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

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (p. 87-110). Also available in print.

To study the detrimental effects of hypokinesia, many models of reduced muscular activity (i.e., reduced-use), including alterations in the size of the living environment, have been developed. Although significant structural and functional changes have been documented, the effect of reduced-use on muscle fatigability remains unclear. This project was designed to study the effects of cage-size on selected properties of rat hindlimb muscle, with particular emphasis on fatigue. Further, in view of the lack of information on the potential effect of gender, both males and females were studied. The rats were raised in either a small, conventional cage or one approximately 133 times larger. Subsequently, terminal experiments were performed to characterize the contractile properties, fiber-type composition and oxidative potential of two hindlimb muscles of the small- and large-cage-reared rats. The test muscles, soleus and extensor digitorum longus, were selected on the basis of their pronounced differences in function, usage and fiber-type composition. The results suggest that reductions in cage-size can influence the properties of skeletal muscle (specifically, muscle mass, force and fatigability) and that this effect is a function of both gender and interanimal differences. However, due to the large variability exhibited by all three factors, their overall effect will be minimal. An analysis of the response of the test muscles to a 6 min fatigue test revealed three findings. First, both muscles exhibited a wide range of fatigability, an unexpected finding particularly for soleus but in keeping with the multiplicity of factors discussed above. Second, the association observed between whole-muscle force and the electromyogram (e.m.g.) was found to be dependent upon the measure used to quantify the e.m.g., the fiber-type composition of the muscle and its degree of fatigability. And third, a coexistence of twitch potentiation and muscle fatigue was observed which also was dependent upon the fiber-type composition and the extent of fatigue. Finally, a comparison of qualitative and quantitative histochemical analyses revealed broad, overlapping ranges for oxidative enzyme activity for each of the three muscle-fiber types. This suggests that differences in fatigability usually attributed to different fiber types are not due solely to differences in oxidative potential.

The metabolic response to muscle unloading and disuse was studied in rats subjected for six days to tail-cast suspension which leads to non-weight bearing hindlimbs, while the forelimbs are utilized for mobility. Under these conditions the soleus muscle atrophied, growth of the gastrocnemius and plantaris muscles declined, and the extensor digitorum longus and tibialis anterior muscles grew normally. Differences in muscle weight and protein content were associated with slower protein synthesis, particularly in the sarcoplasmic fraction, and faster protein degradation. Atrophy was accentuated by the administration of glucocorticoids to adrenalectomized rats causing a further reduction in protein synthesis. The effects of disuse and glucocorticoids were additive. Amino acid metabolism is altered in disuse of the soleus muscle as demonstrated by higher concentrations of tyrosine and glutamate and lower concentrations of glutamine, aspartate and asparagine. The lower glutamine concentration is the result of slower de novo synthesis despite higher glutamine synthetase activity, the result of glucocorticoid action. Slower glutamine synthesis was due to a lack of free ammonia for its synthesis, probably due to slower flux through AMP deaminase as a result of decreased muscle use and ATP utilization. Alanine production by the atrophied soleus muscles was higher and glutamate and aspartate utilization lower than by muscles from weight bearing controls. Branched chain amino acid degradation is faster in both the soleus and extensor digitorum longus muscles of suspended rats; a difference partially mediated by glucocorticoids. The resistance of amino acid uptake to insulin in these muscles was abolished in adrenalectomy. Passive stretch of the non-weight bearing soleus muscle, by immobilization in dorsiflexion, prevented the metabolic changes associated with hindlimb suspension while plantar flexion had no effect on the atrophy. Muscles subjected to hypokinesia/hypodynamia demonstrated a loss of muscle protein due to slower protein synthesis and faster degradation. The increased availability of free amino acids from protein coupled to differences in hormone responsiveness and slower utilization of energy stores results in a substantial shift in the metabolic equilibrium of the muscle cell, particularly with regard to amino acid interconversions.

Thesis (M. Phil.)--University of Hong Kong, 2005. / Title proper from title frame. Also available in printed format.

published_or_final_version / abstract / Paediatrics and Adolescent Medicine / Master / Master of Philosophy

No description available.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 152-181).

published_or_final_version / Education / Master / Master of Philosophy

Background: Decades of research indicate that physical activity is an important behavior for health promotion and disease prevention. Despite dissemination of these research findings, many American adults are sedentary. The rates for sedentary behavior vary by race/ethnicity and gender. Women and adults from minority groups are most likely to be sedentary. Research on adults who are physically active has identified several factors that predispose, enable, and reinforce this behavior. The presence of social support is one such factor. Purpose: The purpose of this study was to identify the nature and extent of social influence on physical activity in a nationally-representative sample of minority women. Methods: A telephone survey of 2912 women ages 40 and older from various racial/ethnic groups was conducted from July 1996 to June 1997. Information on physical activity as well as other preventive health behaviors was collected. Analysis: Descriptive analyses were done on physical activity levels (including an accumulation of household and occupational physical activity), physical activity-related social support (PASS), support network, and measures of social contact. Logistic regression was used to determine differences in PASS levels and physical activity. Linear Regression was used to determine the relationship between social influence and physical activity level. Results: Women with high levels of physical activity- related social support were more likely to meet recommended levels of physical activity. There was no difference by racial/ethnic group. An index of social influence was not a significant predictor or physical activity level among all women in the sample. Conclusion: While women with higher levels of specific support for physical activity were more likely to be physically active, a more general measure of social support did not predict level of physical activity. More research is needed in assessment of both physical activity and social support in this population. / Graduation date: 1999