Browsing by Author "Hisey, Brandon"
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- ItemOpen AccessEffects of fiber type on force depression after active shortening in skeletal muscle(Elsevier, 2015-07-16) Joumaa, Vénus; Power, Geoffrey A.; Hisey, Brandon; Caicedo, A.; Stutz, J.; Herzog, WalterThe aim of this study was to investigate force depression in Type I and Type II muscle fibers. Experiments were performed using skinned fibers from rabbit soleus and psoas muscles. Force depression was quantified after active fiber shortening from an average sarcomere length (SL) of 3.2µ m to an average SL of 2.6 µm at an absolute speed of 0.115f iber length/s and at a relative speed corresponding to 17% of the unloaded shortening velocity (V0) in each type of fibers. Force decay and mechanical work during shortening were also compared between fiber types. After mechanical testing, each fiber was subjected to myosin heavy chain (MHC) analysis in order to confirm its type (Type I expressing MHC I, and Type II expressing MHC IId). Type II fibers showed greater steady-state force depression after active shortening at a speed of 0.115 fiber length/s than Type I fibers (14.5±1.5% versus 7.8±1.7%). Moreover, at this absolute shortening speed, Type I fibers showed a significantly greater rate of force decay during shortening and produced less mechanical work than Type II fibers. When active shortening was performed at the same relative speed (17% V0), the difference in force depression between fiber types was abolished. These results suggest that no intrinsic differences were at the origin of the disparate force depressions observed in Type I and Type II fibers when actively shortened at the same absolute speed, but rather their distinct force-velocity relationships.
- ItemOpen AccessMechanics of Amphibian Skeletal Muscle at Long Lengths(2017) Hisey, Brandon; Herzog, Walter; Biewener, Andrew; Syme, Douglas; Stefanyshyn, Darren; MacIntosh, Brian; MacDonald, JustinLittle is known about the mechanical behavior of skeletal muscle at long lengths, or how these behaviors scale to different hierarchical levels. The purpose of this thesis is to examine the mechanical behavior of skeletal muscle leading up to, and at the point of failure. Failure was defined as a compromise in the muscles’ ability to produce force, as indicated by a decrease in force, during a steady stretch. Stretches were performed in active (i.e. contracting) and passive muscles in three different preparations from the semitendinosus muscle of the frog Rana pipiens – myofibrils, permeabilized fibres, and whole muscles. Stress in active myofibrils was significantly greater than in passive ones with the progression of stretch to failure, and was persistent despite being stretched to lengths beyond overlap of actin and myosin filaments (who’s interactions are responsible for the production of contractile force). This divergence in stress was reduced at the cellular level, and was abolished in whole muscles. It is suggested that higher active compared to passive stress is a result of an increased contribution by the large molecular spring, titin. As higher hierarchical levels are examined, the introduction of other passive elements and connections may break during stretch and mask the divergent behavior observed in myofibrils. Histology and electron microscopy showed complete loss of regular striation patterns in both active and passive fibres stretched to sarcomere lengths of approximately 5 um. Whole muscles showed indicators of damage as well, but to a much lesser extent, and with active muscles showing more evidence of damage. Mechanical data and histology suggest that failure in whole muscles occurs outside of the cell, perhaps in the extracellular matrix or at the myotendinous junction. Finally, it was demonstrated that whole muscles possessing a low passive compliance (in this case, the tibialis anterior from R. pipiens) were more prone to failure at short lengths than muscles having a higher compliance (i.e. semitendinosus). It is suggested that differing muscle compliances represent adaptive strategies to prevent damage according to functional demands of the specific muscle.