# Physical health and fitness index in Chinese adolescents: a four-year cross-sectional study in Shandong Province

## TL;DR

This study examines the physical health and fitness of Chinese adolescents in Shandong Province over four years, finding a link between BMI and fitness levels.

## Contribution

The study reveals an inverted 'U'-shaped relationship between BMI and physical fitness in adolescents.

## Key findings

- Normal-weight adolescents showed the highest physical fitness levels.
- Females demonstrated higher PFI changes than males with comparable BMI.
- Overweight/obese prevalence increased despite improved fitness levels.

## Abstract

To explore the relationship between physical health and physical fitness index (PFI) in adolescents aged 10 to 19 in Shandong Province. We aimed to offer evidence to support the local implementation of the National Student Physical Health Standard.

Data were obtained from 51,764 adolescents aged 10 to 19 through the Shandong Student Physical Fitness and Health Surveys conducted in 2015, 2016, 2017, and 2020. Assessment of physical fitness included five core items: 50 running, sit and reach, standing long jump, 1,000 running/800 running, and pull-ups/sit-ups, which were then used to calculate the overall PFI. Body Mass Index (BMI) is defined according to the thresholds specified in the National Student Physical Health Standards (2014 Revision), categorized by gender and grade level: underweight, normal weight, overweight/obese. Socioeconomic data come from provincial statistical yearbooks. We used generalized additive models and logistic regression analyses to examine the associations between PFI and BMI and between PFI and the prevalence.

Normal-weight individuals had the greatest fitness, and fitness declined in underweight and overweight groups. There was an inverted “U”-shaped curve relationship between BMI-Z and PFI. With comparable BMI, PFI changes was higher in females than males. The PFI and the prevalence of overweight/obese showed a consistent upward trend over the years.

Females outperformed males in physical fitness, and fitness levels have improved over time. However, the prevalence of overweight/obese continues to rise, indicating a persistent imbalance between muscle and fat. This suggests that the region may be facing a “development–health paradox.”