Serum irisin levels are regulated by acute strenuous exercise.

Area of Science:

• Exercise Physiology
• Endocrinology
• Human Metabolism

Background:

• Irisin, a newly discovered myokine, is hypothesized to impact obesity and metabolism by promoting white adipose tissue browning.
• Existing clinical and functional studies on irisin's association with obesity, muscle mass, and metabolic status present controversial findings.

Purpose of the Study:

• To investigate the effect of four distinct exercise regimens on serum irisin levels in children and young adults.
• To systematically evaluate the influence of diurnal rhythm, anthropometric and metabolic parameters, and exercise on irisin levels.

Main Methods:

• Assessed serum irisin levels in relation to age, sex, obesity status, and body composition (fat-free mass, body cell mass) using bioimpedance analysis.
• Monitored irisin levels across different exercise interventions, including acute strenuous exercise, a 30-minute intensive bout, and longer-term physical activity.
• Examined the impact of diurnal variations, meal intake, and oral glucose tolerance tests on serum irisin.

Main Results:

• Serum irisin levels exhibited no diurnal variation and were unaffected by meals or glucose load.
• Irisin levels decreased with age, were higher in adult men than women, and significantly elevated in obese subjects compared to lean controls.
• A clear, immediate increase in serum irisin was observed after acute strenuous exercise and a 30-minute intensive bout, but not after longer-term physical activity interventions.

Conclusions:

• Irisin levels are significantly influenced by age, sex, obesity, and muscle mass, with no contribution from diurnal rhythms or meals.
• Short bursts of intensive exercise acutely and transiently elevate serum irisin levels in both children and adults.
• Long-term increases in physical activity do not appear to sustain elevated irisin levels.