## 2 Materials and Methods
### Procedures  
A standardised 1 RM protocol was developed, following the guidelines previously described by [PERSON] and [PERSON] [32]. Participants performed a specific warm-up consisting of a set of BPs with a light load that allowed them to easily perform 10 repetitions (approximately 50% of estimated 1 RM). In the next set, 4 to 9 kg was added, and the subjects completed 3 to 5 repetitions. Then, another set was performed, where 4 to 9 kg was added again, and the subject attempted to complete 2 to 3 repetitions. In the following set, an additional 4 to 9 kg was added, and the subject tried to complete 1 repetition. If they succeeded, more load was added according to the subject's judgement until they were unable to perform a complete repetition. The 1 RM was considered the last load lifted when failure occurred [32], and all sets were normalised (%RM) based on that 1 RM. Recovery times between sets were 5 min. Participants were encouraged to raise the barbell at maximum velocity in order to measure and compare the maximum power that could be produced at each load interval. A strength and conditioning coach supervised all participants during the warm-up and every set to ensure that the movement pattern was performed correctly. Afterward, the sets in which participants worked within the established intensity ranges were recorded and compared. The Xsens MVN Link system [33] and the MVN Analyse software [34] (2020 version) were used to collect data and record the kinematics of the entire dynamic system with the load [35]. These data were carefully stored for subsequent digital processing. Vertical position (\(\overrightarrow{x}\)) was calculated through mean of hands' vertical position, while linear velocity (\(\overrightarrow{v}\)) and linear acceleration (\(\overrightarrow{a}\)) were calculated through time derivation of vertical bar position. These data underwent a smoothing process using GCV quintic splines [36], enabling velocity and acceleration analysis without noise while preserving position magnitudes and curves, as shown in Figure 1.  
After data smoothing, mechanical power (\(P\)) and work (\(W\)) were calculated using the following equations:  
\[P=\overrightarrow{F}\cdot\overrightarrow{v} \tag{1}\]  
where \(\overrightarrow{v}\) is barbell velocity, and \(\overrightarrow{F}\) is the force according to [PERSON]'s 2 nd law \(\overrightarrow{F}=m\overrightarrow{a}\), where \(m\) is the load raised and \(\overrightarrow{a}\) is the acceleration of the barbell. \(W\) is defined as the measurement of the energy transferred from one body to another over a specific period of time. In this case, muscle A performs work on segment B if the energy flows from the muscle to the segment. \(W\) is measured in joules (\(J\)) and is calculated as the integral of mechanical power (\(P\)) over the time interval [\(t_{1}\), \(t_{2}\)] and the time it takes  
Figure 1: From left to right: barbell position, velocity and acceleration of one selected sample. Red lines: raw data. Blue lines: smoothed data. for this work to be performed; in this case, it is said that muscle A can perform work in segment B if the energy flows from the muscle to the segment. It is measured in joules [30]. \[W=\int_{t1}^{t2}Pdt \tag{2}\]  
The sets of repetitions were divided into cycles (each repetition) and phases by detecting local maxima and minima in the vertical position and velocity of the bar, resulting in four phases: acceleration of the downstroke, braking of the downstroke (eccentric phase), acceleration of the upstroke (concentric phase) and braking of the upstroke. Only phases 2 (henceforth called \"eccentric\") and 3 (henceforth called \"concentric\") were analysed since these are the phases where the muscular action performed by the subject is the most important [37]. Phases 1 and 4 were not analysed because they are mainly determined by gravity forces and not by muscle action.