Basic Biomechanics: Newton's Laws of Motion

Sir Isaac Newton formulated 3 physical “laws” that became the basis for classical mechanics.  Through these laws he describe the relationship of forces, objects, and motion.  For three centuries this has been the foundation for understanding motion and physical force systems.Keep in mind that although these 3 laws changed the way scientist looked at the world, it is by no means complete.  Further revelations dealing with quantum physics and theories of relativity have shown that these laws are only the basis for mechanics and not all-inclusive.  Nonetheless, understanding these 3 laws is a pre-requisit to studying motion and their physical systems.

Newton's 3 Law's of Motion

The first rule of newton’s laws is you do not talk about newton’s laws.The second rule of newton’s laws is you do not talk about newton’s laws!But seriously, here they are...

1) Law of Inertia

An object in a state of constant velocity tends to remain in that state of motion unless an unbalanced force is applied to it.  In other words, it is the resistance to motion changes.  There are important considerations when conceptualizing inertia.  One of these considerations is that rest is a constant velocity and can be considered to have inertia.  Another consideration is that gravity is an unbalanced force acting on all objects.

1) How Inertia Applies to Biomechanics

Consider the late swing phase of gait and the forces going forward with the lower extremity.  Just prior to heel-strike there are almost no muscles activated that bring the extremity forward, yet it is still proceeding to travel forward in space.  This is inertia.  To deal with this inertia the body deploys an eccentric contraction of the hamstrings to slow down the extremity to prepare for heel-strike and to reduce harsh reactionary forces.

2) Force = Mass x Acceleration (F = ma)

The net force applied to a body (mass) produces a proportional acceleration.  This law describes the relationship between an object's mass, acceleration, and the applied force.  Both acceleration and force must have the same vector direction.This can also be viewed in different terms:

Momentum = mass x velocity.  The change of momentum of a body is proportional to the impulse impressed on the body, and happens along the straight line on which that impulse is impressed.  Momentum cannot be changed unless acted upon by an outside force; it can only be conserved.

Acceleration is proportional to the unbalanced forces acting on it and inversely proportional to the mass of the object (a = F/m)

How F=ma Applies to Biomechanics

Pretty much every static and dynamic movement has a force.  Muscles are the tissues that contract and create force on the body’s levers (connective tissue, bones).  With any human movement, F=ma can be used to create a simplified calculation of force.  This equation can even be used with static positions.  Consider the static forward head posture.  Gravity and the mass of the head imposes an antero-inferior force.  To counter this force and prevent your neck from snapping off at your desk, you have to constantly contract your levator scapulae, upper trapezius, and posterior cervical muscles to counter this force.  By calculating the acceleration of gravity and mass of the head, you can begin to calculate the muscle forces necessary to prevent movement.

3) Action Reaction Law

For every action there is an equal and opposite reaction.  This law describes how forces always come in pairs, meaning that anytime objects are contacting each other, they are exerting a force.  An important consideration here is the concept that gravity is ALWAYS touching every object.

How Action-Reaction Applies to Biomechanics

Putting that ankle weight on a patients leg will create an increase in the force of the mass and downward pull with gravity, the reaction is that the opposing muscle will have to create a force to overcome this mass.  Another example of this law is with ground reaction forces.  Running on soft ground will result in much less impact forces than running on hard concrete.

Bottom Line

Newton's 3 laws of motion are the basis for understanding motion and the correlative force systems.  Each law can be applied to biomechanics in it's own way.

• Inertia = An object of a constant velocity tends to remain in that state of motion unless an unbalanced force is applied to it
• F=MA = The net force applied to a body (mass) produces a proportional acceleration
• Action-Reaction = For every action there is an equal and opposite reaction

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships

Dig Deeper

http://www.physicsclassroom.com/class/newtlaws/http://zonalandeducation.com/mstm/physics/mechanics/forces/newton/newton.htmlhttp://www.youtube.com/watch?v=iH48Lc7wq0U&feature=related  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics: Force

The most important aspect of biomechanics to consider is force. Force is simply a push or a pull exerted by one object on another.  For an example, when a muscle contracts it creates a force that is transferred to the tendon to pull on the bony attachment, thus resulting in motion.  An important consideration with force is that it is a vector quantity.

A vector quantity always has 3 variables:

1. A Point of Application
2. A Magnitude
3. A Direction

Types of Forces

There many types of forces to consider when looking at biomechanics.  A detailed consideration of these forces is necessary to achieve a full picture of the biomechanical system.  There are 4 types of forces to consider with biomechanics mentioned below.  However, this is by no means an exhaustive list of all the forces involved with biomechanics.  It is only meant to display the amount of complexity involved with human biomechanics and to help compose a free-body diagram.

• Motion Forces -Rotatory, Tranlatory, Curvilinear
• External Forces - Gravity, Wind, Objects, Other People
• Internal Forces - Muscles, Connective Tissue (Elastic), Bone
• Reactionary Forces - Ground Reaction, Joint Reaction, Gliding/Shear/Friction

Bottom Line

Force is the basic component that biomechanics are built upon.  Force is a vector component that has a point of application, a magnitude, and a direction.  There are many types of forces that act on a biomechanical system.  Being able to construct a detailed free-body diagram of the primary segment and adjacent segments will help to develop the full static and/or dynamic biomechanical picture.

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Basic Biomechanics

Basic Biomechanics

Over the years there has been an abundance of different theories and concepts as to how to best treat orthopedic patients and athletes.  With so many different approaches to assessment and treatment it is easy to get overwhelmed.  Even evidence-based practice has contradicted itself over the years when new research arises proving the old research obsolite.  However, there is one concept that never changes and is always the foundation for treating orthopedic patients. This solid foundation of our profession is biomechanics, the study of the mechanics of the human body.  Beginning with a strong understanding of basic biomechanics will allow for a detailed assessment of movement and postures as well as the ability to implement specific interventions.

Application of Biomechanics

To use basic biomechanics to increase your ability to study movement you must consider the body a complex multi-segmented system.  This segmented system consists of skeletal levers connected by a series of joints, which produce motion through muscle action and are coordinated through the mechanisms of the nervous system.  Once you are able to identify all the parts of the system, you can then begin to look at the movement (kinematics) and the forces involved (kinetics).  

Kinematics and Kinetics

It’s important to consider the kinematic and kinetics when it comes to analyzing human movement.  Kinematics are the geometry/description of movement exclusive of the forces that cause/interact to produce movement; whereas kinetics are the internal and external forces that act on the body.  These two systems combine to give the complete picture of biomechanics.

Kinematics

In an attempt to simplify movement analysis you can break it down into 5 variables of kinematic motion.  These variables include:

1. The type of motion that is occurring
2. The location of the movement
3. The direction of the motion
4. The magnitude of the motion
5. The rate or duration of motion

Kinetics

Once you are able to understand these variables it would then be necessary to assess the internal and external forces (kinetics) that are affecting the motion.  This is a much more complex task and requires a much more in-depth description.  Start by understanding the principles of force and how they interact (internally and externally) with the human body.

Identifying Biomechanical Errors

Studying the kinematic variables and correlative kinetics can help to identify where the “biomechanical error” is coming from.  Another way to think about this biomechanical error is to look at all of the variables (kinetics, reaction forces, technique, posture, gravity, kinetic chain, etc) from both an external and internal perspective.  Regardless of your preferred method, assessing the details of biomechanics will aid you in a more detailed examination and a more patient specific intervention.

Basic Biomechanic Concepts

The purpose of this post series is to attempt to simply describe basic biomechanics that are the foundation for orthopedics and movement analysis.

Topics

ForceNewtonian LawsLeversTorqueGravityPressureBiomechanic Relationships

Bottom Line

Biomechanics are the foundation of both static human position and dynamic movement.  A strong understanding of these concepts are necessary for anyone working with the human body and movement.

• Efficient movement assessment and intervention is dependent on sound biomechanical reasoning
• Identify all of the parts of the system
• Identify the biomechanical systems involved (kinematics, kinetics)
• Kinematics = descriptions of motion without regard for the forces producing the motion
• Kinetics = analysis of the forces producing motion or maintaining equilibrium
• Look for biomechanical errors (compensations & inefficiencies)
• Implement interventions aimed at correcting the biomechanical error

Dig Deeper

http://www.physicsclassroom.com/Class/http://www.exrx.net/Exercise.html (great section on kinesiology)http://www.pt.ntu.edu.tw/hmchai/Kines04/KINoutline.htm  --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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Treatment-Based Classification System for LBP

Low back pain patients are not a homogeneous group, but unfortunately they are often times treated like one.  There is an overwhelming amount of causes of pain (disc, ligaments, facet joint capsules, muscle strain/spasm, stress fracture, etc.) and possible diagnosis for low back pain.  However, research has shown that the specific "diagnosis"  of low back pain rarely correlates with the cause.  Imaging studies have shown that there are tons of people walking around with an asymptomatic disc herniation, so even if your patient has an MRI with a L4-L5 disc herniation it might not be the driving cause of their pain and dysfunction.If an effective treatment is preceded by an accurate diagnosis, then we can see why so many healthcare professionals have a difficult time getting their LBP patients better.  To deal with this conundrum a treatment-based classification system was developed to allow for interventions based on a continuous assessment instead of a one-time diagnosis.  Over the years it has become more refined and detailed, but the core concepts are the same.  The overall concept is to assess which of the 3 categories (manipulation, stabilization, and specific exercise) your patient falls into and treat accordingly within that category.  Below is a chart with the 4 categories and associated possible examination findings and treatment interventions.

Treatment-Based Classification System

There are more than 3 categories described here, but the other categories are either subcategories or irrelevant.  Specific exercise category has 3 subcategories (flexion, extension, and lateral shift).  And I personally do not consider traction a valid category to consider.

Example

A patient comes in with low back pain that has been insidiously increasing over the past few months and can't pinpoint any event that caused the on-set of pain.  They prefer a sitting posture, sleeping on their side with their hips and knees flexed, and have increased pain when standing.  During AROM assessment the patient states that the pain increases when testing lumbar extension and the pain decreases with lumbar flexion.  What category would you place this patient in?  Pretty obvious, right?While placing this patient in a flexion based intervention category, it is important to keep in mind that you need to always assess and re-assess throughout the plan of care.

Bottom Line

Of course this is not a method that is intended to be dogmatic.  This is a simplification process used to help classify a difficult patient population for an effective treatment.  It gives healthcare professionals a logical and methodical means of how to begin low back patients rehab.  Assessing before, during, and after interventions will always help to ensure that your patient is on the right path to recovery.Key Authors: Delitto A, Fritz J, Cleland J, Childs J --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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The Trio of a Simple Assessment

When examining and assessing patients it's easy to get caught up in all of the esoteric and minute details.  With the overwhelming amount objective measurements (joint mobility, AROM, PROM, MMT, DTR, etc.) and the endless list of special tests, it can be difficulty to obtain a clear clinical picture.  While a full examination is necessary to prevent overlooking any possible impairments/pathologies; it is also just as important to make sure you come away with a strong simple assessment and clear clinical picture of your patient.  I have found that focusing on 3 simple assessments helps to maintain clinical clarity throughout the plan of care.

3 Simple Assessments

Range of Motion

First examine the kinetic chain to find what tissues are shortened or lengthened.  Then assess for which tissue structure is restricting movement (contractile tissue, joint capsule, connective tissue, fascia, neural tension).  This can be achieved most of the time with attention to detail of the end-feels, positional isolation of certain structures, and/or through palpation.There are many professionals that believe the lack of ROM is the most important aspect to consider when treating patients.  Resolving the impaired ROM will correlate with resolution of other impairments.  Some believe this is specifically a result of the joint mechanics, whereas other believe it is a result from multiple tissues (joints, nervous system, muscle length).  Either way, this emphasis on increasing ROM is a common approach in orthopedic practice.An increase in ROM can have 3 potential results:1.) Increase of muscle length range (length-tension relationship)2.) Decrease of antagonistic force/tension and restricted movement3.) Increase of stimulation of mechanoreceptors to relay information regarding body position to the CNS              Of course this is just the tip of the iceberg to this theory.  There are a great deal of biomechanical and physiological concepts involved in fully understanding the complexity of the ROM theory.  Regardless of whether you believe in this theory or not, achieving normal ROM is a necessary prerequisite to restoring normal biomechanics and functional movement.

Stability

 

This is an aspect of assessment that I feel alot of clinicians overlook.  Having stability throughout the kinetic chain requires a great deal of muscle strength, adequate joint ROM, and sensorimotor balance.  It is especially important in higher level patients that may have normal ROM and strength.

Placing a patient in a closed chain position that forces them to balance their COG over their BOS will allow for an assessment of aberrant motions and compensations.  An important part of this assessment is to allow for enough time for the patient to display instability.  A quick 15 second single leg stance won't show much, but if you extend it to 45 seconds you may see all sorts of ankle pronation, femur IR, and compensated trendenlenberg.Of course not all joints can be placed in this closed chain position for assessment.  For example, you might have a lawsuit if you put a neck patient in a headstand to assess stability.  So try using a combination of ROM, strength, and sensorimotor system assessment to determine your patients functional stability.

Strength

           Einstien helped create the theory of relativity in the early 20th century that overturned Newton's concept of uniform motion.  With this new theory all motion is relative.  This changed physics and brought the concept of relativity to the forefront.   Of course assessing for strength is by no means quantum physics, but I think applying relativity to the musculoskeletal system has it's place.So what can you make one little MMT muscle strength grade relative to?  I look to 3 area's to assess for "Relative Strength":1) Kinetic Chain2) Antagonist Muscle3) Contralateral Muscle (Bilaterally)Assessing for relative strength can often give clinicians a good idea of the integrity of an individuals musculoskeletal system and where a possible compensation is coming from.  A lack of muscle strength in one area almost always leads to a compensation in another area (e.g. decreased peri-scapular strength → decreased rotator cuff strength).  Keep in mind that sometimes the patient's main complaint may be at the area of the compensation and not at the culprit of the injury.Last but not least, don't get caught up in worrying about + and - of MMT grades.  Arguing between a 3+ and a 4- is a waste of time.  It's either weak or strong.

Bottom Line

Just an examination and diagnosis do not give a full clinical picture of a patient or allow for an individualized plan of care.  An assessment is necessary for an individualized clinical picture and can lead you in the right direction for developing a unique plan of care for each patient.Using these 3 assessments tools will give you a simplified clinical picture of your patient.  In most cases addressing these 3 major impairments (ROM, Strength, Stability) will help your patients achieve optimal function.I hope this post will remind you to take a step back and look at the simple major impairments that may be the culprit of your patients physical problems. --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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The Best Posterior Chain Stretch

Inflexibility of the hamstring muscle is often a prominent kink in most people's posterior kinetic chain.  It's the reason why we have to sit down to tie our shoes, can't sit up-right with our legs straight out in front of us, and the reason why most of us would be very pathetic at martial arts.  Having a tight hamstring is a major concern as it can lead to increased risk of injury, decrease athletic performance, and cause pain and symptoms both proximally and distally (low back pain, achilles pain, etc.).A possible cause of this common impairment could be that the majority of the population spends a substantial amount of their time in the seated position (jobs, communting, watching tv, reading this post, etc.).  This seated position puts the hamstring in a shortened position.  The body responds and adapts to this habitually shortened position by decreasing the hamstring muscle length.To further complicate the problem, hamstring tightness is not just a result of muscle tightness.  Fascia and neural tension are a major component of posterior leg tightness.  So how can we address all of these aspects of hamstring tightness without spending 30 minutes of stretching a night?

90-90 Active Hamstring Stretch

This stretch will hit the entire posterior kinetic chain from your plantar fascia to your low back.  It also works all 3 aspects of hamstring tightness (muscle, fascia, neural tension).

How to Perform

1. Start on your back and grab the back of your thigh with both hands
2. Your thigh should be at 90° throughout the entire stretch
3. Slowly use your quadriceps to kick your leg up while flexing your foot towards you at the same time
4. Pause for a second when you reach your limit
5. Slowly relax your foot and drop your lower leg back to the starting position
6. Repeat for 3 sets of 10-15 reps

http://www.youtube.com/watch?v=s4wgP4wjeDc

Other Considerations:

• If you are very tight and not getting much motion at all, start off with your other knee bent (in hooklying) instead of straight
• Try not to flex your neck and upper back up during the stretch, use a pillow to support your head if you need to
• Best time to stretch is within 15 minutes after working out while your body is still warm
• 3 sets of 10 a day is not a limit - adjust to what your mobility needs are

Of course there are many other considerations when addressing hamstring tightness (posture, ergonomics, muscle weakness, compensations, etc.).  But I hope this article will at least give you a new way to stretch your hamstring and posterior kinetic chain.  Just taking a few minutes a day for this exercise can help improve your hamstring flexibility and possibly decrease your risk for injuries. --The main reason I do this blog is to share knowledge and to help people become better clinicians/coaches. I want our profession to grow and for our patients to have better outcomes. Regardless of your specific title (PT, Chiro, Trainer, Coach, etc.), we all have the same goal of trying to empower people to fix their problems through movement. I hope the content of this website helps you in doing so.If you enjoyed it and found it helpful, please share it with your peers. And if you are feeling generous, please make a donation to help me run this website. Any amount you can afford is greatly appreciated.

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