scholarly journals Stressor-induced increase in muscle fatigability of young men and women is predicted by strength but not voluntary activation

2014 ◽  
Vol 116 (7) ◽  
pp. 767-778 ◽  
Author(s):  
Manda L. Keller-Ross ◽  
Hugo M. Pereira ◽  
Jaclyn Pruse ◽  
Tejin Yoon ◽  
Bonnie Schlinder-DeLap ◽  
...  
Keyword(s):  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Men And Women ◽  
Task Failure ◽  
Initial Strength ◽  
Math Task ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Induced Changes ◽  
And Control

This study investigated mechanisms for the stressor-induced changes in muscle fatigability in men and women. Participants performed an isometric-fatiguing contraction at 20% maximal voluntary contraction (MVC) until failure with the elbow flexor muscles. Study one ( n = 55; 29 women) involved two experimental sessions: 1) a high-stressor session that required a difficult mental-math task before and during a fatiguing contraction and 2) a control session with no mental math. For some participants (n = 28; 14 women), cortical stimulation was used to examine mechanisms that contributed to muscle fatigability during the high-stressor and control sessions. Study two ( n = 23; nine women) determined the influence of a low stressor, i.e., a simple mental-math task, on muscle fatigability. In study one, the time-to-task failure was less for the high-stressor session than control ( P < 0.05) for women (19.4%) and men (9.5%): the sex difference response disappeared when covaried for initial strength (MVC). MVC force, voluntary activation, and peak-twitch amplitude decreased similarly for the control and high-stressor sessions ( P < 0.05). In study two, the time-to-task failure of men or women was not influenced by the low stressor ( P > 0.05). The greater fatigability, when exposed to a high stressor during a low-force task, was not exclusive to women but involved a strength-related mechanism in both weaker men and women that accelerated declines in voluntary activation and slowing of contractile properties.

scholarly journals Sex differences in response to cognitive stress during a fatiguing contraction

2009 ◽  
Vol 107 (5) ◽  
pp. 1486-1496 ◽  
Author(s):  
Tejin Yoon ◽  
Manda L. Keller ◽  
Bonnie Schlinder De-Lap ◽  
April Harkins ◽  
Romuald Lepers ◽  
...  
Keyword(s):  
Voluntary Contraction ◽  
Rate Pressure Product ◽  
Men And Women ◽  
Cognitive Stress ◽  
Task Failure ◽  
Initial Strength ◽  
Flexor Muscles ◽  
Target Force ◽  
Cognitive Stressor ◽  
And Control

This study compared the time to task failure for a submaximal fatiguing contraction in the presence and absence of a cognitive stressor in men and women. In study 1, 10 men and 10 women (22 ± 3 yr of age) performed an isometric fatiguing contraction at 20% maximal voluntary contraction force until task failure with the elbow flexor muscles during two separate sessions. Subjects performed a mental-math task during one of the fatiguing contractions that aimed to increase anxiety and stress (stressor session). Salivary cortisol and reported levels of arousal (visual analog scale for anxiety, and State-Trait Anxiety Inventory scores) were elevated during the stressor session compared with a control session for both sexes ( P < 0.05). Time to task failure, however, was briefer during the stressor session compared with control ( P = 0.005) but more so for the women (27.3 ± 20.1%) than the men (8.6 ± 23.1%) ( P = 0.03). The briefer time to task failure was associated with target force ( r2 = 0.21) and accompanied by a higher mean arterial pressure, heart rate, and rate-pressure product during the fatiguing contraction in the stressor session compared with control in women. In study 2 (11 men and 8 women, 20 ± 3 yr of age), time to task failure was similar for a fatiguing contraction with simple mental-math that did not increase stress (mental-attentiveness session) and control for both men and women. The greater change in fatigability of women than men with performance of a cognitive stressor involved initial strength and increases in indexes of sympathetic neural activity and cardiac work compared with control conditions.

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.

scholarly journals Supraspinal fatigue does not explain the sex difference in muscle fatigue of maximal contractions

2006 ◽  
Vol 101 (4) ◽  
pp. 1036-1044 ◽  
Author(s):  
Sandra K. Hunter ◽  
Jane E. Butler ◽  
Gabrielle Todd ◽  
Simon C. Gandevia ◽  
Janet L. Taylor
Keyword(s):  
Sex Difference ◽  
Young Men ◽  
Motor Evoked Potential ◽  
Silent Period ◽  
Elbow Flexor ◽  
Cortical Stimulation ◽  
Voluntary Activation ◽  
Men And Women ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles

Young women are less fatigable than young men for maximal and submaximal contractions, but the contribution of supraspinal fatigue to the sex difference is not known. This study used cortical stimulation to compare the magnitude of supraspinal fatigue during sustained isometric maximal voluntary contractions (MVCs) performed with the elbow flexor muscles of young men and women. Eight women (25.6 ± 3.6 yr, mean ± SD) and 9 men (25.4 ± 3.8 yr) performed six sustained MVCs (22-s duration each, separated by 10 s). Before the fatiguing contractions, the men were stronger than the women (75.9 ± 9.2 vs. 42.7 ± 8.0 N·m; P < 0.05) in control MVCs. Voluntary activation measured with cortical stimulation before fatigue was similar for the men and women during the final control MVC (95.7 ± 3.0 vs. 93.3 ± 3.6%; P > 0.05) and at the start of the fatiguing task ( P > 0.05). By the end of the six sustained fatiguing MVCs, the men exhibited greater absolute and relative reductions in torque (65 ± 3% of initial MVC) than the women (52 ± 9%; P < 0.05). The increments in torque (superimposed twitch) generated by motor cortex stimulation during each 22-s maximal effort increased with fatigue ( P < 0.05). Superimposed twitches were similar for men and women throughout the fatiguing task (5.5 ± 4.1 vs. 7.3 ± 4.7%; P > 0.05), as well as in the last sustained contraction (7.8 ± 5.9 vs. 10.5 ± 5.5%) and in brief recovery MVCs. Voluntary activation determined using an estimated control twitch was similar for the men and women at the start of the sustained maximal contractions (91.4 ± 7.4 vs. 90.4 ± 6.8%, n = 13) and end of the sixth contraction (77.2 ± 13.3% vs. 73.1 ± 19.6%, n = 10). The increase in the area of the motor-evoked potential and duration of the silent period did not differ for men and women during the fatiguing task. However, estimated resting twitch amplitude and the peak rates of muscle relaxation showed greater relative reductions at the end of the fatiguing task for the men than the women. These results indicate that the sex difference in fatigue of the elbow flexor muscles is not explained by a difference in supraspinal fatigue in men and women but is largely due to a sex difference of mechanisms located within the elbow flexor muscles.

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.

Neuromuscular recovery from severe- and extreme-intensity exercise in men and women

2022 ◽  
Author(s):  
Andrew M Alexander ◽  
Shane M Hammer ◽  
Kaylin D Didier ◽  
Lillie M Huckaby ◽  
Thomas J. Barstow
Keyword(s):  
Knee Extension ◽  
Voluntary Contraction ◽  
Voluntary Activation ◽  
Partial Recovery ◽  
Men And Women ◽  
Task Failure ◽  
Isometric Knee Extension ◽  
Severe Intensity ◽  
Time Courses ◽  
Knee Extension Exercise

Maximal voluntary contraction force (MVC), potentiated twitch force (Qpot), and voluntary activation (%VA) recover to baseline within 90s following extreme-intensity exercise. However, methodological limitations masked important recovery kinetics. We hypothesized reductions in MVC, Qpot, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Qpot and MVC following extreme-intensity exercise would show significant recovery within 120s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed two severe-intensity (40, 50%MVC) and two extreme-intensity (70, 80%MVC) isometric knee-extension exercise bouts to task failure (Tlim). Neuromuscular function was measured at baseline, Tlim, and through 150s of recovery. Each intensity significantly reduced MVC and Qpot compared to baseline. MVC was greater at T¬lim (p<0.01) and at 150s of recovery (p=0.004) following exercise at 80%MVC compared to severe-intensity exercise. Partial recovery of MVC and Qpot were detected within 150s following Tlim for each exercise intensity; Qpot recovered to baseline values within 150s of recovery following exercise at 80%MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Qpot, future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly. NOVELTY: •Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. •Recovery of MVC and Qpot occurs much faster following extreme-intensity exercise in both men and women.

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.

scholarly journals Influence of aging on sex differences in muscle fatigability

2004 ◽  
Vol 97 (5) ◽  
pp. 1723-1732 ◽  
Author(s):  
Sandra K. Hunter ◽  
Ashley Critchlow ◽  
Roger M. Enoka
Keyword(s):  
Heart Rate ◽  
Young Women ◽  
Young Men ◽  
Emg Activity ◽  
Men And Women ◽  
Task Failure ◽  
Old Adults ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles ◽  
Old Men

The purpose of this study was to compare time to task failure for a sustained isometric contraction performed at a submaximal intensity with elbow flexor muscles by young and old men and women. Twenty-seven young (14 men and 13 women, 18–35 yr) and 18 old (10 men and 8 women, 65–80 yr) adults sustained an isometric contraction at 20% of maximal voluntary contraction torque until target torque could no longer be achieved for ≥5 s. Young adults were stronger than old adults (66.8 ± 17.9 vs. 47.7 ± 18.1 N·m, P < 0.05), and men were stronger than women (69.8 ± 17.9 vs. 47.1 ± 15.3 N·m, P < 0.05), with no interaction between age and sex ( P > 0.05). Time to task failure was longer for old than for young adults (22.8 ± 9.1 vs. 14.4 ± 7.6 min, P < 0.05) and for young women than for young men (18.3 ± 8.0 vs. 10.8 ± 5.2, P < 0.05), but there was no difference between old women and men (21.3 ± 10.7 and 24.1 ± 8.0 min, respectively, P > 0.05) or between young women and old adults ( P > 0.05). Mean arterial pressure, heart rate, average electromyographic (EMG) activity, and torque fluctuations of elbow flexor muscles increased during the fatiguing contraction ( P < 0.05) for all subjects. Rates of increase in mean arterial pressure, heart rate, and torque fluctuations were greater for young men and old adults, with no differences between old men and women ( P > 0.05). Similarly, the rate of increase in EMG activity was greater for young men than for the other three groups. EMG bursts were less frequent for old adults ( P < 0.05) at the end of the fatiguing contraction, and this was accompanied by reduced fluctuations in torque. Consequently, time to task failure was related to target torque for young, but not old, adults, and differences in task duration were accompanied by parallel changes in the pressor response.

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.

MUSCLE ENDURANCE OF THE ELBOW FLEXOR MUSCLES IN MEN AND WOMEN MATCHED FOR STRENGTH

2003 ◽  
Vol 35 (Supplement 1) ◽  
pp. S295 ◽  
Author(s):  
S K. Hunter ◽  
A Critchlow ◽  
I S. Shin ◽  
R M. Enoka
Keyword(s):  
Elbow Flexor ◽  
Muscle Endurance ◽  
Men And Women ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles
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