Physical fitness, the ability to do activities or motions effectively and efficiently, is widely considered to be an important component of health because of its links with a range of non-communicable diseases.1 Lower levels of physical fitness are associated with several health problems, including higher risks of later-life cardiovascular disease, hypertension, diabetes, cancer, and mental disorders across all ages.2, 3, 4 The 2018 Physical Activity Guidelines for Americans indicated that regular physical activity and good physical fitness could improve bone health, weight status, cardiorespiratory and muscular fitness, cardiometabolic health, and cognition and reduce risks of depression in children and adolescents.5 Peak physical fitness typically occurs in adolescence, with strong continuities into later life; therefore, the fitness levels of a country's children and adolescents are likely to provide insight into the future health profile of that country's adult population.6, 7 Previous studies have shown a worldwide decline in aerobic performance in children since the late 1950s,8 and a particularly marked decline in the maximal long-distance running performance of Asian children and adolescents, including those from China.9
Research in context
Evidence before this study
China has undergone a rapid nutritional transition in the past few decades, bringing remarkable reductions in stunting and underweight in children, but sharp increases in overweight and obesity. To our knowledge, the overall effect of these substantial changes in growth and nutritional status on the physical fitness of Chinese children and adolescents has not been comprehensively assessed. We searched PubMed, China National Knowledge Infrastructure, and Wanfang on July 14, 2019, using the terms “physical fitness” AND (“nutritional status” OR “nutritional problems” OR “nutritional burdens”) OR (“stunting” AND “thinness” AND “overweight and obesity”) AND “trends” AND “children and adolescents” AND “China” for articles published in English and Chinese, without date restrictions. Our search found some relevant studies, but no comprehensive reports of changing patterns of physical fitness and nutritional status in children and adolescents either in China or elsewhere. In this context, the nationally representative Chinese National Survey on Students' Constitution and Health provided a unique opportunity to analyse trends in child and adolescent physical fitness over 30 years and their association with growth and nutritional status.
Added value of this study
To our knowledge, this is the first study to comprehensively assess trends in physical fitness and their association with nutritional transition in children and adolescents in China. From 1985 to 2014, 1 494 485 Chinese students were included in these analyses of physical fitness using a summary indicator that combined six components of physical fitness (forced vital capacity, standing long jump, sit-and-reach, body muscle strength, 50 m dash, and endurance running). Children and adolescents at both extremes of growth and weight ranges had poorer physical fitness than those with normal weight and height. We observed a comprehensive decline in physical fitness from 1995 to 2014, particularly in boys with obesity. Physical fitness of children and adolescents improved more in areas with lower levels of urbanisation, largely driven by reductions in undernutrition. However, rapid urbanisation was associated with increases in overweight and obesity and an overall decline in physical fitness.
Implications of all the available evidence
30 years of rapid economic development in China have been accompanied by a decline in the physical fitness of children and adolescents, including respiratory function, strength, explosive power, and cardiorespiratory endurance. Government policies should refocus away from underweight status to the maintenance of a normal weight and prevention of obesity. Advancing urbanisation seems to be a useful indicator of the need to adopt strategies to promote healthy and diverse diets, maintain physical activity, and reduce sedentary time.
The definition of physical fitness has evolved to include both metabolic and morphological components, and it commonly consists of four elements: muscular strength, muscular endurance, cardiorespiratory endurance, and motor ability.7 Although differences in measures of physical fitness exist, core items typically include endurance running (reflecting cardiopulmonary function),10 standing long jump, 1-min pull-ups and sit-ups (reflecting body muscle strength),11 sit-and-reach (reflecting hamstring and lower back flexibility),12 forced vital capacity (FVC; reflecting respiratory function),13 and the 50-m (or 60-m) dash (reflecting explosive force and speed). Therefore, physical fitness measurement integrates the different functions and structures that are activated during exercise, including musculoskeletal, cardiorespiratory, haemato-circulatory, endocrine-metabolic, and psychoneurological functions.14 Combining the core items into a summary physical fitness indicator (PFI)15, 16 allows the assessment of physical fitness at both individual and population levels.
Concerns about lower physical fitness and greater physical inactivity in children and adolescents have been raised in some areas of China. Changing patterns of weight might be one contributor to this change, given the association of obesity with poor physical fitness and cardiovascular risk.17, 18 In adults, a reverse U-shaped relationship between body-mass index (BMI) and physical fitness seems to exist, but this has been less explored in children.16 Upward shifts in BMI might become a major contributor to poor physical fitness in children and adolescents, even though undernutrition remains the major nutritional problem globally.19 In addition to the effects of a rapid nutrition transition, urbanisation is another potential contributor to low physical fitness, not only through increasing risks for obesity, but also through diminishing opportunities for physical activity.20
No previous study has comprehensively assessed trends in physical fitness among Chinese children and adolescents nor examined the effects of the nutrition transition and urbanisation. For these reasons, we aimed to assess secular trends in the physical fitness of Chinese students, including cardiovascular fitness, muscular strength, muscular endurance, speed, power, and flexibility from 1985 to 2014; assess the association between physical fitness and growth and nutritional status; and explore the effects of urbanisation on physical fitness in Chinese students.