Increasing skeletal muscle carnitine availability does not alter the adaptations to high-intensity interval training

Area of Science:

• Exercise Physiology
• Nutritional Biochemistry
• Sports Science

Background:

• Skeletal muscle carnitine availability influences energy metabolism during exercise.
• Elevating muscle carnitine may enhance acetyl-group buffering capacity.
• The impact of increased carnitine on adaptations to high-intensity interval training (HIIT) is not fully understood.

Purpose of the Study:

• To investigate if augmenting muscle carnitine affects metabolic and physiological adaptations to 24 weeks of HIIT.
• To determine if increased carnitine alters acetyl-group buffering during intense exercise.
• To compare performance and metabolic responses between carbohydrate (CON) and l-carnitine+carbohydrate (CARN) groups post-HIIT.

Main Methods:

• Twenty-one healthy males performed two intense cycling bouts before and after 24 weeks of HIIT.
• Participants consumed either CON or 3g l-carnitine twice daily.
• Muscle metabolites (phosphocreatine, glycogen, lactate, acetylcarnitine) and performance (VO2max, Wattmax) were measured.

Main Results:

• HIIT increased VO2max, Wattmax, and work output similarly in both CON and CARN groups.
• Muscle carnitine supplementation increased resting and pre-exercise free carnitine levels.
• No significant differences were observed in PCr degradation, glycogenolysis, lactate accumulation, or PDC activation between groups post-HIIT.

Conclusions:

• Increased reliance on non-mitochondrial ATP synthesis during intense exercise is associated with carnitine acetylation.
• Augmenting muscle carnitine during 24 weeks of HIIT did not alter this metabolic response.
• Carnitine supplementation did not enhance muscle metabolic adaptations or performance gains beyond those achieved with HIIT alone.