Y. Kawakami et Rl. Lieber, Interaction between series compliance and sarcomere kinetics determines internal sarcomere shortening during fixed-end contraction, J BIOMECHAN, 33(10), 2000, pp. 1249-1255
The interaction between contractile force and in-series compliance was inve
stigated for the intact skeletal muscle-tendon unit (MTU) of Rana pipiens s
emitendinosus muscles during fixed-end contraction. It was hypothesized tha
t internal sarcomere shortening is a function of the length-force character
istics of contractile and series elastic components. The MTUs (n = 18) were
dissected, and, while submerged in Ringer's solution, muscles were activat
ed at nine muscle lengths(-2 to +6 mm relative to optimal length in 1 mm in
tervals), while measuring muscle force and sarcomere length (SL) by laser d
iffraction. The MTU was clamped either at the bone (n = 6), or at the proxi
mal and distal ends of the aponeuroses (n = 6). Muscle fibers were also tri
mmed along with aponeuroses down to 5-20 fibers and identical measurements
were performed (n = 6). The magnitude of shortening decreased as MTU length
increased. The magnitude of shortening ranged from -0.08 to 0.3 mu m, and
there was no significant difference between Delta SL as a function of clamp
location. When aponeuroses were trimmed, sarcomere shortening was not obse
rved at L-0 and longer. These results suggest that the aponeurosis is the m
ajor contributor to in-series compliance. Results also support our hypothes
is but there also appear to be other factors affecting internal sarcomere s
hortening. The functional consequence of internal sarcomere shortening as a
function of sarcomere length was to skew the muscle length-tension relatio
nship to longer sarcomere lengths. (C) 2000 Elsevier Science Ltd. All right
s reserved.