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Brendan R. Scott, Robert G. Lockie, Timothy J. Knight, Andrew C. Clark and Xanne A.K. Janse de Jonge

Purpose:

To compare various measures of training load (TL) derived from physiological (heart rate [HR]), perceptual (rating of perceived exertion [RPE]), and physical (global positioning system [GPS] and accelerometer) data during in-season field-based training for professional soccer.

Methods:

Fifteen professional male soccer players (age 24.9 ± 5.4 y, body mass 77.6 ± 7.5 kg, height 181.1 ± 6.9 cm) were assessed in-season across 97 individual training sessions. Measures of external TL (total distance [TD], the volume of low-speed activity [LSA; <14.4 km/h], high-speed running [HSR; >14.4 km/h], very high-speed running [VHSR; >19.8 km/h], and player load), HR and session-RPE (sRPE) scores were recorded. Internal TL scores (HR-based and sRPE-based) were calculated, and their relationships with measures of external TL were quantified using Pearson product–moment correlations.

Results:

Physical measures of TD, LSA volume, and player load provided large, significant (r = .71−.84; P < .01) correlations with the HR-based and sRPE-based methods. Volume of HSR and VHSR provided moderate to large, significant (r = .40−.67; P < .01) correlations with measures of internal TL.

Conclusions:

While the volume of HSR and VHSR provided significant relationships with internal TL, physical-performance measures of TD, LSA volume, and player load appear to be more acceptable indicators of external TL, due to the greater magnitude of their correlations with measures of internal TL.

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Yuji Matsuda, Yoshihisa Sakurai, Keita Akashi and Yasuyuki Kubo

Center of mass (CoM) velocity variation in swimming direction is related to swimming performance and efficiency. However, it is difficult to calculate the CoM velocity during swimming. Therefore, we aimed to establish a practical estimation method for the CoM velocity in swimming direction during front crawl swimming with underwater cameras. Ten swimmers were recorded during front crawl swimming (25 m, maximal effort) using a motion capture system with 18 underwater and 9 land cameras. Three CoM velocity estimation methods were constructed (single-hip velocity, both-hips velocity, and both-hips velocity with simulated arm velocity correction). Each model was validated against the actual CoM velocity. The difference between the single-hip velocity and the actual CoM velocity in swimming direction was significantly larger compared with that of the other 2 models. Furthermore, the accuracy of CoM velocity estimation was increased when both-hips velocity was corrected using the simulated arm velocity. The method allowed estimation of the CoM velocity with only 2 underwater cameras with a maximal difference of 0.06 m·s−1. This study established a novel and practical method for the estimation of the CoM velocity in swimming direction during front crawl swimming.

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Takeo Nagura, Hideo Matsumoto, Yoshimori Kiriyama, Ajit Chaudhari and Thomas P. Andriacchi

The aim of the study was to estimate the tibiofemoral joint force in deep flexion to consider how the mechanical load affects the knee. We hypothesize that the joint force should not become sufficiently large to damage the joint under normal contact area, but should become deleterious to the joint under the limited contact area. Sixteen healthy knees were analyzed using a motion capture system, a force plate, a surface electromyography, and a knee model, and then tibiofemoral joint contact forces were calculated. Also, a contact stress simulation using the contact areas from the literature was performed. The peak joint contact forces (M ± SD) were 4566 ± 1932 N at 140 degrees in rising from full squat and 4479 ± 1478 N at 90 degrees in rising from kneeling. Under normal contact area, the tibiofemoral contact stresses in deep flexion were less than 5 MPa and did not exceed the stress to damage the cartilage. The contact stress simulation suggests that knee prosthesis having the contact area smaller than 200 mm2 may be problematic since the contact stress in deep flexion would become larger than 21 MPa, and it would lead damage or wear of the polyethylene.

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Kai Yan Lui, Patricia Hewston and Nandini Deshpande

During sit-to-stand (STS), the vestibular system is highly stimulated in response to linear acceleration of the head and may play an important role, in addition to vision, for postural control. We examined the effects of aging on visual–vestibular interaction for postural control during STS in 15 young (22.5 ± 1.1 years) and 15 older (73.9 ± 5.3 years) participants. Vestibular information was manipulated using galvanic vestibular stimulation. Vision conditions involved normal (eyes open), suboptimal (blurring goggles), and no (eyes closed) vision. Older participants had significantly greater mediolateral peak-to-peak trunk roll (p = .025) and center of mass displacements (p < .001) than young participants. However, despite having greater mediolateral instability, older participants utilized similar strategies as young participants to overcome sensory perturbations during STS. Overall visual inputs were more dominantly used for mediolateral trunk control during STS than vestibular inputs.

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Elizabeth Coker and Terry Kaminski

The purpose of this study was to investigate the effects of visual condition (low light, full light, and full light with mirror) on balance control and technical form during two technical dance movements in a group of elite collegiate dance students. Dancers demonstrated higher center of pressure velocity indicating lower control while performing a static dance task (parallel relevé retiré) and a dynamic dance task (fondu relevé en croix) under low light conditions than either lighted condition. Measures of Western ballet technique (pelvic obliquity, knee extension, and ankle plantar flexion) showed no decrement under low light conditions. No effect of concurrent mirror feedback was found on either center of pressure velocity or technical requirements of the dance tasks.

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Catherine A. Stevermer and Jason C. Gillette

Variation in the timing indicators separating sit-to-stand (STS) into movement phases complicates both research comparisons and clinical applications. The purpose of this study was to use kinetic reference standards to identify accurate kinematic and kinetic indicators for STS movement analysis such that consistent indicators might be used for STS from varied initial postures. Healthy adults performed STS using 4 foot placements: foot-neutral, foot-back, right-staggered, and left-staggered. Kinetic and kinematic data were collected from force platforms and an 8-camera video system. Initiation, seat-off, vertical posture, and termination were detected with 5% start and 7.5% end thresholds for changes in kinetic and kinematic STS indicators. Timing differences between kinetic and kinematic indicator time points and the reference vertical seated reaction force end point (seatoff) were determined. Kinematic indicators were compared with selected kinetic indicators using timing differences, statistical similarity, and internal consistency measures. Our results suggest that a single force platform system measuring vertical GRF or a simple camera system to evaluate the shoulder marker position and velocity can accurately and consistently detect STS initiation, seat-off, and vertical posture. In addition, these suggested STS indicators for initiation, seat-off, and vertical posture were not dependent upon foot placement.

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Joanna Diong and Robert D. Herbert

Contracture after stroke could be due to abnormal mechanical interactions between muscles. This study examined if ankle plantarflexor muscle contracture after stroke is due to abnormal force transmission between the gastrocnemius and soleus muscles. Muscle fascicle lengths were measured from ultrasound images of soleus muscles in five subjects with stroke and ankle contracture and six able-bodied subjects. Changes in soleus fascicle length or pennation during passive knee extension at fixed ankle angle were assumed to indicate intermuscular force transmission. Changes in soleus fascicle length or pennation were adjusted for changes in ankle motion. Subjects with stroke had significant ankle contracture. After adjustment for ankle motion, 9 of 11 subjects demonstrated small changes in soleus fascicle length with knee extension, suggestive of intermuscular force transmission. However, the small changes in fascicle length may have been artifacts caused by movement of the ultrasound transducers. There were no systematic differences in change in fascicle length (median between-group difference adjusting for ankle motion = -0.01, 95% CI -0.26–0.08 mm/degree of knee extension) or pennation (-0.05, 95% CI -0.15–0.07 degree/degree of knee extension). This suggests ankle contractures after stroke were not due to abnormal (systematically increased or decreased) intermuscular force transmission between the gastrocnemius and soleus.

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Bhupinder Singh, Thomas D. Brown, John J. Callaghan and H. John Yack

During seated forward reaching tasks in obese individuals, excessive abdominal tissue can come into contact with the anterior thigh. This soft tissue apposition acts as a mechanical restriction, altering functional biomechanics at the hip, and causing difficulty in certain daily activities such as bending down, or picking up objects from the floor. The purpose of the study was to investigate the contact forces and associated moments exerted by the abdomen on the thigh during seated forward-reaching tasks in adult obese individuals. Ten healthy subjects (age 58.1 ± 4.4) with elevated BMI (39.04 ± 5.02) participated in the study. Contact pressures between the abdomen and thigh were measured using a Tekscan Conformat pressure-mapping sensor during forward-reaching tasks. Kinematic and force plate data were obtained using an infrared motion capture system. The mean abdomen-thigh contact force was 10.17 ± 5.18% of body weight, ranging from 57.8 N to 200 N. Net extensor moment at the hip decreased by mean 16.5 ± 6.44% after accounting for the moment generated by abdomen-thigh tissue contact. In obese individuals, abdomen-thigh contact decreases the net moment at the hip joint during seated forward-reaching activities. This phenomenon should be taken into consideration for accurate biomechanical modeling in these individuals.

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Stephen M. Glass, Alessandro Napoli, Elizabeth D. Thompson, Iyad Obeid and Carole A. Tucker

The balance error scoring system (BESS) is a human-scored, field-based balance test used in cases of suspected concussion. Recently developed instrumented alternatives to human scoring carry substantial advantages over traditional testing, but thus far report relatively abstract outcomes that may not be useful to clinicians or coaches. In contrast, the automated assessment of postural stability (AAPS) is a computerized system that tabulates error events in accordance with the original description of the BESS. This study compared AAPS and human-based BESS scores. A total of 25 healthy adults performed the modified BESS. Tests were scored twice each by 3 human raters and the computerized system. Interrater (between human) and intermethod (AAPS vs human) agreement (interclass correlation coefficient2,1) were calculated alongside Bland–Altman limits of agreement. Interrater analyses were significant (P < .01) and demonstrated good to excellent agreement. Intermethod agreement analyses were significant (P < .01), with agreement ranging from poor to excellent. Computerized scores were equivalent across rating occasions. Limits of agreement ranges for AAPS versus the human average exceeded the average limits of agreement ranges between human raters. Coaches and clinicians may consider a system such as AAPS to automate balance testing while maintaining the familiarity of human-based scoring, although scores should not yet be considered interchangeable with those of a human rater.

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Bjørn Harald Olstad, Christoph Zinner, João Rocha Vaz, Jan M.H. Cabri and Per-Ludvik Kjendlie

Purpose:

To investigate the muscle-activation patterns and coactivation with the support of kinematics in some of the world’s best breaststrokers and identify performance discriminants related to national elites at maximal effort.

Methods:

Surface electromyography was collected in 8 muscles from 4 world-class (including 2 world champions) and 4 national elite breaststroke swimmers during a 25-m breaststroke at maximal effort.

Results:

World-class spent less time during the leg recovery (P = .043), began this phase with a smaller knee angle (154.6° vs 161.8°), and had a higher median velocity of 0.18 m/s during the leg glide than national elites. Compared with national elites, world-class swimmers showed a difference in the muscle-activation patterns for all 8 muscles. In the leg-propulsion phase, there was less triceps brachii activation (1 swimmer 6% vs median 23.0% [8.8]). In the leg-glide phase, there was activation in rectus femoris and gastrocnemius during the beginning of this phase (all world-class vs only 1 national elite) and a longer activation in pectoralis major (world champions 71% [0.5] vs 50.0 [4.3]) (propulsive phase of the arms). In the leg-recovery phase, there was more activation in biceps femoris (50.0% [15.0] vs 20.0% [14.0]) and a later and quicker activation in tibialis anterior (40.0% [7.8] vs 52.0% [6.0]). In the stroke cycle, there was no coactivation in tibialis anterior and gastrocnemius for world champions.

Conclusion:

These components are important performance discriminants. They can be used to improve muscle-activation patterns and kinematics through the different breaststroke phases. Furthermore, they can be used as focus points for teaching breaststroke to beginners.