Mechanical advantage and joint function of the lower limb during hopping at different frequencies. (30th March 2021)

• Record Type: Journal Article
• Authors: Monte, Andrea; Nardello, Francesca; Zamparo, Paola
• Is Part Of: Journal of biomechanics. Volume 118(2021)
• Publication Date: 2021-03-30
• Subjects: Effective mechanical advantage -- Joint mechanical power -- Hopping -- Functional joint behaviour -- Elastic energy; Animal mechanics -- Periodicals; Biomechanics -- Periodicals; Biomechanics -- Periodicals; Mécanique animale -- Périodiques; Biomécanique -- Périodiques; Electronic journals; 571.4305
• DOI: 10.1016/j.jbiomech.2021.110294
• Languages: English
• ISSNs: 0021-9290

Abstract

Abstract: Mechanical output at a joint level could be influenced by its leverage characteristics and by its functional behaviour and both could change to accommodate the demands of a given locomotor task. In this study, the mechanical power generated at the knee and ankle joints and their functional indexes (i.e. damper, strut, spring and motor like-function) were calculated by using 3D kinematic and kinetic data during hopping at 2, 2.5, 3 and 3.5 Hz. The effective mechanical advantage (i.e. the ratio between internal and external moment arm) of the knee (EMAK ) and ankle (EMAA ) and joint stiffness were calculated as well. Joint stiffness increased with frequency whereas positive and negative joint power decreased with it, the ankle power values being always larger (20–50%) than those at the knee. EMAA reached its highest value (0.4) during the propulsive phase at 3 Hz whereas no significant changes in EMAK were observed as a function of frequency in both the absorption and propulsive phases. Knee joint-functional index shifted from a spring to a strut-like function with increasing frequency (from 56 to 8% and from 4 to 51%, respectively) while the ankle operated mainly as a spring (from 90 to 53%), its damper and motor-like indexes being negligible at all frequencies (<5%). Therefore, in hopping, the knee works to dissipate mechanical energy (the combination of its damper and strut indexes increase from 23 to 72% at these frequencies) and the primary source of mechanical power is attributable to the elastic function of the ankle.