Sarcomere dynamics and contraction‐induced injury to maximally activated single muscle fibres from soleus muscles of rats.

Abstract

1. The focal nature of contraction-induced injury to skeletal muscle fibres may arise from heterogeneities in sarcomere length that develop during contractions. We tested the hypothesis that when a maximally activated single permeabilized fibre segment is stretched and a deficit in maximum isometric force (force deficit) is produced, the regions of sarcomeres with the longest lengths prior to the stretch contain the majority of the damaged sarcomeres when the fibre is returned to optimum length (L.) after the stretch.2. Single fibre segments (n = 16) were obtained from soleus muscles of rats. Average sarcomere length at five discrete positions along the length of each fibre was determined by lateral deflection of a diode laser spot. Diffraction patterns were obtained while fibres were relaxed and immediately before, during and after a single stretch of 40% strain relative to L..Following the stretch, the regions of each fibre that potentially contained damaged sarcomeres were identified by an increased scatter of the first-order diffraction patterns. The damage was confirmed by light and electron microscopy. 3. While single fibre segments were in relaxing solution, the mean value for all of the average sarcomere lengths sampled (n = 80) was 2-53 + 0-01 #m (range, 2-40-2168 ,um). During the maximum isometric contraction before each stretch, the mean sarcomere length decreased to 2 42 + 0'02 gm and the range increased to 2 12-3 01 /um. 4. During the stretch of 40 % strain, all regions of sarcomeres were stretched onto the descending limb of the length-force curve, but sarcomere lengthening was non-uniform. After the stretch, when the maximally activated fibres were returned to L., the force deficit was 10 + 1 %. Microscopic evaluation confirmed that the regions with the longest sarcomere lengths before the stretch contained the majority of the damaged sarcomeres after the stretch. We conclude that when heterogeneities in sarcomere length develop in single permeabilized fibre segments during a maximum isometric contraction, the sarcomeres in the regions with the longest lengths are the most susceptible to contraction-induced injury.

Isolation and Characterization of Satellite Cells from Rat Head Branchiomeric Muscles

“…In contrast, cleft muscles contain a higher proportion of fast fibers and also a reduced capillary supply compared with normal soft palate muscles [29][30][31] . Fast fibers are more prone to contraction-induced injury [31][32][33] . The accompanying poor capillary supply may also promote fibrosis 34,35 .…”

Short vs. long length of rectus femoris during eccentric exercise in relation to muscle damage in healthy males

“…An animal study indicated that muscle length is an important factor in exercise-induced muscle damage (Hunter and Faulkner, 1997). Animal studies have also revealed that sarcomeres under stretching are more susceptible to injury than non-stretched sarcomeres (Macpherson et al, 1997), leading to a greater degree of inhomogeneity and disruption of the weaker ones (Morgan, 1990).…”

Effects of Strenuous Exercise with Eccentric Muscle Contraction: Physiological and Functional Aspects of Human Skeletal Muscle

“…This decrease may be partly attributed to the disruption of muscle contractile elements resulting from eccentric contraction 2,9 ; repetitive lengthening actions lead to reduced overlap between actin and myosin laments in sarcomeres, and the reduced number of cross bridges could thereby aŠect the ability to generate force. 3 Judging from MRˆndings in this study, this structural disruption should be prominent in the MG. In addition, the MTJ displacement of the MG during MVIP generation signiˆcantly decreased one day after exercise.…”

“…13 Moreover, structural muscle damage was expected to contribute to loss of muscle strength and decreased displacement of the MTJ during maximal isometric force generation because of the reduced number of cross bridges present in disrupted myoˆbrils. 3 …”

“…[1][2][3][4] Biopsy analysis of muscle has revealed that eccentric exercise causes Z-band streaming and broadening and destroys sarcomeres in myobrils. 1,2 Therefore, after eccentric exercise, in‰ammatory response and muscle dysfunction frequently occur with delayed onset muscle soreness (DOMS).…”