I'm a 21 yo F. BMI 25. I started running last autumn, I've always been slightly overweight, and not very fit. I'm training to run my first 5km, and I recently bought a heart rate monitor. I calculated my resting heart rate, 59-60 bpm. This morning I went to the gym for the first time with the HR monitor. I walked to the gym at a fast pace, and when I put the strap on, it already read 154bpm. I jumped on the treadmill, thinking that it would go down during the first minutes of warm up at 6.0 km/h. It didn't. Here is the graph:
http://i68.tinypic.com/11so08z.png
I walked for the first 10 minutes at 6.0km/h, then I tried running at 7.5 km/h (the first spike in the graph, reaching zone 5). I went back to walking but I increased the incline to 10%, staying for 22 minutes in what the HR monitor says is zone 5.
Now, I know zone 5 is an exercise intensity not sustainable for more than 3 minutes, so something's surely wrong. Also, it wasn't even too hard, I stopped just because it was late and I had to go to lectures. I know the monitor was picking out the right heart rate since I measured it myself as soon as I stepped down from the treadmill.
Can you tell me what this means?