Isokinetic elbow flexion and coactivation following eccentric training
TL;DR: The influence of eccentric training on the torque gains under eccentric conditions and for the highest velocities was attributed essentially to neural adaptations.
About: This article is published in Journal of Electromyography and Kinesiology.The article was published on 1999-01-01. It has received 72 citations till now. The article focuses on the topics: Eccentric training & Eccentric.
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TL;DR: The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education).
Abstract: It is generally accepted that neural factors play an important role in muscle strength gains. This article reviews the neural adaptations in strength, with the goal of laying the foundations for practical applications in sports medicine and rehabilitation. An increase in muscular strength without noticeable hypertrophy is the first line of evidence for neural involvement in acquisition of muscular strength. The use of surface electromyographic (SEMG) techniques reveal that strength gains in the early phase of a training regimen are associated with an increase in the amplitude of SEMG activity. This has been interpreted as an increase in neural drive, which denotes the magnitude of efferent neural output from the CNS to active muscle fibres. However, SEMG activity is a global measure of muscle activity. Underlying alterations in SEMG activity are changes in motor unit firing patterns as measured by indwelling (wire or needle) electrodes. Some studies have reported a transient increase in motor unit firing rate. Training-related increases in the rate of tension development have also been linked with an increased probability of doublet firing in individual motor units. A doublet is a very short interspike interval in a motor unit train, and usually occurs at the onset of a muscular contraction. Motor unit synchronisation is another possible mechanism for increases in muscle strength, but has yet to be definitely demonstrated. There are several lines of evidence for central control of training-related adaptation to resistive exercise. Mental practice using imagined contractions has been shown to increase the excitability of the cortical areas involved in movement and motion planning. However, training using imagined contractions is unlikely to be as effective as physical training, and it may be more applicable to rehabilitation. Retention of strength gains after dissipation of physiological effects demonstrates a strong practice effect. Bilateral contractions are associated with lower SEMG and strength compared with unilateral contractions of the same muscle group. SEMG magnitude is lower for eccentric contractions than for concentric contractions. However, resistive training can reverse these trends. The last line of evidence presented involves the notion that unilateral resistive exercise of a specific limb will also result in training effects in the unexercised contralateral limb (cross-transfer or cross-education). Peripheral involvement in training-related strength increases is much more uncertain. Changes in the sensory receptors (i.e. Golgi tendon organs) may lead to disinhibition and an increased expression of muscular force. Agonist muscle activity results in limb movement in the desired direction, while antagonist activity opposes that motion. Both decreases and increases in co-activation of the antagonist have been demonstrated. A reduction in antagonist co-activation would allow increased expression of agonist muscle force, while an increase in antagonist co-activation is important for maintaining the integrity of the joint. Thus far, it is not clear what the CNS will optimise: force production or joint integrity. The following recommendations are made by the authors based on the existing literature. Motor learning theory and imagined contractions should be incorporated into strength-training practice. Static contractions at greater muscle lengths will transfer across more joint angles. Submaximal eccentric contractions should be used when there are issues of muscle pain, detraining or limb immobilisation. The reversal of antagonists (antagonist-to-agonist) proprioceptive neuromuscular facilitation contraction pattern would be useful to increase the rate of tension development in older adults, thus serving as an important prophylactic in preventing falls. When evaluating the neural changes induced by strength training using EMG recording, antagonist EMG activity should always be measured and evaluated.
675 citations
Cites background from "Isokinetic elbow flexion and coacti..."
...2 Methodological Considerations studies also recorded antagonist SEMG and found Normalisation is a recurring theme in the explano change in co-activation.[124,125] nation of differences between training-related studComplicating the issue further is the fact that new ies of antagonist co-activation....
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...[96] The effect on force produced curve.[31,32,124,125] of contracting the ipsilateral antagonist is not so clear....
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...Several research groups have entities, which likely lies closer to ensuring joint examined the effects of a training regimen consistintegrity (by increasing joint stiffness via elevated ing of eccentric contractions on the torque-velocity antagonist co-activation) in situations of uncertainty profile.[30,31,124,125] The studies reported a significant about the motor task and/or in unstable movement increase in the overall magnitude and shape of the conditions....
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TL;DR: These results contribute to an evolving body of contemporary evidence regarding the efficacy of high-intensity training in neurorehabilitation and the physiological mechanisms that mediate neural recovery.
Abstract: Background: Repetitive task practice is argued to drive neural plasticity following stroke. However, current evidence reveals that hemiparetic weakness impairs the capacity to perform, and practice, movements appropriately. Here we investigated how power training (i.e., high-intensity, dynamic resistance training) affects recovery of upper-extremity motor function post-stroke. We hypothesized that power training, as a component of upper-extremity rehabilitation, would promote greater functional gains than functional task practice without deleterious consequences. Method: Nineteen chronic hemiparetic individuals were studied using a crossover design. All participants received both functional task practice (FTP) and HYBRID (combined FTP and power training) in random order. Blinded evaluations performed at baseline, following each intervention block and 6-months post-intervention included: Wolf Motor Function Test (WMFT-FAS, Primary Outcome), upper-extremity Fugl-Meyer Motor Assessment, Ashworth Scale, and Functional Independence Measure. Neuromechanical function was evaluated using isometric and dynamic joint torques and concurrent agonist EMG. Biceps stretch reflex responses were evaluated using passive elbow stretches ranging from 60 to 180o/s and determining: EMG onset position threshold, burst duration, burst intensity and passive torque at each speed. Results: Primary outcome: Improvements in WMFT-FAS were significantly greater following HYBRID vs. FTP (p= .049), regardless of treatment order. These functional improvements were retained 6-months post-intervention
235 citations
Cites methods from "Isokinetic elbow flexion and coacti..."
...Using data reported by Colsen et al [30] (see Figure 1) to estimate the power produced (i.e., torque x velocity) per contraction, the program was systematically progressed by increasing workload by 44% (Sessions 5-8 relative to 1-4) and 84% (Sessions 9-12 relative to 1-4). was eccentric (e.g., resisting an externally imposed load) and the second two sets were concentric, delivered at different criterion speeds....
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...Using data reported by Colsen et al [30] (see Figure 1) to estimate the power produced...
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TL;DR: It is suggested that, for the same time under tension, fast velocity eccentric exercise causes greater muscle damage than slow velocity exercise in untrained subjects.
Abstract: Debate exists concerning the effect of contraction velocity on muscle damage, and few human studies have yet to address this issue. This study examined whether the velocity of eccentric exercise affected the magnitude of muscle damage. Twelve untrained subjects performed a series of slow velocity isokinetic eccentric elbow flexions (SV: 30 degrees . s (-1)) of one arm and a fast velocity exercise (FV: 210 degrees . s (-1)) of the other arm, separated by 14 days. In order to standardise the time under tension (120 s) for the two conditions, the number of muscle actions for SV was 30 and 210 for FV. Criterion measures consisted of maximal voluntary torque for isometric, concentric (4 velocities) and eccentric contractions (2 velocities), range of motion (ROM) and relaxed elbow joint angle (RANG), upper arm circumference, muscle soreness and plasma creatine kinase (CK) activity. Measures were taken before, immediately after, 0.5 hour and 24 - 168 hours (240 hours for CK) after each eccentric exercise protocol, and changes in the measures over time were compared between FV and SV by two-way repeated measures ANOVA. Both protocols resulted in significant decrements in isometric and dynamic torque (p < 0.01), but FV showed significantly (p < 0.05) greater reductions over time ( approximately 55 %) and a slower recovery compared to SV ( approximately 30 %). Significantly (p < 0.05) larger decreases in, and delayed recovery of, ROM and RANG were evident after FV compared to SV. FV had significantly (p < 0.05) larger increases in upper arm circumference and soreness compared to SV, and peak plasma CK activity was 4.5-fold greater (p < 0.05) following FV than SV. These results suggest that, for the same time under tension, fast velocity eccentric exercise causes greater muscle damage than slow velocity exercise in untrained subjects.
202 citations
Journal Article•
TL;DR: The greater alterations in the contractile properties observed during the CON contractions indicate that intracellular Ca2+‐controlled excitation–contraction (E–C) coupling processes, possibly associated with a higher energy requirement, are affected to a much greater degree than during ECC contractions.
172 citations
TL;DR: In this paper, the authors compared the contribution of central and peripheral processes to muscle fatigue induced in the ankle dorsiflexor muscles by tests performed during concentric (CON) and eccentric (ECC) conditions.
Abstract: We compared the contribution of central and peripheral processes to muscle fatigue induced in the ankle dorsiflexor muscles by tests performed during concentric (CON) and eccentric (ECC) conditions. Each fatigue test consisted of five sets of 30 maximum voluntary contractions at a constant speed of 50 degrees /s for a 30 degrees range of motion of the ankle joint. The torque produced by the dorsiflexors and the surface electromyogram (EMG) of the tibialis anterior muscle were recorded during the fatigue tests. Before, during, and after the tests, the compound muscle action potential (M wave) and the contractile properties in response to single and paired electrical stimuli, as well as the interpolated-twitch method and postactivation potentiation (PAP), were recorded during isometric conditions. Compared with ECC contractions, the CON ones resulted in a greater (P < 0.05) loss of force (-31.6% vs. -23.8%) and a decrease in EMG activity (-26.4% vs. -17.5%). This difference was most pronounced during the first four sets of contractions, but was reduced during the last set. Activation was not altered by the tests because neither the interpolated-twitch response nor the ratio of the voluntary EMG to the amplitude of the M wave was changed in the two fatigue tests. Although there was no significant difference in M-wave amplitude between the two tests, changes in the twitch parameters and in the PAP were found to be greater in the CON than ECC contractions. It is concluded that the greater alterations in the contractile properties observed during the CON contractions indicate that intracellular Ca(2+)-controlled excitation-contraction (E-C) coupling processes, possibly associated with a higher energy requirement, are affected to a much greater degree than during ECC contractions.
171 citations
References
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Journal Article•
TL;DR: The results indicated that neural factors accounted for the larger proportion of the initial strength increment and thereafter both neural factors andhypertrophy took part in the further increase in strength, with hypertrophy becoming the dominant factor after the first 3 to 5 weeks.
Abstract: The time course of strength gain with respect to the contributions of neural factors and hypertrophy was studied in seven young males and eight females during the course of an 8 week regimen of isotonic strength training. The results indicated that neural factors accounted for the larger proportion of the initial strength increment and thereafter both neural factors and hypertrophy took part in the further increase in strength, with hypertrophy becoming the dominant factor after the first 3 to 5 weeks. Our data regarding the untrained contralateral arm flexors provide further support for the concept of cross education. It was suggested that the nature of this cross education effect may entirely rest on the neural factors presumably acting at various levels of the nervous system which could result in increasing the maximal level of muscle activation.
1,352 citations
"Isokinetic elbow flexion and coacti..." refers methods or result in this paper
...Thus, under these conditions, and in line with other reports [17,27], we suggest that the increase in EMG activity of the agonist muscle during maximal voluntary action after training, can be mediated by an increase in both number and discharge frequency of motor units, especially the fast motor units....
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...This relationship has been used to evaluate the processes underlying the torque gains [26,27]....
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TL;DR: The possible mechanisms of neural adaptation are discussed in relation to motor unit recruitment and firing patterns and the relative roles of neural and muscular adaptation in short- and long-term strength training are evaluated.
Abstract: Strength performance depends not only on the quantity and quality of the involved muscles, but also upon the ability of the nervous system to appropriately activate the muscles. Strength training may cause adaptive changes within the nervous system that allow a trainee to more fully activate prime movers in specific movements and to better coordinate the activation of all relevant muscles, thereby effecting a greater net force in the intended direction of movement. The evidence indicating neural adaptation is reviewed. Electromyographic studies have provided the most direct evidence. They have shown that increases in peak force and rate of force development are associated with increased activation of prime mover muscles. Possible reflex adaptations related to high stretch loads in jumping and rapid reciprocal movements have also been revealed. Other studies, including those that demonstrate the "cross-training" effect and specificity of training, provide further evidence of neural adaptation. The possible mechanisms of neural adaptation are discussed in relation to motor unit recruitment and firing patterns. The relative roles of neural and muscular adaptation in short- and long-term strength training are evaluated.
1,308 citations
"Isokinetic elbow flexion and coacti..." refers background in this paper
...originating from joint receptors, Golgi tendon organs, free nerve endings, cutaneous receptors [11] or from muscle fiber spindles [12]....
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...Indeed, a decrease in number of activated motor units of the agonist muscle originating from Golgi tendon organs and/or from motor spindles [12,11] could limit torque production....
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TL;DR: The possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast‐twitch motor units, accompanied by derecruitment of slow‐ twitch motor units is investigated.
Abstract: 1. We have investigated the possibility that voluntary muscle lengthening contractions can be performed by selective recruitment of fast-twitch motor units, accompanied by derecruitment of slow-twitch motor units. 2. The behaviour of motor units in soleus, gastrocnemius lateralis and gastrocnemius medialis muscles was studied during (a) controlled isotonic plantar flexion against a constant load (shortening contraction, S), maintained plantar flexion, or dorsal flexion resisting the load and gradually yielding to it (lengthening contraction, L), (b) isometric increasing or decreasing plantar torque accomplished by graded contraction or relaxation of the triceps surae muscles, (c) isometric or isotonic ballistic contractions, and (d) periodic, quasi-sinusoidal isotonic contractions at different velocities. The above tasks were performed under visual control of foot position, without activation of antagonist muscles. The motor units discharging during foot rotation were grouped on the basis of the phase(s) during which they were active as S, S + L and L. The units were also characterized according to both the level of isometric ramp plantar torque at which they were first recruited and the amplitude of their action potential. 3. S units were never active during dorsal flexion; some of them were active during the sustained contraction between plantar and dorsal flexion. Most S + L units were active also during the maintenance phase and were slowly derecruited during lengthening; their behaviour during foot rotations was similar to that during isometric contractions or relaxations. L units were never active during either plantar or maintained flexion, but discharged during lengthening contraction in a given range of rotation velocities; the velocity of lengthening consistently influenced the firing frequency of these units. Such dependence on velocity was not observed in S + L units. 4. A correlation was found between the amplitude of the action potential and the threshold torque of recruitment among all the units. In addition, the amplitudes of both the action potential and the threshold torque were higher in the case of L units than in the case of S and S + L units. Most L units could be voluntarily recruited only in the case of ballistic isometric or isotonic contraction. 5. Occasionally, L units were directly activated by electrical stimulation of motor fibres and their conduction velocity was in the higher range for alpha-axons. In contrast, nerve stimulation could induce a reflex activation of S and S + L units.(ABSTRACT TRUNCATED AT 400 WORDS)
674 citations
"Isokinetic elbow flexion and coacti..." refers background in this paper
...The enhancement of torque gains under eccentric and at highest concentric angular velocities could perhaps be explained by a recruitment of fast twitch fibers during eccentric training [39,40,46]....
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TL;DR: This review examines the experimental evidence that provides the foundation for the current understanding of the benefits, consequences, and control of eccentric contractions and suggests a new hypothesis: that the neural commands controlling eccentric contraction are unique.
Abstract: Enoka, Roger M. Eccentric contractions require unique activation strategies by the nervous system. J. Appl. Physiol. 81(6): 2339–2346, 1996.—Eccentric contractions occur when activated muscles are ...
645 citations
"Isokinetic elbow flexion and coacti..." refers background in this paper
...This special mechanism appears to be favored by eccentric action training [32]....
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604 citations
"Isokinetic elbow flexion and coacti..." refers background in this paper
...This capability appears to depend on the muscles involved [36] and, there may also be an effect due to task (isokinetic versus isometric action) on the ability to achieve maximum activation [37]....
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