Isometric exercises are centuries old, but there is still a place for them in your fitness program. Anybody can use them, but they are particularly useful for those of us over the age of 50 for whom lifting weights can be more difficult. However, you don't have to wait until you are 50 to work them into your program. There are good reasons to use them as part of your workout rotation. We will cover that, along with the history of isometrics and some examples of what isometric exercises look like, below.
It probably makes sense, at the outset, to answer the question, "what are isometric exercises?" This can best be explained by a comparison. Isotonic exercises are the exercises that most of us do in our weight lifting program. You take a fixed amount of weight (resistance) and move it; usually up and down. This exhausts your muscles and makes them grow (along with proper nutrition, hydration and rest). Isometrics flips that formula around by making the position of the resistance static (you don't move) and having the resistance variable (your muscles resist less as they tire. The picture above shows a gentleman working his chest (plus some other muscles) using isometrics. Contrast that with the picture below working the same muscles with butterflies. Isometrics are essential pushing/pulling and holding position. The muscle fibers don't change length.
As I mentioned, isometrics have been around a very long time. The origins can be traced back at least to the 12 century AD as yoga was taught in India. Moving forward in history, the Knights Templar used isometrics as their strength training ritual to gain strength without lengthy exercise. In the 20th century their use became common among body builders like Charles Atlas. He even created his own version of the exercise form. While they have faded into the background from a popular culture standpoint, those that understand their effectiveness still use them to great effect today.
There are two basic types of isometrics. 1. Overcoming isometrics - In these exercises, the muscle is used against an immovable object (tree, car, house, etc.). You push/pull as hard as you can as long as you can. 2. Yielding isometrics - By contrast, this type is used with a movable object (weights, a rock, a log, a tire, etc.) held at a partial shortening/lengthening of the muscle. With a biceps curl, you would lift the weight from fully-extended arms to half-way and hold it until you can't any longer. I recommend a spotter for these exercises so you don't drop a weight on your feet or your head (in a bench press, for example).
Before discussing "why", I want to mention that the main reason we don't hear about isometrics much is that, for athletes, they don't have a range of motion in the exercises by their nature. Athletes, in particular, want to gain strength through a full range of motion for each muscle group. Having said that, there are still good reasons to use them for those of us just focusing on getting and staying lean and fit.
Using isometrics can definitely be used when a person has limited access to fitness equipment but still has the goal of building muscle and burning fat. In addition, the lack of motion inherent in these types of exercises can give rest to sore joints. For the same reason, isometrics can be used for injury recovery, too. I do recommend them as a change of pace in your training, also. See what the Mayo Clinic has to say about it.
Now let's look at some examples of isometric exercise. I won't cover every possible exercise, but I am certain that you will get the idea.
I'll just focus on "overcoming isometric" exercises because the "yielding" variety is pretty self-explanatory and can be done with most any weight lifting exercise.
Do each exercise 3-5 times with 15 seconds rest in between.
Plank - Put yourself in push-up position, then move down to having your elbows and forearms on the floor. Clench your butt, thighs, abs and chest. Hold the position for as long as you can.
Wall Sit - Place your back flat against a wall. Slide down to where your knees are bent at a 90 degree angle (thighs parallel to the floor). Hold until it burns.
Glute Bridge - Lie on your back with your palms, arms & feet flat on the floor and knees bent. Force your hips up into air by pressing down with your palms and feet and clenching your butt. Hold until it burns.
Body Hold - Sit on your bottom with feet flat on the floor and knees bent. Raise your arms forward to be parallel to the floor as you straighten your legs to make a "V" out of your body (see below). This will take some balance and getting used to. Hold 15 seconds and longer as you get stronger.
Tree Hugger - Not a political commentary...Go out and find a tree that does not have really rough bark. Wrap your arms around it and squeeze as hard as you can for as long as you can.
Static Push - Brace your feet 2-3 feet away from a basement or other solid wall. One foot should be closer to the wall than the other. As if you are trying to move the wall, push at full power for as long as you can.
You get the idea. For more ideas, just Google Isometric Exercises.