Adipose tissue thickness affects in vivo quantitative near-IR spectroscopyin human skeletal muscle

The influence of adipose tissue thickness (ATT) on near-IR spectroscopy (NI RS) measurements in vivo was studied in the human flexor digitorum superfic ialis muscle at rest and during sustained isometric handgrip exercise. NIRS was used for the quantitative measurement of muscle O-2 consumption (mV(O2 )) and forearm blood flow (FBF) in 78 healthy subjects. Skinfold thickness ranged from 1.4 to 8.9 mm within the group. Resting mV(O2) was 0.11 +/-0.04 ml of O-2 (.) min(-1) (.) 100 g(-1), and FBF was 1.28 +/- 0.82 ml (.) min( -1) (.) 100 ml(-1). There was a negative correlation (r = -0.70, P less tha n or equal to 0.01), indicating a decrease in mV(O2) with increasing ATT. m V(O2) in the 10 leanest subjects appeared to be twice as high as that in th e 10 subjects with the highest ATT. A poor correlation (r = 0.29, P less th an or equal to 0.01) was found between ATT and FBF. The gender difference t hat we found for mV(O2) was due to the difference in ATT between female and male subjects. No correlation was found between maximum voluntary contract ion and mV(O2), nor between maximum voluntary contraction and ATT, indicati ng that the contraction force did not confound our results. These results s how that ATT has a substantial confounding influence on in vivo NIRS measur ements, and that it is essential to incorporate this factor into future NIR S muscle studies in order to justify comparisons between different groups. To facilitate such comparisons, upper and lower boundaries for normal value s of mV(O2) and FBF in relation to ATT are presented.