±5% range around a target speed may be too large to deem a running trial acceptable. Due to differences in joint kinematics and GRF when subjects ran at the same speed or their preferred speed, caution should be given when selecting a standard vs. preferred running speed in gait analysis.