Abstract
Exercise-induced release of irisin may mediate the beneficial effects of exercise on cognition. Although exercise induces a short-term transient acute increase in circulating irisin, a longer-term adaptative improvement in basal irisin concentrations may also be possible in older adults. Whether an increase in basal and acute irisin is a mechanism that underpins training-induced cognitive gains in older people is unclear and warrants investigation. Thirty healthy adults aged >65 years were recruited into a 12-week single-arm exercise trial. Twenty-four subjects completed 12 weeks of progressive resistance training, 3 times per week, at 80% 1-repetition maximum, with a convenience sample of 6 subjects continuing normal activity as a reference group. Body composition, cognition measures, and circulating irisin concentrations were collected pre- and post-training intervention. Circulating irisin concentrations were sampled pre- and 0, 30, and 60 minutes postresistance exercise at the first and final exercise session. Twelve weeks of resistance training did not increase basal irisin concentrations and seemed to attenuate response. Peak irisin concentrations increased only after a single bout of resistance exercise before 12 weeks training (1.8 ± 3.6 ng·ml−1, p < 0.001). Verbal fluency improved (1.0 ± 1.7 points, p = 0.007) after resistance training, while memory change correlated with pretraining basal and posttraining peak irisin levels (r < 0.423, p < 0.040). These findings implicate regular doses of irisin in response to exercise, but not longer-term basal improvement, as the most important outcome of exercise training in healthy older adults. However, attenuation of acute irisin over the training period suggests that the ability of irisin to influence brain health may decline as training progresses.