Sarcomeres and Stretching
There is evidence at least from animal experiments that the number of
sarcomeres (in series) within muscle fibres alters in response to
immobilisation in shortened or lengthened positions, for example
Tabary, JC, Tabary, C, Tardieu, C, Tardieu, G & Goldspink, G (1972). J.
Physiol 224: 231-244.
This article showed increases in sarc number in cat soleus of ~20% when
held at long lengths, and a decrease of ~40% when held at shorts lengths.
A similar study (Williams, PE & Goldspink, G (1978). J. Anat 127:
459-468), showed evidence that after immobilisation sarcomere number alters
so that filament overlap is brought back to 'optimum' (for tension
generation).
There is also evidence that this adaptation is not neurally based but
rather a 'built-in' capability of muscle fibres, see Goldspink, G, Tabary,
JC, Tabary, C, Tardieu, C & Tardieu, G (1974). Effects of denervation on
the adaptation of sarcomere number and muscle extensibility to the
functional length of the muscle. J. Physiol. Lond. 236: 733-742.
There is recent evidence that the growth factor IGF-1 is heavily involved
in this process (or atleast the increases in sarcomere number):
Yang, H, Alnaqeeb, M, Simpson, H & Goldspink, G (1997). Changes in muscle
fibre type, muscle mass and IGF-I gene expression in rabbit skeletal muscle
subjected to stretch. J. Anat. 190: 613-622.
It has been shown that even brief periods of daily stretch (1/2 hr per day)
not only reversed the effects of immobilisation in a shortened position,
but could cause a slight increase in sarc number and prevent much of the
atrophy normally associated with immobil in the shortened position. See:
Williams, PE (1990). Use of intermittent stretch in the prevention of
serial sarcomere loss in immobilised muscle. Ann. Rheum. Dis. 49: 316-317.
An excellent review (although somewhat old now) is by Goldspink, G (1985).
Malleability of the motor system: A comparative approach. Journal of
Experimental Biology 115: 375-391. Hope this is of some interest
Regards,
Trevor Allen
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Trevor Allen
Human Movement Laboratory
School of Physiotherapy
University of Melbourne
200 Berkeley St, Parkville Vic 3010
Office: (03) 9344 6435
Lab: (03) 9344 4841
Fax: (03) 9344 4188
Mobile: 0409 351 747
http://www.physioth.unimelb.edu.au/
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