AUTHOR=Chen Shiqin , Wang Dan , Zhang Qin , Shi Yue , Ding Haiyong , Li Fei 

TITLE=Relationship Between Isokinetic Lower-Limb Joint Strength, Isometric Time Force Characteristics, and Leg-Spring Stiffness in Recreational Runners

JOURNAL=Frontiers in Physiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2021.797682

DOI=10.3389/fphys.2021.797682

ISSN=1664-042X

ABSTRACT=<p>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 (<italic>K</italic><sub>leg</sub>)/vertical stiffness (<italic>K</italic><sub>vert</sub>) in recreationally trained runners. Thirty-one male runners were recruited and underwent three separate tests. In the first session, the body composition, <italic>K</italic><sub>leg</sub>, and <italic>K</italic><sub>vert</sub> at running speeds of 12 and 14 km⋅h<sup>–1</sup> were measured. In the second session, isokinetic knee and ankle joint PT at 60°⋅s<sup>–1</sup> 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 (<italic>r</italic> = 0.473–0.654, <italic>p</italic> &lt; 0.05) were moderate to largely correlated with <italic>K</italic><sub>leg</sub> and <italic>K</italic><sub>vert</sub> at 12 and 14 km⋅h<sup>–1</sup>. The knee extensor eccentric PT (<italic>r</italic> = 0.440, <italic>p</italic> = 0.050) was moderately correlated with the 14 km⋅h<sup>–1</sup><italic>K</italic><sub>vert</sub>. The ankle plantar flexor concentric and dorsiflexor eccentric PT (<italic>r</italic> = 0.506–0.571, <italic>p</italic> &lt; 0.05) were largely correlated with <italic>K</italic><sub>leg</sub> at 12 km⋅h<sup>–1</sup>. The ankle plantar flexor concentric and eccentric and dorsiflexor eccentric PT (<italic>r</italic> = 0.436–0.561, <italic>p</italic> &lt; 0.05) were moderate to largely correlated with <italic>K</italic><sub>vert</sub> at 12 and 14 km⋅h<sup>–1</sup>. For IMTP testing, high correlation was only found between the IMPT peak force (PF) and <italic>K</italic><sub>vert</sub> at 14 km⋅h<sup>–1</sup> (<italic>r</italic> = 0.510, <italic>p</italic> = 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.</p>