Biomechanics study questions
BME 315,BME 615
University of Wisconsin
Questions for thought.
We will learn the answers to some of these during the semester.
1. A weight lifter pulls down on a bar connected to some weights via a pulley system. He rises in the air. A second weight lifter comments that the first is not strong enough to lift the weights. The first lifter claims to be very strong, and asks for assistance to hold him down. The second lifter presses down on the shoulders of the first, who is then able to move the weights. Who is correct? Why?
2. Why don't elephants jump out of trees, even big trees?
3. A total hip replacement stem breaks, but the surrounding bone is not broken. The stem is made of a strong cobalt chromium alloy which is stronger than bone. Why, then, did it break? How can one prevent stems from breaking?
4. Is the droop of the nose of older people due to gravity? Would a head-stand exercise help?
5. How is it possible that karate practitioners can break boards and concrete, when one considers that people accidentally break bones in falls on wood or concrete?
6. An ant can lift about ten times its weight. If a large human size ant were to arise via mutation, could it demolish a building with its great strength?
7. A sprinter runs 100 yards in 10 seconds. (i) Show that this is equivalent to an average speed of 20.5 miles per hour. (ii) The sprinter has thicker legs than the cheetah, but cannot run as fast as the cheetah (70 miles per hour). Why not? (iii) The same sprinter can approach a rate of 40 miles per hour in a bicycle sprint. Why the difference in speed? Remark: the four minute mile corresponds to a rate of 15 miles per hour.
8. A driver suddenly sees a large obstruction (a straight wall) appear through the fog. Is it better to turn or brake to prevent injury, assuming there is pavement to the right and left?
9. If a surgeon has a choice what angle to make an incision, how is that choice made rationally?
10. Why are bones tubular rather than solid?
11. The skull consists of sandwich of dense compact bone outer layers and a spongy inner layer. Is this mechanically advantageous? Would it be better to have a skull made of solid compact bone?
12. Ear bone is denser (more calcified) than leg bone, which is denser than antler bone. Why?
13. A blow on one side of the head sometimes causes injury to the opposite side of the brain. Why?
14. Long term pressure on the skin greater than 32 mmHg can cause pressure sores in wheelchair patients or the chronically ill. Why? What is the significance of that pressure?
15. Why are diving mammals usually large?
16. People are taller in the morning than in the evening by a few centimeters. Why?
17. To go as fast as possible on a bicycle on level ground, what gear should you choose? Should it be the highest one available? Explain in light of the properties of the relevant tissues.
18. How is it possible that some lizards can protrude their tongues a significant fraction of their body length? What is the purpose?
19. How fast could a tyrannosaurus run?
20. Replacement heart valves in the past were designed with flexible plastic leaflets in an attempt to imitate the natural valves. The plastic broke after a while and some of the patients died. Why did the plastic perform so much worse than the natural tissue?
21. Does ear wax have a function? If so, what might it be?
22. Some babies develop misshapen heads after being guided to sleep on their backs for long periods. Such a sleeping position may be chosen by parents, to prevent sudden infant death due to suffocation in the bedding. What aspects of the baby's tissue is responsible for the change in head shape?
23. To treat the above misshapen baby heads, consider two options. One option is that a surgeon may saw the baby's skull into segments and re-shape the head surgically. This will cause pain, bleeding, suffering, a risk of death or disability, and the certainty of scarring. The other option is for the baby to wear a spring-loaded helmet to gently reform the head back into shape. Discuss how these options work. Discuss which you would choose (i) if you were the baby, (ii) if you were the parent, (iii) if you were the baby's older brother or sister, (iv) if you were the surgeon?
24. Referring to the above question, discuss the importance of the following characteristics in a surgeon or physician: (i) honesty / dishonesty, (ii) concern for the well-being of others, (iii) awareness of the options available, (iv) willingness to judge correctly among humane and inhumane options. If you are a pre-medical student, what kind of physician do you want to be?
25. Refer to the rank of nations according to healthy life expectancy. More recent rank via CIA data are of particular interest and are shown below in the embedded frame. How might your studies help you improve the health of citizens of your country? If you are a pre-medical student from the U. S., account for the fact that some countries which achieve success in health also practice less invasive medicine than we do in the U. S.. How could we help the system to rate better? Consider this pdf in your literature review.
26. Some markers of cardiovascular disease, including blood pressure, serum cholesterol, and carotid artery thickening, can be reversed by reducing food intake as presented in this article, Fontana, L., Meyer, T. E., Klein, S., and Holloszy, J. O., "Long-term calorie restriction is highly effective in reducing the risk for atherosclerosis in humans", Proceedings of the National Academy of Sciences (PNAS), 101 (17), 6659-6663, April 27, 2004. get pdf.
Moreover, cognitive function in older adults can be improved by reducing food consumption. See Witte, A. V., Fobker, M., Gellner, R., Knecht, S. , and Floel, A., "Caloric restriction improves memory in elderly humans", Proceedings of the National Academy of Sciences (PNAS), 106 (4), 1255-1260, Jan. 27, 2009. get pdf. Macular degeneration can be slowed or prevented by reducing food consumption. See Li, D. Sun, F. and Wang, K. "Caloric restriction retards age-related changes in rat retina", Biochemical and Biophysical Research Communications 309, 457-463 2003.
Discuss the implications of these observations in the context of the biomechanics of the circulatory system and in the broader context of public health. If you become a health professional after graduation, how might you use the results found in these articles? How might the economic aspects of these conditions affect your ability to attend school now? Some additional health related results are shown in Professor Webster's resource, living green (available within University of Wisconsin), or from anywhere Webster's living green pdf.
27. The US rank was number 41 in maternal mortality according to the World Health Organisation (WHO). The likelihood of a woman dying in childbirth in the US is five times greater than in Greece and ten times greater than in Ireland. Childbirth is safer in Hungary, Poland, and the Czech Republic than it is in the United States. See the following references.
The CIA web site provides up to date rank order data comparing national performance.
infant mortality rank via CIA
maternal mortality rank via CIA
Here is a link to some data from 2010.
also the 2007 report
How do you plan to improve this aspect of health in your career? How could you help us rate better?