What's Cool In Road Cycling

Spin Vs Push: Interval Physiology 101

– Stephen S. Cheung, Ph.D. – Associate Professor, Dalhousie University –
We’ve been posting a number of articles discussing the use of power devices and the proper way to perform intervals. I have also been receiving a number of questions from you concerning the physiology behind intervals, so it seems like a good time to lay down some basic fundamentals before the season really kicks into full swing.

The big question that I always get asked is what power output, speed, or heart rate should I train at? This is a really simple question to answer – if you know you need to ride at a particular speed/power in a critical race situation, then that is what you train for! If your goal is to break the hour for the 40 k TT, then you are building up to be able to handle intervals at about that speed or higher as you peak for the event. If the pack flies out of the corner of your local crit at 50 km/h, then guess what speed you should ultimately be able to handle during your intervals?

Remember that power is a function of force and cadence. This means that you can generate the exact same power or speed by mashing a big gear slowly (think Jan Ullrich) or by spinning a small gear (think about some dude named Lance). A higher cadence tends to stress the aerobic and cardiovascular system, while a lower cadence tends to stress the muscular system. Which do you think generally gives out first? For long-distance cycling, you generally want to save your legs and transfer the stress to your aerobic system. Lance’s high cadence style is so effective precisely because he is blessed with a huge aerobic capacity to handle this stress, and this helps to save his legs and allow him to make deadly attacks at the end of epic mountain stages.

A smart cyclist can make literally an infinite number of interval workouts at the exact same power output that focus on training one or the other system, and this is why scientific training means more than laying down power or heart rate intensities alone. Manipulating the effects of the workout can be done by changing not only the gearing/cadence, but also the duration of both intervals and recovery periods. For example, if climbing strength is a limiter or during the early season, you might focus on high gears and low cadence intervals. Make sure you start off with relatively short (30-90 s) efforts and build up to longer (4-6 min) efforts rather than the other way around, and make the recovery periods fairly long to keep the legs fresh. When the longer efforts become easy, then it’s time to increase the speed/power and start again with shorter efforts.

Why do I recommend building up from shorter to longer intervals at the same power? Think of it as focusing first on the quantity of training and then making the transition to quality of training. With shorter efforts, you will be able to do many more reps (e.g., 32 x 1.5 min = 48 min versus 5 x 6 min = 30 min), meaning that you maximize the total time spent at that power output. This gives you that broader base of physiological adaptation that will eventually permit you to simulate the race effort of maintaining that same intensity for prolonged periods at a time (e.g., TT’s, climbing, breakaways).

But remember that it’s March! Unless you’re Museeuw and need to be flying now, then you aren’t going to be able to handle mid-season speeds or power outputs yet. Therefore, you need to gradually build up the intensity. Next time, I’ll focus on the concept of lactate threshold and how to train it. Keep the questions and comments coming!

About Stephen:
Stephen Cheung is an Associate Professor of Kinesiology at Dalhousie University in Halifax, Nova Scotia, Canada, with a research specialty in the effects of thermal stress on human physiology and performance. He has been an avid roadie since beginning university in the mid-eighties, and still has non-indexed downtube shifters on his winter bike and wool jerseys hanging in his closet. He can be reached for advice or comments at [email protected]

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