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In Remembrance: The Life and Legacy of Michael T. Turvey (1942–2023)

Michael A. Riley and Dagmar Sternad

Michael T. Turvey passed away on August 12, 2023 at the age of 81. This obituary aims to honor his life and career by highlighting some key events in his personal and professional life, noting some of his many remarkable accomplishments, and emphasizing his exceptional mentorship, friendship, and generosity.

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Prism Exposure Affects the Proprioceptive Frames of Reference for Interlimb Rhythmic Coordination

Michael A. Riley and David P. Black

Adaptation to prisms can produce a change in felt arm position, termed proprioceptive shift. We studied the effects of prism-induced proprioceptive shift on interlimb rhythmic coordination performed under proprioceptive guidance, in the absence of vision. Relative to interlimb rhythmic coordination performed before prism exposure, the observed steady states of relative phase for postexposure coordination were shifted by a small but reliable amount. The shift was in the direction expected, given the direction of optical displacement. The amount of variability of interlimb rhythmic coordination was unaffected by prism exposure. The results suggest that the same spatial frames of reference altered by prism adaptation are involved in the production of interlimb rhythmic coordination patterns.

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Synergies in Intra- and Interpersonal Interlimb Rhythmic Coordination

David P. Black, Michael A. Riley, and Christopher K. McCord

The authors conducted two experiments that served as a test bed for applying the recently developed uncontrolled manifold (UCM) approach to rhythmic motor coordination, which has been extensively investigated from a coordination dynamics perspective. The results of two experiments, one investigating withinperson and one investigating between-persons rhythmic movement coordination, identified synergistic behaviors in both of those types of coordination. Stronger synergies were identified for in-phase than antiphase coordination, at the endpoints of the movement cycles compared with the midpoints, for movement frequencies closer to the intrinsic frequency of the coordinated limbs, and for within-person coordination. Frequency detuning did not weaken the strength of interlimb rhythmic coordination synergies. The results suggest the synergistic behavior captured by the UCM analysis may be identifiable with the strength of coupling between the coordinated limbs. The UCM analysis appears to distinguish coordination parameters that affect coupling strength from parameters that weaken coordination attractors.

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Influences of Body Lean and Vision on Unperturbed Postural Sway

Michael A. Riley, Suvobrata Mitra, Thomas A. Stoffregen, and Michael T. Turvey

We examined the potentially exploratory and performatory nature of postural sway. Subjects stood upright or leaned forward, with eyes open or closed. Postural data were analyzed using a statistical mechanics analysis of center of pressure (COP) trajectories, which examines the fractional Brownian nature of postural sway. Positive correlations (persistence) over short time scales are hypothesized to reflect exploratory behavior, and negative correlations (antipersistence) over long time scales are hypothesized to reflect performatory behavior. When leaning, subjects exhibited decreased levels of persistence (decreased correlation) and increased levels of antipersistence (increased correlation) than when upright. With eyes open, subjects showed decreased levels of persistence and decreased levels of antipersistence than with eyes closed. Effects of vision were more pronounced when leaning. Evidence for direction-specific exploration (based upon root mean square variability analysis) was considered. Task-specificity and trade-offs between biomechanical and task constraints in models of postural control were discussed.

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Effects of Temporal Scaling and Attention on the Asymmetrical Dynamics of Bimanual Coordination

Michael A. Riley, Eric L. Amazeen, Polemnia G. Amazeen, Paul J. Treffner, and Michael T. Turvey

Handedness and attentional asymmetries in bimanual rhythmic coordination were examined as a function of movement speed. In an in-phase 1:1 frequency locking task, left-handed and right-handed subjects controlled the oscillations of either the right or the left hand so as to contact spatial targets. The task was performed at three frequencies of coupled movement. Coordination dynamics incorporating the body's functional asymmetry predicted that left-handers and right-handers would deviate from zero relative phase in opposite directions, that the deviation would be greater for preferred-hand targeting, and that this deviation would be greater at higher movement frequencies. The results confirmed the major predictions and suggested that asymmetry due to handedness is magnified by attention.

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A Dynamical Approach to the Uncontrolled Manifold: Predicting Performance Error During Steady-State Isometric Force Production

Francis M. Grover, Valéria Andrade, Nicole S. Carver, Scott Bonnette, Michael A. Riley, and Paula L. Silva

The uncontrolled manifold (UCM) approach quantifies the presence of compensatory variability between musculoskeletal elements involved in a motor task. This approach has proved useful for identifying synergistic control strategies for a variety of everyday motor tasks and for investigating how control strategies are affected by motor pathology. However, the UCM approach is limited in its ability to relate compensatory motor variance directly to task performance because variability along the UCM is mathematically agnostic to performance. We present a new approach to UCM analysis that quantifies patterns of irregularity in the compensatory variability between motor elements over time. In a bimanual isometric force stabilization task, irregular patterns of compensation between index fingers predicted greater performance error associated with difficult task conditions, in particular for individuals who exploited a larger set of compensatory strategies (i.e., a larger subspace of the UCM). This relationship between the amount and structure of compensatory motor variance might be an expression of underlying processes supporting performance resilience.

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Differential Predictors of Adherence in Exercise Programs with Moderate versus Higher Levels of Intensity and Frequency

Stephen D. Anton, Michael G. Perri, Joseph Riley III, William F. Kanasky Jr., James R. Rodrigue, Samuel F. Sears, and A. Daniel Martin

This study examined whether specific participant characteristics (age, sex, BMI, exercise history, and self-efficacy) differentially predicted adherence to exercise programs of moderate vs. higher levels of intensity and frequency. Sedentary adults (N = 379) were randomly assigned in a 2 × 2 design to walk 30 min/day at a frequency of either 3 to 4 days/week or 5 to 7 days/week, at an intensity of either 45–55% or 65–75% of maximum heart rate reserve. Exercise adherence was assessed via daily exercise logs completed during Months 2–6 of the exercise program. The major finding of this study was that participants with higher levels of past exercise showed better adherence to higher intensity exercise but tended to have poorer adherence to moderate intensity exercise. Our results suggest that a person’s previous experience with exercise should be considered when prescribing higher intensity exercise, and that individuals with an extensive exercise history can be prescribed higher intensity exercise.

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Injury Risk Factors Integrated Into Self-Guided Real-Time Biofeedback Improves High-Risk Biomechanics

Scott Bonnette, Christopher A. DiCesare, Adam W. Kiefer, Michael A. Riley, Kim D. Barber Foss, Staci Thomas, Katie Kitchen, Jed A. Diekfuss, and Gregory D. Myer

Context: Existing anterior cruciate ligament (ACL) injury prevention programs have failed to reverse the high rate of ACL injuries in adolescent female athletes. Objective: This investigation attempts to overcome factors that limit efficacy with existing injury prevention programs through the use of a novel, objective, and real-time interactive visual feedback system designed to reduce the biomechanical risk factors associated with ACL injuries. Design: Cross-over study. Setting: Medical center laboratory. Participants: A total of 20 females (age = 19.7 [1.34] y; height = 1.74 [0.09] m; weight = 72.16 [12.45] kg) participated in this study. Methods: Participants performed sets of 10 bodyweight squats in each of 8 training blocks (ie, 4 real-time and 4 control blocks) and 3 testing blocks for a total of 110 squats. Feedback conditions were blocked and counterbalanced with half of participants randomly assigned to receive the real-time feedback block first and half receiving the control (sham) feedback first. Results: Heat map analysis revealed that during interaction with the real-time feedback, squat performance measured in terms of key biomechanical parameters was improved compared with performance when participants squatted with the sham stimulus. Conclusions: This study demonstrates that the interactive feedback system guided participants to significantly improve movement biomechanics during performance of a body weight squat, which is a fundamental exercise for a longer term ACL injury risk reduction intervention. A longer training and testing period is necessary to investigate the efficacy of this feedback approach to effect long-term adaptations in the biomechanical risk profile of athletes.

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Movement Regularity Differentiates Specialized and Nonspecialized Athletes in a Virtual Reality Soccer Header Task

Christopher D. Riehm, Scott Bonnette, Michael A. Riley, Jed A. Diekfuss, Christopher A. DiCesare, Andrew Schille, Adam W. Kiefer, Neeru A. Jayanthi, Stephanie Kliethermes, Rhodri S. Lloyd, Mathew W. Pombo, and Gregory D. Myer

Background: Young athletes who specialize early in a single sport may subsequently be at increased risk of injury. While heightened injury risk has been theorized to be related to volume or length of exposure to a single sport, the development of unhealthy, homogenous movement patterns, and rigid neuromuscular control strategies may also be indicted. Unfortunately, traditional laboratory assessments have limited capability to expose such deficits due to the simplistic and constrained nature of laboratory measurement techniques and analyses. Methods: To overcome limitations of prior studies, the authors proposed a soccer-specific virtual reality header assessment to characterize the generalized movement regularity of 44 young female athletes relative to their degree of sport specialization (high vs low). Participants also completed a traditional drop vertical jump assessment. Results: During the virtual reality header assessment, significant differences in center of gravity sample entropy (a measure of movement regularity) were present between specialized (center of gravity sample entropy: mean = 0.08, SD = 0.02) and nonspecialized center of gravity sample entropy: mean = 0.10, SD = 0.03) groups. Specifically, specialized athletes exhibited more regular movement patterns during the soccer header than the nonspecialized athletes. However, no significant between-group differences were observed when comparing participants’ center of gravity time series data from the drop vertical jump assessment. Conclusions: This pattern of altered movement strategy indicates that realistic, sport-specific virtual reality assessments may be uniquely beneficial in exposing overly rigid movement patterns of individuals who engage in repeated sport specialized practice.

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Brain-Behavior Mechanisms for the Transfer of Neuromuscular Training Adaptions to Simulated Sport: Initial Findings From the Train the Brain Project

Dustin R. Grooms, Adam W. Kiefer, Michael A. Riley, Jonathan D. Ellis, Staci Thomas, Katie Kitchen, Christopher A. DiCesare, Scott Bonnette, Brooke Gadd, Kim D. Barber Foss, Weihong Yuan, Paula Silva, Ryan Galloway, Jed A. Diekfuss, James Leach, Kate Berz, and Gregory D. Myer

Context: A limiting factor for reducing anterior cruciate ligament injury risk is ensuring that the movement adaptions made during the prevention program transfer to sport-specific activity. Virtual reality provides a mechanism to assess transferability, and neuroimaging provides a means to assay the neural processes allowing for such skill transfer. Objective: To determine the neural mechanisms for injury risk–reducing biomechanics transfer to sport after anterior cruciate ligament injury prevention training. Design: Cohort study. Setting: Research laboratory. Participants: Four healthy high school soccer athletes. Interventions: Participants completed augmented neuromuscular training utilizing real-time visual feedback. An unloaded knee extension task and a loaded leg press task were completed with neuroimaging before and after training. A virtual reality soccer-specific landing task was also competed following training to assess transfer of movement mechanics. Main Outcome Measures: Landing mechanics during the virtual reality soccer task and blood oxygen level–dependent signal change during neuroimaging. Results: Increased motor planning, sensory and visual region activity during unloaded knee extension and decreased motor cortex activity during loaded leg press were highly correlated with improvements in landing mechanics (decreased hip adduction and knee rotation). Conclusion: Changes in brain activity may underlie adaptation and transfer of injury risk–reducing movement mechanics to sport activity. Clinicians may be able to target these specific brain processes with adjunctive therapy to facilitate intervention improvements transferring to sport.