Characterizing the profile of muscle deoxygenation during ramp incremental exercise in young men
ABSTRACT This study characterized the profile of near-infrared spectroscopy (NIRS)-derived muscle deoxygenation (Δ[HHb]) and the tissue oxygenation index (TOI) as a function of absolute (PO(ABS)) and normalized power output (%PO) or oxygen consumption (%VO(2)) during incremental cycling exercise. Eight men (24 ± 5 year) each performed two fatigue-limited ramp incremental cycling tests (20 W min(-1)), during which pulmonary VO(2), Δ[HHb] and TOI were measured continuously. Responses from the two tests were averaged and the TOI (%) and normalized Δ[HHb] (%Δ[HHb]) were plotted against %VO(2), %PO and PO(ABS). The overall responses were modelled using a sigmoid regression (y = f ( 0 ) + A/(1 + e(-(-c+dx)))) and piecewise 'double-linear' function of the predominant adjustment of %Δ[HHb] or TOI observed throughout the middle portion of exercise and the 'plateau' that followed. In ~85% of cases, the corrected Akaike Information Criterion (AIC(C)) was smaller (suggesting one model favoured) for the 'double-linear' compared with the sigmoid regression for both %Δ[HHb] and TOI. Furthermore, the f ( 0 ) and A estimates from the sigmoid regressions of %Δ[HHb] yielded unrealistically large projected peak (f ( 0 ) + A) values (%VO(2p) 114.3 ± 17.5; %PO 113.3 ± 9.5; PO(ABS) 113.5 ± 9.8), suggesting that the sigmoid model does not accurately describe the underlying physiological responses in all subjects and thus may not be appropriate for comparative purposes. Alternatively, the present study proposes that the profile of %Δ[HHb] and TOI during ramp incremental exercise may be more accurately described as consisting of three distinct phases in which there is little adjustment early in the ramp, the predominant increase in %Δ[HHb] (decrease in TOI) is approximately linear and an approximately linear 'plateau' follows.
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ABSTRACT: PURPOSE: The present investigation assessed tissue oxygenation and local blood volume in both vastus lateralis muscles during 3000 m race simulations in elite speed skaters on ice and the effects of leg compression on physiological, perceptual and performance measures. METHODS: Ten (6 female) elite ice speed skaters completed two on-ice trials with and without leg compression. Tissue oxygenation and local blood volume in both vastus lateralis muscles was assessed by applying near-infrared spectroscopy (NIRS). Continuous measures of oxygen uptake, ventilation, heart rate and velocity were conducted throughout the race simulations as well as blood lactate concentration and ratings of perceived exertion before and after the trials. In addition, lap times were assessed. RESULTS: The investigation of tissue oxygenation in both vastus lateralis muscles revealed an asymmetry (P<0.00; effect size=1.81) throughout the 3000 m race simulation. The application of leg compression did not affect oxygenation asymmetry (smallest P=0.99; largest effect size=0.31) or local blood volume (P=0.33; 0.95). Lap times (P=0.88; 0.43), velocity (P=0.24; 0.84), oxygen uptake (P=0.79; 0.10), ventilation (P=0.11; 0.59), heart rate (P=0.21; 0.89), blood lactate concentration (P=0.82; 0.59) and ratings of perceived exertion (P=0.19; 1.01) were also unaffected by the different types of clothing. CONCLUSION: Elite ice speed skaters show an asymmetry in tissue oxygenation of both vastus lateralis muscles during 3000 m events remaining during the long gliding phases along the straight sections of the track. Based on our data, we conclude no performance enhancing benefits from wearing leg compression under a normal racing suit.International journal of sports physiology and performance 12/2012; 9(1). DOI:10.1123/IJSPP.2012-0210 · 2.68 Impact Factor
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ABSTRACT: PURPOSE: We tested the hypothesis that the maximal lactate steady state (MLSS) can be accurately determined in healthy subjects based on measures of deoxygenated hemoglobin (deoxyHb), index of oxygen extraction measured non-invasively by near-infrared spectroscopy (NIRS). METHODS: 32 healthy men (average age 48±17 yrs, range 23-74 yrs) performed an incremental cycling test to exhaustion and square wave tests for MLSS determination. Cardiorespiratory variables were measured bbb and deoxyHb was monitored non-invasively on the right vastus lateralis with a quantitative NIRS device. The individual values of V˙O2 and heart rate (HR) corresponding to the MLSS were calculated and compared to the NIRS-derived MLSS (NIRSMLSS) that was, in turn, determined by double linear function fitting of deoxyHb during the incremental exercise. RESULTS: V˙O2 and HR at MLSS were 2.25±0.54 L·min (76±9 % V˙O2max) and 133±14 b·min (81±7 %HRmax) respectively. Muscle O2 extraction increased as a function of exercise intensity up to a deflection point, NIRSMLSS, at which V˙O2 and HR were 2.23±0.59 L·min (76±9 % V˙O2max) and 136±17 b·min (82±8 %HRmax) respectively. For both V˙O2 and HR, the difference of NIRSMLSS from MLSS values was not significant and the measures were highly correlated (r=0.81 and r=0.76). The Bland Altman analysis confirmed a not significant bias for V˙O2 and HR (-0.015 L·min and 3 b·min, respectively) and a small imprecision of 0.26 L·min and 8 b·min. CONCLUSIONS: A plateau in muscle O2 extraction was demonstrated in coincidence with MLSS during an incremental cycling exercise, confirming the hypothesis that this functional parameter can be accurately estimated with a quantitative NIRS device. The main advantages of NIRSMLSS over lactate-based techniques are the non-invasiveness and the time/cost efficiency.Medicine and science in sports and exercise 12/2012; DOI:10.1249/MSS.0b013e3182828ab2 · 4.46 Impact Factor
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ABSTRACT: During ramp incremental cycling exercise increases in pulmonary O2 uptake (VO2p) are matched by a linear increase in systemic cardiac output (Q). However, it has been suggested that blood flow in the active muscle microvasculature does not display similar linearity in blood flow relative to metabolic demand. This study simultaneously examined both systemic and regional (microvascular) blood flow and O2 extraction during incremental cycling exercise. Ten young men (VO2peak = 4.2±0.5 L•min(-1)) and 10 young women (VO2peak = 3.2±0.5 L•min(-1)) were recruited to perform two maximal incremental cycling tests on separate days. The acetylene open-circuit technique and mass spectrometry and volume turbine were used to measure Q (every minute) and breath-by-breath VO2p, respectively; systemic arterio-venous O2 difference (a-vO2diff) was calculated as VO2p/Q on a minute-by-minute basis. Changes in NIRS-derived muscle de-oxygenation ([HHb]) were used (in combination with VO2p data) to estimate the profiles of peripheral O2 extraction and blood flow of the active muscle microvasculature. The systemic Q-to-VO2p relationship was linear (approximately 5.8 L•min(-1) increase in Q for a 1 L•min(-1) increase in VO2p) with a-vO2diff displaying a hyperbolic response as exercise intensity increased towards VO2peak. The peripheral blood flow response profile was described by an inverted sigmoid curve indicating non-linear responses relative to metabolic demand. The [HHb] profile increased linearly with absolute VO2p until high intensity exercise thereafter displaying a "near-plateau". Results indicate that systemic blood flow and thus O2 delivery does not reflect the profile of blood flow changes at the level of the microvasculature.AJP Regulatory Integrative and Comparative Physiology 03/2013; 304(9). DOI:10.1152/ajpregu.00016.2013 · 3.53 Impact Factor