INTERVAL TRAINING OVERVIEW

A comprehensive conditioning program incorporates interval work along with endurance (“steady-state”) training. While the optimal mix for a given athlete depends on numerous factors, interval training is imperative because it enables athletes to work at greater intensity. To understand the importance of intensity, consider this very brief summary of muscle fiber characteristics:

An individual’s muscle fibers display characteristics along a spectrum from pure slow to pure fast. A given fiber may be categorized “slow” or “fast” based on its myosin components, but within that slow or fast type, there is quite a bit of variation. Not all fibers of the same type exhibit identical characteristics. Spectrum is the key idea.

Slower muscle fibers are preferentially recruited for lower-intensity, steady-state type work. Faster fibers are preferentially recruited for high intensity, short-duration efforts.

Training works because it produces physiological adaptations. An effective conditioning program increases the volume, density and enzyme content of muscle cell mitochondria. It also increases capillary density. Collectively, conditioning increases oxygen supply to cells, oxygen extraction by cells, and waste product removal from cells, benefiting multiple energy systems. However, these adaptations are not universally distributed to every muscle every time you exercise. The frequency and intensity of muscle cell contractions are correlated with these adaptations. Interval training recruits a greater portion of muscle fibers, so that conditioning adaptations are more broadly distributed.

Using Interval Training

Perhaps the most important parameter for designing an interval training program is the work-to-rest ratio, because it directly influences intensity. For example, the power output during work intervals in :45 work / 1:15 rest will, in general, be higher than power output during :45 work / :15 rest. During a WOD, an athlete’s “race pace” is their maximum sustainable aerobic power output plus maximum sustainable anaerobic power output. Therefore, it makes sense to develop both energy systems. The work-to-rest ratio is the key parameter for balancing energy system contribution to power output.

Again, the idea of a spectrum is useful. Classic anaerobic training utilizes a 1:5 work to rest ratio. An example of this would be :30 work / 2:30 rest. The long rest periods allow for more complete recovery from strenuous work, clearance of lactic acid and return to equilibrium, permitting another very high intensity work interval. The point of developing anaerobic power is to increase top-end power output, so full recovery between work intervals is imperative. Shorter rests preclude recovery, and necessitate a shift in energy production to aerobic power, reducing intensity. Therefore, for pure anaerobic sessions, we suggest a 1:5 work to rest ratio, and further, keep all working sessions under 45-60 seconds, so that the high power-generating capacity of the glycolytic system does not “time out”.

For aerobic power, we typically recommend a 1:1 or lower work-to-rest ratio to target aerobic power. For example, something like :30 work / :30 rest is a classic aerobic-dominant interval. The short rest periods do not allow much recovery, so that if an athlete is relying on anaerobic power, they will soon be forced to shift gears to aerobic energy. We have also seen athletes derive substantial benefit from intervals where the work period is longer than the rest period. Examples of this include 1:40 work / :20 rest or 3:00 work / 1:00 rest, and as many other combinations as your creativity will allow.

By keeping the work interval longer than the rest interval, the aerobic system takes priority, mirroring the demands of WODs. In general, though, intervals should remain short enough to permit athletes to work above their race pace for most of the session. There is a lot of room for coaches to design training sessions with intervals between the 1:1 classic aerobic and 1:5 classic anaerobic workout. The best mix of work-rest ratios depends on the athlete and their goals. The following chart is a reference point for manipulating the work-rest intervals to elicit the desired stimulus.