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.

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.

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 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.

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.

The effect of a contralateral contraction on maximal voluntary activation and central fatigue in elbow flexor muscles

2003 ◽  
Vol 150 (3) ◽  
pp. 308-313 ◽  
Author(s):  
Gabrielle Todd ◽  
Nicolas T. Petersen ◽  
Janet L. Taylor ◽  
S. C. Gandevia
Keyword(s):  
Central Fatigue ◽  
Elbow Flexor ◽  
Voluntary Activation ◽  
Flexor Muscles ◽  
Elbow Flexor Muscles
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