Hi all,
I have not read the Sutta’s so I will not comment on them, but this is how I understand this topic.
For any effect there are causes. not just one cause but many. Kamma always plays a part in it, it is the underlying cause but may not be the major cause. A good example is to take a boy hitting a cat. If he hits the cat with his bare hand we will say that he hit the cat with his hand. If he hits the cat with a stick we will say he hit it with a stick. Now, when he hit the cat with the stick, was the hand involved? It definitely was, but we refer to as”hitting with the stick” because the stick was the main cause or more prominent. So in this way there can be numerous causes like weather or genes which are more prominent (like the stick) but the kamma still has a part to play and is the underlying cause (like the hand).
A person will not have some sort of bodily pain if he doesn’t have some sort of kamma to give that specific vipaka. This is how we can explain why only some people get sick even when others are exposed to the same external conditions. If there is no kamma to be repaid he may not get sick.
If a person decides to cross the road with his eyes closed, that is a foolish act, but he will only get knocked down by a car if he has a previous kamma to give vipaka in that particular way. That is why everyone who crosses the road without looking does not get knocked down, while people sitting inside a shop may get knocked down by a car that skids off the road. In conventional terms we call this luck. I see that luck being caused by kamma. In Buddha Dhamma there is nothing called luck or random events, all events have causes.
If one decides to stand on one leg, the initial thought that came across to his mind that he needs to stand on one leg may be due to a kamma vipaka, but if he is wise enough he will not take that action. Thus he does not have to go through that pain. But if he does decide to stand for long on one leg, the physiological aspects will come into play, and now we might only focus on them and not the initial decision taken to stand on one leg.
What the Niganta’s in the Buddhas time were doing was to stand on one leg to erase the bad kamma collected in previous lives. The Buddha saw that as foolish, as not all vipaka is due to past kamma in previous lives. Some are due to kamma in this lives as well. Just like standing on one leg. The decision to stand on one leg is a kamma in itself.