First of all how does he transfer? Is he totally bed bound or does he get up into a chair/device? How does he get around? How long can he tolerate being up in that device? Does he get sob? Does he get dizzy? Since he's a quad, I'm assuming he uses a power chair of some sort. His endurance may be quite a long time since he is just sitting, however there may be contraindications for him to be up for so long ie..pressure sore management.
So you might say, patient is transferred out of bed with a hoyer lift into a wheelchair. He can tolerate being up for two hours and has to go back to bed for pressure relief measures. If his blood pressure bottoms every time he gets up into a chair and he's dizzy then he has very little endurance related to dizziness.
Hope this helps