Introduction:
The development of medicine has allowed researchers to determine in detail the composition of the body, so that they can not only treat with great effectiveness, but also prevent, the development of modern civilization diseases. Measuring body fat and fat-free mass to determining the amount of water and minerals is a technique used in the daily work of doctors, dieticians, and personal trainers. Thanks to this knowledge they can establish diets, a preferred lifestyle, and physical effort levels. The most frequently used methods are anthropometric methods, hydrodensitometry, or bioelectric impedance analysis. Aim of the research: To analyse the influence of physical activity on body composition in both women and men using bioelectric impedance.

Material and methods:
The survey was conducted twice at a monthly interval, from 10.2019 to 02.2020. The participants were the same people, regularly attending the “36 Minutes Kielce” gym. The analysis of body composition was performed using the InBody 170-MEDFitness device. This analyser uses the electric impedance method. The results were obtained using a diagnostic survey recording the following: height, gender, age, body weight (kg), total body water content (l), adipose tissue mass (kg, %), muscle mass (kg), protein content (kg), mineral content (kg), fat-free body mass (kg), body mass index (BMI), visceral fat area, the basal metabolic rate (BMR), waist-hip ratio (WHR), segmental fat-free body mass (kg, %), segmental fat body mass (kg, %), muscle-fat control (kg), body composition history, the impedance of each segment and frequency, the Fitness scale, and obesity analysis.

Results:
The following changes were observed in the study group: average body weight decreased by 0.7 kg and skeletal muscle mass increased by 0.2 kg. The average adipose tissue mass was reduced by 1.1 kg, and consequently the water content increased by 0.2 l and the fat-free mass level increased by 0.3 kg. The WHR score decreased by 0.003 points and the visceral fat area decreased by 0.7, hence the average value of the basal metabolic rate increased from 1436.1 kcal to 1442.6 kcal. Normal BMI was achieved by 36.67% of the participants.

Conclusions:
The muscle mass gain is related to the total body mass gain, and our own research has shown a statistically significant relationship between these parameters. The reduction of body fat as a result of physical training reduces the overall body weight, and the difference between the amount of fat and the overall body weight is statistically significant. Height and weight have an impact on the body’s caloric requirements. Analysis of the value of the basic metabolic index confirms that the higher the weight and height, the greater the daily caloric demand. Physical activity affects changes in body composition, and the recorded values of body weight reduction, amount of fat, BMI, visceral fat level and skeletal muscle mass increase, and water and protein content are statistically significant.