Last week we looked at how our hands use muscles and tendons to hold, grip and grasp.
Today we're going to squeeze a clothes peg with our fingers to discover how our bodies send energy to our muscles and why those muscles get tired.
The background: To be able to run, jump and throw, our bodies need energy, which comes from the food we eat. Our bodies then convert that into a type of energy that can be used by our muscles.
But because only a little bit is stored in the muscle cells at any time, our body has to keep making more and more as soon as we start using our muscles for action.
This kind of energy, called adenosine triphosphate (ATP), is so important,the body has three different ways of producing it. Depending on how you use your muscles-in different sports,for example - determines how the body produces the energy to fuel your activity.
What you need: * Spring-loaded plastic clothes peg * Stop watch
What to do: 1. Hold the clothes peg between your thumb and forefinger. Use the hand you write with. You can try later with your non writing hand and see which is stronger. 2. Ask a friend to time you for 30 seconds and count how many times you can fully open and close the peg. Try to do it as fast as you can and notice the muscles working in your forearm. 3. Give your fingers a rest and then try for 60 seconds. Try another time for 90 seconds. 4. After a while our fingers get tired from all this work! During this time, the body is going through a startling number of processes to transport more energy to our muscles.
What'shappening? Fast blast - All muscle cells have a little bit of'immediate use' energy ready to go, but only enough to last about three seconds! Those cells then get to work to produce more energy for the muscles. This next blast of energy is available to the muscles at a very high rate but only for about 8-10 seconds, which makes it ideal for runners doing the 100 metre sprint, or weightlifters.
Slower supply - When this energy supply gets used up, muscles rely on the stores of a carbohydrate, called glycogen, which can be used to make energy from glucose.This supply happens more slowly but produces enough energy to last for about 90 seconds, enough for a longer fast run, although not at the same intensity as the sprint.
Because this energy is made without using oxygen, it produces a by-product, called lactic acid, which is what causes our muscles to tire. At about 90 seconds we can feel our fingers get really tired from squeezing the peg and the lactic acid eventually prevents our muscles from contracting.
House of Science fit fingers experiment. A simple clothes peg can help explain why our muscles get tired. Photo/supplied
At that stage we either have to slow down or stop altogether and rest.
Continued endurance-If you're still running or exercising after two minutes, the body starts to supply the working muscles with oxygen.
Called aerobic respiration, it's the slowest of all three systems, but can continue to supply energy for several hours.
* The House of Science Tauranga is a charitable trust which exists to connect and resource the local science community in order to celebrate the power and potential of science. Contact Chris Duggan on 027 337 9342 or see www.houseofscience.org.nz for more information.
