## Introduction

Soccer is a very popular game. It is a common game for the youth to play during downtime and recreation time. Many people don't think about the factors that go in to playing it. As you get older and play more frequently, more people drop out and resort to easier, less demanding sports and activities. On this page i willl talk about the factors of soccer, the training, angles of shooting, and much more.

## Training

Most coaches will argue that training time is a valuable commodity (advantage). This is especially true for colloge programs. In the US, the amount of time spent traing is strictly regulated by the NCAA. In addition, college coaches must compete with acedemic demands placed on student athletes. So, a question that is at the forefront of training is, how to best use limited training time to improve fitness as well as tactical and technical abilities. One concept that is gaining interest is the use of high-intensity training(HIT) to improve fitness. These programs require athletes to perform a few very high-intensity efforts rather than prolonged, moderate-intensity exercise to improve endurance capacity. The advantage of HIT programs is the potential to affect fitnes with a much shorter time requirement. A new study focused on using HIT to improve fitness in female college soccer players. The researchers found that HIT worked very well- it was effective in improving V02max (amount of oxygen taken in) an it required less training time compared to the average endurance training program.

## The Experiment

The subjects for the study were all members of a women's Division lll college soccer team( Williamette University in Salem OR). The study was taken place over a 5 week period that coincided with their spring training season(non-competitive). Half of the team was put on the average endurance training program and the remainder of them were placed on a high-intensity, interval program.

Before and after the training, each player's maximal oxygen consumption (VO2max) was measured using a labratory-based treadmill test. Performance on the Yo-Yo endurance test was also measured. The Yo-Yo test is an intermittent shuttle run wher the performance is determined by the number of shuttle circuits the athlete is able to complete before exhaustion.(it shows stopping and starting at intervals...otherwise known as suicides by the average athlete)

As for training the 2 groups completed their traing protocol twice per week for the 5 week test period. The HIT players performed 5 repetitions of a 30 second maximum sprint seperated by a 4.5 minute recovery interval. This resulted in a total training time of 25 minutes. After 3 weeks of traing the recovery interval was reduced to 3.5 minutes. This shortened the total training time to 20 minutes. On the other hand, the endurance training group performed 40 minutes of running at 80% of their VO2max.

The researchers found that both HIT and endurance training, twice per week for 5 weeks, improved VO2max by about 4%, from 50.7 to 52.7 ml 02/kg/min. It also increased performance on the Yo-Yo test by about 12%. When comparing the effectiveness of the training programs, the magnitudes of improvement were very similar. That is, both programs resulted in similar gains in VO2maxand Yo-Yo test performances.

The important finding of the study is that the HIT concluded the same amount of improvement in fitness in about half the traing time. The HIT players trained for 20-25 minutes per session while the endurance group trained for 40 minutes. The authors of the study argue that this more economical use of training time can have advantages. Given that the amount of time spent training is governed by the NCAA, spending 20 fewer minutes on fitness allows more time to be spent on technical and tactical training. They also point out a more efficient use of practice time gives the players more time to focus on non-soccer activities such as school work.

Before and after the training, each player's maximal oxygen consumption (VO2max) was measured using a labratory-based treadmill test. Performance on the Yo-Yo endurance test was also measured. The Yo-Yo test is an intermittent shuttle run wher the performance is determined by the number of shuttle circuits the athlete is able to complete before exhaustion.(it shows stopping and starting at intervals...otherwise known as suicides by the average athlete)

As for training the 2 groups completed their traing protocol twice per week for the 5 week test period. The HIT players performed 5 repetitions of a 30 second maximum sprint seperated by a 4.5 minute recovery interval. This resulted in a total training time of 25 minutes. After 3 weeks of traing the recovery interval was reduced to 3.5 minutes. This shortened the total training time to 20 minutes. On the other hand, the endurance training group performed 40 minutes of running at 80% of their VO2max.

The researchers found that both HIT and endurance training, twice per week for 5 weeks, improved VO2max by about 4%, from 50.7 to 52.7 ml 02/kg/min. It also increased performance on the Yo-Yo test by about 12%. When comparing the effectiveness of the training programs, the magnitudes of improvement were very similar. That is, both programs resulted in similar gains in VO2maxand Yo-Yo test performances.

The important finding of the study is that the HIT concluded the same amount of improvement in fitness in about half the traing time. The HIT players trained for 20-25 minutes per session while the endurance group trained for 40 minutes. The authors of the study argue that this more economical use of training time can have advantages. Given that the amount of time spent training is governed by the NCAA, spending 20 fewer minutes on fitness allows more time to be spent on technical and tactical training. They also point out a more efficient use of practice time gives the players more time to focus on non-soccer activities such as school work.

## Drag, Force, And Trajectory On The Ball

When a soccer ball is traveling through the air it's trajectory is influenced by a number of factors, including wind flow and air pressure. As the player strikes the ball, the drag and force excperienced by the ball strongly influences it's trajectory especially, if the ball is spinning. When the player strikes the ball attempting to induce a shot that bends, a reaction known as Magnus Force causes an imbalance of pressure.

## Lift Force

As an object moves through the air, the air is disturbed by the object. The disturbance generates an aerodynamic force on the object. Since a force is a vector quantity , having both a magnitude and a direction , we can split the aerodynamic force into 2 components. Drag acts in the direction of the travel of the object. Lift acts perpindicular to the direction of travel. Many different objects are capable of generating a lift force. In paticular, a spinning ball generates a force that is perpindicular to both the flow direction and to the axis of rotation. The lift force is used to move the ball parrellel to the surface of the earth, side-to-side. The lift force on the ball can also be used loft or dive the ball.The details of how a moving soccer ball creates lift are fairly complex. If we move with an object through the air, the object appears to stand still and the air moves past the object at the speed of the object. Next to the surface of the object, the molecules of the air stick to the surface, as discussed in the properties of air slide. This thin layer of molecules entrains or pulls the surrounding flow of air. For a spinning ball the external flow is pulled in the direction of the spin. If the ball is not translating, we have a spinning, vortex-like flow set up around the spinning ball, neglecting three-dimensional and viscous effects in the outer flow. If the ball is translating through the air at some velocity, then on one side of the ball the entrained flow opposes the free stream flow, while on the other side of the ball, the entrained and free stream flows are in the same direction. Adding the components of velocity for the entrained flow to the free stream flow, on one side of the ball the net velocity is less than free stream; while on the other, the net velocity is greater than free stream. The flow is then turned by the spinning ball, and a force is generated. Because of the change to the velocity field, the pressure field is also altered around the ball. The magnitude of the force can be computed by integrating the surface pressure times the area around the ball. The direction of the force is perpendicular (at a right angle) to the flow direction and to the axis of rotation. On another page we develop the mathematical equation for the ideal theoretical lift of a spinning, smooth ball.

L = (4 * pi^2 * b^3 * s * rho * V) * 4 / 3

where b is the radius of the ball, s is the spin of the ball, rho is the density of the air, V is the velocity of the ball, and pi is the standard 3.1415...

The equation given above describes the theoretical lift force generated on a smooth, rotating ball. The ideal streamlines around a smooth ball are shown on the figure at the top left, marked "Theory". But in reality, the flow around a spinning soccer ball is very complex and looks more like the "Actual" flow shown on the figure. Viscosity generates a boundary layer on the ball and the stitches used to hold the covering of the ball together stick up out of the boundary layer and disturb both the boundary layer and free stream flow. On the ball, the boundary layer transitions to turbulent flow which affects the amount of aerodynamic force. The stitches are not symmetrically distributed around the ball. So the real flow around the ball is separated, unsteady, and not uniform.

We can use the theoretical lift as a first order, or preliminary, estimate of the lift on a soccer ball. But to account for these real-world effects that we have neglected in our ideal flow model, we define a lift coefficient. The lift coefficient is an experimentally determined factor that is multiplied times the ideal lift value to produce a real lift value. The ideal simplified model tells us the relative importance of the factors that affect the lift force on the soccer ball, while all of the complex factors are modeled by the lift coefficient. Using experimental data for the movement of a kicked ball, Goff and Carre determined the average value of the lift coefficient to be about .25.

We have used this value as the default value for the lift coefficient in the SoccerNASA simulation program You can further investigate the lift of a spinning soccer ball by changing the value of any of the factors that affect lift in the program. The lift force on the soccer ball is very similar to the lift generated by an airplane wing or a big league curve ball.

L = (4 * pi^2 * b^3 * s * rho * V) * 4 / 3

where b is the radius of the ball, s is the spin of the ball, rho is the density of the air, V is the velocity of the ball, and pi is the standard 3.1415...

The equation given above describes the theoretical lift force generated on a smooth, rotating ball. The ideal streamlines around a smooth ball are shown on the figure at the top left, marked "Theory". But in reality, the flow around a spinning soccer ball is very complex and looks more like the "Actual" flow shown on the figure. Viscosity generates a boundary layer on the ball and the stitches used to hold the covering of the ball together stick up out of the boundary layer and disturb both the boundary layer and free stream flow. On the ball, the boundary layer transitions to turbulent flow which affects the amount of aerodynamic force. The stitches are not symmetrically distributed around the ball. So the real flow around the ball is separated, unsteady, and not uniform.

We can use the theoretical lift as a first order, or preliminary, estimate of the lift on a soccer ball. But to account for these real-world effects that we have neglected in our ideal flow model, we define a lift coefficient. The lift coefficient is an experimentally determined factor that is multiplied times the ideal lift value to produce a real lift value. The ideal simplified model tells us the relative importance of the factors that affect the lift force on the soccer ball, while all of the complex factors are modeled by the lift coefficient. Using experimental data for the movement of a kicked ball, Goff and Carre determined the average value of the lift coefficient to be about .25.

We have used this value as the default value for the lift coefficient in the SoccerNASA simulation program You can further investigate the lift of a spinning soccer ball by changing the value of any of the factors that affect lift in the program. The lift force on the soccer ball is very similar to the lift generated by an airplane wing or a big league curve ball.

## Shot Taking

When you get in close to goal, knowing the best angles for scoring is crucial. You need to make a quick decision as to whether your position is better for shooting or passing off. Although you always want to play the best angles, occasionally you can get away with what looks impossible. Many a World Cup player -- such as Japan's Karina Maruyama, Brazil's Roberto Carlos and Landon Donovan of the U.S. -- have gotten away with scoring from a tough angle on the big stage of international competition.

SWEET SPOT

The best angles for scoring are from straight in front of the goal or just very slightly to the side. Imagine dotted lines extending out onto the field from the goalposts and flaring enough to intersect with where the penalty circle intersects with the straight line at the top of the 18-yard box. In a diagram in his book "Soccer: Steps to Success," coach Joseph Luxbacher labels this sweet spot "the most dangerous shooting zone." This central area is where shots are most likely to find the back of the net.

NEXT BEST

Envision a second dotted line extending from the goalposts and intersecting with the corners of penalty box. Luxbacher observes that shots from this area can achieve moderate scoring success. Coach Alan Hargreaves adds in his book "Skills and Strategies for Coaching Soccer" that the reason shots from narrower angles are less successful is that the goalkeeper standing in the way creates a much smaller target area of open net compared to shots from the midline of the pitch.

LOWEST ODDS

Subtracting the zones of good and moderate shooting success leaves an area that offers poor shooting angles. This zone forms a triangle bound by the touchline -- as a soccer sideline is called -- the end line, and an imagined diagonal line from the goalpost to the penalty box corner, extended out to the sideline. Shots taken from this flank area, with its narrow shooting angle "will rarely beat a competent goalkeeper," Luxbacher writes.

SWEET SPOT

The best angles for scoring are from straight in front of the goal or just very slightly to the side. Imagine dotted lines extending out onto the field from the goalposts and flaring enough to intersect with where the penalty circle intersects with the straight line at the top of the 18-yard box. In a diagram in his book "Soccer: Steps to Success," coach Joseph Luxbacher labels this sweet spot "the most dangerous shooting zone." This central area is where shots are most likely to find the back of the net.

NEXT BEST

Envision a second dotted line extending from the goalposts and intersecting with the corners of penalty box. Luxbacher observes that shots from this area can achieve moderate scoring success. Coach Alan Hargreaves adds in his book "Skills and Strategies for Coaching Soccer" that the reason shots from narrower angles are less successful is that the goalkeeper standing in the way creates a much smaller target area of open net compared to shots from the midline of the pitch.

LOWEST ODDS

Subtracting the zones of good and moderate shooting success leaves an area that offers poor shooting angles. This zone forms a triangle bound by the touchline -- as a soccer sideline is called -- the end line, and an imagined diagonal line from the goalpost to the penalty box corner, extended out to the sideline. Shots taken from this flank area, with its narrow shooting angle "will rarely beat a competent goalkeeper," Luxbacher writes.