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Advanced Search Scratch-digging mammals are commonly described as having large, powerful forelimb muscles for Claar high force to excavate earth, yet studies quantifying the architectural properties of the musculature are largely unavailable. To further test hypotheses about traits that represent specializations for scratch-digging, we quantified muscle architectural properties and myosin expression in the forelimb of the groundhog Marmota monaxa digger that constructs semi-complex burrows.
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Architectural properties measured were muscle moment arm, muscle mass MMbelly Ckara MLfascicle length lFpennation angle and physiological cross-sectional Dd PCSAand these metrics were used to estimate maximum isometric force, joint torque and power. Groundhogs have large limb retractors and elbow extensors that are capable of applying moderately high torque at the shoulder and elbow joints, respectively.
Most of these muscles e. The unipennate triceps brachii long head has the largest PCSA and is capable of the highest joint torque at both the shoulder and elbow joints. Moreover, the digital flexors have the capacity for both appreciable fascicle shortening and force production, indicating high muscle work potential. Overall, the forelimb musculature of the groundhog is capable of How Did Clara Barton Impact Society low sustained force and power, and these properties are consistent with the findings of a predominant expression of the MHC-2A isoform. Aside from the apparent modifications to the digital flexors, the collective muscle properties observed are consistent with its behavioral classification as a less-specialized burrower and these may be more representative of traits common to numerous rodents with burrowing habits or mammals with some fossorial ability.
The force and power that a whole muscle can apply at a limb joint are strongly influenced Imapct the arrangement of the muscle fibers relative to the axis of force production within the muscle Eng et al. Pennate muscles with short fibers have larger physiological cross-sectional area PCSA http://pinsoftek.com/wp-content/custom/life-in-hell/rhetorical-analysis-of-john-f-kennedy-inaugural-address.php, and thus the ability to produce high isometric force Alexander, Alternatively, muscles with long fibers arranged in parallel with the axis of force production have a greater ability to shorten and produce force over a large range of joint motion Peters and Rick, ; Zajac, ; Zajac, A trade-off between these two functional designs indicates that a muscle is capable of How Did Clara Barton Impact Society appreciable mechanical work at high power.
At the cellular level, the myosin heavy chain MHC isoforms expressed within a muscle fiber directly determine fiber isometric tension, unloaded shortening velocity and power Reiser et al.
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Similar to muscle architectural properties, few studies have evaluated muscle fiber type in the forelimbs of scratch-diggers. Using similar histochemical approaches, Alvarez et al.
Alvarez et al. These findings suggest that overall, more oxidative fiber types are required for sustained burrowing activity in rodents, yet comparison of function with homologous muscles from other scratch-diggers is limited because the MHC isoforms of the fiber types are unknown.]
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