Dairy Consumption During a High-intensity, High-volume Training Week in Young Athletes

The proposed study is a randomized, double-blinded, cross-over trial. The protocol will consist of an information session, two identical training camps consisting of 5 consecutive days of intensified soccer training, differing only by nutritional intervention, and identical pre-and post-training session testing. Each testing block will be separated by 28-d to allow for an adequate wash-out and recovery period, during which participants would resume their regular soccer activities

Study Procedures:

All tests and measurements will be performed within eight-weeks. Specifically, participants will attend 1 information session, two identical pre- and post- training/testing sessions and two identical soccer specific training camps.

Information session:

One week prior to the initial soccer specific training camp, participants will be informed of all tests and procedures that will take place and be familiarized with all testing protocols.

Pre- and Post-training testing:

All participants will be tested twice: on the day before (pre) and day following (post) the 5-d soccer specific training camp. Specifically, Participants, will arrive at the University for pre- and post-training testing in the morning at the same time. Body composition measurements will be performed (e.g., standing/seated height, mass, % body fat) followed by fasted venous blood and saliva sampling. A standardized breakfast would then be provided followed by an adequate rest and digest period before performance testing (~1.5h). Performance testing would include a battery of soccer specific tests that cover, power (counter-movement jump, broad jump), speed (10m and 20m sprint), agility (modified 5-0-5) and aerobic capacity (beep-test). During both pre-and-post-testing sessions participants would consume the same standardised breakfast and perform the same tests in the same order for consistency amongst trials which would be repeated between the two testing blocks.

Soccer training:

The simulated 5-d soccer-specific training will be structured to mimic a heavy-volume, high-intensity training camp. Training sessions would occur at the same time each day in the evening for consistency. Drills/exercises will be administered by a certified technical soccer coach and knowledgeable training staff. Each session will began with a 15 min dynamic warm-up followed by 90 min of soccer-specific training, ending with a 15 min cool-down. The 90 min of soccer-specific training will be performed at maximal effort and consist of agility, sprinting and plyometric exercises as well as ball-handling, small-sided games (rondo) and shooting. Following each training session rating of perceived exertion (RPE) will be measured as an indicator of internal load.

Food/Drink supplement consumption:

During the study, three servings of 160 g of 0% plain GY (~115 kcals, 17 g protein, ~11.5 g carbs, 0 fat), or 30 g of isoenergetic CHO (~115 kcal, 0.04 g protein, ~28.6 g carbs, 0 fat) will be provided to participants immediately following the training session, 1 h prior to bedtime, as well as one serving between breakfast and lunch on the subsequent day. The yogurt will be sweetened or flavored with a non-caloric vanilla flavouring to match the taste of the control supplement. The CHO control supplement group will be an isoenergetic dose of a maltodextrin-based semi-solid pudding. This product will be made from non-fat vanilla pudding powder (1 part), maltodextrin (4 parts) and water. This product has been designed to resemble the consistency and texture of Greek yogurt.

Measurements

Questionnaires: Participant Screening and Medical History, Training History, Food frequency Questionnaire (FFQ), sessional RPE.

Anthropometric and body composition measurements: height, seated height, body mass and body fat percentage (%) using bioelectrical impedance analysis (BIA, InBody520; Biospace Co., Ltd., Seoul, S. Korea).

Somatic maturity: maturity offset (years from the age of peak height velocity) will be calculated based on height, seated height and weight measurements.

Exercise performance: will be examined prior to, as well as following each training intervention week. These tests are common in soccer and athletes are familiar with them. To limit confounding exercise influence on both biochemical and performance parameters, participants will be asked to refrain from other activities outside those prescribed to them during the training sessions and 48h prior to the initial pre-assessment visit.

Venous blood and saliva samples: will be collected on 4 separate occasions (24h prior and 24h following the last training session of each training intervention week). To control for circadian rhythm, the exercise session and related blood and saliva samples will be conducted at the same time of day. Saliva samples will be used to examine endocrine response. Venous blood samples will be used to examine inflammatory markers (cytokines - IL-6, IL-10 and TNF-α), c-reactive protein (CRP), IGF-I and indicators of muscle fatigue/damage (CK). Secondary measures may include irisin, oxidative stress (TBARS and ROS) and bone turnover by examining circulating markers of bone formation (PINP, Osteocalcin, BAP, OPG) and of bone resorption (CTX, TRAP, RANKL).