I will do my best to explain.
This move is done lying on your back and is similar to lying tricep extension, however, cross body extensions are done one arm at a time. You will lie back and have the weight in one hand, you can use the other hand to "support" your arm to keep it stablized during the movement. (You just want to lightly hold on to the weighted arm again, to keep it from moving.) Now you take the weighted arm, bend at the elbow and take your hand across your body and then extend for a peak contraction and repeat.
This move as also done as a "bonus" with the band. I don't think I can explain it very well at all...but I'll try. You will assume the same lying position, but the arm not doing the work will be used to hold the band (down at you side by your chest-gripping tightly) as you extend the working arm. If you find that you don't have enough tension, you will have to decrease the length of the band between your hands. She does several pulses and you will not be able to bend the arm with as much control. You have to concentrate on the Peak contraction and keep the tension in the band at all times in order for this move to be effective.
Hope this makes sense...
~Marietta
FITXME