Post on 29-Mar-2015
Muscle Biomechanics
• Study of the human body as a mechanical system
Remember Biomechanics?
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
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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
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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
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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
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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
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Modeling Muscles
• Finally, we can replace the upper arm with another beam
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Modeling Muscles
• And finally, let’s treat the proximal end of the humerus as a pulley, and our model is finished!
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Modeling Muscles
• If we pull on the bicep, we create more tension, which will cause the forearm to move
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Modeling Muscles
• What will happen if we add a weight to the end of the forearm?
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Modeling Muscles
• The tension will increase!• So what does that mean for your muscle?
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Modeling Muscles
• Your muscles has to work harder to contract to maintain a higher tensile force
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Modeling Muscles
• So we now have a completed working model of the biceps muscle and its associated skeletal elements!!
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Modeling Muscles
• Now that we have our completed model, what can we do with it?
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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