You weren't cheating in PE class - knee press-ups have been proven to be just as effective in building strength as the normal exercise.
New research from Penn State University published in the Journal of Applied Biomechanics has shown that knee press-ups provide as much benefit to your body as press-ups with your toes.
Although the typical toe press-ups carry 60-70 percent of bodyweight, compared to 40-50 percent with the knees, as the upper body muscles are activated by both, you can still get the gains on those muscles using your knees.
The results show the press-ups are not worthless, as long as you are performing enough to feel exhausted, says Associate Professor Jinger Gottschall, who led the study of 12 healthy participants, The Sun reports.
Chest, shoulder and arm muscles are best targeted with knee press-ups - and no, don't call them "girl" press-ups.
The research also found press-ups may be better for regular gym-goers looking to gain muscle than other exercises like bench pressing weights.