Introduction

In myotonometry, the mechanical behavior of soft tissues is assessed by analyzing their oscillatory response to external mechanical stimuli. Among the parameters used, logarithmic decrement serves as a primary descriptor of the tissue’s damping characteristics.

However, a widespread misinterpretation persists in the scientific literature: the assumption that a higher logarithmic decrement indicates greater elasticity. In fact, the relationship is the opposite.

This article clarifies the inverse relationship between logarithmic decrement and tissue elasticity, explains the underlying biomechanical principles, and highlights the importance of correct interpretation in soft tissue assessment.

Logarithmic Decrement: What It Measures

Logarithmic decrement characterizes the damping behavior of tissue oscillations following a measurement impulse. It quantifies how quickly the oscillation amplitude decreases over time, reflecting the dissipation of mechanical energy within the tissue during oscillatory motion.

Note: Logarithmic decrement is inversely related to tissue elasticity.

A higher decrement value indicates faster damping, greater energy loss. In this context, decrement serves as an inverse indicator of elasticity: the greater the decrement, the lower the elasticity and the higher the energy dissipation.

In theoretical terms, a decrement of zero would imply perfect (absolute) elasticity—i.e., no damping and full preservation of oscillation amplitude across cycles (e.g., a₁ = a₃ = a₅, etc.; see Figure 1). Perfect elasticity, however, does not occur in natural tissues or materials.

Figure 1: Relationship of the displacement (S), velocity (V), and acceleration (a).

Elasticity: Definition and Relevance

Elasticity refers to a tissue’s ability tissue’s ability to return to its original shape after deformation.

It is a fundamental biomechanical property of soft tissues that enables them to undergo reversible deformation. This property relies on the temporary storage of mechanical energy, which drives the tissue's return to its original shape after being deformed.

During oscillations, this stored energy enables return motion but is progressively dissipated with each cycle. In contrast, plasticity refers to permanent deformation, where the tissue does not return to its original form once the external force is removed.

Common Misinterpretation

Despite its clear physical meaning, logarithmic decrement is often incorrectly interpreted as a direct measure of elasticity. This misunderstanding leads some researchers to associate higher decrement values with more elastic tissue behavior.

In reality, a higher logarithmic decrement indicates greater damping and energy loss, which correlates with lower elasticity.

Therefore: The higher the decrement, the lower the elasticity.

Conclusion

Logarithmic decrement should be understood as an inverse indicator of elasticity.

Higher decrement values reflect greater internal energy dissipation. Recognizing this inverse relationship is essential for accurate interpretation of biomechanical measurements and for avoiding misleading conclusions in soft tissue analysis.