Intense physical exercise and sperm count

Dear Professor Winston,

I’m currently training for a Half Marathon which is in three weeks time, however I am concerned that the intense exercise will affect my sperm count.

My wife & I are trying for a second baby and I am worried that after 6 months of trying, my training is doing more harm than good.

Should I stop training to improve my sperm’s chances or shall I continue running 30-50k for the next 3 weeks and then focus on the baby?

Kind regards,


Dear J.,

It’s too late now.

Sperm formation and maturation takes approximately three months so what you do in the next three weeks won’t make much difference – though I suppose there’s a faint chance whilst you speed up your sperm might swim slower.

Robert Winston