Pulmonary O2 uptake and muscle deoxygenation kinetics are slowed in the upper compared with lower region of the moderate-intensity exercise domain in older men

During step transitions in work rate (WR) within the moderate-intensity (MOD) exercise domain, pulmonary O2 uptake (V̇o2p) kinetics are slowed, and V̇o2p gain (ΔV̇o2p/ΔWR) is greater when exercise is initiated from an elevated metabolic rate. High-intensity interval training (HIT) has been shown to speed V̇o2p kinetics when step transitions to MOD exercise are initiated from light-intensity baseline metabolic rates. The effects of HIT on step transitions initiated from elevated metabolic rates have not been established. Therefore, this study investigated the effects of HIT on V̇o2p kinetics during transitions from low and elevated metabolic rates, within the MOD domain. Eight young, untrained men completed 12 sessions of HIT (spanning 4 wk). HIT consisted of 8–12 1-min intervals, cycling at a WR corresponding to 110% of pretraining maximal WR (WRmax). Pre-, mid- and posttraining, subjects completed a ramp-incremental test to determine maximum O2 uptake, WRmax, and estimated lactate threshold (θ̂L). Participants additionally completed double-step constant-load tests, consisting of step transitions from 20 W → Δ45% θ̂L [lower step (LS)] and Δ45 → 90% θ̂L [upper step (US)]. HIT led to increases in maximum O2 uptake ( P < 0.05) and WRmax ( P < 0.01), and τV̇o2p of both lower and upper MOD step transitions were reduced by ∼40% (LS: 24 s → 15 s; US: 45 s → 25 s) ( P < 0.01). However, the time course of adjustment of local muscle deoxygenation was unchanged in the LS and US. These results suggest that speeding of V̇o2p kinetics in both the LS and US may be due, in part, to an improved matching of muscle O2 utilization to microvascular O2 delivery within the working muscle following 12 sessions of HIT, although muscle metabolic adaptations cannot be discounted.

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Effect of Respiratory-Alkalosis On VO2, Mean Blood Velocity and Muscle Deoxygenation Kinetics During Moderate-Intensity Exercise

Medicine & Science in Sports & Exercise ◽

10.1249/01.mss.0000274411.07192.4d ◽

2007 ◽

Vol 39 (Supplement) ◽

pp. S360

Author(s):

Lisa M. K. Chin ◽

Donald H. Paterson ◽

John M. Kowalchuk

Keyword(s):

Respiratory Alkalosis ◽

Blood Velocity ◽

Moderate Intensity ◽

Moderate Intensity Exercise ◽

Muscle Deoxygenation

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Influence of the fitting window on the O2 uptake kinetics at the onset of moderate intensity exercise

Journal of Applied Physiology ◽

10.1152/japplphysiol.00154.2021 ◽

2021 ◽

Author(s):

Maria Pia Francescato ◽

Valentina Cettolo

Keyword(s):

Exponential Function ◽

Mixed Method ◽

Simulated Data ◽

Moderate Intensity ◽

Initial Time ◽

O2 Uptake ◽

Moderate Intensity Exercise ◽

Estimated Parameters ◽

Time Period ◽

O2 Uptake Kinetics

The O2 uptake (V'O2) data at the onset of an exercise are usually fitted with a mono-exponential function, after removal of the data pertaining to a conventional initial time period (ΔTr) lasting ~20s. We performed a thorough quantitative analysis on the effects of removing data pertaining to different ΔTr, aiming at identifying an objective method to establish the appropriate ΔTr. Breath-by-breath O2 uptake responses, acquired on 25 healthy adults performing a step moderate-intensity exercise, and 104 simulated bi-exponential responses, were analyzed. For all the responses, the kinetic parameters of a mono-exponential function, and the corresponding Asymptotic Standard Errors (ASE), were estimated by non-linear regression, removing the data pertaining to progressively longer initial periods (1s each) up to 60s. Four methods to establish objectively ΔTr were compared. The minimum estimated tau was obtained for ΔTr≅35s in both the V'O2 and simulated data, that was about 30% lower compared to that obtained for ΔTr≅0s. The average ASE values remained quite constant up to ΔTr≅35s, thereafter they increased remarkably. The tau used to generate the simulated response fell within the confidence intervals of the estimated tau in ~85% of cases for ΔTr=20s ("20s-w" method); this percentage increased to ~92% of cases when ΔTr was established according to both the minimum tau and its narrowest confidence interval ("Mixed" method). In conclusion, the effects of removing the V'O2 data pertaining to different ΔTr are remarkable. The "Mixed" method provided estimated parameters close to those used to generate the simulated responses and is thus endorsed.

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Are the parameters of VO2, heart rate and muscle deoxygenation kinetics affected by serial moderate-intensity exercise transitions in a single day?

European Journal of Applied Physiology ◽

10.1007/s00421-010-1653-x ◽

2010 ◽

Vol 111 (4) ◽

pp. 591-600 ◽

Cited By ~ 37

Author(s):

Matthew D. Spencer ◽

Juan M. Murias ◽

Heather P. Lamb ◽

John M. Kowalchuk ◽

Donald H. Paterson

Keyword(s):

Heart Rate ◽

Moderate Intensity ◽

Moderate Intensity Exercise ◽

Muscle Deoxygenation ◽

Exercise Transitions

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Effects of hyperventilation on phosphocreatine kinetics and muscle deoxygenation during moderate-intensity plantar flexion exercise

Journal of Applied Physiology ◽

10.1152/japplphysiol.00895.2006 ◽

2007 ◽

Vol 102 (4) ◽

pp. 1565-1573 ◽

Cited By ~ 18

Author(s):

S. C. Forbes ◽

J. M. Kowalchuk ◽

R. T. Thompson ◽

G. D. Marsh

Keyword(s):

Near Infrared ◽

Plantar Flexion ◽

High Energy ◽

Ion Concentration ◽

Moderate Intensity ◽

High Energy Phosphates ◽

Moderate Intensity Exercise ◽

Hydrogen Ion Concentration ◽

Muscle Deoxygenation ◽

Plantar Flexion Exercise

The effects of controlled voluntary hyperventilation (Hyp) on phosphocreatine (PCr) kinetics and muscle deoxygenation were examined during moderate-intensity plantar flexion exercise. Male subjects ( n = 7) performed trials consisting of 20-min rest, 6-min exercise, and 10-min recovery in control [Con; end-tidal Pco2 (PetCO2) ∼ 33 mmHg] and Hyp (PetCO2 ∼17 mmHg) conditions. Phosphorus-31 magnetic resonance and near-infrared spectroscopy were used simultaneously to monitor intramuscular acid-base status, high-energy phosphates, and muscle oxygenation. Resting intracellular hydrogen ion concentration ([H+]i) was lower ( P < 0.05) in Hyp [90 nM (SD 3)] than Con [96 nM (SD 4)]; however, at end exercise, [H+]i was greater ( P < 0.05) in Hyp [128 nM (SD 19)] than Con [120 nM (SD 17)]. At rest, [PCr] was not different between Con [36 mM (SD 2)] and Hyp [36 mM (SD 1)]. The time constant (τ) of PCr breakdown during transition from rest to exercise was greater ( P < 0.05) in Hyp [39 s (SD 22)] than Con [32 s (SD 22)], and the PCr amplitude was greater ( P < 0.05) in Hyp [26% (SD 4)] than Con [22% (SD 6)]. The deoxyhemoglobin and/or deoxymyoglobin (HHb) τ was similar between Hyp [13 s (SD 8)] and Con [10 s (SD 3)]; however, the amplitude was increased ( P < 0.05) in Hyp [40 arbitrary units (au) (SD 23)] compared with Con [26 au (SD 17)]. In conclusion, our results indicate that Hyp-induced hypocapnia enhanced substrate-level phosphorylation during moderate-intensity exercise. In addition, the increased amplitude of the HHb response suggests a reduced local muscle perfusion in Hyp compared with Con.

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