The V4 model in swimming: why lactate beats heart rate for setting training paces

What the V4 model actually measures

The V4 model comes from the work of Dr. Jan Olbrecht, a physiologist and biomechanist by training. He advised swimmers who together brought home more than 600 Olympic, World, European, and Commonwealth medals, and his book The Science of Winning is still a standard reference for anyone digging into how swim training should be structured.

The core idea: V4 is the swimming speed at which blood lactate reaches 4 mmol/L, a commonly used marker for assessing endurance and setting training paces. The more lactate a swimmer produces at a given pace, the more that pace draws on the anaerobic energy system. V4 roughly marks the point beyond which effort becomes harder and harder to sustain.

You don't need a lab for this, contrary to what you might expect. A two-speed test is enough in most cases: the swimmer completes two repeats at different speeds, and the resulting lactate-versus-speed curve pinpoints V4 fairly precisely, along with the zones around it.

Why heart rate alone falls short

Heart rate is still useful, but it has two real limits for a swim coach.

First, it behaves differently in water. Horizontal body position, immersion, and restricted breathing all change the heart rate response compared to running or cycling. A zone borrowed from a land-based model doesn't automatically match what a swimmer actually experiences in the pool.

Second, it says nothing about where the energy is coming from. Two swimmers can have the exact same heart rate at a given pace while producing very different amounts of lactate: one is still drawing mainly on the aerobic system, the other has already shifted to anaerobic. Heart rate doesn't capture that difference. Lactate does.

None of this means heart rate or perceived effort should be thrown out. The V4 model complements them, adding a physiological marker specific to each swimmer instead of a one-size-fits-all estimate.

What this actually changes for a session

Once a swimmer's V4 is known, the surrounding training zones (base endurance, threshold, VO2max, speed) can be derived as a percentage of that reference speed. Which means precise split times for each block of a session, tailored to that specific swimmer rather than the group as a whole.

That's exactly what SwimConsult calculates automatically: the coach writes the set in plain language (distance, stroke, zone), and every swimmer gets their target time and start, recalculated from their own V4 profile. No spreadsheet to keep updating by hand for every swimmer in the group. Curious how that approach stacks up against paper, Excel, or WhatsApp? We break it down in our honest comparison for swim coaches.

In practice

A V4 test isn't repeated every session, more like a few times per season, ahead of major preparation blocks. Swimmers improve at different rates, so the same percentage of V4 can map to very different split times for two swimmers in the same group. That's normal, and it's actually the whole point of the method. The trade-off is that it needs a test per swimmer, not a group-wide guess. No lactate meter at your club? The 30-minute field test already gives you a reliable reference pace with nothing but a stopwatch.

Sources

Olbrecht, J., The Science of Winning (the historical reference for the V4 model)

Validating Physiological and Biomechanical Parameters during Intermittent Swimming at Speed Corresponding to Lactate Concentration of 4 mmol·L⁻¹, PMC study (NCBI)

lactate.com, resources and animations on Olbrecht's model (aerobic/anaerobic)

Scientific Triathlon, episode on Jan Olbrecht (biographical context)