Thursday, February 21, 2013

How Did The Cooper Test Become a Part of Soccer?

There is little doubt that fitness is an essential part of a soccer player’s success. As pre-season training gets underway, coaches often administer a variety of tests designed to determine how fit their players are. One of these is the Cooper Test. To “pass” the Cooper Test, players are expected to complete a 2-mile run in 12 minutes or less. Players often dread testing because failing to come in under the 12 minute mark may mean the player is viewed as lacking fitness and being unprepared for the upcoming season. And, players who cannot pass may suffer consequences until they can record a passing time. How did the Cooper Test become such a popular evaluation of player performance? What exactly do the results tell the coach about player fitness? The Cooper Test has a long and interesting history since its development and adoption by the soccer community. However, it has several limitations that need to be understood before using it as a test of player fitness.

In the 1960’s exercise physiologists began to better understand how fitness, health and disease are linked. They saw that the lack of cardiovascular fitness raises the risk of developing various cardiovascular diseases. In 1967, they settled on maximal oxygen consumption (VO2max) as the standard reference of cardiovascular fitness. VO2 is the amount of oxygen consumed per minute, divided by body mass (ml O2/kg/min) ad VO2max is the value achieved during a subject’s maximal exercise effort. Having a high VO2max indicates high cardiovascular or aerobic fitness as well as high endurance exercise capacity. Unfortunately, in the late 1960’s, measuring VO2max was difficult and required a laboratory, some rather sophisticated equipment as well as considerable manpower. Thus, in order to estimate VO2max in large numbers of individuals, several field tests were developed. Among these, was the Cooper Test.

The Cooper Test was originally developed in 1968 by Dr. Kenneth Copper (Cooper, 1968). Dr. Cooper was working with the US Air Force trying to come up with a way to predict fitness and VO2max in military personnel. Basically, he correlated laboratory measured VO2max values with the distance covered during a 12-min walk/run. This is a simple test where subjects are asked to walk or run for 12 minutes on a track. At the 12-min mark, they stop and the distance covered is measured. Dr. Cooper found that he was able to predict VO2max fairly closely from the field test. At the extreme end of his data, covering 2 miles in 12 minutes predicted a VO2max of ~60 ml/kg/min.
The original Cooper Test was designed to estimate VO2max easily in a large number of individuals with varying levels of fitness (military personnel). The original study concluded by providing a table describing different categories of fitness. For example, a person covering 1.25 – 1.49 miles in 12 minutes was considered to have a “fair” level of fitness. Performance on the test was considered “as an indication of cardiovascular fitness and as a method for monitoring changes in fitness”. Because field tests have some error in the predictions, the Cooper Test wasn’t meant as a precise measurement of VO2max, only an estimate of fitness.

Eight years later, Dr. Cooper and his colleagues used his test along with a battery of other test to describe the physiological characteristics of professional soccer players (Raven et al., 1976). For this study, they used players from the Dallas Tornado Soccer Club, a member of the North American Soccer League (NASL). They found the players VO2max (laboratory measured) averaged 58.4 ml/kg/min. The players also averaged 1.86 miles during the 12-minute Cooper Test. Basically, this study showed that the average professional player has a VO2max of approximately 60 ml/kg/min and can run about 2 miles run in 12 minutes.

How did we go from the original 12-min run for distance to a 2-mile run for time? Note that the Cooper Test was first used for a military population then later for the general population. Some who lack fitness may not be able to complete a 2-mile walk/run. So stopping the test and 12 minutes and recording distance (no matter how short) made sense. In 1984, a research group from the US Army reversed the Cooper Test and focused on a run for time rather than distance. They correlated laboratory measures of VO2max with the time required to complete 2 miles. This group also found a close correlation between VO2max and time. Their equation again predicted a VO2max of 59.5 ml/kg/min for a 12 minute, 2-mile run.
  
There is little doubt that soccer has a tremendous fitness component. Players can run more than 6 miles (10km) over the course of a match. Clearly, players who are more fit, perform better at the end of each period. Thus, some level of fitness is essential to performance. But why did 2 miles in 12 minutes become a “gold standard” for soccer fitness? Part of the rationale stemmed from the Dallas Tornado study. Their players had an average VO2max of 60 ml/kg/min and completed about 2 miles in 12 minute. Later, renowned soccer researcher, Tom Reilly argued that success in professional soccer required a VO2max greater than 60 (Reilly & Doran, 2003). Given this, it seems logical to test players for a VO2max of 60. Enter the modified Cooper Test, a 2-mile run and the 12-minute threshold that predicts this value.
   
How accurate is the Cooper Test and how much emphasis should be placed on the 12-minute threshold? There are a few problems with this criterion being used as a gold standard for soccer fitness. First, Dr. Reilly’s VO2max requirement of 60 ml/kg/min may be a bit of an over estimate. Since the 1970s, the average VO2max of a professional player has crept upward. However, most studies suggest that the average is around 60 and highly successful players’ values may range from 50-70 ml/kg/min. Thus, a VO2max slightly below 60 or a 2-mile run time that is a bit above 12 minutes doesn’t necessarily indicate a poor player. Second, all field tests of fitness have some error in their prediction. Most tests estimate true VO2max within about ~10%. In fact, using Dr. Cooper’s original data, a player who runs 2 miles in 12 minutes may have a VO2max anywhere between 54 and 66 ml/kg/min. Third, coaches should remember that the 12 minute, 60 ml/kg/min values were measured in professional players, not youth or females. Expecting younger players and women to perform at the same level is probably unrealistic. Finally, the Cooper Test is not a terribly valid test of match fitness. It asks players to run at a constant pace for 2 miles. This never happens during the course of a match. Players stop, start, jog, sprint and change directions often during a match. For this reason, several “soccer specific” fitness tests have been developed such as the yo-yo intermittent running test, repeated sprint tests, and the Hoff Test. Most think these give a better estimate soccer fitness better than a continuous running test.

The Cooper Test does have a place in the coach’s bag of evaluation tools. But, remember that it is one tool that estimates one dimension of player performance. No doubt that a poor 2-mile run time indicates a lack of aerobic fitness. A sudden drop in Cooper Test performance during the season can indicate a nagging injury, illness or some chronic fatigue condition that needs to be addressed. Also, an off-season goal of “passing” the Cooper Test may be a useful motivational tool for the player as he/she trains for the upcoming season. How well the player performs on the first day of practice may also tell the coach how seriously the player has tackled the off-season training program. However, distinguishing fitness levels between players who are a few seconds over or under the 12 minute mark is not possible. The difference between times of 11:50 and 12:10 means very little in terms of a VO2max or fitness estimate. So, the Cooper Test has its place among the tools used to assess performance. However, it is important that coaches and trainers understand its limitation and use it as it was originally intended, an estimate of cardiovascular fitness.

References

Cooper KH (1968) A means of assessing maximal oxygen intake, Journal of the American Medical Association, 203: 135-138.

Mello RP, Murphy MM, Vogel JA (1984) Relationship between the Army Two Mile Run Test and maximal oxygen uptake. Technical Report, Army Medical Research and Development Command. Accession No. ADA15394.

Raven PB, Gettman LR, Pollock ML, Cooper KH (1976) British Journal of Sports Medicine, 10: 209-216.

Reilly T, Doran D (2003) Fitness assessment, in: Science and Soccer (2nd edition), Reilly T, Williams MA (eds), Routledge, New York, pp 21-46.

Thanks to Jeremy Williams for helping with this article.

Note: Dr. Kenneth Cooper, the “Father of Aerobics” later founded the Institute for Aerobics Research in Dallas, TX. He also authored two books, Aerobics and The Aerobics Way that emphasize the importance of cardiovascular fitness as part of a healthy lifestyle. He is considered one of the true pioneers in the area of aerobic fitness, exercise training and disease prevention. Many credit him and his books with the fitness boom that swept the US in the 1970s.