Sex Differences in Fatigue Resistance Are Muscle Group Dependent

Abstract

Purpose-Females are often reported to be generally more resistant to fatigue than males for relative intensity tasks. This has been observed repeatedly for elbow flexors, whereas at the ankle sex differences appear less robust, suggesting localized rather than systemic influences. Thus, the purpose of this study was to examine sex differences in fatigue resistance at muscle groups in a single cohort and which factors, if any, predict endurance time.Methods-Thirty-two (16 female) young adults (19 to 44 yrs) performed sustained isometric contractions at 50% maximum voluntary isometric contraction to failure for elbow flexion and ankle dorsiflexion. Pain, exertion, and muscle electromyography (EMG) were assessed throughout. Selfreported baseline activity was measured using the International Physical Activity Questionnaire.Results-Females (112.3 ± 6.2 sec) were significantly more resistant to fatigue than males (80.3 ± 5.8 sec) at the elbow (p=0.001); but not at the ankle (p=0.45; 140.6 ± 10.7 vs. 129.2 ± 10.5 sec). Peak torque was greater in males than females (p < 0.0001) at the ankle (45.0 ± 1.7 vs. 30.1 ± 1.0 Nm) and the elbow (75.7 ± 3.1 vs. 34.4 ± 2.2 Nm). Peak torque was significantly related to endurance time at the elbow (R 2 = 0.30), but not at the ankle (R 2 = 0.03). Peak pain, rate of pain increase, peak exertion, EMG, and baseline physical activity did not differ between sexes.Conclusion-Sex differences in fatigue resistance are muscle group specific. Women were more fatigue-resistant at the elbow but not the ankle during a sustained isometric contraction. Further, factors which may contribute to fatigue-resistance for one muscle group (e.g. sex, peak torque) may not be critical at another.

Biomechanical constraints on the feedforward regulation of endpoint stiffness

“…3). At 30% of maximum muscle force, a value that typically can be sustained for Ն2 min (Avin et al 2010), the orientation of endpoint stiffness could be changed by 19°in the counterclockwise direction and 50°in the clockwise direction, for a total range of 69°. At 10% maximum muscle force, this range was reduced to only 52°.…”

Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

“…A 50-min resting period was given to the subject between the tasks to limit the potential influence of the first fatiguing task on the second one, performed with a different muscle group. This 50-min recovery period was longer than those reported in previous studies with comparable protocols [10 min of recovery in Smolander et al (69), 20 min in Avin et al (6), and 30 -60 min in Williams (76)]. The order of the two sessions was randomized, and the order between tasks within a session was counterbalanced between subjects.…”

“…TIME TO TASK FAILURE of a sustained submaximal isometric contraction (i.e., endurance time, ET) depends on physiological factors such as relative force level (30,35), muscle fiber type composition (16,51,77), muscular activation strategy (6,19,38), muscle size (36), and length (54,58) but also depends on psychological factors such as motivation, mood, and expectation (24). Whereas the task dependency of ET is well documented (23,25,26), little is known about muscle fatigue characteristics induced by a given task sustained until failure in different muscle groups, in the same individuals.…”

Sex differences in human fatigability: mechanisms and insight to physiological responses

“…(Maughan et al, 1986, Fulco et al, 1999, Hunter and Enoka, 2001, Hunter et al, 2002, Clark et al, 2003, Russ and Kent-Braun, 2003, Hunter et al, 2006b, Hunter et al, 2009, Guenette et al, 2010)] (Figure 1A). Some muscle groups, such as the ankle dorsiflexors, demonstrate less of a sex difference in fatigability than the elbow flexor muscles (Kent-Braun et al, 2002, Hunter et al, 2008, Avin et al, 2010), and for the elbow extensor muscles there is no sex difference for a sustained contraction (Dearth et al, 2010). The explanation for the differences in the magnitude of the sex difference between muscle groups likely involves a combination of muscular mechanisms which include contractile properties, fibre type proportion and perfusion.…”