Advancing age is associated with a decline in the strength of the skeletal muscles, including those of respiration. Respiratory muscles can be strengthened with nonrespiratory activities. We therefore hypothesized that regular exercise in the elderly would attenuate this age-related decline in respiratory muscle strength. Twenty-four healthy subjects older than 65 years were recruited (11 males and 13 females). A comprehensive physical activity survey was administered, and subjects were categorized as active (n = 12) or inactive (n = 12). Each subject underwent testing of maximum inspiratory and expiratory pressures (PI(max) and PE(max)). Diaphragmatic thickness (tdi) was measured via two-dimensional B-mode ultrasound. There were no significant differences between the active and inactive groups with respect to age (75 vs. 73 years) or body weight (69.1vs. 69.9 kg). There were more women (9) than men (3) in the inactive group. Diaphragm thickness was greater in the active group (0.31 +/- 0.06 cm vs. 0.25 +/- 0.04 cm; p = 0.011). PE(max) and PI(max) were also greater in the active group (130 +/- 44 cm H(2)O vs. 80 +/- 24 cm H(2)O; p = 0.002; and 99 +/- 32 cm H(2)O vs. 75 +/- 14 cm H(2)O; p = 0.03). There was a positive association between PI(max )and tdi (r = 0.43, p = 0.03). Regular exercise was positively associated with diaphragm muscle thickness in this cohort. As PE(max) was higher in the active group, we postulate that recruitment of the diaphragm and abdominal muscles during nonrespiratory activities may be the source of this training effect.
The diaphragm and abdominal muscles can be recruited during nonrespiratory maneuvers. With these maneuvers, transdiaphragmatic pressures are elevated to levels that could potentially provide a strength-training stimulus. To determine whether repeated forceful nonrespiratory maneuvers strengthen the diaphragm, four healthy subjects performed sit-ups and biceps curls 3-4 days/wk for 16 wk and four subjects served as controls. The maximal transdiaphragmatic pressure was measured at baseline and after 16 wk of training. Maximum static inspiratory and expiratory mouth pressures and diaphragm thickness derived from ultrasound were measured at baseline and 8 and 16 wk. After training, there were significant increases in diaphragm thickness [2.5 +/- 0.1 to 3.2 +/- 0.1 mm (mean +/- SD) (P < 0.001)], maximal transdiaphragmatic pressure [198 +/- 21 to 256 +/- 23 cmH2O (P < 0.02)], maximum static inspiratory pressure [134 +/- 22 to 171 +/- 16 cmH2O (P < 0.002)], maximum static expiratory pressure [195 +/- 20 to 267 +/- 40 cmH2O (P < 0.002)], and maximum gastric pressure [161 +/- 5 to 212 +/- 40 cmH2O (P < 0.03)]. These parameters were unchanged in the control group. We conclude that nonrespiratory maneuvers can strengthen the inspiratory and expiratory muscles in healthy individuals. Because diaphragm thickness increased with training, the increase in maximal pressures is unlikely due to a learning effect.
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