Biomechanics: what, why, and how to apply it to your exercise routine

I emphasize the importance of biomechanics all the time, but I've never taken the time to define what it means, why it's important, and how to apply it to your exercise. 

Check out my video I created here that teaches biomechanics for fitness instructors.

What is biomechanics?

 

According to dictionary.com, biomechanics means "the study of the mechanical laws relating to the movement or structure of living organisms." 

 

Let's break that down a little, because there are a few key terms within that definition. 

 

Mechanical laws mean the laws of physics (remember Newton's laws from third grade?) that play into movement under different conditions. Each time you lift a weight, certain laws dictate how heavy it feels and how much "stress" will be applied to your system. This is important because it helps to provide a "framework" using mathematics to determine optimal exercise.

 

A second important term from that definition is the "structure of living organisms." To optimize exercise using biomechanics, you want to honor human anatomy, or "structure" as much as possible. It's important to honor the boundaries set by human anatomy.

 

When you go beyond those boundaries, injury can happen. For example, your head cannot turn in 360 degrees. The vertebrae of our cervical spine are not built to do this without severely injuring our spinal cord. 

 

A more subtle (and commonly misinterpreted example) is the relationship between the shoulder and scapula. Our scapula is built to upwardly rotate (move up and out) as we lift our arms above our heads. This allows for space between your acromion process (a portion of your scapula) and your humerus (shoulder bone). However, you'll often hear the cue "press your shoulder blades back and down" in an overhead lift. This violates human "structure," therefore is not optimally using biomechanics and can cause shoulder injuries like impingement syndrome. 

 

Combining the laws of physics with an understanding of joint structure and movement will create exercises that provide the highest rewards (strength) with the lowest risk of injury. 

 

 

 

Why are biomechanics important?

 

Some people refer to "incorrect" biomechanics and "correct" biomechanics to determine the risk of the exercise you're doing. I don't love using "incorrect" and "correct" because there are exceptions to almost everything. Instead, I'll use a more generic "sub-optimal" and "optimal" terminology to describe these exercises. 

 

Sub-optimal biomechanics

 

Sub-optimal exercises are more likely to result in injury. These are exercises that I try to stay away from in my Levo membership but are commonly found in the fitness world. A sub-optimal exercise will violate human structure, present with a higher risk than reward, or mismatch resistance curves and strength curves (explained below). These exercises will place the body at a higher risk of compensations and will not as effectively produce strength results. Some examples of sub-optimal exercises are upright rows, tricep kickbacks, bent over rows, curtsy lunges, many banded exercises, preacher curls, supine pec flies, lateral and front raises, Russian twists, tricep dips, and more. 

 

These are not "evil" exercises by any means! And many people can do these for life and have no problem. I'm just presenting that there are more optimal (i.e., "safer") ways to strengthen the same muscles. However, if you're wondering why your body is in pain after you exercise, it could be because your exercise selection isn't optimal.

 

Not only can an exercise itself be sub-optimal, but the technique or form can be sub-optimal. An example is using too much weight in a bicep curl and compensating by arching your back. Although the exercise selection was optimal for the bicep, the execution was poor.

 

Although form is essential, I find that choosing an optimal exercise over a sub-optimal exercise is more valuable. If a sub-optimal exercise is violating joint structure, you're going to be at a higher risk, despite the perfect form.

 

In other words, exercise selection comes first, form comes next. 

 

Optimal biomechanics 

 

On the other hand, optimal biomechanics uses the laws of physics to challenge a tissue with the least risk of injury. 

 

Another way to frame this is to think about risk vs. reward. A suboptimal exercise will not have a desirable risk vs. reward ratio. I try to choose exercises where the reward is always greater than the risk, and I consider an exercise "sub-optimal" (and therefore use them sparingly) if the risk is equal to the reward, or higher than the reward. 

 

Optimal biomechanics will present with lower risk and higher reward. If you use optimal biomechanics, you will have a lower risk of injuring yourself while providing an optimal environment for strengthening and loading a muscle. 

 

 

How to apply biomechanics

 

I put together a biomechanics basics video for fitness instructors that you can find here.

To apply biomechanics, you have to understand some basics:

 

  1. The structure of the joint you are moving or stressing 
  2. The forces applied to that joint
  3. Strength and resistance curves 

 

Structure: 

 

I can't give you an entire anatomy lesson discussing human structure in detail in one blog post (but fitness professionals MUST know this stuff), but I'll give you some of the basics, starting from the neck and moving down.

 

Neck: 

 

The neck rotates (looks side to side), laterally flexes (side-bends), flexes (looks down), and extends (looks up). There is a more subtle movement of the neck even still, with the skull's ability to move on top of the first vertebrae in the neck. This is called "capital" movement, and usually is a subtle tilt of the chin up or down. 

 

Shoulder: 

 

The glenohumeral joint (what most people consider your "shoulder") is considered a ball-and-socket joint and moves in 360 degrees of motion. The shoulder complex is complicated because it is made up of three bones, your humerus (arm), scapula (shoulder blade), and clavicle (collar bone) that articulate with each other to form a "rhythm." This rhythm is important to understand when you are working the shoulder and is a discussion for another post. 

 

Elbow: 

 

Your elbow is considered a hinge joint, meaning it bends in one direction. It flexes (bends) and extends (straightens). There is also a joint right below your elbow called your humeroradial joint that turns your forearm (pronation and supination). 

 

Wrist/hand:

 

Your wrist moves in four primary directions. Extension (bending back, like in a plank), flexion (bending towards the pit of your elbow), radial deviation (thumb moving closer to your forearm), and ulnar deviation (pinky moving closer to your forearm). 

 

Thoracic spine: 

 

Your thoracic spine is slightly "hunched," called kyphosis, which serves to distribute the forces from the head onto the rest of the spine. Many people try to over-correct this hunch by trying to "stand up straight," causing a military-looking spine. This can adversely affect the spine by throwing it out of its natural kyphotic state.

 

The thoracic spine can extend slightly (backbend), but the spinous processes (boney protrusions) cause a hard "stop." The thoracic spine can also flex (bend forward) and laterally flex (side-bend). The thoracic spine's primary movement is rotation, as the vertebrae are oriented so they can easily rotate one on top of the other without damaging the discs. 

 

Lumbar spine: 

 

The lumbar has the opposite curve as the thoracic spine, more like an "arch," called lordosis. This relationship between the thoracic spine in kyphosis and the lumbar spine in lordosis helps balance the body, properly distributes load, and keeps structures like nerves and discs healthy. Many try to "flatten" the curve in an attempt to correct posture, which is not desirable for the spine. 

 

The lumbar spine's primary role is to flex (bend forward) and extend (bend backward). It also laterally flexes (side-bends). It has little room for rotation, and over-rotating or cranking yourself into a twist (like you will often see in a yoga class) can shear the discs. 

 

Hips: 

 

The hips, like the shoulder joint, are a ball-and-socket joint and can move in 360 degrees. The structure of hips (how your leg bone or femur sits in it's socket or acetabulum) can vary greatly person-to-person. Have you ever seen someone walk with their toes pointing outwards or inwards? This is usually due to their hip structure. Their hips could be structured in a more externally rotated position (toes pointing outwards), or their hips could be structured in a more internally rotated position (toes pointing inwards). 

 

The structure of an individual's hips will change how they should position their bodies in lower extremity exercises like a squat. This is why standard cues like "point your toes straight forward" can be damaging because it could violate an individual's "structure." 

 

Knees: 

 

Your knees flex (bend) and extend (straighten). Because they primarily move forward and backward, they are considered a hinge joint. However, the knees have a TINY bit of rotation capability to lock your knees. But rotational forces through the knees during exercise should be limited for the most part. 

 

Ankles/feet: 

 

There are SO many joints of the ankles/feet. I'll keep it simple. But do not neglect your foot anatomy! It's vital during exercise. 

 

Your ankles plantarflex (point) and dorsiflex (flex). They also supinate (turn out) and pronate (turn in). All of these motions are vital for gait (walking). 

 

Forces:

 

Now that you understand the basics of joint movement, let's get into the optimal way to move and place forces through your joints (i.e., EXERCISE!) 

 

You have a few key pieces to evaluate the optimization of an exercise. 

 

  1. The load (the weight you're using)
  2. The axis (the joint you're moving)
  3. The working muscle (the muscle that's moving the axis)
  4. The line of force (if you're using a weight, the line that travels straight down from that weight)
  5. A moment arm (the distance from that line of force to the axis). 

 

The longer the moment arm, the more force will be applied to the joint. In other words, a longer moment arm will make the exercise feel "harder." 

 

You could probably feel this in a lateral raise for your shoulder. When your elbow is straight, you have a "longer" moment arm at the top of the movement, and the exercise feels "harder." When you bend your elbow, you have a shorter moment arm, and exercise feels "easier."

 

Let look at a picture to visualize what these terms mean in an exercise.

 

 

In this example, the dumbbell is the load. 

 

The axis is the elbow. 

 

The working muscle is the bicep. 

 

The line of force is straight down or perpendicular to the floor. 

 

The moment arm is a perpendicular line drawn starting at the line of force, and going to the axis (the elbow). 

 

 

Strength curves and resistance curves:

 

Each muscle has a strength curve, which means it is the strongest when it is elongated or in the middle range, and weakest when it is shortest. 

 

Each exercise has a resistance curve, which means the moment arm gets longer (the exercise feels harder) and shorter (the exercise feels easier) as you complete it. 

 

An optimal exercise will match the strength curve of the muscle to the resistance curve of the exercise. An optimal exercise will challenge the muscle the most when it is in its middle range of motion, and feel "less" challenging when the muscle is the shortest. You'll feel this in a bicep curl.

 

Picture A

Picture B

In the pictures above, the longest moment arm (most work) is when the muscle is in its middle range (picture A). As you approach the top of the curl (picture B), the moment arm is very small, which means there is not much load into the bicep. You might feel this when you do a curl. It feels the hardest in the middle, and once you get past a certain point, it feels easier to complete the top part of the movement. 

 

A bicep curl could be considered an optimal exercise because the exercise's resistance curve matches the muscle's strength curve. In other words, the exercise feels the "hardest" when the muscle is in its middle range of shortening.

 

You might notice this more strongly if you are doing a sub-optimal exercise like a tricep kickback. The exercise feels easy for most of the motion until you get to the very end, where it feels like you have to use your entire body to straighten your elbow. 

 

 

This is a sub-optimal exercise because the resistance curve is the opposite of the muscle's strength curve. The triceps are not getting loaded in the middle range (where they should be loaded the most), and getting a ton of load at the end, when they are the shortest and least capable of tolerating force. If you flip this exercise on your back and do a skull crusher, you will more optimally strengthen the tricep. 

 

 

In summary, biomechanics are an important tool for any fitness professional or exercise enthusiast to understand. It will help guide you towards results in your training program while minimizing the risk of injury. It is the basis of what I use in my Levo programs to teach people to exercise safely. Once you learn this stuff, you'll never go back! 

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