Abstract
Motor adaptations are a useful tool in the study of the neurophysiology and motor control of the lower limbs. However, motor adaptation paradigms for the lower limbs are typically based on locomotion tasks, where the necessity of maintaining a stable gait pattern is the main driver of adaptations and could possibly mask other underlying processes. The aim of this study was to investigate whether small temporal or spatial asymmetries can trigger motor adaptations during stationary cycling tasks where stability is not directly compromised. Therefore 14 healthy individuals participated in two experiments: in one the angle between the crank arms of the pedals was altered by 10° to induce a temporal asymmetry; in the other the length of one pedal was shortened by 2.4 cm to induce a spatial asymmetry. We recorded the acceleration of the crank arms during the exercises and the EMGs of 16 muscles. The analysis of the accelerometer data was used to investigate the presence and extent of motor adaptations. Muscle synergies analysis was used to quantify changes in neuromuscular control. We found that motor adaptations are present in response to temporal asymmetries. This adaptation was obtained, at the neuromuscular level, mostly by rotating two synergies on the perturbed side. Spatial asymmetries, on the other hand, appear to trigger a feedback-driven response that does not present an aftereffect and is not consistent with a motor adaptation. All the changes in neuromuscular control were well explained by changes in recruitment of a fixed set of muscle synergies.
New and Noteworthy The processes driving lower limb motor adaptations are not fully clear, as such adaptations are mainly driven by stability. Here we show that lower limb adaptations can be obtained also in the absence of an explicit balance threat. We also show that adaptations are present also when kinematic error cannot be compensated for, suggesting the presence of intrinsic error measures regulating the timing of activation of the two legs.