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 .

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 ).

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 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.