Associations between cardiorespiratory fitness and muscle strength with body composition among adults

Introduction
Cardiorespiratory fitness (CRF) was reported to be associated with anthropometric measurements, including body mass, body mass index (BMI), fat mass (FM) and fat free mass (FFM). This study aimed to investigate the impact of FM and FFM on muscle strength and CRF.

Material and methods
This study was carried out on 270 randomly selected adults in Tehran, Iran. Anthropometric measurements, including weight, BMI, FM and FFM, were assessed using a bio-impedance analyzer (BIA) (InBody 720, Biospace, Tokyo, Japan). Muscle strength and CRF were assessed by handgrip dynamometer and Bruce graded treadmill protocol, respectively. The International Physical Activity Questionnaire (IPAQ) was used to measure health-related physical activity. A p-value less than 0.05 was statistically significant.

Results
Significant associations were found between maximum oxygen uptake (VO2 max) and muscle strength with FM and FFM (p < 0.001). After adjusting for confounders, the association of VO2 max with FFM remained significant (p < 0.001). Muscle strength was significantly associated with FM (p = 0.036) and FFM (p < 0.001) after adjustment for confounders.

Conclusions
High FM was associated with poor CRF, and low fat-free mass was related to poor muscle strength. FM and FFM can be good indices for CRF fitness in adults. Further longitudinal studies are needed to confirm these findings.