Sex- and Training-Related Differences in Metabolic, Sex Steroid and Growth Hormone Responses During Prolonged Exercise

Selected metabolic and hormonal variables were measured and compared at rest (2 hours), and during exercise (1 hour at 60% VO(,2) max) and recovery (15 minutes) in four groups of subjects (N = 7/group), ages 18-30, categorized as: (1) male controls, (2) female controls, (3) male runners, and (4) female runners. Sex- and training-related differences in resting levels and responses were described for glucose (GLU), lactic acid (HLa), hematocrit (Hct), respiratory exchange ratio (R), growth hormone (hGH), estradiol-B17 (E(,2)), and testosterone (T). Blood samples were drawn at predetermined intervals from an indwelling venous catheter inserted in the forearm. GLU and HLa levels were measured with enzymatic assay kits; hGH, E(,2), and T levels were measured by radioimmunoassay. The main purposes of the study were to determine: (1) the relationship between sex steroid (E(,2), T) profiles and hGH responses, (2) the influence of endurance training on hGH responses in males and females, and (3) the relative importance of hGH for fat utilization during prolonged activity compared in males versus females, and moderately active controls versus well-trained runners. Data was statistically analyzed using one-way ANOVA and multiple regression. Results indicated that while sex steroid profiles predicted hGH levels at rest, during exercise hGH responses were related to training with runners exhibiting a greater response. Both sex- and training-related differences were observed in fat utilization with females using a proportionately greater amount than males. Both male and female runners exhibited a greater utilization of fat that was related to hGH response. Based on the results, a hypothetical model for control mechanisms and actions of hGH during exercise was proposed. Practical implications were discussed in terms of the direct and indirect actions of sex steroids on factors important for performance of endurance activity and directions for future research were outlined.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physical Education

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Bunt, Joy Carol

• Education, Physical

Identifier

(UMI)AAI8521729

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71873