The reciprocal relationship between body mass index categories and physical fitness: A 4-year prospective cohort study of 20 000 Chinese children.
INTRODUCTION
Body mass index (BMI) categories and physical fitness are associated but the reciprocal relationship between BMI categories and physical fitness has not been investigated. This study aims to investigate the longitudinal reciprocal relationship between BMI categories and physical fitness.


METHODS
This is a population-based 4-year cohort study in 48 elementary schools. Children aged 6 to 9 years at recruitment were included. BMI categories and physical fitness including handgrip strength, core muscle endurance, flexibility, and cardiorespiratory fitness were measured using standard equipment and protocol.


RESULTS
Among 26 392 eligible participants, 19 504 (73.9%) were successfully followed for 3 years. Baseline obesity prevalence was 5.9%. After 3 years, those who were unfit at baseline had an increased risk of obesity (risk ratio [RR] 1.41, 95% CI 1.16-1.71, P < .001) and those who were fit at baseline had a decreased risk of obesity (RR 0.69, 95% CI 0.60-0.80, P < .001) compared with moderately fit children. Furthermore, improvement of fitness predicted decreased risk of obesity. Similarly, normal body weight also predicted better physical fitness. The path analysis confirmed a strong reciprocal relationship between physical fitness and obesity.


CONCLUSIONS
Better physical fitness was prospectively associated with normal weight and vice versa. Physically fit children were more likely to maintain a healthy weight and those with a healthy weight were more likely to be physically fit, which is important for healthy development.
['Ho|Frederick K|FK|0000-0001-7190-9025', 'So|Hung-Kwan|HK|', 'Wong|Rosa S|RS|', 'Tung|Keith T S|KTS|', 'Louie|Lobo H T|LHT|', 'Tung|Joanna|J|', 'Mirpuri|Sheena|S|', 'Chow|Bik|B|', 'Wong|Wilfred H S|WHS|', 'Lee|Albert|A|', 'Ip|Patrick|P|0000-0002-6797-6898']
D044466:Asians D015992:Body Mass Index D001835:Body Weight D000072599:Cardiorespiratory Fitness D002648:Child D002681:China D015331:Cohort Studies D005260:Female D005500:Follow-Up Studies D018737:Hand Strength D006801:Humans D008297:Male D063766:Pediatric Obesity D010807:Physical Endurance D010809:Physical Fitness D011446:Prospective Studies D012307:Risk Factors D012574:Schools
reciprocal relationship body mass index physical fitness prospective cohort study