The magnitude of failure in voluntary drive after fatiguing contractions of different intensities in men and women is not known. The purpose of this study was to compare the time to task failure and voluntary activation of men and women for a sustained isometric contraction performed at a low and high intensity with the elbow flexor muscles. Nine men and nine women sustained an isometric contraction at 20% and 80% of maximal voluntary contraction (MVC) force until task failure during separate sessions. The men had a shorter time to failure than women for the 20% but not the 80% MVC task. Voluntary activation was reduced to similar levels for the men and women at the end of the fatiguing contractions but was reduced less after the 80% MVC task than the 20% MVC contraction. Twitch amplitude was reduced similarly at task failure for both sexes and to similar levels at termination of the 20% and 80% MVC tasks. The rate of change in mean arterial pressure was the main predictor of time to failure for the low-force sustained contraction. These results suggest that women experienced greater muscle perfusion, less peripheral fatigue, and a longer time to task failure than men during the low-force fatiguing contraction. However, the low-force task induced greater central fatigue than the high-force contraction for both men and women. Thus, low-force, long-duration fatiguing contractions can be used in rehabilitation to induce significant fatigue within the central nervous system and potentially greater neural adaptations in men and women.

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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 (r(2) = 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.

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Introduction Whether there is a gender difference in fatigue and recovery from maximal velocity fatiguing contractions and across muscles is not understood. Methods Sixteen men and 19 women performed 90 isotonic contractions at maximal voluntary shortening velocity (maximal velocity concentric contractions, MVCC) with the elbow flexor and knee extensor muscles (separate days) at a load equivalent to 20% maximal voluntary isometric contraction (MVIC). Results Power (from MVCCs) decreased similarly for men and women for both muscles (P > 0.05). Men and women had similar declines in MVIC of elbow flexors, but men had greater reductions in knee extensor MVIC force and MVIC electromyogram activity than women (P < 0.05). The decline in MVIC and power was greater, and force recovery was slower for the elbow flexors compared with knee extensors. Conclusions The gender difference in muscle fatigue often observed during isometric tasks was diminished during fast dynamic contractions for upper and lower limb muscles.

Supraspinal fatigue contributed to fatigability of the knee extensors more for men than for women after a maximal isometric task, whereas contractile mechanisms explained the sex difference in torque recovery after the fast-velocity dynamic task. The mechanisms for the sex difference in fatigability are task dependent.

This study provides a robust measuring method of the femoral neck anteversion angle for use in a total hip replacement pre-planning program. The femora of 24 patients (69.3 +/- 6.3 years old) were CT-scanned and converted into three-dimensionally volume-rendered models in ORTHODOC (ISS Inc., CA, USA) which is the pre-planning software for ROBODOC surgery. The Mod.ISS method (the modified ISS method), designed by authors, measures the anteversion angle of the proximal-most femoral neck confluence on the plane perpendicular to the femoral mechanical axis. 3D FNC method proposed by the authors of the present study involves measurement of the anteversion angle of three-dimensional femoral neck center on a plane perpendicular to the posterior femoral plane and parallel to the posterior condylar axis. Here, we found that interobserver reproducibility was 1.8 degrees (SD = 1.3) for the Mod.ISS method and 2.4 (SD = 1.9) for the proposed 3D FNC method. The anteversion angle of the local femoral neck axis was measured as theta = 25.3(L/D) + [corrected] 5.4 in L/D = 0.1-0.6, where L/D is distance (L) from the proximal-most neck confluence along the femoral mechanical axis, normalized with respect to the diameter of the femoral head (D). At L/D = 0.5, the anteversion angle of the femoral neck axis was coincident with the average femoral neck anteversion determined by the 3D FNC method. We conclude that the 3D FNC method is a gold standard for measuring the femoral neck anteversion applicable during both pre-operative and post-operative stages, because its femoral neck center can be determined in three-dimensional space during both stages.

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