Reliability and Validity of NIRS Mitochondrial Capacity Protocol in Human Skeletal Muscle

To establish reliability of a near‐infrared spectroscopy (NIRS) mitochondrial capacity protocol and assess validity using heating and cooling interventions. We recruited 13 young, healthy participants (men=8, women=5), who were asked to attend four visits. Two of the visits consisted of a protocol which included a series of blood pressure occlusions proximal to the NIRS probe and electrical stimulation to the vastus lateralis (thigh), gastrocnemius (calf) and flexor carpi radialis (forearm), to establish reliability. Participants returned 24 hours after visit 2 to participate in one of two treatments, heating (40° Celsius) or cooling (15.6° Celsius) of the thigh, calf and forearm muscle also using the same protocol as above. The order of the visits was counterbalanced. The between day reliability coefficient of variation in the forearm (CV) was 3% and the time constants (TC) average was 42.5 ± 8.9 seconds (s). The within day CV in the forearm was 4.5%, calf 5.5% and thigh was 4.6% (n=13). The within day cold treatment testing CV for reliability in the forearm was 5.9%, calf 4.3% and thigh 4.4% and for the within day hot treatment testing CV in the forearm was 6.4%, calf 5.3% and thigh 4.6%. In the forearm (41.5 ± 2.4 s) and calf (51.6 ± 2.0 s), cold increased the mitochondrial capacity time constant however heat caused a decrease (p<0.05). Similarly, in the thigh (27.2 ± 1.2 s), heat decreased mitochondrial capacity (p<0.05), but cold was not different from control. These results suggest that the NIRS mitochondrial capacity has good within and between day reliability in all three muscles. Mitochondrial capacity time constants are increased by cold and decreased by heating in the forearm and calf, which suggests good construct validity. This study suggests the possibility of the involvement of NIRS in a clinical setting to monitor muscle health as well as utilize hot and cold treatment results to better understand the properties of the muscle's mitochondrial capacity. Support or Funding Information This work was supported and funded by The School of Kinesiology at Auburn University. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .