Voluntary activation and variability during maximal dynamic contractions with aging

Abstract

Whether reduced supraspinal activation contributes to age-related reductions in maximal torque during dynamic contractions is not known. The purpose was to determine whether there are age differences in voluntary activation and its variability when assessed with stimulation at the motor cortex and the muscle during maximal isometric, concentric and eccentric contractions. Thirty young (23.6±4.1 years) and 31 old (69.0±5.2 years) adults performed maximal isometric, shortening (concentric) and lengthening (eccentric) contractions with the elbow flexor muscles. Maximal isometric contractions were performed at 90° elbow flexion and dynamic contractions at a velocity of 60°/s. Voluntary activation was assessed by superimposing an evoked contraction with transcranial magnetic stimulation (TMS) or with electrical stimulation over the muscle during maximal voluntary contractions (MVCs). Old adults had lower MVC torque during isometric (−17.9%), concentric (−19.7%) and eccentric (−9.9%) contractions than young adults, with less of an age difference for eccentric contractions. Voluntary activation was similar between the three contraction types when assessed with TMS and electrical stimulation, with no age group differences. Old adults however, were more variable in voluntary activation than young (standard deviation, 0.99±0.47% vs 0.73±0.43%, respectively) to both the motor cortex and muscle, and had greater coactivation of the antagonist muscles during dynamic contractions. Thus, the average voluntary activation to the motor cortex and muscle did not differ with aging, however, supraspinal activation was more variable during maximal dynamic and isometric contractions in the old adults. Lower predictability of voluntary activation may indicate subclinical changes in the central nervous system with advanced aging.

The key role of physical activity against the neuromuscular deterioration in patients with Parkinson's disease

“…An important finding of the current investigation is the existence of a central origin of the force modulation in patients with PD. For maximal isometric contractions in healthy old population, increased variability of activation could suggest marked neural or supraspinal deficits, which are a precursor in limiting capacity and activation with advanced aging 46 . Regarding the pathology of PD, basal ganglia dysfunction may interfere with efficient cortical motor activation 47 .…”

Effects of elevated H+ and Pi on the contractile mechanics of skeletal muscle fibres from young and old men: implications for muscle fatigue in humans

“…2016; Rozand et al . 2017). Similarly, we found no age differences in any contractile properties of the isolated fibres, other than a lower absolute P o and power output in MHC II fibres from old compared to young adults (Figs and ).…”

Muscle coactivation: definitions, mechanisms, and functions

“…1; Aruin et al 1996) as well as during adjustments to perturbations, both anticipatory (Aruin and Almeida 1997) and corrective (Latash et al 1993). A number of studies reported increased levels of coactivation during movements performed by healthy older adults (Lee et al 2015;Nagai et al 2011;Rozand et al 2017). Patients with a variety of neurological disorders show increased levels of muscle coactivation.…”