What Beginners Ought To Know About Biomechanics


What is biomechanics?

Biomechanics is the study of forces and their effects on living systems.

There are two main facets of biomechanics; we’ll get to those momentarily.

"Why should I learn this stuff?"

It boils down to two points.

  1. Biomechanics will take your training to an entirely new level. The subject will give you an understanding of your body that you didn’t have previously. That level of understanding will give you the ability to optimize further your training.
  2. Power. The power to decipher a good exercise from a great one, and perhaps more importantly, what exercises to ignore.

External Forces

Refers to the forces that are acting on the body and their effects on movement. There are many types of external forces including:

Concurrent: when forces do not act along the same line, but act through the same point.

Colinear: forces that have the same line of action.

Friction: a component of contact force, which is a force that is generated when two things make contact with one another.

Internal Forces

Refers to internal forces and their effects on the human body. These include:

Tension: Created when two attachments pull on one another.

Compression: when pushing forces act on the ends of a structure

Shear: a type of stress that pushes in one direction near the top and one direction near the bottom. (You may have heard this word used about the leg extension machine. “Leg extensions apply shear to the knee.” Knee shear being enforced by the leg extension is not true).

For this article, we don’t need to go too deep into the concepts of internal and external forces.

"What do I NEED to know?"

Three things.

Line of Resistance (LoR)

Refers to the direction of the resistance. A good rule of thumb is; if it’s a free weight exercise, then the resistance is coming from straight down (because of gravity). If you are doing a cable exercise, the LoR is the cable.

LoR is important because it gives us a far deeper insight into the effectiveness of an exercise. Also, remember that muscles pull in the direction of their fibers. A proper exercise will accomplish three things,

  • Place the target muscle opposite the line of resistance.
  • Put the line of resistance in the same direction as the muscle fibers that your are trying to train.
  • Take the muscle through it’s entire functional range of motion (or most of it).

Moment Arm

The distance between the line of resistance and an imaginary line that goes through the axis of rotation.


Torque refers to the turning effect produced by a force. Anytime a force is exerted on your body; the joints being recruited will generate torque.

On any given exercise, torque will change throughout the range of motion because the moment arm changes as you complete the lifting and lowering portions of the exercise.

A 90-degree angle between the line of resistance and the parallel line going through the axis of rotation will ALWAYS be the most difficult part of a movement because that is where the moment arm will be the longest and also where torque will be the greatest.

The further away from a 90-degree angle, the easier the movement is.

"How do I apply biomechanics to my training?"

In a few ways.

The best way to apply biomechanics to bodybuilding is using it as a tool for assessing the merits of an exercise.

You can accomplish this by examining the line of resistance of the exercise and the direction of the muscle fibers of the muscle that you want to train.

For example, based on the orientation of the pec fibers, a decline bench press or pec fly is better than a flat or incline bench press (you would still need an incline press for the uppermost fibers). A decline angle being superior is also backed up by research.

Also, based on a wealth of research, we know that exercise variation is critical when it comes to muscle building. Exercise variation being imperative is because of many complicated reasons that I will not get into here (I’m going to write a monster post on this soon).

In theory, the reason exercise variation is so important is because of torque. As I said, torque varies throughout a movement. As torque varies, so too does the amount of stress on a muscle, and the region of tissue under stress.

The line of resistance and the moment arm dictate torque.

The logical way to apply this information is to work a muscle through its proper range of motion with varying lines of resistance. The point of greatest torque will change based on the line of resistance, so changing the line of resistance, even slightly, will place stress on a different portion of a muscle.

Region-specific hypertrophy is a very real thing. The problem is, we don’t know exactly how to apply this phenomenon to training yet. Varying the line of resistance is about as close as we can get to having some control over region specific hypertrophy.


  • Antonio, J. (2000). Nonuniform response of skeletal muscle to heavy resistance training: Can bodybuilders induce regional muscle hypertrophy? The Journal of Strength & Conditioning Research, 14(1), 102-113. Retrieved from Google Scholar.
  • Lauver, J. D., Cayot, T. E., & Scheuermann, B. W. (2015). Influence of bench angle on upper extremity muscular activation during bench press exercise. European journal of sport science, (ahead-of-print), 1-8.
  • McGinnis, Peter Merton. Biomechanics of Sport and Exercise. Champaign, IL: Human Kinetics, 2013. Print.
  • Trebs, A. A., Brandenburg, J. P., & Pitney, W. A. (2010). An electromyography analysis of 3 muscles surrounding the shoulder joint during the performance of a chest press exercise at several angles. The Journal of Strength & Conditioning Research, 24(7), 1925-1930