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

Abstract

Purpose: This study aimed 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 wk of IMST (30 breaths per day, 6 d·wk -1 , 55%-75% maximal inspiratory pressure) versus low-resistance sham training (15% maximal inspiratory pressure) in healthy men and women 50-79 yr old. 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 wk of training.

Results: Thirty-five participants (17 women, 18 men) completed high-resistance IMST ( n = 17) or sham training ( n = 18). Cardiorespiratory fitness (V̇O 2peak ) 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 RER (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 -1 ⋅min -1 ; end intervention, 22.1 ± 1.1 mL·kg -1 ⋅min -1 ; 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 after 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.

Figure 1.

A) Total treadmill exercise time, a measure of exercise tolerance; B) peak oxygen consumption (V̇O₂peak), a measure of cardiorespiratory fitness; and C) respiratory exchange ratio (V̇CO₂/V̇O₂) at peak exercise before (pre) and at the end of (post) 6 weeks of high-resistance IMST (n=15, 7 men, 8 women) or sham training (n=18, 10 men, 8 women). Statistical analyses were done with a two-way (group x time) ANOVA with Sidak’s post-hoc test. Box indicates interquartile range and mean, whiskers indicate minimum and maximum values; individual data points are shown.

Figure 2.

Oxygen consumption (V̇O₂) at a submaximal workload requiring ~80% of V̇O₂peak before (pre) and at the end of (post) 6 weeks of high-resistance IMST (n=15: 7 men, 8 women) or sham training (n=18, 10 men, 8 women). Pre and post workload (i.e., treadmill speed and grade) were kept consistent within subjects. Statistical analyses were done with a two-way (group x time) ANOVA with Sidak’s post-hoc test. Box indicates interquartile range and mean, whiskers indicate minimum and maximum values; individual data points are shown.