There isn’t a whole lot more that I wanted to say about low-intensity exercise other than for some indivuals, particularly those very sensitive to stress, may fare better keeping intensity level very low. But I did want to get a few words in about lactic acid and growth hormone, as there is a huge blind infatuation with growth hormone these days.
Growth hormone is far from being worthy of blind worship. Growth hormone is something that surges when the body is subjected to major stresses. Two of the most major stresses – fasting and high-intensity exercise at or near one’s maximum heart rate, stimulate the most dramatic increase in growth hormone. Anorexics, for example, have much higher levels of growth hormone, and are even thought to develop resistance to growth hormone similar to what happens in rats when carbohydrates are removed from the diet. Growth hormone interacts with other hormones, like IGF-1, and high levels of growth hormone with low levels of IGF-1 are hallmarks of type 2 diabetes.
So growth hormone isn’t necessarily good or bad. It depends, like most things, on context. I suspect that very large elevations in growth hormone induced by intense stress may not yield the effect many people think they will get from growth hormone. Most think of growth hormone as being synonymous with the fountain of youth. Phil Campbell, one of the leading researchers promoting high-intensity exercise and the Peak 8 or Sprint 8 program he developed, even states that growth hormone should be called “youth hormone.” Through his growth hormone lens, he even recommends avoiding carbohydrates post-workout despite the giant wealth of research unanimously pointing towards the superiority of big, high-glycemic index carbohydrate supplementation before, during, and immediately after exercise. Others avoid carbohydrates at night to get a bigger nighttime growth hormone secretion during sleep.
In fact, if you were only trying to maximize growth hormone without any other considerations, the best way to do that would be fasting, carb-restriction, keeping calories low, and regularly performing maximum intensity exercise. Great for short-term weight loss. Horrible for long-term health, metabolism, and future body composition.
Like just about anything, there are multiple angles of investigating something. A myopic view on growth hormone without any regard for other growth factors needed for that equation to be successful, or regard for the possibility of developing growth hormone resistance and having the exact opposite intended result long-term, is a dangerous view. A great example of this in action is bone loss in anorexics with raised growth hormone levels – ironic considering growth hormone’s direct, active role in growing new bone.
As far as how lactic acid ties into this – lactic acid, presumed by Ray Peat and others to be a harmful byproduct in any context, increases in proportion to the cardiovascular intensity of exercise. More lactic acid – more growth hormone secretion. To keep lactic acid production low, heart rate shouldn’t exceed about 70% of one’s estimated maximum heart rate (220 – Your Age). And lots of low to moderate exercise is even thought to improve lactic acid clearance – probably a good thing. It might be a little quick to state that “cardio” is dead and that high intensity interval training, circuit training, and other forms of breathless exercise are unquestionably superior in every situation. That may certainly not be true for you, the individual.
Anyway, not trying to scare anyone away from hard exercise. Just trying to even the playing field between the modern high-intensity fad and the old, low-intensity fad. There are pros and cons to each approach, and most probably need a blend of both for health and well-rounded fitness and functionality.
As always, keep an open mind and find what you like, what works, and what increases your metabolism, lowers stress, and enhances your life overall. These kinds of considerations don’t even seem to enter into scientific debate, which speaks volumes about the limitations of a purely science-guided approach to living a long and prosperous life.