## 2 Materials and Methods
### Equipment  
The exercise was conducted using the HandyGym portable isoinertial resistance training device (HandyGym, Global Traktus, Pontevedra, Spain; dimensions: 10 \(\times\) 12 \(\times\) 20 cm; weight: 0.9 kg). Exercises were performed on a custom-built platform designed to support the HandyGym device and ensure stability during the half-squats, while also providing sufficient space for the sensors, allowing for an unobstructed range of motion. This setup ensured that participants could achieve the desired range of movement, from 90\({}^{\circ}\) of knee flexion to full extension of the hips and knees, without interference from the measurement equipment (Figure 1).  
The HandyGym device incorporates an integrated wireless rotary encoder that measures angular velocity. These data are transmitted via Bluetooth to an associated mobile application (HandyGym APP v. 1.1.0 for Android). Once the load parameters and exercise configuration are set in the app, the software calculates the mean force and power for each repetition, during both the concentric and eccentric phases of the movement.  
For criterion measurements, a strain gauge combined with a linear encoder (Muscle Lab 6000, Ergotest Technology, Porsgrunn, Norway) was used. This method has previously been used as a reference measurement system in isinertial training [39; 40; 41]. The strain gauge (accuracy: 63 g, sampling rate: 200 Hz) was attached between the flywheel strap and the vest, while the linear encoder (accuracy: 0.019 mm, sampling rate: 200 Hz) was secured to the structure using adhesive tape. The string from the linear encoder was redirected by a pulley to align parallel with the HandyGym rope and then attached to the vest (see detailed view in Figure 1) [39; 40].  
The HandyGym device utilizes two small-diameter inertia discs, with resistance amplified by an internal gear system. The load can be adjusted by using pairs of interchangeable discs with different masses (Yellow: 120 g each; Blue: 180 g each; Red: 205 g each). Additionally, the load can be increased by incorporating an intermediate pulley, which distributes the force applied by the user between a fixed anchor point on the structure and the cable that drives the system. This mechanism, commonly used in other isoinertial training systems, approximately doubles the load provided by the device [42].  
Five different load configurations were tested in this study to cover the full range of resistances and the force-velocity spectrum available on the HandyGym device, from the lowest to the highest possible loads. Intermediate configurations represented varied resistances. This range is relevant for practical training scenarios, as configurations with higher loads and pulley multipliers provide increased resistance, making them suitable  
Figure 1: Setup of the training system and sensors used in the study. (**A**): Front view; (**B**): Side view; (**C**): Detailed view. The exercise was performed on a custom-built platform made of metal and wood to accommodate the space required by the sensors, which otherwise would have restricted the range of motion. This platform allowed for an adequate range of motion and ensured the comfortable execution of the exercise.  
for hypertrophy and near-maximal strength training [43]. In contrast, lower loads without pulley configurations are typically used in rehabilitation, beginner training, or power development [19; 43; 44]. The configurations used, described in more detail in Figure 2, were as follows: Yellow/Yellow (Yellow), Blue/Blue (Blue), Red/Red (Red), Blue/Blue with a multiplier pulley (BlueWP), and Red/Red with a multiplier pulley (RedWP).