In overweight women, high-intensity circuit training can raise the number of calories burned at rest by 6–10%, which helps reduce body fat over time even without changing food intake, due to...
Mechanism
Synthesis from 1 study
When overweight women do intense circuit workouts, their muscles grow bigger and burn more calories even when resting, and their bodies keep burning extra calories for hours after each session to recover — together, this creates a daily calorie deficit that leads to fat loss without changing diet,...
Most probable mechanism
When overweight women do high-intensity circuit workouts, their muscles grow bigger because the lifting and pushing movements trigger muscle-building signals, and bigger muscles burn more calories even at rest. After each workout, their bodies keep using extra oxygen to clean up waste, restore energy stores, and cool down, which burns more calories for hours afterward. Together, these two effects raise their daily calorie burn enough to lose fat without changing what they eat, as shown in the study with DOI 10.1371/journal.pone.0202390.
Mechanical tension from resistance-based circuit training activates mTOR signaling in skeletal muscle, leading to muscle fiber hypertrophy and increased fat-free mass, as directly measured by gains in lean tissue and strength in overweight women.
Increased fat-free mass raises basal metabolic rate by elevating ATP demand for protein synthesis, ion transport, and cellular maintenance in metabolically active muscle tissue.
High-intensity exercise depletes ATP and phosphocreatine and accumulates lactate, triggering prolonged elevation of oxygen consumption after exercise (EPOC) to restore energy stores, clear lactate, and normalize ion gradients and body temperature.
Elevated post-exercise oxygen consumption and sympathetic nervous system activity sustain elevated energy expenditure and lipolysis, contributing to a daily negative energy balance.
Mitochondrial biogenesis is enhanced via AMPK and PGC-1α activation due to exercise-induced ATP depletion, increasing oxidative capacity and fat oxidation efficiency, which supports sustained energy expenditure and fat loss.
Less supported by current evidence, but not ruled out
High-intensity exercise may trigger the release of stress hormones like adrenaline, which signal fat cells to break down stored fat into fatty acids that can be burned for energy, though this was not directly measured in the study.
High-intensity circuit training activates the sympathetic nervous system, increasing circulating catecholamines such as epinephrine and norepinephrine.
Catecholamines bind to β-adrenergic receptors on adipocytes, activating adenylate cyclase and increasing cAMP, which triggers hormone-sensitive lipase to break down triglycerides into free fatty acids.
Released free fatty acids are transported to muscle and liver for oxidation, contributing to fat loss independent of dietary intake.
Evidence from Studies
Supporting (1)
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