In Lesson 5, students analyze two experiments that deal with the effect of diet and weight-bearing activities on bone mineral content. In the first experiment, students make predictions about the effects of milk and a weight-bearing activity (resistance training) on strength and bone-mineral content. They analyze actual data to test their predictions. In the second experiment, students consider how playing different sports with different weight-loading levels affects bone-mineral content.
After completing this lesson, students will be able to
See the following sections in Information about the Musculoskeletal and Skin Systems:
|1||No||Master 5.1, Description of Milk Study, 1 transparency
Master 5.2, Data from Milk Study, 1 copy per team of 2
|None except photocopies and transparencies|
|2||No||Master 5.3, Description of Sports Study, 1 transparency
Master 5.4, Data from Sports Study, 1 copy per team of 2
|None except photocopies and transparencies|
Prepare photocopies and transparencies.
Note to teachers: The study described in this activity is based on actual research by J.S. Voltek et al. (see References section, number 59). The data we use are authentic, although in some cases, numbers were rounded off to make them easier to work with.
Ask the class, “On the basis of what you have learned about bone, what can you do to increase the strength and health of your bones?”
Write their responses on the board. Student responses will vary. Some will mention changing diet. Others may mention exercise. Make sure these two responses are on your list.
Students may mention that bone strength can be measured by having people perform fitness tests. To such a response, point out that these tests are largely measuring muscle, not bone, strength. If students respond that the bone itself can be subjected to a chemical analysis, mention the problem of having to remove it from the person being studied!
Note to teachers: The specialized X-rays referred to here are called bone mineral density (BMD) scans. The most widely used method of BMD scan is dual X-ray absorptiometry (DEXA scan). DEXA scans use two different X-ray beams. Bone mineral density scans provide quantitative information about bone that cannot be obtained from standard X-rays.
The important points for students to understand are that teenagers in both groups experienced the same resistance training (bench pressing) and that those in the group that drank juice did not receive the extra minerals, especially calcium, which were consumed by those in the milk group.
Student responses will vary. Some may predict that teenagers in the milk group will display greater strength and have more minerals in their bones than teenagers in the juice group. At this time, accept all answers.
Give the teams about five minutes to write down their conclusions. Students should notice that the amount of weight that study participants bench-pressed increased for both the juice group and the milk group. They should also notice that although the bone minerals increased in both groups, bone minerals increased more for the milk group than the juice group.
Note to teachers: Students may notice that in Week 6, the bench-pressed weight is slightly greater for the milk group than the juice group. Explain that you would expect the average bench-pressed weight to be similar but not necessarily the same for the juice group and milk group because of variation among individuals in this study. Emphasize how similar the values are, considering that each group had 15 teenagers who might respond differently to resistance training.
Some of the predictions will have been supported by the data, while
others will not.
Student responses will vary. The discussion should bring out two main conclusions: 1) both groups of teenagers showed the same increase in strength (as measured by the amount of weight they could bench-press), and 2) the milk group’s increase in bone minerals was twice that of the juice group.
Some students may respond that since both the juice and milk groups showed the same increase in strength, calcium and other minerals found in milk are not important. Point out that the study measured bone-mineral content as well as strength and that the milk group showed a greater increase in bone-mineral content. If bone-mineral content goes up, then bones are stronger and less likely to break. Healthy bones with greater bone-mineral content may also help protect against disease and fractures later in life.
Tip from the field test: Some students may realize that milk contains protein as well as calcium, neither of which is present in orange juice. Explain that more studies would have to be done to determine whether the greater increase in bone-mineral content for milk drinkers compared with juice drinkers resulted from the calcium or protein in the milk. Use this as an opportunity to point out the tentative nature of science. Scientists must use results from many studies to establish the influences on bone-mineral content.
Note to teachers: The study described in this activity is based on actual research by D.L. Creighton et al. (see References section, number 16). The study includes estimates of bone-mineral density obtained by analyzing X-ray films. Because these measurements are made on two-dimensional pieces of film, the data are expressed in units of mass (grams) per area (cm2) and not per volume (cm3), as is expected for a density measurement. In this activity, we refer to bone-mineral content and not to bone-mineral density.
Students should recognize that resistance training increases bone minerals, because the data in the previous study showed increases in bone minerals for those in the juice group as well as for those in the milk group.
Answer any questions about how the study was performed. It is important to stress that students in the various groups were similar to each other except for their exercise habits.
Students should write in the spaces provided on Master 5.3, Description of Sports Study. The group with the highest level of bone minerals should be labeled “1,” while the group with the lowest level of bone minerals should be labeled “4.”
Most students will conclude correctly that the control group (those who exercise very little) has the lowest level of bone minerals.
Students will probably not agree, however, on which sports produce the highest level of bone minerals. At this time, do not reveal the correct sequence. Students will confirm or refute their predictions in the next steps.
Note to teachers: Students may ask why the study only provided bone-mineral content for the spine and hip and not bones in other parts of the body such as the leg or arm. Explain that the spine and hip are the most common areas tested for bone-mineral content because they generally have the most bone loss and are more likely to fracture when weakened by low mineral content.
After teams have completed their task, ask whether any teams have reordered their groups. Ask them to explain why.
Students should explain that they reordered their groups based on the bone-mineral content data given in Master 5.4. These data showed that for both spine and hip measurements, the basketball and volleyball group had the highest bone-mineral content, followed by soccer and short-distance track, followed by swimming. The control group, which did not exercise, had the lowest bone-mineral content.
Make it clear that you are referring to an astronaut who has spent time in space and had his or her bone minerals measured after returning to Earth. Encourage students to think about what might be different for an astronaut in space as compared to someone on Earth.
Student answers will vary. Students are likely to rank the astronaut near swimming (3) and the control group (4) because astronauts cannot be as active as an individual playing basketball or soccer. Students might also rank the astronaut near 3 or 4 because they recognize that astronauts are in a weightless environment and thus are unable to do activities that put weight on their bones.
Make sure students understand that astronauts lose minerals from their bones even if they exercise in space (such as ride a stationary bike). Students should recognize that astronauts are in a weightless (gravity-less) environment. Guide the discussion to bring out the importance of putting stress on bone and that weight is necessary to put stress on bone. In a weightless environment, astronauts put very little stress on their bones.
Make sure students understand that weight-bearing activities include any activity in which feet and legs carry a person’s weight or any activity that involves carrying, lifting, or pushing a heavy object. Therefore, walking and jumping are considered weight-bearing activities.
Make sure students understand that basketball, volleyball, soccer, and short-distance track are weight-bearing activities. In both groups, the sports involve carrying a person’s weight while running and jumping. Swimming is not a weight-bearing activity because water supports the body. Students should recognize that astronauts are unable to do weight-bearing activities because they are in a weightless environment.
On the basis of the study discussed in this activity, students should recognize that weight-bearing forms of exercise lead to gains in bone-mineral content. They may suggest running. You might suggest that students think about how basketball and volleyball differ from soccer and short-distance running. Remind them that the basketball and volleyball group had the highest bone-mineral content. Students might recognize that basketball and volleyball involve more jumping than soccer. If necessary, remind the class that placing the bones under high levels of stress helps to increase the amount of minerals in bone. Jumping has been found to be an especially effective form of exercise in this regard. As a result, jumping exercises are being recommended as a part of physical education programs in schools.
As each sport is discussed, make sure that students explain why the bone-mineral content differs between groups. Look for explanations that point out that bones under weight-bearing stress, as from gravity and physical activity, will have increased mineral content.
|Activity 1: Got Milk?|
|What the Teacher Does||Procedure Reference|
Remind the students of what they learned in Lesson 2, What Makes Bones Strong;
Ask students, “On the basis of what you have learned about bone, what can you do to increase the strength of your bones?”
Explain that students will investigate how diet and different types of exercise influence bones.
|Steps 2 and 3|
Explain that students will read about a study that investigates the influences of diet and physical activity on the health of bone.
Ask students to predict the results of the experiment. Write their predictions on the board.
Divide the class into teams of two. Give each team one copy of Master 5.2, Data from Milk Study.
Remind the students of their earlier predictions:
|Steps 7 and 8|
|Activity 2: Is All Exercise the Same?|
|What the Teacher Does||Procedure Reference|
Remind the students of the data presented in the previous activity:
|Steps 1 and 2|
Divide the class into teams of two.
Instruct teams to discuss the study and place the groups in order of increasing bone-mineral content. Ask for volunteers to report their rankings and explain their reasoning.
|Steps 4 and 5|
Give each team one copy of Master 5.4, Data from Sports Study. Allow teams to review the data and reorder their groups as desired. If any teams have reordered their groups, ask them to explain why.
|Steps 6 and 7|
Ask teams where they would rank the bone-mineral content of an astronaut who had spent considerable time in space and then returned to Earth.
|Steps 8 and 9|
Explain that the astronaut would have less bone-mineral content than the control group. Ask students why this would be. Remind students that
|Steps 10 and 11|
Instruct students to revisit the data from the sports study. Facilitate a discussion about which activities can be considered weight bearing.
Describe the disease osteoporosis to the students. Ask, “What type of physical activity (not a sport) do you think would lead to the greatest gains in bone-mineral content?”
As a homework assignment, instruct students to write a brief explanation of why the bone-mineral contents of astronauts and each of the groups from the sports study are different.
|= Involves making a transparency.|
|= Involves copying a master.|