The goal of this randomized crossover clinical trial is to investigate whether exercise-induced hypoalgesia (EIH) is influenced by circadian rhythm in healthy adults aged 18-40 years.
The main questions it aims to answer are:
* Does the time of day (morning vs. evening) influence changes in pain perception following exercise? * Do chronotype, sex, or stimulation site (bony vs. muscular) alter the magnitude of this effect?
Participants will:
* Complete questionnaires * Undergo quantitative sensory testing * Attend both morning and evening sessions in randomized crossover order
Healthy participants
age 18 to 40 years
good level of English that allow the enrolled participant to provide informed consent and complete the questionnaires provided
being categorized as "moderate" in the International Physical Activity Questionnaire (IPAQ)
inability to report pain intensity reliably
consumption of narcotics or tobacco products
regularly taking pain medications and analgesics
pregnant or planning to get pregnant
Crossover
High-Intensity Functional Training (HIFT)
BehavioralA 12-minute, instructor-led HIFT protocol delivered via the same video to all participants. After a 5-minute warm-up, participants perform six exercises targeting major muscle groups. The exercises are 4 lunges followed by one push-up, 10 high knees followed by 10 shuffles, burpees, squat jumps, skaters, and plank up-downs. Each exercise is done for 40 seconds then 20 seconds rest. The cycle repeats twice for a total of 12 minutes. Rate of Perceived Exertion (Borg scale) is recorded at baseline, post-warmup, during each rest interval, and immediately post-exercise. A physiotherapist supervises performance, ensures correct technique, and enforces safety and target intensity while motivating and encouraging the participant.
Supervised Deep Breathing
BehavioralA 12-minute deep breathing session delivered via a prerecorded audio and supervised by a physiotherapist. The breathing rhythm includes inhaling for 4 seconds and exhaling for 6 seconds for a total 1 minute, followed by 1 minute of normal breathing. This cycle is repeated six times for a total duration of 12 minutes. Participants lie supine in a comfortable position and wear headphones. A self-reported Rate of Perceived Relaxation (RPR, 0-10) is recorded before and after. This serves as a non-exercise control to account for relaxation and attention effects.
Pressure Pain Threshold (PPT)
Pressure Pain Threshold (PPT) will be measured using an algometer at standardized bony and muscular landmarks. Pressure Pain Threshold (PPT) is defined as the minimal pressure at which a participant first perceives pain. Changes in Pressure Pain Threshold (PPT) will be used to assess the magnitude of exercise-induced hypoalgesia (EIH). Unit: kg/cm²
Pressure Pain Tolerance (PPTol)
Pressure Pain Tolerance (PPTol) will be measured using an algometer at standardized bony and muscular landmarks. Pressure Pain Tolerance (PPTol) is defined as the maximal pressure the participant is willing to tolerate. Changes in Pressure Pain Tolerance (PPTol) will be used to assess pain modulation in response to exercise across circadian phases. Unit: kg/cm²
Munich Chronotype Questionnaire (MCTQ)
Chronotype will be assessed using the Munich Chronotype Questionnaire (MCTQ). Participants will be classified as morning or evening chronotypes to examine whether individual circadian preference moderates exercise-induced hypoalgesia.
Pain Catastrophizing (PCS)
Pain-related cognitions will be measured using the Pain Catastrophizing Scale (PCS) to control for potential psychological influences and understandings on pain perception. PCS is scored according to a 5-point Likert scale ranging from 0 = not at all to 4 = all the time with a maximum score of 52, with higher scores \>30 indicating increased pain catastrophizing.
Fear of Pain (FPQ-9)
Fear of pain will be assessed using the Fear of Pain Questionnaire-9 (FPQ-9), as psychological fear responses may influence pain reporting. Fear of Pain Questionnaire-9 (FPQ-9) is scored by using a 5-point Likert scale with a score ranging from 9 to 45 with higher scores indicate greater fear of pain.
Brief Version of the Pittsburgh Sleep Quality Index (B-PSQI)
The Brief Pittsburgh Sleep Quality Index (B-PSQI) will be used to assess participants' sleep patterns and their potential influence on pain modulation. Total score ranges between 0 and 15, where higher values suggest worse quality of sleep. Scores from 0 to 5 indicate good sleep quality and scores of ≥6 poor sleep quality.
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