The "endocrine evolution" of the aging male refers to the gradual, progressive decline in androgen activity—specifically testosterone—mediated by the degradation of the hypothalamic-pituitary-gonadal (HPG) axis. Unlike female menopause, this process (often termed Late-Onset Hypogonadism or LOH) involves a slow attrition of testosterone at a rate of approximately 1% to 2% per year after age 30 or 40.

Clinical Physiology and Symptoms

This decline is characterized by a "saturation model," where physiological functions become impaired once testosterone falls below a critical threshold. Symptoms are categorized into three primary domains:

• Sexual: Loss of libido, erectile dysfunction (ED), and fewer morning erections are considered the specific "core triad" of symptoms.
• Physical/Metabolic: Includes sarcopenia (muscle loss ...