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Purpose: To report the morphologic and spatial relationships of a bilateral sternalis muscle variant. Methods: Routine cadaveric dissection in an undergraduate anatomy laboratory revealed two sternalis muscles parasternal to the sternal body. Subsequent fine prosection of the anterior thoracic wall and neck was carried out to uncover the soft tissue attachments of both sternalis muscles. Positional relationship to neighboring anterior thoracic and neck structures, and geometric dimensions of the muscle bellies and tendons, were documented. Results: Both sternalis muscles were imbedded in the pectoral fascia, with their muscle fibers running obliquely to the midsternal line. The right sternalis muscle was notably larger in length, width, and thickness compared to the sternalis muscle on the left. The right sternalis muscle featured a distinct superior cord-like intermediate tendon that traversed superolateral and fused directly with the contralateral sternomastoid and sterno-occipital portions of the left sternocleidomastoid muscle. The superior tendon of the left sternalis muscle was aponeurotic and affixed to the cord-tendon of the right sternalis muscle. A distinct tendinous entheses for the sternal head for both sternocleidomastoid muscles were noted at the manubrial body. Conclusions: This case report describes a unique bilateral sternalis muscle variant with conjoined sternocleidomastoid muscle integration. This anatomical description of a sternalis-sternocleidomastoid muscle morphology may supplement radiographic interpretations and support diagnostic accuracy. [ABSTRACT FROM AUTHOR]

Purpose: Following a shortening or lengthening muscle contraction, torque produced in the isometric steady state is lower (residual torque depression; rTD) or higher (residual torque enhancement; rTE), respectively, compared to a purely isometric contraction at the same final muscle length and level of activation. This is referred to as the history dependence of force. When matching a given torque level, there is greater muscle activation (electromyography; EMG) following shortening and less activation following lengthening. Owing to these differences in neuromuscular activation, it is unclear whether perception of effort is altered by the history dependence of force during plantar-flexion. Methods: Experiment 1 tested whether perception of effort differed between the rTD and rTE state when torque was matched. Experiment 2 tested whether perception of effort differed between the rTD and rTE state when EMG was matched. Finally, experiment 3 tested whether EMG differed between the rTD and rTE state when perception of effort was matched. Results: When torque was matched, both EMG and perception of effort were higher in the rTD compared to rTE state. When EMG was matched, torque was lower in the rTD compared to rTE state while perception of effort did not differ between the two states. When perception of effort was matched, torque was lower in the rTD compared to rTE state and EMG did not differ between the two states. Conclusion: The combined results from these experiments indicate that the history dependence of force alters one's perception of effort, dependent on the level of motor command. [ABSTRACT FROM AUTHOR]

Background: Following active muscle lengthening, there is an increase in steady-state isometric force as compared with a purely isometric contraction at the same muscle length and level of activation. This fundamental property of skeletal muscle is known as residual force enhancement (RFE). While the basic mechanisms contributing to this increase in steady-state isometric force have been well documented, changes in central nervous system (CNS) excitability for submaximal contractions during RFE are unclear. The purpose of this study was to investigate spinal and supraspinal excitability in the RFE isometric steady-state following active lengthening of the ankle dorsiflexor muscles. Methods: A total of 11 male participants (20-28 years) performed dorsiflexions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 130°), and the other half were during the RFE isometric steady-state following active lengthening (2 s isometric at 90°, a 1 s lengthening phase at 40°/s, and 5 s at 130°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs), and compound muscle action potentials (M-waves) were recorded from the tibialis anterior during the purely isometric contraction and RFE isometric steady-state. Results: Compared to the purely isometric condition, following active lengthening, there was 10% RFE (p < 0.05), with a 17% decrease in normalized CMEP amplitude (CMEP/Mmax) (p < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) (p > 0.05). Discussion: These results indicate that spinal excitability is reduced during submaximal voluntary contractions in the RFE state with no change in supraspinal excitability. These findings may have further implications to everyday life offering insight into how the CNS optimizes control of skeletal muscle following submaximal active muscle lengthening. [ABSTRACT FROM AUTHOR]