Muscle Mass Development Research Articles

A study of maximum bite force during growth and development.

Bilateral bite force was measured in a sample of 457 subjects (231 males and 226 females) from 6 years through 20 years. The mean maximum bite force was found to increase from 78 Newtons at 6 to 8 years to 176 Newtons at 18 to 20 years. While earlier studies have shown adult males have a greater mean bite force than females, this difference is not evident during growth and development. Gender-related bite force difference likely develops during the postpubertal period in association with greater muscle mass development in males.

Effects of Protein and Amino Acids on Poultry Growth and Bone Elastic Modulus

The effect of protein and amino acid levels and age on body mass, tibiotarsal growth characteristics, and elastic modulus of proximal tibiotarsal subchondral cancellous bone in roaster chickens was investigated. Heavy meat strain birds were grown from hatch to nine weeks of age while being fed five dietary treatments with varying levels of protein and amino acids. The treatments included levels of protein and amino acids varying from 80 to 120% of the national recommended concentration (NRC), as well as an early protein and amino acid restriction treatment. The effects of dietary treatment, and indirectly the effects of muscle mass development on body mass, tibiotarsal growth, bone mineral content, and elastic modulus of subchondral cancellous bone were measured at one, three, five, seven, and nine weeks of age. The elastic modulus results were compared with bone mineral content measurements taken at the same ages and the same dietary treatments. Early protein and amino acid restriction did not adversely affect marketable body mass; instead, body mass at harvest age for birds fed this treatment were greater than body mass for birds fed other treatments. However, properties relating to mineral content decreased for all treatments at the harvest age of nine weeks, especially percent-ossified tissue and bone mineral content. Increased levels of protein and amino acids are believed to positively influence body mass and muscle mass; the early restriction of protein and amino acids did not inhibit body mass or tibial growth. At nine weeks of age, dietary treatments that provided higher percentages of amino acids than proteins displayed significantly lower mineral contents and higher elastic moduli than other dietary treatments. If the desired outcome is larger birds at harvest age without decreased bone development, then the early restriction of protein and amino acids is recommended.

Protein and Amino Acid Needs of the Strength Athlete

The debate regarding optimal protein/amino acid needs of strength athletes is an old one. Recent evidence indicates that actual requirements are higher than those of more sedentary individuals, although this is not widely recognized. Some data even suggest that high protein/amino acid diets can enhance the development of muscle mass and strength when combined with heavy resistance exercise training. Novices may have higher needs than experienced strength athletes, and substantial interindividual variability exists. Perhaps the most important single factor determining absolute protein/amino acid need is the adequacy of energy intake. Present data indicate that strength athletes should consume approximately 12-15% of their daily total energy intake as protein, or about 1.5-2.0 g protein/kg.d-1 (approximately 188-250% of the U.S. recommended dietary allowance). Although routinely consumed by many strength athletes, higher protein intakes have not been shown to be consistently effective and may even be associated with some health risks.

2 EFFECTS OF REFEEDING ON BODY HABITUS IN MALNOURISHED ADOLESCENTS WITH ANOREXIA NERVOSA

Weight gain is one of the therapeutic goals for adolescents with anorexia nervosa. The quality of such weight gain in terms of tissue deposition has not been studied. We determined the distribution of weight gain between fat and muscle tissue upon refeeding. Percent body fat (from skin fold thickness), % muscle mass (from creatinine excretion) and muscular development (from corrected upper arm diameter) were obtained on 6 malnourished teenagers initially and upon refeeding. Subjects (5 female, 1 male) ranged in age from 13-19 years (x=15); average weight gain was 5.9 ± 1.3(SE) kg. Two pts., who were the most wasted and gained the most weight (43% and 23% of initial weight, respectively) put on a disproportionate amount of body fat (285,263%). The % muscle mass and upper arm diameter remained essentially constant and considerably below normal for age/sex. The remaining 4 pts. increased their body weight by 8-12% and gained both muscle and fat in similar proportions: the % body fat increased by 27 ± 6 (SE)% and muscle mass by 20 ± 7%. Muscular development calculated from the square of the increment in upper arm diameter increased by 16 ± 4%.We conclude that there are at least two patterns of weight gain with refeeding. Pts. who were extremely malnourished with severe fat and muscle wasting gained a disproportionate amount of fat, while those who were less malnourished gained by the accretion of similar amounts of fat and muscle. Reasons for the observed differences may relate to variations in fat and muscle wasting, diet, habitus, and type and amount of exercise. Therapeutic goals should consider the quality, as well as quantity, of weight gain achieved during refeeding.

Genesis of oestrogenic inhibition of soleus muscle development in female mice

The mechanism by which oestrogen inhibits development of muscle mass was investigated in the soleus muscle of 20 sexually immature female mice. Half of the population were injected weekly (from one to nine weeks old) with a physiological dose of 0.01 mg stilboestrol dipropionate (synthetic oestrogen). After each mouse was killed at 10 weeks old, the weight and muscle index was determined for each muscle. The number of muscle fibres was counted in each soleus muscle. The muscle fibre size for each muscle was determined by measuring the greatest diameter of at least 100 fibres. The number of muscle fibres was similar in both normal and oestrogen treated animals but the individual muscle fibre sizes were significantly smaller in oestrogen treated animals. These observations indicated, therefore, that oestrogen inhibits development of muscle mass in females by limiting the size of individual muscle fibres and not by inhibiting the multiplication of muscle fibres.

Muscle fiber regeneration in nerve-intact and free skeletal muscle autografts in cats.

Extensor digitorum longus (EDL) muscles of adult cats were transplanted as free autografts (FRA) with the nerve severed or as nerve-intact autografts (NIA) with the nerve retained. Histochemical and contractile properties of NIA and FRA were analyzed at selected times from 1 to 14 wk after surgery. Regeneration was qualitatively similar in NIA and FRA. Regenerating fibers were observed in both NIA and FRA within 2 wk. After 14 wk there were fewer type I fibers in both NIA and FRA than in control EDL muscles. Capillarity was greater in NIA than FRA, but both types of autografts had significantly reduced capillarity relative to control muscles. Mean fiber area, muscle mass, and absolute tension development were greater in NIA than FRA but did not reach control muscle values. Muscle mass, mean fiber area, and contractile properties, but not the proportion of type I fibers, develop toward control values more quickly in autografts with the nerve left intact.

‘Post-Coronary’ Rehabilitation, Body Composition, and Recurrent Infarction

Changes in body composition have been studied in patients with ischemic heart disease over a 2-year period, commencing 3–12 months after a well-documented myocardial infarction. Findings have been related to diet, the exercise undertaken (random allocation of volunteers to high intensity and low intensity exercise programmes) and the recurrence of myocardial infarction. When first recruited, subjects were not much more obese than other middle-aged men. In contrast with experience in the ‘healthy’ middle-aged exerciser, compliance of postcoronary patients with the required regimen was uninfluenced by body build. Over the 2 years of observation, both high and low intensity exercise groups showed small losses of fat and gains of lean mass. It is suggested that these changes reflect responses to dietary regulation and an increase of physical activity rather than a specific effect of the prescribed effort; the potential advantage of the high intensity exercise programme was lost through a larger food intake. Patients who sustained a recurrence of their infarction had an average percentage of body fat, but a low excess weight and lean mass; although isometric exercise is not frequently implicated in the recurrence of an infarction, the development of muscle mass might be advantageous to patients who must continue to work in occupations that demand sustained isometric muscular activity.

HEMATOCRIT: MATURITY RELATIONSHIP IN ADOLESCENCE

The time of onset of adolescence, the velocity of change, and the age at which somatic maturity occurs varies with each individual. Chronologic age, per se, provides little information as to growth and development. The sequential changes in secondary sex characteristics can be divided into five stages and then one of these assigned as a "maturity rating" to any patient. Hematocrit determinations were performed on 1,007 girls and 1,000 boys, aged 11 to 20 years. All patients were from low-income families and each boy or girl was examined and classified according to maturity rating, sex, and color. In boys, correlation of hematocrit determinations and sex maturity ratings showed an increase in the hematocrit percentage with an increase of maturity rating. Boys have a smooth, progressive rise in hematocrit levels as they mature and this increase is apparently associated with the production of testosterone and the development of greater muscle mass. Hematocrit values increase in relation to chronologic age, only when sexual maturation is taking place, thus evaluation of anemia based only on age may be incorrect. Hematocrit determinations related to sex maturity ratings provide a logical criterion for the diagnosis of anemia and of therapeutic response in its treatment.

The Estimation of Relative Nutrient Intake and Nutritional Status by Biochemical Methods: Proteins

When the intake of dietary proteins is reduced, some biochemical changes occur in the body, which may be grossly grouped into three stages of development: (1) decrease in the metabolic expenditure of body proteins, (2) decrease in the “protein reserves,” and (3) decrease in some protein moieties with key metabolic function. Biochemical methods applicable at these different stages, which will give information on the protein intake and nutritional status, are suggested. The urinary excretion of urea under fasting conditions, particularly its ratio to creatinine, is proposed as an informative test at stage 1. The preliminary evidence presented points to its usefulness as a simple way to estimate levels of “utilizable protein” intake. Urinary creatinine per unit of time per centimeter of height is discussed as a practical indicator of muscle mass development during stage 2. Alterations in total plasma protein and its electrophoretic fractions, as well as of some enzymes of plasma and tissues (stage 3), can be detected biochemically but seem to appear only at the last stage of protein deficiency when the condition is severe enough to be clinically evident.