When training stops working, check iron and thyroid before programming

Iron deficiency without anaemia

Ferritin can be low enough to cause fatigue, breathlessness on effort and poor training response while haemoglobin is still entirely normal — so a standard blood count comes back reassuring. This is common in menstruating women, especially with heavy or lengthening perimenopausal bleeding, and in endurance athletes. Ferritin is an acute-phase reactant, so it rises with inflammation; that is why it is read alongside hs-CRP and transferrin saturation rather than alone.

Thyroid, including the antibodies

Autoimmune thyroid disease is several times more common in women than men and its prevalence rises with age. TPO antibodies can be positive while TSH is still within range, which identifies who is likely to drift. Over-replacement is its own problem: too much thyroid hormone accelerates bone loss and provokes palpitations, so the target is correct, not high.

What to do about the training itself

Once those are addressed: progressive resistance work at least twice a week taken close enough to effort that the last repetitions are genuinely hard, protein above the minimum and spread across meals, and enough easy aerobic volume to build a base with one or two genuinely hard interval sessions on top. Under-fuelling is the other common cause of a stalled response, and in women it also suppresses the reproductive axis.

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