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  • F E Zajac
  • 1989
Skeletal muscles transform neural control signals into forces that act upon the body segments to effect a coordinated motor task. This transformation is complex, not only because the properties of muscles are complex, but because the tendon affects the transmission of muscle force to the skeleton. This review focuses on how to synthesize basic properties of(More)
1. A variety of physiological properties of single motor units have been studied in the gastrocnemius muscle (primarily in the medial head) of pentobarbitone-anaesthetized cats. Intracellular stimulation of individual motoneurones ensured functional isolation of the muscle units innervated by them.2. A system for muscle unit classification was developed(More)
We have developed a model of the human lower extremity to study how surgical changes in musculoskeletal geometry and musculotendon parameters affect muscle force and its moment about the joints. The lines of action of 43 musculotendon actuators were defined based on their anatomical relationships to three-dimensional bone surface representations. A model(More)
Are fingertip forces produced by subject-independent patterns of muscle excitation? If so, understanding the mechanical basis underlying these muscle coordination strategies would greatly assist surgeons in evaluating options for restoring grasping. With the finger in neutral ad- abduction and flexed 45 degrees at the MCP and PIP, and 10 degrees at DIP(More)
Evidence suggests that the nervous system controls motor tasks using a low-dimensional modular organization of muscle activation. However, it is not clear if such an organization applies to coordination of human walking, nor how nervous system injury may alter the organization of motor modules and their biomechanical outputs. We first tested the hypothesis(More)
Walking is a motor task requiring coordination of many muscles. Previous biomechanical studies, based primarily on analyses of the net ankle moment during stance, have concluded different functional roles for the plantar flexors. We hypothesize that some of the disparities in interpretation arise because of the effects of the uniarticular and biarticular(More)
The ankle plantar flexors were previously shown to support the body in single-leg stance to ensure its forward progression [J. Biomech. 34 (2001) 1387]. The uni- (SOL) and biarticular (GAS) plantar flexors accelerated the trunk and leg forward, respectively, with each opposing the effect of the other. Around mid-stance their net effect on the trunk and the(More)
Seated ergometer pedaling is a motor task ideal for studying basic mechanisms of human bipedal coordination because, in contrast to standing and walking, fewer degrees of freedom are being controlled and upright balance is not a factor. As a step toward understanding how individual muscles coordinate pedaling, we investigated how individual net muscle joint(More)
We developed a method for studying muscular coordination and strength in multijoint movements and have applied it to standing posture. The method is based on a musculoskeletal model of the human lower extremity in the sagittal plane and a technique to visualize, geometrically, how constraints internal and external to the body affect movement. We developed(More)
Isometric responses of individual gastrocnemius muscle units of both fast (F) and slow (S) twitch type were studied during repetitive intracellular stimulation of the innervating motoneurons in anesthetized cats. Paired stimuli usually produced maximum responses (measured in terms of tension-time area) with interpulse intervals between 5 and 10 msec.(More)