Will Wu

Allowing Learners to Choose: Self-Controlled Practice Schedules for Learning Multiple Movement Patterns.

Abstract For this study, we investigated the effects of self-controlled practice on learning multiple motor skills. Thirty participants were randomly assigned to self-control or yoked conditions. Participants learned a three-keystroke pattern with three different relative time structures. Those in the self-control group chose one of three relative time structures before each of 90 practice trials; yoked participants were not allowed to choose but were yoked to a self-control participant and followed that individuals sequence of practice trials. Results of the 24-hr serial transfer test revealed the self-control group exhibited significantly lower relative timing error, absolute error, and total error than the yoked group. Findings further support the efficacy of self-controlled learning.

Contextual interference and augmented feedback: is there an additive effect for motor learning?

Learning to perform a skilled behavior is affected by the context of the practice session and the frequency of augmented feedback. We studied the combined effect of these variables in the acquisition of a ballistic, bi-directional lever movement pattern involving four different target locations as measured by performance in practice, retention, and transfer tests. Augmented feedback was presented in either an every-trial or a faded schedule during random and blocked practice. Consistent with the contextual interference effect, the blocked practice group produced lower errors in acquisition, but the random practice group outperformed the blocked practice group in both retention and transfer. In contrast, faded feedback did not have a beneficial effect on learning and degraded learning when provided during blocked practice. While the results were consistent with previous findings of random and blocked practice, they were not consistent with previous findings of reduced feedback frequencies.

Effects of Knee Extension Constraint Training on Knee Flexion Angle and Peak Impact Ground-Reaction Force:

Background: Low compliance with training programs is likely to be one of the major reasons for inconsistency of the data regarding the effectiveness of current anterior cruciate ligament (ACL) injury prevention programs. Training methods that reduce training time and cost could favorably influence the effectiveness of ACL injury prevention programs. A newly designed knee extension constraint training device may serve this purpose. Hypothesis: (1) Knee extension constraint training for 4 weeks would significantly increase the knee flexion angle at the time of peak impact posterior ground-reaction force and decrease peak impact ground-reaction forces during landing of a stop-jump task and a side-cutting task, and (2) the training effects would be retained 4 weeks after completion of the training program. Study Design: Controlled laboratory study. Methods: Twenty-four recreational athletes were randomly assigned to group A or B. Participants in group A played sports without wearing a knee extension constraint device for 4 weeks and then played sports while wearing the device for 4 weeks, while participants in group B underwent a reversed protocol. Both groups were tested at the beginning of week 1 and at the ends of weeks 4 and 8 without wearing the device. Knee joint angles were obtained from 3-dimensional videographic data, while ground-reaction forces were measured simultaneously using force plates. Analyses of variance were performed to determine the training effects and the retention of training effects. Results: Participants in group A significantly increased knee flexion angles and decreased ground-reaction forces at the end of week 8 (P ≤ .012). Participants in group B significantly increased knee flexion angles and decreased ground-reaction forces at the ends of weeks 4 and 8 (P ≤ .007). However, participants in group B decreased knee flexion angles and increased ground-reaction forces at the end of week 8 in comparison with the end of week 4 (P ≤ .009). Conclusion: Knee extension constraint training for 4 weeks significantly altered lower extremity movement patterns and transferred these changes in lower extremity movement patterns to stop-jump and side-cutting tasks in which ACL injuries frequently occur. Training effects were retained 4 weeks after the training was completed but were diminished in magnitude. Clinical Relevance: A knee extension constraint device may be a useful training tool in future ACL injury prevention programs to alter movement patterns without extra training time.

Vibrotactile device for rehabilitative training of persons with lower-limb amputation

Individuals with prostheses use sensations experienced through the residual limb during ambulation to perceive the state of the prosthesis. For lower-limb prosthetic users, the loss of proprioception can affect stability and contribute to falls. In this work, we developed a vibrotactile device to enhance residual limb proprioception, which can be used for rehabilitation training of persons with transtibial amputation. The system consists of two vibrating motors, a solenoid, a goniometer, and a control interface. Two types of vibrotactile feedback can be generated: a short vibration via the motors and a single knock via the solenoid. The device is universally designed to fit standard prosthetic components and is inserted in line between the pylon and the socket adapter allowing the vibration to propagate from the unit to the residual limb. The design and the results of the initial functionality test of the vibrotactile unit are reported.

Investigating the Constrained Action Hypothesis: A Movement Coordination and Coordination Variability Approach

ABSTRACT The purpose of this study was to examine the effects of focus of attention cues on movement coordination and coordination variability in the lower extremity. Twenty participants performed the standing long jump under both internal and external focus of attention conditions. A modified vector coding technique was used to evaluate the influence of attentional focus cues on lower extremity coordination patterns and coordination variability during the jumps. Participants jumped significantly further under an external focus of attention condition compared with an internal focus of attention condition (p = .035, effect size = .29). Focus of attention also influenced coordination between the ankle and knee, F(6, 19) = 2.87, p = .012, effect size = .388, with participants primarily using their knees under the internal focus of attention, and using both their ankles and knees under the external focus of attention. Attentional focus cues did not influence ankle-knee, F(1, 19) = 0.02, p = .98, effect size = .02, or hip-knee, F(1, 19) = 5.00, p = .49, effect size = .16, coordination variability. Results suggest that while attentional focus may not directly influence movement coordination condition, there is still a change in movement strategy resulting in greater jump distances following an external focus of attention.

Movement screens: Are we measuring movement dysfunction or movement skill?:

Movement screens are commonly used for assessing athletic readiness or injury potential. However, these screens fail to distinguish between movement dysfunction and movement skill. The purpose of this study was to compare performance on a common movement screen test, the overhead squat, when using no instructions (Baseline), instruction from a commercial movement screen, and instructions which include verbal cues, demonstration, and practice (Instructions, Demonstration, and Practice [IDP]). Fourteen individuals performed the overhead squat under the three different conditions while their movements were recorded using a 12-camera motion capture system. Specific scoring criteria for the overhead squat such as joint angles, depth of squat, torso and shank orientation, and weight distribution were compared between instructional conditions. Compared to the Baseline and commercial movement screen conditions, IDP resulted in greater vertical center of mass displacement, better alignment of the torso and shank segments, and greater peak flexion at the hip and knee. These results show that incorporating verbal cues, providing demonstration, and allowing for practice during movement screening significantly improve performance in the overhead squat assessment. Based on these results, the authors recommend that coaches or clinicians using movement screens to identify movement dysfunction should provide demonstrations of the movement, allow the participant to practice, provide verbal instructions about the movement prior to assessment, and provide corrective feedback during practice. Excluding these elements limits the ability to distinguish between true dysfunctional movement patterns and a simple lack of movement skill.

Does Focus of Attention Improve Snatch Lift Kinematics

Abstract Schutts, KS, Wu, WFW, Vidal, AD, Hiegel, J, and Becker, J. Does focus of attention improve snatch lift kinematics? J Strength Cond Res 31(10): 2758–2764, 2017—Recent motor control literature has demonstrated that using verbal instructions to direct a performers attention externally (i.e., toward the movement outcome) enhances motor skill performance. The purpose of this study was to investigate how an athletes focus of attention impacts kinematic performance of the snatch. Using a counterbalanced within-participant design, 12 competitively trained athletes (8 male and 4 female athletes) performed 2 instructional blocks of 3 snatch repetitions at 80% of their most recent training 1 repetition maximum. Blocks of internal and external instructions were given to the athlete in a random fashion. Results showed that, when focusing internally, athletes significantly (p ⩽ 0.05) increased elbow velocity relative to focusing externally, whereas the external instructions significantly increased horizontal barbell velocity, relative to internal instructions. Additionally, an internal focus resulted in significantly larger barbell-cervical-hip angles at maximum height of the barbell compared with an external focus, indicating that the athletes squatted under the barbell too soon. This information adds to the literature suggesting small changes in coaching instructions can impact performance significantly. It is recommended that coaches use instructions that direct an athletes attention externally, toward the movement outcome, rather than the action itself.