Metabolic health and biomarkers

What happens to your blood when you train: why certain values rise without cause for concern, and when you should pay attention.

Why you hurt after training (and when to actually worry)

Delayed onset muscle soreness arrives 12–72 h after an unaccustomed effort, especially eccentric work, and comes with a genuine rise in blood creatine kinase (CK) that can take days to come down. It is a normal adaptive response, not serious damage, and it does not correlate well with how sore you will end up. The real warning sign is different: dark urine ('cola-coloured'), extreme swelling and disproportionate pain after a very intense, unaccustomed effort, which can indicate rhabdomyolysis and requires urgent medical attention.

How to apply it

• Do not use your soreness level as a thermometer of whether a session was 'good': they do not correlate well
• If after a very intense, unusual effort you notice very dark urine or extreme swelling, seek medical attention: that is not normal soreness

Why blood work after a marathon can look like a heart attack without being one

After a very long endurance effort (marathon, triathlon), it is normal for markers to rise that in another context would suggest a cardiac problem (troponins, BNP): up to 90% of marathon runners have elevated troponins that normalise on their own within 24–48 h. The typical pattern ('rises fast, falls fast') differs from a real heart attack, and it is explained by the temporary stress on the heart during extreme effort, not by permanent damage. Even so, the clinical context (history, symptoms) is still what decides whether further investigation is needed.

How to apply it

• If you get blood work after a long endurance event and come back with slightly elevated cardiac markers, do not panic: discuss it with your doctor, giving the context of the event
• These markers must be interpreted knowing when the blood test was taken relative to the effort

The extreme exercise paradox: when 'more' stops protecting your heart

Regular moderate-to-vigorous exercise (150–300 min/week) reduces cardiovascular risk by 35–45% and is one of the best tools available against hypertension and type 2 diabetes. But extreme, chronic endurance exercise over decades (ultramarathons, very high intensity training sustained for years) has been associated with some fibrosis of the heart muscle and more atrial fibrillation in veteran athletes. The benefit-versus-amount curve is shaped like an inverted J: maximum benefit sits in the moderate-to-high range, not at the extreme.

How to apply it

• More is not always better for your long-term cardiovascular health: the moderate-to-high range already gives you almost all the benefit
• If you do extreme endurance chronically over years, periodic cardiological follow-up is worth it

Inflammation after training is normal (and sometimes necessary)

After an intense effort, your body raises inflammatory markers (C-reactive protein, IL-6) transiently for 24–72 h: it is not an infection or a problem, it is part of the normal repair response. In fact, the muscle itself releases IL-6 as a useful metabolic signal (it mobilises fat and helps maintain glucose), and regular long-term training lowers your baseline chronic inflammation rather than raising it.

How to apply it

• Do not read a slightly elevated CRP in blood work taken shortly after hard training as a health problem: ask when the test was done relative to exercise
• Long term, training regularly lowers your baseline inflammation, even though each individual session raises it temporarily

Why antioxidant pills can block your training gains

Exercise generates free radicals (ROS) that for a long time were seen purely as something harmful to neutralise, but they are in fact a necessary signal for adaptation: they activate the pathways that increase your own antioxidant defences, the creation of new mitochondria and improved insulin sensitivity. A widely cited study found that high doses of vitamin C and E in pill form block precisely those pathways, cancelling out part of the improvement in insulin sensitivity and mitochondria that exercise should give you.

How to apply it

• Do not take megadoses of vitamin C or E in pill form expecting to 'protect' your recovery: you may be blocking the very adaptation you are after
• Prioritise antioxidants from food (fruit, vegetables, green tea) over high-dose supplements: they appear to be more beneficial and less blocking

The danger of drinking too much water during exercise

Losing 2% of your body weight in sweat already reduces performance and concentration, and losing more than 5% is a genuine emergency (heat stroke, kidney risk). But the opposite mistake is also dangerous and less well known: drinking excessive water during very long efforts (more than 4 hours) can dilute your blood sodium so much that it causes hyponatraemia, with symptoms ranging from nausea to seizures, and it can be fatal without treatment. It is not the same as dehydration and is treated differently.

How to apply it

• In long efforts (>3–4 h), do not drink 'as much as you can': hydrate according to thirst and with some sodium, not just plain water non-stop
• If in a very long event you feel nauseous and confused after drinking a lot of water, consider that it may be excess water rather than dehydration

Electrolytes: what you actually replace in a normal session

Sodium is the electrolyte you lose most through sweat and the one that matters most to replace in long efforts or in high heat (it prevents cramps and helps you absorb fluids); potassium, magnesium and calcium are lost in smaller amounts and are usually covered by a normal varied diet. For a one-hour gym session in a normal environment, you do not need sports drinks or extra electrolytes: water and your food for the day are already enough.

How to apply it

• Save electrolyte drinks for long efforts (>60–90 min) or high heat/sweating, not for any gym session
• If you often cramp in long efforts, sodium is usually the first thing to check, not potassium or magnesium