Time-dependent diastolic blood pressure and heart rate changes following acute inspiratory muscle strength training

PURPOSE: Hypertension is the most prevalent and modifiable contributor to cardiovascular diseases, yet many individuals struggle to control blood pressure due to barriers that limit participation in traditional exercise. Inspiratory muscle strength training (IMST) is a brief and time-efficient alternative that may offer cardiovascular benefit in only minutes per day. Chronic IMST has been associated with blood pressure reductions, but little is known about the acute cardiovascular and psychological effects, or whether the time of day modifies these responses. This study examined blood pressure, heart rate (HR), and psychological outcomes following a single high-resistance IMST session completed in the morning and evening. METHODS: Fourteen young (age 18-30 years) and generally healthy adults (7 men/7 women) completed a randomized crossover study comparing high-resistance IMST, consisting of 30 resisted breaths at 75 percent maximal inspiratory pressure, with a control condition ( time-matched seated rest). Each participant completed both conditions on separate days once in the morning (6 to 9 AM) and once in the evening (4 to 7 PM). Blood pressure and HR were collected after a 15 minute seated rest, immediately after each condition, and throughout 30 minutes of recovery. Psychological outcomes including anxiety, affect, mood state, and equanimity (STAI-State, PANAS, POMS, ES16) were recorded pre and post sessions. RESULTS: Systolic blood pressure (SBP) remained unchanged across all sessions, showing no effect of IMST in either the morning (p = .80) or evening (p = .79), and no differences were detected within the control conditions (p = .55). Diastolic blood pressure (DBP) demonstrated time-of-day–specific responses: during evening IMST, DBP increased by +5 mmHg at 1 minute (p = .02) and +5 mmHg at 30 minutes (p = .01), whereas morning IMST showed no DBP changes (p = .49). DBP was unchanged in the control conditions. Heart rate (HR) displayed time-dependent variation during both IMST and control. Evening IMST produced an immediate +5 bpm rise relative to pre (p = .01), while no specific HR differences emerged during evening rest. Morning IMST elicited delayed increases, with HR rising +4 bpm from 10 to 20 minutes (p = .02) and +6 bpm at 30 minutes (p < .001). Morning control also showed later HR elevations, including +5 bpm at 20 minutes (p = .03) and +4 bpm at 30 minutes (p = .05), suggesting the morning changes in HR were an effect of time and not of IMST. Psychological outcomes showed no meaningful or consistent changes attributable to IMST. CONCLUSION: Acute IMST did not change SBP across sessions. DBP and HR increased with IMST only in the evening, suggesting a potential time-of-day influence that warrants further investigation. Psychological outcomes showed no evidence of stress reduction or meaningful mood changes. Overall, IMST produced transient cardiovascular responses, and the emerging evening-specific DBP and HR pattern may help inform future chronophysiological IMST prescription strategies. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.