Did You Know You Can Build Muscle and Not Even Move (Kinda)?
I'm not going to judge you for clicking on this link. It sounded kinda lazy, I'll admit, but this is actually an overlooked way of working out that would greatly benefit a lot of people. What I'm talking about is an isometric contraction. Normally we contract a muscle and it makes something on our body move. We contract our bicep and it helps bend our elbow to put food in our mouth. Well an isometric contraction is when a muscle contracts, but nothing moves.

Think of it this way. Go up to a large rock and try to push it over. Odds are that rock doesn’t move and neither do you. So again, an isometric is a muscle contraction when the muscle is contracting, but no movement happens.
DB, whats so special about an Isometric? That seems kinda silly if I'm not really moving anything.
Here's the lowdown. You don't have to try your hardest to produce the force needed to push over the rock. You actually just have to give about 20%~ effort and you get a lot of benefit in a lot of areas. Here's a few perks of using an isometric contraction in your workouts.

Increased Muscle Activation
When you contract a muscle and no movement occurs, your brain senses that and thinks “dang this isn’t moving” and yells for help. The result is a greater recruitment of muscle fibers of that muscle and other muscles that may help do the task that is trying to occur. Here is why this is a benefit. Your brain remembers this. So next time you're using that muscle in a similar way and you start to struggle, you're more likely to call on more muscle fibers to help. This can lead to increased strength and increased efficiency when doing certain exercises.
Reduces Pain
Pain is arguably the most misunderstood part of life. Sometimes we think we know what causes it, and then sometimes we have no earthly explanation. What we do know is that there are pathways that inhibit(block) pain perception. Isometric contractions seem to have a similar effect in blocking pain in those with tendon pain. For example knee cap pain. Isometrics in those with patellar tendon pain find pain relief up to 45 minutes or longer after a few isometric contractions. The same has been shown with Achilles tendon/heel pain.
Improves strength
Even though isometrics have no movement of a joint, they are what we call joint specific. So if you are weaker in a certain portion of a range of motion you can strengthen that very spot by using isometrics. What’s even more beneficial is that we see strength gains at that very joint angle AND 20 more degrees each way. So if we have a sticking point in a lift, using an isometric at that very spot can help overcome weak points. Also, if we are experiencing pain in a certain part of a movement, we can back off of that pain and if we are within 20~ degrees of that pain, potentially reduce pain and improve strength in that area.
Increases flexibility
Remember earlier when we said that the brain senses an isometric contraction and will call on more muscle fibers to work and try to complete that movement? Well the brain will also produce a relaxing effect to the muscle opposite to the one that is doing the work. So if your hamstring flexibility is lacking, you can produce an isometric contraction of the opposite muscle, the quadriceps, to help relax the hamstring and increase flexibility. This is a very effective way to get "tight" muscles to feel relaxed and improve your flexibility.