Exercise Induced Hypoalgesia

Strength exercise is an active and dynamic activity that involves applying force against a resistance. This produces fatigue, seen as a reduced ability to apply force during and after the exercise, and perceived effort, which is a person's subjective feeling of how hard they are working. Strength exercise can also be used for therapy, as it has many benefits for different parts of the body. One of these is changing how the individual feels pain. It has been shown that doing strength exercises can reduce pain perception, a phenomenon called exercise-induced hypoalgesia (EIH), although the exact physical reasons and the amount of exercise needed to cause this effect are not yet known. One of the most studied exercises in this area is the leg extension machine. This is a specific exercise where the legs move freely (open kinetic chain) and the machine guides the movement, which helps keep things stable and limits the effect of other factors. It is usually used to strengthen and grow the muscles in the front of the thigh, especially the quadriceps, but it can also be used to study the effects on EIH. The main goal of this study is to see if fatigue and perceived effort during strength exercise are important for EIH to happen in healthy people. Participants will complete 3 sessions, at least 7 days apart. These will include a control session and 2 sessions designed to show different levels of fatigue. Before, during, and after the sessions, the investigators will measure pain sensitivity, isometric strength, and perceived effort. Also, there will be a test to find the maximum weight for 10 repetitions and several questionnaires to collect basic info (sex, age, height...), weekly physical activity, experience with strength training, and other factors like sleep quality, stress, and mood. All this information will be completely anonymous when the study results are shared.

Exercise has shown multiple beneficial effects in both healthy and post-stroke populations. One of these is the acute reduction in sensitivity to painful stimuli, called exercise-induced hypoalgesia (EIH). This phenomenon has been studied since 1979 and has shown improvements in pain thresholds with both aerobic and resistance training in healthy, pain-free populations and different chronic pain conditions. Although there has been extensive research on EIH in healthy populations and those with chronic musculoskeletal pain, surprisingly little attention has been given to individuals with neurological pathologies. Chronic pain is found in more than 50% of patients after stroke, and 70% of affected individuals experience pain on daily activities. Reported prevalences of post-stroke pain (PSP) between different studies, but there is a general consensus that it is an underreported phenomenon. Patients with pain experience greater cognitive and functional decline, fatigue, depression and lower quality of life. Multiple factors contribute to PSP, and various approaches exist to treat all the variables influencing it. This study aims to compare the effects of exercise on pain perception in healthy individuals and stroke patients without pain, using the same cardiovascular training protocol, to better understand the mechanisms of EIH and its maintenance after stroke, ultimately aiming to improve the treatment of people with stroke.

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