Effects of Protein and NAC Co-ingestion on Skeletal Muscle Recovery

Participants will initially undergo baseline testing including assessment of their (i) anthropometrics, (ii) body composition via DXA, (iii) habitual physical activity level via accelerometry, (iv) resting metabolic rate via indirect calorimetry, (v) daily dietary intake via 7-day dietary recalls and (vi) cardiorespiratory fitness using a treadmill ramp test. After baseline testing, participants will be assigned to (a) a Placebo, (b) a N-acetylcysteine (NAC) or (c) a N-acetylcysteine + Whey protein (PRoNAC) group, in a randomized, double-blind, placebo-controlled, parallel group, repeated measures design. In all groups, participants will execute an eccentric exercise protocol on an isokinetic dynamometer consisted of 150 eccentric muscle contractions. Before exercise as well as at 1-, 2-, 3-, 24-, 48- and 72-hours post-exercise they will undergo assessment of their maximal voluntary isometric peal torque, maximal countermovement jump height and muscle soreness level. In addition, blood sample will be drawn before exercise and at 24-, 48- and 72-hours post-exercise for the determination of myoglobin concentration, reduced (GSH) and oxidized (GSSG) glutathione content, protein carbonyl formation and catalase activity.

Throughout the 4-day experimental period (Day 1: exercise day, Days 2, 3 and 4: 24-, 48- and 72-hours post-exercise, respectively) participants will receive daily, 3 doses from the respective supplement as follows: the 1st dose at mid-morning (between breakfast and lunch), the 2nd dose at mid-afternoon (post-exercise on day 1 and between lunch and dinner on days 2-4) and the 3rd dose before sleep. In Placebo group, participants will be supplemented with 0.31 gr of maltodextrin per kg of body weight in the first two servings (at mid-morning and mid-afternoon supplements) and with 0.49 gr of maltodextrin per kg of body weight in the pre-sleep serving (1.1 gr maltodextrin/kg BW/day). In NAC group, participants will be supplemented with 13.33 mg of N-acetylcysteine per kg of body weight per serving (40 mg NAC/kg BW/day). In PRoNAC group participants will be supplemented with 0.31 gr of whey protein and 13.33 mg of N-acetylcysteine per kg of body weight in the first two servings (at mid-morning and mid-afternoon supplements) and with 0.49 gr of whey protein and 13.33 mg of N-acetylcysteine per kg of body weight in the pre-sleep serving (1.1 gr Whey protein + 40 mg NAC /kg BW/day).

Inclusion criteria

• Free of asthma, kidney disease, bleeding disorders, peptic ulcers.
• Free of musculoskeletal injuries and limitations.
• Abstain from dietary energy restriction.
• Do not use medication such as anti-inflammatory drugs, antibiotics, antihypertensive drugs or anticoagulants.
• Do not use dietary supplements such as protein, carbohydrate, antioxidants, vitamins etc.
• Free of N-acetylcysteine intolerance.
• Non-smokers.
• Abstain from alcohol throughout the study.

Exclusion criteria

• Presence of asthma, kidney disease, bleeding disorders, peptic ulcers.
• Musculoskeletal injuries and limitations.
• Dietary energy restriction.
• Use of anti-inflammatory drugs, antibiotics, antihypertensive drugs or anticoagulants.
• Use of dietary supplements such as protein, carbohydrate, antioxidants, vitamins etc.
• N-acetylcysteine intolerance.
• Smoking.
• Alcohol consumption during the study.