Rotations of a few cross-bridges in muscle by confocal total internal reflection microscopy

In order to measure the cycling of a few (∼6) myosin heads in contracting skeletal muscle, myofibrils were illuminated by Total Internal Reflection and observed through a confocal aperture. Myosin heads rotated at a rate approximately equal to the ATPase rate, suggesting that bulk ATPase of a whole muscle reflects the cycle frequency of individual heads.