Do You Know Your Ape Index?

This article originally appeared on Triathlete

Swimming is full of a variety of complicated concepts like SWOLF (number of strokes + swim time), stroke rate and length, kick beats, breathing patterns, and Ape Index. That last one you might not have heard of before...

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What is Ape Index?

Ape index is a term taken from rock climbing and refers to your height to wingspan ratio. First, measure your wingspan, from outstretched fingertip to fingertip. Then, divide by your height. A typical ratio is about one, with a higher number meaning your arms and wingspan are longer. An alternative way to measure Ape Index is to subtract your height from your wingspan to get a positive, neutral, or negative value. In this case, if the number is zero, your height is about equal to your wingspan.

Let's compare two swimming phenoms and their Ape Index. Michael Phelps has a wingspan of 6'6" (198 cm) and a height of 6'4" (193 cm); 198/193 = 1.025 or 198-193 = 5 (depending on which version of Ape Index you use). On the other hand, Caleb Dressel has a shorter wingspan of 6'4" (193 cm), but is almost the same height as Phelps at 6'3" (191 cm). His Ape Index is 1.01 or 2, depending on method of calculation.

What does this mean for you, as a swimmer? Studies have found higher Ape Indexes in elite swimmers, climbers, NBA players, and even soccer goalies--all activities where a bigger wingspan is likely beneficial. When it comes to swimming, it's certainly advantageous to have long, Phelps-like arms to propel yourself through the water, but it's not necessarily a requirement in order to be an efficient swimmer. Some swimmers have shorter arms and a higher cadence, while others have longer and smoother strokes. The Ape Index is simply a tool to help you learn more about your swimming mechanics.

How to use your Ape Index

If you have a negative Ape Index, meaning your arms are shorter than your height, you won't travel as far in the water with each stroke as someone with a positive index, simply because your reach is shorter. Instead, those with a negative index might have to adopt a faster turnover (or stroke rate).

While a swimmer with longer arms is able to cover more distance per stroke, the force being placed on the shoulder will be greater, so those with a positive index should pay attention to shoulder strength and mobility.

The Ape Index might also help determine if a swimmer has a more hip-driven or shoulder-driven stroke, said Wendy Mader, a former competitive distance swimmer and triathlon coach with T2 Coaching. It could affect aspects like how deep a swimmer's catch sits in the water, as well as extension in the front and back of the stroke.

"There are four main phases of the stroke: recovery, hand entry, catch, and the push that makes up the pull. Based on a swimmer's limiters, we try a variety of drills and techniques to see what provides them with the technique to swim faster with less effort."

"Swimming is a technique sport. Once you develop the technique, you build strength, and then increase arm speed to swim faster. Ape Index doesn't seem to impact arm strength and arm speed with the correct technique." The key here is correct technique.

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Brian Botzman, head coach and owner of the Unified Aquatics Club, provides a few form errors to look out for when considering your Ape Index. "For a positive [or higher] Ape Index, look for entering the water too close to the head or exiting the water before the hips. For a negative Ape Index, make sure a swimmer isn't entering the water flat."

Because men tend to have longer arms, relative to their height, than women, Botzman does see a difference in tempo, or stroke rate, among the sexes. "In general, males go a little slower in stroke per minute; but, for me, a lot of it is also about mobility. Swimmers who don't have a lot of mobility may need to swim at a higher frequency."

RELATED: What is the Ideal Stroke Rate?

"Some triathletes come from a swimming background with natural water awareness, but others come from sports like running, where shoulder mobility isn't very important."

Botzman says swimmers with a higher Ape Index might focus on a stroke rate closer to the mid-40s per minute, while someone with a negative index might try the mid-50s. But, finding the right stroke rate for your swim style is a process.

Botzman likes using a tempo trainer, which can be set to beep at an ideal rate and tucked under your swim cap. Then, test different stroke rates to see which is most efficient and fastest for you. You can't change your Ape Index, but you can use the information to be the best swimmer you can be.

Fun Fact: In addition to the Ape Index, there's also something called the Hobbit Index--ratio of hand and foot length--and Sloth Index--difference between leg length and arm length. But we haven't discovered how those relate to triathlon...yet.

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