 Well, on the other extreme of bulkiness, we also have like crazy extreme flexibility. And bulkiness and strength and flexibility often are in contrast with each other. As we can see, really, that's awesome. Some of us are more flexible than others of us. Flexibility, there's definitely some joint issues that affect flexibility, but if you just look at the muscle, flexible muscles are literally longer than inflexible muscles. The more you stretch, you actually are physically making your muscle organ longer. How? Well, but of course, we must have an answer for that. Now, speculate, you don't add new muscle fibers on the ends of your muscle organ. So we know we can't add muscle fibers. So what are you going to do? How are you going to make the myofibril... How are you going to make the muscle organ longer? I kind of gave it away. You could start by making the myofibrils longer. And the way to think about making myofibrils longer is to think about adding sarcomeres. Does that work? If you want to increase the diameter, you're going to increase the diameter. You're going to add new myofibrils, period. But if you want to increase the length, then you're going to need to add sarcomeres. So remember this, little sweet darlings. Remember that from here to here, that's one sarcomere. So if we bust a move, we stretch our muscles. That stretching, that tension, that moment that you get to like, I can't stretch more than I've stretched. You take a deep breath and maybe you can get a little bit farther. But there's a point where you're sending some pretty strong messages to those muscles that are going, dude, what are you thinking? Slow your roll, quit stretching me. Then they send all these chemical messages to the muscle itself and the myofibrils generate additional sarcomeres on the ends. If they build new sarcomeres into their myofibrils, myofibrils are going to get longer and you are more flexible. That's why one of the things that is really dangerous, if you are trying to bulk up, so you're doing a lot of heavy weightlifting, you're trying to increase the diameter of your myofibers so that they're just, they're bigger and they're filled with more myofibrils, which means they have more myofilaments in there. If you don't stretch, you're going to have these muscles that are so inflexible that you can't move very well. And doing all that hard work, like you're not really going through, if you're doing bicep curls, you're not really going through your full range of motion. And your muscle actually shortens after doing all those bicep curls as a consequence of the workout. Your muscle shortens. And if you don't stretch it out and re-lengthen it back to where you started, it can chronically shorten for good. In fact, if you, you can lose sarcomeres just as easily as you can put them back in. In fact, probably it's easier to lose your sarcomeres than it is to buckle down and have a stretching routine and make it happen every day so that you actually add those sarcomeres back on. There are some consequences for not stretching yourself. And we can talk about some of those in class. Okay. The next section, we're going to talk about how not all muscle fibers are equal.