Time-Efficient, High-Resistance Inspiratory Muscle Strength Training Increases Exercise Tolerance in Midlife and Older Adults

Abstract

ABSTRACT Purpose To determine if time-efficient, high-resistance inspiratory muscle strength training (IMST), comprising 30 inhalation-resisted breaths per day, improves cardiorespiratory fitness, exercise tolerance, physical function and/or regional body composition in healthy midlife and older adults. Methods We performed a double-blind, randomized, sham-controlled clinical trial (NCT03266510) testing 6 weeks of IMST (30 breaths/day, 6 days/week, 55%-75% maximal inspiratory pressure) versus low-resistance sham training (15% maximal inspiratory pressure) in healthy men and women aged 50-79 years. Subjects performed a graded treadmill exercise test to exhaustion, physical performance battery (e.g., handgrip strength, leg press), and body composition testing (dual x-ray absorptiometry) at baseline and after 6 weeks of training. Results Thirty-five participants (17 women, 18 men) completed high-resistance IMST (n = 17) or sham training (n = 18). Cardiorespiratory fitness (V̇O2peak) was unchanged, but exercise tolerance, measured as treadmill exercise time during a graded exercise treadmill test, increased with IMST (baseline: 539 ± 42 s, end-intervention: 606 ± 42 s; p = 0.01) but not sham training (baseline: 562 ± 39 s, end-intervention: 553 ± 38 s; p = 0.69). IMST increased peak respiratory exchange ratio (baseline: 1.09 ± 0.02, end-intervention: 1.13 ± 0.02; p = 0.012), peak ventilatory efficiency (baseline: 25.2 ± 0.8, end-intervention: 24.6 ± 0.8; p = 0.036) and improved submaximal exercise economy (baseline: 23.5 ± 1.1 ml/kg/min, end-intervention: 22.1 ± 1.1 ml/kg/min; p < 0.001); none of these factors were altered by sham training (all p > 0.05). Changes in plasma acylcarnitines (targeted metabolomics analysis) were consistently positively correlated with changes in exercise tolerance following IMST but not sham training. IMST was associated with regional increases in thorax lean mass (+4.4%; p = 0.06) and reductions in trunk fat mass (-4.8%; p = 0.04); however, peripheral muscle strength, muscle power, dexterity and mobility were unchanged. Conclusions These data suggest that high-resistance IMST is an effective, time-efficient lifestyle intervention for improving exercise tolerance in healthy midlife and older adults.