Background: Near-infrared spectroscopy (NIRS) has been used to measure muscle mitochondrial capacity (mVO 2 max) as the recovery rate constant of muscle metabolism after exercise. The current method requires as many as 50 short ischemic occlusions to generate two recovery rate constants. Purpose: To determine the validity and repeatability of using a 6-occlusion protocol versus one with 22 occlusions to measure muscle mitochondrial capacity. The order effect of performing multiple Mito6 test was also evaluated. Method: In two independent data sets (bicep n = 7, forearm A n = 23), recovery curves were analyzed independently using both the 6 and 22 occlusion methods. A third data set (forearm B n = 16) was generated on the forearm muscles of healthy subjects using four 6-occlusion tests performed in succession. Recovery rate constants were generated using a MATLAB routine. Results: When calculated from the same data set, the recovery rate constants were not significantly different between the 22 occlusion and 6 occlusion methods for the bicep (1.43 ± 0.33 min −1 , 1.43 ± 0.35 min −1 , p = 0.81) and the forearm A (1.97 ± 0.40 min −1 , 1.97 ± 0.43 min −1 , p = 0.90). Equivalence testing showed that the mean difference was not different than zero and the 90% confidence intervals were within 5% of the average rate constant. This was true for the Mito6 and the Mito5 * approaches. Bland-Altman analysis showed a slope of 0.21 min −1 and an r of 0.045 for the bicep dataset and a slope of −0.01 min −1 and an r of 0.045 for the forearm A dataset. When performing the four 6-occlusion tests; recovery rate constants showed no order effects (1.50 ± 0.51 min −1 , 1.42 ± 0.54 min −1 , 1.26 ± 0.41 min −1 , 1.29 ± 0.47 min −1 , P > 0.05). Conclusion: The Mito6 analysis is a valid and repeatable approach to measure mitochondrial capacity. The Mito6 protocol used fewer ischemic occlusion periods and multiple tests could be performed in succession in less time, increasing the practicality of the NIRS mitochondrial capacity test. There were no order effects for the rate constants of four repeated 6-occlusion tests of mitochondrial capacity, supporting the use of multiple tests to improve accuracy.

Near Infrared Spectroscopy (NIRS) has been used to noninvasively measure muscle mitochondrial capacity. Previous protocols have required 2 tests and up to 50 cuff inflations.PURPOSEDevelop a new protocol for testing mitochondrial capacity that decreases the number of ischemic cuffs, increases comfort for participants, and improves curve fitting of the data, all while retaining reliability of the test.METHODSThe forearm flexor muscles of sixteen young, healthy individuals were tested (23 ± 4.1 years). A resting metabolism value was collected after 5 min of complete rest before and after the test. The test involved 4 sets of 6 ischemic cuff inflations, preceded by 30s of electrically induced twitch contractions. Analysis was performed on mitochondrial metabolic rates using a customized MATLAB program.RESULTSThe post‐test resting metabolism values were higher than the pre‐test resting values (−0.038 ± 0.02, −0.018 ± 0.01, optical density units P<0.01). There was no significant difference in the mitochondrial capacity for the four sets (1.50 ± 0.51, 1.42 ± 0.54, 1.26 ± 0.41, 1.29 ± 0.47, P=0.76).CONCLUSIONThe main finding of this study is that a test of mitochondrial capacity using four sets of 6 cuffs can be performed in less time (t ≈ 25 min) than two sets of 22 cuffs (t ≈ 45 min). While the use of a post‐test resting metabolism value did slightly lengthen the time needed to complete the study in relation to using the pre‐test value, this value appeared to be more accurate than using the pre‐test resting metabolism. The use of the post‐test resting values provided lower residuals and better agreement with previous data on the forearm muscles. Improved data collection can enhance the usefulness of NIRS based measurements of mitochondrial capacity.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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