Influence of Body Weight Support on Lower Extremity Kinematics in an Anti-Gravity Treadmill

Student: Cristina Martello*
Mentor: Matthew Moran
Major: Exercise Science

Context: Treadmills that unload runners via a differential air pressure bladder (DAP; e.g. AlterG® Anti-Gravity Treadmill) are used to reduce effective body weight (BW) in clinical settings, however, the relationship between the level of unloading and lower extremity kinematics are currently unknown. Objectives: To investigate the relationship between level of body weight support (BWS) and lower extremity kinematics with increasing levels of BWS. Design: Repeated measures study. Setting: University motion-analysis laboratory. Participants: Ten collegiate distance runners with a rearfoot strike pattern (9F, 1M; 19.9 ± 0.9 yo; 56.7 ± 3.5 kg; 52.5 ± 10.1 mi/wk self-reported running volume). Main Outcome Measures: Temperospatial variables (stride length (SL), stride rate (SR), and stance-swing duration) and lower extremity kinematics (ankle angle, tibial touchdown angle, stance phase knee range of motion (ROM)) were measured with Kinovea software from a 30-min continuous treadmill run that simulated reduced BW conditions via a DAP bladder. Each trial began with a 10-min run at 100% BW at self-selected velocity, followed by four 5-min stages where BW was systematically reduced from 100% to 70% in 10% increments, while maintaining velocity. Sagittal plane hi-speed video (100Hz) was collected during the last 45-sec of each stage. Results: As BWS increased, runners significantly reduced their SR, increased SL and spent more time in swing phase (p < .01). Despite these significant temperospatial changes, there were no significant differences in ankle angle at initial contact, ankle angle at toe off, and tibial touchdown angle as BWS levels increased (p > .05). However, runners did significantly reduce stance phase knee ROM as BWS increased (p < .01). Conclusion: Increasing BWS in a DAP treadmill changes the timing of a runner’s normal motion but does not influence their ankle kinematics. Only knee motion appears to change as a runner is progressively unloaded in an anti-gravity treadmill. Reduction of knee ROM may indicate that the quadriceps are performing less work, thus explaining how metabolic cost is reduced when running at increasing levels of BWS levels. The current study proves that running kinematics are adjusted when running in an anti-gravity treadmill.

*Honors Senior