Training-induced changes in neuromuscular performance under voluntary and reflex conditions.
01 Jan 1986-European Journal of Applied Physiology (Eur J Appl Physiol Occup Physiol)-Vol. 55, Iss: 2, pp 147-155
TL;DR: The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.
Abstract: To investigate training-induced changes in neuromuscular performance under voluntary and reflex contractions, 11 male subjects went through heavy resistance (high loads of 70–120% of one maximum repetition) and 10 male subjects through explosive type (low loads with high contraction velocities) strength training three times a week for 24 weeks. A large increase (13.9%,p<0.01) in voluntary unilateral maximal knee extension strength with only slight and insignificant changes in time of isometric force production were observed during heavy resistance strength training. Explosive type strength training resulted in a small insignificant increase in maximal strength but in considerable shortening (p<0.05) in the time of force production. A significant increase (p<0.05) noted in the averaged maximal integrated electromyogram (IEMG) of the knee extensors during heavy resistance strength training correlated (p<0.01) with the increase in maximal strength. No changes were noted during training in reflex time components, but significant decreases (p<0.05) occurred in the peak-to-peak amplitudes of the reflex electromyograms (EMG) in both groups. The individual changes during training in the reflex EMG/force ratio were related (p<0.01) to the respective changes in IEMG/force ratio in voluntary contractions. The present observations support the concept of specificity of training, and suggest that specific training-induced adaptations in the neuromuscular system may be responsible for these changes in performance.
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TL;DR: Increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training, which could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.
Abstract: The maximal rate of rise in muscle force [rate of force development (RFD)] has important functional consequences as it determines the force that can be generated in the early phase of muscle contraction (0-200 ms). The present study examined the effect of resistance training on contractile RFD and efferent motor outflow ("neural drive") during maximal muscle contraction. Contractile RFD (slope of force-time curve), impulse (time-integrated force), electromyography (EMG) signal amplitude (mean average voltage), and rate of EMG rise (slope of EMG-time curve) were determined (1-kHz sampling rate) during maximal isometric muscle contraction (quadriceps femoris) in 15 male subjects before and after 14 wk of heavy-resistance strength training (38 sessions). Maximal isometric muscle strength [maximal voluntary contraction (MVC)] increased from 291.1 +/- 9.8 to 339.0 +/- 10.2 N. m after training. Contractile RFD determined within time intervals of 30, 50, 100, and 200 ms relative to onset of contraction increased from 1,601 +/- 117 to 2,020 +/- 119 (P < 0.05), 1,802 +/- 121 to 2,201 +/- 106 (P < 0.01), 1,543 +/- 83 to 1,806 +/- 69 (P < 0.01), and 1,141 +/- 45 to 1,363 +/- 44 N. m. s(-1) (P < 0.01), respectively. Corresponding increases were observed in contractile impulse (P < 0.01-0.05). When normalized relative to MVC, contractile RFD increased 15% after training (at zero to one-sixth MVC; P < 0.05). Furthermore, muscle EMG increased (P < 0.01-0.05) 22-143% (mean average voltage) and 41-106% (rate of EMG rise) in the early contraction phase (0-200 ms). In conclusion, increases in explosive muscle strength (contractile RFD and impulse) were observed after heavy-resistance strength training. These findings could be explained by an enhanced neural drive, as evidenced by marked increases in EMG signal amplitude and rate of EMG rise in the early phase of muscle contraction.
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Cites background or result from "Training-induced changes in neuromu..."
...Other studies have observed similar increases in normalized RFD after explosive-type resistance training, typically measured as the time to reach 30% MVC with no changes occurring at force levels of 60 and 90% MVC (24, 25)....
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...In contrast, normalized RFD has also been found to remain unchanged (24, 35) or even decrease (21) in response to resistance training....
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..., the rate of force development (RFD) exerted within the early phase of rising muscle force (24, 41, 44, 46) (Figs....
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...In fact, RFD has been reported to increase after bilateral resistance and jump training when measured in bilateral tests (21, 25), whereas no change was observed during unilateral test conditions (24)....
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TL;DR: Ecc is more effective than Con isokinetics training for developing strength in Ecc isokinetic muscle actions and that Con is moreeffective than Ecc iskinetic training fordeveloping strength in Con iskinetics muscle actions.
Abstract: Higbie, Elizabeth J., Kirk J. Cureton, Gordon L. Warren III, and Barry M. Prior. Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation.J. Appl...
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TL;DR: Cutting maneuvers performed without adequate planning may increase the risk of noncontact knee ligament injury due to the increased external varus/valgus and internal/external rotation moments applied to the knee.
Abstract: BESIER, T F, D G LLOYD, T R ACKLAND, and J L COCHRANE Anticipatory effects on knee joint loading during running and cutting maneuvers Med Sci Sports Exerc, Vol 33, No 7, 2001, pp 1176–1181PurposeTo determine how unanticipated performance of cutting maneuvers in sport affects the ext
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TL;DR: Quadriceps motoneuron activation was lower during maximal voluntary eccentric and slow concentric contractions compared with during fast concentric contraction in untrained subjects, and, after heavy resistance training, this inhibition in neuromuscular activation was reduced.
Abstract: Despite full voluntary effort, neuromuscular activation of the quadriceps femoris muscle appears inhibited during slow concentric and eccentric contractions. Our aim was to compare neuromuscular ac...
408 citations
TL;DR: Extended exercise may induce homeostatic disturbances within the central nervous system (CNS) that subsequently attenuates motor activation, and strenuous exercise is a challenge not only to the cardiorespiratory and locomotive systems but also to the brain.
396 citations
Cites background from "Training-induced changes in neuromu..."
...…appears to involve adaptive changes in the CNS that contribute to increase the efferent neuronal outflow during maximal efforts (Komi, 1986; Hakkinen and Komi, 1986; Aagaard et al., 2002; Aagaard, 2003), and central adaptations may also be responsible for the decrease in force sensation…...
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References
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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
TL;DR: It was concluded that improvement in strength may be accounted for by neural factors during the course of very intensive strength training, especially in highly trained subjects.
Abstract: Eleven male subjects (20-32 years) accustomed to strength training went through progressive, high-load strength training for 24 weeks with intensities ranging variably between 70 and 120% during each month. This training was also followed by a 12-week detraining period. An increase of 26.8% (P less than 0.001) in maximal isometric strength took place during the training. The increase in strength correlated (P less than 0.05) with significant (P less than 0.05-0.01) increases in the neural activation (IEMG) of the leg extensor muscles during the most intensive training months. During the lower-intensity training, maximum IEMG decreased (P less than 0.05). Enlargements of muscle-fibre areas, especially of fast-twitch type (P less than 0.001), took place during the first 12 weeks of training. No hypertrophic changes were noted during the latter half of training. After initial improvements (P less than 0.05) no changes or even slight worsening were noted in selected force-time parameters during later strength training. During detraining a great (P less than 0.01) decrease in maximal strength was correlated (P less than 0.05) with the decrease (P less than 0.05) in the maximum IEMGs of the leg extensors. This period resulted also in decreases (P less than 0.05) of the mean muscle-fibre areas of both fibre types. It was concluded that improvement in strength may be accounted for by neural factors during the course of very intensive strength training. Selective training-induced hypertrophy also contributed to strength development but muscle hypertrophy may have some limitations during long-lasting strength training, especially in highly trained subjects.
758 citations
TL;DR: It is suggested that supraspinal connections from motor cortex directly to spinal motoneurons may be enhanced as a result of training to the point where they produce a significant synchronization of motor units during steady, voluntary contractions.
455 citations
"Training-induced changes in neuromu..." refers background in this paper
...It is also possible (Milner-Brown et al. 1975) that, while direct supraspinal connections from the motor cortex to spinal motoneurons may be enhanced as a result of training, no differences might be obtained in earlier spinal reflexes resulting from the passive stimulation of the "resting" primary muscle spindle sensory fibers....
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TL;DR: It was concluded that the early change in strength may be accounted for largely by neural factors with a gradually increasing contribution of hypertrophic factors as the training proceeds.
Abstract: Fourteen male subjects (20-30 yr) accustomed to weight training went through progressive strength training of combined concentric and eccentric contractions three times per week for 16 wk. The training was followed by the 8-wk detraining period. The training program consisted mainly of dynamic exercises for leg extensors with the loads of 80-120% of one maximum concentric repetition. Significant improvements in muscle function were observed in early conditioning; however, the increase in maximal force during the very late training period was greatly limited. Marked improvements (P less than 0.001) in muscle strength were accompanied by significant (P less than 0.01) increases in the neural activation (IEMG) of the leg extensor muscles. The relationship between IEMG and high absolute forces changed (P less than 0.01) during the training period. The occurrence of these changes varied during the course of training. It was concluded that the early change in strength may be accounted for largely by neural factors with a gradually increasing contribution of hypertrophic factors as the training proceeds. It was suggested that the magnitudes and occurrence of these changes may vary due to the differences in conditioning periods, in individual muscles of muscle groups, in subject material, and in conditioning methods. During detraining, the decrease in muscle force seemed to be explainable also by the neural and muscular adaptations caused by the inactivity.
419 citations
317 citations