Can Your Muscles Make It?

From Unlocking Science with Roger Patterson

God created our bodies with three types of muscle: smooth, cardiac, and skeletal. Smooth muscle lines your digestive tract and can work nonstop. Cardiac muscle keeps your heart perpetually pumping through your entire life. Neither of these muscle types get fatigued (tired or sore). But that is not the case with skeletal muscles, the muscles that move your arms, legs, and head. You’ve probably experienced muscle fatigue while hiking up a mountain, crossing the monkey bars, or holding a smile for family portraits.

Skeletal muscles can create a lot of power, but only for a relatively short time. As the long fibers contract, getting shorter and pulling on a bone, they require lots of energy. They need a chance to reset, and they can’t stay contracted or keep contracting forever. After lots of aerobic exercise, lactic acid can build up in the muscles, making them sore. When your muscles start to tremble or twitch, they are reaching the point of fatigue and need rest.

Continually working your skeletal muscles will cause them to grow, giving you more power and endurance the next time you need to reach the top of that mountain for an amazing view of God’s creation.

How long can your muscles make it before giving out? Find out with these simple experiments.

Materials Needed

Foam ball
Tennis or racquetball (or any hollow ball)
Weights of various sizes (approximately 1–5 pounds). A fillable container like a milk jug would also work if you have a scale to weigh it.
Stopwatch

Experiment One—Get a Grip

You will need two balls of different densities, such as a foam ball and something hollow like a racquetball or tennis ball. One ball should be firmer and harder to squeeze than the other ball.
Squeeze the ball as firmly as you can, and hold the squeeze for as long as you can. Try to continue for three minutes.
Use a stopwatch to measure the time until you start to feel the muscles in your forearm trembling.
Record the time.
Repeat with the opposite hand and then repeat with the other ball, giving yourself a short rest between the trials.

Analysis Questions

When squeezing the foam ball, were you able to endure three minutes with your right or left hand? What about when squeezing the firmer ball?
Which is your dominant hand? Why were you able to grip the ball longer with your dominant hand before your muscles fatigued?

Experiment Two—Hold It!

Take a light weight in your hand and raise your arm out to the side so it is parallel to the ground.
Use a stopwatch to measure the time until you start to feel the muscles in your arms tremble.
Record the weight and time.
Repeat with the opposite arm.
Using increasing weight, continue the process alternating between arms. Give yourself a rest between the trials.
Record the weight and time.

Analysis Questions

How did increasing the weight affect the time until your arm muscles fatigued?
If you tested different people, how can you explain the different levels of muscle endurance?
What would happen if your heart were made of the same type of muscle as the muscles in your arms?

Think It Over

The Bible uses many metaphors to talk about the endurance needed to live a righteous life as a Christian. Read 1 Corinthians 9:24–27 and Hebrews 12:1–6. How can you relate these passages and their metaphors to the activities you performed?

Roger Patterson helps kids understand science from a biblical perspective through experiments and hands-on activities in his Answers TV show Unlocking Science.