A letter was submitted by Ferrari, Quaresima, and Fantini with regard to our recent article (2). Although recognizing the interest of our work in the field of sport sciences, the letter points out imprecision in the Methods section. Furthermore, the letter raises vague questions about some of the conclusions drawn by our study. Overall, the main aim of the letter seems to be the confirmation of the recommendations summarized by Ferrari et al. (4) in their recent review on the use of near-infrared spectroscopy in muscle physiology.
Two errors, for which we apologize, actually appeared in the online publish-ahead-of-print version of our article (i.e., incorrect definition of the instrument type used in the study and erroneous deoxyhemoglobin concentration units). Both mistakes have since been corrected in the published hardcopy article.
A third issue was raised by the letter on the basis of an incorrect interpretation of our (perhaps not well-worded) phrase: “The main limitation of a NIRS-based approach is related to the inability to evaluate the underlying muscle when a large fat layer (>30 mm) is present.” We indeed agree that the typical depth sensitivity of NIRS equals half of the distance between the light emitter and the light receiver (that in our case would be approximately 1.5 cm). This figure corresponds to a measure of 30 mm of the double skinfold as measured by plicometry, as stated in our study.
In addition, the letter infers that some conclusions drawn by our study may be hampered by the lack of the inclusion in our analysis of some NIRS indexes (muscle percent hemoglobin saturation and total hemoglobin). In doing so, the letter cites, as an example of “good practice,” an article (8) that indeed reports all NIRS parameters yet does not display any “novel comparison” or any enlightening physiological interpretation from the combined analysis of all indexes.
We are not NIRS experts, and some technical issues raise a very mild enthusiasm for us. On the contrary, we are simple users of this technology (1,3) that we find very useful thanks to its noninvasiveness, high sampling frequency, and low signal-to-noise ratio.
Like others (5–7), we have decided to use deoxygenated hemoglobin concentration on the basis of the assumption that it represents an index of the balance between oxygen delivery and oxygen utilization within a small portion of tissue that is assumed representative of an entire muscle.
We have nothing against the idea that NIRS studies report deoxygenated and oxygenated hemoglobin as well as percent hemoglobin saturation if such a comprehensive analysis will increase our insight into the underlying physiology and/or if and when this will become a recognized standard.
University of Verona
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2. Bellotti C, Calabria E, Capelli C, Pogliaghi S. Determination of maximal lactate steady state in healthy adults: can NIRS help? Med Sci Sports Exerc. 2013; 45 (6):1208– .
3. De Roia G, Pogliaghi S, Adami A, Papadopoulou C, Capelli C. Effects of priming exercise on the speed of adjustment of muscle oxidative metabolism at the onset of moderate-intensity step transitions in older adults. Am J Physiol Regul Integr Comp Physiol. 2012; 302 (10): R1158–66.
4. Ferrari M, Muthalib M, Quaresima V. The use of near-infrared spectroscopy in understanding skeletal muscle physiology: recent developments. Philos Transact A Math Phys Eng Sci. 2011; 369 (1955): 4577–90.
5. Ferreira LF, Koga S, Barstow TJ. Dynamics of noninvasively estimated microvascular O2
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6. Koga S, Poole DC, Fukuoka Y, et al. Methodological validation of the dynamic heterogeneity of muscle deoxygenation within the quadriceps during cycle exercise. Am J Physiol Regul Integr Comp Physiol. 2011; 301: R534–41.
7. Poole DC, Barstow TJ, McDonough AP, Jones AM. Control of oxygen uptake during exercise. Med Sci Sports Exerc. 2008; 40 (3): 462–74.
8. Wittekind A, Cooper CE, Elwell CE, Leung TS, Beneke R. Warm-up effects on muscle oxygenation, metabolism and sprint cycling performance. Eur J Appl Physiol. 2012; 112 (8): 3129–39.