Intramuscular lipids represent a potentially important energy source in the contraction of human skeletal muscle. Recently, several investigators have developed the technology to noninvasively measure intracellular lipids in human muscle by Proton NMR spectroscopy (1H-MRS).
The aim of this study was to evaluate intra- (IMCL) and extramyocellular lipids (EMCL) in skeletal muscle in sprint and endurance-trained athletes.
Four sprint trained athletes (SPR:n = 4, Age = 21.5 ± 0.5, BMI = 21.4 ± 0.4) and six endurance-trained athletes (END:n = 6, Age = 21.0 ± 0.5, BMI = 20.7 ± 0.3) and seven healthy controls (CON:n = 7, Age = 21.0 ± 0.5, BMI = 20.1 ± 0.5) were studied. All subjects were collegiate male students who were matched in age and BMI. 1H-MR spectra were acquired from the tibialis anterior (TA), soleus (SOL) and medial gastrocnemius (MG) muscles. IMCL and EMCL were quantified relative to muscle water by using units of mmol/kg. Finally, the data were converted into units of mmol/kg wet wt.
IMCL content in TA and MG in END was higher compared with that in TA and MG in SPR and CON (p < 0.01). IMCL content in SPR was slightly lower in TA, MG and SOL than that in CON (p = not significant). There were no differences in IMCL in SOL among the three groups. The IMCL content in the three muscles may be different in the descending order of END > CON > SPR. There were no differences in EMCL content of each muscle among the three groups. The area of subcutaneous fat on lower leg in END was lower than that in CON(p < 0.01).
These results suggest that stored IMCL on skeletal muscle, as assessed by 1H-MRS, may reflect adaptation to endurance training and aerobic capacity.