Human evolution and barefoot running

Jim Haber writes:

Our speaker [in the Joint Biology/Neuroscience Colloquium at 4 pm  in Gerstenzang 121] on Nov 14 is Prof. Daniel Lieberman from Harvard.  He is the second of our Distinguished Biology Lecturers.  Dan is one of the world’s experts on human evolution and running (how our necks balance our stride, among other things) .  His interests have also made him a major advocate for barefoot running.


Here’s a summary:

Ever since the human lineage diverged from the African apes, hominins have been bipeds of some sort.  Comparative and fossil evidence suggest that the earliest hominins were capable, habitual bipedal walkers but were also adept at climbing trees.  At some point, however, hominins lost the ability to climb trees very well, and became superlative long distance runners.  Comparisons of human endurance running performance with other mammals show that we excel at speed, distance, and running in the heat. Further, human distance running capabilities far exceed those of any other primate, and they match or even surpass the best mammalian runners in hot conditions over very long distances.  The human body is thus replete with many adaptations that improve endurance running performance, and many of these adaptations first appear about two million years ago in the fossil record of the genus Homo.

The evolution of human running is also relevant from the perspective of evolutionary medicine.  Perhaps the most important legacy is that humans evolved to be physical active endurance athletes compared to other apes, which helps explain why an absence of physical activity is not only abnormal but also pathological.  Another interesting legacy of our evolution history is that since humans ran barefoot for most of the last two million years, the study of barefoot running provides an opportunity to study how natural selection adapted the human body to run, potentially offering insights on preventing injury.

How much torque is on my elbow?

A recent article in l. Biomech. Eng. by Davide Piovesan, a former post-doctoral fellow in Brandeis’ Ashton Graybiel Spatial Orientation Laboratory, with Alberto Pierobon, a staff engineer, and Paul DiZio and James Lackner, the laboratory’s directors has advanced the empirical and analytic tools used to quantify human arm segment inertias.  The new methodology enables studies of the neuromotor control of naturalistic reaching movements unfettered by heretofore necessary laboratory constraints, in healthy and clinical populations,

Arm segment inertias are key parameters of inverse dynamics equations which compute movement kinetics (joint torques and muscle forces) from measurements of movement kinematics.  Existing methods for estimating arm segment parameters did not provide sufficient resolution for calculation of a class of joint torques called interaction torques.  During natural reaching, interaction torques are generated by an arm segment’s motion relative to other moving segments, in addition to  normal inertial torques which are due to motion relative to fixed space.  The technical solution provided in this paper involves statistical techniques for partitioning variance in inertial estimates due to task-related (arm angular acceleration) and extraneous factors (different estimation techniques and subject body shape variations) and eliminating the extraneous sources.

The Graybiel Lab researchers have previously shown that current neuromotor models of muscle activation fail to account for movement errors that occur when large interaction torques are experimentally induced, and the new methods will enable development of better experiments and models.

Multi-body representation of the torso and arm during planar reaching.  Joint torques (τ) and forces (θ) of this multi-link sysytem can be computed knowing the motions and the inertial properties (mass, center of mass, and moment of inertia) of each segment.  The torso frame of reference is at the shoulder (S), and each other segment’s reference frame (x‑y) is fixed at its center of mass.  The environmental frame of reference (E) is shown at the upper left.

Seeing key hinges in the lever arm of myosin at the atomic level

In this week’s on-line issue of the Proceedings of the National Academy of Sciences (PNAS), Brandeis researchers Jerry H. Brown, V. S. Senthil Kumar, Elizabeth O’Neall-Hennessey, Ludmila Reshetnikova, and Michelle Nguyen-McCarty ’10, together with Professors Andrew Szent-Györgyi and Carolyn Cohen, and Brookhaven National Laboratory researcher Howard Robinson, reveal the existence of a pair of major new hinges in the muscle protein myosin.

Muscle consists of myosin-containing thick filaments with projections, i.e. myosin heads, that exert force on actin-containing thin filaments during contraction. Previous crystal structures of the myosin head from bay scallop striated muscles and vertebrate muscles have already shown how this motion is produced by the amplification of small conformational changes about hinges in the motor domain (MD) by the so-called lever arm, which consists of the converter and elongated light chain binding domain (LCD).  Just like a baseball bat or other lever arms we are all familiar with in the “real world”, this LCD of myosin has appeared to be relatively rigid in these crystal structures, as it needs to be to transmit force effectively. But it has also long been expected that in muscle the myosin head, including its lever arm, is likely to contain elastic elements so that force can be produced under various strains.

(Left) Schematic of a myosin molecule and (right) the two conformations of the heavy chain portion of the LCD.

The Brandeis researchers originally set out to crystallize a myosin LCD corresponding to that from the catch muscle of sea scallop because it contains a specialized sequence whose structure was predicted to give insight into how muscle contraction of smooth muscles is turned on and off. Remarkably, however, as described in the PNAS article, this LCD forms two different conformations in the crystal, about mechanically linked hinges in the part of the lever arm distal from the motor. For the first time — and quite unexpectedly— a potential major elastic element in the lever arm has been visualized at atomic resolution, one that allows the length of the lever arm to change by about 10%. Sequence comparisons strongly suggest that these specific hinges are likely to be found in the lever arms of all muscle myosins. These comparisons also indicate differences in the degree of flexibility about these hinges in the different myosins, perhaps helping to account for the different properties (e.g., speed of contraction) of different types of muscle.

This result may also be important for mechanical engineers. In 2009, one of the authors (JHB) wrote an article in American Scientist that expands the concept of biomimicry by describing potentially novel joints, switches, and other mechanical designs that can be derived from the structures of various proteins. The current results in the PNAS seem to add one more. As described by Olena Pylypenko and former Brandeis researcher Anne Houdusse in a commentary scheduled to accompany the print version of the PNAS article, the motion about the hinge of the myosin LCD resembles the motion of a foot relative to a leg about an ankle. A lever “arm” that can extend or compress about an “ankle” may thus be one more novel mechanical design that nature can teach us about.

Protected by Akismet
Blog with WordPress

Welcome Guest | Login (Brandeis Members Only)