Locomotor advantages of Neandertal skeletal morphology at the knee and ankle

We quantified Neandertal knee extensor and ankle plantarflexor moments to determine whether differences between Neandertal and recent human skeletal morphology represent important functional differences. Neandertal skeletal differences in the patella, tibial tuberosity, and calcaneus were used to modify a computer model of recent humans to calculate the moment arms and moments of Neandertal knee extensor and ankle plantarflexor muscles. We also conducted sensitivity studies on the effect of musculotendon parameters on the Neandertal moments. As expected, we found that Neandertal moment arms were greater than recent humans at the ankle (122-141%); however, the magnitude of the increase was not well-predicted from measurements of size differences between Neandertal and recent human skeletons. At the knee, Neandertal moment arms were greater than those of recent humans in the locomotor range (108%) but less so at more flexed knee angles (102%). Not all Neandertal skeletal adaptations at the knee contributed to increased moment arm. Knee extensor moments were enhanced in the Neandertal models in the locomotor range (111%), regardless of musculotendon parameters. At the ankle, however, Neandertal plantarflexor moment was greater than that of recent humans (149-200%) at all joint angles only if muscle fiber length increased proportionately with moment arm. Our results demonstrate that Neandertal skeletal morphology, compared to that of recent humans, generated greater moments at both the knee and ankle in the locomotor range but not at higher angles of knee flexion or ankle plantarflexion.