Compression garments are worn during and after exercise on the basis of several proposed mechanisms. The mechanisms are plausible and their measured effects differ considerably in size and reliability.
External pressure assists venous return
Blood returning from the limbs travels against gravity through veins that rely on muscle contraction and one-way valves rather than on pump pressure.
Applying external pressure narrows those vessels slightly, which raises the velocity of flow within them and assists the return of blood toward the heart.
Graduated garments apply more pressure at the extremity and less proximally, creating a gradient intended to move fluid in the desired direction.
Swelling is limited by reducing available space
Fluid accumulating in tissue after exercise has to displace something, and external pressure raises the tissue pressure it must work against.
Less accumulation means less mechanical distension of the tissue, which is a plausible route to the reduced soreness that wearers consistently report.
The same principle underlies medical compression for swelling, where the evidence base is considerably stronger than in the sporting application.
Muscle oscillation is damped during activity
Each foot strike causes soft tissue to vibrate, and that oscillation is thought to contribute to muscle damage over the volume of impacts in a long event.
Compression restricts that movement, reducing the vibration, which is the reasoning behind wearing garments during exercise rather than only afterwards.
The size of this effect is difficult to measure directly, and the performance benefits reported during activity are small and inconsistent.
Perceptual effects are the most reliable finding
Reduced soreness and a sensation of reduced fatigue are reported consistently, and those reports are more robust than any measured change in physiological markers.
Whether this reflects the pressure itself, the sensory input from the garment, or expectation is difficult to separate in practice.
Separating them matters less than it appears. An athlete who feels less sore moves more freely and trains more willingly the day after, and that change in behaviour is a real consequence even where the tissue underneath is unaltered.
Fit determines whether any of this applies
The mechanisms depend on achieving a specific pressure range, and off-the-shelf garments sized by height and weight frequently deliver pressures outside it.
The pressure delivered also falls as the fabric ages and stretches, so a garment that once sat within the intended range drifts below it after repeated washing, while limb circumference itself changes across a day and across a season.
A garment that is too loose does nothing, while one that is too tight can restrict circulation, so anyone with a vascular condition should seek medical advice before use.
