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Isotonic Contractions Might Be More Effective than Isokinetic Contractions in Developing Muscle Strength

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.

Cover Journal of Sport Rehabilitation

In Journal of Sport Rehabilitation Volume 10 (2001): Issue 2 (Jan 2001)

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The Effect of General Anesthesia on Passive-Knee-Extension Range of Motion

Thomas P. Dompier, Craig R. Denegar, W.E. Buckley, S. John Miller, Jay Hertel, and Wayne J. Sebastianelli

Context:

Flexibility is promoted as essential to physical fitness, but the mechanisms limiting it are not fully understood.

Objective:

To investigate the effects of general anesthesia on hamstring extensibility.

Design:

Repeated measures.

Setting:

Hospital operating room.

Subjects:

Eight volunteers undergoing orthopedic surgeries unrelated to the tested limb.

Measurement:

Three measurements of passive knee extension (PKE) taken before and after administration of general anesthesia. The force applied during the measurements was consistent between trials.

Results:

Mean PKE range of motion (ROM) was significantly greater before anesthesia (75.0° ± 11.8°) than after (53.3° ± 17°; t = 5.6, P < .001). Pearson product correlation revealed a significant correlation between the mean difference in PKE ROM between treatment conditions and subjects’ body weight (r = .91, P < .05).

Conclusions:

The findings might be attributable to diminished neural drive to the antagonist muscle groups and suggest a more complex neural control of flexibility than simply neural drive to an agonist muscle.

Cover Journal of Sport Rehabilitation

In Journal of Sport Rehabilitation Volume 10 (2001): Issue 4 (Jan 2001)

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Premovement Changes in Corticospinal Excitability of the Biceps Brachii are Not Different Between Arm Cycling and an Intensity-Matched Tonic Contraction

David B. Copithorne, Davis A. Forman, and Kevin E. Power

The purpose of this study was to determine if supraspinal and/or spinal motoneuron excitability of the biceps brachii were differentially modulated before: 1) arm cycling and 2) an intensity-matched tonic contraction. Surface EMG recordings of motor evoked potentials (MEPs) and cervicomedullary motor evoked potentials (CMEPs) were used to assess supraspinal and spinal motoneuron excitability, respectively. MEP amplitudes were larger and onset latencies shorter, before arm cycling and tonic contraction when compared with rest with no intent to move, but with no difference between motor outputs. CMEP amplitudes and onset latencies remained unchanged before cycling and tonic contraction compared with rest. Premovement enhancement of corticospinal excitability was due to an increase in supraspinal excitability that was not task-dependent. This suggests that a common neural drive is used to initiate both motor outputs with task-dependent changes in neural excitability only being evident once the motor outputs have begun.

Cover Motor Control

In Motor Control Volume 19 (2015): Issue 3 (Jan 2015)

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A Gender Comparison of Central and Peripheral Neuromuscular Function After Exercise

Ashley Stern, Chris Kuenze, Daniel Herman, Lindsay D. Sauer, and Joseph M. Hart

Context:

Central and peripheral muscle fatigue during exercise may exacerbate neuromuscular factors that increase risk for noncontact anterior cruciate ligament injury.

Objective:

To compare lower extremity motor-evoked potentials (MEPs), muscle strength, and electromyography (EMG) activation after an exercise protocol.

Design:

Pretest, posttest group comparison.

Setting:

University laboratory.

Participants:

34 healthy volunteers (17 female, age = 21.9 ± 2.3 years, weight = 77.8 ± 3.0 kg, height = 171.1 ± 6.6 cm, and 17 male, age = 23.4 ± 6.5 years, weight = 81.6 ± 3.3 kg, height = 179.6 ± 7.3 cm).

Intervention:

A standardized 30-min exercise protocol that involved 5 repeated cycles of uphill walking, body-weight squatting, and step-ups.

Main Outcome Measures:

Quadriceps and hamstring MEP amplitude (mV) and transmission velocity normalized to subject height (m/s) were elicited via transcranial magnetic stimulation and measured via surface EMG. Quadriceps and hamstring peak EMG activation (% MVIC) and peak torque (Nm/kg) were measured during MVICs. Separate ANCOVAs were used to compare groups after exercise while controlling for baseline measurement.

Results:

At baseline, males exhibited significantly greater knee-extension torques (males = 2.47 ± 0.68 Nm/kg, females = 1.95 ± 0.53 Nm/kg; P = .036) and significantly higher hamstring MEP amplitudes (males = 223.5 ± 134.0 mV, females = 89.3 ± 77.6 mV; P = .007). Males exhibited greater quadriceps MEP amplitude after exercise than females (males = 127.2 ± 112.7 mV, females = 32.3 ± 34.9 mV; P = .016).

Conclusions:

Males experienced greater peripheral neuromuscular changes manifested as more pronounced reductions in quadriceps torque after exercise. Females experienced greater central neuromuscular changes manifested as more pronounced reduction in quadriceps MEP amplitude. Reduced central neural drive of the quadriceps coupled with knee-extension torque preservation after exercise may increase risk of knee injury in females.

Cover Journal of Sport Rehabilitation

In Journal of Sport Rehabilitation Volume 21 (2012): Issue 3 (Jan 2012)

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The Acute Effects of Fast-Paced Walking on Isometric Peak Torque and Rate of Torque Development in Regularly Exercising and Inactive Older Women

Ty B. Palmer, Jarrod Blinch, Ahalee C. Farrow, Chinonye C. Agu-Udemba, and Ethan A. Mitchell

walking ( LaRoche, Millett, & Kralian, 2011 ). Operating at a greater capacity contributes to fatigue and more specifically, a decrease in neural drive ( Spinoso et al., 2019 ; Taylor, Amann, Duchateau, Meeusen, & Rice, 2016 ), which may reduce one’s ability to rapidly generate torque. Consequently, knee

Cover Journal of Aging and Physical Activity

In Journal of Aging and Physical Activity Volume 30 (2022): Issue 3 (Jun 2022)

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Physical and Mental Fatigue Reduce Psychomotor Vigilance in Professional Football Players

Luca Angius, Michele Merlini, James Hopker, Mattia Bianchi, Francesco Fois, Francesco Piras, Paolo Cugia, James Russell, and Samuele Maria Marcora

motor commands. As previously observed, the reduced brain oxygenation is, in part, associated with reduced cognitive performance, 12 and neural drive to the locomotor muscles (ie, central fatigue) thus impairing physical performance. 10 , 13 The first aim of our study was to investigate the effect of

Cover International Journal of Sports Physiology and Performance

In International Journal of Sports Physiology and Performance Volume 17 (2022): Issue 9 (Sep 2022): Special Issue: Focus on Football (Soccer) in Conjunction With the FIFA World Cup 2022

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Adaptations of the Upper Body to Plyometric Training in Cricket Players of Different Age Groups

Deepika Singla and M. Ejaz Hussain

protocols is an increase in the EMG activity due to increase in the neural drive to the muscles (neural adaptation) and due to hypertrophy of muscle fibers (muscular adaptation). 19 Substantial balance, power, and strength are required for performance enhancement and to prevent injuries in sports persons

Cover Journal of Sport Rehabilitation

In Journal of Sport Rehabilitation Volume 29 (2020): Issue 6 (Aug 2020)

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Bilateral Improvements Following Unilateral Home-Based Training in Plantar Flexors: A Potential for Cross-Education in Rehabilitation

Sumona Mandal, Liang Zhi Wong, Niall D. Simmons, Andreas Mirallais, Flaminia Ronca, and Bhavesh Kumar

and neural drive play an important role in CE. The utilization of a supervised 6-week lab-based strength training program with calf raises and foot press exercises being performed 4 times a week each could explain the stronger correlation in their study. Our study shows that even without supervision

Cover Journal of Sport Rehabilitation

In Journal of Sport Rehabilitation Volume 32 (2023): Issue 1 (Jan 2023)

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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

enhanced agonist neural drive. Isometric force at specific time points has also been expressed in relation to PF in an attempt to explain training adaptations 15 , 16 and differences between sexes, 17 demonstrating that differences in early force production between sexes may be explained by differences

Cover International Journal of Sports Physiology and Performance

In International Journal of Sports Physiology and Performance Volume 15 (2020): Issue 4 (Apr 2020)

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Age-Related Changes in Concentric and Eccentric Isokinetic Peak Torque of the Trunk Muscles in Healthy Older Versus Younger Men

A. Dallaway, J. Hattersley, J. Tallis, D. Renshaw, C. Griffen, and M. Duncan

analysis, it is unlikely that atrophy of the paravertebral muscles caused decreases in concentric extension torque. Neurological changes in older age are more likely to have contributed to declines in trunk strength. Neuropathic processes in older age bring about a decline in neural drive and cause muscle

Cover Journal of Aging and Physical Activity

In Journal of Aging and Physical Activity Volume 29 (2021): Issue 6 (Dec 2021)