Onset times during reach movement in healthy elderly

Abstract

Introduction: Reaching is an essential human attribute [1]. Functional tasks, such as pointing to targets and reaching for objects, have been used to evaluate the motor performance of people with physical impairments [2]. Muscle onset times expressed in relation to the start of movement were used to reflect the temporal activation of the muscle during a task [3]. A good knowledge of the normal movement is essential to improve interventions aimed to recovery the motor control mechanisms. This study investigates temporal pattern of muscle activity in the upper limb during reach movement in healthy elderly people.

Materials and methods: Surface EMG was recorded from 7 muscles; triceps, biceps, anterior deltoid, posterior deltoid, upper trapezius, wrist extensors and wrist flexors. A standard procedure [4], was used for skin preparation and electrode placement for all muscles. With full vision, participants reach toward, grasped one cone and returned to the initial position at a comfortable self-paced speed and surface EMG was recorded. All subjects signed an informed consent form. This project was approved by the local medical ethics committee.

Results: Eighteen (10 men) healthy individuals between age of 50 and 70 years completed the study. In this study, the anterior deltoid (−0.058s ± 0,09), upper trapezius (−0.051s ± 0.09) and biceps (−0.016s ± 0.09) were the muscles with earliest onset times (Figure 1).

Figure 1. Average onset times for the participants. The vertical line at zero seconds represents the start of the movement. The *symbol represents significant differences (p < .05) to anterior deltoid according to Kruskal-Wallis test and Dunn’s multiple comparisons test.

Discussion and conclusions: The earlier activation of the movement by the anterior deltoid agrees with the literature [5]. The upper trapezius showed a fundamental role as stabilizer of the movement.