RESUMO
This study tested the hypothesis that the respiratory compensation point (RCP) and breakpoint in deoxygenated [heme] [deoxy[heme]BP, assessed via near-infrared spectroscopy (NIRS)] during ramp incremental exercise would occur at the same metabolic rate in the upright (U) and supine (S) body positions. Eleven healthy men completed ramp incremental exercise tests in U and S. Gas exchange was measured breath-by-breath and time-resolved-NIRS was used to measure deoxy[heme] in the vastus lateralis (VL) and rectus femoris (RF). RCP (S: 2.56 ± 0.39, U: 2.86 ± 0.40 L·min-1, P = 0.02) differed from deoxy[heme]BP in the VL in U (3.10 ± 0.44 L·min-1, P = 0.002), but was not different in S in the VL (2.70 ± 0.50 L·min-1, P = 0.15). RCP was not different from the deoxy[heme]BP in the RF for either position (S: 2.34 ± 0.48 L·min-1, U: 2.76 ± 0.53 L·min-1, P > 0.05). However, the deoxy[heme]BP differed between muscles in both positions (P < 0.05), and changes in deoxy[heme]BP did not relate to ΔRCP between positions (VL: r = 0.55, P = 0.080, RF: r = 0.26, P = 0.44). The deoxy[heme]BP was consistently preceded by a breakpoint in total[heme], and was, in turn, itself preceded by a breakpoint in muscle surface electromyography (EMG). RCP and the deoxy[heme]BP can be dissociated across muscles and different body positions and, therefore, do not represent the same underlying physiological phenomenon. The deoxy[heme]BP may, however, be mechanistically related to breakpoints in total[heme] and muscle activity.
Assuntos
Metabolismo Energético , Exercício Físico , Hemoglobinas/metabolismo , Contração Muscular , Mioglobina/sangue , Consumo de Oxigênio , Troca Gasosa Pulmonar , Músculo Quadríceps/metabolismo , Decúbito Dorsal , Adolescente , Adulto , Biomarcadores/sangue , Eletromiografia , Voluntários Saudáveis , Humanos , Masculino , Espectroscopia de Luz Próxima ao Infravermelho , Fatores de Tempo , Adulto JovemRESUMO
PURPOSE: We tested the hypothesis that incremental ramp cycling exercise performed in the supine position (S) would be associated with an increased reliance on muscle deoxygenation (deoxy[heme]) in the deep and superficial vastus lateralis (VLd and VLs, respectively) and the superficial rectus femoris (RFs) when compared to the upright position (U). METHODS: 11 healthy men completed ramp incremental exercise tests in S and U. Pulmonary [Formula: see text]O2 was measured breath-by-breath; deoxy[heme] was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs. RESULTS: Supine exercise increased the overall change in deoxy[heme] from baseline to maximal exercise in the VLs (S: 38 ± 23 vs. U: 26 ± 15 µM, P < 0.001) and RFs (S: 36 ± 21 vs. U: 25 ± 15 µM, P < 0.001), but not in the VLd (S: 32 ± 23 vs. U: 29 ± 26 µM, P > 0.05). CONCLUSIONS: The present study supports that the impaired balance between O2 delivery and O2 utilization observed during supine exercise is a regional phenomenon within superficial muscles. Thus, deep muscle defended its O2 delivery/utilization balance against the supine-induced reductions in perfusion pressure. The differential responses of these muscle regions may be explained by a regional heterogeneity of vascular and metabolic control properties, perhaps related to fiber type composition.
Assuntos
Exercício Físico/fisiologia , Oxigênio/metabolismo , Músculo Quadríceps/metabolismo , Posição Ortostática , Decúbito Dorsal , Ciclismo/fisiologia , Voluntários Saudáveis , Humanos , Masculino , Espectroscopia de Luz Próxima ao Infravermelho , Adulto JovemRESUMO
NEW FINDINGS: What is the central question of this study? Does the presence and extent of heterogeneity in the ratio of O2 delivery to uptake across human muscles relate specifically to different muscle activation patterns? What is the main finding and its importance? During ramp incremental knee-extension and cycling exercise, the profiles of muscle deoxygenation (deoxy[haemoglobin + myoglobin]) and diffusive O2 potential (total[haemoglobin + myoglobin]) in the vastus lateralis corresponded to different muscle activation strategies. However, this was not the case for the rectus femoris, where muscle activation and deoxygenation profiles were dissociated and might therefore be determined by other structural and/or functional attributes (e.g. arteriolar vascular regulation and control of red blood cell flux). ABSTRACT: Near-infrared spectroscopy has revealed considerable heterogeneity in the ratio of O2 delivery to uptake as identified by disparate deoxygenation {deoxy[haemoglobin + myoglobin] (deoxy[Hb + Mb])} values in the exercising quadriceps. However, whether this represents a recruitment phenomenon or contrasting vascular and metabolic control, as seen among fibre types, has not been established. We used knee-extension (KE) and cycling (CE) incremental exercise protocols to examine whether differential muscle activation profiles could account for the heterogeneity of deoxy[Hb + Mb] and microvascular haemoconcentration (i.e. total[Hb + Mb]). Using time-resolved near-infrared spectroscopy for the quadriceps femoris (vastus lateralis and rectus femoris) during exhaustive ramp exercise in eight participants, we tested the following hypotheses: (i) the deoxy[Hb + Mb] (i.e. fractional O2 extraction) would relate to muscle activation levels across exercise protocols; and (ii) KE would induce greater total[Hb + Mb] (i.e. diffusive O2 potential) at task failure (i.e. peak O2 uptake) than CE irrespective of muscle site. At a given level of muscle activation, as assessed by the relative integrated EMG normalized to maximal voluntary contraction (%iEMGmax ), the vastus lateralis deoxy[Hb + Mb] profile was not different between exercise protocols. However, at peak O2 uptake and until 20% iEMGmax for CE, rectus femoris exhibited a lower deoxy[Hb + Mb] (83.2 ± 15.5 versus 98.2 ± 19.4 µm) for KE than for CE (P < 0.05). The total[Hb + Mb] at peak O2 uptake was not different between exercise protocols for either muscle site. These data support the hypothesis that the contrasting patterns of convective and diffusive O2 transport correspond to different muscle activation patterns in vastus lateralis but not rectus femoris. Thus, the differential deoxygenation profiles for rectus femoris across exercise protocols might be dependent upon specific facets of muscle architecture and functional haemodynamic events.
Assuntos
Hemoglobinas/metabolismo , Microvasos/metabolismo , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiologia , Oxigênio/metabolismo , Adulto , Exercício Físico/fisiologia , Humanos , Masculino , Microvasos/fisiologia , Mioglobina/metabolismo , Consumo de Oxigênio/fisiologia , Músculo Quadríceps/metabolismo , Músculo Quadríceps/fisiologia , Espectroscopia de Luz Próxima ao Infravermelho/métodos , Adulto JovemRESUMO
Relative perfusion of active muscles is greater during knee extension ergometry (KE) than cycle ergometry (CE). This provides the opportunity to investigate the effects of increased O2 delivery (QÌo2) on deoxygenation heterogeneity among quadriceps muscles and pulmonary oxygen uptake (VÌo2) kinetics. Using time-resolved near-infrared spectroscopy, we hypothesized that compared with CE the superficial vastus lateralis (VL), superficial rectus femoris, and deep VL in KE would have 1) a smaller amplitude of the exercise-induced increase in deoxy[Hb + Mb] (related to the balance between VÌo2 and QÌo2); 2) a greater amplitude of total[Hb + Mb] (related to the diffusive O2 conductance); 3) a greater homogeneity of regional muscle deoxy[Hb + Mb]; and 4) no difference in pulmonary VÌo2 kinetics. Eight participants performed square-wave KE and CE exercise from 20 W to heavy work rates. Deoxy[Hb + Mb] amplitude was less for all muscle regions in KE (P < 0.05: superficial, KE 17-24 vs. CE 19-40; deep, KE 19 vs. CE 26 µM). Furthermore, the amplitude of total[Hb + Mb] was greater for KE than CE at all muscle sites (P < 0.05: superficial, KE, 7-21 vs. CE, 1-16; deep, KE, 11 vs. CE, -3 µM). Although the amplitude and heterogeneity of deoxy[Hb + Mb] were significantly lower in KE than CE during the first minute of exercise, the pulmonary VÌo2 kinetics was not different for KE and CE. These data show that the microvascular QÌo2 to VÌo2 ratio, and thus tissue oxygenation, was greater in KE than CE. This suggests that pulmonary and muscle VÌo2 kinetics in young healthy humans are not limited by QÌo2 during heavy-intensity cycling.
Assuntos
Ciclismo , Músculo Esquelético/fisiologia , Oxigênio/metabolismo , Treinamento Resistido , Tecido Adiposo , Adolescente , Hemoglobinas/metabolismo , Humanos , Masculino , Mioglobina/metabolismo , Adulto JovemRESUMO
PURPOSE: We investigated the influence of inorganic nitrate ([Formula: see text]) supplementation on local sweating and cutaneous vascular responses during exercise in hot conditions. METHOD: Eight healthy, young subjects were assigned in a randomized, double-blind, crossover design to receive [Formula: see text]-rich beetroot (BR) juice (140 mL/day, containing ~ 8 mmol of [Formula: see text]) and [Formula: see text]-depleted placebo (PL) juice (140 mL/day, containing ~ 0.003 mmol of [Formula: see text]) for 3 days. On day 3 of supplementation, subjects cycled at an intensity corresponding to 55% of [Formula: see text]O2max for 30 min in hot conditions (30 °C, 50% relative humidity). Chest and forearm sweat rate (SR) and skin blood flow (SkBF), were measured continuously. Cutaneous vascular conductance (CVC) was calculated by SkBF/mean arterial pressure (MAP). RESULTS: Prior to exercise, plasma [Formula: see text] (21 ± 6 and 581 ± 161 µM) and nitrite ([Formula: see text], 87 ± 28 and 336 ± 156 nM) concentrations were higher after BR compared to PL supplementation (P ≤ 0.011, n = 6). Oesophageal, mean skin, and mean body temperatures during exercise were not different between conditions. In addition, BR supplementation did not affect SR, SkBF, and CVC during exercise. A lower MAP was found after 30 min of exercise following BR supplementation (112 ± 6 and 103 ± 6 mmHg for PL and BR, respectively, P = 0.021). CONCLUSION: These results suggest that inorganic [Formula: see text] supplementation, which increases the potential for O2-independent NO production, does not affect local sweating and cutaneous vascular responses, but attenuates blood pressure in young healthy subjects exercising in a hot environment.
Assuntos
Beta vulgaris , Suplementos Nutricionais , Exposição Ambiental , Exercício Físico , Sucos de Frutas e Vegetais , Temperatura Alta , Nitratos/administração & dosagem , Pele/irrigação sanguínea , Sudorese , Adulto , Velocidade do Fluxo Sanguíneo , Pressão Sanguínea , Estudos Cross-Over , Método Duplo-Cego , Feminino , Humanos , Japão , Masculino , Fluxo Sanguíneo Regional , Fatores de Tempo , Adulto JovemRESUMO
We investigated the influence of exercise intensities and regional differences in the sudomotor recruitment pattern in boys. Six prepubertal boys (age 11 ± 1 yr) cycled at light, moderate, and high exercise intensity (35%, 50%, and 65% VO2max) for 30 min in a temperate condition (28 °C, 40% relative humidity). Local sweat rate (ventilated capsule) and number of activated sweat glands (starch-iodine technique) at five body sites were assessed and sweat gland output was calculated. Responses in boys were compared with those in nine young men (23 ± 1 yr) tested under identical conditions. The forehead, chest, back, and forearm, but not thigh, sweat rate increased from light to moderate and at high intensities in boys (all p ≤ 0.005) but not from moderate to high (all p ≥ 0.071). The sweat rate on the forehead was relatively higher (p ≤ 0.045) and thigh was lower (p ≤ 0.050) than other sites in boys at moderate and high intensities. Exercise intensity-dependent sweating was associated with activating more sweat glands but not increasing glandular output in boys. The sweat rate in boys was attenuated versus men heterogeneously across body sites concurrent to low glandular outputs (all p ≤ 0.027). We conclude that exercise intensity modulates the sweat rate in boys by changing the number of activated sweat glands heterogeneously among skin sites. Age-related differences in the sudomotor pattern are evident at higher exercise intensities. Development of glandular output per gland occurring from boys to young men may play a key role in modulating sweat rate with respect to exercise intensity and regional differences.
Assuntos
Temperatura Corporal , Sudorese , Criança , Exercício Físico , Temperatura Alta , Humanos , Masculino , Temperatura Cutânea , Glândulas SudoríparasRESUMO
Seasonal acclimatization from winter to summer is known to enhance thermoeffector responses in hot-dry environments during exercise whereas its impact on sweat evaporation and core temperature (Tcore) responses in hot-humid environments remains unknown. We, therefore, sought to determine whether seasonal acclimatization is able to modulate whole body sweat rate (WBSR), evaporated sweat rate, sweating efficiency, and thermoregulatory function during cycling exercise in a hot-humid environment (32°C, 75% RH). We also determined whether the increase in air velocity could enhance evaporated sweat rate and sweating efficiency before and after seasonal acclimatization. Twelve males cycled for 1 h at 40% VÌo2max in winter (preacclimatization) and repeated the trial again in summer (after acclimatization). For the last 20 min of cycling at a steady-state of Tcore, air velocity increased from 0.2 (0.04) m/s to 1.1 (0.02) m/s by using an electric fan located in front of the participant. Seasonal acclimatization enhanced WBSR, unevaporated sweat rate, local sweat rate and mean skin temperature compared with preacclimatization state (all P < 0.05) whereas sweating efficiency was lower (P < 0.01) until 55 min of exercise. Tcore and evaporated sweat rate were unaltered by acclimatization status (all P > 0.70). In conclusion, seasonal acclimatization enhances thermoeffector responses but does not attenuate Tcore during exercise in a hot-humid environment. Furthermore, increasing air velocity enhances evaporated sweat rate and sweating efficiency irrespective of acclimated state. NEW & NOTEWORTHY Seasonal acclimatization to humid heat enhances eccrine sweat gland function and thus results in a higher local and whole body sweat rate but does not attenuate Tcore during exercise in a hot-humid environment. Sweating efficiency is lower after seasonal acclimatization to humid heat compared with preacclimatization with and without the increase of air velocity. However, having a lower sweating efficiency does not mitigate the Tcore response during exercise in a hot-humid environment.
Assuntos
Temperatura Corporal , Temperatura Alta , Aclimatação , Regulação da Temperatura Corporal , Humanos , Umidade , Masculino , Estações do Ano , SudoreseRESUMO
Oxygen uptake (VÌo2) kinetics are slowed in the supine (S) position purportedly due to impaired muscle O2 delivery ([Formula: see text]); however, these conclusions are predicated on single-site measurements in superficial muscle using continuous-wave near-infrared spectroscopy (NIRS). This study aimed to determine the impact of body position [i.e., upright (U) versus S] on deep and superficial muscle deoxygenation (deoxy[heme]) using time-resolved (TR-) NIRS, and how these relate to slowed pulmonary VÌo2 kinetics. Seventeen healthy men completed constant power tests during 1) S heavy-intensity exercise and 2) U exercise at the same absolute work rate, with a subset of 10 completing additional tests at the same relative work rate as S. Pulmonary VÌo2 was measured breath-by-breath and, deoxy- and total[heme] were resolved via TR-NIRS in the superficial and deep vastus lateralis and superficial rectus femoris. The fundamental phase VÌo2 time constant was increased during S compared with U (S: 36 ± 10 vs. U: 27 ± 8 s; P < 0.001). The deoxy[heme] amplitude (S: 25-28 vs. U: 13-18 µM; P < 0.05) and total[heme] amplitude (S: 17-20 vs. U: 9-16 µM; P < 0.05) were greater in S compared with U and were consistent for the same absolute (above data) and relative work rates (n = 10, all P < 0.05). The greater deoxy- and total[heme] amplitudes in S vs. U supports that reduced perfusive [Formula: see text] in S, even within deep muscle, necessitated a greater reliance on fractional O2 extraction and diffusive [Formula: see text]. The slower VÌo2 kinetics in S versus U demonstrates that, ultimately, these adjustments were insufficient to prevent impairments in whole body oxidative metabolism.NEW & NOTEWORTHY We show that supine exercise causes a greater degree of muscle deoxygenation in both deep and superficial muscle and increases the spatial heterogeneity of muscle deoxygenation. Therefore, this study suggests that any O2 delivery gradient toward deep versus superficial muscle is insufficient to mitigate impairments in oxidative function in response to reduced whole muscle O2 delivery. More heterogeneous muscle deoxygenation is associated with slower VÌo2 kinetics.
Assuntos
Músculo Esquelético , Consumo de Oxigênio , Exercício Físico , Teste de Esforço , Humanos , Cinética , Masculino , Músculo Esquelético/metabolismo , Oxigênio/metabolismo , Troca Gasosa PulmonarRESUMO
We examined whether partial clothing removal is an effective thermoregulatory behaviour to attenuate both thermoregulatory and perceptual strain in a moderate environment (23 °C, 65% RH) during and after exercise. Ten healthy males (age: 21.9 (0.9) years; height: 173.9 (6.2) cm; mass: 62.3 (8.2) kg; body surface area: 1.8 (0.1) m2; VO2max: 51.8 (13.3) mL.kg-1.min-1) wore a long sleeve polyester shirt and performed two randomized cycling trials for 40 min at 40% VO2max followed by 20 min recovery. In one trial, they were permitted to roll up their sleeves at any time they wanted (Roll) whereas in the other trial, they were instructed to remain with long sleeves (No Roll) until the end of the recovery. Thermoregulatory variables were measured continuously whilst thermal perceptions (forearm wettedness perception (WPForearm), forearm and whole-body thermal discomfort (TDForearm, TDWhole), local and whole-body thermal sensation (TSForearm, TSWhole) and whole-body wettedness perception (WPwhole)) were measured every 10 min. All subjects behaved by rolling up their sleeves at 21.6 (4.7) minutes. Tskin (32.3 (0.2) °C, vs 32.0 (0.1) °C, p = 0.03), local sweat rate on the forearm (0.24 (0.08) mg.cm-2.min-1 vs 0.2 (0.04) mg.cm-2.min-1, p = 0.05), WPForearm, TDForearm, TSForearm and WPWhole were all lower in Roll than No Roll (all p < 0.05) whilst Tcore and cutaneous vascular conductance (CVC) on the forearm were not different (all p > 0.7) throughout the entire trial. We conclude that this behavioural response is an effective thermoregulatory behaviour to modulate local sudomotor function and thermal perceptions, WPWhole during exercise but only Tsk, TDForearm WPForearm and WPWhole persisted throughout the recovery in a moderate environment.
Assuntos
Sistema Nervoso Autônomo/fisiologia , Comportamento/fisiologia , Regulação da Temperatura Corporal/fisiologia , Sensação Térmica/fisiologia , Limiar Anaeróbio , Ciclismo/fisiologia , Temperatura Corporal , Vestuário , Antebraço/irrigação sanguínea , Humanos , Masculino , Fluxo Sanguíneo Regional/fisiologia , Autorrelato , Sudorese/fisiologia , Adulto JovemRESUMO
We hypothesized that the performance of prior heavy exercise would speed pulmonary oxygen uptake (VÌo2) kinetics (i.e., as described by the time constant, [Formula: see text]) and reduce the amplitude of muscle deoxygenation (deoxy[heme]) kinetics in the supine (S) but not upright (U) body position. Seventeen healthy men completed heavy-intensity constant-work rate exercise tests in S and U consisting of two bouts of 6-min cycling separated by 6-min cycling at 20 W. Pulmonary VÌo2 was measured breath by breath; total and deoxy[heme] were determined via time-resolved near-infrared spectroscopy (NIRS) at three muscle sites. Priming exercise reduced [Formula: see text] in S (bout 1: 36 ± 10 vs. bout 2: 28 ± 10 s, P < 0.05) but not U (bout 1: 27 ± 8 s vs. bout 2: 25 ± 7 s, P > 0.05). Deoxy[heme] amplitude was increased after priming in S (bout 1: 25-28 µM vs. bout 2: 30-35 µM, P < 0.05) and U (bout 1: 13-18 µM vs. bout 2: 17-25 µM, P > 0.05), whereas baseline total[heme] was enhanced in S (bout 1: 110-179 µM vs. bout 2: 121-193 µM, P < 0.05) and U (bout 1: 123-186 µM vs. bout 2: 137-197 µM, P < 0.05). Priming exercise increased total[heme] in both S and U, likely indicating enhanced diffusive O2 delivery. However, the observation that after priming the amplitude of the deoxy[heme] response was increased in S suggests that the reduction in [Formula: see text] subsequent to priming was related to a combination of both enhanced intracellular O2 utilization and increased O2 delivery.NEW & NOTEWORTHY Here we show that oxygen uptake (VÌo2) kinetics are slower in the supine compared with upright body position, an effect that is associated with an increased amplitude of skeletal muscle deoxygenation in the supine position. After priming in the supine position, the amplitude of muscle deoxygenation remained markedly elevated above that observed during upright exercise. Hence, the priming effect cannot be solely attributed to enhanced O2 delivery, and enhancements to intracellular O2 utilization must also be contributory.
Assuntos
Consumo de Oxigênio , Oxigênio , Exercício Físico , Teste de Esforço , Humanos , Cinética , Masculino , Músculo Esquelético/metabolismo , Oxigênio/metabolismo , Troca Gasosa PulmonarRESUMO
It was recently demonstrated that an O2 extraction reserve, as assessed by the near-infrared spectroscopy (NIRS)-derived deoxygenation signal ([HHb]), exists in the superficial region of vastus lateralis (VL) muscle during an occlusion performed at the end of a ramp-incremental test. However, it is unknown whether this reserve is present and/or different in magnitude in other portions and depths of the quadriceps muscles. We tested the hypothesis that an O2 extraction reserve would exist in other regions of this muscle but is greater in deep compared with more superficial portions. Superficial (VL-s) and deep VL (VL-d) as well as superficial rectus femoris (RF-s) were monitored by a combination of low- and high-power time-resolved (TRS) NIRS. During the occlusion immediately post-ramp-incremental test there was a significant overshoot in the [HHb] signal ( P < 0.05). However, the magnitude of this increase was greater in VL-d (93.2 ± 42.9%) compared with VL-s (55.0 ± 19.6%) and RF-s (47.8 ± 14.0%) ( P < 0.05). The present study demonstrated that an O2 extraction reserve exists in different pools of active muscle fibers of the quadriceps at the end of a ramp exercise to exhaustion. The greater magnitude in the reserve observed in the deeper portion of VL, however, suggests that this portion of muscle may present a greater surplus of oxygenated blood, which is likely due to a greater population of slow-twitch fibers. These findings add to the notion that the plateau in the [HHb] signal toward the end of a ramp-incremental exercise does not indicate the upper limit of O2 extraction. NEW & NOTEWORTHY Different portions of the quadriceps muscles exhibited an untapped O2 extraction reserve during a blood flow occlusion performed at the end of a ramp-incremental exercise. In the deeper portion of the vastus lateralis muscle, this reserve was greater compared with superficial vastus lateralis and rectus femoris. These data suggest that the O2 extraction reserve may be dependent on the vascular and/or oxidative capacities of the muscles.
Assuntos
Exercício Físico/fisiologia , Oxigênio/metabolismo , Músculo Quadríceps/metabolismo , Músculo Quadríceps/fisiologia , Fluxo Sanguíneo Regional/fisiologia , Adulto , Teste de Esforço/métodos , Feminino , Humanos , Masculino , Consumo de Oxigênio/fisiologia , Adulto JovemRESUMO
To date our knowledge of skeletal muscle deoxygenation as measured by near-infrared spectroscopy (NIRS) is predicated almost exclusively on sampling of superficial muscle(s), most commonly the vastus lateralis (VL-s). Recently developed high power NIRS facilitates simultaneous sampling of deep (i.e., rectus femoris, RF-d) and superficial muscles of RF (RF-s) and VL-s. Because deeper muscle is more oxidative with greater capillarity and sustains higher blood flows than superficial muscle, we used time-resolved NIRS to test the hypotheses that, following exercise onset, the RF-d has slower deoxy[Hb+Mb] kinetics with reduced amplitude than superficial muscles. Thirteen participants performed cycle exercise transitions from unloaded to heavy work rates. Within the same muscle (RF-s vs. RF-d) deoxy[Hb+Mb] kinetics (mean response time, MRT) and amplitudes were not different. However, compared with the kinetics of VL-s, deoxy[Hb+Mb] of RF-s and RF-d were slower (MRT: RF-s, 51 ± 23; RF-d, 55 ± 29; VL-s, 18 ± 6 s; P < 0.05). Moreover, the amplitude of total[Hb+Mb] was greater for VL-s than both RF-s and RF-d (P < 0.05). Whereas pulmonary VËO2 kinetics (i.e., on vs. off) were symmetrical in heavy exercise, there was a marked on-off asymmetry of deoxy[Hb+Mb] for all three sites i.e., MRT-off > MRT-on (P < 0.05). Collectively these data reveal profoundly different O2 transport strategies, with the RF-s and RF-d relying proportionately more on elevated perfusive and the VL-s on diffusive O2 transport. These disparate O2 transport strategies and their temporal profiles across muscles have previously been concealed within the "global" pulmonary VËO2 response.
Assuntos
Exercício Físico , Consumo de Oxigênio , Músculo Quadríceps/fisiologia , Humanos , Masculino , Oxiemoglobinas/metabolismo , Músculo Quadríceps/irrigação sanguínea , Músculo Quadríceps/metabolismo , Adulto JovemRESUMO
This study investigated the influence of dietary inorganic nitrate (NO3-) supplementation on pulmonary O2 uptake (VËO2) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo-controlled, cross-over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak VËO2 over separate 4-day supplementation periods with NO3--rich (BR; providing 8.4 mmol NO3-âday-1) and NO3--depleted (placebo; PLA) beetroot juice. Pulmonary VËO2 was measured breath-by-breath and time-resolved near-infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the rectus femoris, vastus lateralis, and vastus medialis There were no significant differences (P > 0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three-site) end-exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 µmol/L, P < 0.05), with a tendency to increase the mean (three-site) area under the curve for total [Hb + Mb] responses (PLA: 3650 ± 1188 vs. BR: 4467 ± 1315 µmol/L sec-1, P = 0.08). The VËO2 slow component reduction after BR supplementation (PLA: 0.27 ± 0.07 vs. BR: 0.23 ± 0.08 L min-1, P = 0.07) correlated inversely with the mean increases in deoxy [Hb + Mb] and total [Hb + Mb] across the three muscle regions (r2 = 0.62 and 0.66, P < 0.05). Dietary NO3- supplementation increased O2 diffusive conductance across locomotor muscles in association with improved VËO2 dynamics during heavy-intensity cycling transitions.
Assuntos
Exercício Físico , Músculo Esquelético/efeitos dos fármacos , Nitratos/farmacologia , Consumo de Oxigênio , Oxigênio/metabolismo , Adulto , Suplementos Nutricionais , Hemoglobinas/metabolismo , Humanos , Masculino , Músculo Esquelético/metabolismo , Músculo Esquelético/fisiologia , Mioglobina/metabolismo , Nitratos/administração & dosagemRESUMO
It is axiomatic that greater aerobic fitness (VËO2peak) derives from enhanced perfusive and diffusive O2 conductances across active muscles. However, it remains unknown how these conductances might be reflected by regional differences in fractional O2 extraction (i.e., deoxy [Hb+Mb] and tissue O2 saturation [StO2]) and diffusive O2 potential (i.e., total[Hb+Mb]) among muscles spatially heterogeneous in blood flow, fiber type, and recruitment (vastus lateralis, VL; rectus femoris, RF). Using quantitative time-resolved near-infrared spectroscopy during ramp cycling in 24 young participants (VËO2peak range: ~37.4-66.4 mL kg-1 min-1), we tested the hypotheses that (1) deoxy[Hb+Mb] and total[Hb+Mb] at VËO2peak would be positively correlated with VËO2peak in both VL and RF muscles; (2) the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) during submaximal exercise would not differ among subjects differing in VËO2peak Peak deoxy [Hb+Mb] and StO2 correlated with VËO2peak for both VL (r = 0.44 and -0.51) and RF (r = 0.49 and -0.49), whereas for total[Hb+Mb] this was true only for RF (r = 0.45). Baseline deoxy[Hb+Mb] and StO2 correlated with VËO2peak only for RF (r = -0.50 and 0.54). In addition, the deoxy[Hb+Mb] slopes were not affected by aerobic fitness. In conclusion, while the pattern of deoxygenation (the deoxy[Hb+Mb] slopes) did not differ between fitness groups the capacity to deoxygenate [Hb+Mb] (index of maximal fractional O2 extraction) correlated significantly with VËO2peak in both RF and VL muscles. However, only in the RF did total[Hb+Mb] (index of diffusive O2 potential) relate to fitness.
Assuntos
Hemoglobinas/metabolismo , Treinamento Intervalado de Alta Intensidade , Músculo Esquelético/metabolismo , Consumo de Oxigênio , Humanos , Masculino , Músculo Esquelético/fisiologia , Aptidão Física , Adulto JovemRESUMO
Novel time-resolved near-infrared spectroscopy (TR-NIRS), with adipose tissue thickness correction, was used to test the hypotheses that heavy priming exercise reduces the VÌO2 slow component (VÌO2SC) (1) by elevating microvascular [Hb] volume at multiple sites within the quadriceps femoris (2) rather than reducing the heterogeneity of muscle deoxygenation kinetics. Twelve subjects completed two 6-min bouts of heavy work rate exercise, separated by 6 min of unloaded cycling. Priming exercise induced faster overall VÌO2 kinetics consequent to a substantial reduction in the VÌO2SC (0.27 ± 0.12 vs. 0.11 ± 0.09 L·min(-1), P < 0.05) with an unchanged primary VÌO2 time constant. An increased baseline for the primed bout [total (Hb + Mb)] (197.5 ± 21.6 vs. 210.7 ± 22.5 µmol L(-1), P < 0.01), reflecting increased microvascular [Hb] volume, correlated significantly with the VÌO2SC reduction. At multiple sites within the quadriceps femoris, priming exercise reduced the baseline and slowed the increase in [deoxy (Hb + Mb)]. Changes in the intersite coefficient of variation in the time delay and time constant of [deoxy (Hb + Mb)] during the second bout were not correlated with the VÌO2SC reduction. These results support a mechanistic link between priming exercise-induced increase in muscle [Hb] volume and the reduced VÌO2SC that serves to speed overall VÌO2 kinetics. However, reduction in the heterogeneity of muscle deoxygenation kinetics does not appear to be an obligatory feature of the priming response.
RESUMO
Near-infrared assessment of skeletal muscle is restricted to superficial tissues due to power limitations of spectroscopic systems. We reasoned that understanding of muscle deoxygenation may be improved by simultaneously interrogating deeper tissues. To achieve this, we modified a high-power (â¼8 mW), time-resolved, near-infrared spectroscopy system to increase depth penetration. Precision was first validated using a homogenous optical phantom over a range of inter-optode spacings (OS). Coefficients of variation from 10 measurements were minimal (0.5-1.9%) for absorption (µa), reduced scattering, simulated total hemoglobin, and simulated O2 saturation. Second, a dual-layer phantom was constructed to assess depth sensitivity, and the thickness of the superficial layer was varied. With a superficial layer thickness of 1, 2, 3, and 4 cm (µa = 0.149 cm(-1)), the proportional contribution of the deep layer (µa = 0.250 cm(-1)) to total µa was 80.1, 26.9, 3.7, and 0.0%, respectively (at 6-cm OS), validating penetration to â¼3 cm. Implementation of an additional superficial phantom to simulate adipose tissue further reduced depth sensitivity. Finally, superficial and deep muscle spectroscopy was performed in six participants during heavy-intensity cycle exercise. Compared with the superficial rectus femoris, peak deoxygenation of the deep rectus femoris (including the superficial intermedius in some) was not significantly different (deoxyhemoglobin and deoxymyoglobin concentration: 81.3 ± 20.8 vs. 78.3 ± 13.6 µM, P > 0.05), but deoxygenation kinetics were significantly slower (mean response time: 37 ± 10 vs. 65 ± 9 s, P ≤ 0.05). These data validate a high-power, time-resolved, near-infrared spectroscopy system with large OS for measuring the deoxygenation of deep tissues and reveal temporal and spatial disparities in muscle deoxygenation responses to exercise.
Assuntos
Exercício Físico , Oximetria/métodos , Consumo de Oxigênio , Oxigênio/sangue , Músculo Quadríceps/metabolismo , Espectroscopia de Luz Próxima ao Infravermelho , Adolescente , Ciclismo , Desenho de Equipamento , Teste de Esforço , Hemoglobinas/metabolismo , Humanos , Cinética , Masculino , Mioglobina/metabolismo , Oximetria/instrumentação , Imagens de Fantasmas , Valor Preditivo dos Testes , Músculo Quadríceps/diagnóstico por imagem , Reprodutibilidade dos Testes , Espectroscopia de Luz Próxima ao Infravermelho/instrumentação , Espectroscopia de Luz Próxima ao Infravermelho/métodos , Ultrassonografia , Adulto JovemRESUMO
Muscle deoxygenation (i.e., deoxy[Hb + Mb]) during exercise assesses the matching of oxygen delivery (QÌO2) to oxygen utilization (VÌO2). Until now limitations in near-infrared spectroscopy (NIRS) technology did not permit discrimination of deoxy[Hb + Mb] between superficial and deep muscles. In humans, the deep quadriceps is more highly vascularized and oxidative than the superficial quadriceps. Using high-power time-resolved NIRS, we tested the hypothesis that deoxygenation of the deep quadriceps would be less than in superficial muscle during incremental cycling exercise in eight males. Pulmonary VÌO2 was measured and muscle deoxy[Hb + Mb] was determined in the superficial vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF-s) and the deep rectus femoris (RF-d). deoxy[Hb + Mb] in RF-d was significantly less than VL at 70% (67.2 ± 7.0 vs. 75.5 ± 10.7 µM) and 80% (71.4 ± 11.0 vs. 79.0 ± 15.4 µM) of peak work rate (WR(peak)), but greater than VL and VM at WR(peak) (87.7 ± 32.5 vs. 76.6 ± 17.5 and 75.1 ± 19.9 µM). RF-s was intermediate at WR(peak) (82.6 ± 18.7 µM). Total hemoglobin and myoglobin concentration and tissue oxygen saturation were significantly greater in RF-d than RF-s throughout exercise. The slope of deoxy[Hb + Mb] increase (proportional to QÌO2/VÌO2) in VL and VM slowed markedly above 70% WR(peak), whereas it became greater in RF-d. This divergent deoxygenation pattern may be due to a greater population of slow-twitch muscle fibers in the RF-d muscle and the differential recruitment profiles and vascular and metabolic control properties of specific fiber populations within superficial and deeper muscle regions.