I would like to follow the 4 week plan (3 running sessions/week) on this site but I already run on average 4 times a week for about 9 to 10 km each session. Will that mean that I'm going backwards as on the plan, the runs cover less in distance. Also, I don't understand what the 'M' means in '2M easy'. Does it mean miles? Also, what does stride means? I only have a heart rate monitor and I'm not too sure of the distance as the route's not marked except for a small part. Is there a correlation between heart rate and speed?