Time course and temporal order of changes in movement kinematics during learning of fast and accurate elbow flexions

Abstract

Learning of a motor task, such as making accurate goal-directed movements, is associated with a number of changes in limb kinematics and in the EMG activity that produces the movement. Some of these changes include increases in movement velocity, improvements in end-point accuracy, and the development of a biphasic/triphasic EMG pattern for fast movements. One question that has remained unanswered is whether the time course of the learning-related changes in movement parameters is similar for all parameters. The present paper focuses on this question and presents evidence that different parameters evolve with a specific temporal order. Neurologically normal subjects were trained to make horizontal, planar movements of the elbow that were both fast and accurate. The performance of the subjects was monitored over the course of 400 movements made during experiments lasting approximately 1.5 h. We measured time-related parameters (duration of acceleration, duration of deceleration, and movement duration) and amplitude-related parameters (peak acceleration, peak deceleration, peak velocity), as well as movement distance. In addition, each subject's reaction time and EMG activity was monitored. We found that reaction time was the parameter that changed the fastest and that reached a steady baseline earliest. Time-related parameters decreased at a somewhat slower rate and plateaued next. Amplitude-related parameters were slowest in reaching steady-state values. In subjects making the fastest movements, a triphasic EMG patterns was observed to develop. Our findings reveal that movement parameters change with different time courses during the process of motor learning. The results are discussed in terms of the neural substrates that may be responsible for the differences in this aspect of motor learning and skill acquisition.

The relation between movement parameters and motor learning

“…The model was a simplified description of the task used by Flament et al (1999). They studied 50° movements, which subjects learned to perform faster during 40 blocks of learning (10 trials each).…”

“…As the task in the experiment by Flament et al (1999 ) was to move over a fixed distance l (50°), the assumption was that this parameter did not vary considerably during learning. The MT was thus the only input of the model that changed during learning.…”

“…In a recent paper, Flament et al (1999 ) reported that for this task the time course of learning differed for different kinds of movement parameters. They found that timing-related parameters (e.g.…”

“…Two questions will be addressed regarding the development of these magnitude-related parameters during learning: firstly, whether the development of these parameters is also exponential when the MT decreases exponentially; secondly, whether the development of these parameters is characterised by the same time constant as the development of MT. Flament et al (1999 ) based the interpretation of their results on the assumption that the answer to both these questions is "yes". Using a hypothetical single process of learning to move faster, the answer to both questions is proved to be "no".…”

“…In a recent paper, Flament et al (1999) studied the process of learning to flex the elbow faster. They concluded from their data that time-related parameters (e.g.…”