Sex and Stride Impact Joint Stiffness During Loaded Running

This study determined changes in lower limb joint stiffness when running with body-borne load, and whether they differ with stride or sex. Twenty males and 16 females had joint stiffness quantified when running (4.0 m/s) with body-borne load (20, 25, 30, and 35 kg) and 3 stride lengths (preferred or 15% longer and shorter). Lower limb joint stiffness, flexion range of motion (RoM), and peak flexion moment were submitted to a mixed-model analysis of variance. Knee and ankle stiffness increased 19% and 6% with load (P <.001, P =.049), but decreased 8% and 6% as stride lengthened (P =.004, P <.001). Decreased knee RoM (P <.001, 0.9 degrees-2.7 degrees) and increased knee (P =.007, up to 0.12 N.m/kg.m) and ankle (P =.013, up to 0.03 N.m/kg.m) flexion moment may stiffen joints with load. Greater knee (P <.001, 4.7 degrees-5.4 degrees) and ankle (P <.001, 2.6 degrees-7.2 degrees) flexion RoM may increase joint compliance with longer strides. Females exhibited 15% stiffer knee (P =.025) from larger reductions in knee RoM (4.3 degrees-5.4 degrees) with load than males (P <.004). Stiffer lower limb joints may elevate injury risk while running with load, especially for females.

Automated summary

Running with body-borne load increases lower limb joint stiffness, especially at the knee and ankle; joint stiffness decreases as stride lengthens; females exhibit higher knee joint stiffness than males when running with load.