Training Specificity of Inspiratory Muscle Training Methods, A Randomized Trial
Authors: Marine Van Hollebeke, Rik Gosselink, Daniel Langer
DOI / Source: https://doi.org/10.3389/fphys.2020.576595
Date: 03 December 2020
Reading level: Intermediate
Why This Matters for Freedivers
If you use inspiratory muscle training (IMT) to help with deeper, calmer, more controlled breathing, this paper shows an important truth: your results depend on how you train, not just that you train. Some common IMT methods mainly strengthen you at low lung volumes, while others improve strength and airflow across the whole inhale, which is closer to what freedivers actually need when taking a big final breath and controlling breathing under stress.
Synopsis
Inspiratory muscle training (IMT) is usually marketed as a simple idea: breathe in against resistance, get stronger. But your breathing muscles don’t produce the same force at every point of an inhale. They’re generally strongest when the lungs are emptier and get weaker as the lungs fill. That means the “same” training load can feel very different depending on where you start the breath — and it can accidentally train you for a narrow part of the inhale.
This study tested exactly that. Forty-eight healthy adults were split into three groups for 4 weeks of IMT (three short sessions per day, 30 breaths per session, using the highest tolerable load). The three methods were: 1) Standard pressure-threshold training starting from residual volume (RV) (very empty lungs). 2) Tapered flow resistive loading (TFRL) starting from RV, where the resistance gradually eases as you inhale. 3) Pressure-threshold training starting from functional residual capacity (FRC) (a more normal “resting” lung volume).
Before and after training, they measured: - Max inspiratory pressure (PImax) at three lung volumes (RV, FRC, and mid-to-high volume). - Max inspiratory flow (VImax) at the same volumes, and against different external loads.
The results were a clear lesson in “you get good at what you practice”: - The standard method (threshold from RV) improved strength mainly at lower lung volumes and did not meaningfully improve maximal inspiratory flow. - TFRL from RV improved both strength and maximal inspiratory flow at all lung volumes, suggesting a more “full-range” training stimulus. - Threshold from FRC improved strength and flow especially at higher lung volumes, which is closer to the mechanics of breathing during exercise (and closer to the “big inhale” part that matters to many divers).
In practical terms: if your goal is not just “stronger inhale” but also the ability to inhale powerfully and smoothly when the lungs are already filling, then training method and starting lung volume matter a lot. The paper argues that the standard approach can turn into a high-pressure, low-flow grind at higher lung volumes, while TFRL and FRC-start training better support improvements where the standard method tends to stall.
Abstract
Inspiratory muscle training (IMT) is commonly performed with pressure threshold loading starting from residual volume. This randomized trial compared three IMT protocols—pressure threshold loading from residual volume, tapered flow resistive loading from residual volume, and pressure threshold loading from functional residual capacity—over four weeks in healthy volunteers. Maximal inspiratory pressure (PImax) and maximal inspiratory flow (VImax) were assessed at multiple lung volumes before and after training. Standard threshold training primarily improved PImax at lower lung volumes and did not significantly improve VImax. In contrast, tapered flow resistive loading and threshold training initiated from functional residual capacity produced more consistent improvements in inspiratory muscle function at higher lung volumes, with broader gains in both pressure and flow outcomes.