Currently exercise professionals are often faced with a client population enamored of high-intensity exercise. With the epidemic of "bro science" surrounding exercise selection and program design plaguing social media, let's take a step back and evaluate the soundness of high-intensity exercise for the general population as well as athletes.
A very common presentation in athletes and non-athlete exercisers is overtraining syndrome. It's easy for the casual observer to synonymize 'fitness' with 'health,' but a large percentage of those capable of displaying a high level of fitness are far from being truly healthy. The popular combination of grueling exercise with a carbohydrate-stuffed diet can easily drive a massive production of free radicals and inflammation, as well as a strong, biased shift toward carbohydrate oxidation and away from fatty acid oxidation [1]. A few of the potential results from excessive high-intensity training include: hormonal imbalance, depression of the immune system, malnutrition, reduced heart rate variability, and a host of inflammation-associated conditions such as adrenal insufficiency, hypothyroidism, type 2 diabetes, anemia of inflammation, and even celiac disease [2]. What's usually not understood is that increases in physical activity do not parallel increases in energy expenditure [3]. In other words, total energy expenditure largely plateaus as cumulative activity increases, for the human body compensates to keep the total energy expenditure within an acceptable range [4]. The body simply isn't too concerned with how many steps you try and accumulate each day, its primary focus is ensuring your survival in each moment – and its last priority is the enhancing of its fitness (bigger biceps and better abs). The "no pain, no gain" attitude, coupled with the frequent psychological and emotional stressors of everyday life, steal away potential energy that the body would otherwise be able to utilize in properly adapting to any kind of exercise. Thus, repeated "balls to the wall" training can easily force the body to draw from vital reserves to meet the imposed demands [5]. Continued drawing from this well places the body into a physiological debt that promotes ongoing catabolism, thwarting all efforts to build muscle and burn fat. Typical high-intensity interval training doesn't really lead to desirable and lasting improvements in mitochondrial fat oxidation, even though elevations in OXPHOS (mitochondrial oxidative phosphorylation) can be seen with such training [6]. And although in general, more total calories will be expended acutely with higher intensity exercise, the proportion of total calories expended coming from fat oxidation will decrease as exercise intensity increases [7]. Accordingly, we can't simply compare the EPOC (excess post-exercise oxygen consumption) values of both low and high intensity exercise [8]. We have to remember that the higher the intensity of the exercise, the greater the stress that will be imposed on the body. Insulin, leptin (the satiety hormone), ghrelin (the hunger hormone), dopamine, and serotonin all play a role in regulating the body's energy homeostasis [9]. When we bombard the body with too much exercise, and/or we restrict calories from the diet, the body's righting or equilibrating actions will prevent the intended accomplishment of an increase in muscle mass plus a decrease in fat mass. So simply exercising more in order to lose more fat can be counterproductive [10]. In conclusion, listen to your body. When it's ready and is genuinely craving some higher intensity work at the gym, it'll let you know. When it's not ready and is giving you the finger at the suggestion of higher intensity work at the gym, back it down and respect your physiology's cycles. References:
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AuthorDenton Coleman is an Exercise Physiologist and Medical Researcher. Archives
October 2023
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