Older adults use a motor plan that is detrimental to endpoint control

Stefan Delmas,Basma Yacoubi,Michelle Weintraub,Marcel Komer,Yoon Jin Choi,Evangelos A Christou

doi:10.1038/s41598-021-86959-9

Abstract

Here, we aimed to understand if older adults (OA) use a unique motor plan that is detrimental to endpoint control. We performed two experiments that used ankle ballistic contractions that reversed at the target. In Experiment 1, eight young adults (YA; 27.1 ± 4.2) and eight OA (73.3 ± 4.5) aimed to perform an ankle dorsiflexion–plantarflexion movement that reversed at 9° in 180 ms (target). We found that the coordination pattern (motor plan) differed for the two groups. OA used significantly greater soleus (SOL) activity to reverse the ankle movement than YA and exhibited greater tibialis anterior (TA) muscle activity variability (p < 0.05). OA exhibited worse endpoint control than YA, which associated with the exacerbated TA variability (R2 > 0.2; p < 0.01). Experiment 2 aimed to confirm that the OA motor plan was detrimental to endpoint control. Fifteen YA (20.5 ± 1.4) performed an ankle dorsiflexion–plantarflexion contraction that reversed at 30% MVC in 160 ms by using either a pattern that mimicked OA (High SOL) or YA (Low SOL). With the High SOL coordination pattern, YA exhibited impaired endpoint control and greater TA activation variability. These findings provide strong evidence that OA select a unique motor plan that is detrimental to endpoint control.

Highlights

At the target, older adults exhibit an increased time delay between the activation of the dorsiflexor and plantarflexor muscles
We found that the tibialis anterior (TA) EMG amplitude was not significantly different between young and older adults, but the SOL EMG amplitude was significantly greater in older adults compared with young adults
The TA EMG amplitude variability (t = − 3.27, p = 0.006; Fig. 7D) and TA time-to-peak EMG variability (t = − 2.46, p = 0.027; Fig. 7E) was significantly greater for the High SOL coordination pattern. These findings suggest that the variability of the TA muscle activity is greater when young adults use a High SOL than a Low SOL coordination pattern

Summary

Introduction

At the target (dorsiflexion–plantarflexion), older adults exhibit an increased time delay between the activation of the dorsiflexor (tibialis anterior) and plantarflexor (soleus) muscles. We have shown that a longer time delay between the dorsiflexor and plantarflexor muscles relates to the age-associated differences in endpoint control[1,2,4]. It remains unknown if the motor plan differences between young and older adults are broader and include other parameters, such as the relative contribution in amplitude of muscle activity. We recruited a distinct group of young adults and compared their movement endpoint control while performing ballistic targeted contractions using two unique motor plans. The motor plans mimicked the dorsiflexion–plantarflexion muscle coordination used by young or older adults from experiment 1

Objectives

Methods

Results

Conclusion