Limb length and locomotor biomechanics in the genus Homo: An experimental study

Abstract

The striking variation in limb proportions within the genus Homo during the Pleistocene has important implications for understanding biomechanics in the later evolution of human bipedalism, because longer limbs and limb segments may increase bending moments about bones and joints. This research tested the hypothesis that long lower limbs and tibiae bring about increases in A-P bending forces on the lower limb during the stance phase of human walking. High-speed 3-D video data, force plates, and motion analysis software were used to analyze the walking gait of 27 modern human subjects. Limb length, as well as absolute and relative tibia length, were tested for associations with a number of kinetic and kinematic variables. Results show that individuals with longer limbs do incur greater bending moments along the lower limb during the first half of stance phase. During the second half of stance, individuals moderate bending moments through a complex of compensatory mechanisms, including keeping the knee in a more extended position. Neither absolute nor relative tibia length had any effect on the kinetic or kinematic variables tested. If these patterns apply to fossil Homo, groups with relatively long limbs (e.g. H. ergaster or early H. sapiens) may have experienced elevated bending forces along the lower limb during walking compared to those with relatively shorter limbs (e.g. the Neandertals). These increased forces could have led to greater reinforcement of joints and diaphyses. These results must be considered when formulating explanations for variation in limb morphology among Pleistocene hominins.

Ontogeny of joint mechanics in squirrel monkeys (Saimiri boliviensis): functional implications for mammalian limb growth and locomotor development

“…As illustrated in the current study (Figs 5 and 6) and in previous studies comparing the effects of intra-and interspecific variation in limb length on patterns of joint loading (Polk, 2002;Gruss, 2007), relatively shorter limbs have the potential to shorten joint load arms, thereby mitigating joint moments. The assumption that limb growth determines ontogenetic variation in joint loading motivated Carrier's (Carrier, 1983) and Young's (Young, 2005) morphometric analyses of developmental joint mechanics.…”

“…Path analyses and hierarchical partitioning of the current dataset emphatically demonstrated that walking with erect, strut-like limbs -where the SRF vector is aligned with the limb's axis -was the most effective way of shortening SRF load arms among developing squirrel monkeys. Postural adjustments to SRF load arm lengths have also been cited as the primary means of mitigating limb muscle force requirements between gaits within individuals , between differently sized individuals within the same species (Polk, 2002;Gruss, 2007), and between differently sized species (Biewener, 1983;Biewener, 1989) [but see Day and Jayne (Day and Jayne, 2007)]. In sum, extended joints may constitute an effective behavioral means for relatively precocial infants to shorten joint load arms, reduce joint loading, and limit the muscle force required to maintain joint postures.…”

Secular Change in the Femur Diaphyseal Biomechanical Properties of American Whites

“…The relationship between APM and FML is not surprising since Gruss (2007) found that longer femora have greater AP bending forces at midshaft. The midshaft ML diameter was influence by both weight and stature in females but only femur head diameter in males.…”

“…The results of biomechanical studies suggest that increases in stature may cause greater anteroposterior (AP) bending stress at the midshaft of the femur (Gruss 2007), while a more sedentary lifestyle would result in a decrease in the AP stress (Ruff 1987, Wescott 2006, Shaw and Stock 2011. Likewise, there should be a small decrease in the midshaft ML dimension due to a slight decrease in hip breadth and activity (Rockhold 1998, Driscoll 2010.…”

“…However, lower limb bone biomechanical structural properties (diaphyseal size, shape, robusticity, and strength) are affected by the interaction of numerous factors including mechanical usage, body mass, body shape, and bone length (Ruff 1984, Agostini and Ross 2011, Demes et al 1991, Gruss 2007, Moore 2009, Pearson and Lieberman 2004, Ruff and Larsen 2014, Wescott 2006, 2014. In many industrialized populations, especially the United States, there have been significant secular trends in biological variables such as stature, weight, body proportions, long bone lengths, and skeletal maturation primarily due to better nutrition and health (Fogel 2004, Wescott and Jantz 2005, Fredriks et al 2000, Danubio and Sanna 2008, Driscoll 2010, Floud et al 2011, Jantz and Meadows Jantz 2000, Wescott and Jantz 2005, Godina 2011, Harrington and Wescott 2015.…”