Sedentary behaviors are increasing in the population, so strategies for the increment of physical activity levels are needed. The use of green space seems to be a valid support to be more active. The present study aimed to compare the effectiveness of a period of outdoor training (Nordic walking (NW)) with indoor resistance training (GYM) in a nonclinical population based on anthropometric characteristics, body composition, and functional parameters. This study was conducted on 102 participants (77 middle-aged people performed NW and 25 performed indoor training). Participants were measured twice: at baseline and after three months. Anthropometric measurements (weight, BMI, skinfolds, perimeters), body composition, bioelectrical impedance, vectorial analysis (BIA and BIVA), and physical tests were carried out. A two-way repeated measures analysis of variance (ANOVA) was performed to evaluate the effect of the treatments, groups, and sexes. There were several intervention effects linked to a decrease in fat parameters (such as skinfolds, fat mass, and percentage of fat mass). Considering the type of intervention, NW showed a higher increase in muscle mass and a higher decrease in fat parameters than the GYM group. In conclusion, the two types of training could represent a good way to remain active and prevent sedentary behaviors.