Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity

PURPOSE

Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups.

METHODS

Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ([Formula: see text]O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA.

RESULTS

Superimposing or averaging [Formula: see text]O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin-P < 0.001]. Whereas HHbR (2.35 ± 0.61 min-1) and HHbB (2.34 ± 0.58 min-1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min-1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min-1, P = 0.002; TA: + 0.43 min-1, P = 0.01).

CONCLUSION

Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.

Near-infrared spectroscopy estimation of combined skeletal muscle oxidative capacity and O2 diffusion capacity in humans

The final steps of the O2 cascade during exercise depend on the product of the microvascular-to-intramyocyteP O 2 ${P}_{{{\rm{O}}}_{\rm{2}}}$ difference and muscle O2 diffusing capacity (D m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ ). Non-invasive methods to determineD m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ in humans are currently unavailable. Muscle oxygen uptake (mV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) recovery rate constant (k), measured by near-infrared spectroscopy (NIRS) using intermittent arterial occlusions, is associated with muscle oxidative capacity in vivo. We reasoned that k would be limited byD m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ when muscle oxygenation is low (kLOW ), and hypothesized that: (i) k in well oxygenated muscle (kHIGH ) is associated with maximal O2 flux in fibre bundles; and (ii) ∆k (kHIGH  - kLOW ) is associated with capillary density (CD). Vastus lateralis k was measured in 12 participants using NIRS after moderate exercise. The timing and duration of arterial occlusions were manipulated to maintain tissue saturation index within a 10% range either below (LOW) or above (HIGH) half-maximal desaturation, assessed during sustained arterial occlusion. Maximal O2 flux in phosphorylating state was 37.7 ± 10.6 pmol s-1  mg-1 (∼5.8 ml min-1  100 g-1 ). CD ranged 348 to 586 mm-2 . kHIGH was greater than kLOW (3.15 ± 0.45 vs. 1.56 ± 0.79 min-1 , P < 0.001). Maximal O2 flux was correlated with kHIGH (r = 0.80, P = 0.002) but not kLOW (r = -0.10, P = 0.755). Δk ranged -0.26 to -2.55 min-1 , and correlated with CD (r = -0.68, P = 0.015). mV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ k reflects muscle oxidative capacity only in well oxygenated muscle. ∆k, the difference in k between well and poorly oxygenated muscle, was associated with CD, a mediator ofD m O 2 $D{{\rm{m}}}_{{{\rm{O}}}_2}$ . Assessment of muscle k and ∆k using NIRS provides a non-invasive window on muscle oxidative and O2 diffusing capacity. KEY POINTS: We determined post-exercise recovery kinetics of quadriceps muscle oxygen uptake (mV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ ) measured by near-infrared spectroscopy (NIRS) in humans under conditions of both non-limiting (HIGH) and limiting (LOW) O2 availability, for comparison with biopsy variables. The mV ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ recovery rate constant in HIGH O2 availability was hypothesized to reflect muscle oxidative capacity (kHIGH ) and the difference in k between HIGH and LOW O2 availability (∆k) was hypothesized to reflect muscle O2 diffusing capacity. kHIGH was correlated with phosphorylating oxidative capacity of permeabilized muscle fibre bundles (r = 0.80). ∆k was negatively correlated with capillary density (r = -0.68) of biopsy samples. NIRS provides non-invasive means of assessing both muscle oxidative and oxygen diffusing capacity in vivo.

Myths and Methodologies: The use of equivalence and non-inferiority tests for interventional studies in exercise physiology and sport science

NEW FINDINGS

What is the topic of this review? The traditional null-hypothesis test allows making informed decisions about whether an experimental intervention is superior to a control while controlling the Type I and Type II error rates. Equivalence and non-inferiority tests allow determining whether two interventions are similar in efficacy or whether one is not unacceptably worse than the other. What advances does it highlight? Equivalence and non-inferiority designs may better fit the research questions of exercise physiologists and sport scientists when investigating new interventions that have better cost-effectiveness, are safer and easier to implement, or are less demanding than the standard.

ABSTRACT

Exercise physiology and sport science have traditionally made use of the null hypothesis of no difference to make decisions about experimental interventions. This article aims to review current statistical approaches typically used by exercise physiologists and sport scientists for the design and analysis of experimental interventions and to highlight the importance of including equivalence and non-inferiority studies, which address different research questions than deciding whether an effect is present. Firstly, we briefly describe the most common approaches, along with their rationale, to investigate the effects of different interventions. We then discuss the main steps involved in the design and analysis of equivalence and non-inferiority studies, commonly performed in other research fields, with worked examples from exercise physiology and sport science scenarios. Finally, we provide recommendations to exercise physiologists and sport scientists who would like to apply the different approaches in future research. We hope this work will promote the correct use of equivalence and non-inferiority designs in exercise physiology and sport science whenever the research context, conditions, applications, researchers' interests, or reasonable beliefs, justify these approaches. This article is protected by copyright. All rights reserved.

Effects of endurance training only versus same-session combined endurance and strength training on physical performance and serum hormone concentrations in recreational endurance runners

This study investigated the effects of endurance training only (E, n = 14) and same-session combined training, when strength training is repeatedly preceded by endurance loading (endurance and strength training (E+S), n = 13) on endurance (1000-m running time during incremental field test) and strength performance (1-repetition maximum (1RM) in dynamic leg press), basal serum hormone concentrations, and endurance loading-induced force and hormone responses in recreationally endurance-trained men. E was identical in the 2 groups and consisted of steady-state and interval running, 4-6 times per week for 24 weeks. E+S performed additional mixed-maximal and explosive-strength training (2 times per week) immediately following an incremental running session (35-45 min, 65%-85% maximal heart rate). E and E+S decreased running time at week 12 (-8% ± 5%, p = 0.001 and -7% ± 3%, p < 0.001) and 24 (-13% ± 5%, p < 0.001 and -9% ± 5%, p = 0.001). Strength performance decreased in E at week 24 (-5% ± 5%, p = 0.014) but was maintained in E+S (between-groups at week 12 and 24, p = 0.014 and 0.011, respectively). Basal serum testosterone and cortisol concentrations remained unaltered in E and E+S but testosterone/sex hormone binding globulin ratio decreased in E+S at week 12 (-19% ± 26%, p = 0.006). At week 0 and 24, endurance loading-induced acute force (-5% to -9%, p = 0.032 to 0.001) and testosterone and cortisol responses (18%-47%, p = 0.013 to p < 0.001) were similar between E and E+S. This study showed no endurance performance benefits when strength training was performed repeatedly after endurance training compared with endurance training only. This was supported by similar acute responses in force and hormonal measures immediately post-endurance loading after the training with sustained 1RM strength in E+S.