The aim of this study was to compare the physical activity (PA) and sedentary behavior (SB) levels of young and middle-aged adults living in and around the municipality of Penafiel and to determine whether they meet PA recommendations. The researchers used the “International Physical Activity Questionnaire” (IPAQ) to measure moderate to vigorous PA and time spent on sedentary behavior (high vs. low). A prospective observational cross-sectional sample of 1105 adults aged 18–63 years, living in the municipality of Penafiel and its surroundings (45% women, 55% men), was used. The results indicated that more than half of the population was inactive (53.8%) and sedentary (54.0%). Men were more likely to be sedentary (59.2%) and inactive (55.6%) than women (inactive: 51.7%, high SB: 47.7%). Regarding daily PA and SB levels, women had higher levels of walks (3.8 ± 2.3;p= 0.034) and vigorous PA (2.2 ± 1.8 min;p= 0.005) per days/week, as well as vigorous PA per minutes/week (75.4 ± 82.1 min;p= 0.034). The time spent on vigorous PA per day was also higher in women (26.2 ± 22.8 min;p= 0.030). However, men had higher values in walking minutes per day (26.3 ± 17.1 min;p= 0.030), SB for weekdays (429.2 ± 141.2 min;p= 0.001), SB for weekends (324.7 ± 163.7 min;p= 0.033) and time spent on SB per minutes/week (2795.6 ± 882.0 min;p= 0.001). The results also showed that the older the adults, the lower the frequency and total time of vigorous PA per week. Young adults (18–28 years) had higher levels of vigorous PA (p= 0.005) than the other age groups (29–39; 40–50 and 51–63 years). Finally, the study found no significant correlation between individual level factors, such as number of children, marital status and monthly income, and PA or SB. Conversely, a significant and negative correlation between SB and levels of PA was found, indicating that the higher the level of PA practice, the lower the SB level. The authors suggest that promoting new PA habits and healthy lifestyles is an important future challenge for sustainability and improving the quality of life in public health.