Here is another way to vary pectoral muscle fibers used: Do push ups against a bench. this is a "diagonal way" of doing push ups. Be careful your shoulder blades do not come too close together in the back. Keep your back straight. Do five sets of ten repetitions.
Disclaimer: None of the above information can be taken as a substitute for advice from a medical professional such as a physician.
My third book, Pocket Guide to Fitness, is available on www.louizapatsis.com, http://www.authorhouse.com, www.bn.com and http://www.amazon.com. If you look up my name on those Web sites, you will find my other books The Boy in a Wheelchair and Life, Work and Play: Poems and Short Stories.