Muscle Growth and Fiber Type Composition in Hind Limb Muscles during Postnatal Development in Pigs

Abstract

Rapid postnatal development in pigs is reflected by differentiation in skeletal muscle. This process depends on muscle function and demands, but a comprehensive overview of individual developmental characteristics of quickly growing leg muscles in pigs is still missing. This study focused on the development of 10 hind limb muscles in pigs. To determine these changes in mass, fiber type patterns and fiber diameters were analyzed 0, 2, 4, 7, 14, 28, 42, 56 and 400 days after birth. Generally, the proportion of slow fibers increased from birth to 8 weeks. Thereafter, only minor changes in muscle fiber type composition were observed. The majority of the muscles contained less then 10% slow-twitch fibers at birth, increasing to between 12 (Musculus vastus lateralis) and 38% (M. gastrocnemius medialis) in adult pigs. By contrast, postural muscles already had 20–30% slow fibers at birth, and this contribution increased up to 65% in adults (i.e. M. vastus intermedius). From birth to the 2nd week, only in slow fibers could activity of oxidative enzymes be detected. A differentiation of fast-twitch fibers into subtypes with high (comparable to type IIA) and low oxidative metabolism (equivalent to type IIB) occurred between the 2nd and 4th week of life. The ratio between type II fibers with high and low oxidative enzyme activity did not change markedly through development in any muscle, although there was a trend towards an increasing proportion of type IIA fibers in the soleus. In the majority of the muscles investigated, the fast-twitch fibers with low oxidative metabolism (IIB) obtained the largest cross-sectional area. In contrast, at birth no remarkable differences in the diameter of fast and slow fibers were found. The rapid increase in muscle mass compared to body mass reflects the high performance in meat production of the cross pig investigated.

A macroscopic ansatz to deduce the Hill relation

“…The lowest and highest c˙h 0 values (0.01, 0.3) extracted from literature (Barclay, 1994(Barclay, , 1996Barclay et al, 1993;Elzinga et al, 1987;Günther et al, 2007;Hill, 1938;Houdijk et al, 2006;Wank et al, 2006) (for R P DE = 0: Eq. (16)) with the belonging factor…”

Quantitative analysis of neonatal skeletal muscle functional improvement in the mouse

“…The principal thick filament constituent of the myofibril is myosin heavy chain (MyHC), and developmental heterogeneity across muscles arises in part from differences in the expression of MyHC isoforms, which include at least two early developmental [embryonic (EMB) and neonatal (NEO)] and four mature (I, IIA, IIX and IIB) isoforms (Bottinelli, 2001;Schiaffino and Reggiani, 1994). Postnatal transitions away from early developmental MyHC isoforms and toward muscle-specific distributions of mature isoforms have been observed in a number of mammalian species (Agbulut et al, 2003;Strbenc et al, 2006;Wank et al, 2006). In the lateral force transmission network, an important constituent is the intermediate filament desmin, which is the first muscle-specific structural protein to be expressed in the embryo (Herrmann et al, 1989;Mayo et al, 1992).…”

Optimal Control of Isometric Muscle Dynamics

“…Figure 1 shows the results of the optimal control approach. Regarding Figure 1 (left) we compare the experimentally measured isometric forces F MTC (thin line, see [29]) with the force F MTC * = F MTC (σ * ) computed in the optimal control approach (bold line). Additionally, we have plotted the direct model output Solve q̇= f 1 (q, σ 0 ) with q(0) = q 0 Solve ℓ̇C E = f 2 �ℓ MTC , ℓ̇M TC , ℓ CE , q� with ℓ CE (0) = ℓ CE,0 …”

“…In [22] all model parameters stated above were estimated on the basis of experiments by [29] namely isometric contractions. In the experimental setup, conducted on piglet muscle, all conditions were controlled.…”