Effekt av glykogentillgänglighet på muskelnedbrytning med fokus på ubiquitin proteasome systemet

Little is known about glycogen availability and resistance exercise adaptations. Autophagy is a process responsible for degrading and recycling cellular proteins under conditions of energetic stress and low nutrient availability. Activation of autophagy is mediated by the energy sensing protein AMPK which is activated by high-intensity exercise and low glycogen availability. Performing resistance exercise with low glycogen levels may increase autophagy activation. As a degradative process, potent activation of autophagy may have negative effects on muscle protein balance.

Preliminary data show that performance of resistance exercise with low glycogen availability activates the autophagy pathway. Interestingly, preliminary data also indicate that an additional proteolytic pathway called the ubiquitin proteasome system (UPS) may also be upregulated by low glycogen availability. Whether or not this is the case needs to be determined experimentally.

If true, low glycogen availability may upregulate multiple proteolytic pathways which may infer even more detrimental effects on muscle protein balance and training adaptations than originally hypothesized. However, no previous studies have examined the influence of low glycogen availability on UPS-activity.

One way to mitigate the potentially negative effects on muscle protein breakdown may be through intake of essential amino acids. However, it is currently unknown if amino acids can inhibit UPS-activity.

Thus, the main aims of this project are 1) to investigate if resistance exercise with low glycogen increases UPS activity in addition to autophagy and 2) if this increase is mitigated by amino acid intake.

Twenty men and women have performed resistance exercise with either high or low muscle glycogen and with or without amino acid intake during recovery and muscle samples collected before and after exercise from both legs will be analyzed.

The UPS plays a central role in skeletal muscle remodeling and exercise adaptations, but the role of glycogen availability in this context has never been studied before. The project is highly novel and the research question is very relevant to athletes given the increasing popularity of low-carbohydrate diets and the idea that exercising with low glycogen levels is generally beneficial.

The outcome of the project is likely to influence nutritional recommendations for optimal exercise adaptations, potentially in sex-specific manner.

Syftet med denna studie är att undersöka muskelanpassningar efter styrketräning med höga och låga glykogennivåer, samt med och utan intag av essentiella aminosyror (EAA) hos män och kvinnor. Muskelprover har tagits innan och efter styrketräning och analyserats för aktivering av muskelnedbrytning (autofagi) och proteinsyntes. Preliminära data visar att styrketräning med låga glykogennivåer ger en kraftig aktivering av autofagi, men ger också indikationer på att andra muskelnedbrytande processer också kan vara kraftigt uppreglerade. En sådan process är ubiquitin proteasome systemet (UPS), vars aktivitet kommer att mätas som ett komplement till autofagi. Om UPS är uppreglerat, så kan träning med låga glykogennivåer ge upphov till mycket kraftigare muskelnedbrytning än vad man trott tidigare.