Author(s): ANANTHARAJAH, S., AGGERHOLM LAURSEN, T., HWIID POULSEN, L., VASKOVA KRYGERMEYER, A., GEWECKE, M., FREDERIKSEN, A., STIEPER KARBING, D., KOPP HANSEN, R., Institution: AALBORG UNIVERSITY, Country: DENMARK, Abstract-ID: 1321

INTRODUCTION:
Inspiratory muscle training (IMT) strengthens the inspiratory muscles and is commonly used to improve inspiratory muscle function in healthy and patient populations with impaired respiratory function. Previous studies using pressure-threshold IMT have shown inconsistent results. This may be due to some studies have prescribed training load based on a certain percent of the maximal inspiratory pressure (MIP) measured at baseline, and in doing so fail to account for training-induced increases in inspiratory muscle strength during the study period. Disregarding intervention-induced increases in MIP may lead to suboptimal adaptations as the relative intensity will be overestimated. This study aimed to evaluate the effect of a 4-week IMT program with intermediate load adjustment on maximal inspiratory pressure (MIP).
METHODS:
Fourteen healthy participants (4 males; age 26±3 yrs) completed a 4-week IMT intervention performed 3x/week (30 breaths/session) with a pressure-threshold device (Powerbreathe Classic, Powerbreathe, International Ltd., UK). Training intensity progressively increased throughout the intervention from 50% to 70% of MIP (week 1 = 50%, week 2 = 60%, week 3 = 60%, week 4 = 70%). MIP was assessed at baseline, midpoint (after 2 weeks), and post-intervention (after 4 weeks). The midpoint MIP was applied in calculating training load after two weeks to adjust for training-induced changes. Participants performed a voluntary maximal and sustained inspiratory effort following complete expiration until residual volume. Participants were encouraged to inspire deeply generating as much pressure as possible within 2 seconds and continue to inspire maximally until reaching total lung capacity. The highest of three reproducible MIP measurements (<5% variation) was used. Data were analysed using one-way repeated-measures ANOVA. Bonferroni post-hoc tests was used to identify differences between time points.
RESULTS:
MIP improved across time points (p < 0.001). MIP showed significant increases from baseline (112.6 ± 24 cmH₂O) to midpoint (132.3 ± 31.7 cmH₂O, p = 0.01), from midpoint to post-intervention (149.5 ± 31.5 cmH₂O, p = 0.018), and from baseline to post-intervention (p < 0.001). The intermediate load adjustment had a significant influence on the absolute training load. For example, the load at 60% MIP measured at baseline (before adjustment) was 67.5 ± 14.4 but increased to 79.5 ± 19 cmH₂O after adjustment at the end of week 2 (paired t-test, p = 0.003) corresponding to a 12 cmH₂O higher prescribed training load compared to if the unadjusted value for that week had been used.
CONCLUSION:
Four weeks of pressure-threshold IMT significantly improved MIP in healthy adults. The use of intermediate load adjustment ensured that the relative load adjustment was prescribed based on the most recent measure of MIP, thus matching the participants’ increasing strength across the intervention.