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PubMed2026

Bedtime tetrahydrocannabinol ingestion reduces morning orthostatic cardiovascular reactivity in adults: An exploratory study.

Acute cannabis use and its primary psychoactive constituent tetrahydrocannabinol (THC) can induce postural dizziness, indicating increased risk of orthostatic instability. However, it is unknown if vulnerabilities persist the morning after bedtime THC consumption. This study investigated the influence of bedtime THC consumption on cardiovascular variables during an orthostatic challenge. Nine individuals with no cannabis use and eight individuals who regularly use cannabis participated in a tilt table test associated with a 3-day in-laboratory stay. Participants underwent an acclimatization day, followed by a placebo dosing day, and a 10 mg THC dosing day. Placebo and THC pills were given 1 h before a participant's habitual bedtime, and the tilt table test was performed ~1 h upon awakening. Participants were instrumented with an electrocardiogram and an automated sphygmomanometer. Fluid intake and output were measured throughout the study. The morning after THC administration, individuals with no cannabis use reported a higher frequency of dizziness and exhibited a significant reduction in both diastolic blood pressure and heart rate reactivity to tilt (reactivity = tilt - baseline) compared to the morning after placebo. Our results indicate a potential increased risk for orthostatic instability the morning after cannabis consumption in individuals with no cannabis use history.

Humans↗

PubMed2026

Acute Haemodynamic and Perceptual Responses to Graded Intradialytic Exercise in Patients on Maintenance Haemodialysis: A Randomised Crossover Trial.

BACKGROUND: Acute responses to graded intradialytic exercise in people receiving haemodialysis remain incompletely characterised. OBJECTIVES: To examine acute haemodynamic and perceptual responses to graded intradialytic resistance exercise compared with a non-exercise control condition. DESIGN: Randomised crossover trial. PARTICIPANTS: Forty-eight clinically stable adults receiving maintenance haemodialysis. MEASUREMENTS: Participants completed seated control and graded lower-limb resistance exercise targeting Borg category-ratio 10 ratings of 3, 5 and 7. Systolic and diastolic blood pressure, mean arterial pressure, heart rate, peripheral oxygen saturation, rating of perceived exertion and acute fatigue were measured before, immediately after and 30 min after each condition. RESULTS: Responses increased progressively with perceived intensity. Compared with control, higher perceived intensity increased systolic blood pressure by 14.9 mmHg (95% confidence interval = 12.7-17.0), diastolic blood pressure by 8.4 mmHg (6.8-10.0), mean arterial pressure by 10.6 mmHg (9.2-12.0) and heart rate by 15.5 beats per minute (12.9-18.1). Rating of perceived exertion increased by 6.7 points (95% confidence interval = 6.3-7.1). Mean peripheral oxygen saturation remained between 95.1% and 97.5%, with no value below 90%. Recorded symptoms occurred in 13 out of 48 higher perceived-intensity sessions; no serious adverse events occurred. CONCLUSIONS: Graded, rating-guided intradialytic resistance exercise produced clear acute dose-response haemodynamic and perceptual changes. These findings support supervised individualisation of acute exercise dose but do not establish long-term safety or superiority of higher perceived-intensity training. TRIAL REGISTRATION: Pan African Clinical Trial Registry: PACTR202606476360900.

Humans↗

PubMed2026

Potential Links Between Physiological and Perceptual Strain in High Heat Stress.

The physiological strain index (PhSI) is widely used to quantify thermoregulatory and cardiovascular strain during heat stress. However, direct physiological measurements may not always be feasible in occupational or athletic settings. Therefore, this study aimed to examine the relationship and agreement between perceptual strain and integrated physiological strain indices during high heat stress. Ten healthy, physically active, non-heat-acclimated males (29 (7) yr; 1.79 (0.11) m; 77.4 (9.3) kg) completed two randomized crossover exercise trials in hot-dry (HD) and warm-humid (WH) environments with equivalent wet-bulb globe temperatures. Heart rate, rectal temperature, skin temperature, rating of perceived exertion, and thermal sensation were measured at baseline and every 15 minutes during 60 minutes of cycling. Physiological strain index (PhSI), adaptive physiological strain index (aPhSI), and perceptual strain index (PeSI) were calculated using validated equations. Repeated-measures correlation analyses demonstrated very strong associations between PeSI and both PhSI and aPhSI under HD (Rrm = 0.940-0.943) and WH (Rrm = 0.980-0.982; all p < 0.001). Receiver operating characteristic analyses demonstrated good-to-excellent discrimination of physiological strain by PeSI (AUC = 0.895-0.969). Mixed-effects analyses showed that higher PeSI values were associated with increased PhSI (β = 1.325, p < 0.001) and aPhSI (β = 1.459, p < 0.001). However, Bland-Altman analyses demonstrated relatively small mean biases (0.4-0.9 AU) but wide limits of agreement (-2.8 to 4.2 AU), indicating that PeSI and physiological strain indices are not interchangeable. These findings suggest that PeSI may serve as a practical adjunctive or screening indicator of physiological strain when direct physiological measurements are unavailable.

Humans↗

PubMed2026

Effects of cold-water immersion after rugby-specific training on endurance performance.

BACKGROUND: This study investigated whether whole-body cold-water immersion (CWI) following rugby-specific training influences endurance exercise performance 24 h later. METHODS: Eleven healthy male collegiate rugby players completed an incremental cycling test to determine peak oxygen uptake (V̇O 2peak ) and time to exhaustion at baseline (Pre). One week later, participants performed a standardized rugby-specific training session consisting of warm-up, skill-based passing, contact drills, individual training (i.e., conversion kicking and scrummaging), and a bronco endurance test (total duration: 180 min), followed by one of two recovery interventions in a randomized order: 1) whole-body CWI for 8 min at 15 °C (CWI) or 2) seated rest for 8 min (Control). Participants then performed the incremental cycling test 24 h after each intervention. RESULTS: Training load during the rugby-specific training, assessed using heart rate-based training load and blood lactate concentrations, did not differ between the trials. Time to exhaustion (485±72 vs. 518±77 s, P=0.107, d=0.45) and V̇O 2peak did not differ between the Control and CWI trials, whereas the relative changes in these variables from Pre were greater in the CWI than in the Control trials (both P<0.05). Oxygen uptake, minute ventilation, and rating of perceived exertion during submaximal exercise were similar across the Pre, Control, and CWI trials. CONCLUSIONS: These results suggest that whole-body CWI following rugby-specific training may be associated with favorable changes in endurance exercise performance 24 h post-intervention compared with the control condition. However, the expectancy/placebo effect of water immersion on exercise performance could not be excluded.

Humans↗