Where does preload collide?

In cardiac physiology, preload is the degree to which the heart muscle is stretched by the volume of blood filling the ventricle just before it contracts, usually indexed by end-diastolic volume or pressure. Patterson and Starling's 1914 On the mechanical factors which determine the output of the ventricles established the law that, within limits, greater filling stretches the muscle and yields a more forceful contraction and larger stroke volume. The referent is a physiological filling load on the heart that sets contractile force through fibre stretch, and it is distinct from the tension deliberately built into a bolted joint, sharing only the idea of a load applied in advance.[1]

Unit

End-diastolic volume or pressure (ventricular fibre stretch before contraction)

Recovery means

Not applicable

Measured by

Estimated from end-diastolic volume or pressure and visualised on the Frank-Starling (function) curve relating filling to stroke volume

In mechanical design, preload is the tension deliberately introduced into a fastener or bearing during assembly, before any service load is applied, so that a bolted joint stays clamped and resists loosening and fatigue, or a bearing runs with controlled stiffness and no play. Budynas and Nisbett's Shigley's Mechanical Engineering Design treats how preload is set by tightening torque and how it governs joint stiffness and the share of external load the bolt actually sees. The referent is an engineered initial tension chosen for joint integrity, measured in force or torque, and it is unrelated to the stretch on heart muscle beyond the shared notion of a load set beforehand.[2]

Unit

The initial clamping force (or tightening torque) in the fastener or bearing

Recovery means

Not applicable

Measured by

Set and checked by tightening torque, bolt elongation, or torque-angle methods, and by residual clamping force