I'm a reasonably fit 52 year old, have payed football and trained all my life and despite a few injuries have managed to keep training doing HIIT's, circuits and weights. I'm trying to get back to my running but really finding it hard to keep the pace and times of a few years ago, the other day I had to stop while running 6k as I had "nothing in the tank" after 4k when a few years ago I used to run further than that without breaking sweat!
Might seem a silly question but yesterday on a treadmill I managed 6k in 30mins but was knackered after and my average heart rate was 154BPM. Could it be that I'm trying to run too fast and struggling as I'm spending too much time in a high heart rate zone so fatiguing quicker, is the simple answer to slow down to keep my heart rate lower?
Sorry if it's a dumb question but I'm trying to get my head round the reason for not running as fast as I want.