Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles

2007 ◽  
Vol 103 (3) ◽  
pp. 979-989 ◽  
Author(s):  
John G. Semmler ◽  
Kylie J. Tucker ◽  
Trevor J. Allen ◽  
Uwe Proske
Keyword(s):  
Eccentric Exercise ◽  
Biceps Brachii ◽  
Maximum Voluntary Contraction ◽  
Elbow Flexor ◽  
Twofold Increase ◽  
Force Fluctuations ◽  
Emg Amplitude ◽  
Concentric Exercise ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at four submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24 h after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24 h later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3–4 times larger at 5 and 20% MVC) and in the brachialis muscle at moderate forces (2 times larger at 35 and 50% MVC). Eccentric exercise resulted in a twofold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3–4 times larger at 5% MVC, 2 times larger at 50% MVC), with a twofold increase in physiological tremor at 8–12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.

Low-frequency fatigue and neuromuscular performance after exercise-induced damage to elbow flexor muscles

2008 ◽  
Vol 105 (4) ◽  
pp. 1146-1155 ◽  
Author(s):  
James M. Dundon ◽  
John Cirillo ◽  
John G. Semmler
Keyword(s):  
Eccentric Exercise ◽  
Biceps Brachii ◽  
Maximum Voluntary Contraction ◽  
Low Frequency ◽  
Elbow Flexor ◽  
Triceps Brachii ◽  
Force Fluctuations ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Low Frequency Fatigue

The purpose of this study was to quantify the association between low-frequency fatigue (LFF) and the increase in EMG and force fluctuations after eccentric exercise of elbow flexor muscles. Ten subjects performed two tasks involving voluntary isometric contractions of elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at five submaximal target forces (5, 10, 20, 40, 60% MVC) while EMG was recorded from biceps and triceps brachii. A third task involved electrical stimulation of biceps brachii at 12 frequencies (1–100 Hz). These tasks were performed before, after, and 2 h and 24 h after concentric or eccentric exercise. MVC force declined after eccentric exercise (34% decline) and remained depressed 24 h later (22% decline), whereas the reduced force following concentric exercise (32%) was recovered 2 h later. Biceps brachii EMG and force fluctuations during the submaximal voluntary contractions increased after eccentric exercise (both ∼2× greater) with the greatest effect at low forces. LFF was equivalent immediately after both types of exercise (50–60% reduction in 20:100 Hz force) with a slower recovery following eccentric exercise. A significant association was found between the change in LFF and EMG ( r2values up to 0.52), with the strongest correlations observed at low forces (20% MVC) and at 2 h after exercise. In contrast, there were no significant associations between LFF and force fluctuations during voluntary or electrically evoked contractions, suggesting that other physiological factors located within the muscle are likely to be playing a major role in the impaired motor performance after eccentric exercise.

Activation among the elbow flexor muscles differs when maintaining arm position during a fatiguing contraction

2003 ◽  
Vol 94 (6) ◽  
pp. 2439-2447 ◽  
Author(s):  
Sandra K. Hunter ◽  
Romuald Lepers ◽  
Carol J. MacGillis ◽  
Roger M. Enoka
Keyword(s):  
Biceps Brachii ◽  
Maximum Voluntary Contraction ◽  
Elbow Flexor ◽  
The Other ◽  
Emg Activity ◽  
Inhibitory Input ◽  
Endurance Time ◽  
Rate Of Increase ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

Twenty-four men ( n = 11) and women ( n = 13) supported an inertial load equivalent to 20% of the maximum voluntary contraction force with the elbow flexor muscles for as long as possible while maintaining a constant elbow angle at 90°. Endurance time did not differ on the three occasions that the task was performed (320 ± 149 s; P > 0.05), and there was no difference between women (360 ± 168 s) and men (273 ± 108 s; P = 0.11). The rate of increase in average electromyogram (EMG) for the elbow flexor muscles was similar across sessions ( P > 0.05). However, average EMG during the fatiguing task increased for the long head of biceps brachii, brachioradialis, and brachialis ( P < 0.05) but not for the short head of biceps brachii. Furthermore, the average EMG for the brachialis was greater at the start and end of the contraction compared with the other elbow flexor muscles. The rate of bursts in EMG activity increased during the fatiguing contraction and was greater in brachialis (1.0 ± 0.2 bursts/min) compared with the other elbow flexor muscles (0.5 ± 0.1 bursts/min). The changes in the standard deviation of acceleration, mean arterial pressure, and heart rate during the fatiguing contractions were similar across sessions. These findings indicate that the EMG activity, which reflects the net excitatory and inhibitory input received by the motoneurons in the spinal cord, was not adaptable over repeat sessions for the maintain-position task. Furthermore, these results contrast those from a previous study (Hunter SK and Enoka RM. J Appl Physiol 94: 108–118, 2003) when the goal of the isometric contraction was to maintain a constant force. These results, from a series of studies on the elbow flexor muscles, indicate that the type of load supported during the fatiguing contraction influences the extent to which endurance time can change with repeat performances of the task.

Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles

2008 ◽  
Vol 105 (2) ◽  
pp. 502-509 ◽  
Author(s):  
Tanya S. Turner ◽  
Kylie J. Tucker ◽  
Nigel C. Rogasch ◽  
John G. Semmler
Keyword(s):  
Eccentric Exercise ◽  
Maximum Voluntary Contraction ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Fine Motor ◽  
Triceps Brachii ◽  
Lengthening Contractions ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Exercise Induced

The purpose of this study was to examine the effect of exercise-induced damage of the elbow flexor muscles on steady motor performance during isometric, shortening, and lengthening contractions. Ten healthy individuals (age 22 ± 4 yr) performed four tasks with the elbow flexor muscles: a maximum voluntary contraction, a one repetition maximum (1 RM), an isometric task at three joint angles (short, intermediate, and long muscle lengths), and a constant-load task during slow (∼7°/s) shortening and lengthening contractions. Task performance was quantified as the fluctuations in wrist acceleration (steadiness), and electromyography was obtained from the biceps and triceps brachii muscles at loads of 10, 20, and 40% of 1 RM. Tasks were performed before, immediately after, and 24 h after eccentric exercise that resulted in indicators of muscle damage. Maximum voluntary contraction force and 1-RM load declined by ∼45% immediately after exercise and remained lower at 24 h (∼30% decrease). Eccentric exercise resulted in reduced steadiness and increased biceps and triceps brachii electromyography for all tasks. For the isometric task, steadiness was impaired at the short compared with the long muscle length immediately after exercise ( P < 0.01). Furthermore, despite no differences before exercise, there was reduced steadiness for the shortening compared with the lengthening contractions after exercise ( P = 0.01), and steadiness remained impaired for shortening contractions 24 h later ( P = 0.01). These findings suggest that there are profound effects for the performance of these types of fine motor tasks when recovering from a bout of eccentric exercise.

Reduced short-interval intracortical inhibition after eccentric muscle damage in human elbow flexor muscles

2012 ◽  
Vol 113 (6) ◽  
pp. 929-936 ◽  
Author(s):  
Bradley M. Pitman ◽  
John G. Semmler
Keyword(s):  
Muscle Damage ◽  
Eccentric Exercise ◽  
Muscle Soreness ◽  
Joint Angle ◽  
Short Interval ◽  
Intracortical Inhibition ◽  
Elbow Flexor ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Eccentric Muscle Damage

The purpose of this study was to use paired-pulse transcranial magnetic stimulation (TMS) to examine the effect of eccentric exercise on short-interval intracortical inhibition (SICI) after damage to elbow flexor muscles. Nine young (22.5 ± 0.6 yr; mean ± SD) male subjects performed maximal eccentric exercise of the elbow flexor muscles until maximal voluntary contraction (MVC) force was reduced by ∼40%. TMS was performed before, 2 h after, and 2 days after exercise under Rest and Active (5% MVC) conditions with motor-evoked potentials (MEPs) recorded from the biceps brachii (BB) muscle. Peripheral electrical stimulation of the brachial plexus was used to assess maximal M-waves, and paired-pulse TMS with a 3-ms interstimulus interval was used to assess changes in SICI at each time point. The eccentric exercise resulted in a 34% decline in strength ( P < 0.001), a 41% decline in resting M-wave ( P = 0.01), changes in resting elbow joint angle (10°, P < 0.001), and a shift in the optimal elbow joint angle for force production (18°, P < 0.05) 2 h after exercise. This was accompanied by impaired muscle strength (27%, P < 0.001) and increased muscle soreness ( P < 0.001) 2 days after exercise, which is indicative of muscle damage. When the test MEP amplitudes were matched between sessions, we found that SICI was reduced by 27% in resting and 23% in active BB muscle 2 h after exercise. SICI recovered 2 days after exercise when muscle pain and soreness were present, suggesting that delayed onset muscle soreness from eccentric exercise does not influence SICI. The change in SICI observed 2 h after exercise suggests that eccentric muscle damage has widespread effects throughout the motor system that likely includes changes in motor cortex.

Eccentric Muscle Damage Has Variable Effects on Motor Unit Recruitment Thresholds and Discharge Patterns in Elbow Flexor Muscles

2009 ◽  
Vol 102 (1) ◽  
pp. 413-423 ◽  
Author(s):  
Tamara J. Dartnall ◽  
Nigel C. Rogasch ◽  
Michael A. Nordstrom ◽  
John G. Semmler
Keyword(s):  
Muscle Damage ◽  
Motor Unit ◽  
Eccentric Exercise ◽  
Biceps Brachii ◽  
Discharge Rate ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Recruitment Threshold ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

The purpose of this study was to determine the effect of eccentric muscle damage on recruitment threshold force and repetitive discharge properties of low-threshold motor units. Ten subjects performed four tasks involving isometric contraction of elbow flexors while electromyographic (EMG) data were recorded from human biceps brachii and brachialis muscles. Tasks were 1) maximum voluntary contraction (MVC); 2) constant-force contraction at various submaximal targets; 3) motor unit recruitment threshold task; and 4) minimum motor unit discharge rate task. These tasks were performed on three separate days before, immediately after, and 24 h after eccentric exercise of elbow flexor muscles. MVC force declined (42%) immediately after exercise and remained depressed (29%) 24 h later, indicative of muscle damage. Mean motor unit recruitment threshold for biceps brachii was 8.4 ± 4.2% MVC, ( n = 34) before eccentric exercise, and was reduced by 41% (5.0 ± 3.0% MVC, n = 34) immediately after and by 39% (5.2 ± 2.5% MVC, n = 34) 24 h after exercise. No significant changes in motor unit recruitment threshold were observed in the brachialis muscle. However, for the minimum tonic discharge rate task, motor units in both muscles discharged 11% faster (10.8 ± 2.0 vs. 9.7 ± 1.7 Hz) immediately after ( n = 29) exercise compared with that before ( n = 32). The minimum discharge rate variability was greater in brachialis muscle immediately after exercise (13.8 ± 3.1%) compared with that before (11.9 ± 3.1%) and 24 h after exercise (11.7 ± 2.4%). No significant changes in minimum discharge rate variability were observed in the biceps brachii motor units after exercise. These results indicate that muscle damage from eccentric exercise alters motor unit recruitment thresholds for ≥24 h, but the effect is not the same in the different elbow flexor muscles.

scholarly journals Fatigability of the elbow flexor muscles for a sustained submaximal contraction is similar in men and women matched for strength

2004 ◽  
Vol 96 (1) ◽  
pp. 195-202 ◽  
Author(s):  
Sandra K. Hunter ◽  
Ashley Critchlow ◽  
In-Sik Shin ◽  
Roger M. Enoka
Keyword(s):  
Perceived Exertion ◽  
Maximum Voluntary Contraction ◽  
Elbow Flexor ◽  
Rating Of Perceived Exertion ◽  
Emg Activity ◽  
Men And Women ◽  
Task Failure ◽  
Rate Of Increase ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

The purpose of this study was to compare the time to task failure for a submaximal fatiguing contraction sustained with the elbow flexor muscles by men and women who were matched for strength ( n = 20, 18-35 yr). The maximal torque exerted at the wrist was similar for the men and women [64.5 ± 8.7 (SD) vs. 64.5 ± 8.3 N·m; P > 0.05], which meant that the average torque exerted during the fatiguing contraction [20% of maximum voluntary contraction (MVC)] was similar for the two sexes. The time to task failure was similar for these strength-matched men and women (819 ± 306 vs. 864 ± 391 s; P > 0.05). The mean arterial pressure was similar at the beginning of the contraction for men (97 ± 12 mmHg) and women (96 ± 15 mmHg; P > 0.05) and at task failure (134 ± 18 vs. 126 ± 26 mmHg; P > 0.05, respectively). Furthermore, the increases in heart rate, torque fluctuations, and rating of perceived exertion during the fatiguing contraction were similar for the two sexes. However, the electromyogram (EMG) activity differed for the men and women: the rate of increase in the average of the rectified EMG (% peak MVC) for all the elbow flexor muscles was less for the women compared with the men ( P < 0.05). Furthermore, the bursts of EMG activity for the elbow flexor muscles increased toward exhaustion for all subjects but at a greater rate for the women compared with the men ( P < 0.05). The results indicate that strength-matched men and women experienced similar levels of muscle fatigue and cardiovascular adjustments during a sustained low-force isometric contraction, despite differences in the EMG activity for the two groups of subjects.

Changes in hardness of the human elbow flexor muscles after eccentric exercise

2000 ◽  
Vol 82 (5-6) ◽  
pp. 361-367 ◽  
Author(s):  
Mitsuyoshi Murayama ◽  
Kazunori Nosaka ◽  
Tsugutake Yoneda ◽  
Kazutoshi Minamitani
Keyword(s):  
Eccentric Exercise ◽  
Elbow Flexor ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

Matching different levels of isometric torque in elbow flexor muscles after eccentric exercise

2003 ◽  
Vol 149 (2) ◽  
pp. 141-150 ◽  
Author(s):  
N. Weerakkody ◽  
P. Percival ◽  
D. L. Morgan ◽  
J. E. Gregory ◽  
U. Proske
Keyword(s):  
Eccentric Exercise ◽  
Elbow Flexor ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Isometric Torque ◽  
Different Levels

Sensitivity of muscle proton spin-spin relaxation time as an index of muscle activation

1994 ◽  
Vol 77 (1) ◽  
pp. 84-92 ◽  
Author(s):  
G. Yue ◽  
A. L. Alexander ◽  
D. H. Laidlaw ◽  
A. F. Gmitro ◽  
E. C. Unger ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Spin Relaxation ◽  
Muscle Activation ◽  
Biceps Brachii ◽  
Proton Spin ◽  
Spin Relaxation Time ◽  
Elbow Flexor ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Long Head

The purpose of this study was to determine the minimum number of contractions that are needed to detect an increase in the muscle proton spin-spin relaxation time (T2) at a given exercise intensity. Five healthy human subjects performed five sets of an exercise that included concentric and eccentric contractions of the elbow-flexor muscles with loads that were 25 or 80% of maximum. With the 80% load, the five sets involved 1, 2, 5, 10, or 20 repetitions of the exercise; with the 25% load the five sets were 2, 5, 10, 20, or 40 repetitions. The upper arm of each subject was imaged before and immediately after each set of the exercise. Spin-echo images (repetition time/echo time = 2,000 ms/30, 60, 90, and 120 ms) were collected using an extremity coil, and T2 values were calculated. The signal intensity was measured from the elbow-flexor and -extensor muscles and from the bone marrow of the humerus. With the 80% load, T2 increased in the short head of the biceps brachii after two repetitions of the elbow exercise and after five repetitions in the brachialis and the long head of the biceps brachii. With the 25% load, T2 became longer after five repetitions of the exercise for the short head of the biceps brachii and after 10 repetitions for the brachialis and the long head of the biceps brachii. T2 varied linearly with the number of contraction repetitions for each of the elbow-flexor muscles at either load (r2 > or = 0.97, P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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