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Uncategorized Mar 10, 2019
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Effects of Load on Ground Reaction Force and Lower Limb Kinematics During Concentric Squats

research Mar 10, 2019

The purpose of this study was to examine the effects of external load on vertical ground reaction force, and linear and angular kinematics, during squats. Eight males aged 22.1±0.8 years performed maximal concentric squats using loads ranging from 7 to 70% of one-repetition maximum on a force plate while linear barbell velocity and the angular kinematics of the hip, knee and ankle were recorded. Maximum, average and angle-specific values were recorded. The ground reaction force ranged from 1.67±0.20 to 3.21±0.29 times body weight and increased significantly as external load increased (P<0.05). Bar linear velocity ranged from 0.54±0.11 to 2.50±0.50 m·s−1 and decreased significantly with increasing external load (P<0.05). Hip, knee and ankle angles at maximum ground reaction force were affected by external load (P<0.05). The force–barbell velocity curves were fitted using linear models with coefficients (r...

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The Relationship Between Maximal Jump-Squat Power and Sprint Acceleration in Athletes

research Mar 09, 2019

Thirty male athletes [height: 183.8 (6.8) cm, and mass: 90.6 (9.3) kg; mean (SD)] each completed six 10-m sprints from a standing start. Sprint times were recorded using a tethered running system and the force-time characteristics of the first ground contact were recorded using a recessed force plate. Three to six days later subjects completed three concentric jump squats, using a traditional and split technique, at a range of external loads from 30–70% of one repetition maximum (1RM)

Average power was maximal at all loads between 30% and 60% of 1RM for both squats. Split squat peak power was also maximal between 30% and 60% of 1RM; however, traditional squat peak power was maximal between 50% and 70% of 1RM. Concentric force development is critical to sprint start performance and accordingly maximal concentric jump power is related to sprint acceleration.

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Lower Limb Asymmetry in Mechanical Muscle Function: A Comparison Between Ski Racers With and Without ACL Reconstruction

research Mar 08, 2019

Due to a high incidence of anterior cruciate ligament (ACL) re‐injury in alpine ski racers, this study aims to assess functional asymmetry in the countermovement jump (CMJ), squat jump (SJ), and leg muscle mass in elite ski racers with and without anterior cruciate ligament reconstruction (ACL‐R). Elite alpine skiers with ACL‐R (n = 9; 26.2 ± 11.8 months post‐op) and uninjured skiers (n = 9) participated in neuromuscular screening. Vertical ground reaction force during the CMJ and SJ was assessed using dual force plate methodology to obtain phase‐specific bilateral asymmetry indices (AIs) for kinetic impulse (CMJ and SJ phase‐specific kinetic impulse AI). Dual x‐ray absorptiometry scanning was used to assess asymmetry in lower body muscle mass. Compared with controls, ACL‐R skiers had increased AI in muscle mass (P < 0.001), kinetic impulse AI in the CMJ concentric phase (P < 0.05), and the final...

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Functional Assessment Using the Step-Up-and-Over Test and Forward Lunge Following ACL Reconstruction

research Mar 07, 2019

This investigation compared lower extremity function of a control group and a group of patients who underwent anterior cruciate ligament (ACL) reconstruction using a repeated measures post-test only control group design. The ACL reconstruction group consisted of 18 patients at least 6 months postoperative (mean 58±19 weeks) and the control group consisted of 18 healthy, recreationally active individuals. Both groups performed a step-up-and-over test and a forward lunge on a long force plate. During the step-up-and-over test, the control group produced significantly more force during the initial step than the ACL reconstruction group. Also, when the ACL reconstruction patients led with the involved extremity, they were significantly slower.

During the forward lunge test, the impact index and force impulse measurements were significantly greater for the uninvolved leg than the involved leg in the ACL reconstruction group. The implications are that force generation during...

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Force-Production Asymmetry in Male and Female Athletes of Differing Strength Levels

research Mar 06, 2019

The purpose of this investigation was to determine the existence of bilateral strength and force-production asymmetry and evaluate possible differences based on sex, as well as strength level. Asymmetry was assessed during weight-distribution (WtD) testing, unloaded and lightly loaded static- (SJ) and countermovement-jump (CMJ) testing, and isometric midthigh-pull (IMTP) strength testing. Subjects included 63 athletes (31 male, 32 female) for WtD, SJ, and CMJ tests, while 129 athletes (64 male, 65 female) participated in IMTP testing. Independent-samples t tests were used to determine possible differences in asymmetry magnitude between males and females, as well as between strong and weak athletes

The results of this investigation indicate that females may be more prone to producing forces asymmetrically than males during WtD and jumping tasks. Similarly, weaker athletes displayed more asymmetry than stronger athletes. This may indicate that absolute strength may play a...

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Isometric Force Production Symmetry and Jumping Performance in Collegiate Athletes

research Mar 05, 2019

Collegiate athletes were evaluated for this study (n=36). Subjects performed SJ, CMJ, and isometric mid-thigh pulls (IMTP). Jumps were analyzed for jump height (JH) and peak power (PP). IMTP was analyzed for peak force (PF) for left and right sides, and values were calculated to produce a peak force symmetry index (PF-SI) score. Correlational statistics were performed examining the relationship between PF-SI and jump variables

The results indicate that force production asymmetry may be detrimental to bilateral vertical jumping performance. The findings should be considered for further investigation on sport-specific tasks.

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Relationship Between Isometric Mid-Thigh Pull Variables and Sprint and Change of Direction Performance in Collegiate Athletes

research Mar 03, 2019

Fourteen male collegiate athletes (mean ± SD; age = 21 ± 2.4 years; height =176 ± 9.0 cm; body mass = 72.8 ± 9.4 kg) participated in the study. Maximal strength was assessed via an isometric mid-thigh pull (IMTP). Isometric mid-thigh pull testing involved trials with peak force (IPF), maximum rate of force development (mRFD), impulse at 100 ms (IP 100) and 300 ms (IP 300) determined. Sprint and COD performance was measured using 5- and 20-m sprint performance, and a modified 505 test

Results suggest that IP 300 displayed the strongest relationships with 5- and 20-m sprint performance (r = −0.51 and −0.54, respectively). The results demonstrate maximum force production measures during IMTP correlate to sprint and COD ability in collegiate athletes.

Isometric mid-thigh pull force-time measures are related to athletic performance (acceleration and sprinting), and thus are recommended for use in athlete monitoring and assessment.


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Relationships Between Force–Time Characteristics of the Isometric Midthigh Pull and Dynamic Performance in Professional Rugby League Players

research Feb 18, 2019

The aim of this study was to determine the relationship between isometric measures of force development and dynamic performance. Thirty-nine professional rugby league players participated in this study. Forty-eight hours after trial familiarization, participants performed a maximal isometric midthigh pull, with ∼120–130° bend at the knee, countermovement jump (CMJ), and a 10-m sprint. Force–time data were processed for peak force (PF), force at 100 milliseconds (F100ms), and peak rate of force development (PRFD)

In conclusion, this study provides evidence that measures of maximal strength and explosiveness from isometric force–time curves are related to jump and sprint acceleration performance in professional rugby league players.


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Differences in the Movement Pattern of a Forward Lunge in Two Types of Anterior Cruciate Ligament Deficient Patients: Copers and Non-Copers

research Feb 18, 2019

The movement pattern of a forward lunge was analysed by using a two-dimensional inverse dynamics method. The electromyographic activity of the quadriceps and hamstring muscles were recorded.

The non-copers moved more slowly and loaded the knee joint less than the copers and controls. The copers moved more slowly during the knee flexion phase but as fast as the controls during the knee extension. The EMG results suggest that the copers stabilized their knee joint by increasing the co-contraction of the hamstrings during the extension phase.

Differences between the three groups’ movement patterns could be quantified. The forward lunge test seems appropriate to discriminate between the knee function in coper and non-coper anterior cruciate ligament deficient subjects.

Information about the performance of movements, which significantly load the knee joint in coper and non-coper anterior cruciate ligament deficient patients may contribute to a better understanding of dynamic knee...

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