Relationship Between Vertical Jump, Balance, Muscle Strength, Flexibility, and Foot Posture in Artistic Gymnasts

The active vertical jump performance of participants will be evaluated using the My Jump Lab (MJL) mobile application. My Jump Lab is a practical and portable tool with established validity and reliability. In a validity-reliability study conducted by Balsalobre-Fernández et al. (2024), Cronbach's α was reported to be greater than 0.93. Similarly, Şentürk et al. (2024) compared the application with a force platform and demonstrated an almost perfect correlation between the two methods (r = 0.968, p = 0.001), confirming that MJL is a valid and reliable instrument for real-time assessment of jump performance and active jump height.

Each participant will complete three practice trials at their perceived maximum effort prior to testing. The MJL application will be used on an iPhone 14 (Apple Inc., Cupertino, CA, USA). To record active jump height, the iPhone will be mounted on a tripod positioned to capture the participant's sagittal plane. Participants will be instructed to place their h

Dynamic balance of the participants will be evaluated using the Y-Balance Test (YBT), which is a modified version of the Star Excursion Balance Test. The YBT has been shown to be valid and reliable, with intrarater ICC values ranging from 0.85 to 0.91 and interrater ICC values between 0.99 and 1.00 (Plisky et al., 2009). The test can be performed on the floor or with a custom apparatus, consisting of a Y-shaped system extending in three directions: anterior, posteromedial, and posterolateral. The posteromedial and posterolateral arms are positioned at a 90° angle relative to each other, and both form 135° angles with the anterior arm.

During the test, children will stand at the center of the Y with their hands on their hips, balancing on the dominant leg while reaching in the anterior, posteromedial, and posterolateral directions with the opposite leg, touching the furthest possible point with their toe while maintaining balance. Each direction will be tested three times for both limb

Isolated muscle strength will be assessed using the Lafayette Model 01165A Manual Muscle Testing System, a portable digital hand-held dynamometer with an LCD display and three interchangeable heads (Instrument, 2012). The device provides measures such as peak force, time to peak force, total test duration, and average force in kilograms, Newtons, or pounds.

Measurements will be performed by the same investigator, using the same hand, three times for both dominant and non-dominant lower limbs. The mean value will be used as the final muscle strength score. Maximum isometric strength of bilateral the hip flexors, extensors, abductors and adductors as well as the knee flexors and extensors, will be measured using the "make" test protocol with the digital dynamometer.

Foot posture will be assessed using the Foot Posture Index-6 (FPI-6), developed by Redmond et al. (2006). The FPI-6 evaluates foot posture based on six criteria: palpation of the talar head, observation of supra- and infra-malleolar curvature, calcaneal frontal plane position, prominence of the navicular region, congruence of the medial longitudinal arch, and forefoot abduction/adduction. Each item is scored from -2 (indicating supination) to +2 (indicating pronation), with the total score indicating overall foot posture.

Scores from 0 to +5 represent neutral alignment, positive values above +5 indicate pronation, and negative values below 0 indicate supination. The Turkish version of the FPI-6 has demonstrated excellent reliability, with internal consistency coefficients of Cronbach's α = 0.85 and 0.78, test-retest reliability ICC(2,k) = 0.96 and 0.94, and inter-rater reliability ICC(2,k) = 0.93 for both dominant and non-dominant lower extremities (Yağcıoğlu et al., 2024).

Flexibility in the sagittal plane will be evaluated using the Sit-and-Reach Test. Participants will be seated with their feet flat against a fixed surface, ankles in a neutral position, and knees fully extended. They will be instructed to reach forward with their hands, keeping their knees extended, and touch as far as possible. The distance reached by the third finger will be measured with a tape measure. Scores beyond the toes will be recorded as positive values, while scores short of the toes will be recorded as negative. The test will be repeated three times, and the best score will be recorded in centimeters (Castro-Piñero et al., 2009).