To lighten the work load in apple cultivation, the author investigated the desirable depth of the surface of the ladder rungs, the following ressults were obtained.
1, The use of the wooden ladders soled on the market, induces not only a prominant change of the foot arch but also the instability of the whole body, it also increases the activity of the antigravity muscle of lower limbs.
2, The morphological changes of the antigravity muscle of lower limbs while standing on 5 kinds of wooden rungs (15, 12, 9, 6, and 3cm deep) were compared with the basis when standing on awooden rung 20cm deep. The results indicate that the desirable depth of wooden rungs is over 9cm.
3. To increase the weight of the ladder as little as possible and to ensuce smooth working conditions when standing in the sideways position or resting on the arch of the transverse axis or on the heel, the depth of the rung should be about 6cm.