Metabolic impact of exercise timing: Myonectin dynamics in overweight and obese postmenopausal women following...

Myonectin is a myokine that regulates lipid metabolism, and levels are often reduced in obesity and insulin resistance. This study examined whether the timing of exercise influences myonectin and metabolic responses to high-intensity interval training in obese postmenopausal women.

Fifty-eight sedentary postmenopausal women (body mass index 28-35 kg/m2) were randomized to high-intensity interval training or a control condition. The exercise group completed two counterbalanced cycling sessions (morning 08:00 h, evening 18:00 h). Blood samples were collected at baseline, immediately post-exercise, and 2 h post-exercise to measure serum myonectin, free fatty acids, glycerol, cortisol, and lipid profiles.

High-intensity interval training significantly increased serum myonectin 2 h post-exercise in both morning and evening sessions (p ≤ 0.01). Free fatty acids and glycerol increased (p ≤ 0.01), and triglycerides decreased (evening: -4.8%, p ≤ 0.01). Evening exercise produced a lower peak heart rate (p = 0.042) and perceived exertion (p = 0.031) than morning exercise. No significant changes were observed in high-density lipoprotein, low-density lipoprotein, or total cholesterol.

A single session of high-intensity interval exercise increased serum myonectin and lipolysis-related markers and reduced triglyceride concentrations in overweight and obese postmenopausal women. The higher 2-h myonectin value after evening exercise appears to reflect a time-specific variation rather than clear evidence of an overall evening-exercise advantage. Longitudinal studies using baseline-adjusted and mechanistic analyses are needed to determine whether acute timing-related differences translate into clinically meaningful adaptations. Trial prospectively registered at the Iranian Registry of Clinical Trials: IRCT20180822040849N3.