FOR THE BIRDS
Stride length and speed of birds and humans
relative to the patellar and tibiotarsus joints.
By, Karen Shrader, William Johnson, Laura Parker, Melinda Miller, Norm Dahm
 

Background

        Only arthropods and vertebrates have developed a means of rapid surface locomotion.  In both groups, the body is raised above the ground and moved forward by means of a series of jointed appendages, the legs.  Because the legs provide support as well as propulsion, the sequence of their movements must be adjusted to maintain the body’s center of gravity within a zone of support; if the center is out of this zone the animal loses its balance and falls.  The functional sequence of limb movement is necessary for the animal to maintain proper orientation and locomotion.

        The entire sequence of limb movement can be divided into two major stages.  The propulsive or retractive stage starts with footfall and ends with foot liftoff.  The recovery or protractive stage starts with foot liftoff and ends with footfall. During recovery, the body essentially remains stationary until a leg moves forward.  A step is the advance of one leg whereas a stride is defined as many steps as there are legs.  During a stride, each leg passes through a complete cycle of retraction and protraction.  The distance the body travels is equal to the distance of the longest step in the stride.  The speed of locomotion is the product of the stride length and duration of stride.  Stride is directly affected by the retraction. The longer retraction results in slower gait.  A gait is the sequence of leg movements for a single stride.
 
Purpose
        The purpose of the exercise is to determine whether the hinge mechanism in the knee of parakeets and humans affects stride length and speed when moving across a hard surface.  For birds, the femur tends to be short and constrained within the body, and the lower leg bones, the tibiotarsus and fibula are much more prominent.  In a human, the femur and the tibia and fibula are relatively the same length.
         The knee (a hinged joint) is thought to play a pivotal role in locomotion.  In this study the workers will attempt to quantify the relative affect of the two above said joints in respect to speed and stride length.  The measurements used are distance/time (speed), overall leg length, and stride length.

Null Hypothesis:
There is no relationship between the use of the patellar or tibiotarsus joints in relation to stride length and speed of a human and bird respectively.
 

Materials:

bird (parakeet)
human volunteer
nontoxic washable paint
butcher paper
meter stick
centimeter ruler
string
stopwatch
masking tape
markers
paper towels
petri dish (for paint)
 

Procedure:
 

Measurement of leg length

1. Use a piece of string to measure the leg length (from hip to ankle) of the parakeet and the human volunteer.  Record in your data table.

Parakeet average speed

2. Cut one meter of butcher paper.  Mark the paper with a test path 33.3 cm from start to finish.  Use cardboard or another barrier to form a chute for the bird to travel.

3. Place the parakeet at the starting point, with your timer ready.  Start the timer when the bird’s beak crosses the start, and stop when the bird’s beak crosses the finish. You may have to gently encourage the bird to move.

4. Repeat until you have ten trials.  Record your results and determine the average speed.
 

Human average speed

5. Mark a test path of 10 meters from start to finish.

6. Time the human walking the 10 meters test path.

7. Repeat until you have ten trials.  Record your results and determine the average speed.
 

Parakeet stride length

8. Cut two pieces of butcher paper one meter in length.
9. Dip one of the bird’s feet in the nontoxic paint and allow the bird to walk on the butcher paper to obtain prints for determination of stride length.  Reapply paint to the bird’s feet when necessary.  Note that the bird’s gait should be consistent with the gait recorded for the timed trials.

10. Measure and record the stride length of the bird from the heel of one print to the heel of the next print.

11. Repeat until you have ten trials.  Record in your data table and determine the average stride length.

Human stride length

12. Repeat procedures 9 to 11 for the human volunteer using a three meter length of butcher paper and applying paint to the heel of the volunteer.

13. Cleanup and put away all materials.
 
 

 
Time Trials
 
 Bird Trial (seconds)
 Human Trial (seconds)
2.40
7.66
2.46
7.34
1.72
7.34
3.13
7.85
2.37
7.88
1.03
8.04
1.53
7.62
1.00
8.03
1.56
7.87
1.28
7.56
MEAN

Bird         1.85 sec

Human     7.72 sec
 
 
Stride Length
 
Bird Stride (cm)
Human Stride (cm)
9.4
129.2
6.8
126.7
7.6
128.5
8.4
131.3
8.6
127.6
10.3
 
7.4
 
9.7
 
11.0
 
11.4
 

 

MEAN
Bird            9.1cm
Human        128.66cm

Calculations

Leg Length:

    Bird Leg Length = 5.1cm (0.051m)
    Human Leg Length = 90cm (0.9m)

Relative Stride Length:

    Relative Stride Length = stride length/leg length
 
     Bird Relative Stride Length = 1.78
     Human Relative Stride Length = 1.45
 

Speed:
 
    Speed of Bird = 0.33m/1.85sec =      0.18m/s
    Speed of Human = 10m/7.72sec =     1.29m/s
 

Dimensionless Speed

    Dimensionless Speed = Speed (m/s)/ leg length X gravitational acceleration
 

        Bird Dimensionless Speed      = 0.18/ 0.051(9.8) = 0.25m/s

        Human Dimensionless Speed = 1.29/ 0.9(9.8) = 0.43m/s
 

Conclusion:

The correlation between relative stride length and relative speed of a bird and human seem to fit on the regression line generated by J. Alexander (et. al.1952?)
    The parakeet had a stride length much greater than would be expected for its dimensionless speed of 0.25m/s.  One explanation for this is the inability to maintain consistent speed through the 33.3cm test path.  Prodding the bird was necessary to keep it moving the designated distance.  An additional problem was the measurement of the parakeet stride length.  Short strides were smudged, smeared or unclear.  The longest strides were clearest and therefore selected.  This bias would result in a stride length greater than the observed speed.  Only one bird and one human were used for the experiment which lends itself to the idea that one subject may not be representative of the entire population.  More studies would have to be performed to draw accurate conclusions regarding the purpose of the experiment.
 
 
 
Interesting Questions:

1. What are some methods you could use to measure speed?

2. What units should you use to measure speed?

3. Think about how birds move when they are on the ground.   Do different species of birds have different adaptations for traveling on the ground?  Consider such groups as sparrows, raptures, ducks, wading birds, penguins, ostriches etc.

4. How do different organisms move?  Why?  Explain.

5. Why is the cheetah the fastest terrestrial animal?

6. Why can’t an elephant run?