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softball injuries

An Analysis and Comparison of Soccer Shin Guards

Cynthia A. Bir, MS, RN, Steven J. Cassatta, MSE, David H. Janda, MD
From The Institute for Preventative Sports Medicine, Ann Arbor, Michigan

See the Abstract

World wide soccer is the most popular team sport with an estimated 40 million amateur participants [3]. In addition, soccer is the fastest growing team sport in the United States [6]. The increase in the number of injuries parallels an increase in the popularity of the sport. The Consumer Product Safety Commission has determined through the National Electronic Injury Surveillance System (NEISS) 647,368 injuries have occurred from 1989 to 1992 subsequent to soccer [7]. The NEISS is a system in place since 1972 that is based on accruing information through hospital emergency rooms. Therefore, non-hospitalization physician visits are not included in this injury figure. The distribution of the injuries as determined by the Consumer Product Safety Commission reveals 71% of the injuries were sustained by males and 29% females. Ankle injuries comprised 19.2% of total injuries; knee injuries 12.7%; head and facial injuries 11.3%; lower leg injuries 7.8%, and foot injuries 7.5%.

Pandolf and Holloszy [5] described sports injuries to be due to one of the following: collision, contact and noncontact occurrences. During the play of soccer, collisions are not as common as they are in a sport such as American football. However, contact is common and can be the etiology of serious injuries due to the higher speed at which soccer is played [1]. The contact can be player versus player, player versus ball, player versus goal post or player versus ground. A player versus player contact commonly occurs when players are trying to kick the ball and instead impact each other. This scenario can result in soft tissue injuries as well as fractures to the upper or more commonly to the lower extremities. A study by McCarroll et al [4] revealed, when reviewing the types of injuries occurring in a youth soccer league by location, the area of the shin was the third most common area injured (13.1%). Of the 17 fractures that occurred, four were to the tibia.

The protective ability of shin guards has only been studied to a limited extent [8]. It was the purpose of this study to investigate the usefulness of an experimental model, a Hybrid III crash dummy, to evaluate the force attenuating capabilities of various types of protective equipment currently utilized to prevent injuries to the lower extremity during the play of soccer. An "unprotected leg" served as the control for this study.

METHODS

Pendulum impact apparatus
Each shin guard in this study was tested on a pendulum impact apparatus (figure 1). The basic setup of this apparatus is a free swinging pendulum approximately 34 inches in length from the pivot point and 3 inches wide. A weighted mass was placed at the free swinging end of the pendulum to increase the impact force to approximately 2300 N. A steel piece of piping 1.5 inches in diameter was also mounted transversely across this end of the pendulum to represent the "foot". Although there is little biofedility between the steel pipe and a human foot, the steel pipe allowed for consistent impact loads to be applied to the shin guards.

By changing the height of the pre-swing and the weight at the end of the pendulum, the amount of impact force was controlled. Therefore, a consistent impact force was achieved throughout the entire study by maintaining the same height of pre-swing and weight of the pendulum. This test setup represents one of the possible configurations of lower extremity impacts that occur during the play of soccer. The basic kinematics of one person kicking and the other person with their leg planted is represented by this apparatus.

A 5th-percentile female Hybrid III instrumented leg was utilized to measure the amount of force transferred to the lower leg with each impact. The 5th-percentile female Hybrid III anthropometrically represents a 10-year-old boy and provides the most sensitive means of measuring injury in the adult population. The shin guards tested were fitted to leg appropriately.

Load cells located at the ankle and knee of the Hybrid III leg allowed for the total load transferred to the tibia to be calculated. The relationship of the impact and the resulting force loads can be illustrated by the force diagram depicted in figure 2. The vector equation for this relationship is as follows: sum(Fx) = 0 or Ftotal - Fknee - Fankle = 0 The load cell at the knee measured the moment experienced at the knee. This moment about the axis is product of the force times a known distance. Therefore, the moment data collected was divided by this distance to quantify the force at the knee. The load cell at the ankle measured the force at the ankle directly, therefore no calculation was required.

The time of the peak force was determined and the force values for both the ankle and knee at this time were calculated. These two values were then summed to determine Ftotal: Ftotal = Fknee + Fankle This force was the total load experienced by the tibia. The leg was placed so that the impact would occur at the midpoint of the shin when the pendulum was perpendicular to the horizontal plane. The impact point did not alter the total force measurement.


Figure 1. Pendulum impact apparatus utilized to test shin guards.


Figure 2. Vector diagram representing the forces seen by the tibia during impact.

Test setup
A control was established by performing five impacts without a shin guard on the Hybrid III leg. The target range for these impacts was approximately 2300 N. This target range was determined by maximum impacts performed on the leg by a healthy 26 year old male who was physically active in the area of athletics. These impacts were performed in the same manner as those delivered by the pendulum impact apparatus.

After the control was established the height of the pre-swing and weight of the pendulum remained unchanged throughout the entire study. The control of no pad was also performed at the end of all testing to insure the accuracy of all tests. During the impacts, the lower portion of the leg was allowed to move freely with the knee as the pivot point. After each impact, the leg was returned to its original position. Markings on the leg and testing apparatus insured that the joints were at the same angle and the leg in the same position for each test.

Shin guards tested
Twenty-two different commercially available shin guards, priced from $20-$30, were tested with the pendulum impact apparatus (figure 3). Each shin guard was impacted five times at three different temperatures: 0C, 20C, and 38C. These temperatures represent the average and extreme temperatures that might be encountered during the play of soccer. Each shin guard was placed in an environmental chamber at the desired temperature for at least three hours prior to testing. The guard was then tested within a five minutes time period from the time it was removed from the chamber. All of the guards were tested at each temperature in a random fashion.

Table 1 shows all of the shin guards tested, the manufacturers and weight. A sock was placed over each shin guard tested as if a player was wearing the guard. All straps or retention devices were attached to the Hybrid III leg in the manner in which a player would attach the guard. No further means were used to hold the guard in place.

Biomechanical responses
Leg impact responses were measured. A Texas Micro Systems 486 computer with a RC Electronics A-to-D conversion board and software served as the data acquisition system utilized to record these responses. The sampling rate was 5000 Hz. A total of two channels of load data was collected. The total load transferred to the leg through the shin guard was calculated by determining the time of the peak load and adding the loads measured by two separate load cells; one located near the knee and one located near the ankle.

Statistical methods
Differences in the force attenuating capabilities among the shin guards was statistically evaluated using an analysis of variance (ANOVA). Further analysis involved a Tukey's multiple comparison when the ANOVA was significant (p<0.05).


Figure 3. A total of twenty-two different shin guards were tested in this study.

TABLE 1
Shin guards tested and their corresponding weight


Shin Guard             Manufacturer       Weight (oz)

Body Pro               Albion             2.0
Shin Pal               Ohio Cellular      2.0
The Protector          Ohio Cellular      2.5
Kevlar                 Adidas             3.0
Rick Patrick           Patrick            3.75
Mitre                  Mitre              4.0
Brine                  Brine              4.5
Prostyle               Brine              3.0
Dunlop                 Dunlop             4.5
Pro-Pad                Quassar            3.0
Real Seville           Real               4.5
Trisafe                Uhlsport           3.25
Air Shield             Uhlsport           4.75
Pro                    Uhlsport           3.5
Italia Air             Lotto              4.75
Flex Guard             Lotto              2.5
Italia II              Lotto              5.25
Italia III             Lotto              3.25
Air Silicone           Lotto              5.0
Umbro                  Umbro              3.75
Diadora                Diadora            3.75
Sondico                Seton              6.5

RESULTS

Leg impact responses
Table 2 shows the peak impact force for each shin guard at the three different temperatures. The control of no shin guard demonstrated an average impact force of 2320.6 N for the five trials performed. Table 3 reveals that all shin guards demonstrated at least a 40% reduction in the peak impact force over the control of no shin guard. The greatest reduction (77.1%) was found with the Air Lotto Italia shin guard at 0C which had a peak impact force of 531.33 N. This shin guard also demonstrated the best reduction of force with all factors considered; 74.4% (figure 4). However, there was no statistically significant difference (p>0.05) among the Air Lotto Italia and the following shin guards (percent reduction of impact force): Brine (72.8%), Pro-Pad (71.2%), Uhlsport - Air Shield (70.6%), Lotto Air Silicone (70.2%) and the Lotto Italia II (70.1%). The Uhlsport Trisafe demonstrated the least amount of force reduction with only a 41.2% reduction. This was still a significant reduction in the impact force when compared to the control of no shin guard.

There was a significant increase in the amount of force transferred through the shin guard when the guards were heated to 38C in comparison to the lower temperatures (table 3). The average force transferred for all shin guards increased 146.05 N over the room temperature measurements and 167.33 N over the cold temperature. Even at the higher temperatures, the shin guards were found to significantly decrease the force transferred to the tibia when compared to impacts without a shin guard.

TABLE 2
Total percent reduction of force from control
for all shin guards at varying temperatures


Cold        Room         Hot
                              (0C)      (20C)       (38C)
Shin Guard                     (%)         (%)         (%)

Body Pro                      59.1        58.6        57.2
Shin Pal                      66.3        68.3        64.1
The Protector                 68.3        66.0        64.2
Adidas-Kevlar                 57.9        5l.6        48.4
Rick Patrick                  49.0        50.2        47.2
Mitre                         56.0        61.6        53.8
Brine                         76.0        75.7        66.4
Brine Prostyle                49.4        45.5        46.5
Dunlop                        49.3        47.7        45.3
Pro-Pad                       73.8        71.5        68.0
Real Seville                  69.8        63.4        56.1
Uhlsport-Trisafe              41.8        41.5        39.3
Uhlsport-Air Shield           72.8        71.2        67.5
Uhlsport-Pro                  64.6        62.3        56.6
Air Lotto Italia              77.1        75.5        70.2
Flex Guard                    43.8        46.3        40.7
Lotto Italia II               72.3        73.0        64.7
Lotto Italia III              5l.2        55.0        45.7
Lotto Air Silicone            72.9        66.5        70.4
Umbro                         68.5        72.2        64.1
Diadora                       59.2        57.5        51.3
Sondico                       71.4        68.9        63.1

TABLE 3
Total peak impact forces for all shin guards
at varying temperatures


Cold        Room        Hot
                               (0C)      (20C)      (38C)
Shin Guard                      (n)         (n)        (n)

Body Pro                      949.63      962.30     1035.46
Shin Pal                      784.49      735.75      869.57
The Protector                 737.23      790.59      865.40
Adidas-Kevlar                 979.60     1124.66     1249.25
Rick Patrick                 1185.77     1157.27     1276.62
Mitre                        1021.89      893.18     1116.91
Brine                         557.04      565.06      858.59
Brine Prostyle               1176.63     1266.05     1294.41
Dunlop                       1179.27     1215.65     1323.97
Pro-Pad                       609.32      662.82      774.23
Real Seville                  702.91      850.12     1062.43
Uhlsport-Trisafe             1353.81     1359.50     1469.80
Uhlsport-Air Shield           632.22      669.00      785.48
Uhlsport-Pro                  822.17      876.11     1050.07
Air Lotto Italia              531.33      569.90      721.24
Flex Guard                   1306.32     1249.25     1435.57
Lotto Italia II               645.08      627.29      853.04
Lotto Italia III             1135.23     1046.84     1314.66
Lotto Air Silicone            629.13      777.77      717.02
Umbro                         732.61      645.97      868.18
Diadora                       947.88      986.81     1179.05
Sondico                       665.81      722.89      891.92


Figure 4. Impact forces transferred through shin guards utilizing pendulum impact device.

DISCUSSION

This study reinforces the utilization of shin guards to attenuate the forces seen by lower extremities during the play of soccer. An analysis of our data reveals a statistically significant reduction of force (40-77.1%) transferred to the lower leg when the protective guards were tested. A reduction in force of impact could prevent injuries that would normally occur without the use of a shin guard. Even at varying temperatures the guards were effective in dissipating the impact forces (Table 2).

The results of this study seem intuitive since the shin guards are made of soft compliant materials. However, in previous studies it was determined that soft compliant materials do not always attenuate the forces they encounter [2]. Therefore, the conclusion that soft compliant materials always reduce the amount of impact force is not indisputable.

In order for the shin guards to prevent lower extremity injuries, they must be utilized by the players on the fields. Comfort is one factor in whether a player will utilize the guard and weight of the guard is an important component of comfort of wear. The lighter the guard the easier it will be for the player to run, kick and compete in the play of the game. The weight of the guards tested varied from 2.0 to 6.5 ounces per guard (Table 1). The Shin Pal had the highest reduction of force (64.1-68.3%) in relationship to the lightest weight (2 oz).

Based on this study, the utilization of shin guards would help attenuate the amount of impact force seen by the tibia and thus may prevent injuries. Like any other type of protective gear, the guards must be applied properly and worn during the play of the game in order to reduce the risk of injuries.

ACKNOWLEDGMENTS

The authors wish to express their appreciation to the University of Michigan Men's Soccer Club for funding this project as well as Mr. Mike Malley for advising us on general soccer issues. In addition, the authors would like to thank Mr. Don Nelson for his help and guidance in procuring the shin guards tested. The authors would also like to express their appreciation to General Motors Biomedical Science Department for the donation of the Hybrid III leg and instrumentation for testing purposes. Thanks must also go to Mr. Scott Lukas for his photography skills utilized.

REFERENCES

  1. Fried T, Lloyd GJ. An overview of common soccer injuries. Sports Med 1992; 14(4):269-275.
  2. Janda DH, Viano DC, Andrzejak DV, Hensinger RN. An analysis of preventive methods for baseball-induced chest impact injuries. Clin J Sports Med 1992;2(3):172-179.
  3. Maehlum S, Daljord OA. Football injuries in Oslo: a one year study. Br J Sports Med 1984; 18(3):186-190.
  4. McCarroll JR, Meaney C, Sieber JM. Profile of youth soccer injuries. Phy and Sportsmed 1984; 12(2): 113-117.
  5. Pandolf KB, Holloszy JO (Eds.) Exercise and sport sciences reviews, Vol. 18, Williams & Wilkins, Baltimore, 1990.
  6. Sullivan JA, Gross RH, Grana WA, Garcia-Moral CA. Evaluation of injuries in youth soccer. Am J Sports Med 1980; 8(5):325-327.
  7. United States Consumer Product Safety Commission summary reports, National Electronic Injury Surveillance-System, 1990 through 1992.
  8. van Laack W. Experimentelle untersuchungen uber die wirksamkeit verschiedener schienbeinschoner im fubballsport. Z Orthop 1985; 123:951-956.

This article was published as:
"An Analysis and Comparison of Soccer Shin Guards"
Clinical Journal of Sports Medicine
Vol. 5, No. 2, 1995; pp. 95-99
Bir CA, Cassatta SJ, Janda DH

It is possible to order a copy of this article.


Copyright 2001 The Institute for Preventative Sports Medicine. All rights reserved.