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Dissertation Defense: High Levels of Total Energy Expenditure in Ultra-Endurance Athletes: Is There Evidence for Constraint?

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K Howard

Dissertation Defense: High Levels of Total Energy Expenditure in Ultra-Endurance Athletes: Is There Evidence for Constraint?

Kristen Howard

Graduate Student, Translational Biology, Medicine, and Health
Graduate Research Assistant, Davy Lab
April 24, 2024, at 10 a.m.
Room 332, Wallace Hall

About this Dissertation

The benefits of an active lifestyle are undisputed, yet our understanding of the contribution of physical activity (PA) to the daily energy budget is limited. The prevailing model of a linear relationship between PA and total energy expenditure (TEE) has been challenged by models that predict an upper limit of TEE (constrained) or a compensatory decrease elsewhere in the budget in response to increased PA (compensated).
The purpose of this study was to determine the equation of best fit between PA and TEE using linear and non-linear modeling in the light of existing models. Secondarily, we sought to explore relationships between PA and postulated means of behavioral (time sedentary) and physiologic (immune, reproductive and basic metabolic) compensation.

We measured TEE in 57 healthy weight stable adults (18 to 58 yrs., F = 28) from sedentary to ultra-endurance trained runners (0 to 78 mi/wk.) using the doubly labeled water technique and PA and sedentary time using a waist mounted triaxial accelerometer during the same 14-day period. We obtained fasting serum (albumin, cortisol, TNFα, C-reactive protein, free testosterone, TSH and T3), plasma (leptin) and whole blood (WBC with differential) concentrations.
Using linear and non-linear modeling, we observed a positive linear relationship between PA (Vector Magnitude Counts per Minute ) and TEE (R2=0.313, Y = 1.427*X + 1930
& adjusted for fat free mass (FFM) R2=0.363, Y = 1.151*X + 2155 ). We identified no association between PA and RMR ( R2=0.015 & adjusted for FFM R2=0.010). In addition, we observed an association between higher PA and lower % time sedentary (R2=0.723). Although inconsistent, there was a general trend for higher PA to be associated with lower immune and reproductive biomarkers.
These findings support a conventional linear model though we cannot exclude energetic trade off associated with immune function or reproductive function. Intervention studies will be needed to further address this issue.

More About the Candidate and Project


Virginia Tech, Translational Biology, Medicine, and Health, Ph.D. Candidate

Pacific Lutheran University, MSN Family Nurse Practitioner

Washington State University, B.S., Psychology


Graduate Research Assistant, Davy Lab


Kevin Davy, Ph.D., Professor, Human Nutrition, Foods, and Exercise

Committee Members

  • Brenda Davy, Ph.D., Professor, Human Nutrition, Foods, and Exercise
  • Ignacio Moore, Ph.D., Professor, Department of Biological Sciences
  • Alexandra DiFeliceantonio, Ph.D., Assistant Professor, Fralin Biomedical Research Institute at VTC
  • John Speakman, Ph.D., Chair, University of Aberdeen


Howard, K. R. , Prado-Nóvoa, O., Zorrilla-Revilla, G., Laskaridou, E., Reid, G. R., Marinik, E., Stamatiou, M., Hambly, C., Davy, B. M., Speakman, J. R., & Davy, K. P. (2024). Physical Activity and Total Energy Expenditure: Is There Evidence for Constraint in Endurance Athletes? Manuscript in preparation

Davy, B. M., Howard, K. R., & Davy, K. P. (2024). Chapter 12: Physical Activity Interventions. In H. A. Raynor & L. M. Gigliotti (Eds.), Health Professional’s Guide to Treatment of Overweight and Obesity (pp. 195–219). Academy of Nutrition and Dietetics .

Prado-Nóvoa, O., Howard, K. R., Laskaridou, E., Reid., G., Marinik, E., Speakman, J. R., Davy, K. P. Validation of classic and new predictive equations to estimate the RMR across different activity levels.

Howard, K.R. (2007) Childhood Overweight: Parental Perceptions and Readiness for Change. The Journal of School Nursing, 23(2), pp 73-79.

Invited speaker : Higher Physical Activity Correlates With Lower White Blood Cell Count but not Resting Metabolic Rate, Howard, K. R., Prado-Nóvoa, O., Laskaridou, E., Marinik, E., Reid, G, Speakman, J. R., Davy, B.M.,Davy, K. P. Obesity Week, Annual Conference of the Obesity Society (TOS), Dallas, TX, October 14 - 17th, 2023.

Invited Lecturer: Clinical Patient Care Status Post Bariatric Surgery, Howard, K.R., Virginia Tech Human Nutrition Food and Exercise Department combined graduate/ undergraduate course: HNFE 4126/5126 Medical Nutrition Therapy – Primary faculty: Valisa Hedrick, PhD, RDN, March 28, 2023, Blacksburg, VA

Poster Presentation: Does exercise make us more sedentary? Insights from ultra-endurance runners. Howard, K. R., Prado-Nóvoa, O., Laskaridou, E., Marinik, E., Reid, G, Speakman, J. R., Davy, K. P. Annual Meeting of the American College of Sports Medicine (ACSM), Denver, Colorado May 30 - June 2, 2023

Poster presentation: Energy expenditure: What’s my Limit?. Howard, K.R., Prado-Novoa, O., Davy, B.M. Speakman, J.R., Davy, K.P., Fall Open House Translational Biology Medicine and Health interdisciplinary program, Virginia Tech, Blacksburg, VA, November 11, 2022.

Invited speaker: Energy Expenditure Across a Spectrum of Physical Activity: Physical Activity and Sedentary Behavior, Howard, K.R., University of Aberdeen Energetics Research Group, Aberdeen UK and Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences Center for Energy Metabolism and Reproduction Shenzhen laboratory of Metabolic Health, Shenzhen China joint meeting. October 31, 2022.

Guest Lecturer: BPD and Duodenal Switch: A Nurse’s Guide to Malabsorption, Howard, K.R., American Society for Metabolic and Bariatric Surgery (ASMBS): Certified Bariatric Nurse Review Course. Obesity Week 2017, Washington D.C., November, October 30, 2017

  • Energetics in Anthropology Work Shop, Duke University May 1-4, Travel Grant