Reliability of near-infrared spectroscopy for measuring intermittent handgrip contractions in sport climbers

Abstract

The use of near infra-red spectroscopy (NIRS) to investigate muscle oxygenation changes during physical tasks such as rock climbing has rapidly increased within recent years; yet there is no known measure of reliability. The current study aimed to determine inter-session reliability and minimal detectable change (MDC) of continuous wave NIRS parameters during intermittent handgrip contractions in rock climbers. Thirty-two sport climbers were tested for exhaustive intermittent handgrip exercise (8s contraction – 2s relief) at 60 % of maximal voluntary contraction on three separate days. During each visit, continuous wave NIRS was used to determine tissue saturation index (TSI) as the measure of tissue oxygenation in the flexor digitorum profundus. To assess the inter-session reliability, the intra-class correlation (ICC), standard error of measurement (SEM), coefficient of variation (CV), and minimal (MDC) were used. Mean de-oxygenation during the contractions provided reliable results (∆ TSI; first trial -8.9 ± 2.9%, second trial -8.8 ± 2.7%, and third trial -8.4 ± 2.6%; ICC = 0.692; SEM = 1.5%; CV=17.2%; MDC = 4.2%). Mean muscle re-oxygenation during the relief periods was similarly reliable (∆ TSI; first trial 9.0 ± 3.1%, second trial 8.8 ± 2.9%, and third trial 8.5 ± 2.7%; ICC = 0.672; SEM = 1.7%; CV=19.0%, MDC = 4.7%). As such, continuous wave NIRS provides a reliable measure of de-oxygenation and re-oxygenation during intermittent contractions to failure in the forearm flexors of rock climbers. Differences exceeding ~4.5% for ∆TSI during contraction and relief periods should be considered meaningful