Soccer is an intermittent sport including a high number of powerful actions such as accelerations, decelerations, changes of direction, jumps and impacts that incorporate a strong eccentric component and may therefore lead to skeletal muscle damage. Indeed, match activity is associated with the onset of muscle damage and an acute inflammatory response that result in attenuated performance for as long as 1 to 3 days. In competitive soccer though, multiple matches are performed within a small-time frame resulting in inadequate muscle recovery and reduced field performance. Supplementation with milk proteins following intense exercise protocols has been shown to stimulate protein synthesis and facilitate muscle recovery. Thus, the aim of the present investigation is to examine the effects of milk protein supplementation on muscle recovery and soccer-specific performance during an in-season microcycle with two matches performed three days apart.

In a double-blind, cross over, repeated measures design 20 men soccer players will receive either placebo (PLA) or milk protein isolate (PRO, 80% casein-20% whey) throughout recovery following two matches performed three days apart. On match days, players will receive a dose immediately after the match (PLA vs PRO: 25g of protein) and then at 3h (PLA vs PRO: 30g of protein) and 6h (PLA vs PRO: 25g of protein) post-match. On each day of the remaining days, players will consume a single dose of PLA or PRO (20g of protein) with breakfast. All players will participate in regular in-season training following matches. Field activity during both matches and daily practices will be monitored using GPS devices. Heart rate will be continuously recorded during each match and training session. Blood samples will be collected at baseline as well as 2 hours after the first match, daily for three days after the first match, 2 hours after the second match and daily for 3 days after the second match. Performance (isokinetic strength, 20-m speed, repeated sprint ability) and muscle soreness will be assessed at baseline daily for 3 days after both matches. Muscle biopsies from vastus lateralis will be collected at baseline and one day after each match.

Inclusion Criteria:

• i) participation at elite level (top three division leagues) of soccer competition for at least five years, ii) abstain from consumption of performance-enhancing supplements, antioxidant supplements and medications (for at least 6 months before and during the study), iv) participate in at least six two-hour training sessions per week and played at least one match per week and v) non-smokers.

Exclusion Criteria:

• i) a known milk intolerance or allergy, ii) a recent febrile illness, iii) history of muscle lesion, iv) lower limb trauma and v) metabolic diseases.