Application of Leg, Vertical, and Joint Stiffness in Running Performance: A Literature Overview

Abstract

Stiffness, the resistance to deformation due to force, has been used to model the way in which the lower body responds to landing during cyclic motions such as running and jumping. Vertical, leg, and joint stiffness provide a useful model for investigating the store and release of potential elastic energy via the musculotendinous unit in the stretch-shortening cycle and may provide insight into sport performance. This review is aimed at assessing the effect of vertical, leg, and joint stiffness on running performance as such an investigation may provide greater insight into performance during this common form of locomotion. PubMed and SPORTDiscus databases were searched resulting in 92 publications on vertical, leg, and joint stiffness and running performance. Vertical stiffness increases with running velocity and stride frequency. Higher vertical stiffness differentiated elite runners from lower-performing athletes and was also associated with a lower oxygen cost. In contrast, leg stiffness remains relatively constant with increasing velocity and is not strongly related to the aerobic demand and fatigue. Hip and knee joint stiffness are reported to increase with velocity, and a lower ankle and higher knee joint stiffness are linked to a lower oxygen cost of running; however, no relationship with performance has yet been investigated. Theoretically, there is a desired "leg-spring" stiffness value at which potential elastic energy return is maximised and this is specific to the individual. It appears that higher "leg-spring" stiffness is desirable for running performance; however, more research is needed to investigate the relationship of all three lower limb joint springs as the hip joint is often neglected. There is still no clear answer how training could affect mechanical stiffness during running. Studies including muscle activation and separate analyses of local tissues (tendons) are needed to investigate mechanical stiffness as a global variable associated with sports performance.

Conflict of interest statement

The authors declare that there is no conflict of interest regarding the publication of this paper.

Copyright © 2021 Artur Struzik et al.

Figures

Figure 1

Selection process of papers focused on mechanical stiffness during running [54].

Figure 2

An example of a simple spring-mass model used to estimate leg and vertical stiffness during vertical body displacements only, where COM denotes the centre of mass, ΔL is the change in “spring length” representing both lower limbs, Δy is the displacement of COM, and GRF means the ground reaction force (based on Blickhan [19]).

Figure 3

An example of a spring-mass model used to estimate leg and vertical stiffness during running tasks, where COM denotes centre of mass, ΔL is change in “spring length” representing both lower limbs, and Δy is displacement of COM (based on McMahon and Cheng [20]).

Figure 4

An example of torsional spring model used to estimate ankle, knee, and hip joint stiffness during running tasks, where αankle denotes the ankle joint angle, αknee is the knee joint angle, and αhip is the hip joint angle (based on Farley et al. [111]).