UNIFORMITY OF STRUCTURAL CHARACTERISTICS THROUGHOUT LENGTH OF SKELETAL MUSCLE FIBERS

Fresh‐frozen, serial cross–sections of the transversus abdominis muscle of four mature chickens (98 fibers) were examined to determine structural and histochemical characteristics throughout the entire length of skeletal muscle fibers. Fiber diameter and nicotinamide adenine dinucleotide diaphorase (NAD‐D) and myosin adenosine triphosphatase (ATPase) activities were used as criteria to classify fibers as Type I or II. Measurements were made at 10 to 22 locations along the length of the fibers. An unimodal distribution of mean fiber diameters ranging from 48 μ to 86 μ was found. Fibers did not appear larger in the belly of the muscle than near the ends. Although small fluctuations in fiber diameter occurred through the length of a fiber, large and small fibers tended to remain relatively large or small at each location. NAD‐D activity was either consistently high or low throughout the length of a fiber. Likewise, myosin ATPase activity was either high or low for an entire fiber. It is concluded that skeletal muscle fibers maintain rather uniform structural and histochemical characteristics along their entire length. Copyright © 1969 Wiley‐Liss, Inc.