Abstract
Neuromuscular characteristics, such as lower-limb joint strength and the ability to rapidly generate force, may play an important role in leg-spring stiffness regulation. This study aimed to investigate the relationship between isokinetic knee and ankle joint peak torque (PT), the force-time characteristics of isometric mid-thigh pull (IMTP), and leg stiffness (Kleg)/vertical stiffness (Kvert) in recreationally trained runners. Thirty-one male runners were recruited and underwent three separate tests. In the first session, the body composition, Kleg, and Kvert at running speeds of 12 and 14 km⋅h–1 were measured. In the second session, isokinetic knee and ankle joint PT at 60°⋅s–1 were tested. The force-time characteristics of the IMTP were evaluated in the final session. Pearson’s product-moment correlations, with the Benjamini–Hochberg correction procedure, showed that the knee flexor concentric and eccentric and extensor concentric PT (r = 0.473–0.654, p < 0.05) were moderate to largely correlated with Kleg and Kvert at 12 and 14 km⋅h–1. The knee extensor eccentric PT (r = 0.440, p = 0.050) was moderately correlated with the 14 km⋅h–1 Kvert. The ankle plantar flexor concentric and dorsiflexor eccentric PT (r = 0.506–0.571, p < 0.05) were largely correlated with Kleg at 12 km⋅h–1. The ankle plantar flexor concentric and eccentric and dorsiflexor eccentric PT (r = 0.436–0.561, p < 0.05) were moderate to largely correlated with Kvert at 12 and 14 km⋅h–1. For IMTP testing, high correlation was only found between the IMPT peak force (PF) and Kvert at 14 km⋅h–1 (r = 0.510, p = 0.014). Thus, superior leg-spring stiffness in recreational runners may be related to increased knee and ankle joint strength, eccentric muscular capacity, and maximal force production.
Highlights
The spring-mass model parameters, such as leg stiffness (Kleg) and vertical stiffness (Kvert), are typically used to characterize the mechanical properties of a “leg-spring,” representing the lower limbs during running (Jaén-Carrillo et al, 2021)
For correlations between the isokinetic strength testing and leg-spring stiffness test, we found that the peak torque (PT) of Kflex−con (r = 0.534, p = 0.018; r = 0.618, p < 0.001, respectively), Kflex−ecc (r = 0.654, p < 0.001; r = 0.610, p < 0.001, respectively), and knee extensor concentric (Kex−con) (r = 0.473, p = 0.040; r = 0.494, p = 0.033, respectively) was moderately to largely correlated with Kleg at 12 and 14 km·h−1
Our study provides evidence that the knee flexor and extensor concentric and eccentric PT, ankle plantar concentric and eccentric PT, and dorsiflexion eccentric PT are significantly correlated with Kleg and Kvert in recreational male runners
Summary
The spring-mass model parameters, such as leg stiffness (Kleg) and vertical stiffness (Kvert), are typically used to characterize the mechanical properties of a “leg-spring,” representing the lower limbs during running (Jaén-Carrillo et al, 2021). Kleg is defined as the ratio between the maximal vertical ground reaction force (vGRF) and the maximum compression in the lower-limb length. Kvert describes the global compression of the runner as the ratio of changes in the ground reaction force, to the respective vertical displacement of the center of mass (COM) (Struzik et al, 2021). Previous cross-sectional studies suggested that legspring stiffness is largely correlated with running economy (Li et al, 2021) and that endurance-trained athletes express higher leg-spring stiffness than untrained individuals (Hobara et al, 2010). Exploring the principal factors that influence Kleg and Kvert is important for optimizing endurance performance
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