SDS - Lab Tools

Impact Test | Flexibility Test | Traction Test | Video Analysis |

The impact test machine is a standard fixture in most sport research labs. The most fundamental use of the impact tester is to measure the cushioning characteristics of a material. Some of the measurements of interest to a sport researcher are listed below.

Peak (g) - A measure of the average rate of deceleration of the impacting missile head into the material. Researchers look for a range between 9-14g for cushioning in the heel area of a midsole, while they look for less than 17g in the fore foot area. In general, the greater the number of g's the worse the cushioning characteristics of the material.

Maximum Penetration (%) - This is a measure of how far the missile penetrates, or compresses the material. Researchers look for penetration no higher than 35%.

Energy Return (%) - Energy return is a measure of how much of the kinetic energy from the system (the falling missile) is returned to the system. Researchers look for energy returns greater than 50%.

Figure 1 - Impact Tester

The impact tester (see figure 1) is a missile weighted with 8.5kg dropped from a 50mm height. The impact tester is designed to model an average runner (defined as 150lb, 5' 10", 7 minute per mile, male) and the forces he would generate in running.

Figure 2 - Close-up of the missile and midsole material

Why do you think that researchers have standardized the drop height, mass, number of pre-impacts and real impacts?

The test consists of 25 impacts, called pre-impacts, that settle the midsole and prepare it for 5 to 10 impacts for which data will be collected. This data is then averaged, and graphed for analysis.

Flexibility Test | Impact Test | Traction Test | Video Analysis |

This machine shows how simple some of the tests can be in a sport research lab. However in its simplicity the importance of the flexibility tester may be lost. A shoe must exhibit the optimal flexibility for the sport it is designed for.

To provide flexibility in the upper, midsole, and outsole, designers often incorporate grooves, or flex lines. These lines are areas of potential creasing or cracking. The flexibility tester, by repeatedly flexing a shoe, can test materials for their potential to crease or crack.

Figure 3 - Flexibility Tester

The flex tester measures how much force, measured in Newtons (N) it takes to bend a shoe 45 degrees. The greater the force required to flex a shoe, the stiffer the shoe is. The flex tester operates at about 2 Hertz, or two flexions per second. What a researcher looks for is dependent on what sport the shoe is designed for.

Traction Test | Impact Test | Flexibility Test | Video Analysis |

This is another somewhat simple test. The traction tester pictured here (see figure 4) is actually two machines in one. When not testing for frictional characteristics of outsoles, it can be fitted with another clamping device to measure the stretch and tearing properties of different materials (see the Dynamic Testing Machine, figure 6, in the Discussion section of the Computer Modeling Activity).

Figure 4 - Traction Tester

The traction tester measures the frictional coefficient (µ). The shoe, or just midsole and outsole unit, are loaded with a mass of 75lbs (1/2 the body weight of the "average" man) and dragged 12 inches across a surface at a constant rate. The amount of force required to move the shoe is recorded and graphed.

In general, shoes with a µ or frictional coefficient that is high offer excellent traction while low numbers represent a shoe that offers little traction. Again, the degree of traction is dependent on the sport. Skate boarders like shoes with optimal "stickiness" or traction, while basketball players want a shoe that offers moderate traction.

The difficulty in considering the traction properties of a midsole revolves around the many variables that influence traction. Some of the variables to keep in mind are:

Material of the outsole
Material of the floor
Design and surface area of the outsole
Temperature
Humidity
Rate of movement (fast speed vs. slowing or stopping)
Direction of movement (running vs. pivot)

Video Analysis | Impact Test | Flexibility Test | Traction Test |

In a sport research lab scientists use one of several methods of video analysis to study motion, specifically rearfoot motion, and stability as it relates to shoe design. The most commonly used method, and least expensive is two dimensional analysis of the rearfoot motion.

Two dimensional analysis consists of placing markers at specific anatomical locations on the rear aspect of the lower leg, ankle and foot or shoe. A high speed film high speed video camera is used to record the motion of the leg while a subject runs on a treadmill or over ground at a set speed. The speed of the run is standardized as are other conditions relevant to the study.

Figure 5 - Video Analysis

This system, available from Peak Performance, Inc., is similar to ones used in sport research labs around the world. The system integrates a video camera with the computer and saves large amounts of time between data collection and analysis.

Once the video is collected, researchers analyze the images digitizing the points and producing a graph of the range of the rearfoot angles seen during the run. The range of the rearfoot angle under different conditions, such as barefoot vs. wearing a shoe, is then compared statistically to determine if the different designs significantly effect this angle and, as a result, stability.

Although the two dimensional method is still used by many researchers, it has been enhanced and, in some cases, data analysis greatly simplified. The "state of the art" technique for video analysis utilizes three dimensional motion analysis optoelectronic video systems.

Three dimensional optoelectronic analysis uses reflective or light emitting markers placed on both the rear and lateral aspect of the athlete's leg. Cameras with special sensors that pick up the coordinates of the markers are used. The data collected by these cameras is automatically digitized and processed by a computer and software. The results are available almost instantaneously.

Two dimensional analysis is adequate for looking at the effect of shoe design on limited aspects of the leg, such as ankle stability. The major advantage of three dimensional analysis is that it allows the researcher much finer resolution when studying the biomechanics of the athlete. For example, three dimensional analysis opens the door for researchers to focus down to the level of the individual segments that make up the leg and foot.


Impact Test		\| Flexibility Test \| Traction Test \| Video Analysis \|

	The impact test machine is a standard fixture in most sport research labs. The most fundamental use of the impact tester is to measure the cushioning characteristics of a material. Some of the measurements of interest to a sport researcher are listed below.
		Peak (g) - A measure of the average rate of deceleration of the impacting missile head into the material. Researchers look for a range between 9-14g for cushioning in the heel area of a midsole, while they look for less than 17g in the fore foot area. In general, the greater the number of g's the worse the cushioning characteristics of the material. Maximum Penetration (%) - This is a measure of how far the missile penetrates, or compresses the material. Researchers look for penetration no higher than 35%. Energy Return (%) - Energy return is a measure of how much of the kinetic energy from the system (the falling missile) is returned to the system. Researchers look for energy returns greater than 50%.
	Figure 1 - Impact Tester


	The impact tester (see figure 1) is a missile weighted with 8.5kg dropped from a 50mm height. The impact tester is designed to model an average runner (defined as 150lb, 5' 10", 7 minute per mile, male) and the forces he would generate in running.
		Figure 2 - Close-up of the missile and midsole material Why do you think that researchers have standardized the drop height, mass, number of pre-impacts and real impacts? The test consists of 25 impacts, called pre-impacts, that settle the midsole and prepare it for 5 to 10 impacts for which data will be collected. This data is then averaged, and graphed for analysis.


Flexibility Test		\| Impact Test \| Traction Test \| Video Analysis \|

	This machine shows how simple some of the tests can be in a sport research lab. However in its simplicity the importance of the flexibility tester may be lost. A shoe must exhibit the optimal flexibility for the sport it is designed for. To provide flexibility in the upper, midsole, and outsole, designers often incorporate grooves, or flex lines. These lines are areas of potential creasing or cracking. The flexibility tester, by repeatedly flexing a shoe, can test materials for their potential to crease or crack.
	Figure 3 - Flexibility Tester The flex tester measures how much force, measured in Newtons (N) it takes to bend a shoe 45 degrees. The greater the force required to flex a shoe, the stiffer the shoe is. The flex tester operates at about 2 Hertz, or two flexions per second. What a researcher looks for is dependent on what sport the shoe is designed for.


Traction Test				\| Impact Test \| Flexibility Test \| Video Analysis \|

	This is another somewhat simple test. The traction tester pictured here (see figure 4) is actually two machines in one. When not testing for frictional characteristics of outsoles, it can be fitted with another clamping device to measure the stretch and tearing properties of different materials (see the Dynamic Testing Machine, figure 6, in the Discussion section of the Computer Modeling Activity).
			Figure 4 - Traction Tester The traction tester measures the frictional coefficient (µ). The shoe, or just midsole and outsole unit, are loaded with a mass of 75lbs (1/2 the body weight of the "average" man) and dragged 12 inches across a surface at a constant rate. The amount of force required to move the shoe is recorded and graphed. In general, shoes with a µ or frictional coefficient that is high offer excellent traction while low numbers represent a shoe that offers little traction. Again, the degree of traction is dependent on the sport. Skate boarders like shoes with optimal "stickiness" or traction, while basketball players want a shoe that offers moderate traction.


		The difficulty in considering the traction properties of a midsole revolves around the many variables that influence traction. Some of the variables to keep in mind are: Material of the outsole Material of the floor Design and surface area of the outsole Temperature Humidity Rate of movement (fast speed vs. slowing or stopping) Direction of movement (running vs. pivot)


Video Analysis			\| Impact Test \| Flexibility Test \| Traction Test \|

	In a sport research lab scientists use one of several methods of video analysis to study motion, specifically rearfoot motion, and stability as it relates to shoe design. The most commonly used method, and least expensive is two dimensional analysis of the rearfoot motion. Two dimensional analysis consists of placing markers at specific anatomical locations on the rear aspect of the lower leg, ankle and foot or shoe. A high speed film high speed video camera is used to record the motion of the leg while a subject runs on a treadmill or over ground at a set speed. The speed of the run is standardized as are other conditions relevant to the study.
		Figure 5 - Video Analysis This system, available from Peak Performance, Inc., is similar to ones used in sport research labs around the world. The system integrates a video camera with the computer and saves large amounts of time between data collection and analysis. Once the video is collected, researchers analyze the images digitizing the points and producing a graph of the range of the rearfoot angles seen during the run. The range of the rearfoot angle under different conditions, such as barefoot vs. wearing a shoe, is then compared statistically to determine if the different designs significantly effect this angle and, as a result, stability.


	Although the two dimensional method is still used by many researchers, it has been enhanced and, in some cases, data analysis greatly simplified. The "state of the art" technique for video analysis utilizes three dimensional motion analysis optoelectronic video systems. Three dimensional optoelectronic analysis uses reflective or light emitting markers placed on both the rear and lateral aspect of the athlete's leg. Cameras with special sensors that pick up the coordinates of the markers are used. The data collected by these cameras is automatically digitized and processed by a computer and software. The results are available almost instantaneously. Two dimensional analysis is adequate for looking at the effect of shoe design on limited aspects of the leg, such as ankle stability. The major advantage of three dimensional analysis is that it allows the researcher much finer resolution when studying the biomechanics of the athlete. For example, three dimensional analysis opens the door for researchers to focus down to the level of the individual segments that make up the leg and foot.