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?

5 Answers 5


Not a scientific answer, but one from a lot of experience... Don't run faster during your jog periods. If you don't recover during these times, you won't perform optimally during your intervals. Addressing the safety part: only change one aspect each workout. So in your next run you might try running at a faster pace, but keep the durations constant. Then next week, keep your pace at its new, faster rate, and bump up the durations a bit. But running faster for a longer time is an invitation to injury.

  • 6
    Something to keep in mind is that even if you keep duration the same, if your speed goes up, your mileage goes up. General wisdom states that you shouldn't increase your mileage more than 10% per week in order to avoid injury.
    – EmmyS
    Feb 8, 2012 at 21:22

To some degree you need to decide what your goal in running the intervals is; that will guide how you adjust.

Basically, if you want to get faster you should run faster intervals and leave the rest the same (i.e. good or full recovery). If you want to get stronger or hold a quick pace longer, you should shorten the recovery periods or extend the length of intervals (make the hard/easy ratio bigger).


I haven't used the interval setting on a treadmill so I can't answer to that.

However, I've usually found that running once around a track (400m or 1/4 mile) hard, walking 1 1/4 (100m) around the track and continuing that process for 'x' miles to be a success.

So, I'd probably recommend increasing your run times and run speed. You may find in doing so that you need to decrease your jog speed.

I'm not sure that there is a scientific answer to this problem and if you ask 10-20 great runners, you'll probably get 5-10 varying opinions.

  • 1
    Also forgot to add that you'll want to slowly increase both. Anything drastic can cause injury. I would probably try increasing your run times first and once you are at a 4:1 ratio for run:jog, then increase your speed or overall workout time. Feb 8, 2012 at 21:31

If you want to run faster, then I would concentrate on interval training based on Jack Daniels work (also on Wikipedia).

You can find a page that will help you with all the relevant numbers here. E.g. if you run 7:15 per mile, then you should consider training intervals where you run 400m in 1:55 then jog 1 minutes and repeat this 4-6 times. That should improve your running speed pretty drastically over 4-6 weeks.

Good luck!


If you have an interval setting that's working out for you, perhaps instead of trying to adjust it, you could adjust other factors at your disposal.

Is there an incline feature, causing you to be moving uphill? This will give you the ability to substantially increase your challenge over time. I grew up in a very hilly area and always found great pleasure and challenge in tackling the hills the long way up.

Another thing to consider is that if this is just to keep up your conditioning, perhaps you shouldn't alter this run. Instead, focus on runs where you do have more flexibility and less time constraints. If this is on your lunch break, is a more challenging run going to interfere with your afternoon of work?

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