Evlo Fitness/Education/Body Composition/Biomechanics, anatomy, and physiology: the trifecta for results
Dr. Payton Busker, PT, DPT
Dark Mode

Biomechanics, anatomy, and physiology: the trifecta for results

Last week we talked all about working smarter, not harder in your workouts. Building on this topic, let’s focus on how we can work with your anatomy and physiology instead of against it using biomechanics and recovery.

How to use biomechanics and anatomy to effectively load your muscles while avoiding wear-and-tear to the joints

How physics plays a significant role in exercise

If you thought you could leave physics back in high school, think again. Physics plays a vital role in fitness. We can use it to our advantage when it comes to both loading the muscles and protecting the joints.


Each muscle has a primary lever within the body that affects the load placed through the muscle. Just as in your physics textbooks, the levers of the body magnify the mechanical load. In the case of the body, the levers are bones and the mechanical load comes from external loads like dumbbells, bands, etc. and/or gravity. 

Simply put: the longer the lever, the more magnification of the load.

Levers can be both active and neutral. A lever is neutral when it is completely parallel to the direction of force. A lever becomes active when it is between perpendicular and parallel with the direction of force. 

Lever example: 

Muscle: Biceps 

Lever: Radius (larger forearm bone) 

Exercise: Bicep curl

90’ of elbow flexion: active lever because radius is directly perpendicular to the direction of force (gravity through the dumbbell you’re holding). 

Top of the bicep curl (weight in front of shoulder): neutral lever because radius is parallel to direction of force.

Phase loading and resistance curves

The biomechanical principles of phase loading and resistance curves are crucial for safely and effectively targeting the muscles. 

Each exercise has a specific resistance curve. In his book, The Physics of Resistance Exercise, Doug Brignole describes resistance curves as “the variations of resistance that occur between zero and maximum, as the operating lever of a target muscle moves through the arc, which produces angles between parallel and perpendicular with the direction of resistance”. 

Let’s take the bicep curl example from above. Based on its resistance curve, the resistance to the biceps is the greatest with the elbow at 90’ of flexion because the lever is perfectly perpendicular to the direction of force. The resistance is the least (nearly zero) at the top range of the motion as the lever is nearly parallel with that line of force. If you think about it, you could probably hold the motion at its top range all day. But maintaining that 90’ position would be fairly difficult to maintain when loaded with a dumbbell!

Phase loading marries the anatomy of a muscle with the resistance curve of the exercise. There are 3 different types of phase loading: early, middle, and late. 

Early phase loading occurs when the heaviest part of the resistance curve for an exercise happens when the muscle is in a lengthened position. This is extremely advantageous as muscles have a greater ability to produce force from a lengthened state as compared to a shortened state. 

Late phase loading is the opposite. The resistance is the heaviest when the muscle is in a shortened position and the muscle has decreased firing capabilities. 

Middle phase loading is right in between.

Here at Evlo, we primarily focus on early and middle phase loaded exercises and sprinkle in late phase loaded exercises to set ourselves up for the best environment for muscle hypertrophy. 

Examples of early phase loaded exercises: 

Bicep curls, step ups, skull crushers, sissy squats, side lying shoulder abduction 

Examples of late phase loaded exercises:

Bridges, hip thrusts, tricep kickbacks, standing lateral raises

Opposite Position Loading

Muscles are most effectively loaded when the resistance is in the opposite direction of the pull of the muscle. This concept is called opposite position loading. The direction of pull of the muscle can be visualized as a line from the insertion of a muscle to its origin.

Let’s head back to our bicep curl example.

Bicep curls perfectly opposite position load the muscle, but only when performed in an upright position (think standing, kneeling, seated). In an upright position, the resistance from the dumbbell, as it is lifted through its arc of motion, is directly perpendicular to the line of pull from the biceps muscle (radius to humerus).

If you were to try performing a bicep curl lying on your side, opposite position loading to the biceps would no longer be present. Instead, you’d be opposite position loading the external rotators of the rotator cuff.

Ground reaction force

Newton’s third law states that for every action there is an equal and opposite reaction. And we utilize this physics principle in each and every class by manipulating the ground reaction force. 

The ground reaction force is the equal and opposite reaction produced by placing pressure into the ground (the action) with your feet, hands, knees, etc. This force creates a moment arm to the muscles and can drastically change which muscle is being loaded by an exercise.

Try this out for yourself: 

Go up into a bridge pose.

Press your feet down and out away from your body without actually moving them. As if you were going to straighten your legs. Notice the quads light up.

Next, press your feet straight down into the mat. Notice the glutes fire up.

Lastly, energetically pull your heels back towards your glutes without actually moving your feet. Notice the hamstrings engage. 

This experiment is the ground reaction force at work.

External support

External support primarily comes into play with single leg exercises. When you take one foot off of the ground, your body naturally seeks to find a new center of gravity. 

This manifests itself as standing leg foot pronation, knee valgus, hip adduction, and spine side bending. It does not automatically signify muscle group weakness. 

To counter these adaptations before loading your body with external load, we recommend incorporating some form of external support.  

Here’s how it looks with a left leg step up for the glutes:

Place your left foot to your chair or step. Option to hold a weight in the left hand. Place your right hand firmly into the wall.

The right hand into the wall takes out the lateral forces through the left knee, a hinge joint that prefers to go forward and backward. It also removes the natural inclination to laterally flex at the spine. Both of these adjustments allow for more effective forces through the working glutes.

Compound vs. simple exercises: which is better?

We never want to say that an exercise is wrong or bad. However, we select exercises with a biomechanical lens as described above. 

Compound exercises like squats and overhead presses have become “gold standard” exercises incorporated into different programs and routines. Oftentimes, this is because they target many muscle groups at once. 

However, when you analyze exercises utilizing biomechanics and anatomy, you realize that working multiple muscle groups at once does not mean you are accurately loading all of those muscle groups. 

In most cases, compound exercises underwork some muscles while overloading others as well as surrounding connective tissue. This is because each muscle has a unique lever, as explained above, that impacts the load to a muscle. Let’s look at some calculation examples!

Squat vs. step up for glutes

Although squats have been highly regarded as an excellent glute builder, step ups actually place more mechanical load through the glutes. 

Body weight squat: 

Resistance= 60 lbs (approximate upper body weight) 

Moment arm= ~18 inches (distance from the line of resistance to the hip-glute axis) 

60 lbs X 18 inches= 1,080/2 (for each leg)= 540 lbs*in

Body weight step ups:

Resistance= 90 lbs (approximate body weight minus the standing leg) 

Moment arm= ~18 inches 90 lbs X 18 inches= 1,620 lbs*in

Squat vs. sissy squat for quads

Sissy squats intentionally load the quads significantly by keeping the lever in mind. The tibia (lower leg bone) is the lever for the quads. As you go into the sissy squat, the lever becomes more and more active as the tibia shifts over the toes and closer to parallel with the ground. The quad is also lengthening making this an early phase loaded exercise! Let’s compare calculations. 

Body weight squat: 

Resistance= 60 lbs (approximate upper body weight) 

Moment arm= ~3 inches (moment arm to the knee- quad axis) 

60 lbs X 3 inches= 180 lbs*in

Body weight sissy squat:

Resistance= 60 lbs (approximate upper body weight) 

Moment arm= ~10 inches (moment arm to the knee)60 lbs X 10 inches= 600 lbs*in


Let’s put this philosophy into action with our 14-day free trial.


Why you should work with the physiology of your nervous system. And how to do it.

While utilizing biomechanics and your anatomy for effective exercise selection is important, it is only half of the equation. Equally as important to your results is recovery.

Divisions of your autonomic nervous system

The autonomic nervous system is responsible for both your flight/fight/freeze functions as well as your rest/digest/recover functions. It is made up of two divisions: sympathetic and parasympathetic.

Sympathetic Nervous System

The sympathetic nervous system (SNS) is responsible for those fight, flight, and freeze responses. I would argue that this is the state we are most familiar with as a society. Being in a sympathetic state is not inherently a bad thing. We want this system to kick in at times. For example, when we are in danger and need to get away.

This system also naturally engages whenever we exercise. We can help ourselves “ramp up” into a sympathetic state prior to exercise through breath work. During your warm up, focus on elongating and deepening your inhale while shortening your exhale. Allow yourself to ease into sympathetic drive as you prepare to exercise.
The issue arises when we stay in a constant sympathetic state. In order to recover from our exercises and grow muscle, we need to be able to shift into the parasympathetic nervous system.

Parasympathetic Nervous System

The parasympathetic nervous system (PNS) leads our rest, digestion, and recovery. It plays a crucial role in recovery from exercise. And we can use diaphragmatic breathing to guide us into this relaxed state. 

After your workouts (or anytime you are feeling overstimulated), practice this breathing technique:

  1. Stack your rib cage over your pelvis (no arched or rounded backs)
  2. Inhale for a count of 4 seconds through your nose as you expand your rib cage in 360’ degrees
  3. Exhale for a count of 6 seconds through pursed lips (as if you were breathing through a straw) until all of the air is released
  4. Repeat 5-10 times.  

This elongated and pursed-lipped exhale will allow you to tap into the PNS almost on demand. The more you practice it, the easier it becomes. This anabolic state allows you to build your muscles back up after intentionally targeting them with exercise. 

Don’t skip your cool downs.

How to measure if you’re recovering properly

There are 2 tests that we go over in detail in this previous blog post

  • CO2 tolerance test
  • Hand grip dynamometer 

You can perform these tests at home with little to no cost to determine if your routine is allowing for enough recovery time.

Another option is a wearable device that prioritizes recovery like the Oura Ring. The Oura Ring uses metrics like heart rate variability, resting HR, sleep time, and more to determine a “readiness” score each day. It also shifts your recommended activity level of the day based on these metrics. This can be a great option if you prefer specific data.
However, we do not advise using your wearable to intensely track your “calories out”. Listen to this episode of Fit Body, Happy joints to learn more. 

What to do if you’re not recovering well

Let’s say you perform the test above or start utilizing a wearable and notice that you are not recovering well. What should you do?

First, analyze your routine. 

One of the first aspects of a routine that we recommend adjusting is the amount of cardio you do. Cardio is something that tends to be overdosed in a routine and can contribute to an inability to recover. Listen to this episode of Fit Body, Happy Joints to learn more. 

Try to change just one variable at a time when tweaking your routine, give yourself a few weeks to test it out, and track your recovery again to see the results.

If you’ve played around with your routine and still feel depleted, it’s time for a Reset Week.

Reset Weeks consist of 4-7 days off of resistance exercise to allow the body to (you guessed it) reset. Learn more about the benefits of Reset Weeks here
If you feel like you’re due for a Reset Week, you can follow our curated Reset Week Program on the platform.