## 2 Materials and Methods
### Muscle Strength Assessment  
To minimize residual fatigue, participants were instructed to avoid moderate to intense physical activity on the day before testing and to refrain from consuming stimulant beverages on the day of testing. Prior to testing, participants completed a standardized warm-up protocol designed to ensure neuromuscular readiness and minimize variability across individuals. The protocol began with 5 min of low-intensity aerobic exercise on an elliptical machine (Reebok OneGX60, Reebok, Boston, MA, USA), performed at a perceived exertion level of 3-4 out of 10. This general warm-up was followed by two maximal-effort handgrip measurements per hand using a Jamar FS658 dynamometer (Patterson Medical, Warrenville, IL, USA), conducted with participants seated, the tested arm hanging naturally, the non-tested hand resting on the thigh, and both feet flat on the ground. Subsequently, participants completed a specific climbing warm-up involving eight unilateral, intermittent isometric contractions for each grip type (three-finger drag and half-crimp). The intensity of these efforts was progressively increased from approximately 50% to 75% of each participant's perceived maximal voluntary contraction. Each repetition lasted 3-4 s, with 20 s of rest between repetitions. This protocol was adapted from previously validated procedures for climbing-specific strength testing [30; 31] and aimed to ensure grip-specific neuromuscular activation while avoiding fatigue. The warm-up also served as a familiarization with the custom testing device and grip positions used in the subsequent maximal strength assessments. The climbing-specific grips were tested using a custom-built device, which was adjusted to correspond to the arm length of each participant. The device, developed by the researchers and shown in Figure 1, consisted of a stationary section fixed to the wall, from which a metal arm extended. A strain gauge (Chronojump 500 kg, frequency 160 Hz) was attached to this metal extension and remained stable throughout the test. On the opposite side of the strain gauge, a 20 mm wooden support bar (150 \(\times\) 40 \(\times\) 20 mm, rounded edges) was positioned, serving as the point where participants applied force during the test. To isolate finger flexor activation, the arm and forearm were immobilized. To evaluate finger flexor strength, participants performed two different unilateral isometric tests in a randomized order. Each participant completed a fixed three-finger drag grip test and a fixed half-crimp grip test. The order of these tests and the hand used at the beginning of each test were randomized to control for potential order effects. Each test consisted of three maximal isometric contractions per hand, with each contraction lasting five seconds. The timing of each contraction was controlled using a mobile application that provided audible cues signaling both the start and end of the test. A 2-minute resting period was provided between each attempt. Participants were instructed to apply maximal force immediately upon hearing the start signal and to maintain this effort for the entire duration until the end signal was heard. To ensure consistency and optimal execution, two evaluators provided uniform verbal encouragement throughout each trial, supporting participants from the beginning to the end of the contraction period. Figure 1: (**A**) Custom-built device for assessment of finger strength; (**B**) finger position in the three-finger drag grip; (**C**) finger position in the half-crimp grip; (**D**) body position during a maximal finger flexor strength in half-crimp position. During the tests of climbing-specific maximal isometric strength, the thumb was excluded to avoid contribution to the measured force [33]. Additionally, participants were instructed to maintain the little finger (fifth digit) in a flexed position without contact with the support bar. This posture was visually verified by the evaluators during each trial to minimize synergistic interference.