Reproducibility of NIRS Oxidative Capacity Measurements in the Vastus Lateralis and Medial Hamstring Muscles

Abstract

Oxidative capacity within selected muscles can be measured non‐invasively using Near Infrared Spectroscopy (NIRS) by employing a series of transient arterial occlusion cuffs after a metabolic stimulus. Traditionally, this protocol involves voluntary contraction of a single limb followed by up to 22 transient ischemic occlusions per measurement. Our lab has adapted an established protocol 1 to develop a novel protocol that allows for an increased number of measurements using fewer (i.e. 6) ischemic occlusions combined with surface electrical stimulation (E‐stim) in both limbs simultaneously. However, reproducibility has not yet been established with this protocol.PURPOSETo determine the within‐day and between‐day reproducibility of this protocol in both the vastus lateralis and medial hamstring muscles.METHODSThe protocol involved 2 NIRS probes placed over the vastus lateralis (VL) muscles or the medial hamstring (MH) muscles in healthy adults to sense changes in muscle oxygenation. E‐stim pads were placed adjacent to the NIRS probe and were used to increase metabolic rate (>3 fold) using a biphasic setting at 20 Hz, with an intensity (mV) that is within the participant’s tolerance. The mitochondrial oxidative capacity protocol involved 4 consecutive sets of 30 seconds of E‐stim followed by 6 x 5 sec cuff inflation/5 sec cuff deflation cycles using upper thigh rapid inflation cuffs. Analysis consisted of calculating oxygenation recovery rate constants (k) for each muscle (i.e., 4 repeated measurements per muscle, per limb) using a customized software program. Coefficient of variation (CV) and intraclass correlation coefficients [ICC(2,k)] were used to assess reproducibility.RESULTSVariability of within‐day repeated tests (CV) averaged 3.8% (0.9%–6.7%) in the VL (n=12) with an average rate constant (min−1) of 1.96 +/− 0.07 and 4.9% (1.0%–14.1%) in the MH (n=10) with an average rate constant (min−1) of 2.05 +/− 0.11. Variability of between‐day repeated tests averaged 11.7% (8.7% – 14.8%) in the VL (n=4) and 10.4% (7.5% – 12.0%) in the MH (n=4). [ICC(2,k)] was calculated as 0.98, 95% CI [0.95, 0.99] for the VL and 0.93, 95% CI [0.81, 0.98] for the MH muscles.CONCLUSIONThese results suggest the proposed protocol demonstrates good to excellent reproducibility in both muscles, with a higher rate associated with the VL. These outcomes provide investigators with an efficient alternative for measuring muscle oxidative capacity non‐invasively in the vastus lateralis and medial hamstring muscles.Support or Funding InformationCenter for Orthopedic Research and Translational Science, Penn State College of MedicineExperimental setup of bilateral NIRS oxidative capacity protocolFigure 1