Split-belt treadmill walking has previously been used as a means to investigate motor adaptations to gait asymmetries in both healthy and clinical populations. Gradual introduction of split-belt walking asymmetries has been shown to lead to better retention and transfer performance in healthy individuals compared to a sudden introduction. However, it remains unknown which kinetic strategies are implemented by the gradual training group to result in improved retention and transfer performance. PURPOSE: To determine the effects of gradual and sudden training on hip and ankle kinetics during split-belt treadmill walking. METHODS: Sixteen participants were recruited for this study and randomly assigned to either the gradual training group (n = 8, 32.85 ± 8.71 years) or sudden training group (n = 8, 29.83 ± 6.15 years). Both groups were first given a 15 minute period of acclimation to treadmill walking. The gradual training group then completed 720 strides of acquisition, where the belt speed started at a 1:1 ratio. Then, the dominant leg speed increased by 0.02 m/s at an acceleration of 0.001 m/s2 every 20 strides to reach a 2:1 asymmetry for the final 20 strides. The sudden training group was immediately accelerated at 10 m/s2 from a 1:1 to a 2:1 asymmetry, and then the participants walked at this asymmetry for the full 720 strides. All participants returned 24 hours later for a readaptation trial, where they were immediately introduced to a 2:1 asymmetry and then walked for 400 strides. Kinematic and kinetic data were recorded during both the acquisition and readaptation trials, and inverse dynamics were used to calculate work done at the hip during the initial swing phase of gait, and ankle work during late stance phase. Work performed at both of these joints on both the fast and slow were compared between groups using ANOVAs, and within-subject differences between acquisition and readaptation were assessed using paired T-tests. RESULTS: The gradual training group performed less work on the slower (non-dominant) hip during acquisition compared to the fast limb (p < 0.001), but increased work at the slow limb hip joint during readaptation to where it was not significantly less than the fast limb (p > 0.05). CONCLUSION: Gradual training caused a novel kinetic strategy to be adopted during the acquisition period. However, after 24 hours this strategy was resolved. This may be the mechanism in which gradual training leads to better retention and transfer performance compared to sudden training, and may help to benefit split-belt walking training in clinical populations as well as advance the concept of practice difficulty during training of locomotion.

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