There is no one exercise that is best for all individuals. It would be, however, a compound exercise (in other words, one that requires using more than one joint). One suggestion would be to do chins. Other candidates include dips and seated military presses.
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To build upper body strength the best chest exercise is lifting weights.Dumbells are the easiest way.Start on smaller weights and build up to heavy weights.
I had read that it is the core exercise
It is possible to do an upper body workout with an exercise ball. You can do push ups, chest flys, and back extensions using an exercise ball.
They are an upper body exercise. They also work core muscles.
everything but mostly upper body
Adjustable dumbbells are a good instrument to use as exercise for you upper body as long as you're doing an exercise right and appropriate for you. Ajustable weights can save you space too.
An elliptical stepper with upper arm moving bars will work both upper and lower body muscles.
Good exercise activities for paraplegics are upper body strength training, if they like to play sports and are still active they can play basketball or tennis too.
AN exercise pushing your upper body up from a prone position.
A bench press machine will be best for your upper body workout.
Throwing the discus isn't really an exercise. It's an activity. It does require a large amount of upper body strength. You can learn to build upper body strength by visiting http://www.squidoo.com/build-upper-body-muscle.
A cheap and easy way to build upper body strength is to do push-ups, pull-ups, and sit-ups at home. If you are able to go to a gym then you can exercise on their machine circuit for a well rounded workout.