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Experimentally Induced Pain Results in Reduced Activity of the Rotator Cuff Muscles in Healthy Subjects

Jennifer L. Cooper and Andrew R. Karduna

Shoulder pain is a complex, prevalent problem that is multifactorial in nature. While there are many potential causes, one common suspect is the rotator cuff musculature. The purpose of the present study was to induce pain in the supraspinatus muscle of healthy subjects and observe the resulting changes in muscle activity. Eight muscles on 23 subjects were assessed using electromyography: anterior, middle, and posterior deltoid; pectoralis major; upper trapezius; latissimus dorsi; serratus anterior; supraspinatus; and infraspinatus. It was hypothesized that the rotator cuff muscles would display reduced activity during pain, and that reductions in activity would remain after the pain had dissipated. Both of the rotator cuff muscles measured did indeed display reduced activity in a majority of the dynamic, isometric, and maximal contractions. Many of those reductions remained after the pain had subsided.

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Commingling Effects of Anterior Load and Walking Surface on Dynamic Gait Stability in Young Adults

Caroline Simpkins, Jiyun Ahn, Rebekah Buehler, Rebecca Ban, Meredith Wells, and Feng Yang

Treadmill walking has been used as a surrogate for overground walking to examine how load carriage affects gait. The validity of using treadmill walking to investigate load carriage’s effects on stability has not been established. Thirty young adults were randomized into 3 front-loaded groups (group 1: 0%, 2: 10%, or 3: 20% of bodyweight). Participants carried their load during overground and treadmill walking. Dynamic gait stability (primary outcome) was determined for 2 gait events (touchdown and liftoff). Secondary variables included step length, gait speed, and trunk angle. Groups 1 and 2 demonstrated similar stability between walking surfaces. Group 3 was less stable during treadmill walking than overground (P ≤ .005). Besides trunk angle, all secondary outcomes were similar between groups (P > .272) but different between surfaces (P ≤ .001). The trunk angle at both events showed significant group- and surface-related differences (P ≤ .046). Results suggested that walking with an anterior load of up to 10% bodyweight causes comparable stability between surfaces. A 20% bodyweight front load could render participants less stable on the treadmill than overground. This indicates that anteriorly loaded treadmill walking may not be interchangeable with overground walking concerning stability for anterior loads of 20% bodyweight.

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Delivering Load-Modifying Gait Retraining Interventions via Telehealth in People With Medial Knee Osteoarthritis: A Pilot Randomized Placebo-Controlled Clinical Trial

Nicole D’Souza, Laura Hutchison, Jane Grayson, Claire Hiller, Sarah Kobayashi, and Milena Simic

We aimed to investigate the effects of delivering 3 gait retraining interventions (toe-in, toe-out, and placebo gait) on proxy measures of medial knee load (early- and late-stance peak knee adduction moment [KAM], KAM impulse, and varus thrust) in people with knee osteoarthritis, using a hybrid model of face-to-face and telehealth-delivered sessions over 5 months. This was an originally planned 3-arm randomized placebo-controlled clinical trial. However, during the 2021 COVID-19 outbreak and lockdown in Sydney, Australia, the study became a pilot randomized controlled trial with the remainder of interventions delivered via telehealth. Nine individuals with symptomatic medial knee osteoarthritis were allocated to receive either a toe-in, toe-out, or posture re-education (placebo) gait retraining intervention. Primary outcomes of early- and late-stance peak KAM, KAM impulse, and varus thrust were assessed at baseline and follow-up. Eight participants returned for their follow-up gait assessment. Participants in both active intervention groups (toe-in and toe-out) achieved foot progression angle changes at follow-up. Overall, knee biomechanics in the placebo group did not change at follow-up. It is possible to achieve biomechanical changes in individuals with medial knee osteoarthritis when delivering gait retraining interventions via a hybrid model of face-to-face and telehealth.

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A New Way to Restrict Free Leg Movement During Unilateral Vertical Jump Test

Christian Schmidt, Mike Perroulaz, Yago Perez, Jérémie Rosset, Gabriel Wüthrich, Davide Malatesta, and Pierre Samozino

The purpose of this investigation was (1) to test the effect of movement restriction of the free leg during unilateral vertical jump on performance and power output comparing 2 different jump techniques: flexed (Classic technique) and straight (FC Luzern technique) free leg, and (2) to test the correlation between performance and power output obtained using these 2 techniques. Twenty elite soccer players performed squat (SJ) and countermovement (CMJ) jumps on each leg. The jump height and peak power output were compared between the 2 techniques for both legs. The jump height and peak power were significantly higher for the classic test for SJ and CMJ (P < .001) with no side effects or interactions. The angular range of motion of the free leg was higher for the Classic test than for the FC Lucerne test (P < .001), with no difference in the angular range of motion of the trunk. A moderate correlation was found between the 2 techniques on peak power (SJ: r = .626; CMJ: r = .649) and jump height (SJ: r = .742; CMJ: r = .891). Consequently, FC Lucerne technique, limiting the contribution of the free leg, is more appropriate to assess lower limb strength capacities during unilateral jump test.

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People With Low Back Pain Exhibit Higher Trunk Muscle Activity and Impaired Postural Control During Static and Dynamic Functional Tasks: A Cross-Sectional Study

Sara Salamat, Saeed Talebian, Nader Maroufi, Gitta Kalbassi, Davood Salamat, and Kieran O’Sullivan

The study compared superficial trunk muscle activity and postural control among an active extension subgroup of people with nonspecific chronic low back pain (AE-NSCLBP) with painfree controls during functional tasks. Thirty-two people (17 people with low back pain [LBP] and 15 painfree controls) participated in this study. Muscle activity of 5 trunk muscles and postural control were investigated during both standing tasks (eyes open/closed; single/double-leg balance) and dynamic functional tasks (spinal forward flexion and return, and a sit to stand transfer). Results showed that during single-leg standing, people with AE-NSCLBP exhibit higher muscle activity than painfree controls for 3 trunk muscles, especially with their eyes closed. There were no significant differences in muscle activity between eye conditions during double-leg standing and sit to stand transfer, forward flexion, and return from flexion. The AE-NSCLBP subgroup also demonstrated significantly impaired postural control (lower time to boundary) in 4 of 8 conditions, especially during single-leg standing and with their eyes closed. These findings show people with LBP typically demonstrated greater trunk muscle activity and poorer postural control while maintaining standing posture. This pattern was most evident when the postural challenge was higher, such as single-leg standing or with eyes closed. While this study design cannot infer causality, these findings have implications for LBP rehabilitation, particularly regarding approaches which seek to alter muscle activation among people with LBP.

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Do Sex and Age Influence Scapular and Thoracohumeral Kinematics During a Functional Task Protocol?

Alexander Waslen, Kenzie B. Friesen, and Angelica E. Lang

There is mixed evidence on the role that biological sex plays in shoulder biomechanics despite known differences in musculoskeletal disorder prevalence between males and females. Additionally, advancing age may contribute to shoulder kinematic changes. The purpose of this study was to determine if sex and age influenced scapular and thoracohumeral kinematics during a range of functional tasks. Sixty healthy participants aged 19–63 years (30 males; 30 females) completed a functional task protocol while their upper limb motion was recorded. Scapular and humeral angles were calculated and compared with multiple linear regressions to assess the interaction effects of sex and age. Shoulder kinematics were not different between sex and age groups for many of the functional tasks. However, females had lower humeral external rotation in the overhead lift task (15°, P < .001), and less scapular anterior tilt angles in the forward transfer task (6°, P < .001) than males. Age was positively associated with humeral elevation (R 2 = .330, P < .001) and scapular rotation (R 2 = .299, P < .001) in the Wash Axilla task. There exist some kinematic differences between sex and with advancing age for select functional tasks, which should be considered for musculoskeletal disorder development.

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Increasing Breast Support is Associated With a Distal-to-Proximal Redistribution of Joint Negative Work During a Double-Limb Landing Task

Hailey B. Fong, Alexis K. Nelson, Deirdre McGhee, Kevin R. Ford, and Douglas W. Powell

Female athletes exhibit greater rates of anterior cruciate ligament injury compared with male athletes. Biomechanical factors are suggested to contribute to sex differences in injury rates. No previous investigation has evaluated the role of breast support on landing biomechanics. This study investigates the effect of breast support on joint negative work and joint contributions to total negative work during landing. Thirty-five female athletes performed 5 landing trials in 3 breast support conditions. Lower-extremity joint negative work and relative joint contributions to total negative work were calculated. Univariate analyses of variance were used to determine the effect of breast support on negative joint work values. Increasing levels of breast support were associated with lower ankle negative work (P < .001) and ankle relative contributions (P < .001) and increases in hip negative work (P = .008) and hip relative contributions (P < .001). No changes were observed in total negative work (P = .759), knee negative work (P = .059), or knee contributions to negative work (P = .094). These data demonstrate that the level of breast support affects lower-extremity biomechanics. The distal-to-proximal shift in negative joint work and relative joint contributions may be indicative of a more protective landing strategy for anterior cruciate ligament injuries.

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Quantitative Muscle Fascicle Tractography Using Brightness-Mode Ultrasound

Hannah Kilpatrick, Emily Bush, Carly Lockard, Xingyu Zhou, Crystal Coolbaugh, and Bruce Damon

A muscle’s architecture, defined as the geometric arrangement of its fibers with respect to its mechanical line of action, impacts its abilities to produce force and shorten or lengthen under load. Ultrasound and other noninvasive imaging methods have contributed significantly to our understanding of these structure–function relationships. The goal of this work was to develop a MATLAB toolbox for tracking and mathematically representing muscle architecture at the fascicle scale, based on brightness-mode ultrasound imaging data. The MuscleUS_Toolbox allows user-performed segmentation of a region of interest and automated modeling of local fascicle orientation; calculation of streamlines between aponeuroses of origin and insertion; and quantification of fascicle length, pennation angle, and curvature. A method is described for optimizing the fascicle orientation modeling process, and the capabilities of the toolbox for quantifying and visualizing fascicle architecture are illustrated in the human tibialis anterior muscle. The toolbox is freely available.

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The Vehicle Seating Intervention Trial: Cross-Over Randomized Controlled Trial to Evaluate the Impact of 2 Car Seat Configurations on Spinal Posture

Diana De Carvalho, Kristi Randhawa, Leslie Verville, Sheilah Hogg-Johnson, Samuel J. Howarth, Carmen Liang, Silvano Mior, and Pierre Côté

Driving posture can lead to musculoskeletal pain. Most work focuses on the lower back; therefore, we know little about automobile seat design and neck posture. This study evaluated an automobile driver seat that individualized upper back support to improve head and neck posture. Specifically, we examined the system’s impact on anterior head translation with secondary outcomes of spine posture and perceptions of comfort/well-being compared with a control. Forty participants were block randomized to experience either the activated or deactivated version of the same seating system first. Participants completed two 30-minute simulated driving trials, separated by washout, with continuous measures of anterior head translation, spine posture, and pelvis orientation. Perceptions of comfort/well-being were assessed by survey and open-ended questions immediately following each condition. Small, but statistically significant decreases in anterior head translation and posterior pelvic tilt occurred with the activated seat system. Participants reported lower satisfaction with the activated seat system. Order of the 2 seat conditions affected differences in pelvis orientation and participant perceptions of comfort/well-being. An anthropometric-based seat system targeting upper back support can significantly affect head and pelvic posture but not satisfaction during simulated driving. Future work should examine long-term impacts of these posture changes on health outcomes.

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Volume 39 (2023): Issue 5 (Oct 2023): Special Issue: International Society of Biomechanics: 50 years of Musculoskeletal Biomechanics