When to test in a training block
Blood tests are sensitive to what you did yesterday. Get the timing right and the numbers describe you; get it wrong and they describe your last session.
Markers that react to hard training
- Creatine kinase, myoglobin, AST climb for one to three days after hard, long or downhill sessions as muscle fibres repair.
- Urea and creatinine rise with dehydration and protein breakdown after a big effort, which can make kidney markers look worse than they are.
- hs-CRP and white cells rise with any inflammation, including the ordinary inflammation of a race.
- Haematocrit and haemoglobin read higher when you are dehydrated and lower once plasma volume expands with endurance training.
- Cortisol and testosterone follow a daily rhythm and respond to sleep and stress, so morning draws on a normal day are the most comparable.
Three good moments
Baseline. At the start of a block, after a couple of easy days, rested and hydrated. This is the reference everything else is compared with.
Mid-block. Six to eight weeks in, again after an easy day. This is where iron stores, vitamin D and the recovery markers show whether the training load is being absorbed.
Pre-race. Two to three weeks before a goal event, during the taper. Early enough to act on a low ferritin or vitamin D, late enough to reflect the block.
On the day
- Drink plenty of water beforehand. A concentrated sample skews several markers.
- Book a morning slot if your profile includes hormones; cortisol and testosterone are highest early.
- Keep the day before easy. Nothing long, nothing hard, no race.
- Test at the same point in the week each time so the trend is clean.
This article is educational. It explains what a marker is and what can move it; it does not interpret your results or replace advice from your GP.
