Interval Training for Runners: How to Structure a Session

The interval session I remember is not the fast one. It is the one where the first rep was a show, the recovery was a token jog, and rep four was a different sport. I got the kilometres. I did not get the session.

Intervals are the sharp day. Short hard repeats, rest between them, aimed at the top of the aerobic work. In Daniels' system that interval pace sits near current 5K effort, sometimes a touch faster, fast enough to stress the ceiling and not so fast that you are sprinting the first one and surviving the rest. The VDOT pace calculator will put that next to every other zone from a recent race. "A bit quicker than I felt like" is how the show starts. (Daniels, 2013)

Because the effort is high, it does not belong in a continuous run. That is what a tempo is for. Seiler and Tønnessen kept landing on the same split: about 80% of sessions clearly below lactate threshold. The hard day is the exception, not the week. One interval day is enough for most people. Two is for someone whose other days are actually easy and who is already in a block that can hold it. Copying a stack of these because a program looked serious is how the easy week disappears. (Seiler & Tønnessen, 2009, Sportscience)

How I build the thing

I want a track, or a path I can repeat without a junction in the middle. Warm up 10 or 15 minutes easy, then a few short strides so the first rep is not also the warm-up.

The repeats themselves are usually a few minutes, the sort of thing that lands around 800 to 1600 metres depending on pace, and I would rather four honest ones than eight that decay. A 10K example I use: 5 × 1000 metres at interval pace, with about 400 metres of easy jog between. The rest is equal to the rep or a little shorter. It is a jog or a walk, not a collapse, and not a full reset either. The point is to start the next one at the right effort. Cut the rest to make it "harder" and you are training fatigue, not the pace.

The first rep should feel controlled. If you nail it and fade by the fourth, you started too fast. One or two words, not a phrase. An effort you can repeat, not an all-out. Cool down easy. Then leave it.

I do not put this on a morning the legs are already loud. This session amplifies whatever you brought. Tired plus fast is where people pick up the niggle they then have to explain to the rest of the plan. If readiness is poor, the honest version is a shorter set, an easier day, or nothing. The kilometres can wait. The injury you talk yourself into cannot.

Runapt schedules the interval day from the goal and your VDOT, and looks at readiness before it tells you to push. A bad night or a week that already spent itself should pull the session down, not dare you through it. Build the plan free and take the first rep slower than the one you would post.

Sources

Daniels, J. (2013). Daniels' Running Formula (3rd ed.). Human Kinetics.

Seiler, S., & Tønnessen, E. (2009). Intervals, thresholds, and long slow distance: the role of intensity and duration in endurance training. Sportscience, 13, 32–53. https://www.sportsci.org/2009/ss.htm