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The objective of this research was to compare the skeletal muscle fiber composition in selected isogenic strains of mice. Six strains of mice were surveyed, one male and one female from each strain. The gastrocnemius and quadriceps muscles were stained for oxidative and glycolytic activities as well as contractile properties by using five histochemical stains. These results indicated that both muscles were composed predominantly of fast glycolytic (FG) and fast oxidativeglycolytic (FOG) fibers. There were few slow oxidative (SO) fibers which were mostly confined to the red portion of each muscle, although in some mice (0113 C57BL/6J black male, 0119 DBA/2J dilute brown female, and 0105 BALB/cJ albino male and female) this fiber type seemed to be lacking completely in one or both muscles surveyed. In addition, it was found through 2 the use of planimetry, that SO fibers (-x = 1140.97 μ2) were significantly smaller (P<0.01) than the FOG and FG fibers (-x = 1514.08μ2).Within the limits of these observations it is concluded that further examination of these strains of mice is necessary in order to better facilitate a quantitative genetic analysis. Moreover, developmental and environmental studies would serve to clarify the genetic influences on muscle fiber composition.

Previous studies have shown that ability to perform anaerobic activities is markedly reduced following prolonged exercise. It has been hypothesized that such changes are the result of reduced glycolytic capability. This study examined the changes in selected glycolytic enzyme activities in the leg muscles of men before, immediately after and 24 hours after prolonged exertion. Muscle biopsies obtained from the vastus lateralis were assayed for glycogen, total phosphorylase, lactate dehydrogenase (LDH), phosphofructokinase (PFK), and alpha glycerophosphate dehydrogenase ((GPDH). Muscle glycogen content was round to decrease significantly (P <.0l) from rest (116 mmoles/kg) Co post exercise (66 mmoles/kg), but 24 hours later it was only 15% lower than the pre exercise value. Phosphorylase and LDH increased significantly (+12.9% and +9.4%, respectively) as a result of the exercise. After 24 hours of rest phosphorylase returned to the pre exercise level, but LDH showed an additional increase of 6.2% in activity above the post exercise value. These data fail to support the hypothesis that prolonged severe exercise inhibits anaerobic capacity by reducing essential glycolytic enzymes.Supported by a grant for NIH (R0l AM17083-01).

Ten trained subjects were studied during and following exercise to determine the effects of fructose ingestion on muscle glycogen depletion and resynthesis. Three subjects cycled for anhour while the other six subjects completed a 3000-yard swim. The subjects ingested 12 grams of fructose before, 46 grams during, and 12 grams in the 30 minutes following the exercise. Muscle biopsies were obtained before, immediately after, and 12 hours post exercise. In -the cyclists, plasma glucose and insulin were also determined. The ingestion of fructose had no effect on the glycogen depletion during exercise. However, in the 12 hours following exercise, fructose ingestion resulted in a 41.4 mmole/kg-wet tissue increase in muscle glycogen. At the same time, the control period resulted in only a 9.53 mmole/kg-wet tissue increase in muscle glycogen. Plasma glucose and insulin levels increased during the fructose feeding. These data suggest that fructose ingestion during exercise has no effect in sparing muscle glycogen during work, but could significantly enhance the resynthesis of glycogen after work.

This study was conducted to determine the variation in stain Intensity between serial sections of muscle biopsies following a periodic acid Schiff (PAS) staining procedure, to assess the reliability of the PAS staining technique for the quantitation of the glycogen content in muscle fibers, and to evaluate the variability in fiber composition between repeated biopsies of the vastus lateralis (VL) muscle. Eight randomly located biopsies (4 right leg and 4 left leg) were obtained from the VL of each of 16 healthy males (26.1 ± 1.1 years). Serial cross sections, 10 um thick, were cut from each biopsy and stained for myosin ATPase following an acid preincubation at pH=4.30 and for glycogen using a PAS staining procedure. No significant difference existed in the fiber composition between the eight repeated biopsies taken from an individual. The variation In type I fiber percentage, expressed as the coefficient of variation, between repeated biopsies of the same leg and between the right and left VL averaged 18.6% and 17.7%, respectively. In many cases, differences of greater than 20% In the percentage of type I fibers were observed between repeated samples. These data suggest an inhomogeneity with regard to the fiber type distribution in the VL of young males and an Inability to predict the fiber composition of a muscle with a single biopsy sample.The optical densities (OD) of the same 50 type I and 50 type II fibers were determined In each of three PAS stained serial sections per biopsy using a computer integrated photometric system. Mean total, fiber type specific, and Individual fiber OD did not differ significantly between the serial sections although a variability was observed. This variability appears to be primarily due to differences In sectional thickness. The comparison of biochemically determined glycogen content (41.0 - 191.0 mmol.kg-lwet weight) to mean total OD in sections from the same samples resulted in a poor relationship (r=0.47) between the two methods for the quantification of muscle glycogen. These results Indicate a variability in PAS stain intensity between serial sections of muscle biopsies and an inability to quantify muscle glycogen concentrations with the photometric determination of OD of the PAS stain in cross sections of muscle. / School of Physical Education

This investigation examined the effects of 4 weeks of non-dominant arm suspension on the functional and structural characteristics of the triceps brachii muscle of 6 normo-active college age males (age: 23.3 ±0.8 yrs, height: 176.1 ±3.7 cm, weight: 75.9 ±5.8 kg). The primary intent of this study was to determine if arm suspension is an effective analogue for simulating the effects of weightlessness on human skeletal muscle. Subjects were tested 2-3 days preceding suspension in a standard arm sling and immediately following removal of the sling. To suspend the arm the sling was worn during waking hours. Subjects were allowed to remove the sling during sleep and bathing. Specific instructions were given to avoid use of the arm. Torque production (Nm) during maximal isometric extensions at 90° significantly declined (p<0.05) in response to arm suspension (53.93 ±5.07 to 47.90 ±5.92; 12%). There was no significant change (p>0.05) in the force-velocity attributes of the triceps over the other measured velocities (60, 90, 120, 180, 240, 300°/sec). Cross-sectional muscle area (CSA) of the upper arm diminished significantly (44.26 +2.66 to 42.43 ±2.54 cm2; 4%) following the 4 weeks of unloading (p<0.05). Histochemical analysis of individual muscle fibers demonstrated reductions in fiber CSA of 27 and 18% for type I and type II fibers, respectively, however these changes were not statistically significant (p>0.05). Amplitude of the IEMG signal during maximal isometric contraction of the long head of the triceps fell (p<0.05) by 21 in response to the 4 week suspension period. The changes in triceps muscle structure and function found with arm suspension are similar in magnitude and direction to data obtained from humans following exposure to real and simulated weightlessness. These findings suggest that arm suspension may provide a useful model for simulating the effects of microgravity on human skeletal muscle. / School of Physical Education

Effects of homologous extracts prepared from mature avian skeletal muscle on the development of isolated myoblasts from the thigh muscle of 11-12 day old chick embryoswere studied in vitro under previously unpublished culture conditions. Results of these experiments indicate that:1) fusion of myoblasts can occur in a predictable manner under the culture conditions described in this report2) some factor(s) present in extracts of homologous adult organ is able to partially inhibit this fusion3) such inhibition occurs maximally between 12 and 24 hours after myoblasts are placed in an in vitro environment, and is only partially reversible by the re-establishment of optimal culture conditions4) the inhibitory factor(s) is apparently long lived, non-dialyzablQ, heat labile, and subject to inactivation by proteolytic enzymes.

Previous reports of the effects of tetrodotoxin (TTX)-induced muscular disuse have demonstrated alterations in muscle force, speed, and fatiguability that might suggest changes in the quality of contractile proteins. These studies were extended to the effects of TTX-induced disuse on the Ca$ sp{2+}$-activation characteristics of myofibrillar ATPase of the rat gastrocnemius. Atrophic responses after TTX treatment were as previously reported with a significant decrease in left gastrocnemius weight (g) compared to the control-pump (C) group (1.25 $ pm$ 0.04 for C vs 0.72 $ pm$ 0.04 for TTX, X $ pm$ SEM, p $ leq$ 0.01). Myofibrillar protein yield (mg$ cdot$g$ sp{-1}$ wet weight) was also depressed (92.8 $ pm$ 4.6 for C vs 70.3 $ pm$ 3.7 for TTX; p $ leq$ 0.01). Maximum ATPase of myofibrils (nmol Pi$ cdot$mg$ sp{-1} cdot$min$ sp{-1}$) was decreased (424 $ pm$ 46 for C vs 199 $ pm$ 27 for TTX, p $ leq$ 0.01). Furthermore, the Hill n which reflects the cooperative aspects of Ca$ sp{2+}$-activation of the myofibrillar ATPase was significantly depressed (1.58 $ pm$ 0.07 for C vs 1.29 $ pm$ 0.09 for TTX; p $ leq$ 0.05) after TTX treatment. The results of the present study suggest that muscle perturbations that result from TTX-induced disuse are at least partially related to changes in the myofibrillar fraction.

The perception of isometric forces was examined under normal conditions, during sustained constant force contractions, and during vibration of the muscle tendon. In these experiments a contralateral limb matching procedure was employed, and force and the brachial biceps and triceps electromyogram (EMG) were recorded from each arm. Under normal conditions it was found that smaller forces were consistently overestimated in magnitude. During sustained constant force contractions the matching forces exerted by the unfatigued arm increased linearly as did the EMG of the fatiguing muscle. These results are consistent with force judgements being made with respect to the excitatory input to the reference muscle. It was further determined that during fatigue subjects were unable to dissociate the force of exertion from the motor command generating the contraction. Muscle tendon vibration increased the variability of force judgements and resulted in the overestimation of forces. This appeared to be due to co-contraction of the antagonist triceps muscle during vibration of the contracting biceps. The increase in the perceived magnitude of force during vibration is again consistent with the centrally-mediated theory of force perception.