T Nation

Biomechanics of Squatting


What Is A Squat?

Continuing our discussion of exercise, today I will talk about squats. This will be the first in a series of posts that will break down squats from a biomechanical standpoint. We will look at different types of squats, noting their similarities and differences, as well as their changing variables.

A squat is a full-body exercise, i.e., an integrated motion where multiple joints are moving in order to â??squatâ?? down and come back up. This integrated motion requires full-body coordination between the joints, muscles, and the neuromuscular system (the communication between the nervous system and the muscular system).

Squat showing hip/knee/ankle relationship from varying positions

Integrated motion is simply when one or more joints move in concert with one another. In squats, the trunk (spine/ribcage and pelvis) moves in concert with the femur (upper leg), which moves in concert with the tibia/fibula (lower leg or shin), which moves in concert with the foot. In essence, it involves the hip, knee and ankle complexes that control the bending of the body segments. The above diagram shows (A) knee angle change in relation to (B) hip angle; where the hip travels back as the knee travels forward allowing the lowering of the body with weight. This demonstrates the integrated motion of the body segments moving in concert together allowing for a controlled descent into the bottom of a squat.

In order to coordinate the motion, muscles need to contract at differing tensions to allow the joint to move, thereby ensuring quality motion and minimizing friction that causes wear and tear.

The mechanical ability of each muscle and its ability to respond to internal or external demand (force) will dictate joint range of motion, strength, stability and mobility. This means that the depth of your squat and amount of weight you can tolerate during a squat are the results of internal mechanical ability.

The nerves innervating both the quadricep and hamstring sending a signal to contract the quad and relax the hamstring to allow movement. There are varying degrees of contraction and relaxation. A muscle is never completely relaxed.

The mechanical relationships between various muscles around a joint will determine joint motion. Muscles work together on each side of the joint to control joint motion. For instance, the hamstring (a hip extensor and knee flexor) works with the quad (a hip flexor and knee extensor) to control both the hip and the knee, --as one increases tension, the other decreases tension. The contraction of one muscle sends a neural signal to the opposing muscle to modulate tension and ensure both stability of the joint (so that it doesnâ??t dislocate) and mobility of the joint (so that it can ensure quality motion) in a refined way (see diagram above).

The concept of opposing forces working in tandem results from neural input and creates a kind of force couple (note that the joint axis of rotation changes location in the joint throughout the range of motion).

The muscles that stabilize the trunk including erectors, abdominals and obliques along with muscles around pelvis

Imagine the spine in the beginning of a barbell back squat as all the contributing spinal extensors (spinal erectors, etc.) working with the spinal flexors (abs) to create enough tension to withstand the external weightâ??s push on the spine.

Change in angle of torso in relation to leg

Visualize maintaining a static spinal posture using the muscles around the trunk, including abs, obliques, spinal erectors, etc. Next, your hips push back, your knees start to bend, and your spine (trunk/torso) is leaning forward, requiring an increase in tension and internal pressure even as there is no movement in the spine itself.

Muscles working together to control joint motion. I’ve only mentioned two muscles for each joint involved but that is a gross simplification. Every muscle around the joint assists in controlling motion

Now focus on the leg and hip movement in a squat. This is negotiated by the hip flexor (psoas) and hip extensors (glutes), creating a force couple to ensure a perfectly-controlled descent into hip flexion where the glutes resist and the psoas shorten to maintain the hip to trunk relationship.

Quad and hamstring working together to control the relationship between the hip and knee allowing the bending of both joint negotiating tension as it moves into a mechanical disadvantage

The quad and hamstrings assist hip motion, maintaining a relationship between the pelvis and the knee. They shorten in concert and maintain the same length as they increase in tension, ensuring the integrity of both joints.

Gastroc, soleus and tibialis anterior muscles controling ankle motion and stability

Finally, the muscles in the calf (gastroc/soleus) have a force couple with the muscles in the shin (tibialis anterior), controlling the knee and ankle relationship. As the calf muscles contract to slow the descent and the tibialis maintains the foot/ankle orientation, the ankle bends to a greater degree.

Improvement of the squat motion can be accomplished in many different ways. In this section, letâ??s continue our focus on integrated movement, changing tension, and quality-coordinated motion in order to build the pieces needed for a great squat. Iâ??ll focus on existing traditional and well-known exercises that will aid the squat motion. The difference will not be on what we do, but on how we do it.

In exercise, we often assume the correct position (form) of an exercise and push or pull without much thought as to what is moving and how we are performing the action. This results in much wasted effort, leaving much to be desired in execution of the exercise.

The next time you lift, focus on the force couple that occurs, creating tension that enables control over the motion. Adding to the idea of force couples, letâ??s also consider that the two opposing muscles are contracting together, rather than one contracting and the other relaxing. For instance the quad and hamstring contract together as the knee extends or bends. This is called co-contraction. The muscles are fighting each other, but one is allowed to overcome the other. This creates movement, but with a much greater tension generated that supersedes the amount applied by the weight. Developing this ability will not only create better results and safer lifts, but will make you great at squats. This quality will have to be developed like any skill and while learning there will be a reduction in the resistance you can use but internally you will get much more out of each rep you perform.

To improve squats, start with improving the components of the motion while applying our force couple/co-contraction approach to lifting. In doing this, we will be responsible for more than the moving part. Weâ??ll be responsible for actively holding still the non-moving part. This conscious effort will make the difference in the lift. We can accomplish this by focusing and establishing our intent during the lift.

Training spinal stability requires developing the core, which includes the muscle of the torso (spine ribcage and pelvis), as well as those specific to the spine. We need only to challenge our spinal position against a force pushing or pulling us out of the position to accomplish this.

Plank in two positions changing the tension requirements of the trunk


Donâ??t just think about holding the position, but focus on how you are holding it. Are your abs engaged? Are they working with spinal extensors? Are your glutes involved? Are they working in concert with the psoas? These force couples might be involuntary for some people, but others can emphasize these dynamic qualities with voluntary effort and attention.
Changing position from flat to some position of hip flexion. A variety of ways of training the core will provide greater versatility in maintaining spinal stability.
Sitting and resisting spinal rotation on a rotational torso machine or cable machines
All of these will directly and indirectly transfer over to the stability needed during squats as physiological and neurological benefits are developed

Lying back extension

Back extension stand

Old school roman chair

Back extension

On a stand or old school roman chair, maintain spinal position at different static positions of hip flexion or during the movement of hip flexion
To train hip movement we can use many traditional lifts.


Standing cable hip extension

Kneeling bent knee hip extension.

Hip extension

From weighted hip extension or with cables
From standing to kneeling on the bench
From straight leg to knee bent, pushing into a straight leg position
From different positions of rotation of the leg (only with straight leg)
Focus on contracting abs and psoas as you squeeze the glute from the beginning of the motion to the end of the motion
Start without weight and see if you can sense the muscle doing all the work. Do you feel the glutes contracting while lifting the leg, or is the leg going up without thought. Can you do it slowly, maintaining the mind/muscle connection? Can you do it faster and still have the same sensation and control?

This can be done with out a band and with knee bent

Hip flexion/leg lifts

Much pelvis instability stems from a weak and tight psoas. But this isnâ??t about corrective exercise; what an individual needs cannot be identified by seeing or assuming some generic condition is an abnormal affliction.
Weighted with free weights or cable machine
Straight leg or knee bent
Multi-hip machine
Focus on psoas initiating the motion while hamstring and glutes provide extra resistance. Make sure you maintain spinal extension or it will be difficult to engage the of glutes with the motion
Can be done standing and can train the hip complex in many ways (abduction, adduction, flexion, extension with knee bent or straight, and anywhere in between)

Lying hamstring curls

Dumb bell lying hamstring curl. Just in case you don’t have a machine or bands

Seated hamstring curl. Good machines accommodates your body’s natural mechanics

A fun alternative, band hamstring curls

Hamstring curls

From every position (seated, lying, standing)
Focus on pelvis position being maintained as the knee flexes, actively contracting abs and glutes to prevent increasing hip flexion or spinal extension. Think about the force couples already mentioned as the quad and hamstring negotiate knee flexion, creating an intense contraction and exemplary control.
What moves first? In lying hamstring curl are you shoving into the pad to create motion or are you trying to lift the leg off the pad and engaging the hamstrings first?

You can build sensitivity of co-contraction without weight. Practice the motion and focus on the muscle

Bands are a good way to develop the challenge as you tried to retain and expand the sensation against resistance.

This machine provides you with the opportunity to really challenge the quads. The co-contraction intent will refine control so that you choose how much the weight move and at what rate it moves instead of the weight moving or moving out of shear panic and desperation to get the next rep.

Leg extension

From seated position (the leg lifts takes care of quads but you still want to do leg extension along with it to create benefit)
Again, check spinal position and pelvis position to prevent superfluous motion.
Contract the hamstrings as you contract the quads, feeling the tug of war between the two as knee slowly extends.
What are your pelvis and spinal positions? Are you slouching, sliding the pelvis forward, or are you actively stabilizing the pelvis as you engage the quads?

Body weight squats controlling the descent. Don’t fall into it but guide it controlling every inch as you develop mastery of the skill that wil transfer over to weighted squats

Changing hand position which will mimic barbell back squats a little more by changing center of mass slightly.

Barbell squats require adjusting balance from body weight. Still control the motion actively engaging abs and glutes as you descend. Actively engaging psoas and glutes, hamstring and quads, gastroc and tibialis through the movement. In the beginning focus on one pair of muscles and then on a different set focus on another. Notice the overall quality of the movement and how changing focus alter or emphasize some aspect.


While performing a body weight squat with the intention to control the lowering of the body, first notice your balance. Sense your weight distribution over your feet, and attempt to distribute your weight evenly over both feet. As you descend into the lowest position, emphasize the contraction of the abs, glutes, quads and hamstrings, which will initiate the change in direction from descending to ascending.
Then use only the bar, stay balanced, and notice the change in form as you move with a light external force (you can also use dumb bells)
Remember, it is not what we do, but how we do it that will improve our squats and increase the benefits we derive from them.

These are not the only exercises you can use to improve squats; they are examples I have used to discuss different approaches to performing traditional exercises.

In future segments, I will focus on different concepts and discuss how to incorporate them into your training. These cues may not be for everyone, and should be tailored to suit individual needs. Often, itâ??s the thing you are not doing well that you will feel has the greatest impact. Unfortunately, itâ??s impossible for me to tell through this medium what is missing.

My next blog will be about structural differences that will impact squat form, as well as joint-by-joint positional relationships and variations that might improve form.

I hope youâ??ve enjoyed this overview and found it useful. Iâ??m still tailoring the blog and invite your feedback on usefulness and practical application of the subject matter, as well as the style of writing. Is it understandable? Is it useful? Is it interesting? Iâ??d love to hear your thoughts.

End of first section

More in depth information on co-contraction. Displaying both the opportunities and limitations.

Short- and Long-Term Changes in Joint Co-Contraction Associated With Motor Learning as Revealed From Surface EMG

Voluntary enhanced cocontraction of hamstring muscles during open kinetic chain leg extension exercise: its potential unloading effect on the anterior cruciate ligament.

Perturbation Training Improves Knee Kinematics and Reduces Muscle Co-contraction After Complete Unilateral Anterior Cruciate Ligament Rupture


Muscle Use During Isometric Co-contraction of Agonist-Antagonist Muscle Pairs in the Upper and Lower Body Compared to Abdominal Crunches and a Commercial Multi Gym Exerciser

Trainability of Muscular Activity Level during Maximal Voluntary Co-Contraction: Comparison between Bodybuilders and Nonathletes

Trunk Muscle Activities During Abdominal Bracing: Comparison Among Muscles and Exercises

Effect of Short-term Maximal Voluntary Co-contraction Training on Neuromuscular Function


sounds good

[quote]scarter79 wrote:
Continuing our discussion[…]

My next blog will be about[…][/quote]
Straight-up minimal effort copy/paste just to plug your blog. Talking as if we’ve all been following you for months when we really have zero idea who the hell you are. Not showing the forum enough respect or courtesy to correct grammatical, spelling, and blatant formatting errors.

Definitely made a great first impression.

Welcome to T-Nation.

[quote]Chris Colucci wrote:

[quote]scarter79 wrote:
Continuing our discussion[…]

My next blog will be about[…][/quote]
Straight-up minimal effort copy/paste just to plug your blog. Talking as if we’ve all been following you for months when we really have zero idea who the hell you are. Not showing the forum enough respect or courtesy to correct grammatical, spelling, and blatant formatting errors.

Definitely made a great first impression.

Welcome to T-Nation.[/quote]

I doubt anybody’s gonna read that shit-pile of disorganized words anyway. It gave me tired head just glancing past it to your post.

Thank you Chris-- you said what needed to be said.