The goal of this clinical trial is to learn how different daily carbohydrate intakes affect training performance in professional male football players during a pre-season training week.

The main questions it aims to answer are:

• Does a higher carbohydrate intake affect how much high-speed running and sprinting players complete during football training?
• Does a higher carbohydrate intake affect players' jumping performance, perceived effort, recovery, and daily readiness?

Researchers will compare two carbohydrate intakes. In one condition, participants will consume a moderate-carbohydrate diet. In the other condition, participants will consume the same base diet plus carbohydrate drinks. The drinks will look and taste similar, but only one type will contain extra carbohydrate.

Participants will complete both conditions during two pre-season training weeks. The order of the conditions will be randomized. This means participants will be assigned by chance to start with either the moderate-carbohydrate condition or the higher-carbohydrate condition.

During the study, participants will:

• Follow a standardized diet during each training week
• Drink three study beverages per day during each condition
• Take part in their regular team football training
• Wear a global positioning system device during training to measure running activity
• Complete countermovement jump tests during the training weeks
• Report their perceived effort, recovery, and daily readiness

This study will help researchers understand whether changing carbohydrate intake during a normal football training week affects training output and recovery-related measures in professional football players.

This study used a single-blind, placebo-controlled, randomized crossover design to examine the effects of different levels of daily carbohydrate availability during a pre-season training microcycle in professional male football players.

The study was conducted in an applied professional football environment during two consecutive pre-season training weeks. Each participant completed both dietary conditions. The order of the two conditions was randomized and counterbalanced. The training schedule and overall training content were matched between the two intervention weeks as part of the club's regular training program.

The two dietary conditions were designed to provide different daily carbohydrate intakes. In both conditions, participants followed a standardized food-based diet that provided 4 grams of carbohydrate per kilogram of body mass per day. In the higher-carbohydrate condition, participants also consumed three carbohydrate-containing study beverages per day, providing an additional 3 grams of carbohydrate per kilogram of body mass per day. This resulted in a total target intake of 7 grams of carbohydrate per kilogram of body mass per day. In the moderate-carbohydrate condition, participants consumed similar placebo beverages without added carbohydrate, resulting in a total target intake of 4 grams of carbohydrate per kilogram of body mass per day.

The study beverages were prepared from water and an artificially sweetened concentrate. In the higher-carbohydrate condition, maltodextrin was added to the beverage. In the moderate-carbohydrate condition, no maltodextrin was added. Beverages were provided in non-transparent bottles to support participant blinding. Participants were not informed of the carbohydrate content of the study beverages.

Dietary targets were individualized according to body mass. Breakfast and snacks were individualized according to participant preferences but standardized for carbohydrate content. Lunch was provided through the club's restaurant and adjusted to meet the carbohydrate target. Dinner targets were communicated using an image-based portion guide to support consistent carbohydrate intake outside the training facility. Participants were instructed to maintain their habitual protein and fat intake across both conditions.

Adherence to supervised meals and beverages at the training facility was monitored by study staff. Evening beverages were distributed for home consumption and returned the following morning so that remaining contents could be inspected. Dietary intake outside the training facility was not fully controlled.

External training load was monitored during football training sessions using a global positioning system device worn by each participant. The same device was used by each participant throughout the study to reduce measurement variation. The training monitoring system was used to quantify running and movement demands during the intervention period.

Neuromuscular function was assessed using countermovement jump testing on repeated occasions during the two training weeks. Self-reported measures were collected to assess perceived exertion after training, perceived recovery before training, and daily readiness upon waking.

The study was designed to compare the two carbohydrate conditions within the same participants while preserving the normal structure of a professional football training environment. This design allowed the researchers to examine whether changing carbohydrate availability during regular team training influenced training-related performance and recovery measures under applied conditions.

Inclusion Criteria:

• Professional male football player
• Outfield player
• Member of the recruited professional football team
• Available to take part in the pre-season training period
• Able to follow the study diet and beverage protocol
• Able to wear a global positioning system device during training
• Provided written informed consent

Exclusion Criteria:

• Goalkeeper
• Injured at the start of the study period
• Expected to leave the team on loan during the study period
• Unable to complete both dietary conditions

Individual participant data will not be made publicly available due to the small sample size and the specific professional team context. These factors may increase the risk of participant identification, even after de-identification of the data.