Background: Motor unit remodelling with advancing age (1) contributes to observed declines in muscle mass and function (i.e., sarcopenia), which are frequently accompanied by concomitant motor control (MC) deficits (2) in both the upper and lower body MC refers to the precise modulation of force applied during activities such as lifting, transporting, and placing objects (3) when considering the arms, and locomotion and positional correction of the joints when considering the legs (4). Cross-education describes the enhancement of contralateral function via the training of an ipsilateral limb, and has proven benefits in multiple muscle groups (5). However, it’s unclear whether combined low-intensity MC training of antagonistic muscle pairs (biceps and triceps) in a single limb can enhance muscle strength in other muscle groups via cross-education. We hypothesized that unilateral MC training would improve the muscle strength (maximal voluntary contraction (MVC)) of trained and untrained arms, and untrained legs.
Methods: This study was approved by University of Nottingham Faculty of Medicine and Health Sciences Research Ethics Committee (FMHS: 331-0723). Ten healthy older adults (7 females, 77±8 y) underwent 4-weeks of unilateral MC training of the extensors and flexors of the dominant arm. Training was performed 3-times each week, comprising 6 sinewave isometric contractions for elbow flexors and extensors at (randomly) 10, 25, or 50% of the individuals’ predetermined MVC. MVC of the left and right biceps brachii (BIC; elbow flexion), triceps brachii (TRI; elbow extension), and tibialis anterior (TA; dorsi flexion) was assessed before and after the intervention period. Data were analysed via two-way ANOVA (limb x time), with statistical significance accepted as p<0.05.
Results: Neither the trained (1.60v ±0.26 vs.1.73 v ±0.25, p=0.63) or untrained (1.41v ±0.20 vs. 0.68v ±0.19 p=0.15) biceps demonstrated significantly improved strength after the u-MCT period. Similar results were seen in the triceps, although a ‘trend’ towards improvement (p<0.1) was observed in both the trained (0.73v ±0.12 vs.1.03v±0.18, p=0.070) and untrained (0.78 v±0.15 vs.1.03v ±0.18, p=0.06) arms. Regarding the lower body, there was no significant increase in the strength of the dorsi flexors (i.e., TA) on either the trained (0.34v ±0.05 vs. 0.35v ±0.06, p=0.98) or untrained (0.41v ±0.07 vs 0.36v ±0.05, p=0.58) side of the body.
Conclusion: Our findings suggest that 4-weeks of low-intensity unilateral upper limb MC is not sufficient to elicit significant improvements in the strength of the ipsilateral and contralateral elbow flexors, elbow extensors, or dorsi flexors. It is possible the training intensities used here were too low to influence muscle strength but may improve other functional aspects such as dexterity and balance, which are key for older adults. This suggestion should be explored in future work, given its potential relevance for numerous clinical cohorts.