Muscles as Springs

Energy Storage in Muscle

One continuing research interest in our laboratory is the adaptive plasticity of vertebrate skeletal muscle. How does muscle adapt to both the nature and intensity of the demands placed upon it (including those of different sized animals)?  These changes involve changes in metabolic properties such as the densities of capillaries and mitochondria as well as contractile properties such as the force, velocity and efficiency of contraction.  Skeletal muscle is remarkable in part because shifts in very few structural components result in mechanical outcomes as varied as burst power, sound production and posture, to name just a few.

During normal locomotion, muscles do much more than produce useful work (by shortening). When the force acting on muscle, such as gravity, exceeds the force produced by the muscle, it will lengthen, absorbing mechanical work. These “lengthening contractions” are used both to convert kinetic energy to heat, like a sock absorber (e.g., hiking downhill) or to store elastic recoil (i.e., elastic strain) energy for subsequent use (e.g., running). Together with Paul LaStayo at the University of Utah, we have investigated the properties and consequences of lengthening (“eccentric”) muscle contractions. When a muscle is subjected to lengthening contraction an acute effect may be injury (Delayed Onset Muscle Soreness, DOMS). Hence these contractions have the reputation of being damaging. However, if muscles are subjected to chronic use of lengthening contractions, there is no damage or injury. What does occur is a shift in a number of structural and functional properties within the muscle fiber. We expect that many of these might be attributed to the gigantic cytoskeletal protein titin. Large gains in strength are accompanied by changes in the “tuned” frequency of muscle use in response to chronic eccentric training. We have used both rat and human models to study these effects.




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Other Interests:

Allometry | Energetics | Clinical Research