Fartlek and threshold runs
Fartlek literally means “speed play” in Swedish (the ideas was invented by Swedish coach Gösta Holmér). It means the introduction of faster bursts into a slower run.
Why do fartleks?
The purpose of fartlek is to increase your fitness. Fartlek recruits your fast twitch muscle fibres during a longer run, so ensuring that the whole muscle is getting a good workout. Fartlek also helps to build speed and strength.
How to do a fartlek
Fartlek runs can be done as an unstructured session (ie running faster as you feel inclined); or in a more structured way (for example, 10 surges of 400m). The best place to do fartlek is generally on a trail run or in a park, though some athletes prefer to do them on a track.
A typical fartlek session might be a ten minute warm up jog; then hard strides for 3-4 minutes, with 1 minute recoveries, for 10-15 minutes; then a ten minute jog to cool down.
Another way to do fartleks is to use landmarks, such as lampposts or trees. For example, you might decide to run hard for the next eight lampposts, and then jog for a minute.
Threshold runs – also known as tempo runs – are favoured by long distance runners (10km and over). They involve running at about your anaerobic threshold (also known as your lactate threshold). This is the maximum speed at which your body can work aerobically for long periods (see Chapter 10 for more details). It is thought that by training at this level, you can gradually increase the body’s capacity to produce energy aerobically and increase its ability to cope with the build-up of lactic acid. Threshold runs are an excellent way to improve your 10km race performances.
How to do a threshold run
A threshold run generally consists of a 10 minute warm up, followed by 20-30 minutes of running at just below your anaerobic threshold, followed by 5 minutes of warm-down.
The tricky part is getting the pace right. One way to gauge the pace of your threshold run is to find the pace at which you can just hold a conversation. You should be able to talk, but perhaps not in complete sentences. If you are too out of breath to speak at all, you are running too fast. But if you can speak normally, you are running too slowly. You are aiming to run “comfortably hard”.
“What doesn’t destroy me makes me stronger.”
Friedrich Nietzsche, The Twilight of the Idols
(Not, apparently, written about threshold runs.)
If you are an experienced runner, your threshold pace should be somewhere between your 10 mile race pace and your half marathon race pace, or about 10-30 seconds a mile slower than your 10km race pace.
Alternatively, you can use a heart rate monitor to ensure that you do your threshold run just below your aerobic threshold. Your anaerobic threshold is generally about 80-90% of your working heart rate, or 85-92% of your maximum heart rate (see the next chapter).
The key to threshold runs is to resist the temptation to go too fast. This is deliberately not a maximum effort workout. As you become fitter, these runs should become easier, until you review your threshold pace. You should not go as fast as you can from one week to the next: as you feel stronger, you should try to achieve the same pace and distance with less effort.