Ape index is the measurement of reach to height disproportion. An average human has a reach (arm span, wingspan), which is roughly equal to the height of the individual, this is proportionate reach and height.
A large ape index signifies a reach which is disproportionately longer than the height. Conversely, a negative ape index means a disproportionately shorter reach for the given height.
But why is it called "ape" index?
That's because the measurement was popularized by the rock-climbing community, where the activity is close to the brachiating apes, who have disproportionately long arms. The concept of comparing reach to height itself is not new.
Ape index can either be expressed as the ratio of reach to height or as the difference between reach and height:
Example: A person with a height of 180 cm and a reach of 187 cm has an ape index of 1.038888888888889 (187 divided by 180) or 7 cm (187 minus 180).
While a unitless ratio is "universal" in nature, the involvement of decimals can make it hard for humans to mentally picture the actual value. Making use of centimeters to express the difference gives a more tangible picture. Use of inches will also result in significant decimals, so it is a good idea to go with centimeters.
So, what is the significance of having a positive ape index? Does it have any impact on performance?
Ape index, just like any other physical attribute, is just an indication of potential not a guarantee of any kind.
A person with a positive ape index will have an unexpected reach — the higher the value, the longer the unexpected reach and vice-versa. That's all there is to ape index.
Imagine you have fought or sparred with regular fighters with the average ±3 cm ape index all your life. From all this experience, you develop a relation about reach with respect to height.
And one day you meet someone with a +33 cm ape index. This person will be able to tag you from distances, which should have been safe from your understanding. This element of confusion is what makes ape index a potential positive factor in the ability to win fights. Whether the fighter is able to make use of this attribute or not, is entirely up to them, just as is the case with other attributes like height, power, speed etc.
What about those with a negative ape index?
Those with a negative ape index may be able to land unexpected effective punches in the closer range.
There may be, but as mentioned earlier, it is not a guarantee but an indication of potential. Let's take a look at some examples from boxing and MMA.
| Athlete | Height | Reach | Ape Index |
|---|---|---|---|
| Sonny Liston | 185 cm | 213 cm | 28 cm |
| Sergei Pavlovich | 191 cm | 213 cm | 22 cm |
| Jon Jones | 193 cm | 215 cm | 22 cm |
| Tommy Fury | 183 cm | 203 cm | 20 cm |
| Edison Miranda | 178 cm | 197 cm | 19 cm |
| Hasim Rahman | 189 cm | 208 cm | 19 cm |
| Lennox Lewis | 196 cm | 213 cm | 17 cm |
| Adonis Stevenson | 180 cm | 196 cm | 16 cm |
| Georges St-Pierre | 178 cm | 193 cm | 15 cm |
| Larry Holmes | 191 cm | 206 cm | 15 cm |
| Terence Crawford | 173 cm | 188 cm | 15 cm |
| Marvin Hagler | 177 cm | 191 cm | 14 cm |
| Conor McGregor | 175 cm | 188 cm | 13 cm |
| Thomas Hearns | 185 cm | 198 cm | 13 cm |
| Emile Griffith | 171 cm | 183 cm | 12 cm |
| Zab Judah | 171 cm | 183 cm | 12 cm |
| Archie Moore | 180 cm | 191 cm | 11 cm |
| Fedor Emelianenko | 183 cm | 193 cm | 10 cm |
| Tyson Fury | 206 cm | 216 cm | 10 cm |
| Deontay Wilder | 201 cm | 211 cm | 10 cm |
| Floyd Mayweather Jr. | 173 cm | 183 cm | 10 cm |
| Jaron Ennis | 178 cm | 188 cm | 10 cm |
| Anderson Silva | 188 cm | 197 cm | 9 cm |
| Sugar Ray Leonard | 179 cm | 188 cm | 9 cm |
| Demetrious Johnson | 160 cm | 168 cm | 8 cm |
| Evander Holyfield | 189 cm | 197 cm | 8 cm |
| George Foreman | 191 cm | 199 cm | 8 cm |
| Michael Spinks | 185 cm | 193 cm | 8 cm |
| Roy Jones Jr. | 180 cm | 188 cm | 8 cm |
| Wladimir Klitschko | 198 cm | 206 cm | 8 cm |
| Muhammad Ali | 191 cm | 198 cm | 7 cm |
| Bernard Hopkins | 185 cm | 191 cm | 6 cm |
| Canelo Álvarez | 173 cm | 179 cm | 6 cm |
| Oscar De La Hoya | 179 cm | 185 cm | 6 cm |
| Naoya Inoue | 165 cm | 171 cm | 6 cm |
| Artur Beterbiev | 180 cm | 185 cm | 5 cm |
| Gervonta Davis | 166 cm | 171 cm | 5 cm |
| James Toney | 178 cm | 183 cm | 5 cm |
| Joe Louis | 188 cm | 193 cm | 5 cm |
| Félix Trinidad | 180 cm | 184 cm | 4 cm |
| Sugar Ray Robinson | 180 cm | 184 cm | 4 cm |
| Román González | 160 cm | 163 cm | 3 cm |
| Mike Tyson | 178 cm | 180 cm | 2 cm |
| Stefan Struve | 213 cm | 215 cm | 2 cm |
| Manny Pacquiao | 168 cm | 170 cm | 2 cm |
| Dmitry Bivol | 183 cm | 183 cm | 0 |
| Gennadiy Golovkin | 179 cm | 178 cm | -1 cm |
| Josh Taylor | 178 cm | 177 cm | -1 cm |
| Naseem Hamed | 164 cm | 163 cm | -1 cm |
| Yuriorkis Gamboa | 166 cm | 165 cm | -1 cm |
| Julio César Chávez | 171 cm | 169 cm | -2 cm |
| Roberto Durán | 170 cm | 168 cm | -2 cm |
| Floyd Patterson | 183 cm | 180 cm | -3 cm |
| Vasiliy Lomachenko | 170 cm | 166 cm | -4 cm |
| Ricky Hatton | 170 cm | 165 cm | -5 cm |
| Rocky Marciano | 179 cm | 173 cm | -6 cm |
| Carl Frampton | 165 cm | 157 cm | -8 cm |
| Artem Lobov | 175 cm | 165 cm | -10 cm |
It can be observed that many of the best boxers and MMA fighters of all time have/had a positive ape index. However, some of them also have/had a negative ape index.
A large ape index, can be a definite success factor in combat sports if one masters how to use it to one's advantage. A negative ape index can not only be overcome with other positive attributes but can also be used to one's advantage.