Biomedical Engineering - Elbows and muscles

Last month, I was asked to lead the Biomedical Engineering workshop of a full-day event introducing engineering to 100 high school girls.  This was my third time leading the biomedical engineering workshop for the local chapter of the Society of Women Engineers.  I didn't want to repeat any lessons quite yet.  I have also been incredibly busy in my personal and professional life, so I hesitated leading.  I was hoping to mentor a younger biomedical engineer into leading a workshop (letting her take the ropes and lead with my guidance), but nobody stepped up as a lead.  Anyways, I decided to do something very easy in terms of preparation and conceptually.  Initially, I thought it might be too easy for high school girls, but it turned out perfect!

MUSCLES - we all have them, why not learn about them.

In particular, my lesson was about muscles for movement.

Time breakdown (total time 50 minutes):

• 7 minute presentation introducing biomedical engineering, giving a brief background of my job as a gait analyst (gait = fancy term for walking), the importance of modeling motion, and giving a very brief lesson on anatomy.
• Anatomy lesson included
• Naming how many bones in the body.
• Showing a picture/diagram the musculoskeletal system, highlighting some of the bigger, more well known muscles (quadriceps, biceps, triceps, etc.).  Muscles have an origin on one bone, cross a joint, and insert on a different bone.  Muscles work in tension only to move the body.  Different muscles move the body in different ways, so flexing is done by one set of muscles whereas extending is done by another set of muscles.
• Briefly describing ligaments and their function to connect bones to bones.
• Introducing tendons, which attach muscles to bones.
• Then we focused specifically on the arm with the elbow joint.
• 3 main bones: humerus, radius, ulna.
• For simplicity, we treated the elbow joint as a hinge.
• Flexor muscles: biceps, brachialis, brachioradialis, their attachment points, and their function(s).  Demonstrated that when I flex my arm, my biceps are activated, but when I release my biceps muscle, my arm doesn't flop down.  I need something to pull it back down.  That's where the extensors come in.
• Extensor muscles: triceps, anconeus, their attachment points, and their function(s).
• Introduced the challenge.
• 35-40 minute challenge exercise.
• 5-10 minute post-activity discussion.

The challenge was to make a model arm that could flex and extend.

I created this arm model worksheet for the girls to use/complete during the activity.  They worked in groups of 2.  Here's a run down with more specifics than the sheet provides (it was a big verbal instruction and feedback activity).

Easy set-up and materials

Materials:

• 3 rulers (one per arm bone) with small holes
• 1 large brad
• 3 paperclips
• 2 pieces of ~50 cm length string

Set-up for flexing the arm

Assembly:

• Place the three rulers one on top of each other and attach a brad through one of the holes on the end
• Pick a hole that the brad won't slide through.
• Open a paperclip, making a hook, and attach a string to the paperclip with a knot.
• Repeat for the second string and paper clip.
• Attach the paperclip (tendon) to the radius/ulna (lower part) of the arm and thread the string through the top most hole on the humerus (upper part).  Pull on the string from the top hole and watch the lower arm move up (flexing).

Flexing the arm

Activities:

• Play with origins and insertion points (put the string through different holes on both the upper and lower arm) and note how the lower arm reacts with different attachment points.
• Now that the arm is up (flexed), can you think of ways to extend it?
• I needed to give them some anatomical guidance/feedback here.
• Reminding them how the triceps are attached (behind the elbow).
• Reminding them that our joints are virtually frictionless (when they had decided to wrap the string around the brad or tightly around the back of the ruler).

Feedback:

• All girls were able to complete and understood the flexing of the arm.
• All girls could point to the direction the forces were pulling or needed to pull for flexion/extension (along the line of the string).
• 1/3 of the girls got the arm to successfully extend (they received a cool shopping bag donated by one of our sponsors).
• Redirecting forces was a tough concept for the girls.  The key to extension was to pull down but still have the muscle located "up" in the arm.  Many understood attaching the muscle from below, but when they attached it to the upper arm, the forces were still pointing upwards.
• This was something I had to think about on the fly and explain it to the girls in their individual groups as they were trying to solve the problem.  I tried to explain it in terms of a pulley system.  If I attach a string to a box, I can lift something directly up, right?  That's basically what the flexor muscle is doing.  But I can also pull down on something to lift it up if I have a pulley.  We need something that will pull the "arm" down when we pull up with the muscle.
• Methods for extension included making a pulley-like system, where force was redirected around the elbow:
• Attach a paperclip (why I suggested 3 paperclip) to the back of the ruler.
• Attach the brad to the little hole next to the big hole in the ruler and use the big hole as the pulley (they flipped the rulers opposite that the ones pictured in this blog).
• Holding the arm horizontally while flexing/extending works best.  That way gravity isn't extending the arm on its own.
• Attachment points: the bigger the muscle length, the easier movement was.  Think of it in terms of lever arms.  It's hard to lift 100 lbs straight up, but if you put it 4 ft away and create a fulcrum/lever system, I bet you can lift it fairly easily.
• This is a simplified version of an elbow.  How would someone change their model if they were going to account for rotation of the lower arm?  The key is that the elbow is actually two joints: the humeroulnar joint (what we modeled) is a hinge.  The radioulnar joint is the one that can rotate (pivot).
• The girls really enjoyed this lesson.  It was complex enough to get them thinking outside of the box but structured enough to where they didn't give up.

**This lesson was adapted from page 16 of these biomedical engineering activities.

Little kid adaptation:

J loved seeing the ruler arm go up and down, and kept asking about it.  I figured it's a good time to start the discussion about anatomy and movement.

It's easy to introduce muscles and that our muscles move our bodies:

• I can bend and straighten my elbows and knees thanks to muscles.
• Point out your bicep muscle.  Have your child touch it when you aren't flexing and then when you are flexing.  How does it feel different?
• See if your child can flex their own muscles.  
• When we exercise, our muscles get big and strong.
• If we are sick or injured, our muscles get weak.

We also talked about bones too.

• Our bones are hard and help us stand up.
• We need calcium for our bones to grow big and strong.  We can get calcium from milk, cheeses, and yogurt.
• We can break our bones if we're not careful.  If that happens, we'll be put in a cast, and we can't use that bone until it heals.

J liked playing with the strings and trying to move the rulers.  It could be fun if you have a marionette to show how different strings move different parts of the body.

Material note, we used these rulers: Charles Leonard Inc. Ruler, 12 Inch, Wood, 36 rulers

End of super long post, whew!

Related Posts:

• Muscles and strings - move a rock
• Bio-X Kids Day - elbows with younger kids