Gender Differences In The Fatigability Of The Inspiratory Muscles

Abstract

It is well documented that gender differences exist in human skeletal muscle fatigue; however, a comparison on the fatigability of the inspiratory muscles between females and males has received relatively little attention. PURPOSE To determine if gender differences are present in the fatigability of the inspiratory muscles during intermittent inspiratory muscle contractions. METHODS Inspiratory muscle strength was assessed noninvasively by measuring maximal inspiratory static pressure (PImax) at the mouth near residual volume. Peak pressures reached during the PImax maneuver were recorded and all PImax values are reported as the average of the two highest efforts within 5%.Females (n=11, age=23.5±1.5 yrs; Mean±SEM)) and males (n=11, age=24.1±1.5 yrs) performed resistive breathing on an inspiratory threshold device at 18 breaths/min, set at a target pressure of 65–75%PImax until task failure. Task failure was defined as the inability of the subject to generate sufficient inspiratory pressure to open the threshold valve. For each subject the rate of inspiratory muscle fatigue was calculated as the slope of PImax measured every 2 min during resistive breathing. Recovery of inspiratory muscle force was assessed by measuring PImax in 5 min increments until 45 min post-task failure. RESULTS Resting PImax was lower in females than males (F:-137.0±7.6 cmH2o;M:-172.5±9.8 cmH2o, p < 0.05). No gender difference was present in time to task failure (F:843.1±123.5 s; M:735.8±99.6 s) or in the drop in PImax at task failure (F:14.9±2.5 %; M:16.5±2.3 %). After 2 min of resistive breathing, PImax was lower in females than males (to 89.8±3.8% vs. 94.9±0.1%, respectively), reaching significance for only the females (p < 0.05). During resistive breathing, females were found to have a slower rate of fatigue than males (F:-1.5±0.4 cmH20·min−1; M:-2.9±0.3 cmH20·min−1; p < 0.05). Following task failure, females exhibited prolonged recovery of inspiratory muscle force that was longer than the recovery period found for males (15 min vs. 5 min post-task failure, respectively). CONCLUSION In spite of similar time to task failure, the rate of inspiratory muscle fatigue was slower for females than males. However, recovery of inspiratory muscle strength following task failure was prolonged for females as compared to males.