Monkey arms

TL:DR

  • Ape index = arm span to height ratio
  • Ape index > 1 = advantage when reach is important (eg. swimming and boxing)
  • Ape index < 1 = advantage when shorter levers allow more torque to be generated for the same amount of force (eg. gymnastic movements such as the iron cross and ring events)

Check your Ape Index here.

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What is the Ape index?

Ape index is the ratio of your arm span to your height. According to Vitruvius, the ideal man will have a ratio of 1. (i.e. Arm spam = height)

3. Just so the parts of Temples should correspond with each other, and with the whole. The navel is naturally placed in the centre of the human body, and, if in a man lying with his face upward, and his hands and feet extended, from his navel as the centre, a circle be described, it will touch his fingers and toes. It is not alone by a circle, that the human body is thus circumscribed, as may be seen by placing it within a square. For measuring from the feet to the crown of the head, and then across the arms fully extended, we find the latter measure equal to the former; so that lines at right angles to each other, enclosing the figure, will form a square

Significance of Ape Index
Having a longer reach makes it easier for basketball players to make and block shots.

A longer reach is an advantage when it comes to the deadlift. As it reduces the range of motion required to get to lockout position

There have been some evidence that faster swimmers have higher ape indexes. The theory is that the longer reach allows them to displace higher volumes of water per stroke.

High ape indexes are also correlated with better performance in other sports such as: baseball, MMA and rock climbing.

But having a high ape index might be a disadvantage for certain sports.

A high ape index increases the distance the weight needs to travel during the bench press.

Since a high ape index equates to longer levers, certain gymnastic moves will require more effort as the arm span increases.

Moment = force multiplied by perpendicular distance between force and pivot arm.

As arm span increases, the perpendicular distance increases, producing a greater moment.

For example the iron cross.  The gymnast needs to generate enough force to overcome the moment experienced at his shoulders.

In the diagram below, the distance X is the  “sleeve length“. A longer arm span means a longer sleeve length.

Assuming the weight is evenly distributed between both arms:
Moment at shoulders (force gymnast needs to overcome) = Weight/2 * X * 2 (because 2 arms)
So for two gymnasts at the same weight (60kg = 588N)  and height but different ape indexes:
X = 1m  – Force required to maintain iron cross = 588Nm
X= 0.8m – Force required to maintain iron cross = 470.4Nm

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Hence high ape indexes are disadvantageous for ring events. As the longer limb gymnast needs to exert more effort to execute the same move.

But, a longer lever will be useful  for bar events. Because it will help the gymnast to produce greater momentum with less effort.

 

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