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A total of 2340 medical students between the ages of 18 and 20 were recruited to Shenyang Medical College after obtaining approval from the Ethics Committee of Shenyang Medical College (Reference No. 2019-006). Of the total sample population, 37 declined to participate in the current study. In addition, eight people with respiratory, cardiovascular and/or metabolic diseases such as diabetes and thyroid disease in recent years were excluded. In addition, data on the anthropometric measurements of one male student and three female students were missing due to the absence of the male students during data collection.
Therefore, 2291 participants (19.09 ± 0.82 years) in total (815 males and 1476 females) were finally eligible for the statistical analyses, of which 1916 (83.63%) were Han Chinese (708 males and 1208 women) and 375 (16.37%) were ethnic minorities: 92 Mongols (30 men and 62 women), 13 Huis (5 men and 8 women), 12 Miaos (7 men and 5 women), 3 Yis (2 men and 1 woman), 7 Zhuangs (2 men and 5 women), 6 Buyis (3 men and 3 women), 4 Koreans (2 men and 2 women), 220 Manchus (52 men and 168 women), 2 Dongs (1 man and 1 female), 1 Bai (female), 7 Tujias (1 male and 6 female), 3 Lis (all female), 1 Mulam (female), 1 Gelao (female), and 3 Xibes (2 male and 1 female). Informed consent was obtained from each participant. The flowchart is shown in Fig. 1.
Study enrollment flowchart
Anthropometric measurement
Participants came to the test site abstaining from exercise and drinking alcohol or stimulants and fasting for at least 2 hours, and were asked to wear light clothing and no hats nor shoes, then their body weight and height were measured using standardized instruments. Body weight was measured to the nearest 0.1 kg and height to the nearest 0.5 cm according to standard procedures.
Body composition including total body water (TBW), fat mass (FM), protein mass (PM) and mineral content (MC) [12, 13], was estimated by the bioelectrical impedance analysis method using the BCA-1B body composition analyzer (Tsinghua Tongfang, China). The measurement was performed by a trained professional, and all participants were instructed to remove all metal accessories and stand barefoot on the analyzer.
Fitness tests
Physical fitness tests were conducted in accordance with China State Student Health Standards [14], which included body mass index (BMI), vital capacity (CV), sitting and lying position, standing long jump, pull-ups/crunches, 50m sprint and 800/1000m run . Detailed information on each test has been reported elsewhere [1, 15].
Body mass index
BMI is an indirect measure of body fat, and it was calculated by dividing body weight (in kilograms) by the square of height (in meters), as follows: BMI = weight (kg)/height (m )2.
vital capacity
Vital capacity is defined as the total volume of air that can be moved from the lungs by maximal expiratory effort, so it assesses respiratory capacity and speaks of respiratory health. VC was measured using model WQS-8888 (Shanghai Wanqing, China). College students had to put their mouths in the blowgun, stand in front of the device, and hold the handle properly. Then the students pressed the button on the device, took a deep breath, and exhaled completely. The device automatically calculates the maximum breathing capacity.
Sit down and reach
The sit-and-reach test was performed to assess lower back flexibility. Participants sat barefoot on the test instrument with their legs stretched out and gradually stretched their hands forward as far as possible. The test was administered twice and the best score was recorded.
Standing long jump
The standing long jump test was performed to assess the explosive strength of the lower extremities. The participants stood on the starting line and had to jump as far as possible. The distance was measured in meters from the starting line to the heel of the nearest foot. The test was administered twice and the best score was recorded.
Go back up
The pull test was used to assess upper body muscle strength. The test was scored based on the number of pull-ups. Participants jumped and pulled the bars with both hands. After stopping, participants fired with both arms at the same time. All male students took the test.
Crunches
Crunches are a commonly performed abdominal endurance training exercise to assess abdominal muscle strength. Participants had to lie down on a mat with their knees bent at 90°, raise their upper body and touch their knees with their elbows. The number of crunches performed in 1 minute was recorded. All the students passed the test.
50m sprint
A 50 m sprint test was conducted to assess the speed and explosive strength of the students. When the interviewer said “go”, the participants started the 50 m race. They finished the race as fast as they could. The time in minutes and seconds was recorded.
800 / 1000 m run
The 800/1000m is a complete sport that requires speed and endurance. The students stood at the starting line and had to complete the 800 or 1000 m test as fast as they could. The time in minutes and seconds was recorded. All female students ran the 800m race and all male students ran the 1000m race.
Fitness Score
According to the China State Student Health Standards, physical fitness was measured by physical fitness test scores, which are composed of three parts, including body shape score (BMI is 15 points ), body function score (CV represents 15 points), and physical quality score (sit and reach counts as 10 points, standing long jump counts as 10 points, pull-ups/crunches count as 10 points, the 50 m sprint counts for 20 points and the 800/1000 m race counts for 20 points). For students, fitness scores were calculated as total values, which were summed by each participant’s weighted score. The formula was expressed as: total fitness score = body fitness score + body function score + fitness score = BMI score × 15% + CV score × 15% + (sit and reach score × 10% + standing long jump score × 10% + pull-ups/crunches score × 10% + 50m sprint score × 20% + 800/1000m run score × 20%) [14].
Generally, BMI values have been divided into four groups. Also, based on the State Students Health Standards of China, the BMI ranges for male students, which are different from the World Health Organization, are as follows: underweight, 2; normal weight, 17.9–23.9 kg/m2; overweight, 24.0–27.9 kg/m2; and obese, > 28.0 kg/m2. In addition, for female students, the BMI ranges are: underweight, 2; normal weight, 17.2–23.9 kg/m2; overweight, 24.0–27.9 kg/m2; and obese, > 28.0 kg/m2. Students with normal BMI score 100 points, underweight and overweight 80 points, and obese 60 points [14]. All fitness test scoring standards are shown in Table 1.
Data analysis
To investigate associations between body composition (x) and fitness score (y), linear regression analyzes were performed. Two regression models were created: (a) unadjusted model and (b) model adjusted for student age and ethnicity. All continuous variables are reported as mean and standard deviation ((overline{x}) ± s). An independent sample you-test was performed to compare the mean difference between sex groups. Percentages were used to describe qualitative variables and the difference between the two sexes was compared using a chi-square test. Statistical analysis was performed using SPSS version 22. All hypothesis tests were two-tailed and one P
