The objective of this paper is to investigate what would be the optimal strategy for voluntary trunk movement, which would minimize hip, knee and ankle torques demanding as well minimal upper limb participation during Functional Electrical Stimulation (FES)-assisted sit to stand motion in person suffering from Spinal cord injury. Our results suggest that paraplegic patients should bend their body forward in order to use linear momentum of the trunk in sit off phase, i.e. they should generate the motion similar to the one of healthy subjects. Those results have been experimentally tested using a closed-loop controller for FES-assisted standing-up. The controller should automatically trigger leg stimulation in optimal moment with respect to the trunk motion in order to decrease arm participation during rising phase of the motion.