Effect of Palmitoylethanolamide on Muscle Recovery Following a Single Bout of Resistance Exercise

Study design The protocol entails a double-blind, placebo-controlled, crossover trial design in which non-elite male athletes (training load >5h/wk, n=14) are enrolled. Participants undergo 2 experimental sessions in which they receive PEA or placebo in a randomized order. The two sessions are separated by a 3-week wash out period to allow a full recovery from the eccentric exercise bout. The scientific rationale to use a within-subjects design is based on the assumption of reduced data variability and increased statistical power compared to a between-subjects design. Additionally, a double-blind placebo controlled trial is used to prevent treatment bias and placebo effects.

Participants are randomly allocated to receive PEA or appearance-matched placebo supplements twice a day for a total of 6 days. Three days before the start of supplementation (D-3), baseline measurements are collected during which participants report to the laboratory in a fasted and rested state and mark their perceived muscle soreness on a visual analogue scale (VAS). Next, blood samples and muscle biopsies are collected, after which maximal isometric, eccentric and concentric voluntary contractions and jump height (Counter Movement Jump and Squat Jump) are assessed. Furthermore, participants complete the Pittsburgh Sleep Quality Index (PSQI) to evaluate sleep quality and quantity of the previous month. Three days after the collection of baseline measurements (D0), participants return to the laboratory in a rested and fasted state. After collection of a fasted blood sample, they receive their first supplement with a light standardized breakfast (~500 kcal, 60% carbohydrates, 20% protein, 20% fat). Afterwards, they rate their perceived muscle soreness and fill in the St. Mary's Hospital questionnaire (to evaluate their sleep quality and quantity from the previous night). One hour after supplement intake, participants perform a unilateral eccentric exercise (EE) bout consisting of 24 sets of 10 eccentric contractions of the knee extensors. Measurements of maximal voluntary contractions and jump height are repeated 24, 48, 72 and 120h following EE. Additionally, blood samples are collected 24, 48, 72, 96 and 120h following EE, and muscle biopsies are collected 48h following EE. Furthermore, participants rate their perceived muscle soreness, complete a food diary and fill in the St. Mary's Hospital questionnaire (daily), for the entire duration of the experimental protocol.

Screening Volunteers are screened to assess their eligibility to participate in the study based on in- and exclusion criteria . During the screening, body mass is measured using a digital balance with an accuracy of 0.1 kg and body height is measured with an accuracy of 1 cm. Furthermore, a medical questionnaire is obtained to assess participants' general health. When volunteers are deemed eligible according to the screening results and the in- and exclusion criteria, they are included in the study.

Familiarization To prevent any learning effect during the intervention trial, all participants are familiarized with the test equipment at least one week before the start of the trial. Participants are invited to perform 3 submaximal isometric, eccentric and concentric voluntary contractions and 3 counter movement jumps and squat jumps as described in detail below (see paragraph 76.3 on page 12). Participants are instructed about the proper technique of the movements and are supervised by a staff member at all times. During the familiarization, individual settings on the isokinetic dynamometer are determined and will be used in all subsequent measurements. Additionally, participants are instructed on how to complete their food diaries.

Randomization: Participants are randomly allocated to one of the supplemental groups (PEA orplacebo) during the first session. After a wash out period of 3 weeks participants are crossed over to the other supplement group. Randomization is performed by a researcher within our lab who is not involved in any of the experimental procedures. As such, the participants as well as the researchers performing the measurements are unaware of the order in which participants receive the different supplements. The randomization sequence will be generated by a member of the research group that is not involved in the current study using an online tool (RANDOM.ORG - Integer Set Generator). Identity concealment codes are used in the randomization list which is in the safe custody of the same member of the research group that is not involved in the current study.