Undergraduate Honors Theses

Thesis Defended

Spring 2016

Document Type


Type of Thesis

Departmental Honors


Integrative Physiology

First Advisor

Dr. William Brynes

Second Advisor

Benjamin Ryan



During spaceflight, humans experience several physiological adjustments. Among these changes there is an energy imbalance that results in the loss of body mass in astronauts. The purpose of this study was to determine if energy expenditure decreased after acute Head-Down-Tilt-Bed-Rest (HDTBR). This decrease in energy expenditure is a potential contributor to the energy imbalance we see, and is likely a result of the decreased muscle activation that occurs in a microgravity environment. This study used acute HDTBR as a ground-based model of spaceflight, which mimicked the decreased muscle activation. We measured resting metabolic rate (RMR) and sub-maximal energy expenditure in seven male subjects before, after and five days after HDTBR. Subjects’ RMR showed no change after experiencing acute HDTBR (p=0.79), and sub-maximal energy expenditure also did not change after acute HDTBR (p=0.98). These results indicate that acute HDTBR has little to no effect on energy expenditure. More research needs to be done to determine if microgravity has an effect on energy expenditure in either the short or long term.