The Case for Cardio

Why “avoid cardio” is horrible advice for midlife women

Photo by Bruno Nascimento on Unsplash

Jane had heard she needed to do strength training in midlife. As a newly menopausal woman, she hired a personal trainer.

The trainer, also a midlife woman, lectured her on the importance of building muscle and strength training. And then she asked Jane a question.

“Do you know how much cardio I do?”

Jane sat silent, feeling like she wasn’t really looking for her to answer.

The trainer made a zero sign with one of her hands.

This avoid-cardio advice is everywhere. I’m not sure exactly where it started or why. It’s most likely due to overblown claims about cortisol.

So, I want to clear the air and by sharing the research on the benefits of cardiovascular exercise. Especially when it comes to the unique needs of midlife women.

In studies, exercise usually means cardio

Interest in exercise surged in 1996 when the American Heart Association released a report highlighting its health benefits. From then on, an overwhelming amount of research has shown the benefits of exercise.

Cardiovascular exercise, specifically aerobic activity at moderate to intense levels, is the dominant form of exercise in most of these research studies. Examples include brisk walking, running, swimming, cycling, climbing stairs, rowing, and other repetitive movements that increase heartrate.

The American College of Sports Medicine (ACSM) defines aerobic exercise as “any activity that uses large muscle groups, that can be maintained and is rhythmic in nature.” The muscle groups activated rely on aerobic metabolism to for energy.

This aerobic capacity relies on the cardiorespiratory system to increase cardiac output to supply oxygen and the skeletal muscle to use oxygen.

A 2024 study in the European Heart Journal with 406 adults with elevated blood pressure and BMI >25 (age 35-70), compared exercise types on cardiovascular disease (CVD) profile. Researchers assigned participants to either an aerobic exercise, resistance exercise, combined aerobic and resistance, or a non-exercise control group.

All the exercise groups included 1 hour of exercise three times per week for one year. The combo group did 30 minutes of resistance and 30 minutes of aerobic exercise.

Compared to the non-exercise control, the CVD risk profile decreased in both the aerobic and combo group, but not the resistance training only group, showing the importance of including a cardio component.

It boosts cardiorespiratory fitness (CRF)

The ability of our body to deliver oxygen to working muscles during physical activity is called cardiorespiratory fitness (CRF). The gold standard for measuring CRF is V02max.

A high V02max means the body is efficient at delivering oxygen to muscles. This is important, as muscles need oxygen to produce energy.

CRF, as measured by V02max, is a powerful predictor of cardiovascular and all-cause mortality. Higher levels of CRF are also associated with a reduced risk of various health outcomes and chronic diseases besides CVD.

According to 38 RCT studies with 1682 participants, aerobic exercise improved V02max more than resistance exercise.

In fact, in 2016, the American Heart Association published a statement advocating to include V02max as a vital sign.

 decades of research have produced unequivocal evidence that CRF provides independent and additive morbidity and mortality data that when added to traditional risk factors significantly improves CVD risk prediction. On the basis of these observations alone, not including CRF measurement in routine clinical practice fails to provide an optimal approach for stratifying patients according to risk.

Ross et al, Circulation, 2016

It promotes vascular health

Engaging in cardiovascular exercise is crucial for keeping our blood vessels healthy. That means it positively affects the endothelium (cells that line blood vessels).

Nine studies with 221 people, revealed that aerobic exercise increases flow mediated dilation (FMD) in both midlife and older people. This is especially true for vigorous-intensity exercise of 8 weeks or more.

FMD is a marker for nitric oxide mediated dilation (that magic midlife molecule). This is important because the risk of endothelial dysfunction rises during menopause.

As I’ve mentioned before, as estrogen lowers in midlife women, the effect of aerobic exercise on vasodilation may lessen, although studies are mixed.

That’s why I’m keeping my eye on studies like the Bee Sweet that use Beetroot juice in postmenopausal women and my interview with Daniel Craighead showcases resistance breathing as an option. So stay tuned.

It protects the aging immune system

As we age, our immune system may not work as well, resulting thymic atrophy and lower amount of killer T cells.

Yet physical activity has been shown to improve this tendency in older adults.

In a 2018 study with 125 adults ages 55-79, those who had maintained high levels of aerobic activity (cycling) for most of their adult lives had higher levels of T cells and thymic emigrants (RTE) compared to age-matched inactive individuals.

Cyclists demonstrated a lower rate of weakened immune systems compared to inactive individuals. This did not entirely protect the older active adults, but it made a big difference.

We conclude that many features of immunesenescence may be driven by reduced physical activity with age.

- Duggal, Aging Cell, 2018 Apr;17(2):e12750

This agrees with other research, demonstrating that regular moderate to vigorous exercise lowers the likelihood and severity of infectious diseases, boosts immune system markers, and enhances the protective effects of vaccines.

It reduces cortisol (except over-training)

One reason midlife women are told not to do cardio (or not to overdo it) has to do with cortisol. The theory is that a high level of aerobic activity increases cortisol production, which puts the body under stress. This can cause weight gain, muscle breakdown, and impaired immune functioning.

Yet, according to 10 studies, physical activity, including aerobic exercise, leads to lower cortisol levels. It’s true that cortisol increases during exercise, especially when it’s intense. But most of the time, regular aerobic exercise results in a lower level of cortisol at rest.

Not only that, but a study with men showed that intense exercise can decrease the cortisol response to daily stressors.

The research remains incomplete, as most studies are conducted on men. A 2021 review states that “Research in women is significantly needed, especially when comparing pre-menopausal to post-menopausal, sedentary to active, and trained too untrained.”

The story of cardio-is-bad typically describes a midlife woman doing hours of cardio a day, which is not the norm. We know that over-training at any age can increase cortisol overall and have negative effects.

“Over-training syndrome” is an excessive training load is mixed with inadequate recovery and rest. As we get older, we need more time to recover than before. Pay attention to signs of over-training, such as poor sleep and fatigue while exercising.

It helps build muscle and protects against losses

Although resistance exercise is the gold standard for increasing strength and skeletal muscle mass, aerobic exercise plays a complementary role.

For instance, while resistance training maintains and improves strength, mobility, joint function and type II muscle fibers, endurance exercise [cardio] improves mitochondrial energetics, enhancing metabolic flexibility, type I muscle fibers, and muscle quality.

After all, during aerobic activity a variety of muscles are activated. When sedentary people performed cycling for 12 weeks, they saw an increase in muscle mass by 11%.

Another reason cardio is “muscle friendly” is that in enhances muscle protein synthesis by stimulating anabolic pathways, improving blood flow, and delivering amino acids to muscles.

Resistance training and endurance training each hold their own unique benefits in the context of sarcopenia and aging.

Harper et al, J Transl Med, 2021

It boosts mood and brain function

Nowhere is the research more important than the effect aerobic exercise has on the brain and mood. Not only is it beneficial to depression and anxiety, it helps with improving brain volume and memory.

These benefits are because of a variety of reasons, including increased blood flow to the brain but most importantly, brain metabolism. Glucose is the primary fuel for the brain and with aging and menopause, the ability to use glucose decreases.

In a 2018 study, researchers assigned younger (18-30) and older (65-80) people free of medical conditions to a week high intensity interval training workout or a control group. They measured resting brain glucose, and it was higher in both exercising age groups compared to the control.

A key reason or this is the increase in neurotrophic growth factors like Brain Derived Neurotropic Factor (BDNF). Aerobic exercise is an established way to increase BDNF with higher intensity activity showing an advantage.

In fact, one study linked low BDNF to memory issues in post-menopausal women. Researchers did not find this effect in pre or perimenopausal women, suggesting that BDNF and memory performance may be important for older ages and after menopause.

These results suggest that in postmenopausal women, BDNF is associated with memory performance and memory circuitry function, thus providing evidence of potential sex-dependent factors of risk and resilience for early intervention.

So, yeah, I’ll keep doing my cardio.

It’s good for our body fat

Aerobic exercise supports healthy fat in two main ways. First, it reduces visceral fat (the harmful fat around your organs) that’s linked to chronic diseases. Second, it helps all types of fat work better and stay healthier.

A meta-analysis on studies with postmenopausal women showed that aerobic exercise had a greater impact on fat loss compared to other types of training, while resistance training was better for building muscle.

This may be due to long-term aerobic exercise increasing adiponectin levels, which helps reduce visceral fat and promote a more efficient metabolism.

Recent research supports these findings. A study on 16 long-term exercisers (who exercised at least 4 times a week for an average of 11 years) found their fat was healthier than inactive individuals of similar age, weight, and body fat.

Exercisers had fat tissue with more blood vessels, more mitochondria, and fewer inflammation-causing fat cells. For more on this study, read my latest roundup.

How much is enough?

A little can go a long way. As far as improving cardiorespiratory fitness, the 2016 statement from the AHA recommends:

Type: exercise that involves major muscle groups that is continuous, such as brisk walking, jogging, running, cycling, rowing, cross country skiing, climbing stairs, active dancing)

Frequency: five or more days a week of moderate exercise, or three days week of vigorous exercise or a combination of moderate and vigorous 3-5 days/week. Those with health conditions need medical clearance.

Time: 30–60 min/d (150 min/week) of moderate-intensity exercise, or 20–60 min/day (75 min/week) of vigorous exercise, or a combination of moderate and vigorous exercise per day for most adults; <20 but ≥10 min/day (<150 min/week).

Summary of cardio benefits

• Boosts Cardiovascular Health and enhances Cardiorespiratory Fitness (CRF):

  • Improves cardiovascular disease (CVD) risk profiles.

  • Higher V02max indicates better oxygen delivery to muscles.

  • Regular aerobic exercise improves VO2max and lowers mortality risk.

• Promotes Vascular Health:

  • Improves blood vessel function, especially in midlife.

  • Vigorous aerobic exercise can enhance nitric oxide production, important for vascular health.

• Supports the Aging Immune System:

  • Regular aerobic exercise boosts immune function and reduces risks of infections.

  • Active individuals have higher levels of T-cells, strengthening immunity.

• Regulates Cortisol Levels:

  • Aerobic exercise reduces cortisol over time, unlike the overtraining effect which can increase it.

  • Benefits from moderate to vigorous exercise, especially in reducing stress-induced cortisol, although we need more studies, especially in midlife women

• Preserves Muscle and Bone Health:

  • Aerobic exercise helps maintain muscle mass and promotes muscle protein synthesis.

  • Complementary to resistance training for aging and sarcopenia prevention.

• Improves Mood and Brain Function:

  • Aerobic exercise enhances memory, mood, and brain volume.

  • Increases neurotrophic factors like BDNF, which supports brain health, especially post-menopause.

• Supports Healthy Body Fat:

  • Reduces visceral fat and improves fat health.

  • Long-term aerobic exercise leads to healthier fat tissue with more blood vessels and mitochondria.

• Exercise Recommendations:

  • Type: Continuous, rhythmic activities like walking, running, or cycling.

  • Frequency: 5+ days/week of moderate exercise or 3 days/week of vigorous exercise.

  • Duration: 30–60 minutes per day of moderate intensity or 20–60 minutes of vigorous exercise.

Cardio is important!

My intention with this post isn’t to suggest that women should prioritize cardio over resistance training, but rather to emphasize the importance of incorporating both into our routines.

While it’s true that women have traditionally focused more on cardio, strength training is essential too. Both forms of exercise complement each other and bring unique benefits, and I plan to dive deeper into that in future posts.

So, the next time someone advises you to avoid cardio, point them to this post! If they have different research or point of view, I’d love to hear about it.

I’d also love to hear your thoughts and experiences with cardio—what benefits have you noticed? What advice confuses you most?