It is possible to workout without weights and see results. The reason behind that is due to the intensity you decide to move at. Your intensity correlates with the speed, pace and effort you put into a routine. Give three people the same workout routine. One does it a leisure pace and takes a minute break between sets. Another moves at fast pace but takes a two minute break between sets to recover. The last person workout at a fast pace and takes short breaks under a minute long. Though their exercises are the same, the three will experience different results based on their intensity. The third person will see the most improvement because they are putting their body in a position to raise their metabolism, burns fat and increases muscular hypertrophy.