The subjective effect of the electric stimulation will be assessed by an 5-item-questionnaire. Since no standardised questionnaire is available to assess the well-being in relation to sitting in a wheelchair, an individual non-validated questionnaire has been developed. It contains five questions: Question 1 and 2 address the number of resting phases while lying down and the respective overall duration of decompression each day. The questions 3 to 5 focus on the fear of pressure sores while sitting, every day limitations based on decompression phases and the subjective well-being while sitting in a wheelchair. The subjects answer the questions using a visual analog scale of 10 cm, indicating 0=no fear/no impairment/no well-being; 10=high fear/high impairment/high well-being. The subjects complete the questionnaire at baseline (start of intervention), after three and after six months.