Ape index, or ape factor, or gorilla index is a measure of the ratio of an individual's arm span relative to their height. A typical ratio is 1, as identified by the Roman

Ancient Rome

Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 writer, architect and engineer Vitruvius

Vitruvius

Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....

 prior to 15 BC. Vitruvius noted that a "well made man" has an arm span equal to his or her height, as exemplified in Leonardo da Vinci's

Leonardo da Vinci

Leonardo di ser Piero da Vinci was an Italian Renaissance polymath: painter, sculptor, architect, musician, scientist, mathematician, engineer, inventor, anatomist, geologist, cartographer, botanist and writer whose genius, perhaps more than that of any other figure, epitomized the Renaissance...

 drawing, the "Vitruvian Man

Vitruvian Man

The Vitruvian Man is a world-renowned drawing created by Leonardo da Vinci circa 1487. It is accompanied by notes based on the work of the famed architect, Vitruvius. The drawing, which is in pen and ink on paper, depicts a male figure in two superimposed positions with his arms and legs apart and...

". In rock climbing

Rock climbing

Rock climbing also lightly called 'The Gravity Game', is a sport in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a pre-defined route without falling...

 it is believed that a positive Ape Index, (a value greater than 1), where the arm span is greater than the height, provides for a competitive advantage, and some climbers have expressed the belief that exercise can result in an improved ratio.

Computation

The ape index is usually defined as the ratio of arm span to height. However, an alternative approach is height subtracted from arm span with the result being positive, 0 or negative. Unlike the unitless ratio, this calculation produces a numeric value in the units of measurement used to represent the height and arm span.

Statistical significance in rock climbing

Multiple studies have been conducted into the effect of physiological factors, such as anthropometry

Anthropometry

Anthropometry refers to the measurement of the human individual...

 and flexibility

Flexibility (anatomy)

Flexibility or limberness refers to the absolute range of movement in a joint or series of joints, and length in muscles that cross the joints. Flexibility is variable between individuals, particularly in terms of differences in muscle length of multi-joint muscles...

, in determining rock climbing ability. A number of these have included the Ape Index as one of the variables. However, the results have been mixed.

One study found that "untrainable" physical factors, including the Ape Index, were not necessarily predictors of climbing ability, (although they did note the significance of grip strength and percentage of body fat), in spite of a general tendency identified in previous studies for elite athletes in the sport to share these characteristics. This was supported by a later study that also found that the Ape Index was not statistically relevant. However, the authors of this second study noted that the findings may have been due to the low variability in the index between the climbers, who all had significantly higher Ape Indexes than those found in the control group. Thus they left open the possibility that the Ape Index may be more significant when there is a greater degree of equivalence between the other traits under consideration.

Countering these studies are other works that have identified the Ape Index as a significant (or potentially significant) factor. A 2001 study comparing teenage male and female rock climbers noted that performance differences between the genders could be explained by a number of factors, one of which was the lower Ape Index found in the female climbers. Similarly, in a later work it was found that the Ape Index was statistically significant, and thus determined that it was one of a number of variables that provided the highest diagnostic value in the prediction of climbing performance.

Other sports

It has been noted that swimmers tend to have longer arms in relation to their body size, perhaps because longer arms provide a stronger means of propulsion and a shorter trunk (or torso) reduces drag in the water. A notable example is Michael Phelps

Michael Phelps

Michael Fred Phelps is an American swimmer who has, overall, won 16 Olympic medals—six gold and two bronze at Athens in 2004, and eight gold at Beijing in 2008, becoming the most successful athlete at both of these Olympic Games editions...

 whose arm span is 3 inches greater than his height, affording him an index of 1.04.

Small ape indexes can also be beneficial, for instance in weightlifting

Powerlifting

Powerlifting is a strength sport. It resembles the sport of Olympic weightlifting, as both disciplines involve lifting weights in three attempts. Powerlifting evolved from a sport known as 'odd lifts' which followed the same three attempt format but used a wide variety of events akin to Strongman...

as shorter arms mean that the weights do not have to be raised so high compared to someone with longer arms and a bigger index. As a result the smaller indexed lifter does less work, and finds the task easier.