Increased enslaving in elderly is associated with changes in neural control of the extrinsic finger muscles

Abstract

Aging has consequences for hand motor control, among others affecting finger force enslaving during static pressing tasks. The aim of this study was to assess whether the extent of finger force enslaving changes with aging during a task that involves both static and dynamic phases. Ten right-handed young (22–30 years) and ten elderly subjects (67–79 years) were instructed to first exert a constant force (static phase) and then flex their index finger while counteracting constant resistance forces orthogonal to their fingertips (dynamic phase). The other fingers (non-instructed) were held in extension. EMG activities of the flexor digitorum superficialis (FDS) and extensor digitorum (ED) muscles in the regions corresponding to the index, middle and ring fingers together with their forces and position of index finger were measured. In both elderly and young, forces exerted by the non-instructed fingers increased (around 0.6 N for both young and elderly) during isotonic flexion of the index finger, but with a different delay of on average 100 ± 72 ms in elderly and 334 ± 101 ms in young subjects. Results also suggest different responses in activity of FDS and ED muscle regions of the non-instructed fingers to index finger flexion between elderly and young subjects. The enslaving effect was significantly higher in elderly than in young subjects both in the static (12% more) and dynamic (14% more) phases. These differences in enslaving can at least partly be explained by changes in neuromuscular control.

Manual Dexterity and Aging: A Pilot Study Disentangling Sensorimotor From Cognitive Decline

“…Our findings also suggest an age-related decline in motor inhibition: longer release duration (during tracking) and reduced finger individuation, both considered to involve processes of motor inhibition ( 31 , 64 , 65 ), were found in elderly subjects and those with cognitive decline. Age-related increase in release duration has been reported previously in healthy subjects ( 62 ), whereas altered finger individuation has not been shown consistently ( 27 , 66 ), probably due to task-related differences. Our tapping task, resembling keyboard typing or piano playing, revealed evidence for a similar reduction of independent finger movements in elderly subjects and, in subjects with cognitive decline.…”

“…Studies have reported age-related impairments in maximal grip force ( 18 ) sensory functioning ( 19 , 20 ) and in grasping and manipulation of objects [Box and Block test ( 21 , 22 ), NHPT ( 23 , 24 )]. Regarding specific manual dexterity components, accuracy in force control tasks is reduced in age ( 25 , 26 ) and independence of finger movements may deteriorate ( 27 ). Increased variability of finger movements ( 28 ) and motor slowing ( 29 ) have also been documented.…”

Single finger movements in the aging hand: changes in finger independence, muscle activation patterns and tendon displacement in older adults

“…This is in contrast to our results, in which enslaving was found to be higher and the range of independent movement was lower, especially for index finger flexion, for the elderly compared to the younger subjects. In a recent study from our group, higher force enslaving in elderly was also found during a static finger pressing task (Mirakhorlo et al 2018). The opposite outcomes compared to most previous studies were explained by not restraining the arm and wrist.…”

“…In the present experiment, the wrist was not secured to the setup. As a consequence, part of the activity of the extrinsic finger flexors and extensors may be related to stabilization of the wrist and not to the finger movements (Mirakhorlo et al 2018). When the wrist is fixed, the function of these muscles is limited to solely produce finger movements.…”

“…Some studies have reported an increased finger force independence with aging during static finger pressing tasks, as indicated by a decreased force exerted by the non-instructed fingers Shinohara et al 2003a;Oliveira et al 2008;Kapur et al 2010). In contrast, a decreased force independence in elderly has recently been found for a dynamic finger force task (Mirakhorlo et al 2018). However, changes in finger movement independence with aging have only been studied for restricted finger movements and not free finger flexion movements, which might better resemble the finger movements in daily life.…”