Effects of a Pneumatic Knee-Actuated Exoskeleton on Gait Stability During Prolonged Walking With Load Carriage

Lower-extremity exoskeletons (EXOs) may be able to assist with performance and injury risk reduction for military-relevant activities, like walking with loads. However, the effects of EXOs on local dynamic stability (LDS), a measure of motor control, have not been established. Eleven active duty Army Soldiers (9 males, aged 22 [4] y) completed a familiarization session, followed by 2 testing sessions where they did (EXO) or did not (NoEXO) wear a pneumatic powered, knee-actuated EXO. Inertial measurement units were attached bilaterally to the shank and posterior pelvis. Participants completed a 2-mile ruck march on a treadmill at a self-selected pace (1.34 [0.10] m/s), carrying a load equal to 30% of body weight and an additional 9.07 kg for the EXO during that session. LDS was calculated using gyroscope data for 100 strides at the 0.25- (Start) and 2-mile (End) marks of the march. For the right shank, LDS was found to be significantly lower for EXO versus NoEXO (mean difference = 0.28, P < .01, partial η2 = .75). A similar effect was found for the left shank, and while not significant, the effect size was large (P = .07, partial η2 = .29). Finally, LDS was higher at the pelvis in the EXO versus NoEXO, and with a large effect size, although the results were not significant (P = .07, partial η2 = .29). Our results suggest that lower-extremity EXOs reduce distal LDS, which may point to the need for habituation periods for new users of EXOs.