Understanding Interval Training

Stephen Seiler has a nice description of what happens in your muscles when you undergo interval training. It really serves to illustrate the differing physiological responses that come about with different durations at any given intensity. It also serves as a reminder as to why you don’t want to go 110% all the time (hint: optimal stimulus for cardiac stroke volume improvement is not the same as that required for widespread capillary growth and oxidative enzyme upgregulation.)

One interesting take on the article, if you look at the data he presents, is that you can have your cake and eat it too, if you exercise strict discipline. If interval duration is kept short enough, you can accumulate many minutes of time at faster than race-pace velocities while keeping the concentration of lactic acid in your muscles about what it would be at a more moderate, steady-state pace. The advantage of introducing that sort of training is that you work on neuromuscular efficiency as well as increasing oxidative capacity of type IIa muscle fibers.

Notice from the data, however, that if you ‘overcook’ the interval duration by even 60 seconds, the lactate concentration can almost double. You cross from a zone where you are training your cells to upregulate pyruvate dehydrogenase, an enzyme that aids in speedy aerobic metabolism, to a no-man’s land where you neither optimally stimulate aerobic or anaerobic metabolic pathways.

Cycling (and cross-country skiing for that matter) are aerobic sports, so next time you work out, give some thought about your specific goals for the day. Are you trying to improve stroke volume? Then go flat out for 3 minute intervals that hurt like the dickens. Do you want to raise your velocity at LT, the number one determinant of endurance performance? Then remember the lessons from the Seiler article and give your muscles the conditions they need to adapt.

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