Abstract
To elucidate the effects of endurance training on circulating irisin levels in young and middle-aged/older adults, and to determine the association between endurance training-induced alteration of irisin and reduction in body fat. Twenty-five healthy young (age 21 ± 1 years; 16 men, 9 women) and 28 healthy middle-aged/older adults (age 67 ± 8 years; 12 men, 16 women) participated in the study. Each age cohort was divided into two groups: the endurance-training group (14 young, 14 middle-aged/older) and the control group. Subjects in the training groups completed an 8-week endurance-training program (cycling at 60-70% peak oxygen uptake [O2peak] for 45 min, 3 days/week). Before and after the intervention, we evaluated serum irisin level, O2peak, and body composition. The increase in O2peak in the young and middle-aged/older training groups after the intervention period was significantly greater than those in the young and middle-aged/older control groups (P < 0.05). Serum irisin level was significantly increased in the middle-aged/older training group after the intervention period (P < 0.01), but not in the young training group. Furthermore, in the middle-aged/older training group, the endurance training-induced reduction in visceral adipose tissue area was negatively correlated with the change in serum irisin level (r = −0.54, P < 0.05). These results suggest a possible role for secreted irisin in the exercise-induced alteration of abdominal visceral fat in middle-aged and older adults.
Highlights
Fat accumulation induces obesity and increases the risk of type 2 diabetes, cardiovascular diseases, hypertension, and dyslipidemia
Given that fibronectin type III domain-containing 5 (FNDC5) expression in muscle [7, 8] and circulating irisin [9] are positively correlated with body mass index (BMI), it is unclear whether irisin plays a role in exercise training-induced reduction of body fat accumulation
In the middle-aged/older training group, % fat, whole-body fat mass, and abdominal visceral adipose tissue were significantly decreased, and VO2peak was significantly increased after endurance training (P < 0.05, Table 2)
Summary
Fat accumulation induces obesity and increases the risk of type 2 diabetes, cardiovascular diseases, hypertension, and dyslipidemia. The FNDC5 gene encodes a type I membrane protein that is proteolytically cleaved and subsequently secreted into the blood as a cytokine called irisin. Bostrom et al [5] demonstrated that irisin secreted by skeletal muscle upregulates uncoupling protein 1 (UCP1) gene expression via activation of PPAR-α protein in white adipose cells, thereby increasing energy expenditure through thermogenesis. A high level of circulating irisin may be associated with resistance to fat accumulation throughout the body. Given that FNDC5 expression in muscle [7, 8] and circulating irisin [9] are positively correlated with body mass index (BMI), it is unclear whether irisin plays a role in exercise training-induced reduction of body fat accumulation
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