I have access to a treadmill, and living in the Northeast during the winter time I generally prefer to run indoors from December through about March. I do occasional long runs, but the goal of my weekday treadmill runs is to keep up my conditioning and perhaps work on some speed.
I've been running intervals one day a week to vary my workouts.
The treadmill I use has an interval setting with "jog" and "run" speeds, which I set to 6.0 and 7.0 miles per hour, respectively. I do a 35-minute workout in which the first five minutes are at the slower pace, run seven intervals spaced four minutes apart (1 minute run and 3 minute jog), then finish with two more minutes of jog.
I do this at work during lunch so increasing my total workout time really isn't an option.
What's the safest and most effective way to progress? As far as I see it, I can
- Increase my jog speed (in my case, 6.1, 6.2, 6.3... mi/hr)
- Increase my run speed (7.1, 7.2, 7.3... mi/hr)
- Increase my run times (e.g., run two minutes, jog two minutes keeping a four minute "block")
- Decrease the "block" time (e.g., run one minute, jog two minutes making a three minute block)
Runners, what have you tried? And what does science say is best?