Association Between Racket Stiffness and Lateral Epicondylalgia in Tennis Players

Lateral epicondylalgia will be assessed using the Patient-Rated Tennis Elbow Evaluation (PRTEE) Questionnaire. This instrument evaluates pain and functional disability in individuals with lateral epicondylalgia. The questionnaire consists of 15 items. The total PRTEE score is transformed to a 0-100 scale, where 0 indicates no pain or disability and 100 represents the worst possible pain and functional impairment.

Racket stiffness will be assessed using the measured stiffness value (RA) or stiffness index. As not all racket models report this parameter, when participants are unaware of the RA value, it will be determined based on the exact brand, model, and year of manufacture, and subsequently obtained from manufacturer catalogs or technical reference tables. The unit of measurement will be the RA rating (Racquet Analysis rating), also referred to as the stiffness index.

String age will be measured as the number of months since the last restringing. This variable will be used as a mechanical proxy for string condition, as commonly applied in biomechanical studies and technical-sport performance recommendations.

Vibration dampener use will be recorded as a dichotomous variable (yes/no). When applicable, the specific dampener model will be documented. This variable is a recognized modifier of the vibratory spectrum, as described in experimental studies.

In this variable, data will be collected on the number of weekly training hours (measured in hours/week).

In this variable, data will be collected on the years of tennis practice (number of years).

In this variable, data will be collected on the number of weekly matches (matches/week).

In this variable, data will be collected on upper-limb dominance (right / left).

In this variable, data will be collected on whether the athlete performs specific weekly upper-limb strength training (yes / no).

In this variable, data will be collected on the number of weekly strength training hours.

In this variable, data will be collected on backhand execution (one-handed / two-handed).

In this variable, data will be collected on competitive level (occasional recreational (≤1 session/week; no tournaments); regular recreational (2-3 sessions/week; occasional local leagues); regional competitive

This will be the variable acting as an a priori effect modifier, with an RA×sex interaction term included in the models, given that sex-related differences in injury patterns have been reported in padel and contextual differences have

This will be assessed using a dichotomous variable (Federated / Non-federated). This variable will act as a potential effect modifier (RA×competitive level), as exposure level, technique, and equipment differ between rec

Age will be measured in years

This variable will be measured in kilograms (kg)

This variable will be measured in meters (m)

Smoking status will be recorded as a dichotomous variable (yes/no). This variable is included because some studies have shown that individuals with a history of smoking present higher odds of developing the condition compared with controls.

This variable will be assessed using ISO 11228-3 screening criteria and temporal exposure. Three dichotomous items anchored to the ISO 11228-3 criteria for repetitive upper-limb tasks will be used, along with a quantification of exposure time in hours per week.

Sleep quality will be assessed using the Pittsburgh Sleep Quality Index. This scale measures global sleep quality over the previous month, including aspects such as sleep latency, duration, efficiency, sleep disturbances, use of sleep medication, and daytime dysfunction. It consists of 19 items grouped into seven domains, with a total score ranging from 0 to 21 (higher scores indicate poorer sleep quality; scores >5 indicate poor sleep quality).