Force-velocity-power and force-pCa relationships of human soleus fibers after 17 days of bed rest.
Soleus muscle fibers from the rat display a reduction in peak power and Ca2+ sensitivity after hindlimb suspension. To examine human responses to non-weight bearing, we obtained soleus biopsies from eight adult men before and immediately after 17 days of bed rest (BR). Single chemically skinned fibers were mounted between a force transducer and a servo-controlled position motor and activated with maximal (isotonic properties) and/or submaximal (Ca2+ sensitivity) levels of free Ca2+. Gel electrophoresis indicated that all pre- and post-BR fibers expressed type I myosin heavy chain. Post-BR fibers obtained from one subject displayed increases in peak power and Ca2+ sensitivity. In contrast, post-BR fibers obtained from the seven remaining subjects showed an average 11% reduction in peak power (P < 0.05), with each individual displaying a 7-27% reduction in this variable. Post-BR fibers from these subjects were smaller in diameter and produced 21% less force at the shortening velocity associated with peak power. However, the shortening velocity at peak power output was elevated 13% in the post-BR fibers, which partially compensated for their lower force. Post-BR fibers from these same seven subjects also displayed a reduced sensitivity to free Ca2+ (P < 0.05). These results indicate that the reduced functional capacity of human lower limb extensor muscles after BR may be in part caused by alterations in the cross-bridge mechanisms of contraction.
Widrick
J J
JJ
Department of Biology, Marquette University, Milwaukee, Wisconsin 53201, USA.
Norenberg
K M
KM
Romatowski
J G
JG
Blaser
C A
CA
Karhanek
M
M
Sherwood
J
J
Trappe
S W
SW
Trappe
T A
TA
Costill
D L
DL
Fitts
R H
RH
D000328:Adult; D002118:Calcium / Q000378:metabolism; D006801:Humans; D007551:Isotonic Contraction / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D018995:Myosin Heavy Chains / Q000378:metabolism; D012146:Rest / Q000502:physiology*
D018995:Myosin Heavy Chains; D002118:Calcium