**Preface**

Research on training and competition quantification, well-being/wellness, fitness, and body composition can be found in the literature, especially in soccer with male athletes. However, there are many other sports that intend to produce knowledge on these topics that also deserve merit. Moreover, more studies should include women athletes rather than only men.

Although some studies have already been produced, the present Special Issue prioritizes research focusing on the understanding of how training and match/competition monitoring can help improve athletes' quality of life. Therefore, the inclusion of well-being/wellness, health, fitness, and body composition variables in the studies was recommended, as well as the analysis of relationships between well-being/wellness (e.g., sleep quality, stress, muscle soreness, fatigue, and mood), exercise training programs, and usual training/match external and internal measures such as total distance, distances at different threshold speeds, accelerometry-based variables (e.g., acceleration, deceleration, and player load), session-rated perceived exertion, heart rate, and others.

Therefore, the aim of this Special Issue, which now constitutes a reprint, was to compile and provide new and updated knowledge on wellness, fitness, body composition, training, and performance monitoring and how they can be used to improve athletes' quality of life.

We believe that this reprint provides relevant information for several sports, namely, soccer, speed skating, triathlon, strength training, and pole dancing, in order to apply better strategies to the training process, helping athletes to improve or maintain their quality of life.
