Muscle Biomechanics

Remember Biomechanics? Study of the human body as a mechanical system

Modeling Muscles Muscles make the body move, so what must they do? Apply a force! How do muscles apply this force? By contracting!

How do Muscles Apply Force? Muscles contract, or get shorter, and they pull on the ligaments and bones to which they are attached

How do Muscles Apply Force? Muscles contract, or get shorter, and they pull on the ligaments and bones to which they are attached

How do Muscles Apply Force? Muscles contract, or get shorter, and they pull on the ligaments and bones to which they are attached We call this pulling force a Tensile Force because it is a result of tension in the muscle T

Modeling Muscles Since muscles contract to create tensile forces, an easy way to model them is using a rope or cable since these can support tensile forces

Modeling Muscles Since muscles contract to create tensile forces, an easy way to model them is using a rope or cable since these can support tensile forces T

Modeling Muscles Let’s further simplify the system by replacing the forearm with a beam since we’re not looking at the hand or wrist T

Modeling Muscles Now we’ve got a joint to look at The elbow is a hinge joint, so we can model it as a hinge T

Modeling Muscles Now we’ve got a joint to look at The elbow is a hinge joint, so we can model it as a hinge T

Modeling Muscles Finally, we can replace the upper arm with another beam T

Modeling Muscles And finally, let’s treat the proximal end of the humerus as a pulley, and our model is finished! T

Modeling Muscles If we pull on the bicep, we create more tension, which will cause the forearm to move T

Modeling Muscles What will happen if we add a weight to the end of the forearm? T

T Modeling Muscles The tension will increase! So what does that mean for your muscle? T

Modeling Muscles Your muscles has to work harder to contract to maintain a higher tensile force T

Modeling Muscles So we now have a completed working model of the biceps muscle and its associated skeletal elements!! T

Modeling Muscles Now that we have our completed model, what can we do with it? T

Who is Really Stronger?

Who is Really Stronger?

Who is Really Stronger? The distance from the applied force to the fulcrum or point of rotation is called a “moment arm”

Who is Really Stronger? The distance from the applied force to the fulcrum or point of rotation is called a “moment arm” Moment arm

Who is Really Stronger? The longer the moment arm, the more torque is applied for the applied tensile force Moment arm

Who is Really Stronger? So, if the moment arm on the right is 4 cm, and the moment arm on the left is 2cm, _____ only has to apply ½ as much force to curl the same amount of weight as ____!! Strength is about more than just the biggest muscles!

Summary Muscles contract to create Tensile Forces Because of this, we can use a rope or a cable to model a muscle The Torque that the biceps can generate depends on the length of its Moment Arm, or how far from the elbow joint it attaches to the forearm Strength depends on not just how big your muscles are, but also how your body is put together