Changes in morphological and functional characteristics of male rat EDL muscle during growth

Abstract

Morphological and functional changes as well as changes in fibre-type composition were investigated in the left extensor digitorum longus (EDL) muscles of male Wistar rats of approximately 40, 60, 120 and 700 days old. A number of morphological changes occurred in the EDL muscle during growth. While from 40 to 120 days muscle mass and cross-sectional area (CSA) increased by 247 and 192%, changes in muscle and fibre lengths were much smaller (44 and 17%, respectively). Besides morphological changes tetanic force was also found to increase (approximately 307%) up to 120 days. Because this increase in force was greater than the increase in CSA, specific force increased by approximately 29% between 40 and 60 days. Thereafter, specific force stayed rather constant. From 40 until 60 days changes were also found in the force-frequency and force-velocity curve, which indicate a slowing of the muscles (until 60 days). Changes in fibre-type composition of the EDL muscle were found to occur later during growth between 60 and 120 days. In this period an increase in the relative total area of Type IIBd fibres and a decrease in the relative total area of Type IIBm fibres (corresponding to the Type 2X and IIB fibres, respectively), were found; this was apparently due to a conversion of many Type IIBm into Type IIBd fibres and not to a difference in cross-sectional growth between these fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

E–C coupling and contractile characteristics of mechanically skinned single fibres from young rats during rapid growth and maturation

“…Our finding of reduced max CaF/skinned fibre CSA in muscle fibres from rats in the early rapid growth phase (4-weeks postnatal), but not in the late rapid growth phase (8-weeks postnatal), is in agreement with the in situ data of Lodder et al [36,37] who showed that the specific force of whole rat EDL muscle at 5-6 weeks was significantly lower (−29%) than at 8-9 weeks, while specific force at 8-9 weeks was not different from that at 17-18 weeks. These findings suggest that in rats aged less than ∼8 weeks, the number of force producing cross-bridges per half sarcomere and/or the magnitude of force produced per cross-bridge are lower than in more mature rats.…”

“…In particular, these studies showed that the specific force (tetanic force/cross-sectional area) of the EDL was approximately 29% lower in rats aged 40 days (5-6 weeks) than in those aged 60 days (8-9 weeks) and 120 days (17-18 weeks). This disparity was not associated with age-related differences in fibre type composition, fibre number or fibre density leading the authors to speculate that there is an intrinsically lower force producing capability in rapidly growing rats compared to adult rats [36]. In a follow up study, Lodder et al [37] found that EDL muscles from rats aged 40 days were more fatigable than those of rats aged 60 and 120 days.…”

“…Indeed, Lodder et al [36,37] have found evidence of reduced muscle function in young, rapidly growing rats in two studies using rat EDL muscle stimulated in situ via the sciatic nerve. In particular, these studies showed that the specific force (tetanic force/cross-sectional area) of the EDL was approximately 29% lower in rats aged 40 days (5-6 weeks) than in those aged 60 days (8-9 weeks) and 120 days (17-18 weeks).…”

Muscle-fiber characteristics in adult mouse-tongue muscles

“…Lodder et al (1993) evaluated the physiological importance of changes in MHC‐2b as fast‐fiber subtypes in the muscle composition, and suggested the association between changes in these isoforms and the contraction rate. He reported that the contraction rate is closely related to the composition of the MHC, and type 2b fibers are faster than type 2a fibers ( Bottinelli et al ., 1991 ).…”

The influence of stimulation frequency on force‐velocity characteristics of in situ rat medial gastrocnemius muscle

“…In contrast, in experiments aimed at studying the capacity of skeletal muscles to sustain a high isometric force during one continuous contraction or a series of repetitive contractions, stimulation frequencies are used which are lower than necessary to obtain maximal isometric force (e.g. de Haan, Jones & Sargeant, 1989;Lodder, de Haan, Lind & Sargeant, 1993). By using lower frequencies loss of force-generating capability due to activation failure can be prevented (Jones, Bigland-Ritchie & Edwards, 1979).…”