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Muammer Altun

external loads to muscles. 14 However, there are external loads acting on the muscles and joints, such as acceleration, deceleration, jumping to certain heights, and the defensive actions of opponents. 12 , 15 These issues might additionally deteriorate sports movement efficiency. Thus, the

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Yusuf Köklü, Utku Alemdaroğlu, Hamit Cihan and Del P. Wong

rating of perceived exertion [RPE]) and external loads (eg, total distance covered; maximum speed; quantity of low-, moderate-, and high-intensity running). While high-intensity aerobic training sessions are used for the development of endurance performance in athletes, 1 for soccer players an

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Carlo Castagna, Stefano D’Ottavio, Stefano Cappelli and Susana Cristina Araújo Póvoas

the relevance of acceleration and deceleration, more than sustained speed in determining external load in all-out SSG. 4 , 5 In this regard, emphasis on players’ maximal or near maximal effort maintenance for a prolonged period of time (ie, 30–40 s) has been proposed as a LSA training aim. 4 The

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Sonia Sahli, Haithem Rebai, Mohamed Habib Elleuch, Zouheir Tabka and Georges Poumarat

Context:

There is limited information about the effects of increasing load while squatting

Objective:

To quantify tibiofemoral joint kinetics during squatting with variable loads.

Setting:

Research laboratory.

Participants:

20 male students.

Intervention:

Tibiofemoral joint kinetics and electromyographic (EMG) activity of four involved muscles were determined by recording the half squat with variable external loads.

Main Outcome Measures:

Tibiofemoral joint force and external moment components and EMG activity of four involved muscles.

Results:

Throughout the exercise, a posterior direction for the antero-posterior shear force and a net extension for the external moment were observed. They increased with knee flexion reaching peak force of 29% of the subject body weight (BW) and moment of 88Nm (without external load). All force and moment components and muscle activities increased as the external load increased.

Conclusion:

These findings suggest that half squat may be safe to use for quadriceps strengthening with very low potential loading on the anterior cruciate ligament (ACL). Our data can help clinicians choose the appropriate external load.

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Carlo Castagna, Matthew Varley, Susana C.A. Póvoas and Stefano D’Ottavio

Purpose:

To test the interchangeability of 2 match-analysis approaches for external-load detection considering arbitrary selected speeds and metabolic power (MP) thresholds in male top-level soccer.

Methods:

Data analyses were performed considering match physical performance of 60 matches (1200 player cases) of randomly selected Spanish, German, and English first-division championship matches (2013–14 season). Match analysis was performed with a validated semiautomated multicamera system operating at 25 Hz.

Results:

During a match, players covered 10,673 ± 348 m, of which 1778 ± 208 m and 2759 ± 241 m were performed at high intensity, as measured using speed (≥16 km/h, HI) and metabolic power (≥20 W/kg, MPHI) notations. High-intensity notations were nearly perfectly associated (r = .93, P < .0001). A huge method bias (980.63 ± 87.82 m, d = 11.67) was found when considering MPHI and HI. Very large correlations were found between match total distance covered and MPHI (r = .84, P < .0001) and HI (r = .74, P < .0001). Player high-intensity decelerations (≥–2 m/s2) were very largely associated with MPHI (r = .73, P < .0001).

Conclusions:

The speed and MP methods are highly interchangeable at relative level (magnitude rank) but not absolute level (measure magnitude). The 2 physical match-analysis methods can be independently used to track match external load in elite-level players. However, match-analyst decisions must be based on use of a single method to avoid bias in external-load determination.

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Susan K. Grimston, Jack R. Engsberg, Reinhard Kloiber and David A. Hanley

Increased incidence of stress fracture has been reported for amenorrheic runners, while some studies have reported decreased spinal bone mass in amenorrheic runners. Based on results from these studies, one tends to associate decreased spinal bone mass with an increased risk of stress fracture. The present study compared regional bone mass and external loads during running between six female runners reporting a history of stress fracture (seven tibial and three femoral neck) and eight female runners with no history of stress fracture. Dual photon absorptiometry measures indicated significantly greater spinal (L2-L4) and femoral neck bone mineral density in stress fracture subjects (p<0.05) but no differences between groups for tibial bone density. Normalized forces recorded from Kistler force plates indicated significantly greater vertical propulsive, maximal medial, lateral, and posterior forces for stress fracture subjects during running (p<0.05).

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Steve Barrett

external loads. 2 – 4 Locomotor activities such as total distance covered (TDC), high-speed running distance covered (HSR), or sprinting distance covered (SP 4 ) are common external load metrics used by practitioners. More recently, accelerometers have been utilized to monitor the external load of soccer

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Andrea Biscarini

A two-dimensional model has been developed to predict and explain the effects of the variation of muscle moment arms during dynamic exercises involving heavy external loads. The analytical dependence of the muscle moment arm on the joint angle and on the origin and insertion position was derived for an ideal uniaxial hinge joint, modeling the muscle as a cable following an idealized minimum distance path from the origin to insertion that wraps around the bony geometry. Analytical expressions for the ratios of muscular force and the joint restraining reaction components to the external load weight were deduced, for isokinetic and static exercises, as a function of joint angle, joint angular velocity, and the other geometric parameters defining the model. Therefore, external load weight, joint angular velocity, and constraints to joint range of motion may be adjusted reciprocally in order to control in advance the peak value of the components of the joint load during isokinetic exercises. A dynamic formulation of forearm flexion/extension was solved numerically under the condition of constant biceps force in order to highlight the key role played by the variation in muscle moment arm in preventing injury during lifting of external loads against gravity. For example, our analysis indicates that the mean and peak resultant joint loads decrease by 5% and 14%, respectively, as a result of the change in muscle moment arm that occurs over the range of motion.

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Marcelo P. de Castro, Daniel Cury Ribeiro, Felipe de C. Forte, Joelly M. de Toledo, Daniela Aldabe and Jefferson F. Loss

The current study aimed to compare the shoulder kinematics (3D scapular orientation, scapular angular displacement and scapulohumeral rhythm) of asymptomatic participants under unloaded and loaded conditions during unilateral shoulder elevation in the scapular plane. We used a repeated-measures design with a convenience sample. Eleven male participants with an age range of 21–28 years with no recent history of shoulder injury participated in the study. The participants performed isometric shoulder elevation from a neutral position to approximately 150 degrees of elevation in the scapular plane in intervals of approximately 30 degrees during unloaded and loaded conditions. Shoulder kinematic data were obtained with videogrammetry. During shoulder elevation, the scapula rotated upwardly and externally, and tilted posteriorly. The addition of an external load did not affect 3D scapular orientation, scapular angular displacement, or scapulohumeral rhythm throughout shoulder elevation (P > .05). In clinical practice, clinicians should expect to observe upward and external rotation and posterior tilt of the scapula during their assessments of shoulder elevation. Such behavior was not influenced by an external load normalized to 5% of body weight when performed in an asymptomatic population.

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Marianne J. R. Gittoes and David G. Kerwin

This study aimed to gain insight into the individual and interactive effects of segmental mass proportions and coupling properties on external loading in simulated forefoot landings. An evaluated four-segment wobbling mass model replicated forefoot drop landings (height: 0.46 m) performed by two subjects. A comparison of the peak impact forces (GFzmax) produced during the evaluated landing and further simulated landings performed using modified (±5% perturbation) mass proportions and coupling properties was made. Independent segmental mass proportion changes, particularly in the upper body, produced a prominent change in GFzmax of up to 0.32 bodyweight (BW) whereas independent mass coupling stiffness and damping alterations had less effect on GFzmax (change in GFzmax of up to 0.18 BW). When combining rigid mass proportion reductions with damping modifications, an additional GFzmax attenuation of up to 0.13 BW was produced. An individual may be predisposed to high loading and traumatic and overuse injury during forefoot landings owing to their inherent inertia profile. Subject-specific neuromuscular modifications to mass coupling properties may not be beneficial in overriding the increased forces associated with larger rigid mass proportions.