Why do athletes often strive to achieve very low body fat levels?

Question

Even lurking just a bit on fitness communities shows that people often talk about single digit body fat levels.

Why is this wanted?

Provided that one is not overweight, what benefits (except for looking better) can one obtain from losing fat alone (as opposed to building strength / stamina / etc?)

Assuming that all other parameters remain unchanged, what feats could one achieve with lower body fat levels? What exercises could one do that would otherwise be impossible, in what disciplines could one outperform a competitor that is similarily built and trained but with slightly higher fat levels, etc?

I know that athletes often drop fat to lowest possible levels just days before a competition and, once the competition is finished, return to slightly higher levels. Why are they doing this? Are they doing this because this allows them to achieve feats they would otherwise be impossible for them? Or, on the contrary, are they doing this because they wish to fit into a lower weight class and thus face a weaker competition at the cost of hampering their own abilities?

Answer 1

The immediate benefit to having lower bodyfat is you're lighter. Lighter people typically can run faster and longer, jump higher and farther, and corner sharper and easier. This is simply because being lighter requires less energy to move. The same amount of strength and power can push you farther if you're lighter.

Whether or not this is an advantage depends entirely on the sport in question. Some sports they want the exact opposite. For example, linebackers or defensive tackle in Gridiron Football have an advantage at being bigger because they're harder to push around. However, running backs need to be swift and agile so it's to their advantage to be on the leaner side. Non-contact sports like basketball have no advantage at being heavy, but often require the athlete to be agile.

Some sports like MMA or wrestling have weight classes. You benefit from being bigger, but being in heavier weightclasses means your opponent is also bigger. So it may make you more competitive to lose enough body fat to drop to a lower weightclass. Then of course, you build as much muscle as you can hold at that weightclass. So the ultimate goal is to be as heavy as you can be in the weightclass with as much muscle as you can have. This means that people will try to hold really low levels of bodyfat to keep weight.

As you noted this does come at a cost. Most people can not perform at single-digit bodyfat percentages; particularly long-term. They need to diet at extreme measures to keep it and won't have the energy to do the competition. So it becomes this balancing act of keeping the bodyfat percentage you can perform at while staying in the weightclass you want to compete in. It is common for people to struggle keeping a weightclass only to find they are far more competitive if they just gained a little weight.

Some people can perform for a short term at excessively low bodyfat percentages, so they'll train at normal levels and then drop to make weight for their competition. Then once the competition is over, they go right back up so they can resume normal training.