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Links between physical characteristics and specific performances in American Football

American football is, as its name suggests, a sport of American origin very popular across the Atlantic. It is a game of "Win field" type where the goal is to stay as long as possible in possession of the ball and to travel as far as possible to reach the opponents' in-goal. The rules require the team in possession of the ball must travel 10 yards minimum (or 9.1 meters) in 4 attempts, otherwise the ball is recovered by the opposing team. For more information on the rules of the sport, we advise you to browse the Wikipedia page dedicated to American football for a global overview or refer to the official rules available on the website of the NFL.

The playing phases are brief and intense, so they require the players physical qualities of speed, strength, power and agility. In addition, these parameters vary according to the positions occupied by the different members of a team. Therefore physical training plays a very important role in training programs before, during and after the competitive season. The objective is to maintain or improve the main physical qualities of each player.

To systematically follow the players' progress, numerous specific tests have been set up. The sprint on 36.6m (i.e., 40 yards), the shuttle test on 18.3m (i.e., 20 yards) and the vertical jump are among the most representative field tests of American Football, but also the most used. Some studies have shown that these tests are strongly correlated with the level of the players and the division in which they evolve at the university level. But is there a significant link between the anthropometric and physical parameters of footballers and these tests ?

The Study

To answer this question, in 2004, a team of American researchers from West Virginia University investigated the links between anthropometric and physical variables and the sprint and jump tests of Division I university players NCAA. Data from 46 West Virginia University footballers from a training camp in the summer of 1999 was retrieved and analyzed retrospectively.

Anthropometric and physical data :

For the anthropometric data of each player, the researchers chose to examine the body mass (in kg), the percentage of fat mass (in%) measured using the 3-skinfold method and the height (in m) (Fig. 1). For physical data, the following variables were determined :

• 1RM Bench Press
• 1RM Hang Clean (Fig. 2) : Movement close to the clean, it consists of standing up with an Olympic bar in the hands and to bringing it up to the shoulders in the most explosive way possible. This movement differs from the "power clean" by the starting position.
• Sit & Reach (Fig. 3) : This is a test to evaluate the flexibility of posterior muscle chains. The subject must place these hands in front of him, as far as possible.

Field tests :

Field tests used in this study included :

• The vertical jump test (Fig. 4) : Standing against a wall, the researchers measured for each participant the height of the arms extended above the head. Then, the footballers made 3 jumps of Abalakov jump type and the maximum height reached by a hand was measured thanks to the Vertec system.
• The 40-yard sprint (ie, 36.6m) (Fig. 5) : On an artificial grass track, each footballer made 15 sprints over a period of 5 weeks at the rate of 3 sprints on one day, and this every week. The sprints were timed manually. For data processing, the slowest and fastest sprints were eliminated, to keep the average of the 13 others.
• The 20-yard shuttle test (ie, 18.3m)(Fig. 5) : The start is in the middle of the 20-yard line. The footballer can go to the right or left. He must come to touch the line with the hand that corresponds to the direction in which he left. Then he changes direction and must touch the opposite line. After touching this line, he must run to the finish line. This test was repeated 3 times, and only the 2 best times were retained.

From the results obtained during these evaluations, the researchers carried out a statistical analysis to find out which anthropometric and physical variables were the most strongly correlated with the different field tests. This allowed them to determine a mathematical model to best predict performance for each field test.

Results & Analyzes

Table 1 presents the mean results as well as the minimum and maximum values obtained in the various tests by American University football players in Division I :

Regarding the 40-yard sprint test, body mass, 1RM Bench Press and 1RM Hang Clean are significantly correlated with performance. Body mass is positively correlated with time over 40 yards which means that heavier the weight, slower the sprint. The other two variables are negatively correlated. The mathematical model to predict the performance on this type of sprint from the 3 variables mentioned can explain for 85% the variability of the results over 40 yards :

With t_{40 yards} the time over 40 yards (in s), BM body mass (in kg), BP_1RM the 1RM bench press (in kg) and HC_1RM the 1RM Hang Clean (in kg).

Concerning the 20-yard shuttle test, body mass, 1RM Bench Press and 1RM Hang Clean and the Sit & Reach test are significantly correlated with performance. Body mass is positively correlated with time, which means that heavier the weight, slower the sprint. The other three variables are negatively correlated. The mathematical model for predicting the performance on this type of test from the 4 variables cited makes it possible to explain for 81% the variability of the results :

With t_shuttle, the time on test shuttle 20 yards (in s), BM body mass (in kg), BP_1RM the 1RM bench press (in kg), HC_1RM the 1RM Hang Clean (in kg) and S&R the Sit & Reach test (in m).

Regarding vertical jump, none of the anthropometric and physical variables were significantly correlated with jump performance. This did not allow to determine a reliable model.

Practical Applications

This study makes it possible to emphasize that certain physical characteristics such as strength and agility are essential components of field performance in American football. The body mass is a determining variable in both models, which is not the case of the percentage of body fat. This implies that the most important thing is to have a high strength / body mass ratio. Moreover, it is not specified in this study that the researchers considered the playing position of each player.

The significant correlation of maximum strength in Bench Press and Hang Clean in both sprint tests can be explained by the need for players to have to balance the maximum strength of the upper and lower body. In the field, the upper limbs are solicited during all the actions of play, while the upper limbs make it possible, for example, to push the opponents.

The two sprint performance prediction models can be used by coaches and physical trainers to evaluate resistance training progress. It is nevertheless recommended to set up this protocol several times a year on its own players, and to determine its own mathematical models of prediction. Here, several points could be improved. Firstly, the time performance during sprints should be evaluated using photocells, which are much more sensitive, reliable and reproducible than manual timing. The measurement of body fat should be performed on the basis of the method of 4 skin folds, much more validated than the 3 folds. And finally, these models are just statistical models, and didn't imply necessarily a cause and effect relationship.

References

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