Lipid storage changes in human skeletal muscle during detraining

Area of Science:

• Exercise physiology
• Muscle metabolism
• Lipid biochemistry

Background:

• Exercise training enhances intramuscular triglyceride (IMTG) content in both trained and untrained limbs.
• Understanding lipid dynamics during detraining is crucial for maintaining training adaptations.

Purpose of the Study:

• To investigate the changes in intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) in both trained and untrained legs during a 4-week detraining period.
• To assess the impact of detraining on muscle adaptations following 6 weeks of strength training.

Main Methods:

• Eight young men underwent unilateral leg strength training for 6 weeks, with the contralateral leg serving as a control.
• Magnetic resonance imaging (MRI) and proton magnetic resonance spectroscopy ((1)H-MRS) were used to measure muscle cross-sectional area (CSA), IMCL, EMCL, and total creatine levels.
• Measurements were taken before training, 3 days post-training, and 28 days post-training.

Main Results:

• Muscle CSA increased in both legs by day 3 and remained elevated at day 28 post-training.
• IMCL levels rose in both legs by day 3 but decreased in the untrained leg by day 28.
• EMCL levels showed no significant change by day 3, but increased in the trained leg and decreased in the untrained leg by day 28.
• Total creatine levels remained unchanged throughout the study.

Conclusions:

• Detraining leads to a reduction in IMCL and EMCL stores, particularly in the previously untrained leg.
• These findings suggest an 'ectopic' influence on tissue lipid storage, driven by differing metabolic demands within the same individual.