Associations of physical activity with cardiorespiratory fitness, muscle strength, and body composition

Introduction
Most studies have indicated the association between physical activity level (PAL) and physical fitness indices in children and adolescents. This study aimed to investigate the association of PAL with cardiorespiratory fitness, muscle strength, and body composition in healthy Iranian adults.

Material and methods
This cross-sectional study was carried out on 120 males and 152 females aged 18–70 years. The participants underwent physical fitness measurements including grip strength, maximal oxygen consumption, and body composition. The PAL was objectively assessed using the International Physical Activity Questionnaire (IPAQ).

Results
We observed a significant association between PAL and body composition measurements (p < 0.05). Controlling for covariates did not change the results except for body mass index and waist circumference. All cardiorespiratory fitness and muscle strength indexes were positively associated with PAL (p < 0.001 and p = 0.001, respectively). However, these associations were disappeared after adjustment for age, gender, and BMI.

Conclusions
Improved body composition profile and function of the muscular and cardiovascular system were associated with higher PA. Further longitudinal studies are required to understand the causal direction of the relationship.