Answer: Thank you for your question - a tricky one in its present form as there are so many variables involved. We have approached a number of our associates about this and opinion is divided.

However, a suggested answer is:

Given that the person has no abnormalities in muscle or heart or blood supplies, then, as the vessel (the aorta) that conducts fresh oxygenated blood supplies to both sides of the body, does so at the same time, there should be no difference in which arm shows fatigue first.

One idea is that when a muscle is forced to contract where the oxygen supply is insufficient, lactic acid builds up and eventually stops the muscle from contracting, so fatigue sets in, until the lactic acid has been dispersed. Some people seem to think that the side of the body that is furthest away from the fresh oxygenated blood will tire first. Ironically, if you are right handed and the muscles are more developed on this side, then you will need more oxygen to keep fatigue away and so this side will show fatigue first.

We contend that this is not so, as more regular exercise can lead to better blood supplies to the muscles, which makes them more efficient and so the aerobic respiration lasts longer and waste products are removed more efficiently; hence the non-preferred arm would tire more quickly, as the muscles in the preferred arm are stronger and therefore more efficient.

Given all this, it seems that as the causes of fatigue are uncertain, that your best course of action would be to establish that all variables are cancelled out and then to conclude that there should be no difference in fatigue in either arm based on blood supply alone.