How do you run a sub-threshold session?

What should your heart rate do during the reps?

Climb a little from rep to rep, finishing each one under your threshold heart rate. Read the number at the end of each rep rather than the rep's average. Early reps finish well under the line, and the last rep finishes nearest to it.

On a watch, a sub-threshold session runs in Zone 4. The line it stays under is your threshold heart rate, the number a 30-minute field test estimates.

Hold one pace and your heart rate rises as the session goes on, so the first rep reads low. In one measured session of 10-minute reps at the same prescribed intensity, heart rate was higher in the second half than in the first.

In Norwegian singles practice, the first couple of reps end 10 to 15 beats under your threshold heart rate. The last ends a few beats under it.

What do you do when you hear Zone 5?

Ease off, unless it's the end of your last rep. Zone 5 at the end of your last rep means the session landed where it should: finish the rep and start the cool-down. In an earlier rep, ease off now and start the next rep a little slower. In most reps, it means the pace is set too fast, and the next session starts slower from the first rep.

We make the Zone 5 call the ceiling because the threshold sits at the top of Zone 4 on either zone method. Zone 5 is the first thing your watch can say that means you've crossed it.

Going over the line costs you fatigue out of proportion to the training it adds, even on a day you feel good. That cost builds up fast, and if you cross the line rep after rep, bring the pace down. One of the method's own runners once went over on purpose, lifting the pace in his last rep for about six minutes, and was trashed the next day. He couldn't have done that three times in a week.

Set your rep distance and 60 seconds of rest in Distance Intervals, with Intervals + HR Zones on. RunBeat calls each rep and speaks your zone as you run it, so Zone 5 is your cue to ease off:

Distance Intervals in RunBeat RunBeat calls the start and end of every rep, measured by GPS.

Which rep length should you run: 3, 6, or 10 minutes?

All three, one length per session. The method's week runs one short session, one medium, and one long.

Short reps are 3 to 4 minutes, 8 to 12 of them. Medium reps are 6 to 8 minutes, 4 to 6 of them. Long reps are 10 to 12 minutes, three of them. In distance, that's 1 km, 2 km, and 3 km.

The method sets each shape's pace from a race distance: 10-mile to 15K pace for the short reps, half-marathon for the medium, and 30K for the long. We run them by heart rate instead. A rep this long gives your heart rate time to settle, and the Zone 5 ceiling catches the last rep whatever pace you started at.

Pick a distance that takes about the intended time. Your 3-minute rep might be 600 m or close to 1 km, depending on your pace. The community guide allows short reps within about half a minute of the intended time, and medium and long reps within about a minute.

We put the work at 30 minutes because 10 short, 5 medium, or 3 long reps make the same session in three lengths. It sits inside the 28 to 35 minutes of work the method prescribes at seven hours a week. Reduce the rep count to fit your current training.

Daniels calls threshold reps with short rests cruise intervals, and asks for at least 30 minutes at threshold pace when the session is broken up. A tempo run spends the same minutes as one continuous block.

How much rest between reps?

60 seconds, standing, walking, or jogging. The rest is short so the next rep starts where the last one left off. It's there to limit the fatigue that builds across the session, and to let you correct a pacing mistake before the next rep.

The sub-threshold archive gives 60 seconds for every shape. The Norwegian singles community guide gives 60 seconds for 3-minute reps, 60 to 90 for 6-minute reps, and 90 to 120 for 10-minute reps. We run 60 for all three because a minute is enough to start the next rep in control. It's also short enough that you're still breathing hard from the last. If the long reps leave you unable to hold the line, take the guide's longer rests.

Shortening the rest, or jogging it faster, isn't a progression. The community guide says the same.

How should you warm up for a sub-threshold session?

10 minutes of easy running, then run the first rep slightly conservatively. Heart rate reads lowest in the first rep, so a pace that feels right there is usually a little too fast.

Finish with 10 minutes easy. The community guide's cool-down is 7 to 10 minutes of easy jogging. We take the top of it because the last rep is the one that ended nearest your threshold.

The guide puts eight 3-minute reps with seven 1-minute rests at about 48 to 51 minutes with the warm-up and cool-down. In Norwegian singles practice, a session runs about 65 minutes with both. Ours lands at about an hour.

How do you know you ran it right?

You finish with another rep in hand, and you don't run it. Your breathing stays controlled and the work manageable through the last rep. If the effort feels unusually high, slow down even when the watch numbers look normal.

The method's own runners put a session at 4 to 6 out of 10 on the watch's effort scale, and finish it able to run another rep.

On the watch, you heard Zone 5 once at most, at the close of the last rep.

The next morning's easy run should feel easy. If it doesn't, the session went over.

Can you run sub-threshold reps on a treadmill?

Yes. The time shapes run unchanged on a belt: 3, 6, or 10 minutes with 60 seconds of rest. The Zone 5 ceiling applies exactly as it does outside.

Set the belt to the speed that puts you in Zone 4. The heart rate at the end of each rep tells you whether to adjust it. For the rest, drop the belt to a walk, or step off and stand.

On a treadmill the belt's speed display stands in for your pace, and it can differ from the belt's true pace. Steer by the heart rate at the end of the rep rather than by the number on the console.