Reaching 40 often represents an important transition period in how you handle stress, both physically and mentally. This is because at 40, your youthful biological ability to manage stress faces off against the maximum stressors that adults have to face in career, caring for older parents, children who become teens, and other financial strains. Burnout at this stage of life does not involve only mental exhaustion but also a systemic breakdown resulting from hormonal, metabolic, and decades-old stress.
Slow Reduction of Free Testosterone

Testosterone levels in men gradually reduce at the rate of 1% annually after the age of 30 years old. After reaching their forties, this reduction may cause chronic tiredness, brain fog, lack of motivation, and a severely diminished ability to recover from both psychological and physical stresses.
Stress from the Cognitive Challenges at the Career Peak

At their midlife stage, many people are typically in positions of responsibility, such as senior managers or specialists who require making decisions, carrying responsibilities, and navigating office politics. All of these things consume one’s mental energies.
Reduced Growth Hormone & Sleep Efficiency

Slow-wave sleep automatically decreases as we grow old primarily because of a fall in growth hormone production. You may sleep for eight hours, but by 40 years of age, the quality of your sleep is not what it used to be, and you feel tired and burnt out even after sleeping for eight hours.
Diminished Biological Margin for Error

If you were a young man or woman, then you could stay awake all night, work hard in the office, and get back into shape within days. But once you become 40, your margin for error is reduced, and one week of unhealthy activities can set you back by weeks before you come back into form.
The Existential Realignment of Middle-Age Life

It’s not just about being physically exhausted; your midlife crisis may also be an existential crisis. Once you become 40, you start questioning yourself and why you spent your life achieving what you did, and how it does not make sense with what your true goals were in the first place.
Gradual Insulin Resistance and Glucose Instability

Metabolism becomes less flexible with age. Should you begin experiencing insulin resistance around your 40s, your body finds it increasingly difficult to effectively extract glucose from your bloodstream to convert into energy, thus leaving you prone to sudden drops in blood sugar and associated cognitive impairment and dependency on coffee, which further exacerbates burnout.
Dehydrated Joints and the Toll They Take

As your tissues become dehydrated, you start feeling pain from stiff joints, aching backs, and old injuries in a regular manner, which saps your strength daily, since your brain is constantly trying to make sense of these signals.
Loneliness and the Village Effect

Due to the demands put upon by life and career, your social life may suffer as you don’t have enough time for it anymore, depriving you of an important way to help your nervous system relieve itself of stress because there is no longer a “village” for you to relax around.