This age coincides with a strong cognitive and emotional load.
By the age of 40, many notice that their previous endurance has disappeared and fatigue has become chronic. However, the reason lies not so much in aging as in a combination of changes in physiological systems. This is reported by The Conversation.
In youth, biological processes operate at their peak: muscle mass is maximized, mitochondria are efficient, and sleep includes more phases of deep recovery. Hormonal rhythms are also stable, as cortisol, melatonin, growth hormone, and sex hormones are produced in predictable cycles, maintaining a steady level of alertness.
With age, these systems do not fail but gradually change. Muscle mass decreases without strength training, mitochondria work less efficiently, sleep becomes fragmented, and even with the overall duration remaining the same, the proportion of restorative phases decreases. In women, hormonal fluctuations play a special role, disrupting thermoregulation and sleep rhythms.
Moreover, at 40, the peak of cognitive and emotional load often coincides: managerial functions, responsibility for family. The work of the prefrontal cortex requires significant energy expenditure. At the same time, research shows that later the situation may stabilize because hormonal systems realign, cognitive load decreases, and physical activity continues to improve metabolism and energy levels.
