Learning a throwing task is associated with differential changes in the use of motor abundance

Abstract

This study sought to characterize changes in the synergy of joint motions related to learning a Frisbee throwing task and, in particular, how the use of abundant solutions to joint coordination changed during the course of learning for successful performance. The latter information was helpful in determining the relative importance of different performance-related variables (PVs) to performance improvement. Following a pre-test, the main experiment consisted of six subjects practicing a Frisbee throw to a laterally-placed target for five days, 150 throws per day, followed by a post-test. A subgroup of three subjects continued to practice for an extended period of extensive practice amounting to 1800-2700 additional throws each, followed by a second post-test. Motor abundance was addressed through the uncontrolled manifold approach (UCM), which was used to partition the variance of joint configurations into two components with respect to relevant PVs, one component leading to a consistent value of the PV across repetitions, and a reflection of motor abundance, and a second component resulting in unstable values of the relevant PV. The method was used to test hypotheses about the relative importance of controlling the PVs that have an impact on successful task performance: movement extent, movement direction, hand path velocity, and the hand's orientation to the target. In addition, the amount of self-motion, or apparently extraneous joint motion having no effect on the hand's motion, compared to joint motion that does affect the hand's motion, was determined. After a week of practice, all subjects showed improvement in terms of targeting accuracy. Hand movement variability also decreased with practice and this was associated with a decrease in overall joint configuration variance. This trend continued to a greater extent in the three subjects who participated in extended practice. Although the component of joint configuration variance that was consistent with a stable value of all PVs was typically substantially higher than variance leading to unstable values of those PVs, both components decreased with practice. However, the decrease in joint configuration variance reflecting motor abundance was less than the other variance component only in relation to control of movement direction and the hand's orientation to the target. These results indicate that improvement of throwing performance in this experiment was more related to improved stabilization of movement direction and to the hand's orientation to the target than to movement extent and hand velocity. Nonetheless, the relative values of the two joint variance components were such that the instantaneous value of both hand path velocity and movement extent were stabilized throughout the experiment and showed a consistent compensatory relationship at the time of Frisbee release, despite not changing with practice. Finally, the amount of self-motion increased significantly with practice, possibly reflecting better compensation for perturbations due to the limb's d...

Motor abundance and control structure in the golf swing

“…However, the variance parallel to the UCM actually increased as a proportion of the overall variance. This suggested that the proportional increase with practice was associated with greater ability to exploit the abundant DOF as well as more stability in the outcome of the skill (Yang & Scholz, 2005). They also found that the variance parallel to the UCM decreased over the course of the movement, while the variance orthogonal to the UCM did not.…”

“…If there is a significantly greater proportion of V UCM then the joint configuration is said to have synergy, in that the abundant DOF in the body are used to minimise the variance in the outcome of the skill . This method has been used to investigate pointing (Domkin, Laczko, Djupsjöbacka, Jaric, & Latash, 2005;Domkin, Laczko, Jaric, Johansson, & Latash, 2002), shooting (Scholz, Schöner, & Latash, 2000), sitto-stand (Reisman, Scholz, & Schöner, 2002;Scholz, Reisman, & Schöner, 2001;Scholz & Schöner, 1999), finger force production (Kapur, Zatsiorsky, & Latash, 2010;Martin, Terekhov, Latash, & Zatsiorsky, 2013;Park, Sun, Zatsiorsky, & Latash, 2011;Scholz, Kang, Patterson, & Latash, 2003;Wu, Pazin, Zatsiorsky & Latash, 2012;Wu, Truglio, Zatsiorsky & Latash, 2015), throwing (Yang & Scholz, 2005) and stone knapping tasks (Rein, Bril, & Nonaka, 2013). Results of these studies have differed with respect to practice, skill level and phase of the skill.…”

“…However, those studies investigating movements more closely related to the golf swing, such as throwing and striking, have yielded some commonalities. Yang and Scholz (2005) studied Frisbee throwing in 3-dimensions and analysed the effect of practice on joint configuration variance. Firstly, they found a decrease in the total variance of the body movement with practice.…”

The role of kinematic redundancy in adaptation of reaching

“…A relatively common thread of those studies which used the UCM approach to address changes in movement coordination has been a decrease in both components of variance with learning (Domkin et al 2005(Domkin et al ,2002Yang and Scholz 2005). Depending on the study, the decrease in V UCM could be smaller than , equal to (Domkin et al 2005) or greater than (Domkin et al 2002) the decrease in V ORT .…”

“…Most studies in adults revealed a decrease in both components of joint configuration variance (V UCM and V ORT ) with practice. However, the decrease in V UCM could be larger than (Domkin et al 2002), equal to (Domkin et al 2005), or smaller than (Kang et al 2004;Yang and Scholz 2005) the decrease in V ORT with practice. A related experiment using a slightly different approach to distinguish variance components revealed primarily decreases in V ORT in an early stage of practice, leading to a higher ratio of the two components, while V UCM decreased more than V ORT at a later stage .…”