Calculation of the stresses exerted by human muscles requires knowledge of their physiological cross-sectional area (PCSA). Magnetic resonance imaging (MRI) has made it possible to measure PCSAs of leg muscles of healthy human subjects, which are much larger than the PCSAs of cadaveric leg muscles that have been used in previous studies. We have used published MRI data, together with our own force-plate records and films of running and jumping humans, to calculate stresses in the major groups of leg muscles. Peak stresses in the triceps surae ranged from 100 kN m-2 during take off for standing high jumps to 150 kN m-2 during running at 4 m s-1. In the quadriceps, peak stresses ranged from 190 kN m-2 during standing long jumps to 280 kN m-2 during standing high jumps. Similar stresses were calculated from published measurements of joint moments. These stresses are lower than those previously calculated from cadaveric data, but are in the range expected from physiological experiments on isolated muscles.
In the field: an interview with Martha Muñoz
Martha Muñoz is an Assistant Professor at Yale University, investigating the evolutionary biology of anole lizards and lungless salamanders. In our new Conversation, she talks about her fieldwork in Indonesia, Costa Rica, the Dominican Republic and the Appalachian Mountains, including a death-defying dash to the top of a mountain through an approaching hurricane.
Graham Scott in conversation with Big Biology
Graham Scott talks to Big Biology about the oxygen cascade in mice living on mountaintops, extreme environments for such small organisms. In this JEB-sponsored episode, they discuss the concept of symmorphosis and the evolution of the oxygen cascade.
Trap-jaw ants coordinate tendon and exoskeleton for perfect mandible arc
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Trap-jaw ants run the risk of tearing themselves apart when they fire off their mandibles, but Greg Sutton & co have discovered that the ants simultaneously push and pull the mandibles using energy stored in a head tendon and their exoskeleton to drive the jaws in a perfect arc.
Hearing without a tympanic ear
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In their Review, Grace Capshaw, Jakob Christensen-Dalsgaard and Catherine Carr explore the mechanisms of hearing in extant atympanate vertebrates and the implications for the early evolution of tympanate hearing.
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