Anaerobic Capacity

Anaerobic Capacity: what is it?

When effort exceeds what the aerobic system can supply, the difference is made up by anaerobic pathways - the stored phosphagens for the first few seconds and glycolysis after that. Anaerobic capacity is the size of that reserve tank. It matters enormously in the 400 m to 800 m range, in the last minute of a hard metcon, in a repeated-sprint passage of a football match, and in the moment a HYROX athlete pushes a sled that is genuinely too heavy. It is also the quality that costs the most to train and recovers the slowest.

Capacity versus power

Two different qualities get run together. Anaerobic power is the peak rate at which energy can be produced without oxygen - it decides the height of a jump and the speed of the first few seconds of a sprint. Anaerobic capacity is the total amount that can be produced before the system fails, which decides how long a near-maximal effort can be held.

Both matter, and they respond to different work durations. Very short, fully recovered efforts train power. Longer near-maximal efforts with incomplete recovery train capacity, and they are far more unpleasant, which is a useful thing to warn a client about before the session rather than during it.

How it is tested

The best-known laboratory test is the Wingate: 30 seconds of all-out cycling against a fixed resistance set from bodyweight. It reports peak power, mean power over the 30 seconds, and a fatigue index describing how much power fell from peak to end. Mean power is the closest thing to a capacity measure the test gives.

The research reference for capacity itself is the maximal accumulated oxygen deficit, which estimates the anaerobic contribution by comparing the oxygen an effort should have required with the oxygen actually consumed. It is precise and impractical. In the field, coaches use repeated-sprint tests, a 300 m or 400 m time trial, or simply the drop-off across a set of repeat efforts.

Training it without wrecking the week

Anaerobic capacity work is the most fatiguing thing in a programme. Efforts of 30 seconds to two minutes at near-maximal intensity, with incomplete recovery, produce a level of systemic fatigue that lingers for days and interferes with everything else. One session a week is enough for most athletes; two is the ceiling, and only in a short block close to competition.

Because of that cost, sequence it late. Build the aerobic base first, because the aerobic system is what clears the by-products and powers recovery between efforts. An athlete with a poor aerobic base cannot repeat anaerobic efforts and therefore cannot train the quality effectively in the first place.

• Build the aerobic base before the anaerobic block, not alongside it.
• One hard capacity session a week; two only in a short pre-competition block.
• Expect the session to feel awful. Warn the client, or they will think something is wrong.
• Keep it in a 4-8 week block rather than year-round - the fatigue cost is not worth carrying permanently.

Who needs it and who does not

Middle-distance athletes, combat sports, team sports with repeated sprints, competitive CrossFit and rowing all need it directly. HYROX athletes need enough of it to survive the hardest station without falling apart, but not as a priority over running.

General-fitness clients need very little of it. The pay-off is small relative to how much recovery it consumes, and the same session time spent on aerobic work or on lifting does more for their goals. If a client just wants to feel fitter and lose fat, this is not the quality to chase.