Plasticity in central neural drive with short-term disuse and recovery - effects on muscle strength and influence of aging

Abstract

While short-term disuse negatively affects mechanical muscle function (e.g. isometric muscle strength) little is known of the relative contribution of adaptions in central neural drive and peripheral muscle contractility. The present study investigated the relative contribution of adaptations in central neural drive and peripheral muscle contractility on changes in isometric muscle strength following short-term unilateral disuse (4 days, knee brace) and subsequent active recovery (7 days, one session of resistance training) in young (n = 11, 24 yrs) and old healthy men (n = 11, 67 yrs). Maximal isometric knee extensor strength (MVC) (isokinetic dynamometer), voluntary muscle activation (superimposed twitch technique), and electrically evoked muscle twitch force (single and doublet twitch stimulation) were assessed prior to and after disuse, and after recovery. Following disuse, relative decreases in MVC did not differ statistically between old (16.4 ± 3.7%, p < 0.05) and young (-9.7 ± 2.9%, p < 0.05) (mean ± SE), whereas voluntary muscle activation decreased more (p < 0.05) in old (-8.4 ± 3.5%, p < 0.05) compared to young (-1.1 ± 1.0%, ns) as did peak single (-25.8 ± 6.6%, p < 0.05 vs -7.6 ± 3.3%, p < 0.05) and doublet twitch force (-23.2 ± 5.5%, p < 0.05 vs -2.0 ± 2.6%, ns). All parameters were restored in young following 7 days recovery, whereas MVC and peak twitch force remained suppressed in old. Regression analysis revealed that disuse-induced changes in MVC relied more on changes in single twitch force in young (p < 0.05) and more on changes in voluntary muscle activation in old (p < 0.05), whereas recovery-induced changes in MVC mainly were explained by gains in voluntary muscle activation in both young and old. Altogether, the present data demonstrate that plasticity in voluntary muscle activation (~central neural drive) is a dominant mechanism affecting short-term disuse- and recovery-induced changes in muscle strength in older adults.

Non-invasively measured central and peripheral factors of oxygen uptake differ between patients with chronic heart failure and healthy controls

“…The lower muscle oxygen saturation at rest and lower exploitation of oxygen reserves during load of the patients may be caused by the reduced peripheral perfusion, the adaptive mitochondrial dysfunction as well as the shift in muscle-fibre types, whereby slow, oxidative type I fibres are being replaced by fast, glycolytic type IIb fibres [ 8 , 14 , 47 ]. Our results concerning isometric peak torque were 111 ± 21 Nm and 173 ± 44 Nm (− 35.8%) for patients and healthy controls, respectively, and are supported by previous studies, which investigated both groups separately (up to − 35.3%) [ 23 , 24 ]. The difference between both groups can be explained by the abovementioned peripheral changes, possibly resulting in the lower muscle mass of the patients with chronic heart failure [ 8 , 23 ].…”

“…Our results concerning isometric peak torque were 111 ± 21 Nm and 173 ± 44 Nm (− 35.8%) for patients and healthy controls, respectively, and are supported by previous studies, which investigated both groups separately (up to − 35.3%) [23,24]. The difference between both groups can be explained by the abovementioned peripheral changes,…”

“…Other studies examined healthy participants on stroke volume, cardiac output [ 21 ], and cardiac power output [ 22 ]. To get more insights into peripheral changes, two studies investigated isokinetic and isometric peak torque of the knee in patients with heart failure [ 23 ] and healthy participants [ 24 ], respectively. Overall, the studies show that patients with chronic heart failure have lower values of up to 45.8% in central factors and up to 35.3% in peripheral factors compared to separately investigated healthy participants.…”

Do Motoneurons’ Discharge Rate Slow With Aging? A Systematic Review And Meta-Analysis

“…Additional evidence for this assertion is provided by the findings that, while disuse can aggravate the deleterious effects of aging on the nervous system, master-level (i.e. older adult) athletes show a substantial preservation of neural function (Aagaard et al, 2010;Hvid et al, 2018;McGregor et al, 2011;Unhjem et al, 2016).…”

The time course of neuromuscular impairment during short‐term disuse in young women

“…These changes are commonly observed during bed rest (Reidy et al, 2017) and single‐limb injury with subsequent immobilization lasting between 7 days up to several weeks (Tesch et al, 2016). While declines in physical function are reversible with rehabilitation (Hvid et al, 2010), all adults are susceptible to disuse‐related muscular impairments, regardless of age (Hvid et al, 2018) and initial strength levels (Deschenes et al, 2017).…”