A Responses of circulating irisin to different exercises in humans

Irisin is a newly characterized myokine that may aid weight reduction and insulin sensitivity. We have recently shown that circulating irisin increases in humans after acute exercise taxing the energy state of muscle. To further explore the types of exercise that upregulate irisin, we measured irisin using enzyme immunoassay in plasma of 30 swimmers before and immediately, 1 h and 24 h after two exercises of different intensities: a set of six 50-m maximal swims raising blood lactate to 17 mmol/l, and 2000 m of continuous swimming raising lactate to 6 mmol/l. Irisin increased (P < 0.05) only after the 6 x 50-m trial and then gradually returned to baseline. As a test of reproducibility of the irisin concentration, 14 swimmers performed two identical 6 x 50-m trials one week apart. Irisin concentration measurements proved highly reliable (intraclass correlation coefficient 0.921). Finally, to test if the blood lactate concentration is a good predictor of the irisin response to exercise, we measured irisin in 14 women who performed whole-body bilateral vibration training for 6 weeks. Despite raising the blood lactate concentration to only 5 mmol/l, vibration exercise increased irisin significantly both at the first and last training sessions. These data suggest that the response of circulating irisin to exercise depends partly on exercise intensity, although other characteristics of exercise may modulate this response.