The critical power (CP) model includes two constants: the CP and the W' P = (W' / t) + CP. The W' is the finite work capacity available above CP. Power output above CP results in depletion of the W' ...complete depletion of the W' results in exhaustion. Monitoring the W' may be valuable to athletes during training and competition. Our purpose was to develop a function describing the dynamic state of the W' during intermittent exercise.
After determination of V˙O(2max), CP, and W', seven subjects completed four separate exercise tests on a cycle ergometer on different days. Each protocol comprised a set of intervals: 60 s at a severe power output, followed by 30-s recovery at a lower prescribed power output. The intervals were repeated until exhaustion. These data were entered into a continuous equation predicting balance of W' remaining, assuming exponential reconstitution of the W'. The time constant was varied by an iterative process until the remaining modeled W' = 0 at the point of exhaustion.
The time constants of W' recharge were negatively correlated with the difference between sub-CP recovery power and CP. The relationship was best fit by an exponential (r = 0.77). The model-predicted W' balance correlated with the temporal course of the rise in V˙O(2) (r = 0.82-0.96). The model accurately predicted exhaustion of the W' in a competitive cyclist during a road race.
We have developed a function to track the dynamic state of the W' during intermittent exercise. This may have important implications for the planning and real-time monitoring of athletic performance.
Key points
Nitric oxide (NO), a potent vasodilator and a regulator of many physiological processes, is produced in mammals both enzymatically and by reduction of nitrite and nitrate ions.
We have ...previously reported that, in rodents, skeletal muscle serves as a nitrate reservoir, with nitrate levels greatly exceeding those in blood or other internal organs, and with nitrate being reduced to NO during exercise.
In the current study, we show that nitrate concentration is substantially greater in skeletal muscle than in blood and is elevated further by dietary nitrate ingestion in human volunteers. We also show that high‐intensity exercise results in a reduction in the skeletal muscle nitrate store following supplementation, likely as a consequence of its reduction to nitrite and NO.
We also report the presence of sialin, a nitrate transporter, and xanthine oxidoreductase in human skeletal muscle, indicating that muscle has the necessary apparatus for nitrate transport, storage and metabolism.
Rodent skeletal muscle contains a large store of nitrate that can be augmented by the consumption of dietary nitrate. This muscle nitrate reservoir has been found to be an important source of nitrite and nitric oxide (NO) via its reduction by tissue xanthine oxidoreductase. To explore if this pathway is also active in human skeletal muscle during exercise, and if it is sensitive to local nitrate availability, we assessed exercise‐induced changes in muscle nitrate and nitrite concentrations in young healthy humans, under baseline conditions and following dietary nitrate consumption. We found that baseline nitrate and nitrite concentrations were far higher in muscle than in plasma (∼4‐fold and ∼29‐fold, respectively), and that the consumption of a single bolus of dietary nitrate (12.8 mmol) significantly elevated nitrate concentration in both plasma (∼19‐fold) and muscle (∼5‐fold). Consistent with these observations, and with previous suggestions of active muscle nitrate transport, we present western blot data to show significant expression of the active nitrate/nitrite transporter sialin in human skeletal muscle. Furthermore, we report an exercise‐induced reduction in human muscle nitrate concentration (by ∼39%), but only in the presence of an increased muscle nitrate store. Our results indicate that human skeletal muscle nitrate stores are sensitive to dietary nitrate intake and may contribute to NO generation during exercise. Together, these findings suggest that skeletal muscle plays an important role in the transport, storage and metabolism of nitrate in humans.
Key points
Nitric oxide (NO), a potent vasodilator and a regulator of many physiological processes, is produced in mammals both enzymatically and by reduction of nitrite and nitrate ions.
We have previously reported that, in rodents, skeletal muscle serves as a nitrate reservoir, with nitrate levels greatly exceeding those in blood or other internal organs, and with nitrate being reduced to NO during exercise.
In the current study, we show that nitrate concentration is substantially greater in skeletal muscle than in blood and is elevated further by dietary nitrate ingestion in human volunteers. We also show that high‐intensity exercise results in a reduction in the skeletal muscle nitrate store following supplementation, likely as a consequence of its reduction to nitrite and NO.
We also report the presence of sialin, a nitrate transporter, and xanthine oxidoreductase in human skeletal muscle, indicating that muscle has the necessary apparatus for nitrate transport, storage and metabolism.
Hypoxia is associated with a reduction in the maximal oxidative metabolic rate of skeletal muscle which is reflected in a slowing of muscle phosphocreatine (PCr) recovery kinetics following exercise. ...For the same metabolic rate, there is a greater muscle metabolic perturbation (e.g., greater fall in PCr) during exercise performed in hypoxia compared to normoxia. Nitric oxide (NO) is a key signalling molecule for hypoxic vasodilatation and it also modulates mitochondrial O2 consumption. Dietary nitrate intake, which increases NO bioavailability, might therefore improve O2 delivery to active muscle and reduce O2 demand during hypoxic exercise. It has been shown that nitrate supplementation lessens muscle metabolic perturbation during high-intensity exercise and considerably enhances exercise tolerance in moderate hypoxia. Nitrate supplementation has also been shown to abolish the reduction in the rate of PCr recovery which is typically observed in hypoxia, indicating enhanced muscle oxygenation and a restoration of muscle oxidative function. Further research is warranted to identify to what extent these effects can be attributed to changes in muscle energy metabolism and/or improved O2 delivery. These findings indicate that dietary nitrate supplementation may have important therapeutic applications for improving skeletal muscle energetics and functional capacity in conditions where muscle O2 delivery is compromised.
Imbalances in the oral microbial community have been associated with reduced cardiovascular and metabolic health. A possible mechanism linking the oral microbiota to health is the nitrate ...(NO3-)-nitrite (NO2-)-nitric oxide (NO) pathway, which relies on oral bacteria to reduce NO3- to NO2-. NO (generated from both NO2- and L-arginine) regulates vascular endothelial function and therefore blood pressure (BP). By sequencing bacterial 16S rRNA genes we examined the relationships between the oral microbiome and physiological indices of NO bioavailability and possible changes in these variables following 10 days of NO3- (12 mmol/d) and placebo supplementation in young (18–22 yrs) and old (70–79 yrs) normotensive humans (n = 18). NO3- supplementation altered the salivary microbiome compared to placebo by increasing the relative abundance of Proteobacteria (+225%) and decreasing the relative abundance of Bacteroidetes (−46%; P < 0.05). After NO3-supplementation the relative abundances of Rothia (+127%) and Neisseria (+351%) were greater, and Prevotella (−60%) and Veillonella (−65%) were lower than in the placebo condition (all P < 0.05). NO3- supplementation increased plasma concentration of NO2- and reduced systemic blood pressure in old (70–79 yrs), but not young (18–22 yrs), participants. High abundances of Rothia and Neisseria and low abundances of Prevotella and Veillonella were correlated with greater increases in plasma NO2- in response to NO3- supplementation. The current findings indicate that the oral microbiome is malleable to change with increased dietary intake of inorganic NO3-, and that diet-induced changes in the oral microbial community are related to indices of NO homeostasis and vascular health in vivo.
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•Dietary nitrate alters the salivary microbiome of healthy young and old adults.•Nitrate supplementation decreases relative abundances of Prevotella and Veillonella.•Nitrate supplementation increases relative abundances of Rothia and Neisseria.•The salivary microbiome modulates nitric oxide bioavailability and blood pressure.
Application of critical power in sport Vanhatalo, Anni; Jones, Andrew M; Burnley, Mark
International journal of sports physiology and performance,
03/2011, Letnik:
6, Številka:
1
Journal Article
Recenzirano
The critical power (CP) is mathematically defined as the power-asymptote of the hyperbolic relationship between power output and time-to-exhaustion. Physiologically, the CP represents the boundary ...between the steady-state and nonsteady state exercise intensity domains and therefore may provide a more meaningful index of performance than other well-known landmarks of aerobic fitness such as the lactate threshold and the maximal O2 uptake. Despite the potential importance to sports performance, the CP is often misinterpreted as a purely mathematical construct which lacks physiological meaning and only in recent years has this concept begun to emerge as valid and useful technique for monitoring endurance fitness. This commentary defines the basic principles of the CP concept, outlines its importance to high-intensity exercise performance, and provides an overview of the current methods available for its assessment. Interventions including training, pacing and prior exercise can be used to alter the parameters of the power-time relationship. A future challenge lies in optimizing such interventions in order to positively affect the parameters of the power-time relationship and thereby enhance sports performance in specific events.
Tree stems are an overlooked source of volatile organic compounds (VOCs). Their contribution to ecosystem processes and total VOC fluxes is not well studied, and assessing it requires better ...understanding of stem emission dynamics and their driving processes. To gain more mechanistic insight into stem emission patterns, we measured monoterpene, methanol and acetaldehyde emissions from the stems of mature Scots pines (Pinus sylvestris L.) in a boreal forest over three summers. We analysed the effects of temperature, soil water content, tree water status, transpiration and growth on the VOC emissions and used generalized linear models to test their relative importance in explaining the emissions. We show that Scots pine stems are considerable sources of monoterpenes, methanol and acetaldehyde, and their emissions are strongly regulated by temperature. However, even small changes in water availability affected the emission potentials: increased soil water content increased the monoterpene emissions within a day, whereas acetaldehyde and methanol emissions responded within 2–4 days. This lag corresponded to their transport time in the xylem sap from the roots to the stem. Moreover, the emissions of monoterpenes, methanol and acetaldehyde were influenced by the cambial growth rate of the stem with 6–10‐day lags.
Scots pine (Pinus sylvestris L.) stems are a considerable source of monoterpenes, methanol and acetaldehyde. Their emissions depend strongly on temperature, but the temperature‐normalized emissions are affected by relatively small changes in soil moisture and cambial growth of stem.
Key points
The power‐asymptote (critical power; CP) of the hyperbolic power–time relationship for high‐intensity exercise defines a threshold between steady‐state and non‐steady‐state exercise ...intensities and the curvature constant (W′) indicates a fixed capacity for work >CP that is related to a loss of muscular efficiency.
The present study reports novel evidence on the muscle metabolic underpinnings of CP and W′ during whole‐body exercise and their relationships to muscle fibre type.
We show that the W′ is not correlated with muscle fibre type distribution and that it represents an elevated energy contribution from both oxidative and glycolytic/glycogenolytic metabolism.
We show that there is a positive correlation between CP and highly oxidative type I muscle fibres and that muscle metabolic steady‐state is attainable <CP but not >CP.
Our findings indicate a mechanistic link between the bioenergetic characteristics of muscle fibre types and the power–time relationship for high‐intensity exercise.
We hypothesized that: (1) the critical power (CP) will represent a boundary separating steady‐state from non‐steady‐state muscle metabolic responses during whole‐body exercise and (2) that the CP and the curvature constant (W′) of the power–time relationship for high‐intensity exercise will be correlated with type I and type IIx muscle fibre distributions, respectively. Four men and four women performed a 3 min all‐out cycling test for the estimation of CP and constant work rate (CWR) tests slightly >CP until exhaustion (Tlim), slightly <CP for 24 min and until the >CP Tlim isotime to test the first hypothesis. Eleven men performed 3 min all‐out tests and donated muscle biopsies to test the second hypothesis. Below CP, muscle PCr 42.6 ± 7.1 vs. 49.4 ± 6.9 mmol (kg d.w.)−1, La− 34.8 ± 12.6 vs. 35.5 ± 13.2 mmol (kg d.w.)−1 and pH (7.11 ± 0.08 vs. 7.10 ± 0.11) remained stable between ∼12 and 24 min (P > 0.05 for all), whereas these variables changed with time >CP such that they were greater La− 95.6 ± 14.1 mmol (kg d.w.)−1 and lower PCr 24.2 ± 3.9 mmol (kg d.w.)−1; pH 6.84 ± 0.06 (P < 0.05) at Tlim (740 ± 186 s) than during the <CP trial. The CP (234 ± 53 W) was correlated with muscle type I (r = 0.67, P = 0.025) and inversely correlated with muscle type IIx fibre proportion (r = −0.76, P = 0.01). There was no relationship between W′ (19.4 ± 6.3 kJ) and muscle fibre type. These data indicate a mechanistic link between the bioenergetic characteristics of different muscle fibre types and the power–duration relationship. The CP reflects the bioenergetic characteristics of highly oxidative type I muscle fibres, such that a muscle metabolic steady‐state is attainable below and not above CP.
Key points
The power‐asymptote (critical power; CP) of the hyperbolic power–time relationship for high‐intensity exercise defines a threshold between steady‐state and non‐steady‐state exercise intensities and the curvature constant (W′) indicates a fixed capacity for work >CP that is related to a loss of muscular efficiency.
The present study reports novel evidence on the muscle metabolic underpinnings of CP and W′ during whole‐body exercise and their relationships to muscle fibre type.
We show that the W′ is not correlated with muscle fibre type distribution and that it represents an elevated energy contribution from both oxidative and glycolytic/glycogenolytic metabolism.
We show that there is a positive correlation between CP and highly oxidative type I muscle fibres and that muscle metabolic steady‐state is attainable <CP but not >CP.
Our findings indicate a mechanistic link between the bioenergetic characteristics of muscle fibre types and the power–time relationship for high‐intensity exercise.
For high-intensity muscular exercise, the time-to-exhaustion (t) increases as a predictable and hyperbolic function of decreasing power (P) or velocity (V ). This relationship is highly conserved ...across diverse species and different modes of exercise and is well described by two parameters: the "critical power" (CP or CV), which is the asymptote for power or velocity, and the curvature constant (W') of the relationship such that t = W'/(P - CP). CP represents the highest rate of energy transduction (oxidative ATP production, V˙O2) that can be sustained without continuously drawing on the energy store W' (composed in part of anaerobic energy sources and expressed in kilojoules). The limit of tolerance (time t) occurs when W' is depleted. The CP concept constitutes a practical framework in which to explore mechanisms of fatigue and help resolve crucial questions regarding the plasticity of exercise performance and muscular systems physiology. This brief review presents the practical and theoretical foundations for the CP concept, explores rigorous alternative mathematical approaches, and highlights exciting new evidence regarding its mechanistic bases and its broad applicability to human athletic performance.
Severe‐intensity constant‐work‐rate exercise results in the attainment of maximal oxygen uptake, but the muscle metabolic milieu at the limit of tolerance (Tlim) for such exercise remains to be ...elucidated. We hypothesized that Tlim during severe‐intensity exercise would be associated with the attainment of consistently low values of intramuscular phosphocreatine (PCr) and pH, as determined using 31P magnetic resonance spectroscopy, irrespective of the work rate and the inspired O2 fraction. We also hypothesized that hyperoxia would increase the asymptote of the hyperbolic power–duration relationship (the critical power, CP) without altering the curvature constant (W′). Seven subjects (mean ±s.d., age 30 ± 9 years) completed four constant‐work‐rate knee‐extension exercise bouts to the limit of tolerance (range, 3–10 min) both in normoxia (N) and in hyperoxia (H; 70% O2) inside the bore of 1.5 T superconducting magnet. The PCr (∼5–10% of resting baseline) and pH (∼6.65) at the limit of tolerance during each of the four trials was not significantly different either in normoxia or in hyperoxia. At the same fixed work rate, the overall rate at which PCr fell with time was attenuated in hyperoxia (mean response time: N, 59 ± 20 versus H, 116 ± 46 s; P < 0.05). The CP was higher (N, 16.1 ± 2.6 versus H, 18.0 ± 2.3 W; P < 0.05) and the W′ was lower (N, 1.92 ± 0.70 versus H, 1.48 ± 0.31 kJ; P < 0.05) in hyperoxia compared with normoxia. These data indicate that Tlim during severe‐intensity exercise is associated with the attainment of consistently low values of muscle PCr and pH. The CP and W′ parameters of the power–duration relationship were both sensitive to the inspiration of hyperoxic gas.
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