1.3: Activity 1

Overview and Introduction

An example of a human body ratio is a person's arm span the distance from the middle fingertip of the left hand to that of the right hand when stretching out both arms horizontally—to their height. This ratio is approximately a one to one ratio, meaning that a person’s arm span is about equal to their height. There are many more human body ratios; some are independent of age, and others change as we grow from a baby to an adult.

In this lab experiment, students will explore the fascinating concepts of body ratios and proportions of the length of the arms to the height of the body, to gain insights into how proportions relate to overall health, physical appearance, and even athletic performance. This activity will involve direct measurements of body segments and the application of mathematical calculations to derive ratios. By engaging in this activity, students will develop skills in both measurement, data analysis and presentation, essential components in the field of anatomy and physiology.

Hypothesis for testing: The length of a person’s upper limb is equal to 0.4 (40%) of the height of the person.
Materials: Meter stick or measuring tape; calculator.

Procedure

1. Select volunteers for the measurements.
2. Instruct volunteers to stand, with heels, head, and back against a wall.
3. Use a flat object (like a book or ruler) placed on top of the head at a right angle to the wall to mark the height accurately.
   • Measure each subject's height (distance from the floor to the mark on the wall) accurately using a meter stick or measuring tape in centimeters (cm).
4. Measure volunteers's upper limb length (arm length) in centimeters (cm).
   • Have the subject stand erect with their arm hanging loosely by their side.
   • Measure from the acromial landmark (most superior lateral point of the shoulder joint) to the tip of the middle finger.
5. Calculate Expected and Actual Percentages: For each subject, calculate the expected upper limb length using the hypothesis (Height x 0.4) and the actual percentage of height (Measured Upper Limb Length / Height).
6. Record Data: Record the information collected for each volunteer in the Table \(\PageIndex{1}\).

Tabular Representation of Data Set

This table presents the collected data from the lab experiment aimed at testing the hypothesis that the length of a person’s upper limb is approximately 40% of their height. The various columns allow for a comprehensive analysis of each subject's measurements, facilitating comparisons between measured values and expected outcomes. Print and fill the Table \(\PageIndex{1}\) as you work with the activity.

Deriving Relationships Between Expected and Actual Data

Deriving relationships between expected and actual data is a fundamental aspect of scientific analysis. This process helps researchers understand how closely their observations align with theoretical predictions, providing insights into the validity of their hypotheses.

• The expected (predicted) correlation between upper limb length and height is determined using the following equation.
  • Height x 0.4 = expected upper limb length
• The observed (actual) correlation to be used to test the hypothesis is determined by:
  • Length of the upper limb/height = actual percentage of height

Key steps

1. Create a graph by plotting Upper Limb Length on the \(x-axis\) (horizontal) and Height on the \(y-axis\) (vertical).
2. Draw a line representing the hypothetical relationship (0.4 upper limb length to height).
   • Plot the collected data points for each volunteer on the graph.
   • Draw a line of best fit through the plotted data of your subjects.
3. Analyze and Conclude:
   • Visually compare the distribution of the collected data points with the line representing the hypothesis.
   • Interpreting the graph
     • Positive correlation - A positive slope on the trend line indicates that as height increases, upper limb length generally also increases.
     • Outliers - Individuals whose data points fall significantly away from the trend line may have unusually long or short upper limbs relative to their height.
4. Conclusion - Does the distribution of the volunteers’ measured upper limb lengths support or disprove the original hypothesis - “The length of a person’s upper limb is equal to 0.4 (40%) of the height of the person.” Explain your answer. If your measurements disprove the original hypothesis, suggest reasons why this might be so.