Male And Female Hearts Respond Differently To Exercise

Picture from Intermountain Health

Our hearts respond differently when we lift weights or perform endurance workouts. Our heart muscles get stronger, more efficient and they also get physically larger in some cases.

However, both men and women respond differently to weight training and endurance training. How different? A randomized crossover study examined how the heart's structure and function change after 12 weeks of endurance versus weight training in males and females (Naylor et al, 2025).

64 untrained but healthy individuals (38 females, 26 males) were randomized to either 12 weeks of endurance training (running or cyling 3 times a week) or 12 weeks of weight training (progressive weights, 3 times a week).

The 2 groups swap training routines after a 12 week cooling off rest period. This allowed researchers to compare how the same participants responded to both types of training.

The results showed that overall, endurance training led to healthier heart adaptations than weight training. weight training in men led to thicker heart walls but this led to worse diastolic function (relaxation), potientially increasing stiffness in walls of the heart.

Endurance training improved the size of the left ventricle and its ability to pump blood (systolic function) and to fill with blood (diastolic function) efficiently.

Men's hearts responded more to weight training, the left ventricle size increase significantly. However, men showed signs of worsened diastolic function after weight training. Their hearts became stiffer.

The women in the study showed no major heart changes after weight training. Their hearts also adapted more to endurance training. Left ventricle size increased in both men and women in the study , but the women showed better diastolic function improvement. 

The womens' hearts also adapted more to endurance training. Left ventricle size increased in both men and women, but the women showed better diastolic function improvement. 

Both men and women had no major changes in systolic function after endurance training.

So what does this mean for runners or endurance athletes and those who favour gym exercises/ weight training? 

Those who favour weight training need to include aerobic training so that their heart walls do not get too stiff to impede diastolic function.

If you are looking at heart health, endurance training improves heart structure without adding stiffness to the walls, this is true especially for women. Since endurance athletes will do more aerobic training they should still include weight training for better heart health and performance.

Even though endurance training improves heart function, weight training definitely benefits health (especially strong bones) and performance too. This is why we do both.

Reference

Naylor LH, Marsh CE, Thomas HJ et al (2025). Impact Of Sex On Cardiac Functional Adaptation To Different Modes Of Exercise Training: A Randomized Cross-Over Study. Med Sci in Sp Ex. DOI:10.1249/ MSS.0000000000003654

Should You Try Fasted Exercise?

Picure from Boycemode

I rode to Kukup, a small fishing village in Johor, Malaysia on Good Friday. My bicycle speedometer showed (pictured below) that I rode 160 km when I got home. I had to lie down on the floor after setting my bike aside. I was super tired and was cramping everywhere. Took me quite a while before I could shower.

160 km

There must have been about 40 riders in that group. We stopped for a drink at a small coffee shop in Kukup and I overhead another rider saying he fasted for the ride. I don't know how he did that.

Fasted training means one abstains from consumption of food for 8-12 hours in advance of a training session. Most people do an overnight fast so training is done in the morning before breakfast. It has become popular among people interested in fat loss, metabolic health and for performance or adaptation reasons (especially endurance athletes).

Why would anyone do fasted training? There are lots of videos and reels online suggesting that when you train in a fasted state, your insulin levels are lower, so your body is more likely to use your fat stores for fuel (lipolysis) and better fat utilization.

There are endurance athletes who use fasted training to encourage adaptations like increased mitochondrial density. This is to allow their cells to make more new mitochondria and increase existing mitchondria.  Our cells often increase mitchondria biogenesis in response to increased energy demands triggered by physical activity. With more mitochondria in our cells we become stronger.

With fasted training, endurance athletes are training for better fat utilization to spare their glycogen stores so they can have better endurance. This may work if you're exercising at lower intensities, not when you are going fast at higher intensities since carbohydrate/ glycogen is still very much needed. With fasted training, there will be a severe restriction on the ability to do anaerobic work.

Moreover, over the course of a day, the net fat loss may not be that much different from fed training.

Fasted training may improve insulin sensitivity and glucose tolerance especially in sedentary or overweight individuals.

I also know people who feel better when  they exercise or train on an empty stomach and most find it logistically easier to exercise right after waking up.

Although fasted training can help metabolic adaptations described above, it can also potentially lead to a deficit in total daily calorie intake and this has been shown in active males.

If this reduction in daily calorie intake is not the intended outcome of fasted training it can potentially lead to a state of low energy availability, which when repeated frequently may lead to stress fractures and poor bone health (Raleigh et al, 2024). 

The incidence of bone injury was 1.61 times higher in those who currently use fasted training compared to those who never used it.

Fasted training is not ideal for everyone since you may feel sluggish, lift less (if you're weight training) and perform worse in high intensity workouts. In prolonged fasted states, there is a higher chance that your muscles will be broken down to be used for fuel with intense workouts.

In summary, weigh the pros and cons of fasted training, be aware of how your body responds to it and ensure that it works for your body in the long run.

References

Raleigh C, Madigan S, Sinnott-O'Connor C et al (2024).Prevalence Of Reducing Carbohydrate Intake And Fasted Training In Elite Endurance Athletes And association With Bone Injury. Eur J Sp Sci. 24(9): 1341-1349. DOI: 10.1002/ejsc.12170

Zouhal H, Saedi A, Salhi A et al (2020). Exercise Training And Fasting: Current Insights. Open Access J Sp Med. 21(11): 1-28. DOI: 10.2147/OAJSM.S224919

X-ray Based Diagnosis Leads To Potientially Unnecessary Surgery

Picture by Balint Botz from Radiopaedia

I've written previously that many patients had back surgery when a doctor sends them for an MRI within the first 6 weeks of an initial visit.

Well, guess what? Taking an X-ray to diagnose knee arthritis may make you more likely to consider potentially unnecessary surgery (Lawford et al, 2025) as well.

Many of my patients who go to a doctor or surgeon for their knee pain end up being sent for an X-ray or even an knee MRI. Many of these patients have osteoarthritis (OA) in their knees. Actually, routine X-rays may not be necessary to diagnose the condition. A skilled and thorough assessment based on symptoms and medical history is good enough to make the diagnosis. 

A huge and common misconception is that OA is caused by 'wear and tear'. Research clearly shows that the structural changes seen in a joint X-ray does NOT correspond with the level of pain or disability a person feels. Nor can X-rays predict how symptoms will change.

In fact, X-rays are NOT recommended in Australia to diagnose knee OA. Nearly half of new patients there with knee OA get sent for a knee X-ray and cost their health system A$104.7 million each year.

Researchers in Australia showed that using X-rays to diagnose knee OA can affect how a person thinks about their knee pain and prompt them to consider potentially unnecessary knee replacement surgery.

Many patients with 'terrible' X-rays have no pain while patients with no damage on X-ray have a lot of knee pain. Hence, X-rays are not recommended for diagnosing knee OA or guiding treatment decisions.

The Australian study had 617 subjects across Australia who were randomly assigned to watch one of three videos. Each video showed a hypothetical consultation with a general practitioner (GP) about knee pain. 

The first group received a clinical diagnosis of knee OA based on their age and symptoms and were not sent for an X-ray. The other 2 groups had X-rays done to determine their diagnoses (the doctor showed one group thier X-ray images but not the other group). After watching their assigned video, the subjects completed a survey of their beliefs about OA management.

The results showed that the group who received an X-ray based on their diagnosis and were shown their images had a 36 percent higher perceived need for knee replacement surgery compared to those who received a clinical diagnosis without X-ray.

What was worse was, they even believed that exercise and physical activity could be harmful to their joint. They were also worried about their condition worsening and were more fearful of movement.

The subjects were slightly more satisfied with a X-ray based diagnosis than a clinical diagnosis. This may reflect the common misconception that OA is caused by 'wear and tear' and the joint needs to be replaced.

The study's finding shows that it may be important to avoid unnecessary X-rays when diagnosing knee osteoarthritis. Changing this can be challenging, since many people still expect or want  X-ray imaging. If we can change this mindset, it will minimize unnecessary concern about joint damage, reduce demand for expensive and potentially unnecessary joint replacement surgery.

In my opinion, we as health professionals should not focus on joint 'wear and tear' since it can make patients more anxious about their conditions and concerned about damaging their joints. There are a range of non surgical, non invasive options that can reduce pain and improve your mobility. Exercise is one of many if you read this Cochrane review.

Our health minister says healthcare spending in Singapore could hit 30 billion a year by 2030 in a Straits Times article just 2 days ago. Perhaps this is an area where we need to be more mindful of unnecessary X-ray imaging and joint replacements to bring healthcare spending lower.

You can read about what actually causes your joints to wear out here if you are keen.

Reference

Lawford BJ, Bennell KL, Ewald D et al (2025). Effects Of X-ray-Based Diagnosis And explanation Of Knee Osteoarthritis On Patient Beliefs About Osteoarthritis management: A Randomised Clinical Trial. Plos One. DOI: 10.1371/journal.pmed.1004537 

Brain Myelin Levels Takes 2 Months To Recover After A Marathon

Picture from MSIF

I ran my first marathon when I was 16 years old, just after finishing my GCE 'O' levels. Despite not training as much as I would have liked, I finished in 4:00:16 hrs. If  I had ran just 17 seconds faster, I would have gone under 4 hours. 

I can still remember the exhaustion and agony I felt after the finishing line. I had willed myself to keep going despite hitting the proverbial wall and that led me to wonder about the brain's response to endurance exercise.

So I am not surprised that a recently published study shows that marathon running can cause a temporary reduction in brain myelin content. Full recovery only takes place after 2 months. Myelin is a fatty substance that covers and protects nerve fibers in the brain and spinal cord. It makes up 40 percent of the brain's white matter. The white matter is in charge of nerve signaling to enable learning, memory, sensory perception, motor control and cognition.

Other than allowing faster transmission of nerve impluses (which helps you move more quickly or learn with better focus), myelin helps convert glucose into energy for the brain. This is very important since so much energy is needed for all those nerve signals, especially when running a marathon.

Researchers used advanced MRI with multicomponent relaxometry to assess the myelin water fraction (MWF) to measure the amount of myelin in the brain. This was done on 10 runners ages 45 to 73,  both before and 48 hours after completing a marathon. 

They found substantial reduction in MWF in 12 areas of white matter after the race. The most significant reductions were observed in the pontine crossing (28%) and corticospinal tracts (26%). The affected areas are crucial for motor function and integrating sensory and emotional inputs, suggesting impact on movement and emotional regulation.

Since this was a small study, they did follow up scans 2 weeks after the marathon and 2 months after to track recovery.

MWF levels begin to rebound within 2 weeks and recovered fully to pre-race levels by 2 months. These findings suggest that brain myelin content is temporarily and reversibly diminished by severe exercise. Analyses of brain volume and hydration status showed that dehydration was not responsible for the changes in MWF. 

Since the brain and your legs are both competing for glucose while running a marathon, the brain turns to myelin lipids for energy. Previous studies have shown that lower brain myelin content is linked to cognitive decline - in areas related to verbal fluency and excutive function.

Should those of us who participate in endurance sports be concerned about myelin depletion in our brains? The authors say the breakdown of myelin from endurance exercise is actually beneficial, especially since it generates between 2 weeks to 2 months as it 'exercises' the brain's metabolic machinery.

Reduction in myelin levels can be similar to how muscles react to strength training. Your muscles break down as glycogen levels get depleted during weight training and endurance exercise before building back stronger with adequate rest. 

Better fueling with carbohydrates help sustain effort during training and races and may possibly reduce the amount of myelin used. Some runners in the research took carbohydrates during the marathon while others none, but there were no differences in this research. 

The authors did not investigate running speed. Perhaps running faster if underfueled may exacerbate brain myelin reduction.

So I was drawing on my myelin lipids to support my brain function in my maiden marathon and many times subsequently while exercising and competing for all those years. 

Can repeated depletion and restoration of myelin have long term consequences for people who frequently engage in prolonged, strenuous exercises and competitions?

The reversible nature of MWF is definitely reassuring (to me at least) and as I am still able to write an article for you readers weekly, I think all those hammer sessions and races definitely helped improve my brain function. 

I don't do those long, intense sessions much compared to before, but  I will make sure to have enough rest after. Make sure you do too.

Reference

Ramos-Cabrer P, Cabrera-Zubizarreta A, Padro D et al (2025).Reversible Reduction In Brain Myelin Content UponMarathon Running. Nat Metab. DOI: 10.1038/s42255-025-01244-7