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The Effects of Zinc Depletion on Peak Force and Total Work of Knee and Shoulder Extensor and Flexor Muscles

Marta D. Van Loan, Barbara Sutherland, Nicola M. Lowe, Judith R. Turnlund, and Janet C. King

In this study we tested the effect of zinc (Zn) on muscle function in humans. After receiving 12 mg Zn/day for 17 days. 8 male subjects received 0.3 mg Zn/day tor either 33 or 41 days. Subjects were divided into two groups for repletion. Group A subjects received overnight infusions of 66 mg Zn on Days 1 and 10 and then were fed 12 mg Zn/day for another 16 days. Group B subjects were fed 12 mg Zn/day for 3 weeks. Peak force and total work capacity of the knee and shoulder extensor and flexor muscle groups were assessed using an isokinetic dynamometer at baseline, at two points during depletion, and at repletion. Plasma Zn declined significantly during depletion and remained below baseline levels after repletion. The peak force of the muscle groups tesied was not affected by acute Zn depletion: however, total work capacity for the knee extensor muscles and shoulder extensor and flexor muscles declined significantly. The data suggest that acute Zn depletion alters the total work capacity of skeletal muscle.

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Normalization of Early Isometric Force Production as a Percentage of Peak Force During Multijoint Isometric Assessment

Paul Comfort, Thomas Dos’Santos, Paul A. Jones, John J. McMahon, Timothy J. Suchomel, Caleb Bazyler, and Michael H. Stone

application of force during such activities. 2 , 3 For example, during high-velocity sprinting, foot contact times can be much less than 250 milliseconds, with a progressive decline in contact time as running velocity increases. 6 , 7 Interestingly, there is a strong association between isometric peak force

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Intratester Reliability and Construct Validity of a Hip Abductor Eccentric Strength Test

Richard A. Brindle, David Ebaugh, and Clare E. Milner

tester exceeds the patient’s maximum isometric force and pushes the limb down. 4 – 6 The peak force recorded by the handheld dynamometer is assumed to be generated while the leg is being lowered (the lowering phase). However, the time of the peak force during this test has not been established. Thus, it

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Criterion and Construct Validity of an Isometric Midthigh-Pull Dynamometer for Assessing Whole-Body Strength in Professional Rugby League Players

Nick Dobbin, Richard Hunwicks, Ben Jones, Kevin Till, Jamie Highton, and Craig Twist

when compared against the same exercise conducted on a force platform. In that study, validity was assessed using a relatively small sample size of recreationally active participants (N = 15) and no attempt was made to understand the ability of the simplified apparatus to differentiate peak-force

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Effect of Sampling Frequency on Isometric Midthigh-Pull Kinetics

Thomas Dos’Santos, Paul A. Jones, Jonathan Kelly, John J. McMahon, Paul Comfort, and Christopher Thomas

Skeletal-muscle function can be evaluated using force-time curves generated during dynamic and isometric activities. Peak force (PF) and peak rate of force development (RFD) are commonly assessed 1 – 5 and have been reported to relate to various athletic performance tasks including baseball

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The Effect of Unilateral Versus Bilateral Strength Training on Isometric-Squat Peak Force and Interlimb Asymmetry in Young, Recreationally Strength-Trained Men

Arthur E. Lynch, Robert W. Davies, Joanna M. Allardyce, and Brian P. Carson

maximal strength are not as well known. This distinction is important, given the test and metric specific nature of ILA. 9 Peak force (PF) assessment in the isometric squat (ISq) is a test of maximal strength that has demonstrated acceptable levels of reliability across multiple investigations

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Effects of Knee Position on the Reliability and Production of Maximal and Rapid Strength Characteristics During an Isometric Squat Test

Ty B. Palmer, Jose G. Pineda, and Rachel M. Durham

Strength-based performance characteristics, such as peak force (PF) and rate of force development (RFD), are commonly measured to assess functional ability, 1 discriminate between athletes of different performance levels, 2 and monitor neuromuscular performance changes in response to training or

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Reliability of the Dynamic Strength Index in College Athletes

Christopher Thomas, Paul A. Jones, and Paul Comfort


To determine the reliability of the Dynamic Strength Index (DSI) in college athletes.


Nineteen male college athletes performed the squat jump (SJ) and isometric midthigh pull (IMTP) to determine peak force, on 2 separate days. Reliability was assessed by intraclass correlation coefficient (ICC), typical error (TE), percentage change in the mean, smallest worthwhile change (SWC), and coefficient of variation (%CV).


Peak force for the SJ was 2137 ± 499 N and 2781 ± 435 N for the IMTP, resulting in a mean DSI of 0.78 ± 0.19. Peak forces in the SJ (ICC = .99, TE = 57.22 N, change in mean = 0.2%, SWC = 4.7%, CV = 2.6%) and IMTP (ICC = .95, TE = 104.22 N, change in mean = 0.5%, SWC = 3.1%, CV = 3.8%) were considered highly reliable between sessions. However, IMTP peak force was the only variable with an overall TE < SWC. The DSI was also highly reliable (ICC = .97, TE = 0.03, change in mean = −0.3%, SWC = 5.1%, CV = 4.6%) between sessions.


This study demonstrates that peak force in the SJ and IMTP are reliable, resulting in a reliable assessment of dynamic-force-production capabilities via the DSI. The DSI may be used to guide individualized training interventions and monitor specific adaptations to training. Changes in SJ peak force, IMTP peak force, and DSI were >4.67%, 3.13%, and 5.13%, respectively, identifying meaningful changes in response to training or competition.

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The Use of Maximum Strength Measures as a Predictor of Rapid Force Production and Strength Endurance

Roger O. Kollock, Bonnie Van Lunen, Stacie I. Ringleb, and James Onate

The ability to produce force rapidly and to maintain it is essential to sports performance. Although rapid force production and endurance are indispensable characteristics of optimal health and performance, assessing these qualities of strength is difficult because of clinician time constraints. The purpose of this study was to determine if peak force is a predictor of rate of force production and strength endurance. The results indicated peak force is a predictor of rate of force development, but not strength endurance. Clinicians should assess both maximum strength and endurance to gain a more complete picture of lower extremity strength deficits.

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Reliability of a Novel Testing Protocol to Assess Upper-Body Strength Qualities in Elite Athletes

Kieran P. Young, G. Gregory Haff, Robert U. Newton, and Jeremy M. Sheppard


The purpose of this study was to evaluate the reliability of an isometric-bench-press (IBP) test performed across 4 elbow angles and a ballistic bench throw (BBT) using a relative load, as well as evaluating the reliability of the dynamic strength index (DSI: BBT peak force/IBP peak force).


Twenty-four elite male athletes performed the IBP and a 45% 1-repetition-maximum BBT on 2 separate days with 48 h between testing occasions. Peak force, peak power, peak velocity, peak displacement, and peak rate of force development (PRFD) were assessed using a force plate and linear position transducer. Reliability was assessed by intraclass correlation (ICC), coefficient of variation (%CV) and typical error.


Performance measures in the BBT, such as peak force, peak velocity, peak power, and peak displacement, were considered reliable (ICC = .85–.92, %CV = 1.7–3.3), while PRFD was not (ICC = .43, %CV = 4.1). Similarly, for the IBP, peak force across all angles was considered reliable (ICC = .89–.97, %CV = 1.2–1.6), while PRFD was not (ICC = .56–.65, %CV = 0.5–7.6). The DSI was also reliable (ICC = .93, %CV = 3.5).


Performance measures such as peak force in the IBP and BBT are reliable when assessing upper-body pressing-strength qualities in elite male athletes. Furthermore, the DSI is reliable and could potentially be used to detect qualities of relative deficiency and guide specific training interventions.