 Now if we zoom all the way out, we have usually, we have muscles that come in pairs. And when they come in pairs, they have opposite actions. We're going to see it, we definitely see it really everywhere. And it's the action of a muscle that's shortening that lengthens a muscle on the other side. My favorite example is biceps and triceps. You can actually like go ahead and make yourself a massive bicep right here, whoa, that's huge. And you can feel your tricep which is inferior on the posterior aspect, okay it was inferior right here, but it's actually on the posterior aspect of your arm. Biceps are on the anterior aspect of your arm. And when I contract my biceps and flex my forearm at the elbow joint, I can feel my biceps brachii becoming quite massive. I can feel how squishy and relaxed my triceps are. And then I extend. Now try to feel both triceps and biceps as you are extending your forearm at the elbow joint. When you feel how triceps is actually going to contract to complete the extension, and biceps is actually going to relax as that extension happens. Now there's all sorts of craziness when it comes to muscle movement. It's called biomechanics of muscle movement. And there's all sorts of really cool things that happen with our muscles when we start looking at gross movements that we make, but I think it's helpful to keep in mind that we end up with muscles in these pairs. And the pairs of muscles, it's awesome to put them together in your brain, talk about a great sorting activity, sort these muscles into their antagonistic pairs because they have opposite actions. And really because of the way muscle contraction occurs at a molecular level, you actually need the antagonistic pair to stretch out your contracted muscle. Like you don't really have much of a mechanism in your muscles to stretch themselves out unless you have somebody apply a force to do that stretching for you. Sometimes gravity will stretch that out for you and you don't have to actually do much contracting of another muscle, but you need to have a muscle there that can do the opposite movement and put you back into a original position. I'm going to come back and we're going to talk about superior limb musculature because that is the lab for the day and I'm going to walk you through those structures.