Association Between Weekly Strength Training Load and Perceived Physical Performance in Non-Professional Soccer Players

This variable will be assessed using the Spanish version of the Perceived Performance in Sports Questionnaire. This instrument measures athletes' subjective evaluation of their own performance during competition or sport practice. It consists of five items rated on a 1-5 Likert scale, with the final score calculated as the mean of the items; higher scores indicate better perceived performance. As no specific cut-off points are established, the score will be interpreted as a continuous variable.

Weekly strength training load will be quantified using the session Rating of Perceived Exertion (sRPE; Borg CR-10). Participants will report session duration and perceived intensity (0-10) for all strength sessions in the previous week. Weekly load will be calculated as the sum of sRPE × duration (minutes) across sessions.

This variable will be assessed using the Spanish version of the Fatigue Severity Scale (FSS). This self-reported questionnaire evaluates the impact of fatigue on daily functioning and consists of nine items rated on a 1-7 Likert scale. The final score is calculated as the mean of the items, with higher values indicating greater perceived fatigue; a mean score ≥4 is considered indicative of clinically significant fatigue.

This variable will be assessed using the Spanish version of the Behavioral Regulation in Exercise Questionnaire-2 (BREQ-2). This self-reported instrument, grounded in Self-Determination Theory, evaluates different types of motivational regulation toward exercise. It consists of 19 items distributed across the dimensions of amotivation, external regulation, introjected regulation, identified regulation, and intrinsic motivation. Higher scores in autonomous regulation, particularly intrinsic motivation, are associated with greater adherence to and engagement in sport practice.

This confounding or moderating variable, used to control for individual characteristics, will be measured in years.

This confounding or moderating variable, used to control for individual characteristics, will be recorded as a dichotomous variable (male/female).

This confounding or moderating variable, used to control for individual characteristics, will be recorded as an ordinal variable (goalkeeper / defender / midfielder / forward).

This confounding or moderating variable, used to control for individual characteristics, will be recorded as an ordinal variable (e.g., first regional division / second regional division, etc.).

This confounding or moderating variable, used to control for individual characteristics, will be measured as a continuous variable, defined as the number of competitive seasons played.

This confounding or moderating variable, used to control for individual characteristics, will be recorded as an ordinal variable (<45 minutes / 45-90 minutes / >90 minutes).

This confounding or moderating variable, used to control for individual characteristics, will be calculated from body mass and height (kg/m²).

This confounding or moderating variable, used to control for individual characteristics, will be assessed as the mean perceived exertion of all training sessions (strength training plus field-based sessions) using a 0-10 rating of perceived exertion scale.