EXSS 323
RUNNING KINEMATICS LAB

This lab was developed by Gerry Smith, Ph.D., formerly of Oregon State University, and is used by permission. Portions in italics are additions/modifications to the original and were made by Gary Christopher, M.S., A.T.C.

INTRODUCTION

Linear motion occurs when all particles of a moving object follow parallel paths, covering the same distance in the same amount of time. However, this type of motion occurs very seldom in human movement since angular motion occurs at the joints of the body. For example, in running, the arms and legs undergo rotation while the center of mass tends to rise and fall during the running cycle. Nevertheless, running and walking are approximately linear motions and can be analyzed using linear relationships as long as we recognize that this involves some slight approximation to the actual motion.

A body's motion may be simplified to deal only with the movement of the center of mass (CM) of the body. Using the distance the CM moves during a period of time is a convenient way of describing the motion. This allows calculation of the body's speed: 

 
                  Distance of CM motion
Average Speed  =  _____________________
 
                          Time
 

In cyclic activities like walking, running, swimming, and cross country skiing, a basic movement pattern is repeated without break. A walking or running cycle connects successively to the next cycle and the next, and the next, etc. If the person is moving at constant speed, then the average speed for each cycle of the movement will equal the overall average speed. Thus the average speed formula could be written: 

 
          Cycle Length
Speed =  ______________
 
           Cycle Time
 

where Cycle Length (CL) is the distance the CM is displaced during one complete cycle of motion and Cycle Time (CT) is the time required for one cycle to be completed.

An alternative form of the above equation involves what is called Cycle Rate (CR), the number of cycles completed per second (measured in cycles per second). Cycle Rate is simply the reciprocal of CT:


Cycle Rate (CR)  = 1 / CT

Thus, average speed is a function of the product of cycle length and rate: 

 
Speed  =  CL * CR


This is one of the most important equations describing locomotion! The speed of motion is directly proportional to the cycle length of the movement pattern as well as the cycle rate. Walking or running speed is increased by increasing cycle length and/or cycle rate. Using this relationship, if any two of the quantities are known, the third variable can be determined.

 

METHODS:

Part 1:

Each student will perform four running trials at speeds described as slow, medium, fast and maximum. At each speed, four steps (two cycles) will be measured for distance and time. A run-up distance of 15 to 20 meters will be used to get up to speed before measurement. Time for the two cycles and distance covered during the two cycles will be recorded and used to determine running speed.

Work in groups of four to collect the data. One person will run, one will time, one will mark the beginning point foot position, and one will mark the end point foot position. Rotate through the four jobs until all four students have completed their trials.

Record the displacement and time for the two cycles at each speed. When you are back in the lab, enter the data into a spreadsheet configured like this illustration. Write formulas to determine the average time for one cycle (CYCLE TIME), CYCLE RATE, the average displacement for one cycle (CYCLE LENGTH), and the average speed for each trial.

Finally, from your spreadsheet data table, create a graph of CYCLE LENGTH and CYCLE RATE vs SPEED (plot both variables on the same graph) and print copies for use in your lab report. Additionally, create a composite graph (average of each group member's CL & CR at each speed).

Part 2:

A runner was recorded on video at five running speeds. These can be viewed as short movies from your computer using the application Quick Time. Links to the five files are provided below. For each running speed, determine the cycle time based on 30 frames (or pictures) per second. Then use the cycle time to calculate cycle rate and cycle length at each speed.

Finally, create CYCLE LENGTH and CYCLE RATE vs SPEED graphs (plot both variables on the same graph) for this example runner similar to those created for yourself.

Short video clips of running at five speeds are available online. Note that these are about 300 to 400 Kbytes in length and will be slow to download over a modem connection.

These video movies can be controlled for playback. For frame counting, the movie can be advanced a frame at a time using the forward framing button or the arrow keys. (Suggestion: Count the number of frames per cycle twice: once for the cycle starting with the right foot, then again for the cycle starting with the left foot. Then average the number of frames per cycle. If you get a fractional number (e.g., 19.5), use it).

 

ANALYSIS:

Based on your personal data and the treadmill runner video data, briefly summarize the methodology and results of these two experiments and the implications for understanding human locomotion. Include responses to the following questions in your discussion. Attach your graphs to the printout and return these to your lab instructor at the beginning of the next lab meeting.

    1. In general, how do cycle rate and length seem to change with speed?
    2. Which method involved a greater range of speeds? (Speed Range = Maximum Speed - Minimum Speed)
      How does the relationship of CR & CL to Running Speed change as one goes from slow to fast running?
    3. Which experimental method allowed more accurate determination of the cycle characteristics? What were the sources of experimental error for each method?