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Kenneth L Knight, Christopher D Ingersoll and John Bartholomew

Problem:

Isokinetic contractions are thought to be superior to isotonic contractions for developing strength because resistance during them is greater. Because isokinetic resistance is accommodating, however, it decreases with fatigue. It is constant during multiple repetitions, so an aggressive isotonic procedure should produce more force as the muscle fatigues, which would be an advantage in strength development.

Purpose:

To compare force production in isokinetic and isotonic muscle contractions at the beginning and end of a set of fatiguing repetitions.

Methods:

Subjects performed 25 maximal-effort isokinetic knee extensions at 60°/s. After 25–72 hours, they performed maximal repetitions isotonically using 70% of the isokinetic peak torque with speed set at a maximum of 300°/s.

Results:

Peak force during the first 3 repetitions was greater isokinetically, but average force was similar. During the last 3 repetitions, isotonic force was higher than isokinetic force.

Conclusion:

Muscle is more active as it nears fatigue during an isotonic contraction. These data support the hypothesis that isotonic contractions recruit extra motor units at the point of fatigue.

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Anis Chaouachi, Monoem Haddad, Carlo Castagna, Del P. Wong, Fathi Kaouech, Karim Chamari and David G. Behm

The objective of this study was to examine the response and recovery to a single set of maximal, low and high angular velocity isokinetic leg extension-flexion contractions with boys. Sixteen boys (11–14 yrs) performed 10 isokinetic contractions at 60°.s−1 (Isok60) and 300°.s−1 (Isok300). Three contractions at both velocities, blood lactate and ratings of perceived exertion were monitored pretest and at 2, 3, 4, and 5 min of recovery (RI). Participants were tested in a random counterbalanced order for each velocity and recovery period. Only a single contraction velocity (300°.s−1 or 60°.s−1) was tested during recovery at each session to remove confounding influences between the recovery intervals. Recovery results showed no change in quadriceps’ power at 300°.s−1, quadriceps’ power, work and torque at 60°.s−1 and hamstrings’ power and work with 60°.s−1. There was an increase during the 2 min RI in hamstrings’ power, work and torque and quadriceps’

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Jordan P.R. McIntyre, Grant A. Mawston and Simeon P. Cairns

Purpose:

To quantify how whole-body power, muscle-function, and jump-performance measures change during prolonged cycling and recovery and determine whether there are relationships between the different fatigue measures.

Methods:

Ten competitive or recreationally active male cyclists underwent repeated 20-min stages of prolonged cycling at 70% VO2peak until exhaustion. Whole-body peak power output (PPO) was assessed using an all-out 30-s sprint 17 min into each cycle stage. Ratings of perceived exertion (RPE) were recorded throughout. Isometric and isokinetic muscle-function tests were made between cycle stages, over ~6 min, and during 30-min recovery. Drop-jump measures were tested at exhaustion and during recovery.

Results:

PPO initially increased or was maintained in some subjects but fell to 81% of maximum at exhaustion. RPE was near maximal (18.7) at exhaustion, with the time to exhaustion related to the rate of rise of RPE. PPO first started to decline only when RPE exceeded 16 (ie, hard). Peak isometric and concentric isokinetic torque (180°/s) for the quadriceps fell to 86% and 83% of pretest at exhaustion, respectively. In contrast, the peak concentric isokinetic torque (180°/s) of the hamstrings increased by 10% before declining to 93% of maximum. Jump height fell to 92% of pretest at exhaustion and was correlated with the decline in PPO (r = .79). Muscle-function and jump-performance measures did not recover over the 30-min postexercise rest period.

Conclusions:

At exhaustion, whole-body power, muscle-function, and jump-performance measures had all fallen by 7–19%. PPO and drop-jump decrements were linearly correlated and are appropriate measures of maximal performance.

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Meghan K. Edwards and Paul D. Loprinzi

performed 3 maximal isokinetic contractions with the right leg at 60°/s. The strength values were corrected to account for gravity, limb weight, and lever arm weight. The peak force recorded was used for analysis. The specific isokinetic knee extensor test performed at 60°/s on the Kin Com MP isokinetic

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Eleni Bassa, Dimitrios Patikas, Konstantinos Hatzikotoulas and Christos Kotzamanidis

We would like to comment on the paper by Dotan et al. (8) entitled “Child-adult differences in muscle activation—a review.” Dotan et al.’s review (8) in conjunction with the commentary of O’Brien et al. (20) constitutes an important contribution to the question “who are stronger: children or adults?” based on specific force comparisons between children and adults and not on absolute values. For simplification reasons, we would like to limit the context of this question to single-joint isometric and isokinetic contractions only. Hence, we will not discuss multi-joint dynamic actions.

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Jeffrey A. Borgmeyer, Bradley A. Scott and Jerry L. Mayhew

Context:

The effect of ice massage on muscle-strength performance is equivocal.

Objective:

To determine the effects of ice massage on maximum isokinetic torque produced during a 20-minute interval.

Design:

Participants performed a maximal isokinetic contraction of the right arm at 30°/s every 2 minutes for 20 minutes, once after a 10-minute ice massage over the right biceps brachii muscle belly and once without ice treatment. Sessions were randomized.

Participants:

11 college men.

Measurements:

Torque was measured with a Cybex® II dynamometer. Biceps skinfold was measured with a Harpenden caliper.

Results:

A repeated-measures ANCOVA revealed no significant interaction between time and treatment condition when the effect of skinfold thickness was held constant. A main effect for time indicated that torque production was significantly higher at 4 and 8 minutes and declined thereafter.

Conclusions:

A 10-minute ice massage neither enhanced nor retarded muscle-force output and thus may be used for its pain-reducing effect to allow resistance exercise during the rehabilitation process

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William H. Clark and Jason R. Franz

The triceps surae muscle–tendon units are important in governing walking performance, acting to regulate mechanical behavior of the ankle through interaction between active muscle and passive elastic structures. Ankle joint quasi-stiffness (the slope of the relation between ankle moment and ankle rotation, kA) is a useful aggregate measure of this mechanical behavior. However, the role of muscle activation and length–tension behavior in augmenting kA remains unclear. In this study, 10 subjects completed eccentric isokinetic contractions at rest and at 2 soleus activation levels (25% and 75% isometric voluntary contraction) prescribed using electromyographic biofeedback. Ultrasound imaging quantified activation-dependent modulation of soleus muscle length–tension behavior and its role in augmenting kA. The authors found that soleus muscle stiffness (kM) and kA exhibit nonlinear relations with muscle activation and both were more sensitive to the onset of activation than to subsequent increases in activation. Our findings also suggest that kA can be modulated via activation through changes in soleus muscle length–tension behavior. However, this modulation is more complex than previously appreciated—reflecting interaction between active muscle and passive elastic tissues. Our findings may have implications for understanding normal and pathological ankle joint function and the design of impedance-based prostheses.

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Rodrigo de Marche Baldon, Daniel Ferreira Moreira Lobato, Lívia Pinheiro Carvalho, Paloma Yan Lam Wun, Cátia Valéria Presotti and Fábio Viadanna Serrão

Context:

Recently, attention in sports has been given to eccentric hip-muscle function, both in preventing musculoskeletal injuries and improving performance.

Objective:

To determine the key isokinetic variables of eccentric hip torque that predict the functional performance of women in the single-leg triple long jump (TLJ) and the timed 6-m single-leg hop (TH).

Design:

Within-subject correlational study.

Setting:

Musculoskeletal laboratory.

Participants:

32 healthy women age 18–25 y.

Intervention:

The participants performed 2 sets of 5 eccentric hip-abductor/adductor and lateral/medial-rotator isokinetic contractions (30°/s) and 3 attempts in the TLJ and TH.

Main Outcome Measurements:

The independent variables were the eccentric hip-abductor and –adductor and medial- and lateral-rotator isokinetic peak torque, normalized according to body mass (Nm/kg). The dependent variables were the longest distance achieved in the TLJ normalized according to body height and the shortest time spent during the execution of the TH.

Results:

The forward-stepwise-regression analysis showed that the combination of the eccentric hip lateral-rotator and -abductor isokinetic peak torque provided the most efficient estimate of both functional tests, explaining 65% of the TLJ variance (P < .00l) and 55% of the TH variance (P < .001).

Conclusions:

Higher values for eccentric hip lateral-rotator and hip-abductor torques reflected better performance. Thus, the eccentric action of these muscles should be considered in the development of physical training programs that aim to increase functional performance.

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Hyun Chul Jung, Myong Won Seo, Sukho Lee, Sung Woo Jung and Jong Kook Song

 al., 2017 ). The reliability of the repeated measurements assessed by the ICC was .96. An isokinetic dynamometer (770 Norm; Cybex, Medway, MA) was used to evaluate muscle strength and endurance. Three maximal isokinetic contractions at 60 deg/s for muscle strength and 20 maximal isokinetic contractions at

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Justin L. Rush, Lindsey K. Lepley, Steven Davi and Adam S. Lepley

recovery strategies after peak torque trials during isokinetic contractions of the quadriceps muscles. Peak torque and EMG data were both collected to see the effects of passive recovery, active recovery, and electromyostimulation recovery after the fatiguing task. 32 The investigators provided evidence