Average Fiber Size Research Articles

Carotid-cardiac baroreflex response and LBNP tolerance following resistance training

The purpose of this study was to examine the effect of lower body resistance training on cardiovascular control mechanisms and blood pressure maintenance during an orthostatic challenge. Lower body negative pressure (LBNP) tolerance, carotid-cardiac baroreflex function (using neck chamber pressure), and calf compliance were measured in eight healthy males before and after 19 wk of knee extension and leg press training. Resistance training sessions consisted of four or five sets of 6-12 repetitions of each exercise, performed two times per week. Training increased strength 25 +/- 3 (SE)% (P = 0.0003) and 31 +/- 6% (P = 0.0004), respectively, for the leg press and knee extension exercises. Average fiber size in biopsy samples of m. vastus lateralis increased 21 +/- 5% (P = 0.0014). Resistance training had no significant effect on LBNP tolerance. However, calf compliance decreased in five of the seven subjects measured, with the group average changing from 4.4 +/- 0.6 ml.mm Hg-1 to 3.9 +/- 0.3 ml.mm Hg-1 (P = 0.3826). The stimulus-response relationship of the carotid-cardiac baroreflex response shifted to the left on the carotid pressure axis as indicated by a reduction of 6 mm Hg in baseline systolic blood pressure (P = 0.0471). In addition, maximum slope increased from 5.4 +/- 1.3 ms.mm Hg-1 before training to 6.6 +/- 1.6 ms.mm Hg-1 after training (P = 0.0141). Our results suggest the possibility that high resistance, lower extremity exercise training can cause a chronic increase in sensitivity and resetting of the carotid-cardiac baroreflex.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of training on central factors in fatigue following two‐ and one‐leg static exercise in man

Leg strength and fatigue developed during 150 repeated two- and one-leg isometric maximal voluntary contractions were determined before and after a 5-week one- (n = 6) or two- (n = 7) leg training programme including a control group of five subjects. Two- and one-leg training increased two- and one-leg strength by 59 (range 8-107) and 36% (-1-69) respectively (P less than 0.01) with no significant difference between the two groups. Two-leg training decreased (P less than 0.05) fatigue only during two-leg maximal voluntary contractions (from 20 [11-26] to 13% [6-27]); and one-leg training fatigue only during one-leg maximal voluntary contractions (from 20 [15-23] to 11% [9-24]) despite the fact that both legs were trained. Surface electromyographic activity decreased during both repeated two- and one-leg maximal voluntary contractions (P less than 0.01) but a reduction in electromyographic decay was seen (P less than 0.05) during two-leg maximal voluntary contractions after two-leg training. Training increased fast-twitch b fibre size (P less than 0.01), and glycogen depletion was seen in fast-twitch (a and b) fibres, but the relative fast-twitch b area did not increase significantly. No training effects were seen in the control group. The results show that an approximately 47% increase in muscle strength may take place without a significant change in the relative percentage of muscle fibre types or in the average muscle fibre size. Furthermore, the specificity of the training response to fatigue developed during repeated two- and one-leg maximal voluntary contractions suggests a change in the nervous influence on the motor units.

The relationship of muscle fibre size to tenderness of beef

Steaks were removed from loins of beef carcasses at 1, 3, 6 or 14 days post mortem for fragmentation index (MFI), Warner-Bratzler Shear Force (SF) and sensory panel tenderness evaluation. Also, after 1 day of storage, samples were removed for histological observations. Greatest improvement in tenderness, SF and MFI occurred within the first 6 days of storage. Sensory panel tenderness was correlated ( P < 0·01) with SF and MFI. Average muscle fibre size was correlated ( P < 0·01) with tenderness and SF at days 1 and 3, but not at days 6 and 14. Evidently, muscle fibre size is important to tenderness prior to post-mortem storage of meat and proteolysis, but becomes less of a factor in tenderness after 6 days of storage.

Commissural size in neonatal rats: Effects of sex and prenatal alcohol exposure

Sex differences have been reported in the size of the adult corpus callosum in both humans and rodents. This experiment investigated whether sex and/or different prenatal treatment conditions would influence commissural size at birth. Male and female 3-day-old Long Evans rats were selected from one of three prenatal treatment histories: prenatal alcohol-exposed (35% ethanol-derived calories, 35% EDC), nutritional control (0% ethanol-derived calories, 0% EDC) or standard control (lab chow). Midline sagittal areas of the corpus callosum and the anterior commissure were determined for these subjects. Male control subjects had significantly larger callosal areas than females. Prenatal alcohol exposure significantly abolished this sexual dimorphism, with 35% EDC males having a significantly smaller callosal area than males from both control groups. This effect was independent of prenatal treatment differences in body or brain size. There were no significant sex differences in the midline sagittal area of the anterior commissure, nor were there any apparent effects of prenatal treatment on this measure. These results indicate that sex differences in the size of the corpus callosum are present at birth. Since a difference in myelination cannot account for this difference in area, there may be a sex difference in the number of fibers or in the average fiber size. Additionally, the effects of prenatal alcohol exposure on male, but not female, offspring suggest that this alcohol-related birth defect is hormonally mediated.

The Influence of Muscle Fiber Size on Tenderness in A‐Maturity Heifers1

ABSTRACTA total of 77 crossbred late‐maturing or intermediate‐maturing heifers were fed an 84% total digestible nutrient diet from 200 kg live‐weight to slaughter at 433 kg. Carcass data and histochemical samples were obtained at 24 h postmortem, and shear and sensory panel evaluation samples were obtained from the longissimus dorsi muscle afier 7 ahys of aging at 2 to 3°C. Average fiber size was correlated (P&lt; 0.01) to sensory panel tenderness and shear force requirements. Cross‐sectional areas of white, intermediate and red fibers were also correlated (P&lt; 0.01) to shear force requirements. Percentages of white, intermediate and red fibers were not consistently correlated to sensory tenderness or shear force. Evidently, the number of myofibrils per unit of mass was associated with meat tenderness. Research needs to be done to determine iffiber size has a causal relationship with tenderness or is a correlated response to other factors that dictate tenderness.

Succinic Dehydrogenase Distribution in the Pectoralis Muscle of Several East African Birds

AbstractThe distribution of succinic dehydrogenase activity was investigated in the pectoralis muscle of thirteen East African birds, representing five Orders. It was found that the pectoralis muscle of the most primitive birds studied (Galliformes) contained all “white” muscle fibres whereas the more advanced birds (Passeriformes) had all “red” muscle fibres. Intermediate Orders had mostly a mixture of red and white muscle fibres. There also appeared to be a direct relationship between body size and average muscle fibre size. However, it was concluded that the most important factor in relation to the muscle structure is the bird's mode of flight. The relationship with the degree of evolution and body size only held true in so far as the birds which had developed the facility for sustained flight, by increasing their red muscle fibre content, were also smaller in size and constituted the more “evolved” Orders of birds. In support of this it was noted that migratory birds (i.e. engaging in sustained flight) from more primitive Orders also had a high red muscle fibre content in their pectoralis muscles.

A study of the development of the characters of the fleece during growth in the different regions of the body

1. A study has been made of the relative development of some regions in the fleece of twin lambs of a Suffolk ♂ × Suffolk (Border Leicester-Cheviot) ♀ cross during growth. The different regions develop in the following order: shoulder → leg → belly → tail. It is concluded that an improved animal is one in which the latest developing part of the fleece has the least possible number of undesirable fibres at the earliest possible age. The breeds of sheep begin their wool improvement by changes in the earliest developing regions (shoulder) and finish it in the latest (tail).2. The properties of the fleece studied were the colour of the fibres, the medullated fibres, the fineness of the fibres, and uniformity of fibre size. In general a relationship is found between the stage and rapidity of development of the area, and the properties of the fibre. The intensity of the colour is stronger during the early active stages of development. There is a tendency to lose some kinds of coloured fibres, and to diminish the intensity of the colour in others as the development of each region in which the fibres grow proceeds.The medullated fibres appeared in greatest quantities in the later developing regions, except the belly which presents few medullated fibres.The staple is much finer at the first month of growth than in the later stages. Frequency curves of fibre size are of more value than average fibre size in estimating the value of the fleece.3. It is suggested that the examination of the fleece of the lamb will give some idea of its genetic constitution and will reveal defects which would be concealed in the adult. Such a “phaeno-genetic” selection can be made best in a “late developing” area of the body such as the tail of the lamb at one month old.