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.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
DOUBLE
Enrollment
20
Milk protein isolate in a powder form consisted of 80% casein and 20% whey protein. 20g were diluted into 500 ml water
500 mL drink that contained water (375 mL), sugar-free cordial (125 mL) and 2 g of low-calorie glucose/dextrose powder.
Exercise Biochemistry Laboratory, School of Physical Education & Sports Sciences, University of Thessaly
Trikala, Greece
Change in creatine kinase in plasma
Concentration of creatine kinase will be measured in plasma
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in uric acid in plasma
Concentration of uric acid will be measured in plasma
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in protein carbonyls in blood
Concentration of protein carbonyls will be measured in red blood cells
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in total antioxidant capacity
Total antioxidant capacity will be measured in plasma
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in reduced glutathione in blood
Concentration of reduced glutathione will be measured in in red blood cells
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in oxidized glutathione in blood
Concentration of oxidized glutathione will be measured in red blood cells
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in malondialdehyde in blood
Concentration of malondialdehyde will be measured in serum
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in catalase activity
Catalase activity will be measured in red blood cells
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in protein carbonyls in muscle
Concentration of protein carbonyls will be measured in muscle
Time frame: At baseline, 24h post-Match 1 and 24h post-Match 2
Change in intracellular signaling proteins in muscle
Phosphorylation levels of Akt, mammalian target of rapamycin (mTOR) and p70S6K will be measure using western blotting.
Time frame: At baseline, 24h post-Match 1 and 24h post-Match 2
Change in proteasome activities in muscle
Chymotrypsin-like (CT-L), caspase-like (C-L) and trypsin-like (T-L) proteasome activities will be assayed with hydrolysis of the fluorogenic peptide LLVY-AMC, LLE-AMC and LSTR-AMC, respectively.
Time frame: At baseline, 24h post-Match 1 and 24h post-Match 2
Change in satellite cells in muscle
Pax7, Myf5, MyoD and Myogenin will be measured in order to quantify quiescent, activated, proliferated-differentiated and fused satellite cells respectively.
Time frame: At baseline, 24h post-Match 1 and 24h post-Match 2
Change in repeated Sprint Ability
5 x 30 m sprints will be performed with 25 seconds rest in-between. Mean time for 5 sprints and fatigue index will be calculated.
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in countermovement jump
Countermovement jump will be assessed on a contact platform
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in isokinetic strength of lower limbs
Isokinetic strength will be assessed on an isokinetic dynamometer for both knee extensors and knee flexors at 120 and 180 degrees.
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Change in match activity
Match activity will be continuously recorded during both matches using GPS technology.
Time frame: During Match 1 and Match 2
Change in heart rate
Heart rate will be continuously recorded during both matches using the Team Polar system.
Time frame: During Match 1 and Match 2
Change in delayed onset of muscle soreness
Muscle soreness will assessed during palpation of the muscle belly and the distal region of relaxed vastus medialis, vastus lateralis and rectus femoris following three repetitions of of a full squat. Subjects will rate their DOMS on a visual analogue scale (0-10).
Time frame: At baseline, at 24h, 48h and 72h post-Match 1 as well as at 24h, 48h and 72h post-Match 2
Dietary intake
Dietary intake will be assessed using 7-day diet recalls.
Time frame: Over a 7-day period at baseline.
Change in white blood cell count.
White blood cell count will be measured using an automatic blood analyzer.
Time frame: At baseline, immediately after Match 1, at 24h, 48h and 72h post-Match 1 as well as immediately after Match 2 and at 24h, 48h and 72h post-Match 2.
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