Hormones and Training: What Actually Moves the Needle

Hormones are chemical signals that tell your body what to do with energy, muscle and recovery. No gym topic attracts more nonsense — from the 30-minute anabolic window to the belief that one set of squats raises your testosterone all day. Here is what actually matters if you train three to five times a week.

The post-workout hormone spike does not build muscle

After a hard session testosterone and growth hormone really do rise — testosterone typically 15–25% above baseline, growth hormone several times over. The catch is that the spike lasts 15 to 60 minutes and then everything returns to where it started. Studies comparing exercises with large and small hormonal responses found no difference in muscle growth once training volume was matched.

Practically: do not pick exercises because they supposedly boost testosterone. Pick them because you can add weight to them week after week. What builds muscle is 10–20 hard sets per muscle group per week, in the 5–30 rep range, taken to within 0–3 reps of failure.

Testosterone: what actually lowers it

In healthy men, day-to-day fluctuation is normal and you will not feel it. What lowers testosterone measurably and persistently is mostly boring stuff:

• Chronic sleep debt. One week at 5 hours of sleep drops daytime testosterone in young men by 10–15%. Aim for 7–9 hours with a bedtime that varies by no more than 30 minutes.
• Too aggressive a deficit. Below roughly 30 kcal per kilogram of fat-free mass per day, the body starts dialling down reproductive and thyroid hormones. For an 80 kg person at 15% body fat that is under about 2,040 kcal a day.
• Very low dietary fat. When fat drops below 20% of total calories, testosterone falls. Keep 0.8–1 g of fat per kilogram of body weight.
• Excess body fat. Above roughly 25% body fat in men, more testosterone converts to estrogen. Losing 5–10% of body weight often fixes this on its own.

Supplements do nothing here unless you have a documented lab deficiency (usually vitamin D or zinc) — and that shows up on a blood test, not in how you feel.

Cortisol is not the enemy

Cortisol mobilises energy and it has to rise during training — without it you would not lift the bar. The problem is when it stays elevated: six hard sessions in a row with no easy day, 5 hours of sleep, work stress and a calorie deficit all at once.

Signs you are there: resting heart rate 5–10 beats higher in the morning for three days running, strength down more than 10% on familiar lifts, broken sleep, no desire to train. The fix is not one more session of grinding it out. It is a deload every 4–8 weeks: cut sets by 40–50%, keep the load, and take 1–2 completely free days.

Insulin and meal timing

Insulin is not a problem unless you have insulin resistance or diabetes. For training, only two things matter: total daily intake and how you spread protein.

1. Protein 1.6–2.2 g/kg of body weight per day, in 3–5 meals of 0.3–0.4 g/kg (for 80 kg that is 25–32 g per meal).
2. Carbohydrates 3–5 g/kg if you lift four times a week, more if you run or play sport.
3. A meal with protein and carbs within 2–3 hours before or after training is plenty. The window is hours wide, not 30 minutes.

Thyroid and long diets

During a prolonged deficit, active thyroid hormone (T3) drops 15–20%, resting energy expenditure falls, and fat loss stalls. That is adaptation, not a broken metabolism. So: run a 300–500 kcal deficit, target 0.5–1% of body weight lost per week, and take a 1–2 week diet break at maintenance calories every 8–12 weeks.

Women and the menstrual cycle

In the luteal phase core temperature is 0.3–0.5 °C higher, so training in heat is harder and heart rate sits slightly higher at the same load. The evidence for programming around cycle phases is still weak — it is more useful to log energy, sleep and strength across 2–3 cycles and then place your hard days where the data says. A missing period for more than three months in a woman who trains is not a sign of good conditioning; it is a sign of eating too little.

When to see a doctor

• Fatigue and strength loss lasting more than 4–6 weeks despite good sleep and a deload.
• Loss of libido or absence of morning erections for over a month.
• No period for three months or longer.
• Unexplained loss or gain of 5 kg or more in 2–3 months, neck swelling, constant thirst, hand tremor.
• Resting heart rate consistently above 90, or below 45 without serious endurance training.

Testosterone is measured in the morning between 7 and 10 a.m. and confirmed with a second test on another day; it is usually run alongside LH, FSH, prolactin, TSH, full blood count, iron and vitamin D. Never start hormone therapy without lab results and medical supervision — it shuts down your own production and affects fertility.

The short version

• The post-workout hormone spike lasts under an hour and does not drive muscle growth — volume (10–20 sets per group per week) and progression do.
• 7–9 hours of sleep, 0.8–1 g/kg of fat and at least 30 kcal/kg of fat-free mass are stronger hormonal levers than any supplement.
• Cortisol is not the enemy; chronically elevated cortisol is — a deload every 4–8 weeks fixes most cases.
• Protein 1.6–2.2 g/kg per day across 3–5 meals; timing is flexible within a few hours.
• Symptoms lasting over 4–6 weeks, no period for 3 months, or sudden weight change mean blood work and a doctor, not a forum thread.