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MODELLING MUSCLE FORCE DISTRIBUTIONS DURING THE FRONT AND BACK SQUAT IN TRAINED LIFTERS

100%
Sinclair J., Atkins S., Hayley V., Richards J. D.
Central European Journal of Sport Sciences and Medicine
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2016
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vol. 14
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issue 2
13 - 20
EN
The barbell squat is a fundamental strength and conditioning exercise, with two principal variants; back and front. Whilst previous studies have examined the mechanical differences of the front and back squat, there is no information comparing the distributions of muscle forces between these variants. This study aimed to compare estimated forces developed by the primary skeletal muscles used in the front and back squat. Twenty-five male participants were recruited with 6.24 ±2.21 years of experience in squat lifting and 1 repetition maximum values of 127.5 ±18.8 and 90.6 ±14.4 kg for the back and front squat lifts. Participants completed both back and front squats at 70% of their front squat 1 repetition maximum. Muscle forces were determined during dynamic situations using motion capture data, in addition to sagittal plane kinematics. Differences between squat conditions were examined using a multivariate analysis of variance. The kinematic analysis showed that the back squat was associated with significantly (p < 0.05) greater flexion of the trunk. Examination of muscles forces indicated that erector spinae forces were also significantly (p < 0.05) larger in the back squat. No significant differences were identified for skeletal muscle forces elsewhere (p > 0.05). Our results indicate that neither the front nor back squat provides any marked difference in muscle force production, aside from that isolated to the lower back. These findings lead the conclusion that neither the front nor back squat conditions confer any additional benefits over the other in terms of the skeletal muscle force output.
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Influence of Different Hip Joint Centre Locations on Hip and Knee Joint Kinetics and Kinematics During the Squat

100%
Sinclair J., Atkins S., Vincent H.
Journal of Human Kinetics
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2014
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vol. 44
|
issue 1
5-17
EN
Identification of the hip joint centre (HJC) is important in the biomechanical examination of human movement. However, there is yet to be any published information regarding the influence of different HJC locations on hip and knee joint kinetics during functional tasks. This study aimed to examine the influence of four different HJC techniques on 3- D hip and knee joint kinetics/kinematics during the squat. Hip and knee joint kinetics/kinematics of the squat were obtained from fifteen male participants using an eight camera motion capture system. The 3-D kinetics/kinematics of the squat were quantified using four hip joint centre estimation techniques. Repeated measures ANOVAs were used to compare the discrete parameters as a function of each HJC location. The results show that significant differences in joint angles and moment parameters were evident at both the hip and knee joint in the coronal and transverse planes. These observations indicate that when calculating non-sagittal joint kinetics/kinematics during the squat, researchers should carefully consider their HJC method as it may significantly affect the interpretation of their data.
3
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The Effects of Various Running Inclines on Three-Segment Foot Mechanics and Plantar Fascia Strain

100%
Sinclair J., Atkins S., Vincent H.
Human Movement
|
2014
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vol. 15
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issue 4
209-215
EN
Purpose. There has yet to be a combined analysis of three-dimensional multi-segment foot kinematics and plantar fascia strain in running gait at various degrees of inclination. The aim of the current study was therefore to investigate the above during treadmill running at different inclines (0°, 5°, 10° and 15°). Methods. Twelve male participants ran at 4.0 m · s-1 in the four different inclinations. Three-dimensional kinematics of the foot segments and plantar fascia strain were quantified for each incline and contrasted using one-way repeated measures ANOVA. Results and conclusions. The results showed that plantar fascia strain increased significantly as a function of running incline. Given the projected association between plantar fascia strain and the aetiology of injury, inclined running may be associated with a greater incidence of injury to the plantar fascia.
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The Reliability of Electromyographic Normalization Methods for Cycling Analyses

76%
Sinclair J., Taylor P. J., Hebron J., Brooks D., Hurst H. T., Atkins S.
Journal of Human Kinetics
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2015
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vol. 46
|
issue 1
19-27
EN
Electromyography (EMG) is normalized in relation to a reference maximum voluntary contraction (MVC) value. Different normalization techniques are available but the most reliable method for cycling movements is unknown. This study investigated the reliability of different normalization techniques for cycling analyses. Twenty-five male cyclists (age 24.13 ± 2.79 years, body height 176.22 ± 4.87 cm and body mass 67.23 ± 4.19 kg, BMI = 21.70 ± 2.60 kg·m−1) performed different normalization procedures on two occasions, within the same testing session. The rectus femoris, biceps femoris, gastrocnemius and tibialis anterior muscles were examined. Participants performed isometric normalizations (IMVC) using an isokinetic dynamometer. Five minutes of submaximal cycling (180 W) were also undertaken, allowing the mean (DMA) and peak (PDA) activation from each muscle to serve as reference values. Finally, a 10 s cycling sprint (MxDA) trial was undertaken and the highest activation from each muscle was used as the reference value. Differences between reference EMG amplitude, as a function of normalization technique and time, were examined using repeated measures ANOVAs. The testretest reliability of each technique was also examined using linear regression, intraclass correlations and Cronbach’s alpha. The results showed that EMG amplitude differed significantly between normalization techniques for all muscles, with the IMVC and MxDA methods demonstrating the highest amplitudes. The highest levels of reliability were observed for the PDA technique for all muscles; therefore, our results support the utilization of this method for cycling analyses.
5
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Effects of Varus Orthotics on Lower Extremity Kinematics During the Pedal Cycle

76%
Sinclair J., Vincent H., Taylor P. J., Hebron J., Hurst H. T., Atkins S.
Human Movement
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2014
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vol. 15
|
issue 4
221-226
EN
Purpose. Cycling has been shown to be associated with a high incidence of chronic pathologies. Foot orthoses are frequently used by cyclists in order to reduce the incidence of chronic injuries. The aim of the current investigation was to examine the influence of different varus orthotic inclines on the three-dimensional kinematics of the lower extremities during the pedal cycle. Methods. Kinematic information was obtained from ten male cyclists using an eight-camera optoelectronic 3-D motion capture system operating at 250 Hz. Participants cycled with and without orthotic intervention at three different cadences (70, 90 and 110 RPM). The orthotic device was adjustable and four different wedge conditions (0 mm - no orthotic, 1.5 mm, 3.0 mm and 4.5 mm) were examined. Two-way repeated measures ANOVAs were used to compare the kinematic parameters obtained as a function of orthotic inclination and cadence. Participants were also asked to subjectively rate their comfort in cycling using each of the four orthotic devices on a 10-point Likert scale. Results. The kinematic analysis indicated that the orthotic device had no significant influence at any of the three cadences. Analysis of subjective preferences showed a clear preference for the 0 mm, no orthotic, condition. Conclusions. This study suggests that foot orthoses do not provide any protection from skeletal malalignment issues associated with the aetiology of chronic cycling injuries.
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