Impact of Body Mass Index on Biomechanics of Recreational Runners

Background Some recreational runners with obesity successfully train or compete without musculoskeletal injury. Insight into the key kinetic strategies of injury-free heavier runners is necessary to appropriately guide development of safe training programs for this population. Objective To determine key biomechanical strategies of running in individuals with body mass index (BMI) values above and equal to and higher than 30 kg/m(2). Design This was a case-control study. Participants Runners with obesity (n =18; 42.7 years, 38.9% women) who were matched by sex, age, footstrike type, footwear characteristics, and running speed with healthy runners (n = 36; 41.7 years, 32.5% women). Setting Research laboratory affiliated with an academic medical center. Methods A seven-camera optical motion analysis system was used to capture running kinematics and an instrumented treadmill captured kinetic data. Main Outcomes Main outcomes were temporal spatial parameters, joint excursions, peak ground reaction forces (GRFs), joint moments, vertical average loading rate (VALR), impulses, and vertical stiffness (K-vert). Results Runners with obesity demonstrated 15% less vertical excursion of the center of mass, 18% wider strides, and 3% longer stance times than nonobese runners (P < .05). Normalized peak GRFs and VALRs were higher in the nonobese group. GRF impulse was higher in the group with obesity compared to the nonobese group (means +/- SD; 339.6 +/- 55.2 Ns vs. 255.0 +/- 45.8 Ns; P = .0001). K-vert was higher in the obese group compared to the nonobese group (238.6 +/- 50.3 N/cm vs. 183.1 +/- 29.4 N/cm; P = .0001). Peak hip moments were higher in runners with obesity in the sagittal and frontal planes (P < .05). Conclusion Runners with obesity dampened impact forces and controlled loading rate more than nonobese runners by increasing lower body stiffness and constraining vertical displacement.