It’s been a beautiful August in Ottawa, just cool enough to feel the fall winds encouraging the trees to drop their leaves and reach out empty-handed for the chilling embrace of winter. The fall is when cross-country skiers start to think about intervals. What I’ve done for this Workout of the Week is provide a bit of a primer to people just getting into thinking about intervals. At XC Ottawa, we start doing intervals twice a week as we get into the fall, and we also have sprints and, on the harder weeks, other types of intensity. Intervals require some creativity and lots of discipline; there are many ways to do intervals, but certain cardinal rules to try and live by.
First, intervals are a controlled way of increasing – depending on the type – your aerobic threshold, your anaerobic threshold, your lactic acid threshold – whatever. They are different from a race in that you set target intensity levels that you try and maintain, in order to generate a given result. Intervals usually involve a period of intensity followed by a rest, repeated several times over. The following are some considerations when designing intervals:
Exercise type: Running, road biking, ski-striding, rollerskiing... I would tend to choose what exercise to do your intervals in based on what you feel comfortable with. Some people have trouble with heart-rate control in specific exercises. Different people will feel different muscle/cardio exertion balances when doing different exercises. Since intervals are generally for your cardiovascular system (although some may have muscular endurance side-benefits), choose an exercise type you feel you have some control over- probably an exercise type you are very familiar with.
Terrain: Again, many choices here. Some coaches/athletes prefer doing loops, which bring athletes back to where they started and therefore have zero net interval gain. Sometimes a continuous course is nice- doing intervals along a trail or set of trails, and adapting your interval to the terrain. In this case, though, it helps to know the trails very well to ensure you’re setting up your interval session well. A very popular terrain choice are– such as the legendary Penguin’s intervals – which are hard. Hill intervals are good because they allow you to raise the heart-rate and control it at a certain level, but they are not good for leg speed when doing intensity, and some athletes complain that hill intervals don’t mimic a real cross-country ski race. Finally, some athletes like flat intervals – on a running track or a flat trail – although those who like that kind usually have a strong running background and can control heartrates while keeping a consistent running stride.
Intensity level: Cross-country skiers usually (though not always) divide exertion levels into zones – 1 through 4 and, depending on the coach, sometimes 5. Zone 1 is an easy exercise pace, zone 4 is race-pace, and zone 5 is sprint-speed or anaerobic exercise. XC Ottawa does intervals in zones 3 and 4 – we start with zone 3 throughout the summer, and build into zone 4 intervals in the fall.
Length of intensity: The length of the intensity session should be inversely correlated to the number of repetitions – ie, if you are doing long intervals, don’t do lots of them. I have done intensity of up to an hour continuous zone 3 (only one rep) to intervals of around 40 seconds (usually no less than 8, up to 14 or 15). Some people like to keep the intensity length the same throughout the workout (ie repeats of 2 minutes), while some people like to vary lengths – the most popular variation is the
pyramid (1 minute, 3 minutes, 5 minutes, 7 minutes, 5 minutes, 3 minutes, 1 minute) or some such. Design your interval session to make the most of what you want – if you are feeling sluggish, do some short ones, but if you get tired later in races, throw in some long ones. If you’re training seriously for a sustained period, do a variety. But if you’re training seriously, get a coach and listen to him instead of me.
Length of rest: Recovery is very important – but you get to choose how much you want your heart rate to recover. Below 120 – virtually full recovery? Below 140 – substantive recovery? Partial recovery? Little or no recovery? Just remember that your recovery allows your body to clear all the gunk and make way for the next one – and varying your recovery time will vary how much your body can recover, and affect how long an interval session you can do before tiring and having to stop.
Number of repetitions: Make sure you are recovering – I usually start with a set number in mind, but then watch my heart rate and perceived level of exertion, and times set, and see how far I get – usually one or two under my set target.
Here are a few Cardinal Rules to follow during your interval sessions..