Effect of Combined Backward and Ankle Resistance on Propulsion During Split-belt Treadmill Walking in Non-impaired Individuals: A Proof-of-concept Study

Research Objectives: To investigate the optimal combination of task mechanics that maximizes propulsive impulses of the leg in non-impaired individuals. We hypothesized that integrating body weight (BW) backward resistance with ankle resistance would maximize propulsion of the leg on the slower belt during split-belt treadmill walking.

Design: This proof-of-concept study employs a repeated measures design to assess propulsion while walking on a split-belt treadmill under different resistance conditions in non-impaired individuals.

Setting: A controlled motion analysis laboratory equipped with a split-belt treadmill, force plates, and devices for applying backward and ankle resistance.

Participants: Twelve non-impaired individuals (8 females, 4 males; age 23.4 ± 1 years).

Interventions: Participants completed four treadmill conditions: (1) Split-belt treadmill without backward resistance, (2) Split-belt treadmill with backward resistance, (3) Split-belt treadmill with ankle resistance on the faster belt, and (4) Split-belt treadmill with combined backward and ankle resistance on the faster belt. Backward resistance of 15% BW was applied to the center of mass, and ankle resistance (2.5-5 kg) was applied to the ankle joint. The non-dominant leg walked at a self-selected speed, while the dominant leg was set at a speed 50% faster across all four conditions.

Main Outcome Measures: The primary outcome measure was the time integral of positive horizontal ground reaction force, normalized to body weight (kg), during the different treadmill conditions for both legs.

Results: For the leg on the slower belt, the paired t-test showed that integrating backward and ankle resistance (0.107 N·Sec/Kg) significantly increased propulsion compared to (1) the condition without backward resistance (0.033 N·Sec/Kg), (2) the condition with only backward resistance (0.092 N·Sec/Kg), and (3) the condition with only ankle resistance (0.035 N·Sec/Kg) (p < 0.05). Backward resistance alone showed greater propulsion on the slower belt leg compared to the faster belt leg during split-belt treadmill walking (t(11)=4.10, p< 0.001). Interestingly, in three non-impaired individuals tested with combined backward and ankle resistance applied to the slower belt, the greatest propulsion (0.135 N·Sec/Kg) was observed in the leg on the slower belt across all conditions, significantly exceeding that of the leg on the faster belt (0.078 N·Sec/Kg) in descriptive analysis.

Conclusions: The combined use of backward and ankle resistance with a split-belt treadmill resulted in maximal engagement of the leg on the slower belt, enhancing propulsion generation. This novel gait training paradigm shows potential for facilitating the use of the paretic leg on the slower belt and improving gait symmetry in individuals with hemiparesis.

Author(s) Disclosures: The authors declare no conflicts of interest.