There are a number of methods of strength training without weights. One of the most common methods is the use of resistance. Many common calisthenics exercises also are effective ways of developing strength without using weights.
There are types of at home workout equipment that are designed specifically for strength training without weights. Instead of using weight to work muscles, these machines use resistance. Very often these types of machines have built-in controls that allow users to increase resistance as the user develops strength and needs a more intense level of resistance, just like one would add more weight to a dumbbell or on a machine that relies on the use of weights.
Another kind of equipment that relies on resistance instead of weights is water aerobics. Water aerobics offers strength training without weights because water creates a natural resistance. Water aerobics often use buoyant dumbbells that, when pulled under the water or held beneath the water for a period of time, help to strengthen the muscles. The buoyant dumbbells constantly try to bob back to the surface, creating a resistance and training the muscles. This is like the reverse effect of gravity, which tries to pull weights back down to the ground and therefore trains the muscles.
There are a number of exercises that require no equipment whatsoever that provide strength training without weights. Push up are a great way to work the arms, shoulders, and back without the use of weights. To add a little extra resistance, place two or three heavy books of similar weight on one's back before performing push ups. This will increase the intensity of the workout by both adding weight and causing one to brace in order to keep the books from toppling over.
In order to target the lower body during strength training without weights, do squats and lunges. These exercises simply use the weight of the body in order to train the muscles in the legs and the glutes. The core of the body, particularly the abs, can be trained through sit ups and crunches. For those interested in strength training without weights, local parks may be a good source of exercise. Many public parks have outdoor fitness equipment such as bars for chin up and pull ups, benches for sit ups and crunches, and low bars for push ups, all of which are great exercises that assist with strength training without weights.