## 1 Introduction  
There has been an exponential increase in the fitness industry during the last decade [1]. The emergence of low-cost gyms and the greater social awareness about the benefits of the regular practice of physical activity and sport to improve the quality of life and health could be some of the reasons for this expansion [2, 3]. Although this growth has been affected by the current COVID-19 crisis, the global gym market generated 84,000 million euros in 2018. These data reported by the International Health, Racquet & Sportsclub Association (IHRSA) are useful to know the magnitude and the importance of the fitness industry not only for people's health but also for the global economy [4]. The rise of fitness also has caused the offer of activities and exercise programs available in the fitness centers, being greater and more varied than ever [5].  
Among the novel trends, the community-based activities directed by an instructor and performed under musical support are the option chosen by more than 30% of the fitness facility users [6]. In fact, group training is placed the third position of the Top 20 Worldwide Fitness Trends for 2020 [7]. Further, the female gender has greater participation in most of these physical group activities [6]. Following this trend, international franchises, such as Les Mills(r) or FITCONCEPTPRO(r), are designing new group fitness programs under musical support every three months. Later, certified instructors reproduce these programs in their respective fitness centers. Some examples of these well-known activities are Body Pump(r), Body Combat(r) or Body Balance(r) by LES MILLS(r) and PYRO(r) or Body Jump(r) by FITCONCEPTPRO(r).  
In this context, the Body Jump(r) training program has become one of the most popular programs in recent years [8]. Body Jump(r) is a novel aerobic-training program rebounding in minitrampolines that are performed with music into community-based classes. The workout session has a duration of about 55 min and is divided into 9 music tracks of 5-7 min' length, each one targeting not only the lower limb musculature but also the core and upper limb musculature. Each track uses various exercises, movements and rebounds variating the range of motion, speed of movement, jump height and body position for providing different workloads to practitioners. The time between tracks is normally used to rest and hydration before immediately beginning the next segment. Body Jump(r) is currently wide-spreading, with a growing number of practitioners in many countries [8].  
The Body Jump(r) program is intended to provide a full-body workout to increase cardiorespiratory and muscular fitness in practitioners into a group-exercise setting. Additionally, these recreational users are usually seeking to improve their body composition. Both improvements of overall fitness and health and the loss of weight and the enhancement of the body composition are two of the main goals for conducting regular physical activity in the adult population [9]. However, current research investigating the effects of community-based physical activities performed under musical support on body composition and physical fitness is scarce [8; 10]. Moreover, to the best of our knowledge, the short-term effects of the Body Jump(r) program on these parameters, particularly in young women, remain uninvestigated. Therefore, this study aimed to analyze the effects of the Body Jump(r) program on physical fitness and body composition after a short-term intervention in a group of physically active young women. Our initial hypothesis was that the Body Jump(r) program would be effective in improving body composition, VO2 max, jump ability and strength of the lower body of healthy young women after a short-term period of intervention.