Variability of triacylglycerol content in human skeletal muscle biopsy samples

The variability of the traicylglycerol store in human skeletal muscle (TG(m)) was examined using the needle biopsy technique. In 13 subjects, three biopsies were sampled from the vastus lateralis muscle of one leg at rest and after 90 min of cycling at 65% of maximal O-2 uptake on one or two occasions. Visible fat and blood were removed before the samples were frozen, and remaining blood, connective tissue, and fat were removed from freeze-dried fiber bundles. TG(m) content was measured in tow aliquots of powdered muscle from each biopsy. Within-biopsy variability was low at 6%. Despite precautions, many biopsies from inactive subjects were contaminated with adipose tissue. The TG(m) between-biopsy coefficient of variation (CV) was 23.5 +/- 14.6% (SD, n = 24) for rest and exercise time points where three noncontaminated biopsies existed. The between-biopsy variability at rest (19.8 +/- 7.9%, n = 10) was not significantly different from that at exercise (26.1 +/- 17.4%, n = 14). The muscle glycogen between-biopsy CV for rest and exercise time points was 10.0 +/- 10.3%. The resting TG(m) content was 26.3 +/- 4.3 mmol/kg dry muscle, and the net utilization during the 90 min of exercise was less than the between-biopsy variability. It is concluded that the TG(m) store measured in repeated biopsies of human skeletal muscle is variable, with a CV of 20-26%. Therefore, because of this high variability, only changes greater than similar to 24% of resting TG(m) content may be considered meaningful.