A new gardening rake with an S-shaped handle reduces compression stress on the spine during the pull stroke to about one-fifth of what it is with a straight-handled rake  During the push stroke, however, compression stress is five times more with the new rake than with a straight-handled rake  Neither the push stroke nor the pull stroke with a straight-handled rake produces enough compression stress to cause injury, but compression stress during the push stroke with the new rake is above the danger level
Ttherefore, straight-handled rakes are better than the new rakes for minimizing risk of spinal injury
It is not possible to design a garden rake with a handle that is other than straight or S-shaped.