Why Does a Belly Flop Hurt (And Can It Seriously Injure You)?

This article will explore a timeless question of “Why does a belly flop hurt?”

When thinking of traditional pool parties involving kids, it’s hard not to think of diving competitions.  Participants in the competition continue to try and one-up each other with each dive, risking more and more with each attempt.  

There are traditional tricks off the diving board such as:

• Swan-Dive: High arching with arms outspread until tucking them right before entering water.
• High-Rotation Twists: Momentum and torque are used to achieve as many rotations as possible.
• Front-Flip: Forward horizontal rotation of at least 360°
• Back-Flip: Backward horizontal rotation of at least 360°
• Pencil Dive: Straight posture that leads down into the water feet first
• Cannon Ball: Knees are tucked to obtain as sphere-like shape as possible in order to create the largest splash possible.  

But, the most infamous jeer-inducing “dive” is always the belly flop!  As most know, a belly flop is when the diver hits the water flat on their stomach.  

Sometimes the belly flop may be an intentional choice to propel the diver into the center of attention.  Other times it may be accidental when the planned dive goes awry.  Regardless, even the toughest on-lookers wince with sympathy as they hear the smack of skin on the water.    

The after-effects of the belly flop are often a combination of stinging skin along with a bruised ego.  While most victims of the belly flop overcome the physical pain shortly, their story may live on for years to follow.

The belly flop’s cousin –the back flop– is a lesser acclaimed dive that often results from a miscalculated front-flip attempt, but results in a similar sting of the skin.

Why Does a Belly Flop Hurt?

Physics can be blamed for the pain involved with belly flops.  Without getting into complex calculations, there are three key factors as to why belly flops hurt:

Diver Surface Area

During a belly flop, the total surface area of the diver is met with a larger force of resistance from the water than a standard dive.  Surprisingly, water does not compress much in which the impact can often feel like smacking against a hard surface.  

In contrast, when performing a swan-dive, the smaller surface area of the hands breaks the resistance of the water.  Once the hands enter the water, the path for the rest of the body is paved to enter with little resistance.  Similar concept applies to other traditional tricks off the board where head, hands, or feet are the entry points to break the resistance.

Dive Height

A key factor that determines the extent of pain during a belly flop is also the height of the dive.  As you may expect, lower height will have less force (less pain) at impact than a higher height.  This is because the height of the dive determines the velocity at impact.  

Here is a simple table that provides an overview of velocity of impact at various heights:

Based on the calculated velocities in the table, standard height residential diving boards could result in an impact velocity of approximately 10 mph.  Whereas, a jump from a 10m (33 ft) Olympic high-dive board could result in an impact velocity in excess of 30+ mph.

Since water does not compress much, the water must instead be moved out of the way as the diver enters the water.  The higher the speed that the diver enters the water, the less time there is for water to be moved out of the way.  This means that the diver’s body must absorb more force when diving from a height of 30 feet versus 5 feet.

You can simulate a belly flop in a rather harmless way by smacking the water with your hand.  With enough force, the water should feel similar to concrete for a passing moment as your hand breaks the resistance.

There are many different factors that can be used to estimate the true force of impact.  If more information is desired, calculations can be found over here.

Water Surface

An additional factor that can affect the amount of pain during a belly flop is the state of the water.  Very calm water maintains normal surface tension that must be broken by the diver during impact. 

Frothy or foamy water has surface resistance already broken by lots of bubbles, which helps reduce force of impact. High dive facilities often use systems that create a large quantity of bubbles to cushion the diver’s impact for safety purposes.

Can Belly Flops Cause Serious Injury?

At standard diving heights, belly flops often result in the brief moment of stinging pain that fades before climbing out of the water.  However, when jumping from taller heights, risk of more traumatic injury increases due to the impact velocity.

For example, a belly flop when cliff diving at a high elevation could pose serious risk of injury.  Injuries may include bruising, lacerations, organ damage, and fractures.  Deep abdominal trauma coupled with internal bleeding is a risk depending on the impact velocity.

Concussions are also a potential risk depending on the position in which the head hits the water.  Tucking the chin prior to impact and covering head with hands are means to reduce head injury

At extreme heights, injuries from diving are not limited to just belly flops and may also occur with other styles.  However, the nature of the belly flop does place the diver into a more vulnerable position due to the amount of internal organs being subjected to the high impact.

Death Dive

Although the belly flop is not intentionally performed in professional competitions, an amateur competition known as Death Diving has been built around it.  The competition is based in Norway, with contestants diving from an Olympic height diving board of 10 meters.

During the competition, belly flop position is held until the very last moment where the diver then enters the fetal position to help avoid direct impact on the stomach.  As one might expect, the competition results in opportunities for many belly flops.

Due to the high force of impact during the belly flops, it is not uncommon for some divers to exit the water with bloodied stomachs or other injuries.

Final Takeaway

In most cases, belly flops result in nothing more than a brief stinging sensation along with some potential embarrassment. 

Diving height is a significant factor that may ultimately determine the intensity of pain along with the level of risk of significant injury.  However, under typical circumstances long-term injuries are uncommon for the average belly flopper.

In the event that you find yourself mid-jump in a belly flop position, a quick reflex of using your hands or knees to break the water may help avoid the typical wrath of a belly flop.

Now that you know why belly flops hurt, you may be interested in knowing whether there’s much risk of being struck by lightning in a pool!

Happy (and safe) diving!