Is a 12 minute mile too slow?

I know this is an older thread, but I am sure I am not the only one who ran across this thread while doing a search. I started working on losing weight back at the beginning of May of this year(2013), and progressed from walking twice a day, 1.2 miles each to the point where I can now run 6.2 miles straight. Now, one thing that is very very helpful when it comes to the subject of what speed is best is to get a heart rate monitor. The heart rate monitor will let you easily see how hard your heart is working, and THAT is what will let you know if you are pushing too hard or too little.

First, if your heart rate is HIGH, then that will limit how long your body will be willing to keep going, almost more than anything else. For myself, if my heart rate is upward of 165 beats per minute, I KNOW I can't sustain that for more than maybe one mile. A 151-155bpm rate on the other hand will let me go for 6.2 miles. At that point though, I feel it in my ankles, and it will take a few more weeks before I want to run any further than that. My normal run, sticking to that rule of 151-155bpm has me doing around an 11 minute, 45 second mile, which translates to roughly a 5.2 mile per hour average speed. When I do a 5K run now, I am aiming for a 10 minute, 20 second mile on my next run, and I generally do the 5K(3.1 miles) in around 33-34 minutes.

So, that is the thing to look at for each person, how fast is your heart beating for the speed you are running. Those who are in GREAT shape have the advantage that their heart doesn't have to work as hard when they are running, so they can run faster while their body is working just as hard. For those new to running, myself included, our bodies are not nearly as efficient when it comes to running, so we do what we can, and over time, it will increase. I have noticed over the past several weeks that my heart rate IS slowly starting to go down while running at these speeds, and as it goes down, it allows me to increase my pace SLIGHTLY. If you don't have a heart rate monitor, you won't see the effect of heart rate on how well you feel on a run.

I STRONGLY suggest a decent watch based heart rate monitor for EVERYONE, and I wish I had bought mine earlier in my journey toward losing weight and getting into better shape. I picked up a Polar RS300X for $90, and while I do wish it had more features, as a beginner monitor, it does the job well enough for the moment. Each person is different, you will need to figure out what your actual maximum heart rate is over time, but you WILL see that if you watch your heart rate, and just aim to keep your heart rate down, you can go longer distances, and if you increase your pace, you will find yourself unable to go very far. You will still need to listen to your body to avoid hurting your ankles, shins, and knees, but using heart rate instead of TIME as my guide on a run, it has allowed me to go from BARELY able to do a 3.1 mile run to now barely able to do a 6.2 mile run in only one month.

So, if you need to stick with a 12 minute mile to keep your heart in the zone to let you run longer distances, then stick with it. I will also point out that your height and weight have a huge amount to do with speeds. Those who are taller will have longer legs generally, and that will let them run faster for the same amount of physical effort. Those who need to lose weight are hauling all that extra weight with them as they run, and that also mean you are doing a LOT of extra work. I've managed to drop 28 pounds since May 1st, and that has a lot to do with the improvements I have seen in my ability to run. I still want to drop another 36 pounds, so I have a lot of room for improvement.