Adaptation of pulmonary O2 uptake kinetics and muscle deoxygenation at the onset of heavy-intensity exercise in young and older adults

Diminished muscle oxygen uptake and fatigue in spinal muscular atrophy

OBJECTIVE

To estimate muscle oxygen uptake and quantify fatigue during exercise in ambulatory individuals with spinal muscular atrophy (SMA) and healthy controls.

METHODS

Peak aerobic capacity (VO_2peak ) and workload (W_peak ) were measured by cardiopulmonary exercise test (CPET) in 19 ambulatory SMA patients and 16 healthy controls. Submaximal exercise (SME) at 40% W_peak was performed for 10 minutes. Change in vastus lateralis deoxygenated hemoglobin, measured by near-infrared spectroscopy, determined muscle oxygen uptake (ΔHHb) at rest and during CPET and SME. Dual energy X-ray absorptiometry assessed fat-free mass (FFM%). Fatigue was determined by percent change in workload or distance in the first compared to the last minute of SME (Fatigue_SME ) and six-minute walk test (Fatigue_6MWT ), respectively.

RESULTS

ΔHHb-PEAK, ΔHHb-SME, VO_2peak , W_peak , FFM%, and 6MWT distance were lower (P < 0.001), and Fatigue_6MWT and Fatigue_SME were higher (P < 0.001) in SMA compared to controls. ΔHHb-PEAK correlated with FFM% (r = 0.50) and VO_2peak (r = 0.41) only in controls. Only in SMA, Fatigue_6MWT was inversely correlated with W_peak (r = -0.69), and Fatigue_SME was inversely correlated with FFM% (r = -0.55) and VO_2peak (r = -0.69).

INTERPRETATION

This study provides further support for muscle mitochondrial dysfunction in SMA patients. During exercise, we observed diminished muscle oxygen uptake but no correlation with aerobic capacity or body composition. We also observed increased fatigue which correlated with decreased aerobic capacity, workload, and body composition. Understanding the mechanisms underlying diminished muscle oxygen uptake and increased fatigue during exercise in SMA may identify additional therapeutic targets that rescue symptomatic patients and mitigate their residual disease burden.

Breath isoprene excretion during rest and low-intensity cycling exercise is associated with skeletal muscle mass in healthy human subjects

The physiological roles of isoprene, which is one of the many endogenous volatile organic compounds contained in exhaled breath, are not well understood. In recent years, exhaled isoprene has been associated with the skeletal muscle. Some studies have suggested that the skeletal muscle produces and/or stores some of the isoprene. However, the evidence supporting this association remains sparse and inconclusive. Furthermore, aging may affect breath isoprene response because of changes in the skeletal muscle quantity and quality. Therefore, we investigated the association between the breath isoprene excretion ([Formula: see text]) and skeletal muscle mass in young (n = 7) and old (n = 7) adults. The participants performed an 18 min cycling exercise after a 3 min rest. The workload corresponded to an intensity of 30% of the heart rate reserve, as calculated by the Karvonen formula. The exhaled breath of each participant was collected during the exercise test. We calculated [Formula: see text] from the product minute ventilation and isoprene concentration and, then, investigated the relationships between [Formula: see text] and muscle mass, which was measured by multi-frequency bioelectrical impedance analysis. Importantly, muscle mass persisted as a significant determinant that explained the variance in [Formula: see text] at rest even after adjusting for age. Furthermore, the muscle mass was a significant determinative factor for [Formula: see text] response during exercise, regardless of age. These data indicated that skeletal muscle mass could be one of the determinative factors for [Formula: see text] during rest and response to exercise. Thus, we suggest that the skeletal muscle may play an important role in generating and/or storing some of the endogenous isoprene. This new knowledge will help to better understand the physiological functions of isoprene in humans (Approval No. 20190079).

Relationship between (non)linear phase II pulmonary oxygen uptake kinetics with skeletal muscle oxygenation and age in 11-15 year olds

NEW FINDINGS

What is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( V ̇ O 2 ) kinetics display linear, first-order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non-linear features of phase II V ̇ O 2 kinetics may be determined by alterations in the dynamic balance between microvascular O₂ delivery and utilization in 11-15 year olds. The recruitment of higher-order (i.e. type II) muscle fibres during 'work-to-work' cycling might be responsible for modulating V ̇ O 2 kinetics with chronological age.

ABSTRACT

This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7-15.7 years) the relationship between pulmonary oxygen uptake ( V ̇ O 2 ) and muscle deoxygenation kinetics during moderate- and very heavy-intensity 'step' cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy-intensity step cycling (i.e. M → VH). Pulmonary V ̇ O 2 was measured breath-by-breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near-infrared spectroscopy. There were no significant differences in the phase II time constant ( τ V ̇ O 2 p ) between U → M and U → VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τ V ̇ O 2 p was slower during M → VH (42 ± 16 s) compared to other conditions (P < 0.001). Quadriceps TOI decreased with a faster (P < 0.01) mean response time (MRT; i.e. time delay + τ) during U → VH (14 ± 2 s) compared to U → M (22 ± 4 s) and M → VH (20 ± 6 s). The difference (Δ) between the τ V ̇ O 2 p and MRT-TOI was greater during U → VH compared to U → M (12 ± 7 vs. 2 ± 7 s, P < 0.001) and during M → VH (23 ± 15 s) compared to other conditions (P < 0.02), suggesting an increased proportional speeding of fractional O₂ extraction. The slowing of the τ V ̇ O 2 p during M → VH relative to U → M and U → VH correlated positively with chronological age (r = 0.68 and 0.57, respectively, P < 0.01). In youths, 'work-to-work' transitions slowed microvascular O₂ delivery-to-O₂ utilization with alterations in phase II V ̇ O 2 dynamics accentuated between the ages of 11 and 15 years.

Functional Electrical Stimulation Changes Muscle Oxygenation in Patients with Chronic Obstructive Pulmonary Disease During Moderate-Intensity Exercise: A Secondary Analysis

We previously showed that functional electrical stimulation during cycle ergometry (FES-cycling) increased oxygen consumption (VO₂), indicating that metabolism during exercise was increased. However, the effects on muscle oxygenation have never been studied. The aim of this secondary analysis was to analyse changes in muscle oxygenation during an FES-cycling session. Eight patients with chronic obstructive pulmonary disease who were participating in a pulmonary rehabilitation programme were enrolled. Each participant carried out 30 minutes of cycle ergometry with a constant load at 50% of peak oxygen uptake, either (i) with FES or (ii) without (Placebo-FES). Oxygenation of the vastus lateralis (VL) muscle over time was measured using near-infrared spectroscopy (NIRS) during both sessions. External power output on the cycle ergometer was the same in both conditions. There were no differences in dyspnoea between the groups, although the concentrations of deoxygenated haemoglobin and myoglobin (deoxy(Hb + Mb)) in the VL were significantly greater during Placebo-FES than FES-Cycling (respectively +212 ± 65% vs. +84 ± 29%; p < 0.001), as was the decrease in muscle oxygen saturation (StO₂) (p < 0.001). When adjusted for VO₂, there was a greater increase over time in the deoxy(Hb + Mb)/VO₂ ratio during Placebo-FES than FES-cycling (p < 0.0001). FES-cycling could be a useful strategy to decrease muscular deoxy(Hb + Mb) and limit decreases in muscle StO₂, however this should be confirmed in larger studies.

Effects of heavy-intensity priming exercise on pulmonary oxygen uptake kinetics and muscle oxygenation in heart failure with preserved ejection fraction

Exercise intolerance is a hallmark feature in heart failure with preserved ejection fraction (HFpEF). Prior heavy exercise ("priming exercise") speeds pulmonary oxygen uptake (V̇o_2p) kinetics in older adults through increased muscle oxygen delivery and/or alterations in mitochondrial metabolic activity. We tested the hypothesis that priming exercise would speed V̇o_2p on-kinetics in patients with HFpEF because of acute improvements in muscle oxygen delivery. Seven patients with HFpEF performed three bouts of two exercise transitions: MOD1, rest to 4-min moderate-intensity cycling and MOD2, MOD1 preceded by heavy-intensity cycling. V̇o_2p, heart rate (HR), total peripheral resistance (TPR), and vastus lateralis tissue oxygenation index (TOI; near-infrared spectroscopy) were measured, interpolated, time-aligned, and averaged. V̇o_2p and HR were monoexponentially curve-fitted. TPR and TOI levels were analyzed as repeated measures between pretransition baseline, minimum value, and steady state. Significance was P < 0.05. Time constant (τ; tau) V̇o_2p (MOD1 49 ± 16 s) was significantly faster after priming (41 ± 14 s; P = 0.002), and the effective HR τ was slower following priming (41 ± 27 vs. 51 ± 32 s; P = 0.025). TPR in both conditions decreased from baseline to minimum TPR ( P < 0.001), increased from minimum to steady state ( P = 0.041) but remained below baseline throughout ( P = 0.001). Priming increased baseline ( P = 0.003) and minimum TOI ( P = 0.002) and decreased the TOI muscle deoxygenation overshoot ( P = 0.041). Priming may speed the slow V̇o_2p on-kinetics in HFpEF and increase muscle oxygen delivery (TOI) at the onset of and throughout exercise. Microvascular muscle oxygen delivery may limit exercise tolerance in HFpEF.

Plasma asymmetric dimethylarginine concentrations are not related to differences in maximal oxygen uptake in endurance trained and untrained men

NEW FINDINGS

What is the central question of this study? Is there an association of plasma concentration of asymmetric dimethylarginine, which is related to exercise capacity in patients with cardiovascular diseases, with oxygen delivery and subsequently exercise capacity in healthy subjects in the absence of the potentially confounding influence of inflammation and oxidative stress? What is the main finding and its importance? Plasma asymmetric dimethylarginine concentrations are not related to exercise capacity in healthy subjects, while O₂ delivery in the working skeletal muscle during the maximal graded-exercise test is not associated with any of the l-arginine analogues. ADMA alone does not play a crucial role in local muscle perfusion and in maintaining exercise capacity.

ABSTRACT

Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthesis that could limit oxygen (O₂ ) delivery in the working skeletal muscles by altering endothelium-dependent vasodilatation. Exercise capacity is associated with plasma ADMA concentrations in patients with cardiovascular diseases, but this issue has still not been investigated in healthy subjects. We aimed to determine whether plasma ADMA concentrations were negatively associated with exercise capacity in young healthy male subjects. Ten men with maximal oxygen uptake ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> ) > 65 mL kg^-1  min^-1 were included in the high exercise capacity group (HI-FIT), and 10 men with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math>  < 45 mL kg^-1  min^-1 were included in the low exercise capacity group (LO-FIT). Plasma ADMA and other l-arginine analogue concentrations were measured before and after a maximal graded-exercise test by liquid chromatography-tandem mass spectrometry. Microvascular O₂ delivery during exercise was estimated through the pattern from the sigmoid model of muscle deoxygenation in the vastus lateralis measured by near infrared spectroscopy. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> was 60% higher in the HI-FIT group (median: 70.2 mL kg^-1  min^-1 ; IQR: 68.0-71.9 mL kg^-1  min^-1 ) than in the LO-FIT group (median: 43.8 mL kg^-1  min^-1 ; IQR: 34.8-45.3 mL kg^-1  min^-1 ). Plasma ADMA concentrations did not differ between the LO-FIT and HI-FIT groups before (0.50 ± 0.06 vs. 0.54 ± 0.07 μmol L^-1 , respectively) and after the maximal incremental exercise test (0.49 ± 0.08 vs. 0.55 ± 0.03 μmol L^-1 , respectively). There was no significant association of plasma ADMA concentrations with the pattern of local muscle deoxygenation and exercise capacity. Exercise capacity and microvascular O₂ delivery are not related to plasma ADMA concentrations in young healthy male subjects. Our findings show that ADMA does not play a crucial role in local muscle perfusion and in maintaining exercise capacity without pathological conditions.

Hypoxia and Fatigue Impair Rapid Torque Development of Knee Extensors in Elite Alpine Skiers

This study examined the effects of acute hypoxia on maximal and explosive torque and fatigability in knee extensors of skiers. Twenty-two elite male alpine skiers performed 35 maximal, repeated isokinetic knee extensions at 180°s^-1 (total exercise duration 61.25 s) in normoxia (NOR, FiO₂ 0.21) and normobaric hypoxia (HYP, FiO₂ 0.13) in a randomized, single-blind design. Peak torque and rate of torque development (RTD) from 0 to 100 ms and associated Vastus Lateralis peak EMG activity and rate of EMG rise (RER) were determined for each contraction. Relative changes in deoxyhemoglobin concentration of the VL muscle were monitored by near-infrared spectroscopy. Peak torque and peak EMG activity did not differ between conditions and decreased similarly with fatigue (p < 0.001), with peak torque decreasing continuously but EMG activity decreasing significantly after 30 contractions only. Compared to NOR, RTD, and RER values were lower in HYP during the first 12 and 9 contractions, respectively (both p < 0.05). Deoxyhemoglobin concentration during the last five contractions was higher in HYP than NOR (p = 0.050) but the delta between maximal and minimal deoxyhemoglobin for each contraction was similar in HYP and NOR suggesting a similar muscle O₂ utilization. Post-exercise heart rate (138 ± 24 bpm) and blood lactate concentration (5.8 ± 3.1 mmol.l^-1) did not differ between conditions. Arterial oxygen saturation was significantly lower (84 ± 4 vs. 98 ± 1%, p < 0.001) and ratings of perceived exertion higher (6 ± 1 vs. 5 ± 1, p < 0.001) in HYP than NOR. In summary, hypoxia limits RTD via a decrease in neural drive in elite alpine skiers undertaking maximal repeated isokinetic knee extensions, but the effect of hypoxic exposure is negated as fatigue develops. Isokinetic testing protocols for elite alpine skiers should incorporate RTD and RER measurements as they display a higher sensitivity than peak torque and EMG activity.

Lack of age-specific influence on leg blood flow during incremental calf plantar-flexion exercise in men and women

PURPOSE

Age-related exercising leg blood flow (LBF) responses during dynamic knee-extension exercise and forearm blood flow responses during handgrip exercise are preserved in normally active men but attenuated in activity-matched women. We explored whether these age- and sex-specific effects are also apparent during isometric calf plantar-flexion incremental exercise.

METHODS

Normally active young men (YM, n = 15, 24 ± 2 years), young women (YW, n = 8, 22 ± 1 years), older men (OM, n = 13, 70 ± 7 years) and older women (OW, n = 10, 64 ± 7 years) were tested. LBF was measured between contractions using venous occlusion plethysmography.

RESULTS

Peak force obtained was higher (P < 0.05) in men compared with women and in young compared with older individuals. However, peak LBF (YM; 971 ± 328 ml min^-1, OM; 985 ± 504 ml min^-1, YW; 844 ± 366 ml min^-1, OW; 960 ± 244 ml min^-1) and peak leg vascular conductance [LVC = LBF/(MAP + hydrostatic pressure)] responses (YM; 6.0 ± 1.8 ml min^-1 mmHg^-1, OM; 5.5 ± 2.8 ml min^-1 mmHg^-1, YW; 5.3 ± 2.1 ml min^-1 mmHg^-1, OW; 5.5 ± 1.6 ml min^-1 mmHg^-1) were similar among the four groups. Furthermore, the hyperaemic (YM; 8.8 ± 3.7 ml min^-1 %F_peak^-1 OM; 8.3 ± 5.4 ml min^-1 %F_peak^-1, YW; 8.2 ± 3.5 ml min^-1 %F_peak^-1, OW; 9.6 ± 2.2 ml min^-1 %F_peak^-1) and vasodilatory responses (YM; 0.053 ± 0.020 ml min^-1 mmHg^-1 %F_peak^-1, OM; 0.048 ± 0.028 ml min^-1 mmHg^-1 %F_peak^-1, YW; 0.051 ± 0.019 ml min^-1 mmHg^-1 %F_peak^-1, OW; 0.055 ± 0.014 ml min^-1 mmHg^-1 %F_peak^-1) were not different among the four groups. These results were accompanied by similar resting LBF responses among groups and were not affected when data were normalised to estimated leg muscle mass.

CONCLUSIONS

Our results demonstrate that exercising LBF responses during isometric incremental calf muscle exercise are preserved in older men and women, suggesting that the previously observed age-related attenuations in leg and forearm hyperaemia among women may be muscle-group specific.

Sex and Exercise Intensity Do Not Influence Oxygen Uptake Kinetics in Submaximal Swimming

The aim of this study was to compare the oxygen uptake (V˙O2) kinetics in front crawl between male and female swimmers at moderate and heavy intensity. We hypothesized that the time constant for the primary phase V˙O2 kinetics was faster in men than in women, for both intensities. Nineteen well trained swimmers (8 females mean ± SD; age 17.9 ± 3.5 years; mass 55.2 ± 3.6 kg; height 1.66 ± 0.05 m and 11 male 21.9 ± 2.8 years; 78.2 ± 11.1 kg; 1.81 ± 0.08 m) performed a discontinuous maximal incremental test and two 600-m square wave transitions for both moderate and heavy intensities to determine the V˙O2 kinetics parameters using mono- and bi-exponential models, respectively. All the tests involved breath-by-breath analysis of front crawl swimming using a swimming snorkel. The maximal oxygen uptake (V˙O2max) was higher in men than in women [4,492 ± 585 ml·min⁻¹ and 57.7 ± 4.4 ml·kg⁻¹·min⁻¹ vs. 2,752.4 ± 187.9 ml·min⁻¹ (p ≤ 0.001) and 50.0 ± 5.7 ml·kg⁻¹·min⁻¹(p = 0.007), respectively]. Similarly, the absolute amplitude of the primary component was higher in men for both intensities (moderate: 1,736 ± 164 vs. 1,121 ± 149 ml·min⁻¹; heavy: 2,948 ± 227 vs. 1,927 ± 243 ml·min⁻¹, p ≤ 0.001, for males and females, respectively). However, the time constant of the primary component (τ_p) was not influenced by sex (p = 0.527) or swimming intensity (p = 0.804) (moderate: 15.1 ± 5.6 vs. 14.4 ± 5.1 s; heavy: 13.5 ± 3.3 vs. 16.0 ± 4.5 s, for females and males, respectively). The slow component in the heavy domain was not significantly different between female and male swimmers (3.2 ± 2.4 vs. 3.8 ± 1.0 ml·kg⁻¹·min⁻¹, p = 0.476). Overall, only the absolute amplitude of the primary component was higher in men, while the other V˙O2 kinetics parameters were similar between female and male swimmers at both moderate and heavy intensities. The mechanisms underlying these similarities remain unclear.

Pulmonary oxygen uptake and muscle deoxygenation kinetics during heavy intensity cycling exercise in patients with emphysema and idiopathic pulmonary fibrosis

BACKGROUND

Little is known about the mechanistic basis for the exercise intolerance characteristic of patients with respiratory disease; a lack of clearly defined, distinct patient groups limits interpretation of many studies. The purpose of this pilot study was to investigate the pulmonary oxygen uptake ([Formula: see text] O₂) response, and its potential determinants, in patients with emphysema and idiopathic pulmonary fibrosis (IPF).

METHODS

Following a ramp incremental test for the determination of peak [Formula: see text] O₂ and the gas exchange threshold, six emphysema (66 ± 7 years; FEV_1, 36 ± 16%), five IPF (65 ± 12 years; FEV₁, 82 ± 11%) and ten healthy control participants (63 ± 6 years) completed three repeat, heavy-intensity exercise transitions on a cycle ergometer. Throughout each transition, pulmonary gas exchange, heart rate and muscle deoxygenation ([HHb], patients only) were assessed continuously and subsequently modelled using a mono-exponential with ([Formula: see text] O₂, [HHb]) or without (HR) a time delay.

RESULTS

The [Formula: see text] O₂ phase II time-constant (τ) did not differ between IPF and emphysema, with both groups significantly slower than healthy controls (Emphysema, 65 ± 11; IPF, 69 ± 7; Control, 31 ± 7 s; P < 0.05). The HR τ was slower in emphysema relative to IPF, with both groups significantly slower than controls (Emphysema, 87 ± 19; IPF, 119 ± 20; Control, 58 ± 11 s; P < 0.05). In contrast, neither the [HHb] τ nor [HHb]:O₂ ratio differed between patient groups.

CONCLUSIONS

The slower [Formula: see text] O₂ kinetics in emphysema and IPF may reflect poorer matching of O₂ delivery-to-utilisation. Our findings extend our understanding of the exercise dysfunction in patients with respiratory disease and may help to inform the development of appropriately targeted rehabilitation strategies.

The effects of skin and core tissue cooling on oxygenation of the vastus lateralis muscle during walking and running

Skin and core tissue cooling modulates skeletal muscle oxygenation at rest. Whether tissue cooling also influences the skeletal muscle deoxygenation response during exercise is unclear. We evaluated the effects of skin and core tissue cooling on skeletal muscle blood volume and deoxygenation during sustained walking and running. Eleven male participants walked or ran six times on a treadmill for 60 min in ambient temperatures of 22°C (Neutral), 0°C for skin cooling (Cold 1), and at 0°C following a core and skin cooling protocol (Cold 2). Difference between oxy/deoxygenated haemoglobin ([diffHb]: deoxygenation index) and total haemoglobin content ([tHb]: total blood volume) in the vastus lateralis (VL) muscle was measured continuously. During walking, lower [tHb] was observed at 1 min in Cold 1 and Cold 2 vs. Neutral (P˂0.05). Lower [diffHb] was seen at 1 and 10 min in Cold 2 vs. Neutral by 13.5 ± 1.2 µM and 15.3 ± 1.4 µM and Cold 1 by 10.4 ± 3.1 µM and 11.1 ± 4.1 µM, respectively (P˂0.05). During running, [tHb] was lower in Cold 2 vs. Neutral at 10 min only (P = 0.004). [diffHb] was lower at 1 min in Cold 2 by 11.3 ± 3.1 µM compared to Neutral and by 13.5 ± 2.8 µM compared to Cold 1 (P˂0.001). Core tissue cooling, prior to exercise, induced greater deoxygenation of the VL muscle during the early stages of exercise, irrespective of changes in blood volume. Skin cooling alone, however, did not influence deoxygenation of the VL during exercise.

Muscle oxygen supply impairment during exercise in poorly controlled type 1 diabetes

Purpose

Aerobic fitness, as reflected by maximal oxygen (O₂) uptake (V˙O_2max), is impaired in poorly controlled patients with type 1 diabetes. The mechanisms underlying this impairment remain to be explored. This study sought to investigate whether type 1 diabetes and high levels of glycated hemoglobin (HbA_1c) influence O₂ supply including O₂ delivery and release to active muscles during maximal exercise.

Methods

Two groups of patients with uncomplicated type 1 diabetes (T1D-A, n = 11, with adequate glycemic control, HbA_1c <7.0%; T1D-I, n = 12 with inadequate glycemic control, HbA_1c >8%) were compared with healthy controls (CON-A, n = 11; CON-I, n = 12, respectively) matched for physical activity and body composition. Subjects performed exhaustive incremental exercise to determine V˙O_2max. Throughout the exercise, near-infrared spectroscopy allowed investigation of changes in oxyhemoglobin, deoxyhemoglobin, and total hemoglobin in the vastus lateralis. Venous and arterialized capillary blood was sampled during exercise to assess arterial O₂ transport and factors able to shift the oxyhemoglobin dissociation curve.

Results

Arterial O₂ content was comparable between groups. However, changes in total hemoglobin (i.e., muscle blood volume) was significantly lower in T1D-I compared with that in CON-I. T1D-I also had impaired changes in deoxyhemoglobin levels and increase during high-intensity exercise despite normal erythrocyte 2,3-diphosphoglycerate levels. Finally, V˙O_2max was lower in T1D-I compared with that in CON-I. No differences were observed between T1D-A and CON-A.

Conclusions

Poorly controlled patients displayed lower V˙O_2max and blunted muscle deoxyhemoglobin increase. The latter supports the hypotheses of increase in O₂ affinity induced by hemoglobin glycation and/or of a disturbed balance between nutritive and nonnutritive muscle blood flow. Furthermore, reduced exercise muscle blood volume in poorly controlled patients may warn clinicians of microvascular dysfunction occurring even before overt microangiopathy.

No acetyl group deficit is evident at the onset of exercise at 90% of maximal oxygen uptake in humans

The existence of an acetyl group deficit at or above 90% of maximal oxygen uptake (VO(2max)) has proved controversial, with contradictory results likely relating to limitations in previous research. The purpose of the present study was to determine whether the "acetyl group deficit" occurs at the start of exercise at 90%VO(2max) in a well-controlled study. Eight male participants (age: 33.6 +/- 2.0 years; VO(2max): 3.60 +/- 0.21 litres . min(-1)) completed two exercise bouts at 90%VO(2max) for 3 min following either 30 min of saline (control) or dichloroacetate (50 mg . kg(-1) body mass) infusion, ending 15 min before exercise. Muscle biopsies were obtained immediately before and after exercise while continuous non-invasive measures of pulmonary oxygen uptake and muscle deoxygenation were made. Muscle pyruvate dehydrogenase activity was significantly higher before exercise following dichloroacetate infusion (control: 2.67 +/- 0.98 vs. dichloroacetate: 17.9 +/- 1.1 mmol acetyl-CoA . min(-1) . mg(-1) protein, P = 0.01) and resulted in higher pre- and post-exercise muscle acetylcarnitine (pre-exercise control: 3.3 +/- 0.95 vs. pre-exercise dichloroacetate: 8.0 +/- 0.88 vs. post-exercise control: 11.9 +/- 1.1 vs. post-exercise dichloroacetate: 17.2 +/- 1.1 mmol . kg(-1) dry muscle, P < 0.05). However, substrate-level phosphorylation (control: 125 +/- 20 vs. dichloroacetate: 113 +/- 13 mmol adenosine triphosphate . kg(-1) dry muscle) and VO(2) kinetics (control: 19.2 +/- 2.2 vs. dichloroacetate: 22.8 +/- 2.5 s), were unaltered. Furthermore, dichloroacetate infusion blunted the slow component of VO(2) and muscle deoxygenation and slowed muscle deoxygenation kinetics, possibly by enhancing oxygen delivery during exercise. These data support the hypothesis that the "acetyl group deficit" does not occur at or above 90%VO(2max).

Central and Peripheral Hemodynamic Adaptations During Cardiopulmonary Exercise Test in Heart Failure Patients With Exercise Periodic Breathing

Some heart failure (HF) patients develop ventilatory oscillation which is composed of exercise periodic breathing (EPB) and sleep apnea. The ventilatory oscillation is associated with exercise intolerance. This study employed an integrated monitoring system to elucidate the way of central and peripheral hemodynamic adaption responding to exercise. This study recruited 157 HF patients to perform exercise testing using a bicycle ergometer. A noninvasive bio-reactance device was adopted to measure cardiac hemodynamics, whereas a near-infrared spectroscopy (NIRS) was used to assess perfusion and O2 extraction in the frontal cerebral lobe (FC) and vastus lateralis muscle (VL) during exercise respectively. Furthermore, quality of life (QoL) was measured with the Short Form-36 (SF-36) and the Minnesota Living with Heart Failure questionnaires (MLHFQ). The patients were divided into an EPB group (n = 65) and a non-EPB group (n = 92) according to their ventilation patterns during testing. Compared to their non-EPB counterparts, the patients with EPB exhibited 1) impaired aerobic capacity with a smaller peak oxygen consumption (VO2peak) and oxygen uptake efficiency slopes; 2) impaired circulatory and ventilatory efficiency with relatively high cardiac output and ventilation per unit workload; 3) impaired ventilatory/hemodynamic adaptation in response to exercise with elevated deoxyhemoglobin levels in the FC region; and 4) impaired QoL with lower physical component scores on the SF-36 and higher scores on the MLHFQ. In conclusion, EPB may reduce circulatory-ventilatory-hemodynamic efficiency during exercise, thereby impairing functional capacity in patients with HF.

Changes of direction during high-intensity intermittent runs: neuromuscular and metabolic responses

BACKGROUND

The ability to sustain brief high-intensity intermittent efforts (HIE) is meant to be a major attribute for performance in team sports. Adding changes of direction to HIE is believed to increase the specificity of training drills with respect to game demands. The aim of this study was to investigate the influence of 90°-changes of direction (COD) during HIE on metabolic and neuromuscular responses.

METHODS

Eleven male, team sport players (30.5 ± 3.6 y) performed randomly HIE without (straight-line, 2×[10× 22 m]) or with (2×[10× ~16.5 m]) two 90°-COD. To account for the time lost while changing direction, the distance for COD runs during HIE was individually adjusted using the ratio between straight-line and COD sprints. Players also performed 2 countermovement (CMJ) and 2 drop (DJ) jumps, during and post HIE. Pulmonary oxygen uptake (VO2), quadriceps and hamstring oxygenation, blood lactate concentration (Δ[La]b), electromyography amplitude (RMS) of eight lower limb muscles and rating of perceived exertion (RPE) were measured for each condition.

RESULTS

During HIE, CODs had no substantial effects on changes in VO2, oxygenation, CMJ and DJ performance and RPE (all differences in the changes rated as unclear). Conversely, compared with straight-line runs, COD-runs were associated with a possibly higher Δ[La]b (+9.7 ± 10.4%, with chances for greater/similar/lower values of 57/42/0%) and either a lower (i.e., -11.9 ± 14.6%, 2/13/85 for semitendinosus and -8.5 ± 9.3%, 1/21/78 for lateral gastrocnemius) or equivalent decrease in electromyography amplitude.

CONCLUSION

Adding two 90°-CODs on adjusted distance during two sets of HIE is likely to elicit equivalent decreases in CMJ and DJ height, and similar cardiorespiratory and perceptual responses, despite a lower average running speed. A fatigue-induced modification in lower limb control observed with CODs may have elicited a selective reduction of electromyography activity in hamstring muscles and may induce, in turn, a potential mechanical loss of knee stability. Therefore, changing direction during HIE, with adjusted COD running distances, might be an effective training practice 1) to manipulate some components of the acute physiological load of HIE, 2) to promote long-term COD-specific neuromuscular adaptations aimed at improving performance and knee joint stability.

Oxygen uptake kinetics

Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

Intensity of daily physical activity is associated with central hemodynamic and leg muscle oxygen availability in COPD

In chronic obstructive pulmonary disease (COPD), daily physical activity is reported to be adversely associated with the magnitude of exercise-induced dynamic hyperinflation and peripheral muscle weakness. There is limited evidence whether central hemodynamic, oxygen transport, and peripheral muscle oxygenation capacities also contribute to reduced daily physical activity. Nineteen patients with COPD (FEV1, 48 ± 14% predicted) underwent a treadmill walking test at a speed corresponding to the individual patient's mean walking intensity, captured by a triaxial accelerometer during a preceding 7-day period. During the indoor treadmill test, the individual patient mean walking intensity (range, 1.5 to 2.3 m/s2) was significantly correlated with changes from baseline in cardiac output recorded by impedance cardiography (range, 1.2 to 4.2 L/min; r = 0.73), systemic vascular conductance (range, 7.9 to 33.7 ml·min(-1)·mmHg(-1); r = 0.77), systemic oxygen delivery estimated from cardiac output and arterial pulse-oxymetry saturation (range, 0.15 to 0.99 L/min; r = 0.70), arterio-venous oxygen content difference calculated from oxygen uptake and cardiac output (range, 3.7 to 11.8 mlO2/100 ml; r = -0.73), and quadriceps muscle fractional oxygen saturation assessed by near-infrared spectrometry (range, -6 to 23%; r = 0.77). In addition, mean walking intensity significantly correlated with the quadriceps muscle force adjusted for body weight (range, 0.28 to 0.60; r = 0.74) and the ratio of minute ventilation over maximal voluntary ventilation (range, 38 to 89%, r = -0.58). In COPD, in addition to ventilatory limitations and peripheral muscle weakness, intensity of daily physical activity is associated with both central hemodynamic and peripheral muscle oxygenation capacities regulating the adequacy of matching peripheral muscle oxygen availability by systemic oxygen transport.

Influence of hormone replacement therapy and aerobic exercise training on oxygen uptake kinetics in postmenopausal women

The purpose of this study was to determine the effects of aerobic exercise training on the adjustment of pulmonary oxygen (O2) uptake ([Formula: see text]O2p) kinetics in postmenopausal women in 2 groups: those using hormone replacement therapy (HRT) (HRT group) (n = 7, aged 56 ± 4 years) and those not using HRT (nonHRT group) (n = 8, aged 60 ± 5 years). The influence of training (cycle-ergometer 3 times per week for 6 weeks) on step transitions to both moderate-intensity (80% of the gas exchange threshold) and heavy-intensity (Δ50) cycling exercise was studied. Breath-by-breath [Formula: see text]O2p data were collected using a mass spectrometer. There were no differences in baseline characteristics between the HRT and nonHRT groups. Moderate-intensity exercise [Formula: see text]O2p kinetics were significantly speeded (p < 0.05) with the τ[Formula: see text]O2p decreasing from 46 ± 8 s before training to 32 ± 4 s after training. Similarly, during the heavy-intensity exercise, on-transient phase 2 τ[Formula: see text]O2p was reduced from before training (48 ± 7 s) to after training (38 ± 6 s). The use of HRT did not influence the effect of the endurance exercise training on τ[Formula: see text]O2p during moderate or heavy exercise in healthy postmenopausal women. To provide insight into the mechanism of adjustment, knee extension exercise was studied, and the [Formula: see text]O2p kinetics were significantly speeded (p < 0.05), with the τ[Formula: see text]O2p of the knee extension exercise decreasing from 62.2 ± 18.3 s before training to 48.0 ± 16.2 s after training. Thus, 6 weeks of exercise training resulted in appreciably faster cycling phase 2 [Formula: see text]O2p kinetics during moderate and heavy exercise in older women, independent of HRT use.

Effects of short-term dietary nitrate supplementation on blood pressure, O2 uptake kinetics, and muscle and cognitive function in older adults

Dietary nitrate (NO3−) supplementation has been shown to reduce resting blood pressure and alter the physiological response to exercise in young adults. We investigated whether these effects might also be evident in older adults. In a double-blind, randomized, crossover study, 12 healthy, older (60–70 yr) adults supplemented their diet for 3 days with either nitrate-rich concentrated beetroot juice (BR; 2 × 70 ml/day, ∼9.6 mmol/day NO3−) or a nitrate-depleted beetroot juice placebo (PL; 2 × 70 ml/day, ∼0.01 mmol/day NO3−). Before and after the intervention periods, resting blood pressure and plasma [nitrite] were measured, and subjects completed a battery of physiological and cognitive tests. Nitrate supplementation significantly increased plasma [nitrite] and reduced resting systolic (BR: 115 ± 9 vs. PL: 120 ± 6 mmHg; P < 0.05) and diastolic (BR: 70 ± 5 vs. PL: 73 ± 5 mmHg; P < 0.05) blood pressure. Nitrate supplementation resulted in a speeding of the V̇o2 mean response time (BR: 25 ± 7 vs. PL: 28 ± 7 s; P < 0.05) in the transition from standing rest to treadmill walking, although in contrast to our hypothesis, the O2 cost of exercise remained unchanged. Functional capacity (6-min walk test), the muscle metabolic response to low-intensity exercise, brain metabolite concentrations, and cognitive function were also not altered. Dietary nitrate supplementation reduced resting blood pressure and improved V̇o2 kinetics during treadmill walking in healthy older adults but did not improve walking or cognitive performance. These results may have implications for the enhancement of cardiovascular health in older age.

Tolerance to high-intensity intermittent running exercise: do oxygen uptake kinetics really matter?

We examined the respective associations between aerobic fitness (V˙O2max), metabolic control (V˙O2 kinetics) and locomotor function, and various physiological responses to high-intensity intermittent (HIT) running exercise in team sport players. Eleven players (30.5 ± 3.6 year) performed a series of tests to determine their V˙O2max and the associated velocity (vV˙O2max), maximal sprinting speed (MSS) and V˙O2 kinetics at exercise onset in the moderate and severe intensity domains, and during recovery (V˙O2τoff SEV). Cardiorespiratory variables, oxygenation and electromyography of lower limbs muscles and blood lactate ([La]) concentration were collected during a standardized HIT protocol consisting in 8 sets of 10, 4-s runs. During HIT, four players could not complete more than two sets; the others finished at least five sets. Metabolic responses to the two first sets of HIT were negatively correlated with V˙O2max, vV˙O2max, and V˙O2τoff SEV (r = −0.6 to −0.8), while there was no clear relationship with the other variables. V˙O2, oxygenation and [La] responses to the first two sets of HIT were the only variables that differed between the players which could complete at least five sets or those who could not complete more than two sets. Players that managed to run at least five sets presented, in comparison with the others, greater vV˙O2max [ES = +1.5(0.4; 2.7), MSS(ES = +1.0(0.1; 1.9)] and training load [ES = +3.8 (2.8; 4.9)]. There was no clear between-group difference in any of the V˙O2 kinetics measures [e.g., ES = −0.1(−1.4; 1.2) for V˙O2τon SEV]. While V˙O2max and vV˙O2max are likely determinant for HIT tolerance, the importance of V˙O2 kinetics as assessed in this study appears limited in the present population. Knowing the main factors influencing tolerance to HIT running exercise may assist practitioners in personalizing training interventions.

Adjustments of pulmonary O2 uptake and muscle deoxygenation during ramp incremental exercise and constant-load moderate-intensity exercise in young and older adults

The matching of muscle O(2) delivery to O(2) utilization can be inferred from the adjustments in muscle deoxygenation (Δ[HHb]) and pulmonary O(2) uptake (Vo(2p)). This study examined the adjustments of Vo(2p) and Δ[HHb] during ramp incremental (RI) and constant-load (CL) exercise in adult males. Ten young adults (YA; age: 25 ± 5 yr) and nine older adults (OA; age: 70 ± 3 yr) completed two RI tests and six CL step transitions to a work rate (WR) corresponding to 1) 80% of the estimated lactate threshold (same relative WR) and 2) 50 W (same absolute WR). Vo(2p) was measured breath by breath, and Δ[HHb] of the vastus lateralis was measured using near-infrared spectroscopy. Δ[HHb]-WR profiles were normalized from baseline (0%) to peak Δ[HHb] (100%) and fit using a sigmoid function. The sigmoid slope (d) was greater (P < 0.05) in OA (0.027 ± 0.01%/W) compared with YA (0.017 ± 0.01%/W), and the c/d value (a value corresponding to 50% of the amplitude) was smaller (P < 0.05) for OA (133 ± 40 W) than for YA (195 ± 51 W). No age-related differences in the sigmoid parameters were reported when WR was expressed as a percentage of peak WR. Vo(2p) kinetics compared with Δ[HHb] kinetics for the 50-W transition were similar between YA and OA; however, Δ[HHb] kinetics during the transition to 80% of the lactate threshold were faster than Vo(2p) kinetics in both groups. The greater reliance on O(2) extraction displayed in OA during RI exercise suggests a lower O(2) delivery-to-O(2) utilization relationship at a given absolute WR compared with YA.

Heliox increases quadriceps muscle oxygen delivery during exercise in COPD patients with and without dynamic hyperinflation

Some reports suggest that heliox breathing during exercise may improve peripheral muscle oxygen availability in patients with chronic obstructive pulmonary disease (COPD). Besides COPD patients who dynamically hyperinflate during exercise (hyperinflators), there are patients who do not hyperinflate (non-hyperinflators). As heliox breathing may differently affect cardiac output in hyperinflators (by increasing preload and decreasing afterload of both ventricles) and non-hyperinflators (by increasing venous return) during exercise, it was reasoned that heliox administration would improve peripheral muscle oxygen delivery possibly by different mechanisms in those two COPD categories. Chest wall volume and respiratory muscle activity were determined during constant-load exercise at 75% peak capacity to exhaustion, while breathing room air or normoxic heliox in 17 COPD patients: 9 hyperinflators (forced expiratory volume in 1 s = 39 ± 5% predicted), and 8 non-hyperinflators (forced expiratory volume in 1 s = 48 ± 5% predicted). Quadriceps muscle blood flow was measured by near-infrared spectroscopy using indocyanine green dye. Hyperinflators and non-hyperinflators demonstrated comparable improvements in endurance time during heliox (231 ± 23 and 257 ± 28 s, respectively). At exhaustion in room air, expiratory muscle activity (expressed by peak-expiratory gastric pressure) was lower in hyperinflators than in non-hyperinflators. In hyperinflators, heliox reduced end-expiratory chest wall volume and diaphragmatic activity, and increased arterial oxygen content (by 17.8 ± 2.5 ml/l), whereas, in non-hyperinflators, heliox reduced peak-expiratory gastric pressure and increased systemic vascular conductance (by 11.0 ± 2.8 ml·min(-1)·mmHg(-1)). Quadriceps muscle blood flow and oxygen delivery significantly improved during heliox compared with room air by a comparable magnitude (in hyperinflators by 6.1 ± 1.3 ml·min(-1)·100 g(-1) and 1.3 ± 0.3 ml O(2)·min(-1)·100 g(-1), and in non-hyperinflators by 7.2 ± 1.6 ml·min(-1)·100 g(-1) and 1.6 ± 0.3 ml O(2)·min(-1)·100 g(-1), respectively). Despite similar increase in locomotor muscle oxygen delivery with heliox in both groups, the mechanisms of such improvements were different: 1) in hyperinflators, heliox increased arterial oxygen content and quadriceps blood flow at similar cardiac output, whereas 2) in non-hyperinflators, heliox improved central hemodynamics and increased systemic vascular conductance and quadriceps blood flow at similar arterial oxygen content.

Influence of exercise intensity on pulmonary oxygen uptake kinetics in young and late middle-aged adults

It is unclear whether pulmonary oxygen uptake (Vo2) kinetics demonstrate linear, first-order behavior during supra gas exchange threshold exercise. Resolution of this issue is pertinent to the elucidation of the factors regulating oxygen uptake (Vo2) kinetics, with oxygen availability and utilization proposed as putative mediators. To reexamine this issue with the advantage of a relatively large sample size, 50 young (24 ± 4 yr) and 15 late middle-aged (54 ± 3 yr) participants completed repeated bouts of moderate and heavy exercise. Pulmonary gas exchange, heart rate (HR), and cardiac output (Q) variables were measured throughout. The phase II τ was slower during heavy exercise in both young (moderate: 22 ± 9; heavy: 29 ± 9 s; P ≤ 0.001) and middle-aged (moderate: 22 ± 9; heavy: 30 ± 8 s; P ≤ 0.001) individuals. The HR τ was slower during heavy exercise in young (moderate: 33 ± 10; heavy: 44 ± 15 s; P ≤ 0.05) and middle-aged (moderate: 30 ± 12; heavy: 50 ± 20 s; P ≤ 0.05) participants, and the Q τ showed a similar trend (young moderate: 21 ± 13; heavy: 28 ± 16 s; middle-aged moderate: 32 ± 13; heavy: 40 ± 15 s; P ≥ 0.05). There were no differences in primary component Vo2 kinetics between age groups, but the middle-aged group had a significantly reduced Vo2 slow component amplitude in both absolute (young: 0.25 ± 0.09; middle-aged: 0.11 ± 0.06 l/min; P ≤ 0.05) and relative terms (young: 15 ± 10; middle-aged: 9 ± 4%; P ≤ 0.05). Thus Vo2 kinetics do not demonstrate dynamic linearity during heavy intensity exercise. Speculatively, the slower phase II τ during heavy exercise might be attributable to reduced oxygen availability. Finally, the primary and slow components of Vo2 kinetics appear to be differentially influenced by middle age.

Speeding of pulmonary VO2 on-kinetics by light-to-moderate-intensity aerobic exercise training in chronic heart failure: clinical and pathophysiological correlates

BACKGROUND

Pulmonary VO2 on-kinetics during light-to-moderate-intensity constant-work-rate exercise, an experimental model mirroring energetic transitions during daily activities, has been shown to speed up with aerobic exercise training (AET) in normal subjects, but scant data are available in chronic heart failure (CHF).

METHODS AND RESULTS

Thirty CHF patients were randomized to 3 months of light-to-moderate-intensity AET (CHF-AET) or control (CHF-C). Baseline and end-protocol evaluations included i) one incremental cardiopulmonary exercise test with near infrared spectroscopy analysis of peak deoxygenated hemoglobin+myoglobin concentration changes (Δ[deoxy(Hb+Mb)]) in vastus lateralis muscle, ii) 8 light-to-moderate-intensity constant-work-rate exercise tests for VO2 on-kinetics phase I duration, phase II τ, and mean response time (MRT) assessment, and iii) circulating endothelial progenitor cell (EPC) measurement. Reference values were obtained in 7 age-matched normals (N). At end-protocol, phase I duration, phase II τ, and MRT were significantly reduced (-12%, -22%, and -19%, respectively) and peak VO2, peak Δ[deoxy(Hb+Mb)], and EPCs increased (9%, 20%, and 98%, respectively) in CHF-AET, but not in CHF-C. Peak Δ[deoxy(Hb+Mb)] and EPCs relative increase correlated significantly to that of peak VO2 (r=0.61 and 0.64, respectively, p<0.05).

CONCLUSIONS

Light-to-moderate-intensity AET determined a near-normalization of pulmonary VO2 on-kinetics in CHF patients. Such a marked plasticity has important implications for AET intensity prescription, especially in patients more functionally limited and with high exercise-related risk. The AET-induced simultaneous improvement of phase I and phase II, associated with an increase of peak peripheral oxygen extraction and EPCs, supports microcirculatory O2 delivery impairment as a key factor determining exercise intolerance in CHF.

Influence of all-out and fast start on 5-min cycling time trial performance

PURPOSE

To examine the influence of two different fast-start pacing strategies on performance and oxygen consumption (VO2) during cycle ergometer time trials lasting ∼5 min.

METHODS

Eight trained male cyclists performed four cycle ergometer time trials whereby the total work completed (113 ± 11.5 kJ; mean ± SD) was identical to the better of two 5-min self-paced familiarization trials. During the performance trials, initial power output was manipulated to induce either an all-out or a fast start. Power output during the first 60 s of the fast-start trial was maintained at 471.0 ± 48.0 W, whereas the all-out start approximated a maximal starting effort for the first 15 s (mean power: 753.6 ± 76.5 W) followed by 45 s at a constant power output (376.8 ± 38.5 W). Irrespective of starting strategy, power output was controlled so that participants would complete the first quarter of the trial (28.3 ± 2.9 kJ) in 60 s. Participants performed two trials using each condition, with their fastest time trial compared.

RESULTS

Performance time was significantly faster when cyclists adopted the all-out start (4 min 48 s ± 8 s) compared with the fast start (4 min 51 s ± 8 s; P < 0.05). The first-quarter VO2 during the all-out start trial (3.4 ± 0.4 L·min(-1)) was significantly higher than during the fast-start trial (3.1 ± 0.4 L·min(-1); P < 0.05). After removal of an outlier, the percentage increase in first-quarter VO2 was significantly correlated (r = -0.86, P < 0.05) with the relative difference in finishing time.

CONCLUSIONS

An all-out start produces superior middle distance cycling performance when compared with a fast start. The improvement in performance may be due to a faster VO2 response rather than time saved due to a rapid acceleration.

Skeletal muscle reoxygenation after high-intensity exercise in mitochondrial myopathy

This study addressed whether O(2) delivery during recovery from high-intensity, supra-gas exchange threshold exercise would be matched to O(2) utilization at the microvascular level in patients with mitochondrial myopathy (MM). Off-exercise kinetics of (1) pulmonary O(2) uptake VO(2P) (2) an index of fractional O(2) extraction by near-infrared spectroscopy (Δ[deoxy-Hb + Mb]) in the vastus lateralis and (3) cardiac output (Q'(T)) by impedance cardiography were assessed in 12 patients with biopsy-proven MM (chronic progressive external ophthalmoplegia) and 12 age- and gender-matched controls. Kinetics of VO(2P) were significantly slower in patients than controls (τ = 53.8 ± 16.5 vs. 38.8 ± 7.6 s, respectively; p < 0.05). Q'(T), however, declined at similar rates (τ = 64.7 ± 18.8 vs. 73.0 ± 21.6 s; p > 0.05) being typically slower than [Formula: see text] in both groups. Importantly, Δ[deoxy-Hb + Mb] dynamics (MRT) were equal to, or faster than, τVO(2P) in patients and controls, respectively. In fact, there were no between-group differences in τVO(2P)MRTΔ[deoxy-Hb + Mb] (1.1 ± 0.4 vs. 1.0 ± 0.2, p > 0.05) thereby indicating similar rates of microvascular O(2) delivery. These data indicate that the slower rate of recovery of muscle metabolism after high-intensity exercise is not related to impaired microvascular O(2) delivery in patients with MM. This phenomenon, therefore, seems to reflect the intra-myocyte abnormalities that characterize this patient population.

Skyscraper running: physiological and biomechanical profile of a novel sport activity

Skyscraper running is here analyzed in terms of mechanical and metabolic requirements, both at the general and at the individual level. Skyscraper runners' metabolic profile has been inferred from the total mechanical power estimated in 36 world records (48-421 m tall buildings), ranked by gender and age range. Individual athlete's performance (n=13) has been experimentally investigated during the Pirelli Vertical Sprint, with data loggers for altitude and heart rate (HR). At a general level, a non-linear regression of Wilkie's model relating maximal mechanical power to event duration revealed the gender and age differences in terms of maximum aerobic power and anaerobic energy resources particularly needed at the beginning of the race. The total mechanical power was found to be partitioned among: the fraction devolved to raise the body center of mass , the need to accelerate the limbs with respect to the body , and running in turns between flights of stairs . At the individual level, experiments revealed that these athletes show a metabolic profile similar to middle-distance runners. Furthermore, best skyscraper runners maintain a constant vertical speed and HR throughout the race, while others suddenly decelerate, negatively affecting the race performance.

Frontal cerebral cortex blood flow, oxygen delivery and oxygenation during normoxic and hypoxic exercise in athletes

During maximal hypoxic exercise, a reduction in cerebral oxygen delivery may constitute a signal to the central nervous system to terminate exercise. We investigated whether the rate of increase in frontal cerebral cortex oxygen delivery is limited in hypoxic compared to normoxic exercise. We assessed frontal cerebral cortex blood flow using near-infrared spectroscopy and the light-absorbing tracer indocyanine green dye, as well as frontal cortex oxygen saturation (S(tO2)%) in 11 trained cyclists during graded incremental exercise to the limit of tolerance (maximal work rate, WRmax) in normoxia and acute hypoxia (inspired O2 fraction (F(IO2)), 0.12). In normoxia, frontal cortex blood flow and oxygen delivery increased (P < 0.05) from baseline to sub-maximal exercise, reaching peak values at near-maximal exercise (80% WRmax: 287 ± 9 W; 81 ± 23% and 75 ± 22% increase relative to baseline, respectively), both leveling off thereafter up to WRmax (382 ± 10 W). Frontal cortex S(tO2)% did not change from baseline (66 ± 3%) throughout graded exercise. During hypoxic exercise, frontal cortex blood flow increased (P = 0.016) from baseline to sub-maximal exercise, peaking at 80% WRmax (213 ± 6 W; 60 ± 15% relative increase) before declining towards baseline at WRmax (289 ± 5 W). Despite this, frontal cortex oxygen delivery remained unchanged from baseline throughout graded exercise, being at WRmax lower than at comparable loads (287 ± 9 W) in normoxia (by 58 ± 12%; P = 0.01). Frontal cortex S(tO2)% fell from baseline (58 ± 2%) on light and moderate exercise in parallel with arterial oxygen saturation, but then remained unchanged to exhaustion (47 ± 1%). Thus, during maximal, but not light to moderate, exercise frontal cortex oxygen delivery is limited in hypoxia compared to normoxia. This limitation could potentially constitute the signal to limit maximal exercise capacity in hypoxia.

Influence of phase I duration on phase II V̇o2 kinetics parameter estimates in older and young adults

Older adults (O) may have a longer phase I pulmonary O2 uptake kinetics (V̇o2p) than young adults (Y); this may affect parameter estimates of phase II V̇o2p. Therefore, we sought to: 1) experimentally estimate the duration of phase I V̇o2p (EE phase I) in O and Y subjects during moderate-intensity exercise transitions; 2) examine the effects of selected phase I durations (i.e., different start times for modeling phase II) on parameter estimates of the phase II V̇o2p response; and 3) thereby determine whether slower phase II kinetics in O subjects represent a physiological difference or a by-product of fitting strategy. V̇o2p was measured breath-by-breath in 19 O (68 ± 6 yr; mean ± SD) and 19 Y (24 ± 5 yr) using a volume turbine and mass spectrometer. Phase I V̇o2p was longer in O (31 ± 4 s) than Y (20 ± 7 s) ( P < 0.05). In O, phase II τV̇o2p was larger ( P < 0.05) when fitting started at 15 s (49 ± 12 s) compared with fits starting at the individual EE phase I (43 ± 12 s), 25 s (42 ± 10 s), 35 s (42 ± 12 s), and 45 s (45 ± 15 s). In Y, τV̇o2p was not affected by the time at which phase II V̇o2p fitting started (τV̇o2p = 31 ± 7 s, 29 ± 9 s, 30 ± 10 s, 32 ± 11 s, and 30 ± 8 s for fittings starting at 15 s, 25 s, 35 s, 45 s, and EE phase I, respectively). Fitting from EE phase I, 25 s, or 35 s resulted in the smallest CI τV̇o2p in both O and Y. Thus, fitting phase II V̇o2p from (but not constrained to) 25 s or 35 s provides consistent estimates of V̇o2p kinetics parameters in Y and O, despite the longer phase I V̇o2p in O.

Quadriceps muscle blood flow and oxygen availability during repetitive bouts of isometric exercise in simulated sailing

In this study, we wished to determine whether the observed reduction in quadriceps muscle oxygen availability, reported during repetitive bouts of isometric exercise in simulated sailing efforts (i.e. hiking), is because of restricted muscle blood flow. Six national-squad Laser sailors initially performed three successive 3-min hiking bouts followed by three successive 3-min cycling tests sustained at constant intensities reproducing the cardiac output recorded during each of the three hiking bouts. The blood flow index (BFI) was determined from assessment of the vastus lateralis using near-infrared spectroscopy in association with the light-absorbing tracer indocyanine green dye, while cardiac output was determined from impedance cardiography. At equivalent cardiac outputs (ranging from 10.3±0.5 to 14.8±0.86 L · min(-1)), the increase from baseline in vastus lateralis BFI across the three hiking bouts (from 1.1±0.2 to 3.1±0.6 nM · s(-1)) was lower (P = 0.036) than that seen during the three cycling bouts (from 1.1±0.2 to 7.2±1.4 nM · s(-1)) (Cohen's d: 3.80 nM · s(-1)), whereas the increase from baseline in deoxygenated haemoglobin (by ∼17.0±2.9 μM) (an index of tissue oxygen extraction) was greater (P = 0.006) during hiking than cycling (by ∼5.3±2.7 μM) (Cohen's d: 4.17 μM). The results suggest that reduced vastus lateralis muscle oxygen availability during hiking arises from restricted muscle blood flow in the isometrically acting quadriceps muscles.

Pulmonary O2 uptake kinetics as a determinant of high-intensity exercise tolerance in humans

Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.

Effect of heliox on heart rate kinetics and dynamic hyperinflation during high-intensity exercise in COPD

Respiratory mechanical abnormalities in patients with chronic obstructive pulmonary disease (COPD) may impair cardiodynamic responses and slow down heart rate (HR) kinetics compared with normal resulting in reduced convective oxygen delivery during exercise. We reasoned that heliox breathing (79% helium-21% oxygen) and the attendant reduction of operating lung volumes should accelerate HR kinetics in the transition from rest to high-intensity exercise. Eleven male ambulatory patients with clinically stable COPD undertook constant work-rate cycle testing at 80% of each individuals' maximum work capacity while breathing room air (RA) or heliox (HX), randomly. Mean response time (MRT) for HR and dynamic end-expiratory lung volume (EELV) were measured. Resting EELV was not affected by HX breathing, while exercise EELV decreased significantly by 0.23 L at isotime during HX breathing compared with RA. During HX breathing, MRT for HR significantly accelerated (p = 0.002) by an average of 20 s (i.e., 17%). Speeded MRT for HR correlated with indices of reduced lung hyperinflation, such as EELV at isotime (r = 0.88, p = 0.03), and with improved exercise endurance time (r = -0.64, p = 0.03). The results confirm that HX-induced reduction of dynamic lung hyperinflation is associated with consistent improvement in indices of cardio-circulatory function such as HR kinetics in the rest-to-exercise transition in COPD patients.

Is tonic sympathetic vasoconstriction increased in the skeletal muscle vasculature of aged canines?

We tested the hypothesis that tonic adrenergic and nonadrenergic receptor-mediated sympathetic vasoconstriction would increase at rest and during exercise with advancing age. Young (n = 6; 22 ± 1 mo; means ± SE) and old (n = 6; 118 ± 9 mo) beagles were studied. Selective antagonists for alpha-1, alpha-2, neuropeptide Y (NPY), and purinergic (P(2x)) receptors were infused at rest and during treadmill running at 2.5 mph and 4 mph with 2.5% grade. Prazosin produced similar increases in vascular conductance in young and old beagles at rest (Young: 158 ± 34%; Old: 98 ± 19%) and during exercise at 2.5 mph (Young: 80 ± 10%; Old: 58 ± 12%) and 4 mph and 2.5% grade (Young: 57 ± 5%; Old: 26 ± 4%). Rauwolscine caused similar (P > 0.05) increases in vascular conductance in old compared with young dogs at rest (Young: 119 ± 25%; Old: 64 ± 22%) and at 2.5 mph (Young: 86 ± 13%; Old: 60 ± 7%) and 4 mph with 2.5% grade (Young: 61 ± 5%; Old: 43 ± 7%). N2-(diphenylacetyl)-N-[4-hydroxyphenyl)methyl]-d-arginine amide (BIBP) caused a smaller increase (P < 0.05) in vascular conductance in old compared with young dogs at rest (Young: 179 ± 44%; Old: 91 ± 22%), whereas similar increases (P > 0.05) of experimental limb vascular conductance in young and old dogs occurred following BIBP during exercise at 2.5 mph (Young: 56 ± 16%; Old: 50 ± 12%) and 4 mph and 2.5% grade (Young: 45 ± 10%; Old: 25 ± 7%). Pyridoxal-phosphate-6-azophenyl-2'-4'-disulfonic acid infusion produced a larger increase in vascular conductance in old compared with young beagles at rest (Young: 88 ± 14%; Old: 191 ± 58%), whereas similar increases were observed at 2.5 mph (Young: 47 ± 18%; Old: 31 ± 11%) and 4 mph with 2.5% grade (Young: 26 ± 13%; Old: -18 ± 8%). At rest, NPY receptor-mediated restraint of skeletal muscle blood flow was reduced with advancing age, whereas P(2x) receptor-mediated restraint of skeletal muscle blood flow was increased. During exercise, the magnitude of adrenergic and nonadrenergic sympathetic vasoconstriction was not different between young and old dogs. Overall, these data demonstrate that adrenergic receptor-mediated vasoconstriction was not elevated at rest, but nonadrenergic sympathetic vasoconstriction was altered under basal conditions in aged beagles.

Performance and physiological responses to repeated-sprint and jump sequences

In this study, the performance and selected physiological responses to team-sport specific repeated-sprint and jump sequence were investigated. On four occasions, 13 team-sport players (22 ± 3 year) performed alternatively six repeated maximal straight-line or shuttle-sprints interspersed with a jump ([RS(+j), 6 × 25 m] or [RSS(+j), 6 × (2 × 12.5 m)]) or not ([RS, 6 × 25 m] or [RSS, 6 × (2 × 12.5 m)]) within each recovery period. Mean running time, rate of perceived exertion (RPE), pulmonary oxygen uptake (V(O)₂), blood lactate ([La](b)), and vastus lateralis deoxygenation ([HHb]) were obtained for each condition. Mean sprint times were greater for RS(+j) versus RS (4.14 ± 0.17 vs. 4.09 ± 0.16 s, with the qualitative analysis revealing a 82% chance of RS(+j) times to be greater than RS) and for RSS(+j) versus RSS (5.43 ± 0.18 vs. 5.29 ± 0.17 s; 99% chance of RSS(+j) to be >RSS). The correlation between sprint and jump abilities were large-to-very-large, but below 0.71 for RSSs. Jumps increased RPE (Cohen's d ± 90% CL: +0.7 ± 0.5; 95% chance for RS(+j) > RS and +0.7 ± 0.5; 96% for RSS(+j) > RSS), V(O)₂(+0.4 ± 0.5; 80% for RS(+j) > RS and +0.5 ± 0.5; 86% for RSS(+j) > RSS), [La](b) (+0.5 ± 0.5; 59% for RS(+j) > RS and +0.2 ± 0.5; unclear for RSS(+j) > RSS), and [HHb] (+0.5 ± 0.5; 86% for RS(+j) > RS and +0.5 ± 0.5; 85% for RSS(+j) > RSS). To conclude, repeated- sprint and jump abilities could be considered as specific qualities. The addition of a jump within the recovery periods during repeated-sprint running sequences impairs sprinting performance and might be an effective training practice for eliciting both greater systemic and vastus lateralis physiological loads.

Heterogeneity of muscle deoxygenation kinetics during two bouts of repeated heavy exercises

This study examines the effect of prior heavy exercise on the spatial distribution of muscle deoxygenation kinetics at the onset of heavy-intensity cycling exercise. Young untrained male adults (n = 16) performed two consecutive bouts of 6 min of high intensity cycle exercise separated by 6 min at 35 W. Muscle deoxygenation (HHb) was monitored continuously by near-infrared spectroscopy at eight sites in the quadriceps. Prior heavy exercise reduced the delay before the increase in HHb (9 +/- 2 vs. 5 +/- 2 s; P < 0.001). The standard deviation of TD HHb of the eight sites was decreased by the performance of prior exercise (1.1 +/- 0.5 vs. 0.8 +/- 0.4 s; P < 0.05). The transient decrease in HHb during the first 10 s of exercise was less during the second bout than during the first bout (0.6 +/- 0.6 vs. 0.3 +/- 0.3 A.U.; P < 0.01). The standard deviation of this decrease was also reduced by prior exercise (0.5 +/- 0.3 vs. 0.3 +/- 0.2 A.U.; P < 0.01). Lastly, prior exercise decreased significantly the standard deviation of the HHb rise during the time period corresponding to the pulmonary VO(2) slow component. These results indicate that prior heavy exercise reduced the spatial heterogeneity of muscle deoxygenation kinetics at the early onset of heavy exercise and during the development of the pulmonary VO(2) slow component. It indicates that the distribution of the VO(2)/O(2) delivery ratio within muscle was improved by the performance of a prior exercise.

Speeding of VO2 kinetics with endurance training in old and young men is associated with improved matching of local O2 delivery to muscle O2 utilization

The time course and mechanisms of adjustment of pulmonary oxygen uptake (V(O(2))) kinetics (time constant tauV(O(2p))) were examined during step transitions from 20 W to moderate-intensity cycling in eight older men (O; 68 +/- 7 yr) and eight young men (Y; 23 +/- 5 yr) before training and at 3, 6, 9, and 12 wk of endurance training. V(O(2p)) was measured breath by breath with a volume turbine and a mass spectrometer. Changes in deoxygenated hemoglobin concentration (Delta[HHb]) were measured by near-infrared spectroscopy. V(O(2p)) and Delta[HHb] were modeled with a monoexponential model. Training was performed on a cycle ergometer three times per week for 45 min at approximately 70% of peak V(O(2)). Pretraining tauV(O(2p)) was greater (P < 0.05) in O (43 +/- 10 s) than Y (34 +/- 8 s). tauV(O(2p)) decreased (P < 0.05) by 3 wk of training in both O (35 +/- 9 s) and Y (22 +/- 8 s), with no further changes thereafter. The pretraining overall adjustment of Delta[HHb] was faster than tauV(O(2p)) in both O and Y, resulting in Delta[HHb]/V(O(2p)) displaying an "overshoot" during the transient relative to the subsequent steady-state level. After 3 wk of training the Delta[HHb]/V(O(2p)) overshoot was attenuated in both O and Y. With further training, this overshoot persisted in O but was eliminated after 6 wk in Y. The training-induced speeding of V(O(2p)) kinetics in O and Y at 3 wk of training was associated with an improved matching of local O(2) delivery to muscle V(O(2)) (as represented by a lower Delta[HHb]/V(O(2p))). The continued overshoot in Delta[HHb]/V(O(2p)) in O may reflect a reduced vasodilatory responsiveness that may limit muscle blood flow distribution during the on-transient of exercise.

Plasma ATP concentration and venous oxygen content in the forearm during dynamic handgrip exercise

Background

It has been proposed that adenosine triphosphate (ATP) released from red blood cells (RBCs) may contribute to the tight coupling between blood flow and oxygen demand in contracting skeletal muscle. To determine whether ATP may contribute to the vasodilatory response to exercise in the forearm, we measured arterialised and venous plasma ATP concentration and venous oxygen content in 10 healthy young males at rest, and at 30 and 180 seconds during dynamic handgrip exercise at 45% of maximum voluntary contraction (MVC).

Results

Venous plasma ATP concentration was elevated above rest after 30 seconds of exercise (P < 0.05), and remained at this higher level 180 seconds into exercise (P < 0.05 versus rest). The increase in ATP was mirrored by a decrease in venous oxygen content. While there was no significant relationship between ATP concentration and venous oxygen content at 30 seconds of exercise, they were moderately and inversely correlated at 180 seconds of exercise (r = -0.651, P = 0.021). Arterial ATP concentration remained unchanged throughout exercise, resulting in an increase in the venous-arterial ATP difference.

Conclusions

Collectively these results indicate that ATP in the plasma originated from the muscle microcirculation, and are consistent with the notion that deoxygenation of the blood perfusing the muscle acts as a stimulus for ATP release. That ATP concentration was elevated just 30 seconds after the onset of exercise also suggests that ATP may be a contributing factor to the blood flow response in the transition from rest to steady state exercise.

Moderate and heavy oxygen uptake kinetics in postmenopausal women

The lack of estrogen in postmenopausal women not using hormone replacement therapy (HRT), compared with those using HRT, may reduce submaximal blood flow during exercise and result in an oxygen delivery limitation constraining oxygen uptake (VO2) kinetics. The adaptation of pulmonary VO2 (VO2p) during the transition to exercise in older women was examined in this study. Thirty-one healthy postmenopausal women (mean age, 61 ± 6 years), 15 not using HRT and 16 using HRT, performed repeated exercise transitions (6 min) on a cycle, to work rates corresponding to 80% of estimated ventilatory threshold (moderate-intensity exercise) and to Δ50 (heavy-intensity exercise). There was no difference in moderate-intensity τVO2p between non-HRT (40 ± 9 s) and HRT (41 ± 9 s) women. Similarly, there was no difference in heavy-intensity τVO2p between non-HRT (44 ± 8 s) and HRT (45 ± 8 s) women. Thus, HRT did not affect the slowing of VO2 kinetics of older women.

Aging blunts the dynamics of vasodilation in isolated skeletal muscle resistance vessels

Aging is associated with an altered ability to match oxygen delivery (QO2) to consumption ((.)VO2) in skeletal muscle and differences in the temporal profile of vasodilation may provide a mechanistic basis for the QO2-to-(.)VO2 mismatching during the rest-to-exercise transition. Therefore, we tested the hypothesis that the speed of vasodilation will be blunted in skeletal muscle first-order arterioles from old vs. young rats. Arterioles from the soleus and the red portion of the gastrocnemius (Gast(Red)) muscles were isolated from young (Y, 6 mo; n = 9) and old (O, 24 mo; n = 9) Fischer 344 rats and studied in vitro. Vessels were exposed to acetylcholine (ACh; 10(-6) M), sodium nitroprusside (SNP; 10(-4) M), and increased intraluminal flow, and the subsequent vasodilation was recorded at 30 frames/s. The data were fit to a monoexponential model and the dynamics of vasodilation [i.e., time delay, time constant (tau), and rate of change (delta/tau)] were calculated. With old age, the rate of vasodilation was significantly blunted in resistance vessels from the soleus to ACh (Y, 27.9 +/- 3.6; O, 8.8 +/- 2.6 microm/s) and flow (Y, 12.8 +/- 2.1; O, 3.1 +/- 0.9 microm/s). In the Gast(Red) the old age-associated impairment of endothelium-dependent vasodilator dynamics was even greater than that of the soleus. With SNP neither the magnitude nor time constant of vasodilation was affected by age in either muscle. The results indicate that aging impairs the dynamics of vasodilation in resistance vessels from the soleus and Gast(Red) muscles mediated, in part, through the endothelium. Thus the old age-associated slower rate and magnitude of vasodilation could inhibit the delivery of O2 during the critical transition from rest to exercise in moderate to highly oxidative skeletal muscle.

Microvascular oxygen delivery-to-utilization mismatch at the onset of heavy-intensity exercise in optimally treated patients with CHF

Impaired muscle blood flow at the onset of heavy-intensity exercise may transiently reduce microvascular O(2) pressure and decrease the rate of O(2) transfer from capillary to mitochondria in chronic heart failure (CHF). However, advances in the pharmacological treatment of CHF (e.g., angiotensin-converting enzyme inhibitors and third-generation beta-blockers) may have improved microvascular O(2) delivery to an extent that intramyocyte metabolic inertia might become the main locus of limitation of O(2) uptake (Vo(2)) kinetics. We assessed the rate of change of pulmonary Vo(2) (Vo(2)(p)), (estimated) fractional O(2) extraction in the vastus lateralis (approximately Delta[deoxy-Hb+Mb] by near-infrared spectroscopy), and cardiac output (Qt) during high-intensity exercise performed to the limit of tolerance (Tlim) in 10 optimally treated sedentary patients (ejection fraction = 29 + or - 8%) and 11 controls. Sluggish Vo(2)(p) and Qt kinetics in patients were significantly related to lower Tlim values (P < 0.05). The dynamics of Delta[deoxy-Hb+Mb], however, were faster in patients than controls [mean response time (MRT) = 15.9 + or - 2.0 s vs. 19.0 + or - 2.9 s; P < 0.05] with a subsequent response "overshoot" being found only in patients (7/10). Moreover, tauVo(2)/MRT-[deoxy-Hb+Mb] ratio was greater in patients (4.69 + or - 1.42 s vs. 2.25 + or - 0.77 s; P < 0.05) and related to Qt kinetics and Tlim (R = 0.89 and -0.78, respectively; P < 0.01). We conclude that despite the advances in the pharmacological treatment of CHF, disturbances in "central" and "peripheral" circulatory adjustments still play a prominent role in limiting Vo(2)(p) kinetics and tolerance to heavy-intensity exercise in nontrained patients.

Bronchodilator effect on ventilatory, pulmonary gas exchange, and heart rate kinetics during high-intensity exercise in COPD

Respiratory mechanical abnormalities in patients with chronic obstructive pulmonary disease (COPD) may impair cardiodynamic responses and convective oxygen delivery during exercise, resulting in slower ventilatory, pulmonary gas exchange (PGE), and heart rate (HR) kinetics compared with normal. We reasoned that bronchodilators and the attendant reduction of operating lung volumes should accelerate ventilatory, PGE, and HR kinetics in the transition from rest to high-intensity exercise. Twelve clinically stable COPD patients undertook constant-work rate cycle testing at 75% of each individual's maximum work capacity after receiving either combined nebulized bronchodilators (BD) or placebo (PL), randomly. Mean response time (MRT) and amplitude of slow component for oxygen uptake (V'O(2)), carbon dioxide production (V'CO(2)), ventilation (V'(E)), and HR together with operating dynamic end-expiratory lung volume (EELV) were measured. Resting and exercise EELV decreased significantly by 0.38 L after BD compared with PL. After BD, V'O(2), V'CO(2), V'(E), and HR MRT accelerated (p < 0.05) by an average of 12, 22, 27, and 22 s, respectively (i.e., 15, 18, 22 and 27%, respectively). The slow component for V'O(2) declined by an average of 55 ml/min compared with PL. Speeded MRT for V'O(2) correlated with indices of reduced lung hyperinflation, such as resting EELV (r = -0.64, p = 0.025) and EELV at isotime (r = -0.77, p = 0.0032). The results confirm an important interaction between abnormal dynamic respiratory mechanics and indices of cardio-circulatory function in the rest-to-exercise transition in COPD patients.

Intercostal muscle blood flow limitation in athletes during maximal exercise

We investigated whether, during maximal exercise, intercostal muscle blood flow is as high as during resting hyperpnoea at the same work of breathing. We hypothesized that during exercise, intercostal muscle blood flow would be limited by competition from the locomotor muscles. Intercostal (probe over the 7th intercostal space) and vastus lateralis muscle perfusion were measured simultaneously in ten trained cyclists by near-infrared spectroscopy using indocyanine green dye. Measurements were made at several exercise intensities up to maximal (WRmax) and subsequently during resting isocapnic hyperpnoea at minute ventilation levels up to those at WRmax. During resting hyperpnoea, intercostal muscle blood flow increased linearly with the work of breathing (R2 = 0.94) to 73.0 +/- 8.8 ml min-1 (100 g)-1 at the ventilation seen at WRmax (work of breathing approximately 550-600 J min-1), but during exercise it peaked at 80% WRmax (53.4 +/- 10.3 ml min-1 (100 g)-1), significantly falling to 24.7 +/- 5.3 ml min-1 (100 g)-1 at WRmax. At maximal ventilation intercostal muscle vascular conductance was significantly lower during exercise (0.22 +/- 0.05 ml min-1 (100 g)-1 mmHg-1) compared to isocapnic hyperpnoea (0.77 +/- 0.13 ml min-1 (100 g)-1 mmHg-1). During exercise, both cardiac output and vastus lateralis muscle blood flow also plateaued at about 80% WRmax (the latter at 95.4 +/- 11.8 ml min-1 (100 g)-1). In conclusion, during exercise above 80% WRmax in trained subjects, intercostal muscle blood flow and vascular conductance are less than during resting hyperpnoea at the same minute ventilation. This suggests that the circulatory system is unable to meet the demands of both locomotor and intercostal muscles during heavy exercise, requiring greater O2 extraction and likely contributing to respiratory muscle fatigue.

Effect of prior exercise on pulmonary O2 uptake and estimated muscle capillary blood flow kinetics during moderate-intensity field running in men

The effect of prior exercise on pulmonary O2 uptake (VO2p) and estimated muscle capillary blood flow (Qm) kinetics during moderate-intensity, field-based running was examined in 14 young adult men, presenting with either moderately fast (16 s<tauVO2p<30 s; MFK) or very fast VO2p kinetics (tauVO2p<16 s; VFK) (i.e., primary time constant, tauVO2p). On four occasions, participants completed a square-wave protocol involving two bouts of running at 90-95% of estimated lactate threshold (Mod1 and Mod2), separated by 2 min of repeated supramaximal sprinting. VO2p was measured breath by breath, heart rate (HR) beat to beat, and vastus lateralis oxygenation {deoxy-hemoglobin/myoglobin concentration (deoxy-[Hb+Mb])} using near-infrared spectroscopy. Mean response time of Qm (Qm MRT) was estimated by rearranging the Fick equation, using VO2p and deoxy-[Hb+Mb] as proxies of muscle O2 uptake (VO2) and arteriovenous difference, respectively. HR, blood lactate concentration, total hemoglobin, and Qm were elevated before Mod2 compared with Mod1 (all P<0.05). tauVO2p was shorter in VFK compared with MFK during Mod1 (13.1+/-1.8 vs. 21.0+/-2.5 s, P<0.01), but not in Mod2 (12.9+/-1.5 vs. 13.7+/-3.8 s, P=1.0). Qm MRT was shorter in VFK compared with MFK in Mod1 (8.8+/-1.9 vs. 17.0+/-3.4 s, P<0.01), but not in Mod2 (10.1+/-1.8 vs. 10.5+/-3.5 s, P=1.0). During Mod2, HR kinetics were slowed, whereas mean deoxy-[Hb+Mb] response time was unchanged. The difference in tauVO2p between Mod1 and Mod2 was related to Qm MRT measured at Mod1 (r=0.71, P<0.01). Present results suggest that local O2 delivery (i.e., Qm) may be a factor contributing to the VO2 kinetic during the onset of moderate-intensity, field-based running exercise, at least in subjects exhibiting moderately fast VO2 kinetics.