The Impact of the Recreational Physical Activity on Irisin Levels, Endothelial Progenitor Cells and Metabolic Profile in Healthy Children

This cross-sectional study was conducted in a representative group of children aged 6 to 14 identified in the Youth Healthcare Centre located near the Federal University of São Paulo (São Paulo, SP, Brazil). A total of 110 children were identified during the study period. However, five individuals with respiratory problems and 12 individuals who did not agree to participate were excluded from the study. In addition, 13 individuals who have not completed anthropometric, metabolic or physical fitness assessments in the post-training period were also excluded. Therefore, 80 children (32 girls and 48 boys) were included for this study. No child had any clinical signs of musculoskeletal or orthopedic disorders that prevented them from performing the proposed physical fitness tests. The Ethics Committee of the Federal University of São Paulo approved the study protocol (Number: 795.262). All parents and children signed written informed consent/assent forms.

Experimental Design: Each child completed the experimental protocol over a period of 10 weeks consisting of the baseline measurements of anthropometric data, body composition, irisin levels, metabolic and physical fitness parameters. All these measurements were repeated after the 10-week recreational physical activity program and were carried out within 72 hours after the last training session.

Recreational Physical Activity Program: Participants performed 10 weeks of recreational physical activity program on circuit training, that consists of exercise program for flexibility, coordination, strength (upper and lower limbs), aerobic resistance controlled by use of the Polar S810i monitor (Polar Electro OY, Finland; sampling rate=100Hz) and dynamic balance to improve the functional capacity. A total of 40 sessions were performed with duration (60 minutes), intensity (65%-85% heart rate reserve), and frequency (4 sessions/week). Each session consisted of three parts: Warm-up (10 minutes), physical activity session (45 minutes) and cool down (5 minutes). Moreover, subjective Borg scale of perceived exertion was applied to all children for control of the training intensity.

Anthropometry: Body weight and height were measured in light clothing without shoes using a standard balance beam scale. Waist and hip circumferences were measured using inextensible tape. Waist circumference was recorded at a level midway between the lower rib margin and the iliac crest at the end of normal expiration. .

Body Composition: Body composition was evaluated using bioelectrical impedance with a single-frequency hand-to-foot (ImpediMed DF50 monitor, Impedimed, Australia). Children were asked to avoid physical activity and to consume liquids 2 hours before evaluation to prevent errors in measurement due to fluid imbalances. This evaluation was performed after 5 minutes of rest in the supine position, and the electrodes were applied to the hand, wrist, ankle and foot of the right-hand side of the body. Body fat was calculated with prediction equations.