Sex differences in the fatigability of arm muscles depends on absolute force during isometric contractions

2001 ◽  
Vol 91 (6) ◽  
pp. 2686-2694 ◽  
Author(s):  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activation ◽  
Pressor Response ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Endurance Time ◽  
Muscle Activation Patterns ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force ◽  
The Absolute

Women are capable of longer endurance times compared with men for contractions performed at low to moderate intensities. The purpose of the study was 1) to determine the relation between the absolute target force and endurance time for a submaximal isometric contraction and 2) to compare the pressor response and muscle activation patterns of men [26.3 ± 1.1 (SE) yr] and women (27.5 ± 2.3 yr) during a fatiguing contraction performed with the elbow flexor muscles. Maximal voluntary contraction (MVC) force was greater for men (393 ± 23 vs. 177 ± 7 N), which meant that the average target force (20% of MVC) was greater for men (79.7 ± 6.5 vs. 36.7 ± 2.0 N). The endurance time for the fatiguing contractions was 118% longer for women (1,806 ± 239 vs. 829 ± 94 s). The average of the rectified electromyogram (%MVC) for the elbow flexor muscles at exhaustion was similar for men (31 ± 2%) and women (30 ± 2%). In contrast, the heart rate and mean arterial pressure (MAP) were less at exhaustion for women (94 ± 6 vs. 111 ± 7 beats/min and 121 ± 5 vs. 150 ± 6 mmHg, respectively). The target force and change in MAP during the fatiguing contraction were exponentially related to endurance time ( r 2 = 0.68 and r 2 = 0.64, respectively), whereas the change in MAP was linearly related to target force ( r 2 = 0.51). The difference in fatigability of men and women when performing a submaximal contraction was related to the absolute contraction intensity and was limited by mechanisms that were distal to the activation of muscle.

Older Adults Use a Unique Strategy to Lift Inertial Loads With the Elbow Flexor Muscles

2000 ◽  
Vol 83 (4) ◽  
pp. 2030-2039 ◽  
Author(s):  
Andrew E. Graves ◽  
Kurt W. Kornatz ◽  
Roger M. Enoka
Keyword(s):  
Young Adults ◽  
Elbow Joint ◽  
Muscle Activation ◽  
Angular Displacement ◽  
Elbow Flexor ◽  
Lengthening Contractions ◽  
Old Adults ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force

The purpose of this study was to determine the effect of age on the ability to exert steady forces and to perform steady flexion movements with the muscles that cross the elbow joint. An isometric task required subjects to exert a steady force to match a target force that was displayed on a monitor. An anisometric task required subjects to raise and lower inertial loads so that the angular displacement around the elbow joint matched a template displayed on a monitor. Steadiness was measured as the coefficient of variation of force and as the normalized standard deviation of wrist acceleration. For the isometric task, steadiness as a function of target force decreased similarly for old adults and young adults. For the anisometric task, steadiness increased as a function of the inertial load and there were significant differences caused by age. Old adults were less steady than young adults during both shortening and lengthening contractions with the lightest loads. Furthermore, old adults were least steady when performing lengthening contractions. These behaviors appear to be associated with the patterns of muscle activation. These results suggest that different neural strategies are used to control isometric and anisometric contractions performed with the elbow flexor muscles and that these strategies do not change in parallel with advancing age.

Task Differences With the Same Load Torque Alter the Endurance Time of Submaximal Fatiguing Contractions in Humans

2002 ◽  
Vol 88 (6) ◽  
pp. 3087-3096 ◽  
Author(s):  
Sandra K. Hunter ◽  
Daphne L. Ryan ◽  
Justus D. Ortega ◽  
Roger M. Enoka
Keyword(s):  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Elbow Flexor ◽  
Emg Activity ◽  
Load Torque ◽  
Endurance Time ◽  
Position Task ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Fatiguing Contractions

Endurance time, muscle activation, and mean arterial pressure were measured during two types of submaximal fatiguing contractions that required each subject to exert the same net muscle torque in the two tasks. Sixteen men and women performed isometric contractions at 15% of the maximum voluntary contraction (MVC) force with the elbow flexor muscles, either by maintaining a constant force while pushing against a force transducer (force task) or by supporting an equivalent inertial load while maintaining a constant elbow angle (position task). The endurance time for the force task (1402 ± 728 s) was twice as long as that for the position task (702 ± 582 s, P < 0.05), despite a similar reduction in the load torque at exhaustion for each contraction. The rate of increase in average electromyographic activity (EMG, % peak MVC value) for the elbow flexor muscles was similar for the two tasks. However, the average EMG was greater at exhaustion for the force task (22.4 ± 1.2%) compared with the position task (14.9 ± 1.0%, P < 0.05). In contrast, the rates of increase in the mean arterial pressure, the rating of perceived exertion, anterior deltoid EMG, and fluctuations in motor output (force or acceleration) were greater for the position task compared with the force task ( P < 0.05). Furthermore, the rate of bursts in EMG activity, which corresponded to the transient recruitment of motor units, was greater for the brachialis muscle during the position task. These results indicate that the briefer endurance time for the position task was associated with greater levels of excitatory and inhibitory input to the motor neurons compared with the force task.

scholarly journals Muscle activity and time to task failure differ with load compliance and target force for elbow flexor muscles

2011 ◽  
Vol 110 (1) ◽  
pp. 125-136 ◽  
Author(s):  
Thorsten Rudroff ◽  
Jamie N. Justice ◽  
Matthew R. Holmes ◽  
Stephen D. Matthews ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activity ◽  
Elbow Flexor ◽  
Rating Of Perceived Exertion ◽  
Isometric Contractions ◽  
Time To Failure ◽  
Task Failure ◽  
Position Task ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Target Force

The primary purpose of this study was to determine the influence of load compliance on time to failure during sustained isometric contractions performed with the elbow flexor muscles at four submaximal target forces. Subjects pulled against a rigid restraint during the force task and maintained a constant elbow angle, while supporting an equivalent inertial load during the position task. Each task was sustained for as long as possible. Twenty-one healthy adults (23 ± 6 yr; 11 men) participated in the study. The maximal voluntary contraction (MVC) force was similar ( P = 0.95) before the subjects performed the force and position tasks at each of the four target forces: 20, 30, 45, and 60% of MVC force. The time to task failure was longer for the force tasks (576 ± 80 and 325 ± 70 s) than for the position tasks (299 ± 77 and 168 ± 35 s) at target forces of 20 and 30% ( P < 0.001), but was similar for the force tasks (178 ± 35 and 86 ± 14 s) and the position tasks (132 ± 29 and 87 ± 14 s) at target forces of 45 and 60% ( P > 0.19). The briefer times to failure for the position task at the lower forces were accompanied by greater rates of increase in elbow flexor muscle activity, mean arterial pressure, heart rate, and rating of perceived exertion. There was no difference in the estimates of external mechanical work at any target force. The dominant mechanisms limiting time to failure of sustained isometric contractions with the elbow flexor muscles appear to change at target forces between 30 and 45% MVC, with load compliance being a significant factor at lower forces only.

Increased ventilation does not impair maximal voluntary contractions of the elbow flexors

2008 ◽  
Vol 104 (6) ◽  
pp. 1674-1682 ◽  
Author(s):  
Janette L. Smith ◽  
Jane E. Butler ◽  
Peter G. Martin ◽  
Rachel A. McBain ◽  
Janet L. Taylor
Keyword(s):  
Exercise Performance ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Voluntary Activation ◽  
Neural Drive ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Muscle Groups ◽  
Voluntary Contractions ◽  
Limb Exercise

Exercise performance is impaired by increased respiratory work, yet the mechanism for this is unclear. This experiment assessed whether neural drive to an exercising muscle was affected by cortically driven increases in ventilation. On each of 5 days, eight subjects completed a 2-min maximal voluntary contraction (MVC) of the elbow flexor muscles, followed by 4 min of recovery, while transcranial magnetic stimulation tested for suboptimal neural drive to the muscle. On 1 day, subjects breathed without instructions under normocapnia. During the 2-min MVC, ventilation was ∼3.5 times that at rest. On another day, subjects breathed without instruction under hypercapnia. During the 2-min MVC, ventilation was ∼1.5 times that on the normocapnic day. On another 2 days under normocapnia, subjects voluntarily matched their breathing to the uninstructed breathing under normocapnia and hypercapnia using target feedback of the rate and inspiratory volume. On a fifth day under normocapnia, the volume feedback was set to each subject's vital capacity. On this day, ventilation during the 2-min MVC was approximately twice that on the uninstructed normocapnic day (or ∼7 times rest). The experimental manipulations succeeded in producing voluntary and involuntary hyperpnea. However, maximal voluntary force, fatigue and voluntary activation of the elbow flexor muscles were unaffected by cortically or chemically driven increases in ventilation. Results suggest that any effects of increased respiratory work on limb exercise performance are not due to a failure to drive both muscle groups optimally.

scholarly journals Men are more fatigable than strength-matched women when performing intermittent submaximal contractions

2004 ◽  
Vol 96 (6) ◽  
pp. 2125-2132 ◽  
Author(s):  
Sandra K. Hunter ◽  
Ashley Critchlow ◽  
In-Sik Shin ◽  
Roger M. Enoka
Keyword(s):  
Perceived Exertion ◽  
Voluntary Contraction ◽  
Elbow Flexor ◽  
Rating Of Perceived Exertion ◽  
Men And Women ◽  
Task Failure ◽  
Rate Of Increase ◽  
Absolute Strength ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

The purpose of this study was to compare the time to task failure for a series of intermittent submaximal contractions performed with the elbow flexor muscles by men and women who were matched for strength ( n = 20, 18–34 yr). The fatigue task comprised isometric contractions at 50% of maximal voluntary contraction (MVC) torque (6-s contraction, 4-s rest). The MVC torque was similar for the men and women [64.8 ± 9.2 (SD) vs. 62.2 ± 7.9 N·m; P > 0.05]. However, the time to task failure was longer for the women (1,408 ± 1,133 vs. 513 ± 194 s; P < 0.05), despite the similar torque levels. The mean arterial pressure, heart rate, and rating of perceived exertion started and ended at similar values for the men and women, but the rate of increase was less for the women. The rate of increase in the average of the rectified electromyogram (AEMG; % peak MVC) for the elbow flexor muscles was less for the women: the AEMG was greater for the men compared with the women at task failure (72 ± 28 vs. 50 ± 21%; P < 0.05), despite similar AEMG values at the start of the fatiguing contraction (32 ± 9 vs. 36 ± 13%). These results indicate that for intermittent contractions performed with the elbow flexor muscles 1) the sex difference in time to task failure was not explained by the absolute strength of the men and women, but involved another mechanism that is present during perfused conditions, and 2) men required a more rapid increase in descending drive to maintain a similar torque.

Gender Differences in the Fatigability of Human Skeletal Muscle

1999 ◽  
Vol 82 (6) ◽  
pp. 3590-3593 ◽  
Author(s):  
John G. Semmler ◽  
Devin V. Kutzscher ◽  
Roger M. Enoka
Keyword(s):  
Muscle Activity ◽  
Human Skeletal Muscle ◽  
Muscle Activation ◽  
Progressive Increase ◽  
Neuromuscular System ◽  
The Novel ◽  
Endurance Time ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Limb Immobilization

After participating in a 4-wk intervention that reduced normal usage of the elbow flexor muscles, all six women, but only one of six men, experienced a marked increase in the endurance time during a low-force fatiguing contraction. The increase in endurance time was associated with an altered pattern of muscle activation that did not involve the commonly observed progressive increase in muscle activity. Rather, the muscle activity comprised intermittent motor unit activity. In those individuals who exhibited this behavior, the novel pattern of muscle activity was only present immediately after 4 wk of limb immobilization and not before the intervention or after 4 wk of recovery. These findings suggest possible differences between women and men in the adaptations of the neuromuscular system.

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)

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.

Sign in / Sign up

Export Citation Format

Share Document