## 2 Materials and Methods
### Procedures and Instruments  
A brief training background survey was conducted to obtain information regarding the training experience (years) and the weekly training volume (hours) of each gymnast. Anthropometric data were collected, namely, the height of push-off (HPO), height, body mass, and fat percentage. HPO is the difference between the right greater trochanter height from the ground (measured at 90\({}^{\circ}\) knee angle in a squat position) and the extended lower limb length with maximal foot plantar flexion (greater trochanter to tiptoe distance) while the subject is in supine position [17]. This measure consists of the lower limbs' length change between the starting position and take-off, collected using a measuring tape and a goniometer (BASELINE, 12-1001). A stadiometer was used for height measurements, and the bioimpedance scale Tanita SC-330 (TANITA Corp, Tokyo, Japan) was used to measure body mass (kg) and fat percentage (%). After the usual training warm-up, a brief familiarization with the Countermovement Jump (CMJ) was facilitated. For the F-V profile assessment, an incremental loading jumping protocol was applied using the scientifically validated smartphone app _My Jump 2_ in an iPhone 5s, with a camera frame rate of 40 fps [18; 19]. This instrument uses basic measures of body mass, lower limb length, jump height, and distance-time or speed-time measurements [17; 20] to measure the CMJ height and F-V profile of each athlete. Each subject performed a maximum CMJ without additional load, followed by three progressive loading conditions, i.e., there was an increment of 5 kg for tops in each condition (body weight, 5 kg, 10 kg, and 15 kg) [21] and 10 kg for bases (body weight, 10 kg, 20 kg, and 30 kg) [22]. For attempts without additional load, the participants were instructed to remain in a standing position with their hands on their hips. For attempts with an external load, tops used weighted vests and bases placed their hands on a barbell, since they used higher loads. From these positions, participants performed the CMJs [23]. A 2 min interval was used for the unloaded condition [10; 11] and a 4-5 min interval was allowed between attempts using additional loads [11]. The protocol was considered successfully finished when gymnasts achieved 20 cm of jump height with the last load selected, as recommended by previous studies [24; 25]. Each gymnast performed two jumping performance evaluations. This instrument also provides information regarding the magnitude and direction of the F-V imbalance of each gymnast and the three variables that summarize the changes in external force generation and power output with increasing movement velocity, such as the theoretical maximal force at null velocity (F\({}_{0}\)); the maximal power output (P\({}_{\text{max}}\)); and the theoretical maximal velocity at which the lower limbs can extend during one extension under zero load (V\({}_{0}\)) [10]. The ratio between F\({}_{0}\) and V\({}_{0}\) (i.e., the slope of the linear F-V relationship) characterizes the F-V profile of the neuromuscular system [10]. There are five F-V imbalance categories according to the percentage of optimal thresholds, namely, a high-force deficit (<60%), low-force deficit (60-90%), well-balanced (90-110%), low-velocity deficit (>110-140%), and high-velocity deficit (>140%) [26]. The relative difference between the actual and optimal F-V profiles for a given individual represents the magnitude and the direction of the unfavorable balance between force and velocity qualities (i.e., the force-velocity imbalance, FV\({}_{\text{imb}}\) in %), allowing us to determine the individual force or velocity deficit [26]. A FV\({}_{\text{imb}}\) value around 0% indicates a F-V profile that is equal to 100% of the optimal profile (a perfect balance between force and velocity qualities), whereas a F-V profile value that is higher or lower than the optimal indicates a profile that is too oriented toward force or velocity capabilities [26].