NIRS-derived skeletal muscle oxidative capacity is correlated with aerobic fitness and independent of sex

Abstract

Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated to indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇O2max), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (mean±SD: 21.9±4.6s) and MG (22.5±6.1s) were similar but unrelated (r2=0.03, p=0.39). Skeletal muscle oxidative capacity for the VL, but not the MG (p>0.05 for all variables), was significantly correlated with V̇O2max (r2=0.24; p=0.01), PPO (r2=0.23; p=0.01), LT (r2=0.23; p=0.01), GET (r2=0.23; p=0.01), and RCP (r2=0.27; p=0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity (p>0.05). Females (54.9±4.5mL/kg LBM/min) and males (56.0±6.2mL/kg LBM/min), matched for V̇O2max (p=0.62), had similar NIRS-derived oxidative capacities for VL (20.7±4.4s vs. 23.2±4.6s; p=0.18) and MG (24.4±6.8s vs. 20.5±4.8; p=0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans.

Muscle mitochondrial capacity in high‐ and low‐fitness females using near‐infrared spectroscopy

“…For instance, males showed a larger stimulation of mitochondrial biogenesis than females upon sprint interval training (Scalzo et al, 2014). Indeed, straightforward extrapolation is warned, as a recent NIRS study showed no correlation between mitochondrial capacity in the gastrocnemius muscle and O 2 peak when males and females were combined (Beever et al, 2020), which contrasted our previous findings in males only (Lagerwaard et al, 2019).…”

“…In the current population, average ATT on the gastrocnemius muscle was 8.1 mm, which was expectedly higher than previously observed in males (5.9 mm) (Lagerwaard et al, 2019). Not many studies have measured in these ranges of ATT in females (Adami et al, 2017; van Beekvelt et al, 2001; Beever et al, 2020; Brizendine et al, 2013; Southern et al, 2014). Yet, studies that did measure close to our range in ATT either reported difficulties (Adami et al, 2017), adapted the penetration depth according to the ATT per individual (Brizendine et al, 2013; Ryan, Southern, et al, 2013) or used a frequency‐domain NIRS device that can better quantify the degree of light scattering (Ryan et al, 2014).…”

“…A correlation between mitochondrial capacity of skeletal muscle tissue and O 2 peak has been established before. For instance, several NIRS studies describe a correlation between mO 2 recovery and O 2 peak, in particular in the gastrocnemius muscle of males (Lagerwaard et al, 2019), and in the vastus lateralis of mixed populations (Beever et al, 2020; Brizendine et al, 2013). Such a correlation has also been observed in a female population, using 31 P‐MRS, showing the rate of PCr resynthesis in the gastrocnemius muscle was correlated to O 2 peak (Larson‐Meyer et al, 2000).…”

The association between lactate and muscle aerobic substrate oxidation: Is lactate an early marker for metabolic disease in healthy subjects?

“…The relationship between NIRS and lactate was of particular interest as it has been shown that NIRS can serve as an in vivo marker of mitochondrial capacity (Ryan et al, 2014). Recently, NIRS has been shown to correlate with aerobic fitness (Beever et al, 2020) although we saw no relationship with VO 2 peak and lactate in our cohort. However, exercise time to exhaustion was negatively related with fasting plasma lactate concentration and was significant in our regression model.…”

Men exhibit faster skeletal muscle tissue desaturation than women before and after a fatiguing handgrip

“…It has been reported, however, that females exhibited 19% and 22% faster peripheral O 2 extraction and desaturation, respectfully, than males during moderate walking exercise tests (Beltrame et al 2017 ). It has been hypothesized, however, that aerobic fitness and adipose tissue thickness likely provoke differences in NIRS-derived outcomes between males and females (Van Beekvelt et al 2001 ; Niemeijer et al 2017 ; Mantooth et al 2018 ; Barstow 2019 ; Ansdell et al 2019 ; Beever et al 2020 ). For example, Beever et al ( 2020 ) demonstrated that NIRS-derived muscle oxidative capacity was similar between males and females only when matched for relative VO 2max (mL O 2 kg lean body mass −1 min −1 ).…”