Introduction: Critical Power: Cardiovascular and Muscle Metabolic Determinants of Oxygen Uptake (03:13)
Andrew M. Jones welcomes the audience and explains he will cover critical features of the critical power, review impactful studies and describe the remainder of the program. Brian Whipp developed the mathematical models of critical power (CP). In "Nature," A.V. Hill created a graph plotting world records and average speed; a hyperbolic relationship exists regardless of exercise modality and species.
What is Critical Power? (03:04)
CP is the highest sustainable oxidative metabolic rate; after two to three minutes there is no anaerobic contribution. Individuals use up their work capacity (W') more rapidly when they go above their CP. Jones describes how different interventions impact the power-time (P-T) relationship.
Limiting Exercise Tolerance? (02:32)
Intramuscular substrates, accumulation of metabolites associated with fatigue, and VO2 kinetic response will hamper an individual's ability to perform exercises above critical power. Jones describes how increased oxygen consumption reacts with W' and CP.
Specific studies (02:51)
David Poole, Sue Ward, Brian Whipp, and Gerald Gardner studied the metabolic and respiratory profile of the upper limit in prolonged exercise. Subjects exercised for 24 minutes at or just under CP; the researchers determined that VO2 stabilized. In an additional study Poole and Gaesser determined blood lactate levels.
Exercise Intensity Domains (04:43)
David Cameron and Jones explored how pH and phosphates concentration alters during exercise. Below CP, phosphate stabilizes rapidly. Subjects could not complete the requested exercise when they went above CP.
Follow Up Study (04:05)
Jones used Hyperoxia as an intervention to determine whether exercises could be sustained for a longer period of time at a high intensity. PCr outputs did not change. Edward Cotes and Brian Whipp determined that individuals who exhaust their VO2 need to work at a subcritical power work rate.
More Studies (03:49)
Individuals who exercise above CP cannot sustain the high intensity. Phosphor concentration replenishes below CP. Bernley studied how people working below CP could exercise for an hour or more.
Jones summarizes the findings for his talk. Muscle metabolic, blood acid-base, and pulmonary gas exchange differ when exercising above or below critical power. Anni Vanhatalo, Poole, and Phil F. Skiba will be speaking during today's symposium.
Introduction to Vanhatalo's Portion (03:41)
Jones introduces Vanhatalo who will be speaking on muscle metabolic determinants and implications for pulmonary oxygen intake. Poole studied pulmonary gas variables and blood acid base balance responses above and below CP. Vanhatalo discovered that max VO2 occurred around 12 minutes in individuals exercising above CP.
Muscle Biopsies (02:32)
Vanhatalo found that blood and muscle lactate accumulated in individuals exercising above CP and the subjects pH dropped. Metabolic prompts mitochondrial respiration.
Defining W' (02:49)
Fewer studies are conducted on the W' parameter in the power-time relationship. PCr and anaerobic glycolysis depletion coincide with accumulated fatigue related metabolites. ADP and Pi stimulate mitochondrial respiration.
Recent Studies Conducted (02:35)
Harry Rossiter studied the similarities between VO2 increase and PCr depletion during heavy intensity exercise. Mark Burnley and Jones hypothesized that the capacity for anaerobic energy production, rate at which VO2 develops, and the VO2 max determines the W'. Vanhatalo suggests that future research focus on the VO2 slow component.
Employing a Pacing Strategy (02:58)
Vanhatalo compares the VO2 max and W' achieved employing different types of exercise. The two-parameter CP model predicts exercise tolerance as long as VO2 max is achieved.
Attaining VO2 max (02:22)
Active skeletal muscles procure the slow component of VO2. Vanhatalo hypothesizes that muscle fibers are recruited in a specific hierarchy at the onset of severe intensity exercise.
Physiological Mechanisms (02:59)
Vanhatalo studied the relationship between the W' and the slow component of VO2. Integrated Electromyography activated the muscles. VO2 max was achieved at 72 seconds for all out exercise participants.
Conclusion of the Study (05:10)
Vanhatalo discusses her findings and why she calculated a VO2 gain. The W' parameter correlated to the slow component VO2 increase. Rossiter used a traditional trial protocol and reached the same conclusion.
Interpreting Confusing Data (03:40)
Scientists became confused when they determined that endurance training reduced the W'. Vanhatalo explains that the VO2 slow component is responsible for the inverse relationship between CP and W' after training.
Vanhatalo's Conclusions (01:23)
W' is greater than CP and is mechanistically linked to the development of the VO2 slow component. Muscle fatigue also contributes to the VO2 slow component. Vanhatalo thanks the audience and her partners in research.
Muscle Hemodynamic Control relative to Clinical Power/Speed (04:26)
Poole wanted to study muscle performance in both athletes and disadvantaged populations. A recent study investigates the pathway of oxygen, focusing on how red blood cells are distributed in capillaries. Poole plans on addressing similarities of CP across different species, differences in vascular control between humans and rats, how vascular control relates to CP, and the role of neuronal nitric oxide
Broad Applicability of CP (03:24)
Human muscles first appear much more homogeneous than rats, but Johnson et al found significant fiber type heterogeneity. Deep muscles possess greater amounts of type one fibers. Poole explains how scientists can understand vascular control in humans by studying specific muscles in rats.
Heterogeneity of Exercising Muscle Blood Flow (02:39)
Paul Armstrong studied fiber composition in specific muscles. Blood flow responds differently in muscular fiber types. Rick McAllister demonstrated a fiber type dependency on endothelial function in rat thighs.
Muscle Fibers and Blood Flow Activity (02:17)
Paul McDonough and Brad Behnke studied different muscle types and blood flow through phosphorescence quenching. Pressure gradients determine how much oxygen goes into a tissue.
Vascular Control Relative to Critical Speed (02:54)
Individuals will achieve VO2 max if they exercise above critical power to exhaustion. Inorganic phosphates and pH demonstrate complementary profiles. Rats have difficulty righting itself when fatigued.
Application of Microsphere Technique (02:07)
Dr. Armstrong and Laughlin pioneered the microsphere technique to determine skeletal muscle blood flow. Poole determined blood flow is more elevated in the highly glycolytic muscle fibers of a rat at critical speed.
Neurologic Oxide in Vascular Control (05:17)
Mike Joyner discovered many variables that affect and impact blood flow. Neuronal Nitric Oxide exists in muscles and is activated by calcium. S Methyl-L thiocitruline SMTC inhibits NOS function.
Critical power provides a framework for addressing vascular control, metabolic regulation, and fatigue. Scientists can understand how a human body functions by studying muscles in rats with similar compositions; neuronal nitric oxide plays a major role in hyperemia above critical speed. Jones introduces Dr. Skiba.
Advising Athletes Using Math (03:05)
Dr. Skiba studies performance engineering using quantitative math in elite athletes. The critical power model can help determine an optimal rate of exercise over a distance. Most W' studies only focus on all out exercise or during steady state, but athletic competitions are not applicable.
Differing Views of W' (02:40)
Dr. Skiba wanted to explore if the depletion hypothesis and the accumulation hypothesis creates a false dichotomy. Hugh Morton created an equation to determine CP. Ferguson looked at the recovery kinetics of the W'.
Once the athlete exceeds CP they begin utilizing W'. Dr. Skiba describes his hypothetical equation to determine CP. As athletes approach CP recovery time slows.
Practical Applications (05:17)
Dr. Skiba found that it was possible to determine an athletes W' in order to conserve it. A correlation exists between the predicted discharge of W' and the delta VO2. The scientists wanted to explore if the model could still predict CP if work or recovery duration altered; they found greater time differentiation between short work and recovery periods.
The current model under predicts work interval duration. Skiba hypothesizes the change is due to vasodilation, and increased oxygen flushes out metabolites that cause fatigue. During stochastic exercise, athletes should maintain short work durations.
Model Utility (02:28)
In a recent study, Skiba analyzed W' in triathletes. He cautioned one athlete to ride at a more steady output instead of surging to conserve energy for the run. All athletes became exhausted when there W' came close to zero.
Linking Changes (03:28)
Dr. Skiba hopes to link the mathematical model with the physiology to determine training patterns. The physiologist studied what occurred in the muscle during recovery of the W' and determined the model predicted small muscle mass movements, but not whole body movements.
Linear recoveries for multiple parts of a system accumulate. W' cannot convert to PCr or VO2 directly, because of the slow component of VO2. Dr. Skiba explains that fatigue-causing metabolites could be creating the discrepancy.
Additional Contributing Factors (02:00)
Dr. Skiba hypothesizes that there is a relationship between recovery of the W' and accumulation of carnosine in the muscle. More research is required to create a unified mathematical model.
Q/A: Allowing for Ventilatory Changes? (03:00)
Jones could not measure gas exchange and ventilation simultaneously in his study which focused on small muscle mass and not the whole body. PH levels fell less rapidly in hyperoxia compared to normoxia.
Q/A: Range of Duty Cycles (02:29)
Skiba explains how the longest exercise duration in his studies was 60 seconds. Although he did not show his VO2 data, the study demonstrated an almost steady state in short durations.
Q/A: Manipulating Variables? (03:44)
Dr. Skiba wants to try the cuffing experiment to determine how function and work capacity changes. Poole's investigation into the circulation system will help determine critical power models. An audience member advocates further research into increasing W'.
Q/A: Key Variables in CP and W'? (01:36)
Vanhatalo believes the biggest variable in her research is whether or not VO2 max is achieved.
Credits: Critical Power: Cardiovascular and Muscle Metabolic Determinants of Oxygen Uptake (00:21)
Credits: Critical Power: Cardiovascular and Muscle Metabolic Determinants of Oxygen Uptake
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