Resting heart rate – slower is better
As your heart gets more efficient and stronger – it can pump more blood with each stroke (and, potentially, require less energy to do that). Eventually, what this leads to is slower resting heart rate. Remember, the heart rate is a product of the demand for oxygenated blood and your heart’s ability to satisfy that demand. As this ability improves, the heart doesn’t need to beat as fast.
This is precisely where the benefit of exercise comes in. Exercise not only strengthens the heart itself and makes it more efficient in accessing oxygen in the blood (by growing more mitochondria) – but it also triggers the growth of new mitochondria (as well as improvement in oxidative capacity of existing mitochondria) at the periphery (i.e. – within the target tissue). All of that means that tissues in need of oxygen could now use less of it to satisfy the same demand for energy – which means your heart doesn’t need to beat as fast.
What benefits does slower heart rate have? There may be a couple:
- Slower heart rate means a bigger “buffer” between current and maximum heart rate to keep up with more demanding situations when the heart needs to beat faster. Remember – the maximum rate is a finite number for everyone – your heart can’t just beat faster and faster in response to the demand – because the heart itself needs oxygen from blood to perform the work. Faster heart rate means higher energy demand for the heart muscle itself – and at some point, the ability to fuel this process by oxygen delivered by the blood will be limited by the supply of that freshly oxygenated blood and the speed at which it is utilized within the aerobic metabolism pathways. No available energy at any given moment means no ability to contract. So a slower heart rate potentially means more energy-efficient heart and a higher capacity to increase that rate to address spontaneous demands for blood delivery;
- As we have already mentioned, muscle contraction requires energy – which comes from oxidation of fat, glucose or ketone bodies. Cellular energy metabolism – while being absolutely essential for life – also generates several chemical and electrical by-products that, in large amounts, can be harmful. For instance – we have already discussed positive hydrogen ions (H+) generated by muscle contraction that raise the acidity of the cell. Also, cellular metabolism generates reactive oxygen species that are known to inflict damage to cell’s DNA and cause various disorders. It follows, then, that less energy required for resting heart rate means less of such by-products – which, by the way, may contribute to the wear and tear and, as a result – the longevity of the heart itself. Perhaps it is no coincidence that animals with generally slower heart rates live longer?