I feel that apart from Kamma and Kamma vipaka, the body pain or pleasure (dukkha vedana and sukha vedana) are conditioned by niyama as under:
Chitta Niyama
Kamma Niyama
Dhamma Niyama
Bija Niyama
Utu Niyama
Eventhough the pains or pleasure encountered seemed to be arising out of Kamma done in the past moment or coming from earlier lives, the other niyama’s certainly have role to play.
From my own personal experience, seem to see all these 5 different niyamas dictating bodily experiences that one undergo moment after moment.
The only thing which is in control of a person as gati is to either react or not to react thus not adding mental inputs which Lal has excellently explained.
As an example, I had a muscle cramp / catch at the knee which had not surfaced for 27 years. Had an accident 27 years ago and this got automatically manifested on 24th December out of nowhere.
From the outset, it seems like past Kamma vipaka which did not have an opportunity to express and my cross legged sitting and a sharp movement of getting up created that vipaka to show its occurrence.
However, upon careful examination I felt that this was not only Kamma vipaka but also due to Dhamma and Utu Niyama which triggered the Vipaka to manifest as physical pain.
After 25th Dec to 7th Jan, did not have any pain at all and it came back as a pain due to again sitting in the same position and getting up carelessly which is Kamma Vipaka.
Thus, I feel it is combination of Niyama which causes the body pain / suffering or pleasure and not just Kamma Vipaka.
Would be glad to hear your views.