Effect of repetition rate on the formation of microtears in tendon in an in vivo cyclical loading model.
Nakama LH; King KB; Abrahamsson S; Rempel DM
J Orthop Res 2007 Sep; 25(9):1176-1184
We reported previously the formation of microtears in an in vivo loaded Flexor Digitorum Profundus (FDP) rabbit tendon with a repetition rate of 60 repetitions per minute and a peak force of 15% of maximum peak tetanic force for 80 cumulative hours. Tear area as a percent of tendon area, tear density (tears/mm2), and mean tear size (µm2) were higher in tendons from the loaded limb compared to the unloaded control limb. The purpose of the present study was to compare those results to results obtained with a repetition rate of 10 while maintaining the same peak force and force-time integral (n = 8). Due to a strain gradient between the inner and outer sides of the FDP tendon, microtears were quantified in four regions, two regions each along the inner and outer sides of the tendon. The tear area as a percent of total tendon area and the mean tear size were significantly greater in the loaded limb compared to the unloaded limb (p < 0.03). However, the effects were less than those observed at 60 repetitions/min. The higher repetition loading pattern resulted in an increase in tear measures in all four regions, while the lower rate produced changes only in the outer regions of the tendon. This finding may establish where the initial sites of damage occur in tendons that insert into bone in a similar arrangement as the FDP. The results suggest that repetition rate or number of loading cycles is associated with increased tendon microtears or fragility in a dose-response pattern.
Ergonomics; Musculoskeletal-system-disorders; Repetitive-work; Animals; Animal-studies; Ergonomics; Cumulative-trauma; Cumulative-trauma-disorders; Laboratory-animals; Muscles; Repetitive-work; Biomechanical-modeling; Biomechanics
David Rempel, Ergonomics Program, Division of Occupational and Environmental Medicine, University of California, San Francisco, 1301 South 46th Street, Building 163, Richmond, CA 94804
Disease and Injury: Musculoskeletal Disorders of the Upper Extremities
Journal of Orthopaedic Research
University of California - San Francisco