WhyHIITBeforeBaseFitnessIsBackwards

Marcin has a specific test he applies before considering any kind of high-intensity interval work with a new client: can they sustain a steady, comfortable tempo run for fifteen minutes? If the answer is no, HIIT is not the next step. It is the much later step, for which this is the prerequisite.

What HIIT actually requires

High-intensity interval training works by alternating between near-maximum effort and partial recovery. The recovery intervals are what make the high-intensity efforts possible - and the quality of that recovery depends on the efficiency of the aerobic system. A client who has not built any aerobic base cannot recover meaningfully within the structure of an interval session. What they experience instead is not productive HIIT - it is maximum effort throughout, which produces excessive fatigue, poor form, elevated injury risk, and the kind of post-session experience that makes people never want to exercise again.

The fitness industry sells HIIT as accessible to beginners because it produces dramatic results and looks engaging on camera. The results it produces are for people who already have base conditioning. For people who do not, it is the wrong prescription applied in the wrong order.

Building the base first

The alternative - steady state cardio at a conversational pace, progressive walking programmes, low-intensity aerobic work done consistently over weeks - builds exactly the aerobic foundation that makes interval training productive later. It does not produce dramatic content. It does not trend on social media. It works. The client who has done six weeks of consistent moderate-intensity cardio before any interval work is introduced is in an entirely different physiological position than the one who skipped straight to the exciting version.

The client management dimension

Clients often arrive wanting HIIT specifically because they have read about it and believe it to be the most effective approach to fat loss. Managing that expectation honestly - explaining why the base-building phase is not just tolerable but necessary - is part of the PT's job. A client who understands why they are doing what they are doing is far more likely to stick with it than one who feels their goals are being ignored. Explain the sequencing. Then get them to a place where the HIIT they wanted is actually appropriate.