ANYONE CONTEMPLATING dynamic roentgenograms of hollow viscera must be impressed that the length changes in the smooth muscles that comprise their walls are larger than the threefold range produced by skeletal muscle having a fixed filament array (1), and studies of muscles isolated from these viscera confirm very long functional ranges. Urinary bladder muscle, for example, has been shown to generate force over a greater than sevenfold length range (10), and airway smooth muscle has been shown to have a nearly flat length-force relationship over a threefold length range (5). But these extensive length ranges in airway smooth muscle are disputed by other studies using the same tissue and similar methods that found shorter functional length ranges (3, 7). The study by Speich et al. (8) in this issue of the Journal of Applied Physiology offers a likely explanation for these differences.
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