Short vs Tall

Some of my first training experience was helping my friend Chris to jump higher. Over two years of training (with some breaks) he made great progress. He went from squatting 185 pounds poorly to squatting 285 well. He started out hang power cleaning less than 100 pounds. He eventually hang power snatched 150 pounds. His 2-foot vertical with an approach went from 28 inches to 40 inches. During all that training progress, his weight went from 130 pounds to 135. Looking at Chris's strength to body weight and power to body weight ratios, he squatted over 2.1 times his body weight and hang power snatched over 1.1 times his body weight. While he was achieving those great numbers, something occurred to me. When my vertical jump peaked at 44 inches, my max squat was just above 1.6-1.7 times BW, and my hang power snatch was around 0.9 times BW. My relative strength and power was significantly less than Chris's, but my vertical reached 4 inches higher. How? We had no meaningful difference in flexibility, and there was no indication that I had better explosive or elastic ability. And the relative strength and power difference was significant. This confused me for a while.

After some thought, I realized the reason for the discrepancy is very simple; I'm 9 inches taller than Chris. Allow me to give an explanation. Consider the physics of leverage. The further a force is from the point of rotation, the more torque it has to rotate that lever. On a teeter-totter, if your friend sits further from the middle, he or she is harder to lift. You're probably familiar with that principle. Now a training movement like a squat or a snatch is really a set of coordinated movements of body segments (foot, lower leg, upper leg, etc). Body segments can be thought of as levers that move by rotating at the joints. Since a taller athlete has longer body segments, more torque is required to drive those rotations. Also, the summation of those rotations results in a larger distance being covered. When I do a squat or a snatch, the bar moves farther than when Chris does a squat or a snatch. Given that, if we both squat the same weight in the same amount of time, I use more torque and generate more velocity and more power. If that's hard to agree with, use a more extreme difference in height; imagine a 100-foot giant standing next to a tall building and doing a squat. Even if he takes three seconds to get from the bottom to the top (a pretty slow squat) the bar will be flying past a few stories per second. Obviously the bar is moving faster than when a normal size human squats it, and more power is being demonstrated.

What I'm getting at here is a difficult concept to describe. Basically, the squat indicates that an athlete can complete a set of body segment rotations against a certain amount of resistance. The snatch requires that a set of rotations is completed against certain amount of resistance AND with a certain velocity. If two athletes are the same weight, squat the same weight, and snatch the same weight, it will translate into those two athletes being able to complete the body segment rotations of the vertical jump movement in a very similar amount of time. The speed of their rotations (for those who know physics, the angular velocity at the joints) is what will likely be the same. However, if one of those athletes is taller, more distance will be covered during those rotations, meaning that the velocity of the center of mass at the end of the movement will be greater. If you have any knowledge of projectiles, you know that an object's velocity at takeoff is what determines the height of the flight. The faster an object leaves the ground, the higher it flies, because it takes longer for gravity to slow it to a stop and bring it back. So picture a 7-foot man and a 5-foot man standing up straight next to each other. At exactly the same time they begin a vertical jump movement. Their movements are identical, and they complete it in the exact same amount of time. During that fraction of a second, the 7-foot man's center of mass covers a greater distance than the 5-foot man's. Since it traveled further in the same amount of time, it has more velocity at the end of the movement. Thus, the 7-foot man will jump higher than the 5-foot man, even though the rotations of their body segments were identical in speed.

To sum up my explanation, first understand that relative strength and power influences the speed at which body segments can be rotated. Then understand that the same speed of rotations generates higher velocity of the center of mass if the body segments are longer. Then understand that the velocity of the center of mass is what determines the height of a jump or the speed of a sprint.

Given those facts, shorter athletes will generally need to have greater strength-to-weight and power-to-weight ratios in order to jump the same height or run the same speed as a taller athlete. Chris and I serve as an example of that. Relative strength and power do serve as a great indicator of athletic ability, but it would be more accurate to use them to indicate athletic ability relative to body size. For example, if you can squat 2 x body weight and snatch 1.2 x body weight, maybe you should be able to jump 60% of your height.

Now the glaring question here is, "If tall people don't need the same relative strength and power, why are the tallest athletes usually not the most athletic?" The answer is that height also plays a large role in how easy it is for someone to get strong. Tall athletes usually have a very hard time reaching high relative strength levels. Trying to explain that is a topic for another article. Just know that it's true; you'll be hard pressed to find a 6'10" guy who can squat twice his body weight.

So there are two factors at play here, how easy it is for a person to get strong and how much strength and power a person needs to achieve great speed and jumping ability. Both are affected by height. The best combination of those two factors seems to occur in the 5'9" to 6'1" range. If you look at world class sprinters and long jumpers, and the people with 50-inch vertical jumps, a large percentage of them fall in that range. Height is obviously only one factor affecting how easy it is to get strong, and relative strength and power are certainly not the only factors that determine athleticism. Thus, we have the 6'5" Usain Bolt dominating the sprinting world. But generally, the best sprinters and jumpers are not that tall.

The main point I want to get across with this article is that shorter athletes need greater relative strength and power than taller athletes to achieve the same sprint speed or vertical jump.