Järvinen M J, Einola S A, Virtanen E O
Department of Physiology, University of Turku, Finland.
Arch Phys Med Rehabil. 1992 Mar;73(3):253-7.
This study compared the tensile properties of the atrophied gastrocnemius unit after immobilization in a shortened position (SP) and lengthened position (LP). The left hind legs of 52 male Wistar rats were fixed with plaster casts either with the knee in flexion and the ankle in extension, or vice versa. After seven to 21 days of immobilization the load-deformation curves and the weights of both gastrocnemius muscle-tendon units from each rat were evaluated. The initial length increased about 4% in the LP immobilized muscles and decreased about 5% in the SP immobilized muscles when compared to the contralateral controls. The decrease in force to failure averaged 21% in the LP and 31% in the SP immobilized muscles after one week and continued to about 26% and 48%, respectively, in three weeks. The corresponding elongation decreased 13% and 21% in one week and 17% and 36% at the end of the third week when immobilized in the LP and SP, respectively. The decrease in elastic stiffness was similar in both groups, but the loss of energy absorption capacity before failure was more prominent in SP fixed muscles (64%) than in LP fixed muscles (49%). The loss of weight of the muscle-tendon units due to the immobilization was greater in the SP (36%) than in the LP (12%). We conclude that immobilization of the rat gastrocnemius muscle-tendon unit in an SP is followed by a more marked muscle atrophy and a greater decrease in tensile properties than immobilization in an LP.
本研究比较了在缩短位置（SP）和延长位置（LP）固定后萎缩的腓肠肌单元的拉伸特性。52只雄性Wistar大鼠的左后腿用石膏固定，膝关节屈曲、踝关节伸展，或反之。固定7至21天后，评估每只大鼠双侧腓肠肌肌腱单元的负荷-变形曲线和重量。与对侧对照相比，LP固定肌肉的初始长度增加约4%，SP固定肌肉的初始长度减少约5%。固定一周后，LP固定肌肉的破坏力平均下降21%，SP固定肌肉下降31%；三周后，分别持续下降至约26%和48%。固定在LP和SP时，相应的伸长率在一周内分别下降13%和21%，在第三周结束时分别下降17%和36%。两组的弹性刚度下降相似，但SP固定肌肉在破坏前的能量吸收能力损失（64%）比LP固定肌肉（49%）更明显。固定导致的肌腱单元重量损失在SP组（36%）大于LP组（12%）。我们得出结论，与在LP固定相比，将大鼠腓肠肌肌腱单元固定在SP后会出现更明显的肌肉萎缩和拉伸特性更大程度的下降。
