Long- and medium-chain fatty acid oxidation is increased in exercise-trained human skeletal muscle.
Level 4 - case-series / case-control
Cross-sectional comparative study comparing endurance-trained and sedentary human subjects.
PubMed 11912554 · doi:10.1053/meta.2002.31326
What was done
Muscle biopsies were taken from 23 young volunteers (approximately 24 years of age; 13 sedentary and 10 endurance-trained). Oxidation was assessed in muscle homogenates by measuring 14CO2 production from radiolabeled long-chain fatty acids (palmitate) and medium-chain fatty acids (octanoate). Activities of carnitine palmitoyltransferase I (CPT1), carnitine octanoyl transferase (COT), and citrate synthase (CS) were also measured.
What was found
Long-chain fatty acid (palmitate) oxidation was significantly higher (P < .05) by approximately 34% in trained versus sedentary subjects (26.9 +/- 3.0 vs 17.8 +/- 1.3 nmol CO2/g x h). Medium-chain fatty acid (octanoate) oxidation was also significantly higher (P < .05) by approximately 26% in trained subjects (21.7 +/- 2.1 vs 16.1 +/- 2.0 nmol CO2/g x h). CPT1 and CS activities were both significantly higher by approximately 25% (P < .05) in endurance-trained individuals, while COT activity showed no significant difference.
Why it matters
These findings suggest that endurance training enhances the skeletal muscle capacity to oxidize both long- and medium-chain fatty acids, mediated by adaptations at CPT1 and downstream mitochondrial processes rather than carnitine-mediated medium-chain transport.
Limits
The study is limited by a small sample size (n = 23) and a cross-sectional design that cannot establish longitudinal within-subject training effects. Measurements were conducted ex vivo in muscle homogenates, which may not capture in vivo metabolic regulation during active exercise.
Cited by
- supports Both moderate-intensity and vigorous-intensity exercise increase carnitine palmitoyltransferase (CPT) enzyme capacity in muscle.