## 3 Methods and Purposes of Eccentric Muscle Training
### Determination of Intensity, Volume, Rest, and Frequency of Eccentric Exercises  
The definition of resistance training load in the literature is still limited to the magnitude of the load, the number of repetitions and series, the rest between series, the number of weekly interventions, and the training period [74]. Nevertheless, this information complements our proposal to prescribe and control eccentric exercises. Figure 3: Reciprocal relationship between eccentric training methods and purposes. The choice of intensity is a critical factor in determining the results of training processes, ranging from simple to complex, easy to difficult, and low to high load. Furthermore, the RPE is used to complement the control and prescription of the intensity, determining the internal load of the exercise [75]. When eccentric exercise is related to concentric 1 RM (sub-maximal, maximal, and supra-maximal), the intensity should range between 75 and 140%, and the rest between series should range from 45 to 240 s [27]. Lower load intensities also apply under specific rehabilitation and muscle development conditions. Recovery between exercises and training sessions also could impact RPE [76], modifying neural and metabolic responses [3; 54]. Accordingly, rest redistributions (e.g., cluster set) could maintain peak force and velocity execution in different exercises [77; 78; 79], highlighting the relevance of controlling training intensity by managing different load components (e.g., load, rest), exercise complexity, and RPE. \begin{table}
\begin{tabular}{c c c c} \hline \hline \begin{tabular}{c} Treatment disorder \\ classification \\ \end{tabular} & \begin{tabular}{c} Recentric Training Methods \\ \end{tabular} & Recentric Training Parameters & Example \\ \hline \multirow{6}{*}{**Basic eccentric exercise**} & \multirow{6}{*}{\
\begin{tabular}{c} Tempo; Moderate Eccentric \\ Load; Eccentric Endurance. \\ \end{tabular} } & Sports Rehabilitation and & \\  & & Return to Sport; Muscle & \\  & & Development; Injury & \\  & & Prevention; Special & \\  & & Populations. & \\ \hline \hline \multirow{6}{*}{**Moderate eccentric exercise**} & \multirow{6}{*}{
\begin{tabular}{c} Tempo; Moderate Eccentric \\ Load; Eccentric Endurance; \\ Plyometrics; Isokinetic \\ Dynamometry. \\ \end{tabular} } & Sports Rehabilitation and & \\  & & Return to Sport; Muscle & \\  & & & Development; Injury \\  & & & Prevention; Special \\  & & & Populations; Sporting \\  & & & Performance. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Methodological classification of eccentric exercises: balancing intensity and technical demand. Regarding the isoinertial method, low inertial loads allow greater concentric and eccentric power output, while high eccentric overload maximizes the eccentric/concentric ratio [27; 80; 81; 82; 83]. According to several studies, it is recommended that to maintain power output between series, 1 min rest is insufficient, 2 min rest allows one to maintain power output with light inertial loads (0.025 kg\(\cdot\)m\({}^{2}\)), and 3 min rest supports physiological recovery, especially when isoinertial loads are high (\(\geq\)0.075 kg\(\cdot\)m\({}^{2}\)) [27; 80; 81; 82; 83]. Concerning volume, there is a lack of research on the influence of this variable on acute and chronic responses following eccentric training. Generally, it is recommended to perform 3-4 series per exercise, 8-12 exercises per session, and 2-20 repetitions depending on the proposed purposes. These recommendations also are valid and reliable for the accentuated, moderate, and isokinetic eccentric methods [77; 78; 79; 84]. Finally, the training frequency for eccentric exercise aligns with the guidelines proposed by traditional strength training models [85; 86; 87; 88; 89]. Eccentric training is prescribed as primary and complementary training one to three times a week with training periods of 4-24 weeks, depending on the selected training method [18; 32; 36; 64].