We have developed a novel method for measuring active tension generated by cultured myotubes using UV-crosslinked collagen film. Skeletal myoblasts cell line C2C12 or human primary skeletal myoblasts were seeded onto a thin (35 mu m) collagen film strip, on which they proliferated and upon induction of differentiation they formed multinucleated myotubes. The collagen film myotube complex contracted upon electric pulse stimulation which could be observed by light microscope. When collagen film myotube complex were attached to force transducer, active tension generation was observed upon electric pulse stimulation. Measurement of active tension was possible for multiple times for more than 1 month with the same batch of collagen film myotube complex. Active tension generation capability of C2C12 myotubes increased with progression of differentiation, reaching maximal value 6 days after induction of differentiation. Using this method, we measured the effect of artificial exercise induced by electric pulse on active tension generation capability of C2C12 myotubes. When the electric pulses of 1 Hz were continuously applied to induce artificial exercise, the active tension augmentation was observed. After 1 week of artificial exercise, the active tension reached similar to 10x of that before the exercise. The increased active tension is attributable to the formation of the sarcomere structure within the myotubes and an increased amount of myotubes on the collagen film. The increased amount of myotubes is possibly due to the suppressed atrophy of myotubes by enhanced expression of Bcl-2. Biotechnol. Bioeng. 2010;106: 482-489. (C) 2010 Wiley Periodicals, Inc.