Originally Posted by GirlyGirl
Outdoor activity will always cause a slightly higher HR than in the gym-weather, terrain changes (even what seems flat has changes compared to a treadmill) and the chest straps (I"m asssuming it's a Polar) are very accurate, as where grabbing onto the handles of a machine for a few seconds, not so much. Go by your monitor, grab some tunes, and find some good scenery! You can also use the tradmill at the gym at 1% incline, use your chest strap monitor and see what it says-supposedly a t-mill at 1% is close to mimicking outdoor walking/running.