Beyond cardio, resistance training is critical for sexual function. Data shows men who actively maintain muscle mass as they age are three times less likely to suffer from erectile dysfunction, low desire, and dissatisfaction with sex.

Muscle atrophy from bed rest or sedentary periods is rapid, with losses of up to two pounds in a week. Crucially, this muscle does not return simply by resuming basic activities like walking. Regaining it requires a deliberate return to resistance training; otherwise, the loss is permanent.

Focusing on building muscle is crucial for long-term health, particularly for women entering perimenopause. Muscle helps regulate blood sugar, reduces inflammation, and protects against osteoporosis, dementia, and heart disease, making it a vital health indicator.

Women should not fundamentally change their training principles during menopause. Data shows that the transition itself does not accelerate muscle loss. Sarcopenia is primarily exacerbated by physical inactivity, making resistance training a crucial constant throughout a woman's life.

Focusing on overall body fat percentage is an outdated approach. A more valuable future biomarker for health will be muscle quality, specifically the amount of fat that infiltrates muscle tissue. This fat is a better indicator of metabolic health and may store environmental toxins.

The common medical focus on excess fat is misguided. Dr. Lyon argues we are "under-muscled," and this is the root cause of metabolic disease. Since muscle is the primary site for glucose disposal, unhealthy muscle cannot absorb glucose effectively, leading to insulin resistance and subsequent fat storage.

Beyond movement, muscle is the most critical organ for healthy aging because it functions as a 'metabolic sink,' absorbing glucose from the bloodstream. Maintaining muscle through strength training is essential for regulating metabolism, preventing inflammation, and reducing the risk of chronic diseases like diabetes and dementia.

The medical focus on fat is misguided. Skeletal muscle is your "body armor" and metabolic currency. Higher muscle mass improves survivability from nearly every injury and disease, regulates glucose, and dictates your ability to remain mobile and autonomous as you age. It is the central organ of longevity.

A major pitfall of intermittent fasting is the loss of lean muscle tissue. To counteract this, it must be combined with dedicated resistance training. This combination allows for the metabolic benefits of fasting while signaling the body to retain and even build muscle, which can be tracked through strength gains.