What was the primary focus of the study conducted by Sallis et al. in 1999?

The primary focus of the study conducted by Sallis et al. in 1999 was to examine physical activity levels specifically in late adolescents and early adults. This study aimed to provide insights into the trends and factors affecting physical activity during a critical developmental period when habits are formed that can impact long-term health and fitness. By concentrating on this age group, the research contributed valuable data to understand how lifestyle choices, including exercise, become ingrained during late adolescence and early adulthood. This focus is essential in the context of promoting active living and addressing public health concerns related to inactivity and its associated health risks.