Danish intervals are a simple session, one that I've used since about 2012, when it was first published. I've found it to be very effective for improving VO2max and running economy.
I've also used it to good effect with cyclists, in which scenario it's best used on a stationary cycle trainer.
It's not one for the faint-hearted. Expect to have a desperate desire to lie on the floor gasping for air and asking yourself what on earth came over you to attempt this.
As always, to be truly effective and to minimise injury risk, you do need to have a reasonable base of low intensity steady state training before doing intervals. As popular as the HIIT concept has become, intervals are a performance intervention and are no more than the cherry on top of a very large, well-iced cake.
The study, linked below, also found a positive effect on the health of trained individuals.
In my notation, the "Danish Intervals" session is written like this...
4 Rounds: 5 x (10s Sprint, 20s Hard Running, 30s Easy Running), Rest 2min
How to do it...
Warm up thoroughly, using a combination of steady state cardiovascular activity and some dynamic mobility exercises.
- 10s Sprint - flat out, as hard as you can go
- 20s Hard Running - this is your race pace for 3-5km event. It's a high intensity effort
- 30s Easy Running - jogging to partially recover
- Repeat 5 times
- Rest 2 minutes
Repeat for up to 4 rounds.
(I would strongly suggest that you limit your first Danish Intervals session to 2 rounds, assess how you respond to that and, only then, add further rounds in subsequent sessions).
After you've completed the intervals, do at least 10 minutes of very easy jogging/walking to cool down properly.