Just as you’ve been enjoying summer’s longer hours of daylight, why do your efforts at increasing mileage get trashed by anaemia? Why might a coach or club see a cluster of cases?
- There’s some evidence (Thirup, 2003) of seasonal variation in haematocrit (% volume of blood that is taken up by red blood cells) with summer haematocrit being lower than winter. However, this is observed more for those living in warm equatorial climates - probably not something to impact those of us running in UK & Ireland.
- Seizing the opportunities of longer daylight, many of us have increased our weekly mileage. Each footfall has squeezed the red blood cells in capillaries to the extent that the more fragile, usually the oldest, have burst. These older cells were less efficient at oxygen delivery anyway; if they can now be replaced by production of new red blood cells we'll benefit from a very efficient population of young red cells. Training will stimulate erythropoiesis (red blood cell production). However, it’s a matter of balance: increase the mileage too suddenly and the destruction of red blood cells is too great to be quickly met by erythropoiesis – there’d be a period of low haematocrit and a concomitant struggle with the oxygen demands of exercise.
- After a winter of being restricted to footpaths under streetlights, runners are venturing off-road to trails and grass. The uneven surface requires greater twisting of the foot and, to better feel the ground, relatively uncushioned shoes are worn. These factors may be why Janakiraman et al (2011) observed that uneven grass surfaces resulted in greater haemolysis (red blood cell bursting) than an asphalt road.
It’s not just foot-ground impact that destroys red blood cells. The repeated contraction of muscles around capillaries can be so intense as to burst cells. Strength training, whilst important, will thus also cause haemolysis. Therefore, build strength gradually and don’t suddenly ramp up the weights and reps.
As there are many, many more causes of anaemia and it’s a condition that has significant impact upon runners, we’ll return to this topic again. For now, take care and don’t suddenly increase your training – make small increments (as a rule-of-thumb no more than 10% per week) and allow your body to reach a new, improved equilibrium. If in any doubt seek medical advice, anaemia may require more intervention than rest, good nutrition and iron supplements.
Further reading :
Mairbaurl, 2013 Red blood cells in sports: effects of exercise and training on oxygen supply by red blood cells.