Fartlek was developed by the Swedish coach Gösta Holmer back in the 1930’s. It was originally used by runners, but a lot of other endurance sports have adapted it as a part of their training. If you read in Wikipedia, you will find a description that sounds like this:
“Fartlek, which means ‘speed play’ in Swedish, is a form of conditioning which puts stress mainly on the aerobic energy system due to the continuous nature of this exercise. The difference between this type of training and continuous training is that the intensity or speed of the exercise varies, meaning that aerobic and anaerobic systems can be put under stress. Most Fartlek sessions last a minimum of 45 minutes and can vary from aerobic walking to anaerobic sprinting.”
Fartlek is unorganized interval training
As you can see Fartlek is a combination of many different intervals with both aerobic and anaerobic events. These intervals are not organized as the intervals you know from regular interval training. Instead you use the terrain, the winds or you friends to get inspired to make attacks of various lengths. I think that the motivating factor in fartlek is the best thing about this kind of cycling training.
Actually I know many riders that do this training without knowing that there is a name for it. They do it because it is great fun, effective and similar to races.
Fartlek with a theme
There are many ways you can use fartlek. You can decide to give your sessions a tactical theme: E.g. Try to make explosive, surprising attack when the group slows down.
Or maybe you could give it a technical theme:
E.g. Ride fast in the areas with many sharp curves.
Or you can make a personal theme with something you want improve. Actually, I always recommend that riders train towards what they are aiming for. There is a high degree of specificity needed to achieve the right adaptations to your training. So, it makes sense to design Fartlek sessions that reflect your goals.
Difficult to reproduce training sessions
If you have a period where your motivation for regular interval training is low or non-existing, then try Fartlek. It is fun and often you will experience that you get a really good workout.
The only problem is that it is impossible to reproduce a good training session. Simply because the amount of aerobic and anaerobic training you get is based on how spontaneous you (or your friends) are. Thus, the outcome will vary from time to time. If you have a power meter you can compare the data files from different training sessions, but you can only use these files for analyses. It is impossible to reproduce a previous training session.
Make a finish time or line
You have to ride on feeling, just like you do in races. But as a thumb of rule, set a time for the duration of the fartlek, so you will now when it is time to make the session harder or be more passive. I have tried to ride these sessions without a defined finish time. Believe me when I say that fartlek without time or finish line is enjoyable only for the strongest rider who can punish his so-called friends.
My experience with fartlek training is that it works best when you have a group of motivated riders who understand the rules of this training type. Then you will have a great time racing with activity that will bring you all physiological benefits that you would have achieved in a criterium.
Enjoy your Fartlek training session
I can only recommend all riders to try fartlek if they haven´t tried it yet. Though it is an unorganized way to train compared to most of the other advice I give here on training4cyclists.com, it is still a very effective and inspiring way to get a good workout for your aerobic and anaerobic systems.