Why do I get tired so fast when exercising?

Learn how mitochondrial function, genetics, nutrition and recovery influence energy, endurance and fatigue in women and how to support it naturally.

There are women who, deep down, have always felt that their body responds differently to physical effort.

Many were completely healthy growing up. But they remember never being naturally good at running, endurance sports or activities that required sustained energy. They got tired faster than other children. Needed longer to recover. Felt physically drained after effort that others tolerated more easily.

And because this often starts early in life, many women simply build their identity around it:

• “I’m just not athletic.”

• “My body has always been like this.”

But sometimes, there can actually be a biological explanation behind this pattern.

Some People Naturally Produce Energy Less Efficiently

Inside every cell in your body, there are small structures called mitochondria. Their role is to produce energy. Everything depends on them: your muscles, your brain, your hormones, your nervous system and your ability to recover after physical or emotional stress.

Some people are born with what we call primary mitochondrial dysfunctions. These are genetic conditions that affect how efficiently mitochondria produce energy. Severe cases are usually diagnosed early in life, but milder forms can go unnoticed for years because the body adapts remarkably well.

The Body Constantly Tries to Adapt

What is fascinating about mitochondria is that the body constantly tries to compensate. Even when energy production is not ideal, cells create alternative pathways and adaptation mechanisms to keep energy flowing as much as possible. This is one reason why symptoms vary so much between people. For some women, this may simply look like:

• lower endurance

• poor recovery after exercise

• fatigue after physical effort

• brain fog

• needing more rest than others

• feeling physically depleted more easily

And this is also why lifestyle matters enormously. Because mitochondria are deeply influenced by sleep, nutrition, movement, stress, inflammation, nutrient deficiencies, and environmental toxins.

This means that even when there is a genetic predisposition, the way you live still impacts how your body produces and manages energy.

Exercise Can Actually Help Build More Mitochondria

This is why exercise, when adapted properly, can actually improve mitochondrial function over time. Not because exercise “pushes” the body harder, but because movement stimulates something called mitochondrial biogenesis, the creation of new mitochondria. In simple terms, the body becomes better at producing energy.

But mitochondria respond much better to gradual and consistent stimulation than to exhaustion.

If your body is already depleted, pushing too hard usually increases inflammation and stress hormones even more, making recovery harder. What works best physiologically is progressive adaptation.

I usually recommend starting like this:

• Walk 10–15 minutes daily after one meal. This helps improve blood sugar regulation, oxygen delivery and mitochondrial stimulation without overstressing the body.

• Add movement snacks during the day instead of one intense session. For example: a few squats, stairs, stretching or 5 minutes of mobility. Mitochondria respond very well to repeated stimulation.

• Prioritise resistance training 2x/week before focusing on intense cardio. Muscle tissue contains a very high number of mitochondria and resistance training helps stimulate mitochondrial biogenesis.

• Keep intensity low enough that you recover well the next day. This is extremely important. If exercise wipes you out for 2 days afterwards, the body is not adapting properly yet.

• Focus first on consistency, not performance. The body needs repeated signals of movement and recovery to improve energy production over time.

• Respect sleep and recovery. Mitochondria repair and adapt during recovery, not only during training.

One of the most important things to understand is this: the goal initially is not burning calories.

It is teaching the body to produce and tolerate energy better again.

Nutrients Also Play a Major Role in Energy Production

Mitochondria need nutrients constantly to produce energy well. And honestly, one of the biggest things I see in women with fatigue is not necessarily “eating badly”, but eating in a way that does not provide enough consistent nutrients for the body to sustain energy production properly.

The goal is not perfection or following an extreme diet. It is progressively creating an environment where your cells receive the nutrients needed to produce energy more efficiently and lower inflammation at the same time.

I usually recommend starting with a few foundational changes first:

• Make at least half of your plate vegetables at lunch and dinner, especially greens like broccoli, spinach, arugula, kale, bok choy and cabbage. These vegetables are rich in magnesium, folate, antioxidants and sulfur compounds that support detoxification and mitochondrial protection.

• Add protein at every meal because mitochondria require amino acids to function and repair properly. Eggs, fish, chicken, greek yogurt, legumes or tofu are simple starting points.

• Include omega 3 rich foods 2–3 times/week like sardines, salmon or mackerel. DHA and EPA help reduce neuroinflammation and improve mitochondrial membrane function.

• Add magnesium-rich foods daily: pumpkin seeds, chia seeds, almonds, spinach, dark chocolate, quinoa and legumes.

• Use extra virgin olive oil regularly. Polyphenols from olive oil help protect mitochondria from oxidative stress.

• Reduce ultra-processed foods slowly instead of trying to remove everything overnight. Highly processed foods, refined sugars and refined oils increase oxidative stress and blood sugar instability, which impair mitochondrial function over time.

One thing I think is important is making these changes progressively. Women often try to completely change their diet in one week and then cannot sustain it. Mitochondria actually respond better to consistency than intensity. For example:

• Week 1: improve breakfast protein

• Week 2: add more greens daily

• Week 3: reduce processed snacks

• Week 4: add omega 3 rich fish

This is much more realistic for long-term adaptation.

Supplements can also be very supportive, especially when someone is already depleted, under chronic stress or recovering from long-term fatigue.

The nutrients most involved in mitochondrial energy production include:

• magnesium

• CoQ10

• B vitamins

• omega 3

• iron (ferritin levels should be tested first)

• selenium

• zinc

• L-carnitine

One of the nutrients most studied in mitochondrial dysfunction is CoQ10. Research has shown that after several months of supplementation, some patients experienced significant improvements in brain and muscle energy metabolism.

But supplementation works best when the body is also receiving nutrients through food. Food provides fibre, antioxidants, phytonutrients, and cofactors that work together in ways supplements alone cannot fully reproduce. This is why I see supplements more as supportive tools to accelerate recovery and replenish deficiencies, while nutrition creates the long-term foundation that keeps mitochondria functioning properly over time.

Clinically, this also makes sense. Because when the body finally receives the nutrients needed to produce energy more efficiently, women often notice:

• better recovery

• more stable energy

• clearer thinking

• improved exercise tolerance

• less physical exhaustion

Maybe Your Body Was Never “Lazy”

I think this conversation matters because many women have spent years blaming themselves for feeling physically weaker, more tired or less resilient than other people.

Many spend years wondering:

“Why do I get tired so fast when exercising?” or believing they simply lack discipline or are “not athletic”.

But sometimes, what looks like poor endurance or difficulty recovering from exercise is actually biology asking for support.

Frequently Asked Questions

Why do I get tired so fast when exercising?

Some women naturally struggle more with energy production and recovery. This can happen when mitochondria are not functioning optimally. It may show up as poor endurance, exhaustion after exercise or needing longer recovery compared to others.

Why have I never been good at running or endurance sports?

For some women, this may simply reflect differences in conditioning or training. But for others, there can also be a biological component related to how efficiently the body produces energy at a cellular level. Mild mitochondrial dysfunction can sometimes go unnoticed for years and appear mainly through lower physical endurance and fatigue.

Can mitochondria be improved naturally?

Yes. Mitochondria are highly adaptable and respond to movement, nutrition, sleep, stress regulation and nutrient status. Consistent resistance training, walking, proper recovery and nutrient-dense foods can help support mitochondrial function and improve energy production over time.

What nutrients support mitochondrial energy production?

Mitochondria require nutrients like CoQ10, magnesium, B vitamins, omega 3 fatty acids, iron, amino acids and antioxidants to produce energy efficiently. These nutrients help support ATP production, reduce oxidative stress and improve cellular recovery.

Why does exercise make me exhausted for days afterwards?

When the body struggles to produce or recover energy efficiently, intense exercise can temporarily increase inflammation and oxidative stress beyond what the body can tolerate well. This is why some women experience prolonged fatigue after workouts and often respond better to gradual, progressive movement.

Can stress affect mitochondrial function?

Yes. Chronic stress increases inflammation, oxidative stress and nutrient depletion, all of which can impair mitochondrial energy production over time. Poor sleep, emotional overload and chronic nervous system activation can also reduce recovery capacity.

Why do I feel physically tired even when my tests are normal?

Many women with fatigue, poor recovery or exercise intolerance have standard blood tests that appear “normal”. But energy production depends on multiple systems working together, including nutrient status, mitochondrial function, inflammation, nervous system regulation and recovery capacity, which are not always fully evaluated in routine testing.