How to Improve VO2 Max: Intensity, Intervals, and Heart Rate

If you’re into running, swimming, or cycling and want to raise your VO2 max (maximal oxygen uptake), you’re not alone. A lot of competitive endurance athletes are constantly searching for the most effective way to push that number higher.

I’m one of those runners myself — always thinking about the training principles behind VO2 max improvement and putting them into practice. In this article, I’ll break down the conditions required to raise VO2 max and how to design science-backed training around them.

By the time you finish reading, you’ll have a clear understanding of what intensity, duration, and frequency you need to improve VO2 max as efficiently as possible.

For specific interval training protocols targeting VO2 max, see the article below.

The Conditions for Improving VO2 Max

Let’s start with what conditions are actually required to drive VO2 max higher.

The Required Intensity: 90–95% HRmax or Above

To provide sufficient stimulus for VO2 max improvement, you need to train at 90–95% HRmax (maximum heart rate) or above. In terms of %VO2 max, this corresponds to roughly 80–88% VO2 max. A practical way to think about it: aim for at least 90% of your maximum heart rate. ※1 ※2

Additionally, if you’re training for races of 5,000m or shorter, you likely need to work at intensities closer to 95–100% VO2 max to prepare for those specific demands.

The Jack Daniels Approach to VO2 Max Intensity

In Jack Daniels’ Running Formula, the recommended intensity for VO2 max training is defined as follows:

Maximizing T@VO2max: The Role of Interval Training

The key principles behind effective VO2 max training are straightforward:

The most effective approach is to sustain exercise as close to VO2 max intensity as possible for the longest duration possible. But maintaining that level of intensity continuously is not realistic in practice.

That’s why interval training is the standard method for targeting VO2 max. By breaking the total effort into repeated bouts, you distribute the fatigue while still accumulating significant time near VO2 max intensity — this total is often called T@VO2max.

When running at near-VO2max velocity, oxygen consumption reaches its ceiling after approximately 2 minutes. As you repeat intervals, the time it takes to reach that ceiling shortens — meaning from the second rep onward, you reach VO2max even faster than in the first.

Accumulating as much total time at near-VO2max intensity as possible — across all reps combined — is what drives improvement in VO2 max.

It’s worth noting that capillary density and mitochondrial content can be improved to some extent with lower-intensity training. Complete beginners can see VO2 max gains from easy jogging alone. However, mitochondrial function adapts specifically to higher intensities — so to keep improving running performance, some high-intensity work needs to be included over time.

How to Structure VO2 Max Intervals

Interval training is the most well-established method for improving VO2 max. Here’s how to think about the key variables: intensity and rest duration.

For practical VO2 max interval sessions including pace targets and session examples, see the article below.

The Most Effective Protocol: Research Overview

“Adaptations to aerobic interval training: Interactive effects of exercise intensity and total work duration” ※3

This study divided participants into four groups (A–D) with different training conditions and measured differences in VO2 max improvement and lactate threshold (LT) changes.

The table below shows the training conditions for each group.

Training Condition	A: Low intensity	B: 16 min × 4	C: 8 min × 4	D: 4 min × 4
Frequency (sessions/week)	4.8±1.2	4.9±1.2	4.6±1.2	4.7±1.2
Interval sessions (times/week)	—	1.8±0.1	1.9±0.1	1.8±0.1
Volume (hours/week)	8.5±1.5	7.6±1.9	5.7±1.5	5.7±2.0
Heart Rate (%HRmax)	—	88±2	90±2	94±2
Blood Lactate (mmol/L)	—	4.9±1.5	9.6±2.9	13.2±2.0

The table below shows the pre- and post-training changes in VO2 max and lactate peak for each group.

	A: Low intensity		B: 16 min × 4		C: 8 min × 4		D: 4 min × 4
	Pre	Post	Pre	Post	Pre	Post	Pre	Post
Lactate Peak (mmol/L)	14.9	13.7	14.8	13.9	14.1	13.4	13.8	14.0
VO2 max (ml/kg/min)	52.7	54.5	51.1	54.4	52.8	58.3	50.4	53.2
VO2 max Improvement		+3.4%		+6.6%		+10.4%		+5.5%
Power @ 4 mmol (W)	222	239	228	249	241	280	220	238

The result: the 8 min × 4 interval group (Group C) showed the greatest improvement in VO2 max.

Comparing Group B and Group C

Weekly training volume was 7.6 hours for Group B and only 5.7 hours for Group C — yet Group C produced far greater VO2 max gains despite less total training time. The key difference was intensity.

Peak heart rate during intervals was 88% HRmax for Group B and 90% HRmax for Group C. Group C trained consistently in a zone closer to maximum heart rate.

The data shows that 16 minutes at 88% HRmax produces smaller VO2 max gains than 8 minutes at 90% HRmax — even with less total volume.

Comparing Group C and Group D

Even compared to Group D — who trained at 94% HRmax for 4 minutes — Group C came out ahead in VO2 max improvement.

The takeaway: effective VO2 max training requires sustaining a moderately high heart rate for long enough. Both intensity and duration matter — not one alone.

Once training intensity drops below a threshold, the stimulus to VO2 max drops off sharply. Falling below 90% HRmax significantly reduces the training effect on VO2 max.

Rest Duration for Maintaining Intensity

As established above, effective VO2 max training requires maintaining an appropriate minimum intensity throughout. In interval training, rest periods must be long enough to allow the next work bout to hit the target intensity — but not so long that you lose the cumulative stimulus.

One study ※4 compared 4 min × 6 intervals at 5% treadmill incline in well-trained runners, using rest periods of 1, 2, and 4 minutes across three conditions.

The result: varying rest from 1 to 4 minutes had little effect on work-bout intensity. When runners were allowed to self-select their rest, they chose an average of approximately 2 minutes.

This suggests that for a 4-minute work bout, around 2 minutes of rest is a reasonable target — a work-to-rest ratio of roughly 2:1.

VO2 Max and Heart Rate

Heart rate is the most practical tool for managing VO2 max training intensity in real time. Here’s how to use it.

Using Heart Rate to Manage VO2 Max Intensity

The target intensity for VO2 max improvement is 90–95% HRmax. If you know your maximum heart rate, you can monitor your intensity in real time using a GPS watch with a heart rate sensor.

For example, a runner with an HRmax of 195 bpm would target a range of 175–185 bpm during work bouts. Checking whether you’re hitting this zone during hard efforts removes guesswork and provides objective intensity control.

Note that %HRmax and %VO2 max do not have a 1:1 relationship. According to Swain et al. (1994) ※2, 90% HRmax corresponds to approximately 80–82% VO2 max. Keep this conversion in mind if you prefer to work in %VO2 max terms.

Measuring HRmax and Individual Variation

Maximum heart rate varies considerably between individuals. The age-based formula (220 − age) is only a rough estimate — people of the same age can differ by 10–20 bpm or more. For better accuracy, recording your actual highest observed heart rate during hard efforts is more reliable.

One reproducible method for measuring HRmax is a near-maximal 800m–1,000m effort, monitoring heart rate in the final section. Garmin and other sports watches measure heart rate automatically, but values fluctuate with course conditions and daily form — so use the highest reading across multiple efforts as your reference.

What Is VO2 Max?

VO2 max (maximal oxygen uptake) is defined as the maximum amount of oxygen the body can take in and use per kilogram of body weight per minute (ml/kg/min).

In general, a higher VO2 max correlates with better long-distance and marathon performance. It is one of the most important indicators of endurance capacity.

For a detailed breakdown of what determines VO2 max — including the Fick equation, cardiac output, and arteriovenous oxygen difference — see the article below.

When 100% VO2 Max Intensity Is Worth It

VO2 max training occupies a “race-sharpening” role in the training hierarchy — it’s the final tuning stage before competition.

Training near VO2 max intensity carries a high physical cost. The fatigue load is substantial, and cost-efficiency relative to other training types is low — “cost” here meaning accumulated fatigue.

If the goal is simply to stimulate fast-twitch fibers and improve mitochondrial function, you don’t necessarily need to grind through painful VO2 max intervals. Hill sprints over 200m or short 400m intervals can accumulate meaningful volume more efficiently with less systemic cost.

That said, the primary case for true VO2 max training is this: it creates race-like conditions through repeated practice, progressively improving running economy at race pace.

The training that best develops running economy at 5,000m pace is training at 5,000m pace. Since running a full 5,000m in a single continuous effort is impractical during training, breaking it into intervals is the practical solution.

My conclusion: high-intensity training at or near 100% VO2 max is sometimes necessary — but only under specific conditions. Specifically, when you have a race of 5,000m or shorter coming up.

The framing matters here. Rather than thinking “I need to train at 100% VO2 max to raise my VO2 max,” the better approach is: “I have a race at 100% VO2 max intensity coming up — so training close to that intensity is necessary to prepare specifically for it.”

References

※1 Helgerud J, Hoydal K, Wang E et al. (2007) “Aerobic high-intensity intervals improve VO2max more than moderate training” Medicine & Science in Sports & Exercise

※2 Swain DP, Abernathy KS, Smith CS, Lee SJ, Bunn SA (1994) “Target heart rates for the development of cardiorespiratory fitness” Medicine and Science in Sports and Exercise

※3 Seiler S, Jøranson K, Olesen BV, Hetlelid KJ (2013) “Adaptations to aerobic interval training: interactive effects of exercise intensity and total work duration” Scandinavian Journal of Medicine & Science in Sports

※4 Seiler S, Hetlelid KJ (2005) “The impact of rest duration on work intensity and RPE during interval training” Medicine & Science in Sports & Exercise