Angular Motion:
A Lesson in Physics, biomechanics and A Bit Of Ranting
This article may be a little over your head and quite frankly it is a little over mine too but that’s precisely why I’m writing it. Let me explain. I am currently a college student immersed in classes, which require studying… lots of studying. I am a huge advocate for education in every aspect of life and most importantly in the sense of training, more specifically proper training. So, I’m gonna kill two birds with one stone here. I am going to write about some biomechanical principles and apply them to weight training so that you can use them to help your training in various ways. They are rather simple when broken down and are very important for training and everyone could benefit from simply reading. So here we go…
First of all biomechanics are mechanical principles that applied to the biological or, in this case, the human body. For the purpose of this article I am only going to cover the principles concerning motion and the force behind motion, meaning kinematics and kinetics, respectively. Even more specific I am only going to talk about angular kinematics and angular motion with possibly a little linear things mixed in.
Angular motion occurs when an object moves around a fixed point. This fixed point is the axis of rotation of the object. The distance of that this object is away from the axis of rotation is the radius of rotation. Most all of your joints, namely your hinge joints, experience angular motion. Just a side note of anatomy here, hinge joints are just like what they sound like, hinges. The knees and elbows are just a few to name. For example when the elbow flexes the motion of the forearm occurs about an axis, which is located within the elbow joint, the radius. Angular displacement then is the angle between the starting and ending points of this object, while the angular distance is the sum of the angular change that the object exhibited while in motion. You can equate this to the movement at the knee throughout a squat. For all intensive purposes lets say that you begin a squat with your knee locked out as your starting position. After initiation of the squat the angle at the knee joint decreases until you reach the bottom of your squat and then return to the standing position. Since you started and ended in the same position the angular displacement is now 0, while the angular distance is the sum of the angles from the start to finishing position. Since the foot is essentially fixed to the floor during a squat this wouldn’t be a great example for angular speed or velocity. The leg extension or leg curl would be a much better example. You can observe angular speed when you see those crazy guys on the leg extension who look like they are going to take off in flight performing reps so fast. An
gular speed tells us how fast an object is changing angle position but does not give us a direction of this speed. That’s where angular velocity comes in. Angular velocity is gives us the angular displacement divided by the time which in turn gives us a directional quality to the number. So, back to the leg extension. During the concentric contraction and eccentric contractions of this exercise the speed and velocity of the leg are changing. It is important to note that space between the knee and the tip of foot would be the radius of rotation about the knee being the axis of rotation. Dependant on the axis of rotation
While angular motion is much more prevalent and observable in sport, there are some things that are very relevant to weightlifting. Joints also exhibit a thing angular motion likes to call torque. More specifically you can examine the bicep curl. When the biceps brachii contracts it pulls on its insertion, which is across the joint and attached at the radial tuberosity. This causes the movement of the forearm and creates torque about the elbow joint. So hypothetically speaking, someone who has a longer radius and ulna would have more torque about his/her joints because the moment arm would be longer and the biceps would have to work harder to move the segment given it had the same distance of attached as someone with shorter limbs. Torque being the perpendicular distance from the line of force and the axis about which an object is rotating is also responsible for those unnerving and more importantly, preventable injuries that you can get in the gym! Proper form revolves a great deal around torque!
Moment of inertia can also be applied in the weight room. Moment of inertia is the sum of the mass and radius of rotation squared. This is relatively simple to observe in the gym considering usually you pick things up and put things down. With a heavier object there is more moment of inertia when holding it and trying to lift it about an axis such as the elbow or shoulder depending on the lift.
However one thing we want to try to av
oid in the gym is momentum. Good form can eliminate momentum. Good form was discussed in a previous article; however, I will briefly touch on why momentum should be eliminated from lifting as a means to better your training. I’m sure you have all seen the men or women on the bench press who look like there lifting with their back half way off the bench, or the guy doing curls who is swinging so much he could take off into flight. This swinging motion is building up momentum throughout segments in the body and adds them up along the way acting as action forces throughout the body. With the summation of these forces one can probably lift more weight than with good form. However, in lifting to heavy of a weight via momentum you are greatly setting yourself up for injury. Usually to gain momentum the body comes out of alignment of proper form and technique and can be injured. Also, the muscle being worked or joint being used to work a certain muscle be not be able to withstand the summated force along with the weight that is being lifted, once again resulting in injury. So go lighter with proper form and you and your muscles will benefit, I promise.
That’s all for today lesson in physics, biomechanics and ranting.
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