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Active Shortening Protects Against Stretch‐Induced Force Deficits in Human Skeletal Muscle
Author(s) -
Saripalli Anjali L.,
Sugg Kristoffer B.,
Mendias Christopher L.,
Brooks Susan V.,
Claflin Dennis R.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.710.3
Subject(s) - isometric exercise , myosin , crossbridge , biophysics , skeletal muscle , actin , chemistry , contraction (grammar) , muscle contraction , anatomy , myosin head , population , protein filament , biology , biochemistry , endocrinology , myosin light chain kinase , medicine , physiology , environmental health
Skeletal muscle contraction results from molecular interactions of myosin “crossbridges” with adjacent actin filament binding sites. The binding of myosin to actin can be “weak” or “strong”, and only strong binding states contribute to force production. During active shortening, the number of strongly‐bound crossbridges declines with increasing shortening velocity. Forcibly stretching a muscle that is actively shortening at high velocity results in no apparent negative consequences whereas stretch of an isometrically (fixed‐length) contracting muscle causes ultrastructural damage and a decline in force‐generating capability. Our working hypothesis is that stretch‐induced damage is uniquely attributable to the population of crossbridges that are strongly‐bound. We tested the hypothesis that stretch‐induced force deficits decline as the prevailing shortening velocity is increased. Experiments were performed on permeabilized segments of individual skeletal muscle fibers obtained from human subjects. Fibers were maximally activated and either allowed to generate maximum isometric force (F o ), or to shorten at velocities that resulted in force maintenance of ≈50% F o or ≈2% F o . For each test condition, a rapid stretch equivalent to 0.1 × optimal fiber length was applied. Relative to pre‐stretch F o , force deficits resulting from stretches applied during force maintenance of 100%, ≈50%, and ≈2% F o were 23.2 ± 8.6%, 7.8 ± 4.2% and 0.3 ± 3.3%, respectively (mean ± SD, n=20). We conclude that stretch‐induced damage declines with increasing shortening velocity, in support of the possibility that the fraction of strongly‐bound crossbridges is a causative factor in the susceptibility of skeletal muscle to stretch‐induced damage. Support or Funding Information NIH R01‐AG050676, R01‐AR063649, F32‐AR067086