The performance of skeletal muscles in vivo is determined by the feedback received when the muscle interacts with the external environment via various morphological structures. This interaction between the muscle and the 'real-world load' forces us to reconsider how muscles are adapted to suit their in vivo function. We must consider the co-evolution of the muscles and the morphological structu...

The mechanical behavior of muscle during locomotion is often predicted by its anatomy, kinematics, activation pattern and contractile properties. The neuromuscular design of the cockroach leg provides a model system to examine these assumptions, because a single motor neuron innervates two extensor muscles operating at a single joint. Comparisons of the in situ measurements under in vivo runnin...

Muscle fiber length is nearly uniform within a muscle but widely different among different muscles. We show that Abelson tyrosine-protein kinase 2 (Abl2) has a key role in regulating myofiber length, as a loss of Abl2 leads to excessively long myofibers in the diaphragm, intercostal and levator auris muscles but not limb muscles. Increased myofiber length is caused by enhanced myoblast prolifer...

In situ studies involving supraphysiological muscle lengths and relative positions have shown that connective tissue linkages connecting adjacent muscles can transmit substantial forces, but the physiological significance is still subject to debate. The present study investigates effects of such epimuscular myofascial force transmission in the rat calf muscles. Unlike previous approaches, we qu...

An a priori model of the whole active muscle length-tension relationship was constructed utilizing only myofilament length and serial sarcomere number for rabbit tibialis anterior (TA), extensor digitorum longus (EDL), and extensor digitorum II (EDII) muscles. Passive tension was modeled with a two-element Hill-type model. Experimental length-tension relations were then measured for each of the...

The synchronous wing depressor muscles of the hawkmoth Manduca sexta undergo large amplitude motions at lengths that lie entirely on the ascending region of their twitch length-tension curve. Moreover, these muscles bear a striking functional resemblance to mammalian cardiac muscle in both the shape of their length-tension curve and in their working length range. Although operation on the ascen...

The influence of length on work production was investigated for rat papillary muscles using the work loop technique. Active and passive length-force relationships were first determined under isometric conditions and the length for maximum force production (Lmax) was derived. Starting from different lengths within the physiological range, a series of work loops was generated using the stimulatio...

Clinical evaluation of clonus in spastic muscles was performed by comparing reflex path length with clonus frequency for different muscles in the same patient. It was found that clonus frequency varied inversely with reflex path length (r = 0.84, p less than 0.001). The findings confirm that clonus is generated by a peripheral mechanism of self re-excitation rather than a central spinal pacemaker.

Nebulin, a family of giant proteins with size-variants from 600 to 900 kD in various skeletal muscles, have been proposed to constitute a set of inextensible filaments anchored at the Z line (Wang, K., and J. Wright. 1988. J. Cell Biol. 107:2199-2212). This newly discovered filament of the skeletal muscle sarcomere is an attractive candidate for a length-regulating template of thin filaments. T...