Physical activity is directly associated with total energy expenditure without evidence of constraint or compensation

The prevailing linear model of physical activity (PA) and total energy expenditure (TEE) has been challenged by models that predict an upper limit of TEE linked to a compensatory reduction elsewhere in the energy budget in response to increased PA. We determined the equation of best fit between PA and TEE and explored relationships between PA and behavioral and physiological compensation. Using linear and nonlinear modeling, we observed a positive linear relationship between PA and TEE either without or after adjustment for fat-free mass (R²= 0.3492, TEE = 0.00685*PA + 7.124: R²=0.3667, TEE_ADJ(FFM) = 0.00511*PA + 8.598). Higher PA was associated with lower sedentary time (R²= 0.7207, %SPA= -0.0211*X + 91.261). There was no association between PA, TEE, or resting metabolic rate and adjusted biomarkers of immune, reproductive, or thyroid function after Bonferroni correction. The findings of this observational study do not support the constrained/compensated model but affirm the conventional additive relationship between PA and TEE across a broad range of PA levels.