World Cup - The Ball

The Ball

There has been much discussion of the Jabulani, the football designed by Adidas that being used in the World Cup. Adidas say that it’s their most accurate ball ever, yet it doesn’t seem to be appreciated by a lot of the players.

It does seem as if players are having trouble controlling it when shooting, as if it doesn’t respond aerodynamically in the way they’re expecting, and it’s possible that playing at altitude may be part of the reason for this. But could there be another factor?

The ball that’s used on the English Premier League is the Nike Total 90 Omni. The manufacturers say that has a special graphic that makes the ball easier to see using peripheral vision. Its yellow colour makes it stand out if it’s in the central part of our vision because the light receptor cells there are particularly sensitive to yellow (the reason why high visibility jackets are yellow). The Jabulani is white with some multi-coloured areas.

What may be important here is not that one ball is necessarily much easier to see than the other, but the simple fact that they are quite different. When a professional footballer kicks a ball, he will be much more accurate in the part of the ball he kicks than a park player. In order to do this, he will have to focus on that particular part of the ball. But he will do it subconsciously, not realising that he’s doing it.

Faced with a different ball design, the subconscious brain will not immediately recognise the correct part of the ball for the shot. The shot is hit less accurately, with the result that it doesn’t follow the intended path.

In time, the brain recalibrates for the new ball. Those who have been training with the ball for longer, such as the Germans, will have an initial advantage. Others will catch up in time, but will they do so quickly enough?

David

http://www.donneroptometrists.co.uk/sports-vision.htm

New Balls Please

I was lucky enough to get Centre Court tickets to Wimbledon recently. Watching Andy Roddick play Michael Llodra, I thought I’d watch their head and eyes as they played the ball.

Ideally for this you need slow motion photography or head-mounted cameras, and all I had was a pair of binoculars. However, it appeared to me that Roddick was looking some way ahead of his racket when he hit the ball. Llodra, however, seemed to look down at the contact between ball and racket when playing backhands, but more in front on forehands. Llodra won the first set 6-4, with his backhands being especially strong.

As time went by, however, I thought Roddick had brought his focus closer to the contact area, though still in front. Llodra, meanwhile, seemed to be less consistent, sometimes looking at he contact area, and sometimes a way in front. There wasn’t a complete correlation between where he looked and whether he won the point or not, but he seemed to be more likely to be successful when his focus was nearer the contact area. Roddick went on to win the next three sets and the match.

It’s certainly possible that my observations were mistaken, or that Roddick’s game improved and Llodra’s deteriorated, their gaze positions altered as a consequence. For instance, if Roddick started hitting the ball harder, Llodra might have had less time to get in position for his shots, including his head position.

So is there any evidence that where you look when you hit the ball is important in tennis? Actually, there is...

In 2007, Damien Lafont presented a paper entitled “Gaze Control during the Hitting Phase in Tennis”. Using high-speed photography, he found that most professional players looked out in front of the racket, sometimes into the opponent’s court at the moment of impact. However, the visual strategy of the very best players, such as Federer and Nadal, differed in two respects. Firstly, they fixated the contact zone, and secondly they maintained this fixation until after they had completed their swing.

This is a bit more than the traditional “keep your eye on the ball”. The ball can be arriving at speeds of over 130mph, which is too fast for the eyes to track accurately all the way. They must be able to make some early judgments about where the ball is going to go by watching their opponent’s actions as he plays the shot. There is likely to be some early pursuit of the ball to confirm this.

Knowing when to time your shot can be estimated from when the ball bounces in front of you, and then the elite players start focusing on the area, some way in front of them, where they intend to hit the ball – the contact area. It seems that they don’t actually watch the ball onto the racket, but instead watch the racket hit the ball in the contact area (as opposed to watching the swing of the racket as it hits the ball).

Federer adds one, possibly unique twist to this. He actually twists his head so that he can see the contact area through the back of the racket. He thus ensures that his head and eyes are still at the point of contact, and immediately afterwards, making it less likely hat he’ll snatch the shot by looking ahead too early.

Federer’s technique may not be for everybody, and he has been perfecting it over a number of years. Photographs show him doing this at the age of three. However, the idea of training yourself to focus on the contact zone as, and immediately after, you play the shot can be practised.

Many courts are surrounded by wire netting. You can push a ball into the netting to hold it in place at different heights and positions for different shots. Then, when you play, imagine the ball is held in place for a millisecond as you swing the racket. You then look for contact between your racket and the ball either from the front of the racket, like Nadal, or from the back, like Federer, whichever seems to suit you best.

David Donner

http://www.donneroptometrists.co.uk/sports-vision.htm

Sports Vision - Fielding in Cricket

A ball is travelling towards you. How do you know when it’s going to arrive, so you can get your hands in the right position to catch it? Muscles in the hand must be prepared so that the hand is widest open before the ball hits just above the palm (ideally), the wrist forearm and elbow must be prepared to absorb the kinetic energy of the ball, and the finger joints must also be prepared to close around the ball after impact. Muscle responses need to start about 100 milliseconds before the ball arrives.

From physics, the time taken for the ball to arrive will be its distance away from you divided by the speed at which it’s travelling. The brain can deduce information about the ball’s position from the size of its image on the retina; the smaller the image, the further away it is. The rate at which the image is getting bigger tells the brain how fast the ball is coming towards you (i.e. its speed).

The brain doesn’t actually calculate the ratio between them, but it knows, through practice, that when this ratio reaches a critical level, it’s time to send the necessary messages to the arm and hand muscles.

Savelsbergh et al conducted an interesting experiment in 1991 using a balloon that deflated as it approached the catcher. Because the image size on the retina did not increase as normal, the catchers overestimated the time to contact, showing that they were using image size for their timing rather than just the speed of the ball. The effect was most noticeable when one eye was covered. It was still there when both eyes were open, but less so, suggesting that stereoscopic information from vision can also be used.

This is fine for a ball that’s travelling at a steady speed, but what about a ball that’s accelerating? An outfielder under a skied catch has to deal with a ball that’s dropping at a rate of 32 ft/sec², and they may have to run to get in line with it as well.

If the fielder is directly under a skier, the brain can use something known as the “zeta angle”. This is the apparent size of a falling object relative to its apparent size at the moment the object started to fall. If it can make an allowance for gravity, the brain can initiate the catching actions when the zeta angle reaches a certain level, as long as the point when the ball started to drop was observed.

Experiments on astronauts on board Space Shuttle Columbia have shown that we do indeed make an adjustment for the effect of gravity. In space, the astronauts were too early in their attempts to catch the ball, because their brains were programmed to take into account the effect of a non-existent gravity.

If the ball is coming straight to the fielder, then his angle of gaze – the angle between the eye and the ball – will remain constant. If it’s not coming straight at him, then the angle of gaze will vary as the ball travels. The brain can use this information by trying to keep the angle constant or within a certain range. This information will get enable the catch to be made (assuming the fielder can run fast enough). The brain doesn’t calculate where the ball will land: it just uses the visual information to get the fielder to where the ball will land.

Finally, the fielder needs to be in a position where the ball appears to be travelling at a constant speed. If it’s speeding up, you need to move back, or move forward if it appears to be slowing down.

The unsurprising conclusion from all of this is that the more experience of catching from a young age that one gets, the better.

For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm

Sports Vision - Bowling in Cricket

After 5 good deliveries, the bowler bowls a poor ball that gets hit for four. A batsman has been tied down by a spell of good bowling, and ten plays a wild shot, throwing his wicket away. A bowler has bowled several good overs, then a poor ball, “the worst ball I’ve bowled all day”, takes a wicket.

These things happen all the time in matches, but how often do they happen in the nets? Rarely, if ever. Most of the time, bowlers are used as fodder to give the batsmen time at the crease. Are they really practising their trade effectively?

In a match, the bowler can put pressure on a batsman by bowling a succession of testing deliveries. So why not get bowlers to ball 6 balls at a time in the nets? Markers on the nets can indicate fielders’ positions, and if you have an umpire in place, judgements can be made on appeals and runs scored.

Bowling is an aiming activity, with the point where the ball pitches being the target. This point will vary according to the type of delivery the bowler wants to bowl, as well as the style and stature of the striker. These can be marked on the floor of the net, and adjusted if necessary, for instance if the striker starts batting out of his crease. These marks may also help the striker pick up the length of deliveries, so they help both bowlers and batsmen.

If no balls are a problem, the popping crease can be highlighted, but it’s essential that he bowler uses their peripheral vision for the popping crease, maintaining fixation on the point where they want the ball to pitch. The no ball problem can often be cured by simply moving he bowler’s mark forward (Note: not back).

For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm

Sports Vision - Batting in Cricket

“The head must be kept upright and turned towards the bowler with the eyes as level as possible” (The MCC Cricket Coaching Book).

But why should the eyes be as level as possible? According to the MCC, only in this position can “the batsman focus both eyes together”. But if you look at an object and twist your head slightly, you’ll notice that things don’t go blurred or double. The reason is that the balance organs in the ears register this head tilt and, via the vestibulo-ocular reflex, produce a counter-rotation of the eyes to maintain clear vision.

Another reason that’s commonly given is that keeping the eyes level helps speed up your reaction time. I have been unable to find much evidence to support this claim, however. I did find one experiment that showed a link between head tilt and lower reaction times, but there are one or two problems with applying it to batting. Firstly, subjects had to react to a sound. They were also sitting down………in the dark.

Even if there were a link, how much of batting is to do with reaction times, anyway? Sir Donald Bradman was found to have slower reactions than the average University student. Yet, as Jim Laker said “Bradman always seemed to know where the ball was going to pitch, what stroke he was going to play, and how many runs he was going to score”. It seems that batting has more to do with anticipation than reaction times.

This is not to say that one shouldn’t have ones eyes level. For some batsmen it might help them focus on the bowler’s action and release of the ball, and for others it might be necessary to ensure a consistency of eye dominance between watching the bowler and playing the shot. But it suggests that there isn’t one perfect technique that should be employed by everyone, but it’s more a question of the individual’s brain working out (ideally subconsciously) what works best for them. And is it possible that the twisting that’s’ required in order to get the eyes level from a sideways stance contributes to the back injuries suffered by many batsmen?

Bradman did not have a classic technique. He was entirely self-taught, and didn’t play on a grass pitch until he was 18, having been brought up on concrete pitches covered in matting. He had an unusual grip, with his right hand nearly facing straight down the pitch, and the “V” of his left hand in line with the splice. His bat was closed and locked between his feet, and he picked it up at an angle of 45 degrees to the flight of the ball. None of this could be found in any coaching manual, and led to much criticism early in his career. He was, however, the master of seeing the ball early, and playing it late.

He also fits into the classic profile of an elite sportsman in having had essentially unlimited access to practice in his developing years whilst pursuing a range of sports. In Bradman’s case, he spent many hours playing imaginary Test matches, throwing a golf ball against the brick base of a water tank and hitting it with a stump. He was a highly proficient billiards player, played off a scratch handicap in golf for many years, and excelled in tennis, which he played before taking up cricket.

There are three key visual stages in batting: watching the bowler’s action and release of the ball; watching the pitch of the ball; and watching the contact between bat and ball.

By observing the bowler’s action, Test match batsmen are able to determine what type of ball a swing bowler is delivering (outswinger, inswinger, short ball) by the time the front foot has landed. They can also determine a leg spinner’s delivery (leg spinner or googly) by the same time from observation of the bowler’s wrist. Accurate determination of the length of the delivery seems to require some early tracking of the ball after release.

Land & McLeod (2000) monitored the eye movements of expert batsmen when facing a bowling machine. They found that even elite batsmen weren’t able to track the ball throughout its flight. They would track it for a while and then jump ahead to the point where they expected the ball to pitch. If the ball was short-pitched, they would make that jump in fixation earlier. If it was over-pitched, they could track almost the whole way.

A very quick delivery may pitch less than a quarter of a second after the bowler releases it. Because novices aren’t so god at anticipating the length of the ball, they make their jump to the bounce point too late. Either they’re still trying vainly to follow the path of the ball, or they are making their jump as the ball pitches. Because vision is suppressed when one makes this jumping (“saccadic”) eye movement, they can lose sight of the ball completely.

If the batsman knows the where the ball has pitched, and the speed at which it’s travelling, he can work out when it will arrive. The brain doesn’t actually work out these calculations in a mathematical way. Rather it develops rules of thumb based on long periods of practice. But it still needs to pick up information about the speed of the ball and where it’s pitched in order to make the correct shot decisions.

A sense of the speed of the ball is obtained from the time it took to leave the bowler’s hand to reach the bounce point. An adjustment then needs to be made for loss of speed after pitching. This is why batsmen generally need to play themselves in: so they can make the necessary adjustments according to whether the pitch is fast or slow.

According to Land & McLeod, the position that the ball pitched can be determined by the formula B/tanФ, where B is the height of the batsman’s eye and Ф is the angle that the batsman’s eyes have had to look down. So the more the batsman has to look down, the closer to him the ball has pitched. It may be, however, that the brain establishes the pitch point from more general principles of how far away things are, for instance by using the different images that form on the two retinas from near objects.

However the brain does it, one clear message should be that it’s more useful to tell a batsman to concentrate on where the ball has pitched, than a general “watch the ball” instruction. If you know accurately where the ball has pitched, you’re most of the way to knowing what shot to play and when. It can be useful to ask batsmen in the nets where they think the ball pitched, so they can feedback on their perception.

The final key visual stage is the contact between bat and ball. In other interception sports, such as tennis, focusing on the contact point has been shown to be highly important for elite players. Some imagine a hitting area into which the ball arrives, and they maintain focus on that area even after the ball has been hit. Batting tees can be useful aids in concentrating on the contact point.

Differences in batting style have been observed when facing a bowling machine compared with facing a bowler (Pinder, Ross & Davids 2006), such as shorter and later backswing and shorter stride length. As an umpire, I’ve seen young batsmen display excellent stroke-play, but with no idea of how to build an innings, no shot placement, and often pre-meditating the shot. They look like they’re playing in a net, rather than in a match. So there’s clearly a danger in over-relying on net practice, and bowling machines in particular, although they clearly have their place.

It is therefore useful to try and make the nets more like a match, for instance by having two batsmen alternating the strike, and by marking fielder’s positions on the nets. Ideally, an umpire could stand and make decisions as well as giving a notional score for each shot.

When the batsman surveys the field, the obvious thing is just to note where the fielders are. However, this can often lead to the ball being struck precisely to where those fielders are. More useful is to focus on the gaps between the fielders, ideally to a specific point between them. This becomes much more powerful if the striker also visualises hitting the ball to that specific point.

For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm

Does Colour Matter?

Researchers at the University of Chichester have found that footballers were more likely to miss a penalty if the keeper was wearing red.

40 university footballers took dozens of penalties against a keeper who saved 46% of them when wearing red, 31% in yellow, 28% in blue and 25% in green. They suggest that the colour red might have an unconscious influence on the perception of failure, causing strikers to perform worse.

The colour of footballers’ jerseys came to prominence in 1996 with Manchester United’s infamous grey kit. Having lost three games and drawn one whilst wearing the grey kit, Man Utd were 3-0 down at half time against Southampton. (Sir) Alex Ferguson ordered the team to change saying the players couldn’t see their team-mates against the background of the stands. There was an improved performance in the second half, but they still lost 3-1.

In 2008, Petr Cech started wearing a bright orange shirt which in theory would distract the opposing striker. In the 1990s, Mexican keeper Jorge Campos designed his own brightly coloured kits with the same purpose. However, these theories weren’t obviously effective in practice, so it could be that elite players aren’t distracted in the way that lesser players might be. The most popular colour for goalkeepers in the Premier League to wear is green, and none wear red. So is there any evidence that red is an advantage at a professional level? Actually, there is.

In 2007, Attrill, Gresty, Hill & Barton found that red shirts were associated with long-term success in English football. Across all league divisions, red teams had the best home record. No significant differences were found in away matches, when teams wear their away kit.

They also found that in all but one city (Sheffield), the team playing in red has been more successful since 1946 than the other available team playing in a different colour. They speculate, however, that in recent times the spending power of clubs might be a more significant factor in their success than shirt colour.

A brief survey of some major football European cities seems less conclusive:

Madrid

Real (white); Getafe (blue); Atletico (red + white stripes)

Barcelona

Barcelona (red + blue stripes); Espanyol (white + blue stripes)

Milan

Inter (blue + black); AC (red + black stripes)

Rome

Roma (red); Lazio (blue + white)

Genoa

Sampdoria (blue); Genoa (red + blue halves)

Turin

Juventus (black + white stripes); Torino (red)

Brussels

Anderlecht (white); Brussels (red + black stripes)

Moscow

CSKA (red + blue); Dynamo (blue); Spartak (red + white stripe); Lokomotiv (red)

What about international teams? Hill & Barton (2005) looked at the Euro 2004 Championships. They found that all teams that wore red in some of their matches, but not in all, had better results when they wore red. This was, however, a small sample.

In Germany, the national team’s away shirts were changed from black to red in November 2004 at the request of Jurgen Klinsmann, in the belief that teams in red were perceived as more intimidating as well as more successful. He hoped to use the red away shirt as first choice for the 2006 World Cup, despite the fact that they had less than impressive results in these colours, notably a 4-1 defeat by Italy. In the end, Germany played in white in every game in the World Cup, reaching the semi-finals. In 2010, the away colours changed back to black shirt and white shorts.

In FIFA’s Top 10 ranking, Spain (1^st) and Portugal (4^th) play in red, and Croatia (10th) play in red and white. But if wearing red has a significant negative psychological effect on ones opponents, one would expect the advantage to be seen in other physical sports, such as rugby and American Football.

Out of the 12 teams in the Guinness Premiership, only one (Gloucester) has a significant amount of red in their home shirt. Out of the 10 teams in the Magners League, only two (Munster and Scarlets) wear red. In international rugby, the most successful colours are currently black, gold, green and blue. And of the 12 teams that made the American Football play-offs this year, only one (Arizona Cardinals) wear red.

There is one area of sport where there is strong scientific evidence that wearing red is an advantage, although it’s because of the effect on the officials, rather than the players. In 2008, Hagemann et al showed 42 experienced tae kwon do referees video clips of 5 different male competitors. Each clip featured one athlete in red and another in blue, and the referees had to score the match. Some time later, they were shown the same clips, but with the colours digitally swapped, so that the athlete originally wearing red was now wearing blue. This single alteration had a significant effect on the outcome, with competitors wearing red scoring on average 13% more points than their opponents in blue. It was dubbed “the Chris de Burgh effect”, and is thought to be due to an assumption by the officials that competitors wearing red are more aggressive.

Professional footballers are less likely to be distracted by the colour of the opponents’ shirts, and more likely to be able to assess the most relevant information in their vision in order to make the most effective pass or shot.

It is 44 years since a team wearing red won the World Cup. If Spain manage it this year, it’s most likely to be down to the skill of players like Xavi, Iniesta and Torres, rather than the colour of their shirts.

Why are boys generally better at throwing a ball than girls?

The answer to this question is not, as you might think, one of strength. It’s one of balance.

Humans have a real problem maintaining balance. It takes quite a long time for us to learn how to stand up and move bout without falling over. An action like throwing a ball is especially destabilising. Throwing with your right arm requires a compensatory activation of the lower leg muscles to stop you from spinning round and falling flat on your face.

How does your brain know which muscles to stimulate and by how much? To start with, it doesn’t know because there are too many variables in the position of your shoulder, elbow and wrist. The brain is programmed to keep us as stable as possible, so to reduce the variations it freezes the joints, so that it can treat the arm as one solid unit. This maintains stability, but at the price of effectiveness, because muscles aren’t very effective when they’re frozen. The only way of getting power is to transfer the kinetic energy from your trunk and legs. This is why when you see someone throw a ball who’s not used to doing it, they look very stiff, they have to put a lot of effort into it, and they may well jump at the same time. Because boys tend to play more ball games than girls, they are more likely to have got past this stage.

Gradually, with practice, the brain works out which combination of muscle stimulation is the most efficient, and starts to unlock the joints. This allows the elastic energy in tendons to be released, so that the ball is thrown further. In the end, the brain works out the most energy-efficient method of carrying out the task. This is an individual thing – different people with different statures and muscle tone shouldn’t come to the same answer.

By this time, the athlete is likely to have developed an effortless, natural-looking style, although it can look slightly unusual in some people, for instance Michael Johnson’s very upright running style.

The ideal is that the person finds their own solution to the problem. Direct coaching, telling someone how to do it, hinders the process of self-discovery. It can give them short term solutions for specific situations, but there’s evidence that skills acquired through self-discovery (implicit learning) are much less likely to fail under pressure than when people have been instructed precisely how to do something (explicit learning).

When people are taught explicitly, their performance in a match situation is likely to be inferior to how they perform in practice. Also, there’s evidence that long-term accumulative injuries can occur from early attempts to acquire techniques which are often anatomically inappropriate for particular individuals. This has been a particular problem for fast bowlers in cricket.

For more information please visit http://www.donneroptometrists.co.uk/sports-vision.htm