In the 1920’s scientists wanted to know what effect inactivity had on muscles. They bound the legs of a group of frogs for extended period of time and then studied the results. Shockingly, at the end of the experiment the frogs who had their legs tied had bigger and stronger legs than the untied frogs of the control group.
The restrained frogs struggled to get loose the whole time they were tied. The constant constricting and tensing greatly improved their leg strength and size. This type of tension without movement is called an isometric contraction.
You do not have to participate in a strange experiment to benefit from isometrics. The two basic isometric techniques that are commonly performed are: pushing or pulling against an immovable object and holding a weight at a point and not letting it move.
For instance, you can load up a bench press with a weight you can’t budge and push as hard as you can for 20-60 seconds.
Don't have a bench press? Push against a wall. Pick a sturdy one though, just trust me on that.
An example of the other technique is the Isometric Paloff press. To perform an Isometric Paloff press, stand perpendicular to a cable crossover, grab a D-handle with both hands, press it straight out at chest level, and hold that position with arms extended. The weight will be constantly pulling you to the side so it is a great core workout.
Don't have a cable crossover? Do you have a friend? Or at the very least someone willing to inflict punishment on you. Clasp your hands together and push them straight out in front of you. Have your "friend" push on the side of your hand trying to move you. Don't let them! They are not the boss of you! Sounds simple, but is actually pretty challenging.
Isometrics are not something you want to do exclusively , they are just another tool to add to your exercise tool box. Constantly challenging your body is the key to changing your body.