|A plumb bob points down|
Gravity pulls all matter toward the center of the Earth, defining the direction "down", and vertical is either down or the opposite, "up". (My engineering background is coming out in this post.) Gravity pulls our bodies down our entire lives, and all our stuff. If you want to move your body, and if you want to move your stuff, dealing with gravity is required.
At the same time that everything is being pulled down, the floor, bench, or pull-up bar supporting you is pushing up with, as we say, an equal and opposite reaction, assuming there's no acceleration. (Acceleration means that something is moving and the rate of movement is changing.) Your feet press on the floor, and the floor presses up with equal force. If you jump, there is momentarily no ground force and the Earth accelerates you down at 1 "G". At the moment of impact when you hit the ground there is a very rapid deceleration(decrease in rate of movement) and correspondingly higher force from the ground pushing up. Landing on a rubber mat feels softer than concrete because the mat compresses more when you land, so the deceleration takes longer and the impact force is lower. Good exercise accounts for these properties of the natural world.
|Hands and feet teamwork|
In sports, typically athletes are on their feet and dynamically moving their own bodies, often plus some implement, eg. a ball. The more capable the athlete is at balancing and overcoming gravity the better his or her performance will be.
An important fitness consideration is injury prevention. Falls are a common source of injury and are what happens when we lose control of our bodies and gravity suddenly pulls us down to the Earth. Also people are often hurt while moving an unusually heavy object, especially in an awkward position, such as reaching into the backseat of a car. Training with weights in stability challenging positions or movements develops the strength and neuromuscular control needed to prevent harmful falls and strains. One helpful exercise is doing walking lunges while shifting a weight from side to side, another is doing single leg deadlifts(sldl video).
The implication of all this is that improving our ability to manage gravity is essential to life in the physical world. How well we cope, or excel, with the effects of gravity is a major indicator of both fitness and athletic performance.
|Turkish Get Up with kettlebell|
|Bret demonstrates what not to do|
So, get on your feet and pick up something heavy!
*Back to physics: The force of gravity is expressed as F=ma, ie. weight equals mass times the acceleration of gravity. Bands and springs are F=kx, ie force equals the spring constant times the change of length of the spring. Gravity is always pulling down, bands and springs pull toward the attachment point. Machines vary, but are generally unnatural in how the resistance acts on your body.