To work on Selva Chi you don't need to be super fit but you do need to be able-bodied and have a great will to give most things a go and a desire to learn and experience new things.

You should be prepared to work 40 hours for every week you stay and usually that will be over five days to give you two days free to explore the local area or get back to "civilization". You could expect a daily work-load such as:

8am a 1pm - planting, weeding and mulching trees.
3pm a 5pm - fruit picking
5pm a 5:15pm - fetching water.
Help with preparing dinner and washing dishes.

The work is variable. Other types of work that you could expect are:
Carpentry
Painting
Mixing and pouring cement
Attending the veggie patch
Cutting and carrying bamboo
Clearing around planted trees
Planting short-cycle crops
Seed collecting in the forest
Planting seeds in the nursery
Mixing soil and Potting up trees
Roof thatching
Putting up fences
Construction of paths and similar landscaping.