Fartlek

Warm-up: 10min

Workout: 5x3min/2min at zone 3/zone 1 (So 3min of running in zone 3, followed by 2min of running in zone 1, and so on ...)

Cool down: 5min zone 1

What is the goal of this workout?

1. Improve your anaerobic threshold: A weak anaerobic threshold is one of the biggest obstacles to a good 1500m to half-marathon​ performance. If you feel that getting out of breath (entering the red zone without turning back) limits the speed/tempo at which you can run a 1500m to half-marathon​, it is usually because your anaerobic threshold is not high enough. That's why these workouts are crucial in your build-up. Indeed, they are the most important workouts of your entire training program!

Guidelines

Read carefully! Running too fast (or too slow) will not improve your anaerobic threshold as much as planned. If you are completely out of breath, you are going too fast. In that case, you are training your VO2max, which is different from your threshold. You should aim for a pace at 85-90% of your maximum heart rate. Also, this is a conitnuous run without break. The break consists of reducing your pace to 'zone 1'-pace, without stopping.

Should I run at the same pace as during a threshold workout?

No, slightly faster actually. The goal of this workout is the same as a threshold workout (i.e. improving your anaerobic threshold), so you should aim for the same average heart rate. However, the repetitions at zone 3 pace are shorter than during a threshold workout, so in order to reach 85-90% of your maximum heart rate, you can run at a slightly higher pace.