Energy Constraint as a Novel Mechanism Linking Exercise and Health

Abstract

Humans and other species adapt dynamically to changes in daily physical activity, maintaining total energy expenditure within a narrow range. Chronic exercise thus suppresses other physiological activity, including immunity, reproduction, and stress response. This exercise-induced downregulation improves health at moderate levels of physical activity but can be detrimental at extreme workloads.

Exercise Degrades Bone in Caloric Restriction, Despite Suppression of Marrow Adipose Tissue (MAT)

“…Although cortical porosity is not a direct measure of strength, it is distinctly associated with reduced strength (86)(87)(88) and thus reflects probable diminution of bone quality as well. (46,47) In conclusion, during the calorie-replete state, exercise induces skeletal anabolism and alters skeletal architecture through effects on a multiplicity of cells. (89) In accordance with our findings in mice, Swift and colleagues demonstrated increased bone resorption in food-restricted, exercised rats.…”

“…(90) Our outcome that exercise can be harmful to the skeleton during calorie restriction is additionally in line with Pontzer's constrained energy expenditure model that suggests increasing quantities of physical activity are not necessarily additive with regard to improved health and may be constrained based on nutrient availability. (46,47) In conclusion, during the calorie-replete state, exercise induces skeletal anabolism and alters skeletal architecture through effects on a multiplicity of cells. (91) In the calorie-replete state, data support that energy stored in marrow adipocytes are utilized for energy during exercise.…”

“…The pathologic bone loss due to anorexia/caloric restriction shows a minimal anabolic-bone response to exercise and maintains a significant fracture risk for years after successful weight gain. Indeed, a high level of physical activity-in combination with caloric restriction-likely results in a decline in overall health, (46) based on Potzner's constrained energy expenditure model. (36)(37)(38)(39)(40)(41)(42)(43)(44)(45) We thus hypothesized that in caloric restriction, MAT's physiologic role differs from the calorie-replete state.…”

“…The reports of increased MAT in calorie restriction, (28,29) combined with increased fracture risk, suggest that the MAT energy depot may be subverted in the energy-depleted state. Indeed, a high level of physical activity-in combination with caloric restriction-likely results in a decline in overall health, (46) based on Potzner's constrained energy expenditure model. (47) Accordingly, we asked if exercise might be harmful to skeletal health in the setting of caloric restriction, simultaneous with exact quantification and characterization of the physiologic response of MAT and bone.…”

Flexibility, variability and constraint in energy management patterns across vertebrate taxa revealed by long‐term heart rate measurements

“…Alternatively, animals may have a ceiling on their rate of energy expenditure, perhaps due to limited musculature (Hammond & Diamond, 1997), or in order to avoid physiological damage (Piersma, 2011) due to, for example, hyperthermia (Nilsson & Nord, 2018;Speakman & Krol, 2010) (Figure 1). Furthermore, energy throughput may be optimised in animals, and any increase in throughput could have fitness consequences such as increased risk of mortality (Daan, Deerenberg, & Dijkstra, 1996;Santos & Nakagawa, 2012), perhaps due to immune suppression (Pontzer, 2018) or oxidative stress (Costantini, Dell'Ariccia, & Lipp, 2008). Although there have been a number of studies about energy management (e.g.…”