In this parallel group crossover randomized trial, young and older adults participants will be randomly assigned to 2 experimental conditions: a LIRT+BFR and HIRT. These two conditions were chosen because acute LIRE+BFR and HIRE have been shown to increase similarly heart rate and blood pressure in older adults. Each participant will report to the Laboratory on 3 occasions, at least 1 week apart. In visit 1, participants will have their body weight and height measured, and be evaluated twice for macro- and microvascular function within 30 min at resting condition (control). After that, they will become acquainted with the exercise protocol and determine their one-repetition maximum (1RM) for the bilateral leg press exercise and knee extension. In visits 2 and 3, participants will perform the experimental conditions in a simple randomized order, to which participants will be blinded until arrival at the laboratory.
The allocation sequence will be generated by Dr. XM, using a web-generated simple randomization scheme (http://www.randomizer.org/), and placed in sequentially numbered, opaque, sealed envelopes to ensure concealment of the allocation process and minimize potential biases to researchers and participants, delivered to field researchers, who will be blind, on the day of the first visit.
Each session will begin with 15 minutes of supine rest on a cushioned examination table. This will be followed by: 1) assessment of brachial blood pressure, heart rate and microvascular function at rest as measured by finger photoplethysmography (Vicorder, Berlin, Germany). Following these assessments, participants will engage in one of the previously randomized resistance training experimental conditions for roughly 30 min. After that, participants immediately return to the examination table and will recover in the supine position for 30 minutes, during which brachial blood pressure, heart rate and microvascular function will be re-evaluated 5-, 30-min intervals into recovery and compared to those at rest. Post-exercise time measurements are aimed to characterize the post-exercise biphasic response of the microvascular function.
Participants will be instructed to avoid caffeine and alcohol for 24 hours, and fully void before the session. They will also be advised to avoid vigorous exercise-related activities 24 hours before each session, including the familiarization session. All evaluations will be led by 4 physiotherapy students per participant (4:1), with over 30h of training in the evaluation and training protocols. During the participant's time in the laboratory, a certified professional in basic life support and automated external defibrillators (AEDs), will be present at the clinic.
Based upon an effect size of 0.141 derived from the mean and dispersion response of carotid-radial pulse wave velocity to Non-Autoregulated Blood Flow Restriction resistance exercise. 48 participants are required, (24 per group), matched for sex, assuming a 5% alpha error, and 20% beta error, with a 1:1 ratio between groups. To account for a 10% dropout rate, a total of 52 will be recruited.
Young adults at Egas Moniz School of Health & Science will be recruited through Instagram ads and strategically placed posters. Interested individuals will use a QR code to access a form with study details and eligibility criteria. Eligible participants will receive an electronic informed consent form to sign before their first visit. Older adults will be recruited from local senior centers, gyms, and community programs via email. Those who meet the eligibility criteria will receive a printed informed consent form to sign before their first clinic visit.
