Abstract
Although the effect of temporal pressure on spatio-temporal aspects of motor coordination and posture is well established in young adults, there is a clear lack of data on elderly subjects. This work examined the aging-related effects of temporal pressure on movement synchronization and dynamic stability. Sixteen young and eleven elderly subjects performed series of simultaneous rapid leg flexions in an erect posture paired with ipsilateral index-finger extensions, minimizing the difference between heel and finger movement onsets. This task was repeated ten times under two temporal conditions (self-initiated [SI] vs. reaction-time [RT]). Results showed that, first, temporal pressure modified movement synchronization; the finger extension preceded swing heel-off in RT, and inversely in SI. Synchronization error and associated standard deviation were significantly greater in elderly than in young adults in SI only, i.e. in the condition where proprioception is thought to be crucial for temporal coordination. Secondly, both groups developed a significantly shorter mediolateral (ML) anticipatory postural adjustment duration in RT (high temporal pressure) than in SI. In both groups, this shortening was compensated by an increase in the anticipatory peak of centre-of-gravity (CoG) acceleration towards the stance-leg so that ML dynamic stability at foot-off, quantified with the “extrapolated centre-of-mass”, remained unchanged across temporal conditions. This increased CoG acceleration was associated with an increased anticipatory peak of ML centre-of-pressure shift towards the swing-leg in young adults only. This suggested that the ability to accelerate the CoG with the centre-of-pressure shift was degraded in elderly, probably due to weakness in the lower limb muscles. Dynamic stability at foot-off was also degraded in elderly, with a consequent increased risk of ML imbalance and falling. The present study provides new insights into the ability of elderly adults to deal with temporal pressure constraints in adapting whole-body coordination of postural and focal components of paired movement.
Highlights
Temporal pressure is known to be a constraint that strongly influences both the spatial and temporal aspects of motor coordination [1], [2], [3], [4], [5], [6]
This work examined the aging-related effects of temporal pressure on two aspects of motor coordination, i.e. synchronization between two voluntary movements, and coordination between posture and movement
We found that Inter-onset latency (IOL) (9 ms in healthy young adults) was much smaller than IOL obtained during simultaneous justheel-raise from the seated posture paired with finger extension (36 ms in the pilot study of the present experiment)
Summary
Temporal pressure is known to be a constraint that strongly influences both the spatial and temporal aspects of motor coordination (defined as the temporal relationship between motor events) [1], [2], [3], [4], [5], [6]. All these studies interpreted these findings based on the Paillard’s model of temporal coordination [1], [2] According to this model, finger (or jaw) precession over heel movement onset in the RT condition reflects the difference in the conduction time of the descending pathways, as if the two motor commands were simultaneously released through a common triggering signal in the motor cortex. Precession of the heel over the finger (or the jaw) in the SI condition suggests that the two motor commands are released by the motor cortex in such a way that the proprioceptive inflow associated with the production of each movement arrives at the same time at the central level, very likely at the cerebellar level [2], a structure often considered to be implicated in the evaluation of movement timing [4,7]. The proprioceptive inflow required for movement synchronization very likely originates from spindles located in the muscles that accelerate the focal limb [5], [8]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
