Why Do Runners Have Lower Heart Rates? Science Behind It

My average resting heartbeat is 45 beats per minute. I am 40 years old and have a fairly stressful job but overall my heart rate is low. Low to the point that a few doctors were concerned but when I shared that I am a runner, they didn't seem to care. So what do runners have lower resting heart rates?

Runners have low heart rates because of a phenomenon called the aerobic effect. The more you run, the lower your heart rate will be. It's pretty logical and it has very little to do with aging.

The main reason why running lowers your heartbeat is due to changes in your cardiovascular system, when you exercise like this repeatedly, these adaptations happen:

You burn fuels at a faster rate through greater oxygen uptake in the lungs which increases cardiac output The muscle cells become more efficient using less oxygen by having more mitochondria and the mitochondria have more enzymes to burn oxygen.

Your heart rate lowers because it becomes more efficient at pumping the blood along with changes in your nervous system so there is less need for nerve impulses to control the muscle contractions.

This allows the muscles to require less energy while contracting to result in a lower resting heartbeat as well. The aerobic effect described above can actually start happening within two weeks of starting a running program, so rapid improvements like that are very possible.

Why Do Runners Have Lower Heart Rates? The Science Behind It Explained

What is the effect of training & running on blood flow into the heart muscle?

The heart is a muscle that has an artery and vein pumping in and out of it with each beat. These vessels are called coronary arteries (the ones that feed the myocyte, or actual heart muscle cells) and coronary veins, respectively.

During physical activity, the oxygen demand is increased by a factor of 2-3x over resting levels and blood flow increases accordingly to provide more oxygen to the muscles being exercised.

The increase in oxygen demand also translates into an increased need for glucose and fatty acids as fuel.

All this extra energy must be transported from where it is stored (in fat cells, in red blood cells which contain fat molecules), through the bloodstream past all other tissues using only a limited amount of transport vasculature.

During exercise, there is also an increase in the metabolic by-products of exercise called free radicals. These free radicals are what trainers call "toxins" and they can harm your cells if not neutralized. 

The best way to deal with them is to have a good antioxidant defense, which comes from increased blood flow and more antioxidants floating around. So having an increased heart rate will mean your muscle tissues can have an increased sensitivity to their environment (oxygen/glucose) as well as better protection against their environment (less oxidative stress).

In contrast, when someone is sitting on the couch watching TV there is no need for extra oxygen so it doesn't make sense for blood flow to be increased. Instead, you want the opposite because you want glucose and oxygen to stay in your muscles, not your heart.

And for that reason, the body must have a decreased heart rate to stop sending these resources to the heart so they can stay where they are needed, namely in your working muscle.

However, this is not the whole story! When you exercise lightly or moderately (such as running at a moderate pace) then many of those by-products are actually produced within your muscle cells rather than being delivered from outside sources.

It's still important for blood flow to be increased in these situations because now it is providing additional oxygen which helps burn food and reduces oxidative stress caused by the burning process itself.

So it turns out there are good reasons why heart rate should be low even when you're doing light or moderate exercise.

Does running increase my oxygen intake?

Another aspect to consider is that during moderate or light exercise your body requires more oxygen than it does glucose.

When you're running slowly and lightly, as well as when digesting food, you are not 100% efficient at taking up glucose from the bloodstream (that's why they call diabetics "insulin resistant").

You can think of insulin resistance/type 2 diabetes as a very mild form of obesity where carbs don't go directly into muscle cells but instead mostly get stored in fat cells for later use, which is exactly what happens when exercising lightly or moderately (though this may also be due to glycogen depletion).

In contrast, vigorous exercise doesn't require as much oxygen so there's no need to prioritize getting extra oxygen and everything goes to the muscle anyway, whereas during resting conditions by-products are transported back to their source (other organs/muscle cells) by heartbeat so it doesn't matter if you've got more oxygen or more glucose at that time.

It's important to understand that, during exercise, less of your oxygen is used for your actual muscles compared to sedentary people. 

While exercising at 70% VO2 max you get about 75% of the oxygen you would if you were resting and at 85% you actually only get 50%. 

This point is interesting because it means that a somewhat low heart rate has an advantage; maybe not in terms of getting all the vitamins from your blood as they pass through the heart but in terms of keeping glucose and fatty acids where they need to be: working muscle cells!

They also showed something else interesting. In the picture below, there are two graphs plotting how much oxygen was consumed over time by someone who had just gotten up from sleeping. 

You can see that in both cases oxygen consumption spiked up for about 15 minutes, which is expected because muscle cells require more energy to start moving; however, in the second case there was much less of a drop-off afterward than in the first case, which suggests that waking up also supplies an increased blood flow to get rid of any by-products released during exercise.

Normal Resting Heartbeat: Do sedentary people have higher heart rates than runners?

It's not just during exercise that a lower heart rate has advantages but most importantly during sitting/sleeping as well, oftentimes referred to as resting heart rate. For example, when you're exercising you don't have to put as much oxygen into your muscles but with no exercise, inactivity has the opposite effect.

In fact, a study showed that sedentary men had 21% higher heart rates than runners and 30% higher heart rates than cyclists (male college students were used for this experiment). 

So what? Lower heart rate is important because:

Sitting/sleeping consumes up to 30 times more glucose per unit time compared to light exercise. This means less time spent during rest burning food and therefore more time available for muscle growth and repair Resting studies show that high RHR individuals are shorter-lived than those with low RHRs so obviously there's an impact on health even if it doesn't directly affect performance.

Placebo or biological effect?

A low heart rate is good for health but does that mean it's better to have a higher resting metabolism and lower RHR, even at the cost of having to eat more? Not necessarily.

It could also be possible that low-RHR runners are actually healthier because they run so much (or something else like genetics), which would result in them having a lower heart rate even if there were no actual biological differences between them.

After all, people with high RHRs spend their lives sitting around behind desks while people with low RHRs are active enough to exercise often.

That being said, controlled clinical trials show that when given the same amount of food, those who burn through more calories (i.e. higher resting metabolism) end up eating more than those who don't, which is an indication that the relationship between calories in and out is not exactly linear.

One thing's for sure: having a lower R (resting hear rate) HR has to help people lose weight easier so there is some kind of biological effect going on here. After all, metabolic rate (number of calories burned per day) decreases with age but resting heart rate increases.

This means that if you live a long life your heart will have to beat many times more each day compared to someone who dies young; just think about how much impact this would have on the tiny blood vessels inside the heart itself! Running beats sitting/sleeping? It seems like it!

What is an ideal heart rate?

Ideal Heart Rate Ranges -Age Recommended Range:

• 20 - 30 years old 55 ± 10 beats / minute
• 30 - 40 years old 60 ± 12 beats / minute
• 40 - 50 years old 65 ± 13 beats / minute
• 50 - 60 years old 70 ± 15 beats / minute
• 60 and above 75 ± 17 beats/minute.

There are many different ways to calculate your heart rate zones depending on where you get the information from, but they all basically come down to the same thing.

Suffice it to say that although I am not an expert in this field, it seems to me that unless you have some particular reason for aiming for an exact heart rate, e.g., wanting to maximize fat burning or something like that, it is probably better to go with the "zone" system.

After all, if you have a target heart rate of 70 percent of your maximum heart rate as calculated...To calculate Max HR, take 220 minus your age. This means someone in their 20s has a max HR of about 200 and 80-year olds will have a max HR of 140 or so.

Remember that this table above gives only approximate values for maintaining aerobic fitness !

The range 70%-75% is often recommended for endurance; the range 75%-80% is recommended for strength training (or interval training aimed at improving speed). 

Athletes should remember that these are maximum heart rates and you shouldn't train your actual maximum every day, at least not for very long.

In fact, the number of intensive sessions per week depends on the volume of training and the workload as much as on the intensity (and it is best to keep them all under 70%, or even 65%) 

From the research data presented it is clear that differences between high-level endurance runners and top-level sprinters are much less than might be imagined by looking at their performances.

Athletes have lower heart rates and sprinters tend to have slightly higher values for V02 max, heart rate, blood lactate concentrations etc., but the differences are not great.

It's hard to make a comparison of values from elite athletes with those from ordinary people without taking age differences into account too; however, Table 2 gives some indication of how your training pace should relate to your maximum heart rate for different types of running and general fitness levels:

The same principle applies to other types of training: a fast run might be 80-85% of your maximum heart rate, and interval training would probably be done in the 75-85% range.

The higher you work above 85%, the shorter your intervals need to be; overall there should perhaps not be more than around 30 minutes or so of hard effort per week....the Lactate Threshold Heart Rate is 67%-75% of one's Maximum Heart Rate... athletes who do some form of fitness training 4 times a week and none on the fifth day have heart rates that are 10 beats lower on the fifth day than on any of the other days.

The reason for this is unclear but it probably reflects a mechanism to help conserve energy. Marathon runners often report that their body tends to burn fat at low heart rates, but switches back to carbohydrate burning when they raise their heart rate above about 80% of their maximum.

Some coaches claim that you can use this tendency to train your body to run slower marathons by training slightly faster; if true (and I'm dubious) it would be just one more advantage of doing threshold runs instead of constant-pace training runs. 

Despite some claims, there is no evidence that training with slow heart rates improves efficiency or reduces lactate production at faster heart rates.

The best advice I can give is to find your maximum heart rate with a treadmill or on the roads, and then train at about 80% of that for all serious training....If you want to be precise, measure your peak oxygen uptake (VO2 max) and multiply by 0.8 for your THR (Training Heart Rate).

In summary: Athlete's heart = lower heart rates for runners:

So in summary, light and moderate exercise requires a higher blood flow to the muscles for both oxygen and glucose and this is why heart rate is lower during these conditions than rest.

However, just because the heart rate is lower doesn't mean there's any wasted effort.

Moderate exercise provides an extra stimulus on top of what your body needs to keep alive (basal metabolism), but one that still allows normal life activity to proceed without much difficulty. This basal stimulus helps increase stamina in addition..