Subcellular localization- and fibre type-dependent utilization of muscle glycogen during heavy resistance exercise in elite power and Olympic weightlifters

Rune Hokken, Simon Laugesen, Per Aagaard, Charlotte Suetta, Ulrik Frandsen, Niels Ørtenblad, Joachim Nielsen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Aim: Glycogen particles are found in different subcellular localizations, which are utilized heterogeneously in different fibre types during endurance exercise. Although resistance exercise typically involves only a moderate use of mixed muscle glycogen, the hypothesis of the present study was that high-volume heavy-load resistance exercise would mediate a pattern of substantial glycogen depletion in specific subcellular localizations and fibre types. Methods: 10 male elite weightlifters performed resistance exercise consisting of four sets of five (4 × 5) repetitions at 75% of 1RM back squats, 4 × 5 at 75% of 1RM deadlifts and 4 × 12 at 65% of 1RM rear foot elevated split squats. Muscle biopsies (vastus lateralis) were obtained before and after the exercise session. The volumetric content of intermyofibrillar (between myofibrils), intramyofibrillar (within myofibrils) and subsarcolemmal glycogen was assessed by transmission electron microscopy. Results: After exercise, biochemically determined muscle glycogen decreased by 38 (31:45)%. Location-specific glycogen analyses revealed in type 1 fibres a large decrement in intermyofibrillar glycogen, but no or only minor changes in intramyofibrillar or subsarcolemmal glycogen. In type 2 fibres, large decrements in glycogen were observed in all subcellular localizations. Notably, a substantial fraction of the type 2 fibres demonstrated near-depleted levels of intramyofibrillar glycogen after the exercise session. Conclusion: Heavy resistance exercise mediates a substantial utilization of glycogen from all three subcellular localization in type 2 fibres, while mostly taxing intermyofibrillar glycogen stores in type 1 fibres. Thus, a better understanding of the impact of resistance training on myocellular metabolism and performance requires a focus on compartmentalized glycogen utilization.

Original languageEnglish
Article numbere13561
JournalActa Physiologica
Volume231
Issue number2
ISSN1748-1708
DOIs
Publication statusPublished - Feb 2021

Keywords

  • fibre types
  • glycogen
  • resistance exercise
  • skeletal muscle fibres
  • transmission electron microscopy

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