You did not get lazy. The stimulus stopped landing the way it used to.
From middle age, skeletal muscle mass begins to decline at roughly 1% per year — and the driver is not simply that people move less. It is anabolic resistance: a desensitization of muscle to the normal signals of feeding and exercise, so the same protein and the same session produce a smaller response than they once did (Wilkinson, Piasecki & Atherton, Ageing Research Reviews, 2018).
What "anabolic resistance" actually means
A one-sentence definition: anabolic resistance is when muscle responds less to the same amount of protein and training than it used to — a measurable change in the signal, not a failure of effort. The input is the same. The output shrank. That is why "I train the way I always have and it isn't holding" is a physiology statement, not a character flaw.
Why your labs won't show it
A standard physical is not built to see this. It measures glucose, cholesterol, a blood count — not body composition, not muscle status, not the drivers of metabolic change. This is the same blind spot that lets a normal fasting glucose sit clean for years while insulin resistance is already climbing (Tabák et al., Lancet, 2009). The panel reads "fine." The trajectory says otherwise.
Insulin sensitivity starts its steep decline about five years before a diabetes diagnosis. Fasting glucose only moves at about three years.
The Whitehall II cohort (n=6,538). The gap between those two curves is the years a standard glucose test reads clean while the system is already working harder to keep it there. Schematic — shape, not measured values.
The input is the same. The output shrank. That is physiology, not a character flaw.
The part that responds
Here is the honest and useful part: it moves. In a randomized trial of older adults with obesity losing weight, a resistance and impact training program produced greater gains in physical function and body composition than aerobic training, with comparable fat and visceral-fat loss over twelve weeks (Mesinovic et al., J Cachexia Sarcopenia Muscle, 2025, n=49 completers). Structured, targeted work still moves the needle — the point is to know which levers are yours to pull.
From middle age, muscle mass declines at roughly 1% per year — and anabolic resistance is a principal driver.
The decline is not simply inactivity. It is a desensitization of muscle to the normal signals of feeding and exercise (Wilkinson, Piasecki & Atherton, Ageing Research Reviews, 2018). Schematic — shape, not measured values.
The response is smaller than at 25, which is why what you measure and how you train matter more, not less. A gradual decline is common — and it is responsive to targeted resistance training.
Want to see which levers are yours to pull?
Kassy Wellness measures the drivers behind metabolic change — fasting insulin and HOMA-IR, visceral adiposity, and body composition — interpreted against optimal ranges by the clinical team.
What to measure instead of the scale
Up to about 30% of people who are "obese" by BMI are metabolically healthy, and plenty of normal-weight people are not (Engin, 2017). The scale is a poor proxy.
Up to about 30% of people who are "obese" by BMI are metabolically healthy, and plenty of normal-weight people are not (Engin, 2017). The scale is a poor proxy for what is actually happening underneath it.
A physician-led read looks at body composition and muscle status, fasting insulin and HOMA-IR, visceral adiposity, and glucose regulation in context — against optimal ranges, interpreted clinically, never as a self-assigned diagnosis.
Where to start
If the pattern in this article is your last few years, the first step is simple: measure your baseline. Kassy Wellness measures the drivers behind metabolic change — fasting insulin and HOMA-IR, visceral adiposity, and body composition — characterized and interpreted by the clinical team against optimal ranges, not disease cut-offs.
You did not get lazy. The stimulus stopped landing — and that is measurable.