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Effects of Static Hamstring Stretching on Maximal Sprint Speed and Relationship With Nordic Hamstring Strength

Yusuke Ozaki and Takeshi Ueda

This study aimed to determine the acute effects of static stretching of the hamstrings on maximal sprint speed and its spatiotemporal variables and lower-limb kinematics during the late swing phase, as well as the relationship with Nordic hamstring strength. The study had a within-participant experimental design. Sixteen healthy male college sprinters were asked to sprint 80 m without static stretching and with static stretching of the hamstrings for 4 × 30 s per leg before the sprint; both conditions were counterbalanced. The knee flexion peak torque was measured using the Nordic hamstring. The differences between no static stretching and static stretching as well as their relationship with Nordic hamstring strength were investigated. The results showed that the touchdown distance (p = .036) significantly increased following static stretching. Although not significant, maximal sprint speed decreased (p = .086), and the theoretical hamstring length (difference between knee angle and hip angle) at ipsilateral touchdown was greater (p = .069) following static stretching. In addition, a lower peak torque of the Nordic hamstring resulted in a more significant decrease in maximal sprint speed following static stretching. Therefore, static stretching of the hamstring just before sprinting may increase the theoretical hamstring length during the late swing phase at maximal sprint speed and induce kinematics that increases the hamstring strain injury risk. Moreover, it is suggested that improving the Nordic hamstring strength may help minimize the negative effects of static stretching on the hamstrings.

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Age-Related Constraints in the Visuomotor Plasticity of Postural Control as Revealed by a Whole-Body Mirror Learning Task

Iasonas Christodoulou, Vasileios Mylonas, Theodoros M. Kannas, Charalampos Sotirakis, Lida Mademli, Evangelia Kouidi, and Vassilia Hatzitaki

Whether visuomotor plasticity of postural control is a trainable feature in older age remains an open question despite the wealth of visually guided exercise games promising to improve balance skill. We asked how aging affects adaptation and learning of a visual feedback (VF) reversal during visually guided weight shifting and whether this skill is modulated by explicit knowledge. Twenty-four older (71.43 ± 2.54 years) and 24 young (24.04 ± 0.93 years) participants were exposed to a 180° VF reversal while tracking a horizontally moving target by voluntarily weight shifting between two force platforms. An explicit strategy was available to half of the participants with detailed instruction to counter the VF rotation. Individual error data were fitted to an exponential function to assess adaptation. Fewer older (12/24) than younger (21/24) participants adapted to the VF reversal, displaying error curves that fitted the exponential function. Older adults who adapted to the VF reversal (responders, n = 12) reached an asymptote in performance in the same weight shifting cycle and displayed a similar mean asymptotic error compared with young participants. Young but not older responders exhibited an aftereffect when the VF reversal was removed. Instruction did not influence spatial error modulations regardless of age. The large individual variations within the older adults’ group during early adaptation suggest age-specific limitations in using explicit cognitive strategies when older adults are exposed to an abrupt mirror feedback reversal that requires a change in weight shifting direction during whole-body postural tracking.

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Volume 28 (2024): Issue 1 (Jan 2024)

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High-Intensity Forward-Backward Plyometrics After the Warm-Up Entail Better Sprint and Change-of-Direction Performance Than Low-Intensity Side-to-Side Plyometrics

Karim Ben Ayed, Raouf Hammami, Javier Gene-Morales, Amira Ajailia, Hanen Werfelli, Haithem Rebai, Pablo Jiménez-Martínez, Jorge Flandez, and Juan C. Colado

This study aimed to determine the acute effects of high-intensity forward-backward and low-intensity side-to-side plyometric jumps performed following the warm-up on sprint (5, 10, and 15 m) and change-of-direction (COD) (T-half test and repeated T-half tests) performance in youth volleyball players. After a familiarization week, 30 male volleyball players (age = 12.04 ± 1.03 years) performed three randomized conditions (no-plyometrics, high-intensity plyometrics, and low-intensity plyometrics) in three sessions. In a within-subject design, three sets of six repetitions of forward-backward 30-cm hurdle jumps (high-intensity) and side-to-side 20-cm hurdle jumps (low-intensity) were completed. Sprint and COD were tested after each of the conditions with a 2-min rest. A significant effect of the plyometric condition was observed on sprint (p < .001, η p 2 range: .56–.70) and COD (p < .01, η p 2 = .24 ), but not on repeated COD. More specifically, the high-intensity plyometric condition exhibited significantly better results compared with the low-intensity plyometric (Cohen’s d range: 0.73–1.21) and control conditions (Cohen’s d range: 0.91–2.21). Due to the importance of speed and COD in volleyball, these results suggest that young volleyball players may benefit from high-intensity forward-backward plyometric protocols following the warm-up to improve subsequent performance.

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The Influence of a Warm-Up on Vigilance in University Students

Francisco Tomás González-Fernández, Alfonso Castillo-Rodriguez, Sixto González-Víllora, and David Hortigüela-Alcalá

The present study aimed to analyze the effects of conducting a warm-up (WC) or not (WWC) on students of the Science Degree in Physical Activity and Sport before starting a practical class. Thirty-two students of the Science Degree in Physical Activity and Sport (age: 22.38 ± 1.81 years; height: 176.09 ± 8.52 cm; weight: 22.38 ± 1.81 kg; body fat: 25.17 ± 3.20%) participated in a counterbalanced cross-sectional study in which three conditions were tested: (a) basal lineal, (b) WC, and (c) WWC. Participants recorded longer times (worse performance) in the Illinois dribbling test (basal lineal condition [20.17 ± 1.35], WWC [20.13 ± 1.37], and WC [19.32 ± 1.35]) and the Psychomotor Vigilance Task test (basal lineal condition [397.88 ± 75.98 ms]; WWC [412.19 ± 91.39 ms], and WC [368.53 ± 68.65 ms]). The warm-up prior to physical activity classes had positive effects on vigilance linked to executive functioning, and physical performance. In this sense, more research on different types of warm-up may be in order to contrast them with each other, as well as to carry out attention measurements according to the content to be imparted after the warm-ups. The present study represents a big opportunity for all physical education teachers due to warm-up is a crucial aspect that occurs in all practical sessions, also linked to the attention processes and motivational factors of the students.

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Increased Ability to Perceive Relevant Sensory Information Minimizes Low Back Exposures in Lifting

Daniel P. Armstrong, Brian C. Horslen, and Steven L. Fischer

We have previously shown evidence that some individuals seem to consistently minimize low back loads when lifting, while others do not. However, it is unknown why. Individual differences in ability to perceive relevant sensory information may explain differences in minimization of low back loads during lifting, consistent with considering load reduction in one’s movement objective in an optimal feedback control theory framework. The purpose of this study was to investigate whether individuals’ ability to perceive proprioceptive information (both force- and posture-senses) at the low back was associated with peak low back loads when performing generic or occupation-specific lifts. Seventy-two participants were recruited to perform 10 barbell (generic) and backboard (occupation-specific) lifts, while whole-body kinematics and ground reaction forces were collected. Peak low back compression and anteroposterior shear forces normalized to body mass were calculated as dependent variables. Both posture matching ability and force matching ability at the heavier force targets were associated with lower means and variability of peak low-back loads in both lift types, albeit with small effect sizes (R 2 ≤ .17). These findings support the utility of an optimal feedback control theory framework to explore factors explaining interindividual differences in low back loads during lifting. Further, this evidence suggests improving proprioceptive ability may be a useful strategy in lift training programs designed for workplace injury prevention.

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Acute Effect of Brace Use on Upper-Extremity Functionality in Adolescent Individuals With Idiopathic Scoliosis: A Cross-Sectional Study

Kamil Yilmaz, Fatih Celik, and Bayram Sonmez Unuvar

It is well known that scoliosis adversely affects the functions of the upper extremities. However, the acute effect of rigid braces, which are widely used in the conservative treatment of scoliosis, on upper-extremity functionality remains unknown. The aim of this study was to investigate the acute effect of a rigid thoracolumbosacral brace use on upper-extremity functionality in individuals with adolescent idiopathic scoliosis (AIS). Thirty-eight individuals diagnosed with AIS participated in this cross-sectional study, with a mean age of 14.55 ± 1.90 years and a range of 10–18 years. The upper-extremity functionality was assessed using the Nine-Hole Peg Test and handgrip strength, with assessments conducted under both in-brace (with their own braces) and out-of-brace conditions. Nine-Hole Peg Test durations of the AIS patients for the nondominant side were significantly lower for in-brace conditions compared with out-of-brace conditions (p = .049, effect size = 0.136). The grip strength of the nondominant side was significantly higher for in-brace conditions compared with out-of-brace conditions (p = .025, effect size = 0.365). A weak negative correlation was found between the degree of curvature and the grip strength of the dominant side for in-brace conditions (r = −.323, p = .048). It was concluded that the brace had a positive effect on upper-extremity functionality on the nondominant side by both shortening the Nine-Hole Peg Test duration and increasing grip strength. In AIS patients, the brace may positively affect daily living by improving the functionality of the nondominant extremity.

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The Effect of an Overhead External Load Lifting and Lowering on Dynamic Postural Control in Subgroups of Low Back Pain

Majid Shahbazi, Javad Sarrafzadeh, Ismail Ebrahimi Takamjani, and Hossein Negahban

Background: Understanding postural control in low back pain (LBP) subgroups can help develop targeted interventions to improve postural control. The studies on this topic are limited. Therefore, the primary purpose of this study was to compare the postural control of LBP subgroups with healthy individuals during overhead load lifting and lowering. Methods: In this cross-sectional study, the participants were 52 with LBP and 20 healthy. The LBP patients were classified based on the O’Sullivan classification system into 21 flexion patterns and 31 active extension patterns. The participants lifted the box from their waists to their overheads and lowered it to their waists. Changes in postural control parameters were measured with a force plate system. Results: The results of the analysis of variance showed that during load lifting, the mediolateral phase plane (p = .044) and the mean total velocity (p = .029) had significant differences between flexion patterns and healthy. Also, the load-lowering results showed that active extension patterns, compared with healthy, had significant differences in the anteroposterior–mediolateral phase plane (p = .042). The patients showed less postural sway than the healthy. Conclusions: The results in this work highlight the importance of identifying the homogenous subgroups in LBP and support the classification of heterogeneous LBP. Different subgroups exhibit different postural control behaviors. These behaviors can be due to the loading of various tissues during different tasks.

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Motor Transfer and Proactive Interference in Cycling With a Noncircular Chainring

Thomas Haab, Peter Leinen, and Stefan Panzer

Athletes must transfer their performance when changing equipment due to innovative developments in sports technology. This kind of transfer has received only moderate attention. The aim of this study was to examine whether a mechanical change in sports equipment disturbs an athlete’s performance and affects biomechanical and neurophysiological parameters. Therefore, an experiment was conducted in which 36 participants in three groups pedaled at 70 rounds per minute on a cycling ergometer with a circular and a noncircular (NC) chainring. The dependent variables were the total variability of the cadence, torque effectiveness, and muscle cocontraction (electromyographic cocontraction) of four antagonistic acting muscle pairs. Data were recorded during an acquisition phase, a transfer phase, and a retention phase. The results revealed that practice on a circular chainring induces a positive transfer on the NC chainring for total variability without a proactive interference effect. Torque effectiveness did not change within or between groups during the acquisition, transfer, and retention phases. Torque effectiveness and electromyographic cocontraction were not affected when the chainrings were altered from Day 1 to Day 2. During the retention phase, electromyographic cocontraction was higher when using the NC chainring, but the difference was small in absolute terms. The results regarding transfer and proactive interference seem to be strongly dependent on the movement task and the change in sports equipment. Transfer from the circular to NC chainring indicates refined neuromuscular control and improved movement coordination.

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Volume 27 (2023): Issue 4 (Oct 2023)