Thirty-Nine

The first hard frost rolled through western Mass last night. Lawns went silver, windshields went opaque, and a lot of bikes got one step closer to the trainer.

Moving indoors usually comes with a sense of dread. Long rides staring at a wall. Twenty-minute threshold intervals where the clock seems to run backward. If we're going to suffer inside, the thinking goes, we'd better suffer for a long time.

Norwegian sport scientist Bent Rønnestad has spent years testing a different idea. In a 2020 study, his team split 18 elite cyclists into two groups. One rode a classic interval workout: 4 × 5 minutes hard, 2.5 minutes easy. The other rode 30/15s: three sets of 13 × 30 seconds hard and 15 seconds easy, with three minutes between sets. Both groups rode their sessions as hard as they could sustain, three times a week for three weeks.

The 30/15s group raised their 20-minute power by 4.7%. The 5-minute group slipped slightly backward.

Why? Fifteen-second recoveries aren’t long enough for your body to fully stand down. Your breathing and heart rate stay high, so you pile up more time near your aerobic ceiling than long intervals usually allow. You also do it in pieces small enough to hold together.

A few caveats: these were elite riders coming off a high-volume base block, the groups were small, and three weeks is a short window. High-intensity 30/15s intervals aren't magic. Still, for a time-crunched rider facing a winter indoors, they're one of the best returns per minute you'll find.

To try it, swap one hard session a week for 30/15s. Ride the 30s hard but even, so the last rep of each set feels like the first, and use the 15s to spin easy. (Fair warning: the hardest part is keeping count to thirteen.)

Thirty seconds is short enough to commit to completely. Fifteen is just long enough to breathe. Hard, then easy, thirty-nine times over, and not a second spent in the grey zone.

Yours in speed, 

Steve