Measurement of sarcomere length during fast contraction of muscle fibers by digital image analysis

A low-cost, high-resolution (spatial and temporal) image analysis system wa s developed to measure sarcomere length (Sl) during fast twitch of isolated striated muscle fibers at different temperatures. Fiber images were examin ed during twitch with an imaging rate of 220 Hz. To increase temporal resol ution beyond 220 Hz, consecutive temporally shifted image sequences (N sequ ences) were acquired. Individual or average Sl was directly measured from a horizontal profile without spatial-frequency assessment. Measurement preci sion (E) was determined and expressed as: E(%) = 100 x P-s/(I-s x Sl), wher e P-s is the pixel size and I-s the involved sarcomere number. At 18 degree s C during isometric twitch, Sis were measured with 220 Hz temporal and 0.2 % spatial resolutions. Sl shortened in the central region (0.21 +/- 0.12 mu m) as tension developed, reaching a maximal shortening of 8.09 +/- 2.05% ( at rest, Sl = 2.59 +/- 0.05 mu m, = 4) in 32.5 +/- 1.96 ms. At 30 degrees C , Sl variations were examined with 880 Hz temporal resolution, in which cas e maximal Sl shortening was reached in 15.74 +/- 1.99 ms, and then decrease d to 5.19 +/- 1.97% (at rest, Sl = 2.6 +/- 0.06 mu m). The twitch tension d eveloped by the whole fiber was recorded and compared with sarcomere length behavior. Sarcomere length variations in the central region were represent ative of overall developed tensions at 18 and 30 degrees C. (C) 1999 Elsevi er Science Ltd. All rights reserved.