Also, low intensity exercise results in your body producing more mitochondria; you may know from Biology that these are found in human cells and it's where respiration and energy production takes place. So, technically the low intensity exercise you do, can give your energy levels a boost. That’s not to say you can simply go for a stroll in the park - it must be proper exercise. (Of course, fresh air is always good for you as is any exercise – however gentle).
Medium intensity training is reasonably strenuous but allows you to still speak in short sentences; on the other hand, at high intensity, you would be breathing hard after a few minutes, unable to talk much and you would feel a burning sensation in your legs (due to the build-up of lactate acid due to exertion).
It’s not just runners who benefit from this kind of high/low interval work, but also competitive cross-country skiers, rowers, cyclists and triathletes too. Researchers have found that using this formula when training for stamina-based sports, improves endurance and reduces the risk of injury, plus performance at competitions is better. When it comes to building endurance, less really is more.
For the rest of us, who are not super-human and who keep fit but don’t aim for demanding, endurance-testing races, we can practise HIIT (high intensity interval training) that has become very popular – short bursts of intense exercise with rest periods in between.
HIIT (High Intensity Interval Training) | The Nutrition Source | Harvard T.H. Chan School of Public Health
What is 80/20 training? (runnersworld.com)
How Pro Endurance Athletes Became The Hardest-Working Creators on the Internet | GQ
When Lower Intensity Leads to Higher Results (hbr.org)
Polarised training for runners | World's Marathons (worldsmarathons.com)
2022 - Stephen Seiler - Science & Cycling (science-cycling.org)