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Foot–Ankle Mechanical Transmission: Age Effects and the Relation to Ankle Push-Off During Walking

Aubrey J. Gray, Kota Z. Takahashi, Howard E. Kashefsky, and Jason R. Franz

Older adults walk with less push-off power than younger adults. Principally attributed to plantar flexor dysfunction, growing evidence implicates interactions between the foot and ankle as critical for generating effective push-off. Our purposes were to measure age effects on foot–ankle mechanical transmission (FAMT, ie, the ratio between metatarsal phalangeal extension and medial gastrocnemius fascicle length change), and its association with ankle push-off during walking. We hypothesized that (1) FAMT would be lesser in older adults and (2) lesser FAMT would positively correlate with slower preferred speeds and reduced ankle push-off intensity. Fourteen younger adults (25 [6] y) and 15 older adults (71 [5] y) participated. Older adults had 45% to 48% lesser FAMT than younger adults from 0° to 30° metatarsal phalangeal extension—an age-related difference that was not evident from 30° to 60° metatarsal phalangeal extension. However, we did not find any significant correlations with walking outcomes. Assuming our findings can be replicated in future studies and represent a genuine phenomenon of relevance to the biomechanics of aging gait, we suspect that compensations may be discovered in older adults to explain this lack of significance. Future work should include measures of muscle activities and foot mechanics during walking and/or perform more controlled comparisons at fixed speeds.

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Spring-Mass Characteristics in Runners Before and After a 56-km Road Ultramarathon

Geoffrey T. Burns, Nicholas Tam, Nelleke G. Langerak, Ronald F. Zernicke, and Robert P. Lamberts

Ultramarathons are a unique model to study the effects of systemic fatigue in athletes. This investigation applied the spring-mass template to study runners before and 2 days after a road ultramarathon to characterize the effects of fatigue on systemic gait patterns. Overground kinetics were captured 7 days before and 2 days after the event in 14 runners. Traditional kinetic and spring-mass parameters were calculated, along with nonlinear regression-derived parameters and spring-mass model fit metrics. After the ultramarathon, vertical force magnitudes and loading rates were unchanged, but impact peaks increased (1.88 ± 0.08–1.95 ± 0.10 bodyweight). Ground contact times were modestly shorter (−3 ± 1 ms), resulting in increased leg stiffness (10.0 ± 0.5–10.3 ± 0.5 kN/m) with equivocal vertical stiffnesses. The deviation from the modeled spring-mass kinetics also increased (171.3 ± 15.0–181.4 ± 16.5 N). Overall, the systemic mechanical behaviors of the runners persisted despite the fatigue and stress induced by a road ultramarathon. These findings support previous observations that runners maintain gross mechanical behavior when fatigued with small compensatory changes in spatiotemporal and traditional spring-mass characteristics. However, these findings also suggest that the variability within that gross behavior may increase after stress, suggesting new opportunities for quantifying those deviations.

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Investigation of a Theoretical Model for the Rotational Shot Put Technique

Tadahiko Kato, Kei Maeda, Jun Mizushima, and Akira Maeda

The biomechanics of the rotational shot put technique have been demonstrated. However, the causal relationships among kinematics and kinetics for achieving higher release velocity remain poorly understood. This study investigated these causal relationships among biomechanical variables for achieving a higher release velocity in the rotational shot put technique. The study included 22 male shot putters whose 3-dimensional motion was captured during official competitions. Key kinematic and kinetic variables throughout the shot put motion were calculated, as suggested by previous studies. Path analysis was used to explore a hierarchical model that postulates both direct and indirect effects among variables. The findings revealed that the impulse of the shot, system angular momentum, and system linear momentum were critical kinetic variables contributing directly to release velocity. Additionally, 8 kinematic variables significantly affected the impulse of the shot, including shoulder rotation, shot path length, and trunk tilt, while movements such as swings and extensions of the lower extremities were related to system momentum. This model not only provides a detailed understanding of the mechanics involved in the rotational technique but also informs technical coaching strategies in the shot put.

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A Potential Mechanism Involved in the Regularity of Center-of-Pressure Displacements During Achieving Unipedal Equilibrium on Stable and Unstable Surfaces

Arunee Promsri

Sample entropy (SampEn) is a widely used measure for estimating the regularity of center-of-pressure (COP) trajectories, with high COP regularity (low SampEn) commonly interpreted as ineffective postural control. The current study aimed to investigate one possible source of COP regularity—agonist–antagonist coactivation—resulting in joint stiffness or action stability. A cross-correlation analysis was conducted to determine the similarity (coactivation) level of 5 pairs of lower limb agonist–antagonist electromyographic signals. SampEn was applied to anteroposterior (ap) and mediolateral (ml) COP displacements. Electromyographic and COP signals were simultaneously derived from 25 active young adults (25.6 ± 4.0 years) during unipedal balancing on stable and multiaxial-unstable surfaces. Then, the correlation between individual agonist–antagonist cross-correlation coefficients and SampEn-COP was explored. The results show that only the tibialis anterior–peroneus longus (TA–PL) coactivations are negatively correlated with SampEn-COPap/ml (P ≤ .030) in both surface conditions, with greater TA–PL coactivation appearing with lower SampEn-COPap/ml. In addition, sex effects as one factor that might influence postural control were also tested. Women exhibited greater TA–PL coactivation (P = .017) and lower SampEn-COPap (P = .005) than men. Together, TA–PL coactivation could be one possible origin of COP regularity, but its effects might be detrimental to unipedal postural control, especially for women.

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Effects of Changing Hip Position on Scapular Kinematics

Sarah E. Schlittler, David N. Suprak, Lorrie R. Brilla, and Jun G. San Juan

The effects of hip position and posture on scapular kinematics have yet to be explored. The purpose of this study was to measure differences in scapular kinematics with changing hip position. Scapular kinematics were measured during scapular plane humeral elevation. Twenty-four subjects were required to elevate the dominant arm up to 120° in the following randomized conditions: standing, seated, seated ipsilateral hip flexion, and seated contralateral hip flexion. Two-way analyses of variance were used to evaluate effects of shoulder elevation and hip position on scapular upward rotation, posterior tilt (PT), and external rotation. For external rotation, there was no significant interaction (P = .714) and no main effect of elevation (P = .618) or condition (P = .390). For PT, there was no significant interaction (P = .693) but significant main effects of elevation (P < .001) and condition (P < .001), with the greatest PT in standing. For upward rotation, there was no significant interaction (P = .698), a significant main effect of elevation (P < .001), and no significant effect of condition (P = .726). The effect on PT may not be clinically significant. These results may serve as a baseline measurement of healthy scapular kinematics across hip positions.

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Normative Extensor Hallucis Brevis Muscle Activity During Locomotion Following the Development of a Novel Ultrasound-Guided Fine-Wire Electromyography Protocol

Kelly A. Robb, Keara Sutherland, and Stephen D. Perry

Fine-wire electromyography (EMG) is a traditional laboratory technique to estimate muscle activity of the small foot muscles, however, recordings have not been reported from extensor hallucis brevis (EHB). As an extensor of the great toe, EHB is an important muscle when studying physiological changes associated with foot pathologies such as hallux valgus. The purpose of this study was to develop an ultrasound-guided fine-wire EMG protocol to record EHB muscle activity and report normative EMG profiles of healthy young adults during locomotion. Sixteen asymptomatic young adults completed 20 walking trials at a self-selected velocity. Ensemble averages were calculated from the time normalized linear envelopes and represented from 0% to 100% of the single stance phase of gait. EHB muscle bursts were observed between 0% and 20% of the stance phase of gait in all participants. A second burst of EMG was observed between 80% and 100% of stance in 50% of the participants. This study introduces a novel ultrasound-guided EMG protocol and normative data from EHB recordings suggest a synergistic role to anterior compartment musculature at contact. These results provide preliminary insights into understanding the functional role of EHB and may help elucidate the biomechanical factors exacerbating the progression of hallux pathologies.

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Kinematic Sequence Differences Between Trained Baseball Players and Untrained Adolescent Individuals

Corey Wukelic, Sean Machak, Michael Gromeier, and Sarah P Shultz

An overhead throwing motion is a common gross motor skill often taught in early childhood to improve physical activity participation. Yet, research investigating motor efficiency in overhead throws often focuses on improving performance in trained individuals. This project compares kinematic sequencing between trained and untrained youth. After a brief warm-up, untrained high school students (N = 9) and trained high school and college students (N = 10) threw a weighted tennis ball for accuracy (N = 10 throws). Upper extremity angular velocities were collected using 3-dimensional inertial sensor motion capture. Kinematic sequencing of joints and segments (pelvis, trunk, shoulder, elbow, and wrist) was assessed using Kruskal–Wallis test; Friedman and Wilcoxon tests identified group differences between sequences. Seven independent kinematic sequences were identified (N = 2 unique trained; N = 3 unique untrained; N = 2 shared). The rankings for the trained group maintained a mostly consistent pattern with only elbow and wrist joints producing similar rankings. The untrained group lacked that consistency with similar rankings of elbow versus wrist and shoulder versus elbow. Trained individuals threw with a more efficient proximal-to-distal sequencing pattern than the untrained participants, specifically at the trunk and shoulder. Continuous training of gross motor skills beyond initial skill development is necessary to maintain motor proficiency.

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Volume 40 (2024): Issue 5 (Oct 2024)

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Do Experienced Adolescent Competition Dancers Alter Landing Kinematics and Kinetics for Split Leaps or Center Leaps After Fatigue?

Zoie R. Mink and Amanda Esquivel

Most injuries that dancers sustain are to the lower extremities, specifically the foot and ankle region. Numerous potential risk factors have been examined for dancer injuries such as technical mistakes and fatigue. The purpose of this study was to compare landing kinematics and kinetics during jumps that are common in dance pre and postfatigue. Ten adolescent advanced level dancers participated in this study. Subjects completed 3 split leaps and 3 center leaps before and after a fatigue protocol performed on a stationary bike. Live motion capture was used to record landing kinematic and kinetic data. Results of this study showed a significant increase in ankle eversion and external rotation angles for center leaps from pre- to postfatigue protocol (P = .020 and P = .020, respectively) as well as significant increases in ankle eversion and knee adduction moments for center leaps (P = .020 and P = .036, respectively). These results show that after a fatigue protocol, there are changes to the kinematics of dancers that may make them more susceptible to ankle injury.

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Effects of Stroboscopic Goggles on Standing Balance in the Spatiotemporal and Frequency Domains: An Exploratory Study

Madeleine E. McCreary, Chloe M. Lapish, Nora M. Lewis, Ryland D. Swearinger, Daniel P. Ferris, and Erika M. Pliner

Balance training paradigms have been shown to effectively reduce fall risk. Visual feedback is an important sensory mechanism for regulating postural control, promoting visual perturbations for balance training paradigms. Stroboscopic goggles, which oscillate from transparent to opaque, are a form of visual perturbation, but their effect on standing balance has not been assessed. In this study, 29 participants stood in bilateral and tandem stances as the center of pressure was recorded for 6 consecutive minutes wherein there were no stroboscopic perturbations in the first and last minutes. Spatial–temporal, frequency domain, and nonlinear standing balance parameters were calculated for each period. More differences in spatial–temporal parameters due to the strobe were found in the medial–lateral direction than the anterior–posterior direction. More differences in frequency domain parameters were observed in the anterior–posterior direction than the medial–lateral direction, but this did not occur for each variable. The nonlinear parameters were strongly affected by the strobe. Stroboscopic perturbations did not affect the bilateral and tandem stances equally. Spatial–temporal parameters for the tandem stance were greater in magnitude during the strobe period than the no strobe periods. This effect was not seen with the bilateral stance. This indicates that the efficacy of stroboscopic perturbations for challenging standing balance depends on task difficulty. Balance training paradigms that utilize stroboscopic perturbations will need to harmonize these perturbations with task difficulty.