Your testosterone panel came back fine. Here's the test most men over 40 never get.

If you're a man in your 40s doing everything right — training consistently, sleeping reasonably well, eating well — and you still feel like something has gradually slipped, you've probably gotten your testosterone checked at some point. And it came back fine.

This is a real and common experience. And it has an explanation that most primary care visits never reach.

There are two hormone axes, and most panels only check one

When men talk about 'checking their hormones,' they almost always mean the sex-hormone axis: testosterone, LH, FSH, sometimes SHBG and free testosterone. These are what primary care physicians run when a man in his 40s reports fatigue, low motivation, or reduced recovery.

But there's a second axis — the somatotropic axis, or GH/IGF-1 axis — that operates completely independently. It's governed by growth hormone (GH), released in pulses from the pituitary gland, and insulin-like growth factor 1 (IGF-1), its downstream signal produced primarily in the liver. These are separate systems with separate decline curves.

Most standard hormone panels don't test either.

The GH/IGF-1 decline curve

Pulsatile GH output peaks in adolescence and begins declining in the mid-20s. The decline continues at roughly 15% per decade — a gradual erosion that's largely invisible until the cumulative effect becomes noticeable. By age 40, most men have meaningfully less GH output than they had at 30. By 50, it's often further down.

IGF-1 follows a similar trajectory. Reference ranges for IGF-1 are age-adjusted precisely because the numbers are expected to drop — but 'within the normal range for your age' and 'optimal' are different things.

The symptoms that look like normal aging

Here's what's characteristic about GH/IGF-1 decline: the symptoms are easy to attribute to something else.

• Sleep quality changes — specifically the deep, restorative sleep that GH pulses are concentrated in. You may sleep seven hours and wake up unrefreshed.
• Slower recovery from training — tissue repair is slower, soreness lasts longer, adaptation feels like it's stalled.
• Body composition shifts — lean mass becomes harder to maintain despite the same effort. Abdominal fat tends to accumulate.
• Energy — not dramatic fatigue, just a slight erosion of baseline that's hard to point at.
• Mental sharpness — a mild fogginess or reduced clarity. Not depression. Just not quite crisp.

None of these symptoms are unique to GH/IGF-1 decline. They can come from testosterone decline, poor sleep hygiene, overtraining, stress, thyroid dysfunction, or just getting older. That's exactly why they get attributed to 'just aging' — they're nonspecific enough that a normal T panel feels like a reasonable explanation for everything.

But if your testosterone is genuinely normal and these symptoms are still present, the GH/IGF-1 axis is the next most logical place to look.

Why most physicians don't test it

• IGF-1 testing costs money and isn't reflexively included in standard male hormone workups
• The conversation about GH-axis support in otherwise healthy adults is newer than the testosterone conversation
• Growth hormone therapy has historically been associated with performance-enhancing use, which makes clinicians cautious — though GHRH-analog therapy (sermorelin) is a pharmacologically different category from synthetic HGH
• Primary care physicians often don't have a clear treatment path even if IGF-1 comes back low — it's not a straightforward 'replace it' situation the way TRT can be

The result: most men experiencing GH/IGF-1 decline never find out.

What the test looks like

IGF-1 is a serum blood test — the same kind of draw as a standard lipid panel. Reference ranges vary by lab, but a common range for men in their 40s is roughly 90–250 ng/mL (with the upper end typically higher in younger men). Low-normal or below-range IGF-1 with consistent symptoms is the profile that tends to respond to GHRH-analog therapy.

A licensed physician should interpret your IGF-1 in the context of your full intake — symptoms, history, and goals — not just the number alone.

What sermorelin does here

Sermorelin (a GHRH analog) signals your pituitary to increase its own GH output. If your pituitary still has functional capacity — which it typically does in men in their 40s with age-related decline, as opposed to men with pituitary disease — sermorelin can stimulate it to produce more. IGF-1 rises in response. Your feedback loop stays intact throughout.

The 6-week IGF-1 retest is how you know whether it's working for you specifically. A protocol that doesn't shift IGF-1 isn't doing what it's supposed to do, and a good physician will adjust.

The bottom line

'Your testosterone looks fine' doesn't mean the hormone picture is complete. The GH/IGF-1 axis is a separate system with a separate decline curve, and most panels simply don't test it. If you're a man in your 40s with the right symptom pattern and a normal T panel that doesn't explain everything, it's the most logical next thing to evaluate.