J-MAT. I agree that women have smaller organs than men, on average the women also have smaller bodies. As I am interested interested in peadiatric exercise science, I am very interested in issues of environment, genetics and scaling (e.g. alometric scaling, relative to kg or kg of fat free mass, etc). The following are mean't as comments not complaints, I'm just interested!!! Hope the points make sense...
Originally posted by J-MAT
2LAP:
I'll have to dig through a pile of information in my "lab," but will do my best to get it to you. In the meantime, women's organs are always smaller than a man's. This is one of the reasons why alcoholism in females is more dangerous to women than men; their livers are smaller, and suffer more damage with smaller amounts of alcohol than men with larger livers. Conversely, men can and do get breast cancer. Breast cancer in men is often much more deadly than in females, because the cancer will metastasize (spread) quicker to surrounding organs. Women have larger breasts, and the cancer will stay there longer, giving women more time to take action before it spreads.
-On average women do have smaller organs, but that is because women are on average smaller than men. Couldn't see any reason why women would have organs reletive to a man when matched for size.
Women also have more bodyfat than men. While fat is not metabolically active like muscle is, it still has a blood supply the heart has to pump through. That's one reason why being overfat is bad; it puts additional load/demand on the heart muscle.
-Agree that body fat and muscle has a blood flow and this provides a demand on the heart. However unable to see how the heart develops differently when that demand is provided by fat or muscle. The heart is unable to differentiate between fat and muscle. Although, being over fat creates additional demand on the heart so does having extra muscle; additional fat is only a problem when taken to extreme (its difficult to gain muscle to this level) and when accompanied by additional symptoms.
When a woman has more fat to pump through (compared to a man) combined with a smaller heart/ventricles, it raises the cardiac output requirements for that person at rest or at exercise. Think of it this way: A car with a small motor is loaded with heavy packages. A bigger truck is empty, with no packages. If they both went down the road at the same speed, which engine would have to work harder??? Even if men and women had idential bodyfat percentages, women with smaller hearts would always have to meet all their cardiac-output requirements through increased heartrate since their left ventricles are always smaller.
-Do women have smaller left ventricles? Why is this? Surely men have a greater muscle mass, would that not raise their RHR to the same level in the same way that a woman's increased body fat?
Women's smaller hearts are also one of the main limiting factors in world-class endurance perfomance (running, cycling) when comparing the fastest male versus the fastest female. Blame God if you don't like it. Nature made us this way!!!
-The heart is a limiting factor in all peoples performance, the difference between men and women can also be explained by muscle mass, body fat, biomechanical differences, hemoglobin concentration, etc.
Let's say your body needed 1000 "units" of oxygenated blood per minute. Your left ventricle ejects 20 units, while someone else with the same 1000 "unit" reqirement can eject 25 units of blood with each stroke. Your heart would have to beat 50 times in one minute to get the 1000 "units." The other person's heart would only have to beat 40 times in one minute to meet the same requirement. Smaller pumps have to work harder/faster to keep up with larger ones.
-But do women have smaller pumps compared to men? Women have smaller bodies too, so the are likely to only need 800 units, think thats 40 pumps for a 20 unit pump! Not sure if any of this answers the original question - environment, scale or genetics?