Written by: Adam Tzur
Posted: February 2, 2017
Last updated: March 29, 2018 ¹

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Summary

This article contains 31 videos, 42 studies, + articles about anatomy, biomechanics, individualization, physics, and exercise technique. You can read or watch the videos, it's up to you!
The article is structured as follows: (1) intro to anatomy and biomechanics, (2) Practical application of strength training biomechanics, (3) other exercises, biomechanical models, discussion, and (4) scientific studies on biomechanics for humans.
Several of the videos discuss how your anatomy affects lifting technique (it's not just about muscle tightness and mobility)
There is no cookie-cutter technique that is ideal for everyone - See McGill's, Henoch's, and Purvis' videos for details.
Moment arms change throughout the exercise (i.e. the squat at the top vs. in the hole). This affect when an exercise becomes difficult and also how difficult it becomes. When we hit the position we are least biomechanically efficient in, we tend to hit the "sticking point". Improving the sticking point is particularly important for 1RMs and competitive lifting.
Overcome the sticking point with ROM-specific training (partials), momentum training, technique alteration, isolation training, and accommodating resistance (i.e. bands):
"If the momentum is supplied to the load at a point in the lift at which the target muscles are in a biomechanically inferior position to exert effective force, this weakness may be overcome" (Arandjelovic, 2012)
Cheating can be useful in some exercises and for some purposes, but should we always use momentum to cheat? What about isolation exercises? (see Purvis videos)
Free weights/cable exercises/machines do not provide constant resistance due to inertia, technique, "momentum cheating", and moment arms: "even a linear resistance has a variable resistance" (Purvis, 2015)
Range of motion can be joint-specific, or exercise-specific (i.e. you can do a full ROM bench without utilizing full shoulder and pectoral ROM)
Check the Customizable exercise simulations-section to play around with a deadlift/bench/squat biomechanics model (change limb length, ROM, etc.)
There are 39 biomechanics studies in the studies-section (footwear, technique comparisons, strength-curves, etc.)

Introduction

This is a collection of biomechanics resources you might find helpful. The resources presented here could help you improve your squat, bench, deadlift, etc. and improve your understanding of why you need to use certain techniques.
Note that some of the arguments made in some of the videos are actively debated in the literature so this isn't the undisputed end-all-be-all of biomechanics.

Anatomy and Kinesiology

The 6 Types of Joints

Functional Anatomy

Explains the following:

Skeletal system: joints, girdles, bones, levers, range of movement, etc.
Muscular system: muscle types, motor units, tendons, muscle insertions and origins, lever system of muscles, agonists, antagonists, types of movement, +++

Ryan Puck - Lecture on Biomechanics of Resistance Exercise (joints, muscles, & planes of motion)

Dr. Akram Jaffar - Lever systems in the human body

"Muscle insertions are so frequently found close to the joints they move, therefore the effort is located between the pivot and the resistance (...) the levers of the human body are adapted for range, speed, and precision of movement rather than for handling weight"

Lever Systems: Bone-Muscle Relationships [Article]

Most skeletal muscles of the body act in third-class lever systems (...) In a third-class lever, the effort is applied between the load and the fulcrum. These levers are speedy and always operate at a mechanical disadvantage

(...) An example is the activity of the biceps muscle of the arm, lifting the distal forearm and anything carried in the hand. Third-class lever systems permit a muscle to be inserted very close to the joint across which movement occurs, which allows rapid, extensive movements (as in throwing) with relatively little shortening of the muscle. Muscles involved in third-class levers tend to be thicker and more powerful."

Example of human lever:

Source (illustration is edited for clarity)

Basics of Biomechanics

Powerlifting leverages [2014]

This is a simplified introduction to leverages, moment arms, and individualized anatomy.

Tom Purvis - Inertia in resistance training [2016]

1:36 - 10 lbs of weight is not necessarily 10 lbs of resistance

3:40 - "five lbs is different when it's sitting still and you try to move it, and five lbs moving becomes a different thing when you try to stop it" (...) "it's about changes in speed: acceleration and deceleration"

5:47 - "the way I choose to move [the weight] makes it zero [lbs] at some parts of the range, and 20 at other parts of the range"

6:10 - "did you know that the speed, or more importantly the acceleration and deceleration rate of your client's movement, of your movement, changes the load"

6:50 - "if your [movement] is always accompanied by a weight that is flying to zero, you're never training that end of the motion" (...) "you're using your (...) own inertia, your own mass to overcome that mass"

7:31 - "we're looking for the most weight moved, with the least amount of effect (...) because that acceleration and deceleration reduces the stimulation from the load"

What are moment arms? [Facebook video]

Moment arms explained + misconceptions [Article]

A moment arm (MA) determines the degree of effectiveness or influence of a force to produce or prevent the rotation of an object around an axis.

Moment arm is the most vital mechanical factor that is consistently ignored by the exercise industry, experts and consumers alike. When presented in formal study it is with such poor examples and lack of reverence that one must assume that the professors themselves don’t really understand its importance in exercise. Below are just a few of the numerous examples of moment arm neglect or misunderstanding.

The only free weight that is constant resistance is one that is not moving. A weight that is moving will be a variable resistance due to the potentially dramatic influence of inertial effects, and a weight moving around an axis will always be a variable resistance due to the constantly changing moment arms to each involved joint.

Strength & Conditioning Research - why squats become more difficult as you descend [Article]

the external moment arms at the hip and knee are very long at the start of a lift like the barbell back squat when the weight is closer to the ground, and they get smaller very quickly as you lift the weight. This means that even though the weight of the barbell does not change, the hip and knee joint torques produced by the barbell are greatest at the start of the lift, and reduce as you rise upwards.

(...)

Partial and full range of motion training are not as different as you might think from isometric training at short and long muscle lengths. Many exercises with free weights are like squats and have external moment arms that are long at the bottom of the movement, and short at the top. So the total range of motion of the exercise (partial or full) determines the muscle length at which the peak contraction occurs.

Determinants of Strength Performance Part 1 [Article]

On limb length:

The further away a weight is from a joint, the more force is required to lift it. People with long limbs therefore must produce more force to lift the same weight as a person with much shorter limbs (i.e. doing biceps curls with really long vs. short forearms)

A secondary effect of this is that longer limbs mean that any given weight has to be lifted through a longer total distance. Long-armed people have to move the weight further in a flat bench and move through a longer distance when they squat for example.

On muscle length and attachments:

Muscles attach to bones via tendons and these tendons can attach at difference places along the bone in different people. Some people have longer muscles and others have shorter muscles or longer or shorter tendons. For example, common to African Americans are calves that insert very high on the bone; this is fantastic for jumping (for reasons I won’t get into) but terrible for calf growth.

You can find people with pecs that simply don’t meet that close together (they lack cleavage), people with shorter or longer biceps, etc. And the end effect of this is that shorter muscles generate less force around a joint (thought they generate it faster) than longer muscles.

What should people with mechanical disadvantages do?

Sumo DL is often superior for people with a very long torso since their low back often gets beaten up or is limiting in the movement: the length of their spine means their low back muscles have to generate more force for the same weight lifted. By making the torso more upright, Sumo eliminates this particular weakness (and the wider stance may additionally benefit long legged folks).

Biomechanical implications of skeletal muscle hypertrophy and atrophy: a musculoskeletal model (Vigotsky et al., 2015)

"By doubling the anatomical cross-sectional area of the biceps brachii and brachialis, the moment arms of each increase by 27.2% and 37.3%, respectively."

What makes some people stronger than others? [Article]

Why are we stronger at some joint angles than others? [Article]

The Myth of Perfect Form – Juggernaut (Greg Nuckols) [Article]

Practical application of strength training biomechanics

Squat

Quinn Henoch - Squat School | Hip Structure and Squat Technique

"Dr. Quinn Henoch takes American Record holding weightlifters Colin Burns and Cortney Batchelor through a hip mobility assessment and along with Max Aita discusses what this means for their squat technique."

Stuart McGill - Hip Anatomy and the squat

"The deep squat is primarily governed by genetics"

From one of McGill's slides:

Illustration below shows how different anatomical structures (genetics) affect our range of movement:

Source: Frederic Delavier (Strength Training Anatomy)

Tom Purvis - Squats part 1 - How does the squat work?

Individual genetics and anatomical variations determine how you need to squat.

Relevant squat quote from another Purvis video:

A 200 pound squat is getting heavier as you lower, due to the changes in moment arms, in other words (...) the torque of resistance at each joint [increases] progressively as you go down and regressing as you go up back to the top and are virtually balanced through each joint with a near-zero moment arm.

Why does this matter? Tom Purvis discusses leg extensions

There is no challenge (...) no moment arm in multiple joints exercises (squats, lunges, leg presses) at full extension (...) if you were to stumble, you need strength at full extension, you need control at full extension, the leg extension is the best way to do that

I assume this is because the leg extension has a ~90 degree moment arm between the line of force (vertical) and your legs at full extension (horizontal), meaning a heavy workload for your quads at full extension. However, this could depend on the construction of the machine.

Tom Purvis - Squats part 2 - Practical examples of different people squatting

Ben Pakulski - Squat mechanics, centre of mass, joints, axes

3:18 - "A lot of people think [they have to squat] ass-to-grass (...) it has to be specific to your mechanics, specific to what you're trying to train"

3:45 - "So here's the synposis (...) the joint that travels the most, gets the greatest amount of stimulus"

"if my knee joint travels the most (...) the muscles around that joint will work the most"

The Movement Fix - Why people have to squat differently [Article]

"Athlete’s won’t squat the same, and they SHOULDN’T! (...) Athlete comfort will dictate the stance that puts their hip in a better bony position. There are narrow squatters and there are wide squatters. That may have nothing to do with tight muscles or “tight” joint capsules and have more to do with bony hip anatomy.

Very few people are at the end range of their hip motion, so hip mobility drills are definitely a good idea."

Bret Contreras - Squat Biomechanics, butt wink, stretching

08:00 - Why stretching isn't always the solution to butt wink or poor ROM

McGill - How Deep Should I Squat?

Tom Purvis - Should you squat like a baby?

Stuart McGill - What are the consequences of butt-wink during squats?

(this view has been challenged but is still interesting)

How to squat - Greg Nuckols

Check out Greg's long and detailed articles on squatting, benching, and deadlifting!

Deadlift

Biomechanical Analysis of the Deadlift (Girvan, 2012) [Article]

"Movements are governed by physical laws. Understanding and applying biomechanical principles to deadlifting technique can result in the lift being more energy efficient and allowing greater peak performance. In contrast, poor body mechanics become less efficient and may cause injury (Stone & O'Bryant, 1987)"

(...)

"Choosing a style of deadlifting can best be suited to a person's individual body mechanics. Many variables come into play that may affect the efficiency of the lift. These factors include torso, leg and arm length (Stone & O'Bryant, 1987)."

Tom Purvis - Deadlift part 1

You can't classify a deadlift variation as "the best"
Bar+weight is a major influence in your centre of mass. Especially for those that lift more than their BW
Bar must follow line of resistance
Hence, forward lean and raised hip is required, compared to squats. Lifting around the knee is a big mistake
Moment arms in the DL are not primarily at the knee. Hip/back muscles are primary workers
Bad anatomical squat proportions may be beneficial for DLs
Goals for the deadlift (power? Speed? Muscle development? Powerlifting?) affect the ideal execution for the exercise
Individual genetics (i.e. anatomical proportions) and environmental influences (i.e. previous injuries) determine how you need to do the exercise
Full ROM isn't necessarily always ideal. Choosing ROM is dependent upon the goal, individual structure, individual control, load, + other factors. Some individuals should not do conventional full-ROM deadlifts.

Tom Purvis - Deadlift part 2

Rippetoe - Deadlift Stance

How to Deadlift - Greg Nuckols [Article]

Check out Greg's long and detailed articles on squatting, benching, and deadlifting

Bench press

Tom Purvis - Pec mechanics part 1

Tom Purvis - Pec mechanics part 2

Ben Pakulski - Pectoral mechanics and practical applications for the BP

How to bench - Greg Nuckols [Article]

Check out Greg's long and detailed articles on squatting, benching, and deadlifting

Other exercises

Tom Purvis - Row Mechanics part 1

Tom Purvis - Row Mechanics part 2

Tom Purvis - Leg Press Mechanics Part 1 - 45 degree Realities

"Biomechanical reality everyone should know about: once the [leg press] is moving at a 45 degree angle, you're only lifting 75% of the weight."

(...)

"If I do put a 1000 pounds on there (...) this is still a variable resistance because as I lower, as the knee bends, as the hip bends, and the moment arms to each joint change as you lower, this resistance is actually getting heavier as you go down, and lighter as you go up. That's the same as a squat or anything else.

A 200 pound squat is getting heavier as you lower, due to the changes in moment arms, in other words (...) the torque of resistance at each joint [increases] progressively as you go down and regressing as you go up back to the top and are virtually balanced through each joint with a near-zero moment arm."

Tom Purvis - Leg Press Mechanics Part 2 - Resistance Profile

"even a linear resistance has a variable resistance"

Tom Purvis - Leg Press Mechanics Part 3 - Individuals and Setup

Ben Pakulski - Bicep Biomechanics & Strength Curves

See 4:10 for a cable demonstration and practical application

Ben discusses the importance of supination to get the bicep to maximally shorten. Rippetoe also describes this phenomenon in this video.

"The full contraction occurs at supination because the biceps are primary supinators of the forearm."

Ben Pakulski - Tricep Cable Biomechanics & Strength Curves

"To understand optimal tricep contraction you need to understand a couple of things:"

The elbow is a hinge joint that can only work in [a vertical] direction (0:32)
Strength curves (0:56): "Where the cable happens to be at 90 degrees to my arm, is where the resistance is going to be greatest" (1:10)

Ben Pakulski - Rear Deltoid Biomechanics & Strength Curves

Perspectives and discussion

Tom Purvis - Should we "cheat" on exercises?

Does cheating pay: the role of externally supplied momentum on muscular force in resistance exercise [Study]

"["Cheating" with momentum] is nearly universally considered counterproductive (Hay et al. 1983; Johnston 2005; Fisher et al. 2011). Indeed, this is readily apparent by noting that in the common vernacular the term used to describe it is ‘‘cheating’’ which is inherently associated with negative connotations.

The principal argument against the use of external momentum in exercise is that it reduces the force applied on the target muscles. When analyzed in more detail, the reduction in muscular force can be seen to emerge from two sources. Firstly, less force needs to be exerted against the load which already has some kinetic energy. Secondly, the ability of the target muscles to produce force is hyperbolically reduced as the speed of contraction is increased (Hill 1953).

While the aforestated argument certainly raises valid points, by itself it does not lead to a conclusive answer regarding the usefulness or lack thereof of external momentum in applying force on the target muscles. The key reason is to be found in the observation that the use of external momentum may facilitate the use of greater loads. If the momentum is supplied to the load at a point in the lift at which the target muscles are in a biomechanically inferior position to exert effective force, this weakness may be overcome allowing greater force to be applied in the range of motion which is better suited for overloading the target muscles. For e.g., at the beginning of the shoulder lateral raise"

Understanding and Overcoming the Sticking Point in Resistance Exercise [Study]

"The phenomenon of a sticking point is multifactorial and underlain by complex interactions between different contributing factors that are both athlete-specific and exercise-specific. This makes the problem of addressing an athlete’s sticking point a major challenge in practice. A systematic approach is necessary—guided by empirical observations made in rigorous and controlled conditions reported in well-designed studies, a detailed analysis of an athlete’s performance should be used to identify the most promising training strategy. We identified five key strategies that a resistance training practitioner (coach or athlete) should understand and consider:

Target muscle strengthening using isolation work,
ROM-specific training using partial repetitions,
Development of momentum preceding the sticking point,
Exercise technique alteration,
Accommodating or variable resistance use."

Customisable exercise simulations

You can use these links to simulate an exercise through its range of motion. You can customize limb lengths, ROM, etc.

Table of Contents

Summary

Introduction

Anatomy and Kinesiology

Basics of Biomechanics

Biomechanical implications of skeletal muscle hypertrophy and atrophy: a musculoskeletal model (Vigotsky et al., 2015)

Practical application of strength training biomechanics

Squat

Deadlift

Bench press

Other exercises

Perspectives and discussion

Customisable exercise simulations

Studies

Practical applications (4 studies)

Lifting technique and exercise comparison (13 studies)

Strength curves (2 studies)

Footwear (2 studies)

Force-length relationships (3 studies)

Misc (18 studies)