In plain terms: Inspiratory Muscle Training has some human trial evidence supporting it, but the evidence is not yet strong enough for EBL to call it established. It is worth knowing about and worth discussing with your clinician.
Inspiratory Muscle Training
The evidence as the record states it
Craighead et al. (Journal of the American Heart Association, 2021; PMID 34184544): double-blind, sham-controlled trial, 36 completers aged 50 to 79 with systolic pressure at or above 120 mmHg, 30 breaths a day at about 75% of maximal inspiratory pressure for 6 weeks; casual systolic pressure fell from 135 to 126 mmHg with training and did not change with sham, and 24-hour systolic pressure was lower than sham. Li et al. (Journal of Clinical Hypertension, 2023; PMID 37803506): 12 articles, 386 participants, systolic -7.93 mmHg and diastolic -3.80 mmHg. Craighead et al. (Journal of Applied Physiology, 2022; PMID 36107991): five sham-controlled pilot trials pooled, systolic -9 mmHg with training and no change with sham. Chen et al. (Sleep and Breathing, 2023; PMID 36576599): 7 trials, 160 patients with sleep apnea, systolic -10.77 mmHg, low certainty, apnea-hypopnea index unchanged. Zuo et al. (Annals of the American Thoracic Society, 2026; PMID 41721779): 10 trials in sleep apnea, systolic -6.63 mmHg, no improvement in apnea-hypopnea index. Silva de Sousa et al. (Journal of Sleep Research, 2024; PMID 37258418): 13 trials at high risk of bias, training may not beat sham on the apnea-hypopnea index. Smaller trials: Vranish et al. (Sleep, 2016; PMID 27091540), single-blind, 24 adults with sleep apnea, systolic 12.3 mmHg lower than sham; Ramos-Barrera et al. (J Appl Physiol, 2020; PMID 32730174), 25 older adults with sleep apnea, systolic fell 8.8 mmHg within the training group while the low-resistance control did not change; Ferreira et al. (Int J Cardiol, 2013; PMID 21985749), 13 hypertensive patients, 24-hour systolic fell from 133.2 to 125.2 mmHg within the training group, no between-group comparison reported; Ublosakka-Jones et al. (Exp Gerontol, 2018; PMID 29604403), 32 older adults with treated systolic hypertension, home systolic fell 20 mmHg with slow loaded breathing against 5 mmHg with deep breathing.
Evidence by specific use
Why Grade B and not Grade A
Grade B reflects moderate human evidence -- typically a single strong trial, multiple smaller trials, or surrogate endpoint data without hard clinical outcome replication. To reach Grade A, Inspiratory Muscle Training would require at least one additional independent randomized trial demonstrating a hard clinical endpoint or objectively measured functional outcome in a comparable population.
What this grade covers and what it does not
What would move this grade
An independent randomized trial demonstrating a hard clinical endpoint -- mortality, major adverse event, or objectively confirmed functional improvement -- in an adequately powered sample, with results independently replicated, would support Grade A.