Characterizing the profile of muscle deoxygenation during ramp incremental exercise in young men

Canadian Centre for Activity and Aging, The University of Western Ontario, London, ON, Canada.
Arbeitsphysiologie (Impact Factor: 2.3). 01/2012; 112(9):3349-60. DOI: 10.1007/s00421-012-2323-y
Source: PubMed

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.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The present study compared peak muscle deoxygenation ([HHb]peak) responses at 3 quadriceps sites during occlusion (OCC), ramp incremental (RI), severe- (SVR) and moderate-intensity (MOD) exercise. Seven healthy males (25±4yr) each completed a stationary cycling RI (20 W/min) test to determine [HHb]peak (at distal and proximal vastus lateralis (VLD and VLP) and rectus femoris (RF)), peak VO2 (VO2peak), gas exchange threshold (GET), and peak work rate (WRpeak). Subjects also completed MOD (WR=80%GET) and SVR exercise (WR corresponding to 120%VO2peak) with absolute [HHb] (quantified by multichannel, time-resolved near-infrared spectroscopy) and pulmonary VO2 (VO2p) monitored continuously. Additionally, [HHb] and total hemoglobin ([Hb]tot) were monitored at rest and during subsequent OCC (250 mmHg). Site-specific adipose tissue thickness was assessed (B-mode ultrasound) and its relationship with resting [Hb]tot was used to correct absolute [HHb]. For VLD and RF, [HHb]peak was higher (p<0.05) during OCC (VLD=111±38; RF=114±26μM) than RI (VLD:64±14; RF=85±20) and SVR (VLD=63±13; RF=81±18). [HHb]peak was similar (p>0.05) across these conditions at the VLP (OCC=67±17; RI=69±17; SVR=63±17μM). [HHb] peaked and then decreased prior to exercise cessation during SVR at all 3 muscle sites. [HHb]peak during MOD was consistently lower than other conditions at all sites. A "[HHb] reserve" exists during intense cycling at the VLD and RF, likely implying either sufficient blood flow to meet oxidative demands or insufficient diffusion time for complete equilibration. In VLP this [HHb] reserve was absent, suggesting that a critical PO2 may be challenged during intense cycling.
    Journal of Applied Physiology 09/2014; 117(10). DOI:10.1152/japplphysiol.00060.2014 · 3.43 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The rate of adjustment (tau) of phase II pulmonary O-2 uptake () is slower when exercise transitions are initiated from an elevated baseline work rate (WR) and metabolic rate (MR). In this study, combinations of cycling cadence (40 vs. 90 rpm) and external WR were used to examine the effect of prior MR on tau . Eleven young men completed transitions from 20 W (BSL) to 90 % lactate threshold, with transitions performed as two steps of equal a dagger WR (LS, lower step; US, upper step), while maintaining a cadence of (1) 40 rpm, (2) 90 rpm, and (3) 40 rpm but with the WRs elevated to match the higher associated with 90 rpm cycling (40(MATCH)); transitions lasted 6 min. was measured breath-by-breath using mass spectrometry and turbinometry; vastus lateralis muscle deoxygenation [HHb] was measured using near-infrared spectroscopy. and HHb responses were modeled using nonlinear least squares regression analysis. at BSL, LS and US was similar for 90 rpm and 40(MATCH), but greater than in 40 rpm. Compared to 90 rpm, tau at 40 rpm was shorter (p < 0.05) in LS (18 +/- A 5 vs. 28 +/- A 8 s) but not in US (26 +/- A 8 vs. 33 +/- A 9 s), and at 40(MATCH), tau was lower (p < 0.05) (19 +/- A 6 s) in LS but not in US (34 +/- A 13 s) despite differing external WR and a dagger WR. A similar overall adjustment of [HHb] and in LS and US across conditions suggested dynamic matching between microvascular blood flow and O-2 utilization. Prior MR (rather than external WR per se) plays a role in the dynamic adjustment of pulmonary (and muscle) .
    Arbeitsphysiologie 09/2014; 114(12). DOI:10.1007/s00421-014-2984-9 · 2.30 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: [Purpose] VO2 is expressed as the product of cardiac output and O2 extraction by the Fick equation. During the incremental exercise test and constant high-intensity exercise test, VO2 results in the attainment of maximal O2 uptake at exhaustion. However, the differences in the physiological components, cardiac output and muscle O2 extraction, have not been fully elucidated. We tested the hypothesis that constant exercise would result in higher O2 extraction than incremental exercise at exhaustion. [Subjects] Twenty-five subjects performed incremental exercise and constant exercise at 80% of their peak work rate. [Methods] Ventilatory, cardiovascular, and muscle oxygenation responses were measured using a gas analyzer, Finapres, and near-infrared spectroscopy, respectively. [Results] VO2 was not significantly different between the incremental exercise and constant exercise. However, cardiac output and muscle O2 saturation were significantly lower for the constant exercise than the incremental exercise at the end of exercise. [Conclusion] These findings indicate that if both tests produce a similar VO2 value, the VO2 in incremental exercise would have a higher ratio of cardiac output than constant exercise, and VO2 in constant exercise would have a higher ratio of O2 extraction than incremental exercise at the end of exercise.
    Journal of Physical Therapy Science 08/2014; 26(8):1283-6. DOI:10.1589/jpts.26.1283 · 0.20 Impact Factor