This paper considers some aspects that characterize launching and continuing sport activities at gym. In concrete, we study the role of some influences in starting sport activities, as well as several motives for maintaining this leisure practice. One concern about sustainability deals with the idea of promoting long-term health behavior. However, some confusion has been showed in approaching health promotion interventions (Swerissen & Crisp, 2004). Consequently, social researchers have been looking for factors and contexts in which sustainable health behavior could be achieved. In this sense, features related to sport activities performance may suggest some ideas about analyzing, stimulating, and sustaining health-related behavior. No doubts about sport activities benefits in health maintenance (e.g., Lake, Stratton, Martin & Money, 2001); even more, in some cases sport as a leisure activity can be an indicator of life and environment satisfaction (Codina, Rosich & Pestana, 2002; Pestana, Rosich & Codina, 2003). A specific questionnaire developed by Codina, Rosich & Pestana (2003, 2004, 2005) was administered to 1,483 participants (799 men, 684 women; mean age 33.21 yrs., SD = 13.64), who attended gyms located in Barcelona metropolitan area. Participants rated on a 4-point scale their perception about how own beliefs and environmental influences (health professionals, family, friends, school) induce sport activities practice, and their reasons for being satisfied with this practice. Results show significant associations among: different perceived influences in starting sport activities; the motives that produce satisfaction in practicing these activities; and these motives and those perceived influences, according to variables such as sex, age, and sport implication. Our outcomes are valued from a psychosocial dimension of health behavior sustainability. Specifically, we consider some conditionings in intervention procedures oriented to make people begin and keep on practicing physical activities. In a more general sense, future directions address us to take into account psychosocial processes like space and time appropriation, and free self-oriented behavior to contribute in explaining health-based sustainable practices.