Relationship between improvements in motor performance and changes in anticipatory postural adjustments during whole-body reaching training

Abstract

Anticipatory postural adjustments (APAs) provide postural stability and play an important role in ensuring appropriate motor performance. APAs also change in various situations. However, it is unknown whether changes in APAs during repetitive movement training contribute to improvement in motor performance. This study aimed to investigate the relationship between improvement in motor performance and changes in APAs during repeated reaching training, as well as the learning effects on APA changes. Sixteen healthy subjects (23 ± 2 years of age) stood barefoot on a force platform and reached as quickly and accurately as possible to a target placed at their maximum reach distance immediately following a beep signal in a reaction time condition. Whole-body reaching training with the right arm was repeated 100 times for three consecutive days. Motor performance and APAs were evaluated on the first day, after discontinuation of training for one day, and again at three months. In addition, reaching with the left arm (untrained limb) was tested on the first and the fifth training day. Body position segments were measured using three-dimensional motion analysis. Surface electromyography of eight postural muscles in both lower limbs was recorded. Kinetics data were recorded using the force platform. Whole-body reaching training induced not only improvements in motor performance (e.g., increased peak hand velocity), but also changes in APAs (e.g., earlier APA onset and increased amplitude). These changes were strongly correlated with and occurred earlier than improvements in motor performance. The learning effects on APAs were retained after the discontinuation of training and were generalized to the untrained limb. These results suggest that change in APAs contributes to improvement in motor performance; that is, the central nervous system may be able to adapt APAs for improvement in motor performance.

Techniques and Methods for Testing the Postural Function in Healthy and Pathological Subjects

“…Amplitude, temporal, and frequency parameters can be differentiated [ 107 ]. Temporal EMG analyses have been extensively used in order to characterize postural responses following platform-movement disturbances or anticipatory postural adjustments with voluntary movements [ 108 ] when identifying bursts of muscle activity [ 109 ]. EMG amplitude analyses, like RMS or area calculations [ 55 ], are used to reflect the magnitude of muscular activity in maintaining specific postural tasks.…”

The Perceptual Shaping of Anticipatory Actions

“…Finally, generalization of adaptive motor responses has been found in limb (28,60) and postural control (29,30). Subjects trained to catch a ball with one arm, perform equally as good when they switch arm (60), a result that cannot be explained in terms of inverse models (by definition, effector-specific).…”

“…In addition, FEL acquires motor commands that are tied to the dynamics of the plant that it controls and cannot easily be generalized to new configurations. However, experimental evidence suggests that in humans anticipatory responses are still effective even if one changes the posture and/or the effector after learning (28)(29)(30). Hence, given that standard forward and inverse models cannot fully account for anticipatory control, alternatives should be considered that both overcome the theoretical and practical limitations of these motor-centric accounts and resolve the forward-inverse model dichotomy.…”

APAs Constraints to Voluntary Movements: The Case for Limb Movements Coupling

“…It was shown, however, that exercises requiring high motor skills rapidly lead to improvements in balance (Aruin et al, 2015; Kanekar and Aruin, 2015) and in a reaching task while standing (Saito et al, 2014). Improvements were invariably associated with an earlier recruitment of the APAs in lower limb muscles.…”