Let's talk about isotonic versus isometric contraction. When you learn a new language, it's so easy to get really confused. Isotonic versus isometric. Isotonic gives you a real little hint in there. It has the word tonic or tone in there.
When we talk about contractions, it's all about the muscle moving. When we look at isotonic contraction, there's actually two kinds of contractions underneath. There's an eccentric contraction and a concentric contraction.
Concentric contraction is what we use all the time. all the time when we're at the gym. So let's take biceps brachii as our classic example.
I want you to feel it. It's this muscle here. A lot of times we do bicep curls. There it is. Its origin is on the superglenoid tubercle and the coracoid process.
Its insertion is the radial tuberosity on the radius. When you feel that muscle belly and we get those muscle fibers to shorten, and that's its job, its action is flexion of the elbow. When we get it to shorten and you feel it bunch up underneath there. that's concentric contraction. Concentric contraction, shortening of the muscle fibers.
Now, let's go in the opposite direction. It's working while those muscle fibers are getting longer and lengthening. So when we look at isotonic contraction, we have concentric contraction and still working, the muscle's still working, we have eccentric contraction.
Now, when we think about isometric contraction, this is where you can take a cup of water, watch the joint. angle it's going to stay the same biceps still engaged and if I start to fill up that water I'm going to fill it up right to the top is my muscle still working absolutely it's still working the muscle is contracting joint angles not changing so we see this all the time in yoga actually where you hold a pose and then the muscle fatigues because it's working for a long period of time so isometric contraction is more muscle work applied more load but no joint change. Under Isotonic, concentric contraction and eccentric contraction. Under Isometric, maintaining joint angle but increasing the workload.