The Role of Fatigue Associated With Strength Training in Exercise-induced Hypoalgesia

The Role of Fatigue Associated With Different Protocols of Strength Training in Exercise-induced Hypoalgesia: A Randomized Crossover Trial

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.

Inclusion Criteria:

• Healthy, asymptomatic subjects
• Being physically active

Exclusion Criteria:

• Experiencing episodes of acute pain in any part of the body.
• Having chronic pain or a recent history of chronic pain conditions considered resolved within the last 6 months.
• Having a serious illness or inability to perform moderate or intense physical activity.
• Having taken pain relievers, fever reducers, anti-inflammatory drugs (NSAIDs), steroids, opioids, or similar medications in the 24 hours before a session.
• Having consumed alcohol or other psychoactive substances, caffeine, or other stimulants in the 24 hours before a session.
• Having performed tiring physical activity or strength exercise in the 24 hours before a session.