Matthieu Clauss is a PhD candidate at the Department of Physical Performance. On September 16, 2025, 10:15—16:00 he will defend his dissertation titled Investigating the effects of endurance exercise on protein metabolism, with a specific focus on urinary nitrogen excretion at the Norwegian School of Sport Sciences, Auditorium Innsikt.
About the study
This doctoral thesis includes four research articles, a systematic review with statistical analysis of previously published research data, and three intervention studies, aiming to investigate the effects of endurance exercise on protein metabolism, with a specific focus on nitrogen excretion in urine.
In Paper I, protein oxidation and the contribution of protein to energy expenditure during endurance training were examined using data from 30 previously published studies.
The main finding is that endurance training consistently increased protein oxidation by 1.02 ± 0.06 mg∙kg-1∙min-1 during the activity, from a baseline of 0.81 ± 0.38 mg∙kg-1∙min-1 measured at rest.
In Paper II, seven well-trained male cyclists cycled to exhaustion (~2.5 hours), while ingesting a placebo drink then the next time a carbohydrate drink. Carbohydrate intake maintained carbohydrate availability, resulting in significantly higher total carbohydrate oxidation and sustained plasma glucose concentrations.
Performance during a time trial the following day improved by approximately 1 minute (2.4%) after carbohydrate intake. Nitrogen and 3-methylhistidine excretion in urine did not differ significantly between the trials during the study period.
Additionally, plasma concentrations of tyrosine and phenylalanine increased significantly after placebo intake but not after carbohydrate intake.
Therefore, carbohydrate intake during standardized training mitigated performance decline the following day by reducing metabolic stress and preventing fatigue. Furthermore, some parameters indicated reduced protein breakdown, which may help preserve muscle function.
In Paper III, in a randomized, balanced crossover study, fifteen young, healthy, moderately to well-trained participants (4 women, 11 men) alternated between a day of 5 hours of exercise and a day without exercise.
Nitrogen and 3-methylhistidine excretion in urine did not differ significantly between the two trials. However, sweat volume increased significantly on the exercise day. By estimating nitrogen excretion in sweat, total nitrogen excretion increased with exercise.
In Paper IV, in a double-blind, randomized, balanced crossover study, fourteen young, healthy, moderately to well-trained participants (6 women, 8 men) consumed one of two isoenergetic test drinks containing either 1.2 g·kg-1 protein or carbohydrate alone in the morning after an overnight fast.
Participants consumed the other isoenergetic drink during the next session. After intake of the drinks, plasma concentrations of insulin, GLP-1, and GIP increased significantly with both protein and carbohydrate alone.
Nitrogen excretion in urine was significantly higher with protein alone over the 24 hours after intake of the drinks. This increase was particularly noticeable between two to eight hours post-intake but remained elevated even up to 24 hours later.
Practical significance of this work for the field and for the general public:
- Endurance exercise significantly increases protein oxidation, especially at high exercise intensity. Therefore, dietary adjustments are crucial when participating in endurance activities.
- Ingesting carbohydrates during prolonged exhaustive exercise can help maintain performance in subsequent activities.
- Protein metabolism is a long-lasting and adaptable process, emphasizing the importance for practitioners to adopt a long-term perspective
Read the thesis here
Committee
Chair
- Olivier Seynes, Professor, Norwegian School of Sport Sciences
Opponents
- Professor Emerita Eva Blomstrand, The Swedish School of Sport and Health Sciences (GIH), Sweden
- Professor Mark E. T. Willems, University of Chichester, United Kingdom
Supervisor
- Main Supervisor: Professor Jørgen Jensen, Norwegian School of Sport Sciences
Program
- 10.15-11.00: Trial lecture: “Plant-based protein: Is there an application for exercise and recovery?”
- 13.00-16.00: Public defense of the thesis: Investigating the effects of endurance exercise on protein metabolism, with a specific focus on urinary nitrogen excretio
Practical info
The defense will be chaired by Rector Aage Radmann
The defense is open to everyone and will be streamed on NIH’s YouTube channel.
