Abstract
A linear relationship between skeletal muscle venous ([Formula: see text]) and oxygenated (ΔHbMbO(2,N)) or deoxygenated (ΔHHbMb(N)) near-infrared spectroscopy (NIRS) signals suggest a main hemoglobin (Hb) contribution to the NIRS signal. However, experimental, and computational evidence supports a significant contribution of myoglobin (Mb) to the NIRS. Venous and NIRS measurements from a canine model of muscle oxidative metabolism (Sun Y, Ferguson BS, Rogatzki MJ, McDonald JR, Gladden LB. Med Sci Sports Exerc 48(10):2013-2020, 2016) were integrated into a computational model of muscle O(2) transport and utilization to evaluate whether the relationship between venous and NIRS oxygenation can be affected by a significant Mb contribution to the NIRS signals. The mathematical model predicted well the measure of the changes of [Formula: see text] and NIRS signals for different O(2) delivery conditions (blood flow, arterial O(2) content) in muscle at rest (T1, T2) and during contraction (T3). Furthermore, computational analysis indicates that for adequate O(2) delivery, Mb contribution to NIRS signals was significant (20%-30%) even in the presence of a linear [Formula: see text]-NIRS relationship; for a reduced O(2) delivery the nonlinearity of the [Formula: see text]-NIRS relationship was related to the Mb contribution (50%). In this case (T3), the deviation from linearity is observed when O(2) delivery is reduced from 1.3 to 0.7 L kg(-1)·min(-1) ([Formula: see text] < 10 mLO(2) 100 mL(-1)) and Mb saturation decreased from 85% to 40% corresponding to an increase of the Mb contribution to ΔHHbMb(N) from 15% to 50% and the contribution to ΔHbMbO(2,N) from 0% to 30%. In contrast to a common assumption, our model indicates that both NIRS signals (ΔHHbMb(N) and ΔHbMbO(2,N) are significantly affected by Hb and Mb oxygenation changes.NEW & NOTEWORTHY Within the near-infrared spectroscopy (NIRS) signal, the contribution from hemoglobin is indistinguishable from that of myoglobin. A computation analysis indicates that a linear relationship between muscle venous oxygen content and NIRS signals does not necessarily indicate a negligible myoglobin contribution to the NIRS signal. A reduced oxygen delivery increases the myoglobin contribution to the NIRS signal. The integrative approach proposed is a powerful way to assist in interpreting the elements from which the NIRS signals are derived.