Why Lifting Heavy Makes Your Zone 2 Easier

By [Sonya Brotherton]

You’ve been told for decades that Zone 2 is about nothing more than heart rate, fat oxidation, and “building your aerobic base,” as if your entire performance could be explained by a smartwatch and some tidy metabolic chart that doesn’t include your lived experience, your motor unit losses, the effects of stress, hormones, sleep, grief, chronic responsibility, or the reality that your nervous system is doing more invisible work now than at any other time in your life — and this, right here, is exactly why most women over 40 cannot understand why their Zone 2 suddenly feels like Zone 3, even though they are supposedly fitter, smarter, more knowledgeable, and more dedicated than they were twenty years ago.

Because the truth — the part nobody bothers to tell you — is that Zone 2 is not merely cardiovascular; it is neuromuscular, mechanical, endocrine, and behavioural, and unless you understand how all these systems interact under load, you will keep blaming yourself for a physiological situation you did not create, do not control, and absolutely can change.

And this is where lifting heavy comes in — not as some aesthetic midlife hobby, not as a way to “tone,” not as the fitness industry’s solution to menopausal panic,but as the exact, specific stimulus that rebuilds the structural, neural and metabolic foundations that make Zone 2 feel like Zone 2 again,rather than a fragile state that disappears the moment you’re tired, stressed, inflamed, under-fuelled, or dealing with the emotional weight of being a woman who has survived enough life to know better than to accept simple answers to complex problems.

Let’s break it down — properly, honestly, and with respect for the science and your lived experience.

🔥 1.

Zone 2 Feels Harder Because Your Neuromuscular System Is Tired, Not Because Your Heart Is Weak

You can be cardiovascularly fit — even exceptionally so — and still feel like Zone 2 requires everything you’ve got.

Because the effort you feel isn’t just coming from your heart.It’s coming from your muscles, tendons, nervous system, and the silent labour of keeping your movement patterns stable under fatigue.

When you lift heavy, you improve motor unit recruitment, coordination, and movement economy,which means your muscles produce the same amount of force with less neural chaos,and that translates into a lower oxygen cost at every pace.

This is what the research shows:

• Heavy strength improves running and cycling economy — the oxygen cost of movement — in trained endurance athletes.

• Strength training reduces unnecessary co-contraction, meaning you waste less energy stabilising joints.

• Stronger tendons and neuromuscular timing reduce energy leaks and improve elastic return.

Zone 2 doesn’t get easier because your VO₂max goes up.It gets easier because your movement becomes cheaper.

🔥 2. Strength Reduces the % of Your Max Force Needed for Zone 2

Zone 2 is not a “light” zone for your muscles — it’s a low-to-moderate force-repeated-thousands-of-times zone.

If your maximum strength is low:every stride, pedal stroke or SUP pull uses a higher percentage of your maximal force.

Increase your maximal force?Zone 2 becomes a smaller slice of the pie.

You don’t fatigue as fast.You don’t recruit unnecessary fibres.You don’t spike your heart rate when terrain, cadence or posture shifts.

This is supported consistently in the literature:

• When max strength increases, submaximal efforts require fewer motor units and lower firing frequencies.

• Lower firing rates = lower energy cost = lower HR drift = easier Zone 2.

This is why runners and cyclists who strength train feel like Zone 2 finally behaves again.

🔥 3. Strength Work Improves Leg Stiffness, Elasticity & Economy

Economy is not mystical. It is your ability to convert metabolic energy into forward motion without wasting half of it wobbling, collapsing, sinking, or leaking force.

Heavy strength + plyometric work improves:

• Leg spring stiffness

• Tendon elasticity

• Ground contact time

• Stride mechanics

• Pedal force timing

• Postural control

• Balance and joint stability

Every one of these changes reduces the oxygen cost of movement.

Better economy =lower heart rate at the same pace

Zone 2 that feels like Zone 2 again.

🔥 4. Type I Fibres Still Dominate Zone 2 — But Type IIa Help More Than You Think

This is where most explanations fall apart, because people forget:

Zone 2 is NOT exclusively Type I fibre territory.

At the lower end, yes — mostly slow-twitch.But at the upper end, or under fatigue, technique breakdown, stress, heat, low glycogen or midlife hormonal shifts,your Type IIa fibres absolutely contribute.

Heavy lifting does not turn Type II fibres into Type I.That’s an endurance adaptation.

But heavy lifting does:

• Improve Type IIa coordination

• Improve their force economy

• Improve their fatigue resistance indirectly

• Reduce their twitch-to-twitch variability

• Support them when they inevitably join in during real-world endurance sessions

• Help them stabilise joints when Type I fibres are tired

So “heavy lifting makes Type II fibres more useful to Zone 2” is correct —not by making them oxidative,but by making them efficient partners rather than sloppy panic recruits.

🔥 5. Strength Training Improves Fuel Handling, Which Makes Endurance Feel Predictable Again

As we move through our 40s and 50s, glucose handling becomes less stable due to:

• Oestrogen fluctuations

• Sleep disruption

• Cortisol changes

• Reduced insulin sensitivity

• Increased inflammatory load

Strength training directly improves:

• GLUT4 expression

• Muscle glucose uptake

• Insulin sensitivity

• Glycogen storage

• Metabolic flexibility

This means:

• Smaller HR spikes

• More stable power output

• Fewer “why is Zone 2 suddenly Zone 4?” days

• Better recovery of submaximal intensity

Zone 2 becomes repeatable, not fragile.

🔥 6. The Ageing Motor Unit Story That Explains Why Zone 2 Gets Harder After 40

This is the part you deserve to know and NO ONE is telling you:

• We lose motor units as we age — especially high-threshold, Type II units.

• Surviving motor neurons “adopt” orphaned fibres, re-innervating them — often converting fast fibres to behave more like slow ones.

• This compensatory system fails later in life, leading to permanent fibre loss.

Strength training is one of the strongest signals preventing this decline.

It protects:

• Neuromuscular junction integrity

• Motor neuron survival

• Motor unit firing quality

• Muscle fibre retention

In other words:

Heavy lifting protects the machinery that lets you move efficiently —the very machinery Zone 2 depends on.

Once those motor units are gone, endurance declines long before aerobic capacity does.

This is why midlife people who strength train age differently — in performance AND in life.

💛 7. If Zone 2 Feels Harder Now, It’s Not You — It’s Physiology

If your Zone 2 feels harder at 45 than it did at 25,you’re not unfit, unmotivated, or doing anything wrong.

You are living in a body:

• With fewer motor units

• With more Type II fibre denervation

• With hormonal instability

• With reduced recovery capacity

• With greater emotional labour

• With disrupted sleep

• With higher systemic inflammation

• With real-world responsibilities 25-year-olds cannot fathom

Strength training doesn’t fix your life —but it stabilises your physiology enough that training stops feeling like punishmentand starts feeling possible again.

⭐ Zone 2 Feels Better When the Whole System Works Better

Zone 2 becomes easier when:

• Movement becomes cheaper

• Muscles produce force efficiently

• Tendons store and return energy

• Glucose is handled smoothly

• Motor units fire cleanly

• The body is strong enough to support the engine

Strength and endurance are not opposites.They exist in partnership — especially in midlife bodies.

If you want easier Zone 2:lift heavy, not lighter.Lift smarter, not smaller.Lift to rebuild the system endurance depends on.

This is how you keep your power — at 40, 50, 60 and beyond.

References

Strength training & endurance performance/economy

• Vikmoen O et al. Heavy strength training improves running and cycling performance in well-trained female duathletes. Scand J Med Sci Sports. 2017.

• Zanini M et al. Strength training improves running economy durability. Med Sci Sports Exerc. 2025.

• Llanos-Lagos C et al. Strength training effects on physiological determinants of cycling performance. Eur J Appl Physiol. 2025.

• Millet GP et al. Concurrent training improves economy and kinetics. Med Sci Sports Exerc. 2002.

• Piacentini MF et al. Strength training improves running economy in master runners. J Strength Cond Res. 2013.

Resistance training & mitochondrial adaptations

• Groennebaek T, Vissing K. Resistance training and mitochondrial function. Front Physiol. 2017.

• Porter C et al. Mitochondrial adaptations to resistance training. Med Sci Sports Exerc. 2015.

• Chilibeck PD et al. RT effects on mitochondrial density. Eur J Appl Physiol. 1999.

Endurance training & Type II oxidative shifts

• Hendrickse PW et al. Endurance training increases oxidative capacity. Eur J Appl Physiol. 2021.

• Yan Z et al. Regulation of fibre type transformation. J Appl Physiol. 2011.

• Li J et al. Histone methylation & fast-to-slow fibre shift. Sci Rep. 2024.

Glucose handling & strength training

• Wang B et al. Resistance exercise and insulin sensitivity. WJGPT. 2021.

• Croymans DM et al. Resistance training improves insulin sensitivity. J Appl Physiol. 2013.

• Pesta DH et al. RT and diabetes management. Nutr Metab. 2017.

Ageing, motor units & denervation

• Piasecki M et al. Age-dependent motor unit remodelling. J Physiol. 2016.

• Gonzalez-Freire M et al. NMJ ageing and remodelling. Front Aging Neurosci. 2014.

• Qaisar R et al. Fiber denervation and ageing. Free Radic Biol Med. 2016.