Altitude: From great to good, and the impact on the game
Yesterday I did a post on altitude and the potential impact it might have on performance at the 2010 Football World Cup. What I didn't do in that altitude post is discuss how the altitude might affect performance - the application of the physiology. And so here is a follow-up to share some thoughts on whether the altitude will affect what you see during this tournament.
A big question mark: Research in short supply
The first point is that research on this is in short supply, so the best we can do is to apply physiological principles, and then infer their effect. Quite why the research hasn't been done is difficult to explain, but mostly, I suspect it's because there is not really a huge need. As I said yesterday, how often do elite sports events face this particular problem? In the USA, teams going to Denver have to face it, but that happens once or twice a year in NFL, maybe half a dozen (out of 72) time in the NBA. In South American football, altitude is an issue, but again, the frequency of games is so low that I think it's been overlooked. So suddenly, the world arrives in South Africa, and there are great big question marks.
But here are my thoughts around what would happen in a match:
- Distance covered per player per match would be reduced. This would be due to two things: One is the decrease in the overall intensity of the game, because players would adjust their "pacing strategy" to conserve energy. Pacing in a team sport is complex, but I've no doubt it exists. Technology will one day provide ways to study it very effectively. The second reason for a drop is that I suspect that the game will slow down more than normal at altitude, as a result of increased levels of fatigue. Which brings me to the second theory:
- Matches will fail to "ignite" in the second half, remaining low tempo. The drop-off in running distances (at various intensities - jogging, medium, high and sprint) will be greater between first and second halves. So if matches fail to "come alive" in the second half, and games seem to be meandering along at a low tempo, this may explain part of the reason
- Reduced number of sprints attempted per match. This is related to the pacing issue, but also, players will not recover between sprints. As we saw in the graph yesterday, if the rest period between sprints is increased, then the effects of altitude are negated. Shorter rests means worse performance per sprint. Therefore, at altitude, players will maximize recovery and sprint less, so that the performance per sprint will be maintained.
- A drop in the number of sprints means a reduction in the distance covered at high speeds - you may recall that on average, players run 2.4km at high speed, and about 600m at sprint speeds. This would fall at altitude, primarily because fewer sprints would be attempted
- Tactical changes would also occur - because the ball flies faster at altitude, it will be more difficult to control, both for outfielders and goalkeepers. Therefore, ball control skills will be affected
- Players will shoot more from long distances - this is actually not a hypothesis, it has already been shown that at altitude, players tend to take more shots from further away. Is this coaching? I doubt it. I think players figure out very quickly that they can't control the ball, and deduce that their chances are increased from further out
Altitude - going from "great" to "good"
Now, let's look at altitude. For the purposes of illustrating the concept, assume that in the graph above, the blue bars now represent elite players at SEA-LEVEL, while the orange bars represent the elite players at ALTITUDE. If the above bullet list of hypotheses was accurate, then the overall impact of altitude on the tournament you're watching would be to cause a drop in high intensity running, efforts made and distances covered. This might be best be summed up as:
Altitude turns "great" players into "good" players because it changes their activity profile in more or less the same direction as we see when comparing the highest level of football to a level below it.
Because the impact is the same for both teams (notwithstanding that a few teams have not based themselves at altitude), the overall "dynamic" of the game would not change too much. Which is why it's unlikely to be decisive, as mentioned yesterday.
Of course, this is just a theory. It requires proof. And proving this is enormously complex. Even analysing matches at the World Cup probably doesn't do it, because there are "only" 64 matches, and perhaps 40 of them are at altitude. This is not a large enough sample, because there are too many other factors that impact on the game and the activity of players in it.
For example, take the France v Uruguay match, which was played in Cape Town. In that match, France covered 101.5km, an average of 9,228m per player. Uruguay were even lower - 9,201m per player. Compare this to South Africa's match against Mexico. This match, at altitude in Johannesburg, saw Mexico covering 10,562m per player, and South Africa 10,805m per player. A huge difference - about 1.5km PER PLAYER.
So now we see how a match at sea-level can have reduced running, a match at altitude increased distances. This is simply because of the way the teams played - France v Uruguay was a conservative, tight match, much in the middle of the field. SA v Mexico was, well, frantic. End to end, a lot of movement, a lot of space, and that probably has nothing to do with altitude.
So the point is that a football match is the result of so many factors, that isolating the impact of altitude is nearly impossible. Of course, this doesn't mean I'm not going to try, and we (UCT) are going to look hard at this question and see what can be found in the data on the 2010 World Cup.
As always, you'll be the first to know if we do find anything!
P.S. Comments on altitude and the ball
In all these discussions on altitude, there is a huge effect that I haven't covered yet - the impact of altitude on the flight of the ball. The Jabulani ball has been slammed left, right and centre (unfortunately, it has not been slammed into the goal often enough!) by coaches and players. Part of this may be the ball - it's certainly different. However, I really do believe that a big part of it is the effect of altitude on ball flight.
For example, a free-kick struck from 30m out with spin, would be expected to curve a total distance of 4m when playing at sea-level. At altitude, because the air density is reduced (in Johannesburg, on a cold night, it would be around 20% lower), the forces acting on the ball are different. The end result is that a ball will fly faster and further, and also deviate LESS than at sea-level.
How much less? Some calculations show that the ball may move 60cm less in Johannesburg than at sea-level. It will also "dip" less, which is why it would be so much more difficult to get up and over the wall, but down in time for the goals. So when you see yet another free kick fly over by a meter, partly blame the altitude
So consider a striker who tries to bend the ball around the wall and into the goals from a free-kick - he misses by 50cm to the right. That was a goal at sea-level. At altitude, he blames the ball...
Meanwhile, the goalkeepers are complaining at the erratic movement of the ball, while strikers are complaining that the ball doesn't move enough. Apart from the obvious contradiction of these complaints, I feel that the keepers are judging the reduced reaction time - a shot from 18m out will get to the goal about two ball diameters earlier in Johannesburg than in Cape Town. That's a significant distance, and it explains why keepers are floundering - their reaction times are 0.1% too slow! Tiny, but enough of a difference.
There's more to be said about this, but it's a post by itself. It's one I'm a little reluctant to tackle, because I'm not an engineer and feel a little out of my depth explaining the details (I'd find an engineer's explanations of physiology frustrating, so I expect they'd frown upon mine!). But I'll certainly discuss it at some point! In the meantime, this article explains it really well.