Running: High heart rate during first 10 minutes

rrowdiness

Hey all,

I recently invested in a HRM (Garmin 910 xt package) and have been tracking zones as part of training for a marathon later in the year.

I've noticed that the first couple of km of any given run, my heart rate is measured in Z4-5, at the high 160s and 170s, then it drops back down into Z2-3 suddenly. It's very consistent across sessions - in 8 out the past 10 there has been a big spike at the outset bumping along at the top of Z4.

Pace, incline etc are consistent across the first couple km and I don't go out hard. Aside from this first period, I would not get up into Z5 unless doing intervals.

Any ideas?