Author(s): VASKOVA KRYGERMEYER, A., ANANTHARAJAH, S., AGGERHOLM LAURSEN, T., HWIID POULSEN, L., GEWECKE THOMSEN, M., FREDERIKSEN, A., KOPP HANSEN, R., STIEPER KARBING, D., Institution: AALBORG UNIVERSITY, Country: DENMARK, Abstract-ID: 1290

INTRODUCTION:
The effects of inspiratory muscle training (IMT), including threshold-based training, have traditionally been evaluated using Maximal Inspiratory Pressure (MIP). While MIP provides a measure of peak inspiratory strength, it does not capture other key aspects of inspiratory muscle performance, such as endurance or total work capacity of the inspiratory muscles. Sustained Maximal Inspiratory Pressure (SMIP) integrates inspiratory muscle strength and endurance (i.e., single-breath work capacity) and may thus offer a more comprehensive assessment of inspiratory muscle function. SMIP is measured in pressure time units (PTU), which quantify the amount of pressure generated per unit of time. This explorative study aimed to compare changes in MIP and SMIP following 4 weeks of threshold-based IMT in healthy adults.
METHODS:
Fourteen healthy participants (4 males; age 26±3 yrs) completed a 4-week IMT program performed 3x/week (30 breaths/session) with a pressure-threshold device. Training intensity increased weekly throughout the intervention from 50% to 70% of individual MIP, adjusting to midpoint MIP after week 2. Inspiratory muscle performance was assessed at baseline, midpoint (2 wk), and post-intervention (4 wk) using an inspiratory flow-resistive device. The highest of three reproducible MIP measurements (<5% variation) was used. Data were analyzed using one-way repeated-measures ANOVA with G-G correction, where appropriate. Bonferroni post-hoc tests was used to identify differences between individual time points. Association between changes (Δ) in MIP and SMIP from baseline to post-intervention was examined using Pearson’s correlation coefficient.
RESULTS:
SMIP improved across time points (p=0.009), with an increase from midpoint (751.3±205.8 PTU) to post-intervention (837.1±232.3 PTU, p=0.036) and from baseline (764±221.2 PTU) and post-intervention (p<0.001). MIP also increased significantly across time points (p<0.001), with 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). There was no significant correlation between ΔMIP and ΔSMIP (r=0.44±1.23; p=0.116).
CONCLUSION:
Four weeks of pressure-threshold IMT improves both MIP and single-breath work capacity, as evaluated by SMIP, in healthy adults. The finding of no significant correlation between changes in MIP and SMIP suggests that improvements in single-breath work capacity cannot be fully explained by concurrent increases in maximal inspiratory strength. These results suggests that SMIP and MIP cannot be used interchangeably and that evaluation of SMIP therefore may provide an important additional insight into inspiratory muscle function