Thursday, July 14, 2011

Gravity, and the Ups and Downs of Weight Training

Being a strong advocate of body weight and free weight training, it seems appropriate to discuss gravity- the force of attraction between matter and the Earth we feel as "weight". Thinking about gravity can help with choosing an exercise program and is central to my ideas on "Functional Strength Training."
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
So much for physics. The next connection is to biology.  Humans have evolved with gravity, and the arrangement of the skeleton shows this. More so than any other form of life, our skeletons hold us vertically oriented. Our bodies adapt, as best they can, by increasing the size and density of muscles and bones used to resist gravity's pull- or decreasing(including osteoporosis) without the stimulus of resisting gravity. Incidentally, our upright, two-legged posture is very energy efficient compared to quadrupeds, which may be faster but lack our ability to run long distances. Bipedalism also allows the hands to do useful things beyond basic locomotion, and requiring the hands and feet to work together is an important part of functional training(Don't Sit Down to exercise.) I will briefly mention that obesity both makes gravity much more problematic and discourages the sort of training discussed here.

Shot putting

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
Given the importance of gravity in training, is it difficult to find ways to do this? No, the opposite is true. First are exercises using just the weight of your body- running, jumping, pushups and pullups are familiar examples. The most next most fundamental type of exercise is simply lifting something heavy. Pick it up, move it around, put it down, repeat. Squats and deadlifts are excellent for building prime mover(the big muscles) strength, and asymmetric or unilateral stances and movements, such as lunges and single leg deadlifts, should be included to emphasize balance and the smaller stabilizing muscles. The wonderfully named Turkish Get Up is the perfect example of an anti-gravity exercise.

Bret demonstrates what not to do
What doesn't work is exercises involving sitting or lying down, or in water. Those types of exercise can be good in some ways, but they don't provide the holistic benefits of training against gravity. Elastic bands, inflatable balls, and machines can't simulate how gravity creates resistance, so free weights are always preferred*. Even when the force is the same at a particular moment, the action is different and the brain and nervous system don't get the same movement training. The fad for trying to exercise on unstable surfaces such as a Bosu is also counter-productive for developing the strength and control for the normal situation of standing on steady ground and moving ourselves and heavy objects. Don't do this unless you live in a bounce house. There is no substitute for weight-bearing exercise.

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.