Hormones: what training does to them and what that means

For a long period, the acute hormonal response to training — the transient rise in testosterone and growth hormone after a hard session — was treated as a key driver of muscle growth. Whole training methodologies were built on maximising it.

The evidence has not been kind to that idea.

The acute hormone hypothesis

Resistance training produces measurable short-term elevations in testosterone, growth hormone and other anabolic hormones, and the magnitude varies with the training protocol — larger muscle mass involved, higher volume, shorter rest periods all produce bigger spikes.

The reasonable-sounding inference was that protocols producing bigger spikes would produce more muscle.

Studies designed to test this have generally not supported it. When researchers compared conditions producing large acute hormonal responses against conditions producing small ones, muscle growth outcomes did not track the hormonal response. Some studies found no relationship between the size of the post-exercise hormone spike and subsequent hypertrophy at all.

The current view is that these transient elevations are a marker of training stress rather than a mechanism of adaptation. Local signalling within the trained muscle — mechanical tension and the pathways it activates — appears to be what matters.

What this does not mean

It does not mean hormones are irrelevant. Chronic hormonal status matters enormously. Testosterone in the physiological range supports muscle mass; supraphysiological levels, as in anabolic steroid use, produce dramatic effects, which is precisely why they are effective and why they are banned.

Clinical deficiency states have real consequences for muscle mass, strength, bone and wellbeing, and they are a medical matter.

The distinction is between baseline hormonal environment, which matters, and the transient post-session fluctuation, which appears not to.

What actually affects baseline

The things that raise or lower resting hormonal status are unglamorous and largely outside the gym.

Sleep. Restriction reduces testosterone measurably within about a week. This is one of the better-supported findings in the area.

Energy availability. Chronic underfuelling suppresses reproductive hormones in both sexes. This is the mechanism behind relative energy deficiency in sport, and it is common.

Body composition. Both very high and very low body fat are associated with altered hormonal profiles.

Chronic stress. Sustained elevation of stress hormones is associated with suppression of the reproductive axis.

Age. A gradual decline in testosterone with age is normal in men, though the extent is variable and lifestyle-modifiable to some degree.

Alcohol, particularly heavy intake.

Notice that this list is essentially the same as the list of things that determine whether your training works. That is not a coincidence.

Testosterone boosters

The supplement category is large and the evidence is poor.

Most products contain herbal extracts with either no controlled evidence or evidence showing effects only in deficient populations. Where a product does raise testosterone in someone with low levels — vitamin D in deficiency, zinc in deficiency — the effect is correcting a deficiency, not enhancing a normal state, and it will do nothing for someone already sufficient.

The reasonable approach is to get blood work if you have symptoms suggesting a genuine problem, and otherwise to address sleep, energy intake and stress, which is where the actual leverage is.

Cortisol, briefly

Cortisol has been badly cast. It is essential, it rises acutely during exercise as part of a normal adaptive response, and trying to suppress the post-training rise makes no sense.

Chronic elevation from sustained stress is a different thing and is genuinely associated with impaired recovery. But the intervention is stress and sleep management, not a supplement.

Growth hormone

Similarly over-marketed. Acute exercise-induced elevation does not appear to drive hypertrophy. Administered growth hormone in healthy adults increases lean mass measurements substantially through fluid retention and connective tissue changes, with much less clear effects on muscle strength — which is a good example of a measurement not being the outcome you wanted.

The practical upshot

Do not design your training to maximise a hormonal response. Design it to progressively load muscle, which is the mechanism that actually operates.

Do protect your baseline hormonal environment by sleeping, eating enough, managing stress and not drinking excessively. That is where hormones are worth your attention, and it happens outside the gym entirely.