The study of muscle physiology is a dynamic area of ongoing research that embodies relationships between structure, function and neural input. Muscle is designed to produce force, and much of our knowledge of these relationships has been generated by investigations into models of extreme performance, i.e. frogs jumping, birds flying, antelope running and many others. This approach is known as the Krogh Principal, after the late August Krogh, who said, "For many problems there is an animal on which it can be most conveniently studied". This means that knowing the "best" solution or design for a particular problem, jumping, flying and so on, will enable researchers to understand the most important parameters for systems to function properly. In the context of muscle physiology, this approach has enabled researchers to ask many different questions about the neuromuscular system: everything from how to maximize performance to neuromuscular pathologies.
I have continued using Krogh's approach to study the neuromuscular system using the Cuban tree frog as a model elite jumper (dissertation work). The Cuban tree frog has the ability to jump over 20 times its body length achieving power outputs in excess of 1500 W/g muscle mass. This enormous power output is completely generated by the muscles of the hind limb, and is substantially more than can be predicted from the contractile properties of individual muscles. Thus, my question is how the neuromuscular system of the frog capable of this type of power output when the muscles, individually, don't seem to be particularly special? Specifically, are there specific activation patterns that lead to higher power outputs? We still do not know enough about the nature of different patterns of muscle stimulation arising from the spinal cord motor neurons, and a ballistic movement, such as frog jumping, may give us insight into what parameters are most important. Preliminary data suggests that extensor muscles may become activated greater than 100 milliseconds prior to extension of the knee and ankle joints. This may enable the animal to store energy like a spring and recover this stored energy during the actual movement. Since muscle is limited in its ability to shorten rapidly while generating force, the storage and recovery of contractile energy may provide the additional power to propel the jumping animal. Additionally, the motor unit firing pattern may be changing during the "preactivation" period. Is there a specific pattern that facilitates storage and recovery of contractile energy?
Currently, and with the help of Dr. Steven Hempleman, Dr. Kiisa Nishikawa, and Dr. David J. Pierotti, I have developed a technique to measure individual action potentials from muscle fibers during their ballistic jumps (see figures and curriculum vitae for more details). Previously, it has been nearly impossible to measure single unit firing behavior in freely behaving animals, particularly during a task for which the animal is highly derived (most data come from human hand muscles). This advance may give us clues as to what neural adaptations are responsible for extreme performance, specifically, and give use insight into control features of the motor system, in general.
Please see my curriculum vitae for more details about publications, employment history, affiliations, and contact information.
O.septentrionalis with electronic measuring device
Postural activity (40 Hz) of one motor unit measure in a freely behaving O.s. just prior to jump