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Max HR vs Lactate Threshold
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, " wrote: On Apr 16, 1:41*am, datakoll wrote: what is "normal" for an upper exercise limit? muscles giving out first, or heart rate topping out as a limit? A little of both, and as age increases, HR can more often become the limiting factor. And training changes the balance too. Riding along at a steady easy level, HR is low and is pumping some amount of blood and thus delivering some amount of oxygen to the working muscles. The muscles are able to use this oxygen to do work. But some of the muscles do not get all the oxygen they need to do the work asked of them. So they work anaerobically and generate lactate. This is only a small amount, and the body is able to easily deal with this lactate before it builds up. At a higher intensisty (more power) level, more oxygen is needed, so the HR picks up to deliver more oxygen. But still not all the muscles get all the oxygen they need, so they produce more lactate. If the amount of lactate produced can be used by the body so that the amount of lactate in the blood does not keep rising, the effort level is said to be below the LT. If more lactate is produced than can be disposed of, the level of lactate in the blood keeps rising, even though the effort level remains constant. This is above LT. This is not sustainable because eventually with high enough concentrations, the hydrogen ions released as part of the lactic acid creation interfere with the mucels ability to do work, and it cannot continue to produc ethe same power, so you slow down. You may have slowed down already, because unpleasantness ensues usually well befor ethis point. But LT isn't at max HR, and more work can be done (power generated) above LT, but just for a limited time. The body can still supply more ans use more oxygen to do work above LT, but it is inhibited from maintaining this level of output for very long. This is also different from peak power, which is more akin to brute strength and usually is at levels well above LT. One addition. As you state, the problem with exercise at high levels is acidosis. Production of lactic acid buffers the H+, and the lactic acid is then transported out of the cell. Check out Biochemistry of exercise-induced metabolic acidosis. Robert A. Robergs,Farzenah Ghiasvand,and Daryl Parker http://ajpregu.physiology.org/cgi/content/full/287/3/R502 -- Michael Press |
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