Effects of Age and Sex on Inspiratory Muscle Activation Patterns During Exercise

Abstract

Purpose: Characterize the effects of age, sex, and their interaction on inspiratory muscle activation patterns during exercise. Methods: Twenty younger (20-30y, n=10 women) and twenty older (60-80y, n=10 women) subjects performed an incremental cycle exercise test. Electromyography of the scalene (EMGsca) and sternocleidomastoid (EMGscm) muscles were measured using skin surface electrodes, while diaphragm electromyography (EMGdi) and esophageal and transdiaphragmatic pressures were measured using an esophageal catheter. Electromyography data were transformed into root-mean-square with a 100ms time constant. Esophageal (PTPes) and diaphragmatic (PTPdi) pressure-time products were used as indices of total inspiratory muscle pressure production and diaphragmatic pressure production, respectively. Results: At absolute minute ventilations (V E), women and older subjects had greater EMGdi than men and younger subjects, respectively (all p<0.05), but no differences were noted when V E was expressed in relative terms (all p>0.05). Women had greater EMGsca activity than men at absolute and relative levels of V E (all p<0.05). Older subjects had greater EMGsca than younger subjects when V E was expressed relative (all p<0.05) but not absolute terms (all p>0.05). At absolute and relative levels of V E, women and older subjects had greater EMGscm than men and younger subjects, respectively (all p<0.05). Women and older subjects had a greater PTPdi/PTPes at a V E of 70 l·min-1 than men and younger subjects, respectively (both p<0.05), but no differences were noted when V E was expressed in relative terms (all p>0.05). No significant interactions between age and sex were noted (all p>0.05). Conclusion: Age and sex significantly affect inspiratory muscle activation patterns during exercise; however, the extent of the effects depends on whether comparisons are made at a solute or relative V E.