Elevate your exercise endurance with Zone 2 training

It’s easy to fall into the trap that the only way to get faster is to train faster. Sure, speed work is important but so are long periods of light work.

Building our aerobic base through lighter work in Zone 2 provides a range of benefits but light work might feel too easy, so let’s dive in.

What is Zone 2?

Zone 2 is often called the ‘fat burning’ zone because it’s the ‘Goldilocks’ work rate that we maximally burn fat with oxygen for energy via ATP and the Krebs Cycle in the mitochondria in our cells [1].

Our bodies create energy through aerobic metabolism until energy demands exceed our ability to utilise oxygen. Fat is the most efficient but slowest substrate to create energy and so, higher intensities shift to glycolysis and then anaerobic processes but let’s dive deep on this another time.

Zone 2 training predominantly utilises slow twitch (Type I) muscle fibres, which are dense in mitochondria and preferentially burn fat, help clear (utilise) lactate, and are resistant to fatigue.

Technically speaking, Zone 2 is the highest energy output of our aerobic metabolism while maintaining blood lactate — an anaerobic by-product — levels below 2 mmol/L. This can also be inferred from the expired gas during a VO2 Max test but is less accurate.

Practically speaking, there are some heuristics we can apply to determine Zone 2. The best place to start is with the talk test.

• Talk test: An intensity that still allows us to hold a conversation without broken sentences

• Rate of Perceived Exertion (RPE): 40-50% intensity, which should equate to a pace that can comfortably be held for hours

• Heart rate: 60-70% of your maximum heart rate is a general rule of thumb

We often feel compelled to push harder so it’s easiest to stay in Zone 2 when we do cardio with a mate and hold a conversation throughout. Alternatively, call a family member or take an internal work call.

Benefits of Zone 2

While training in Zone 2, we burn more fat and recover faster from our overall training load. Regular training will improve our aerobic threshold and provide sustained benefits, including the following.

Metabolic health

Training slow-twitch muscles will stimulate increased mitochondrial density and function and improve our ability to burn fat as fuel and clear lactate during higher-intensity work — but, the key benefit here is everyday energy [2][3].

Recovery

Training at a lower intensity for longer creates a lower stress load and more rapid autonomic recovery compared to higher-intensity forms of exercise [4].

Cognitive function

Mediated through enhanced cerebral blood flow, lower cortisol, and increased endorphins and BDNF [5][6]

Cardiovascular health

Facilitated through left ventricular remodelling and increased stroke volume. Race pace will improve but so will overall biomarkers ranging from visceral fat, blood sugar levels and cholesterol levels [7][8].

How much Zone 2?

If you’re targeting health benefits, ~1-2 hours a week is a good place to start. But, if you’re an aspiring centenarian then 3-4 hours a week is even better. To maximise benefits, each workout should last at least 45 minutes.

More time spent training in Zone 2 will help build endurance for any upcoming athletic event.

A practical guide for Zone 2

Staying in the zone can be tough as you can easily creep into a higher intensity that feels manageable but is no longer Zone 2.

Here’s a practical guide on exercising in Zone 2.

Beginner

Brisk incline walk

• Convenient and accessible for most people (treadmill or outdoors)

• Low impact on joints/muscles

Cycling

• Easy to adjust the intensity on an exercise bike to stay in Zone 2

• Low impact on joints

Advanced

Light jog

• Convenient, no equipment required

• Easy to enter zone 3 or higher unless well-established base cardiorespiratory fitness

Hiking/Rucking

• For the well-trained individual, adding a rucksack to your hike is a good option to enter Zone 2 faster and develop core and lower limb strength

• Lower stress on joints compared to running

Swimming

• Requires a proficient technique to be able to stay in Zone 2

• Full-body workout

• Great option for the Aussie summer if you’re near a pool or beach

Paddle sports

• Targeted upper body and core workout

• Get out in nature! Explore your local rivers, lakes or oceans

• Can be weather-dependent

Rowing

• Near full-body workout engaging muscles in arms, legs, back and core

• Can be very difficult to remain in Zone 2 unless well-established technique and strength

But I keep stretching into Zone 3?

If you happen to enter Zone 3 in your next workout it will not be the end of the world! You will certainly generate some overlapping physiological adaptations similar to Zone 2 or HIIT. It may not be optimal but it’s better than nothing. 

Sometimes momentum is more important than anything so it’s important not to get too obsessed about it.

Focussing on remaining in Zone 2 becomes important for those who are trained and keen to squeeze the most out of their performance and health.

Slow and steady or hard and fast?

At Compound, we adopt a ‘polarisation’ strategy that focuses on splitting training up between Zone 2 and HIIT to take inspiration from high-performance athletes so we can get the most out of our time-poor lifestyles [9].

The barbell-like combination of aerobic sessions (Zone 2) with maximal anaerobic work (HIIT) optimises for a broader spectrum of benefits and avoids the typical plateau that comes from simply ‘running hard’ during each cardio session — don’t fall into this trap.

This post contains general information about health and wellness practices. It is not intended as medical advice and should not be treated as such. Please consult with a healthcare professional before starting any new health regimen. This information is provided without any representations or warranties, express or implied.