Old adults preserve motor flexibility during rapid reaching

Abstract

PurposeOur ability to flexibly coordinate the available degrees of freedom allows us to perform activities of daily living under various task constraints. Healthy old adults exhibit subclinical peripheral and central nervous system dysfunctions, possibly compromising the flexibility in inter-joint coordination during voluntary movements and the ability to adapt to varying task constraints.MethodWe examined how healthy old (75.4 ± 5.2 years, n = 14) compared with young adults (24.3 ± 2 years, n = 15) make use of the available motor flexibility to adapt to physical and dexterity constraints during a rapid goal-directed reaching task. We manipulated physical and dexterity demands by changing, respectively, external resistance and target size. Motor flexibility was quantified by an uncontrolled manifold (UCM) analysis.ResultsWe found that healthy young and old adults employ similar motor flexibility as quantified by the ratio between goal equivalent and non-goal equivalent variability (V Ratio) and were similarly able to adapt to increases in physical and dexterity demands during goal-directed rapid reaching (V Ratio: p = .092; young: 0.548 ± 0.113; old: 0.264 ± 0.117). Age affected end-effector kinematics. Motor flexibility and end-effector kinematics did not correlate.ConclusionThe data challenge the prevailing view that old age affects movement capabilities in general and provide specific evidence that healthy old adults preserve motor flexibility during a reaching task. Future studies applying UCM analysis should examine if experimental set-ups limit movement exploration, leaving possible age differences undetected.

Not all brawn, but some brain. Strength gains after training alters kinematic motor abundance in hopping

“…It was previously suggested that greater motor abundance will emerge in tasks with greater relative physical demand ( Greve, Hortobagyi & Bongers, 2017 ; Greve et al, 2013 ), which contradicts the present findings. It may be that the relationship between physical demand and motor abundance is non-linear with potentially plateauing effects.…”

Peer Review #2 of "Not all brawn, but some brain. Strength gains after training alters kinematic motor abundance in hopping (v0.2)"

“…It was previously suggested that greater motor abundance will emerge in tasks with greater relative physical demand (Greve et al 2017;Greve et al 2013), which contradicts the present findings. It may be that the relationship between physical demand and motor abundance is nonlinear with potentially plateauing effects.…”

“…Wang et al reported that older adults have preserved muscle motor abundance but were more delayed at their recruitment during rapid balance recovery, than younger adults (Wang et al 2017). The tasks used by Greve and Colleagues were either much slower, or required a combination of low muscular force and fast movement speed (Greve et al 2017;Greve et al 2013). It is plausible that the speed-force demands in previous studies were low (Greve et al 2017;Greve et al 2013), such that muscle…”

Coordination in adults with neurological impairment – A systematic review of uncontrolled manifold studies

“…Second, a suitable task-relevant performance variable that is affected by variations in the elemental variables also needs to be chosen for analysis [12,13]. Examples of performance variables stabilized by synergies include the position of the center of mass in transfer and standing tasks, hand position and orientation in reaching tasks, total force in finger pressing tasks [14][15][16].…”