So, you only have a half hour free? Never fear. You have plenty of time for a productive run. Here are a few types of training sessions to choose from.
A Recovery Run

The day after any race or hard training session, and at least a couple of days a week, you’ll need a recovery day. As long as you’re far enough along in your training that the term “easy run” makes sense to you, then an easy run is a perfect recovery plan.

All you have to do is jog at your usual warmup pace for 20–30 minutes. And you’re done. An easy effort like this gets your blood flowing to your muscles to speed recovery and help keep you from getting stiff. It helps you recover more quickly than if you stayed on the couch. It can help boost your energy levels and your mood and make you feel more awake. And it takes hardly any time or effort.

A Short High Intensity Interval Session

Alternatively, if it’s not a day when you need to recover, you might choose a high intensity workout. This plan requires a bit more precision, because you’ll need 10 minutes to warm up. And while sports scientists are conflicted on the need for a cool-down, most runners feel better with at least 5 minutes of easy jogging between their hardest efforts and coming to a full stop. This means you’ve got 15 minutes for the meat of your workout.

Which is enough. There are dozens of possible interval workout plans. Sports science research shows that they all work. The research does not conclusively demonstrate that any one plan is better than any others. Science tells us is that the intensity of the work intervals is the most important factor.

Meanwhile, experience tells us that we’re probably going to plateau after any sustained period of improvement, at which time changing the program is the best solution. So whatever type of interval program you choose, be prepared to change to a different one sooner or later.

Here are a few possible programs for a 15-minute interval workout:

  • 1 minute on, 2 minutes rest, x5
  • 30 seconds on, 2-1/2 minutes rest, x5
  • 4 minutes on, 1-minute rest, x3

In all cases, rest should be either a slow jog, comparable to your warmup pace. Notice that the rest interval gets progressively longer with shorter work intervals. This is because shorter work intervals are going to be more intense. By the end of your final interval, you should be very excited by the prospect of stopping.

You can set a timer to prompt you when to start and stop, or make a custom music play list, or find some rolling hills and let the terrain control the intensity. As long as you can get the intensity up, you can fit a powerful workout into your half hour.

Make the Most of the Last Run Before a Race

If you have a race the next day, you can fit a final prep run into a short time slot. This is typically a low-intensity run with two or three moderately fast efforts thrown in to help you loosen up and get a bit of speed work.

Run at your warmup / recovery pace, and intersperse a few 30-second-long, fast efforts. These aren’t intervals—don’t push yourself until your muscles are burning and you’re breathing too hard to talk. Just run enjoyably fast and drop your speed back down before you feel you’re working hard.

Technique Practice

A final option is to have a technical day. Pick something you know you need to work on, whether it’s cadence, stride length, posture, or forefoot landing.

Or do a specific running-related exercise. After a 10-minute warmup, work on high-knee, butt- kick, or side-step exercises. These exaggerated motions can build strength and coordination, and help your muscles by breaking them out of their repetitive routine.