Purpose: Intra-limb and muscular coordination during gait are the result of the organisation of the neuromuscular system, which have been widely studied on a flat terrain. Environmental factors, such as the inclination of the terrain, is a challenge for the postural control system to maintain balance. Therefore, we hypothesised that the central nervous system flexibly modifies its control strategies during locomotion on slopes.
Methods: Ten subjects walked on an inclined treadmill at different slopes (from - 9° to + 9°) and speeds (from 0.56 to 2.22 m s-1). Intra-limb coordination was investigated via the Continuous Relative Phase, whereas muscular coordination was investigated by decomposing the coordinated muscle activation profiles into Basic Activation Patterns.
Results: A greater stride to stride variability of kinematics was observed during walking on slopes, as compared to walking on the level. On positive slopes, the stride period and width present a greater variability without modification of the time-pattern of the muscular activation and of the variability of intersegmental coordination. On negative slopes, the stride width is larger, the variability of the stride period and of the inter-segmental coordination is greater and the basic activation patterns become broader, especially at slow speeds.
Conclusion: Our findings suggest that the control strategy of downhill walking corresponds to a more conservative gait pattern, which could be adopted to lower the risk of falling at the cost of a greater energy consumption. In uphill walking, where metabolic demands are high, the strategy adopted may be planned to minimise energy expenditure.
Keywords: Basic activation pattern; Continuous relative phase; Coordination; Neuromuscular control.