Normal aging reduces motor synergies in manual pointing

Abstract

Depending upon its organization, movement variability may reflect poor or flexible control of a motor task. We studied adult age-related differences in the structure of postural variability in manual pointing using the uncontrolled manifold (UCM) method. Participants from 2 age groups (younger: 20 -30 years; older: 70 -80 years; 12 subjects per group) completed a total of 120 pointing trials to 2 different targets presented according to 3 schedules: blocked, alternating, and random. The age groups were similar with respect to basic kinematic variables, end point precision, as well as the accuracy of the biomechanical forward model of the arm. Following the uncontrolled manifold approach, goal-equivalent and nongoal-equivalent components of postural variability (goal-equivalent variability [GEV] and nongoal-equivalent variability [NGEV]) were determined for 5 time points of the movements (start, 10%, 50%, 90%, and end) and used to define a synergy index reflecting the flexibility/stability aspect of motor synergies. Toward the end of the movement, younger adults showed higher synergy indexes than older adults. Effects of target schedule were not reliable. We conclude that normal aging alters the organization of common multidegree-of-freedom movements, with older adults making less flexible use of motor abundance than younger adults.

Motor abundance and control structure in the golf swing

“…The only other group difference found were in the ages of the participants, and it is an issue that has been encountered in previous studies with skill level based groups in golf (Fedorcik, Queen, Abbey, Moorman, & Ruch, 2011;Zheng, Barrentine, Fleisig, & Andrews, 2008). Differences in the strength of motor synergy have previously been found with aging (Verrel, Lövdén, & Lindenberger, 2012), where V UCM appeared to be lower in the later stages of a pointing movement in the older group. However, the difference in mean age in that study was approximately 48 years, and no differences were found in the early stages of the movement.…”

Old adults preserve motor flexibility during rapid reaching

“…First, previous studies reported similar total movement time (Verrel et al 2012; Xu et al 2013) and peak velocity (Xu et al 2013) during reaching in old and young participants. These similarities between age groups contrast with the age-related decrease in reaching performance and might represent behavior at the boundary of the natural motor repertoire possibly biasing motor flexibility in favor of old adults (Sleimen-Malkoun et al 2013; Van Halewyck et al 2015).…”

“…However, there is conflicting evidence as to how and if at all old age affects motor flexibility during reaching, as motor flexibility during reaching was less (Dutta et al 2013; Verrel et al 2012), similar (Xu et al 2013), or even greater (Krüger et al 2013) in old compared with young adults. Moreover, old compared to young adults employ less motor flexibility during multi-finger force coordination (Kapur et al 2010; Olafsdottir et al 2007; Shinohara et al 2004) and standing balance tasks (Hsu et al 2013, 2014), but similar motor flexibility during the initiation of a step over an object (Wang et al 2015), walking (Krishnan et al 2013) and hand rotation tasks (Skm et al 2012) and larger motor flexibility in sit-to-stand tasks (Greve et al 2013).…”

Articulated coordination of the right arm underlies control of bow parameters and quick bow reversals in skilled cello bowing

“…Local coordinate systems (LCS) were defined for scapula, upper arm, lower arm, hand, and bow based on a previously described method (Verrel et al, 2012). Briefly, the LCS was defined by applying the Gram-Schmidt process to two well-defined vectors relative to the body segment.…”