Workout of the Week: Short Stack Intervals with Over-Unders

Keep your heart rate consistently high with a serving of short stacks, then maintain power with a side of over-unders.

Woman cycling through grassy hills
Photo: Varnitsin

This session is primarily directed at achieving a high percentage of time above 90% max heart rate to elicit improvements in maximum aerobic power, power at threshold, and improve repeatability at race pace. The first part consists of Seiler-style short stack intervals at 30 seconds on, 15 seconds off while maintaining a consistent heart rate. The second part challenges you to maintain your power through 12 minutes of over-under intervals.

Since this is a maximal workout, specific power targets are not given for the 30/15 sets. Most athletes will start off with higher peak power values early in the sets and then find a sustainable power for each subsequent repetition. The goal for this workout is to maximize the time spent above 90% of your maximum heart rate.

This is what power might look like when executed properly.

This is the heart rate graph you can expect, highlighting the majority of time spent in zone 5, or that max aerobic zone.

This is what the over/under would look like. Note the very slight changes in power output. I generally try to do these on non-erg mode if on the trainer and prefer doing them outdoors to work on pedaling technique, gear shifting, and production of power across a range of pedal speeds and terrain changes.

I like to use this workout as a way to refine technique and encourage high force output by monitoring cadence. Some athletes will default to a higher and higher cadence as they generate fatigue, which may not be realistic to what they do in racing, so I encourage athletes to watch their pedal speed and aim for somewhere in the 85-90 RPM range as a rough starting point. When they feel the fatigue coming on and want to shift down, I’ll have them focus on finding a rhythm and maintaining power at a slightly lower cadence than what they may prefer.

Workout of the Week: Short Stack Intervals with Over-Unders


12 min. @ 65-75% FTP
20-30 sec. max (>130% FTP)
5 min. ramp from 50 to 65% FTP

Main set

2-3 sets of short stack intervals:

  • 10 × 30 sec. max/15 sec. rest
  • 4 min. set rest @ 50-55% FTP

1-2 sets of over-unders:

  • 12 min. alternating between 2 min. @ 95% FTP and 3 min. @ 109% FTP
  • 5 min. set rest @ 50-55% FTP


8-15 min. ramp from 60 to 50% FTP