Tongue protrusion force and fatiguability in male and female subjects.

Limb and respiratory muscle (diaphragm) strength and fatiguability have been extensively studied in man and are known to vary with age and sex. However, in contrast to limb muscles and the diaphragm, force and fatiguability characteristics have not been studied in upper airway muscles. This study examines the hypotheses that tongue protrusion strength or fatiguability, determined by the properties of the intrinsic muscles and genioglossus, may change with age and may be reduced in males compared to females. A force transducer was used to compare maximal tongue protrusion force (Fmax) and fatiguability in 81 males and 86 females matched for age (mean+/-SD, 43+/-19 yrs, 42+/-19 yrs, respectively). Fatiguability indices were based on the time that subjects could maintain 50% of Fmax. Fmax declined with age in both males (r=-0.57, p<0.001) and females (r=-0.56, p<0.001). Fmax in males was greater than in females (males 26+/-8 N; females 20+/-7 N; p<0.001). However, after correction of Fmax for sex differences in total body muscle (fat-free mass) there was no significant difference between males and females (p=0.3). There was also no difference in fatiguability between males and females (p=0.5). In conclusion, tongue protrusion strength is greater in males compared to females, and decreases with age. If these differences also apply to patients with sleep apnoea, the reduction in maximal tongue protrusion force with age could be of relevance to the observed increase in prevalence and severity of sleep apnoea-hypopnoea syndrome in middle age, but would not explain the gender difference in prevalence.