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Anatomy & Physiology

With regards to any  resistance training programme human performance, exercise physiology and functional anatomy is key.  Anatomy is the broad science concerned with the structure of the body and how each of the different parts interacts.  

Within their realm of functional anatomy, movement involves the close interplay of the skeletal, articular (joint) and muscular systems, as well as the nervous system.  

As movement is required to exercise, it is essential to have a basic understanding of these systems.


Energy Systems


There are three main energy systems:

  • ATP-PC System

The body needs a continuous supply of ATP for energy -- whether the energy is needed for lifting weights, walking, thinking or even texting. It’s also the unit of energy that fuels metabolism, or the biochemical reactions that support and maintain life. For short and intense movement lasting less than 10 seconds, the body mainly uses the ATP-PC, or creatine phosphate system. This system is anaerobic, which means it does not use oxygen. The ATP-PC system utilizes the relatively small amount of ATP already stored in the muscle for this immediate energy source. When the body’s supply of ATP is depleted, which occurs in a matter of seconds, additional ATP is formed from the breakdown of phosphocreatine (PC) -- an energy compound found in muscle.

  • Lactic Acid System (Anaerobic)

The lactic acid system, also called the anaerobic glycolysis system, produces energy from muscle glycogen -- the storage form of glucose. Glycolysis, or the breakdown of glycogen into glucose, can occur in the presence or absence of oxygen. When inadequate oxygen is available, the series of reactions that transforms glucose into ATP causes lactic acid to be produced -- in efforts to make more ATP. The lactic acid system fuels relatively short periods -- a few minutes -- of high-intensity muscle activity, but the accumulation of lactic acid can cause fatigue and a burning sensation in the muscles.

  • Aerobic System

The most complex energy system is the aerobic or oxygen energy system, which provides most of the body's ATP. This system produces ATP as energy is released from the breakdown of nutrients such as glucose and fatty acids. In the presence of oxygen, ATP can be formed through glycolysis. This system also involves the Krebs or tricarboxylic acid cycle -- a series of chemical reactions that generate energy in the mitochondria -- the power plant inside the body cells. The complexity of this system, along with the fact that it relies heavily on the circulatory system to supply oxygen, makes it slower to act compared to the ATP-PC or lactic acid systems. The aerobic system supplies energy for body movement lasting more than just a few minutes, such as long periods of work or endurance activities. This system is also the pathway that provides ATP to fuel most of the body’s energy needs not related to physical activity, such as building and repairing body tissues, digesting food, controlling body temperature and growing hair.

The three energy systems work in the body to provide energy. While these systems are well known for their role in fuelling athletic performance, ATP is essential for every energy need in the body -- including all the automatic body processes of growth, development and maintaining vital body functions. These energy systems do not work independently and do not function in isolation. Rather, all systems always operate, but some may predominate based on the body’s activities, including the type, intensity and duration of physical activity as well as a person's fitness level.


The Muscular System


The human muscular system includes skeletal, smooth and cardiac muscle tissue. Skeletal muscles attach to your bones, stabilizing the skeleton and enabling voluntary and reflexive movement. Smooth muscle tissue found in blood vessels and various body organs produces involuntary movement essential for normal function. Cardiac muscle occurs only in the wall of the heart, enabling its pumping action. In addition to structural and movement-related functions, the muscular system helps maintain normal body temperature.

  • Voluntary and Reflexive Movement

Skeletal muscles normally account for at least 40 percent of your body weight and are categorized as appendicular or axial based on body location. The large muscles of your arms and legs are appendicular skeletal muscles. The axial skeletal muscles include those of your trunk, head and neck. Contraction of skeletal muscle produces voluntary gross and fine movements, a primary function of the muscular system.

Gross movement refers to large coordinated movements such as walking, running, jumping, sitting down, standing up, lifting large objects, swimming, and swinging a bat or racket. Gross movements rely primarily on large skeletal muscles. Fine motor skills refer to smaller, more intricate body movements. Examples include speaking, writing and playing a musical instrument. Fine motor skills typically involve small skeletal muscles of your hands, face or feet. Although most skeletal muscles are under voluntary control, they can also contract reflexively -- such as blinking when an insect flies toward your face or pulling your hand away from a hot surface.


  • Skeletal Stability and Organ Protection

Your bones provide the frame for your body. Your skeleton, however, lacks structural stability without the skeletal muscles and their associated tendons that hold your bones together and keep them in place. Even in a static posture, such as when you're standing still, numerous skeletal muscles of the trunk, neck and legs must remain in a contracted state to support your body and head. The axial skeletal muscles are particularly important for maintaining an upright position and enabling you to twist your head and body.

In conjunction with the rib and spinal bones of your trunk, the axial skeletal muscles also provide protection for your internal organs. For example, your rectus abdominus, transverse abdominus and oblique muscles protect your abdominal organs from the front and side. Your latissimus dorsi, quadratus lumborum and psoas muscles protect the organs of your abdominal cavity from the back.


  • Blood Circulation

Your heart is the hardest working muscle in your body, contracting at least 60 to 100 times per minute from cradle to grave. The wall of your heart consists of highly specialized cardiac muscle tissue, which contracts involuntarily in response to electrical signals generated within the heart. With each contraction of your heart, blood is pumped through your circulatory system. This essential function provides life-sustaining oxygen and nutrients to your body organs and tissues.

Smooth muscle cells in the walls of your arteries and veins also contribute to blood circulation by altering the diameter of these blood vessels in different situations. For example, arteries supplying exercising skeletal muscles relax to enable increased blood flow to meet the increased metabolic demand. Conversely, if you're dehydrated or suffer a significant blood loss, the smooth muscle of your blood vessels contracts to help maintain your blood pressure and ensure continued circulation to your brain and other vital organs.

  • Internal Organ Function

Several internal organs contain smooth muscle tissue, which contracts automatically to support their normal function. For example, smooth muscle tissue in the walls of your oesophagus, stomach, and small and large intestines produce rhythmic contractions that propel food through your digestive tract. Similarly, smooth muscle in the wall of your bladder enables you to expel urine. Uterine smooth muscle tissue, called the myometrium, proliferates during pregnancy and provides the strong propulsive force that enables a vaginal delivery. Other internal organs and structures that rely on smooth muscle to support some of their functions include the gallbladder, male reproductive ducts and glands, and the irises of the eyes.


  • Body Temperature Regulation

A normal body temperature of roughly 98.6 F is generally lower than the environmental temperature. Since body heat is lost to the environment in typical conditions, your body must generate heat to maintain a normal temperature. Most of this needed heat is generated by your skeletal muscles. When your body temperature decreases, skeletal muscle activity automatically increases to generate heat. Shivering is the most obvious manifestation of this response. Smooth muscle in the blood vessels supplying your skin also automatically constricts in cold conditions to conserve heat by limiting loss at your body surface. The opposite effect occurs when you're exercising or otherwise overheated. Smooth muscle cells in surface blood vessels relax, increasing blood flow and heat release through your skin.


Muscle Roles and Contraction Types 


When it comes to resistance training understanding the different types of contractions that a muscle can perform is vital.  Muscle contractions are classified according to the movements they cause and in fitness, and indeed Ree-Pump, we are primarily concerned with the following three types of contraction:

  • Concentric contraction

Any contraction where the muscle shortens under load or tension is known as a concentric contraction.  For example, the quadriceps muscles in the thigh contract concentrically (shorten) during the upward phase of the squat movement.


  • Eccentric contraction

Muscles not only ‘shorten’ but can also lengthen under load or tension.  An eccentric contraction refers to any contraction where the muscle lengthens under load or tension.  
For example, in a squat, the quadriceps muscles will contract eccentrically (lengthen) in the downward phase of the movement.


  • Isometric contraction

Muscles don’t actually need to move (shorten or lengthen) at all to contract or develop tension.  An isometric contraction refers to any contraction of muscles where little or no movement occurs.  If during the squat the person stopped moving at a certain point (say halfway up) and held that position for 10 seconds, the quadriceps muscle would be contracting isometrically, it would still be under load or tension but no movement would occur.

Many skeletal muscles contract isometrically in order to stabilise and protect active joints during movement.  So, while the quadriceps muscles are contracting concentrically during the upward phase of the squat, and eccentrically during the downward phase, many of the deeper muscles of the hip contract isometrically to stabilise the hip joint during the movement.

Concentric and eccentric are also terms used to describe the phase of a movement.  The concentric phase is the phase of the movement that is overcoming gravity or load, while the eccentric phase is the phase resisting gravity or load.  So, for push ups the concentric phase is the up phase where gravity is overcome, and the eccentric phase is the downward phase where gravity is resisted.


Muscles in Movement


There are four different roles that a muscle can fulfil during movement, these roles are:

  • Agonist

The agonist in a movement is the muscle(s) that provides the major force to complete the movement.  Because of this “agonists” are known as the “prime movers”.  In the bicep curl which produces flexion at the elbow, the biceps muscle is the agonist, as seen in the image below.
The agonist is not always the muscle that is shortening (contracting concentrically).  In a bicep curl the bicep is the agonist on the way up when it contracts concentrically, and on the way down when it contracts eccentrically.  This is because it is the prime mover in both cases. 


  • Antagonist

The antagonist in a movement refers to the muscles that oppose the agonist.  During elbow flexion where the bicep is the agonist, the tricep muscle is the antagonist.  While the agonist contracts causing the movement to occur, the antagonist typically relaxes so as not to impede the agonist, as seen in the image above.

The antagonist doesn’t always relax though, another function of antagonist muscles can be to slow down or stop a movement.  We would see this if the weight involved in the bicep curl was very heavy, when the weight was being lowered from the top position the antagonist tricep muscle would produce a sufficient amount of tension to help control the movement as the weight lowers. 

This helps to ensure that gravity doesn’t accelerate the movement causing damage to the elbow joint at the bottom of the movement.  The tricep becomes the agonist and the bicep the antagonist when the elbow extends against gravity such as in a push up, a bench press or a tricep pushdown. 

  • Synergist

The synergist in a movement is the muscle(s) that stabilises a joint around which movement is occurring, which in turn helps the agonist function effectively.  Synergist muscles also help to create the movement.  In the bicep curl the synergist muscles are the brachioradialis and brachialis which assist the biceps to create the movement and stabilise the elbow joint.


  • Fixator

The fixator in a movement is the muscle(s) that stabilises the origin of the agonist and the joint that the origin spans (moves over) in order to help the agonist function most effectively.  In the bicep curl this would be the rotator cuff muscles, the ‘guardians of the shoulder joint’.  The majority of fixator muscles are found working around the hip and shoulder joints.



The Mechanics of Movement


Leverage is referred to as the mechanical advent gained by a lever.  It is largely responsible for a muscle’s perceived strength and range of movement.  Strength is affected by the length of the lever itself, or the distance between the effort and the resistance.  If the resistance is close to the effort, or the lever length is small, the force required is considerably less than if the resistance was further away, or the lever was long. 


With both range of movement and strength being dependent on placement of the muscle, yet both being inversely affected by the other, it is not possible to have a muscle which is powerful and able to produce a large range of movement.  

Put simply, the greater the range of movement possible, the less powerful the muscle. 


Biomechanical Considerations 


First and second-class levers enable us to lift heavy weights with a relatively small amount of effort.  Third class levers however do not give this mechanical advantage.  As most levers in the body are third class levers, we can see the body is not designed to make lifting easy. 


With many of the attachments close to joints, and the bones themselves quite long, the force needed to lift even light objects is quite large.  

For example, to abduct your arm with a 5kg weight in your hand, the deltoid muscle would have to use a force equivalent to 150kg, to lift it to shoulder height.  If the deltoid muscle was connected two centimetres further down the humerus, and our arm was 5 centimetres shorter, the force required would be greatly reduced.

Due to the structure of third class levers, they do not offer the body advantages in strength.  When considering range of movement and speed however, we find a much better system with these types of levers. 

If the deltoid was to contract and shorten in length slightly, we would still see a great distance moved by the hand.  This allows us to produce great throwing and striking forces.  This is especially when the length of the lever is increased by holding an object like a squash racquet.  The speed at which the hand would move is also much greater than the speed at which the humerus would move.  Once again, holding a racquet would greatly increase the speed of the most distal point in the lever.  


Other factors which can affect muscle performance include the arrangement of muscle fibres, the number and size of muscle fibres and the neurological training and recruitment or to put it another way how effectively the brain tells the muscles what to do.  

All of these things can be greatly improved with the correct training.

We can vary:

  • The Range

  • The Resistance

  • The Lever Length

  • The Plane of Movement

  • The Rest to Recovery timings

  • The Equipment Used

  • The Rhythm or Movement Pattern 



Any modifications made should be done so to match the individual participants requirement.  We wouldn’t modify any sequence for the whole class to accommodate one person, unless it was equipment or a health safety concern. 



Planes of Movement


Your body is divided into top and bottom, right and left, and front and back halves by three specific planes of motion: transverse, sagittal and frontal. Exercises normally consist of movements in more than one plane. Understanding these planes and incorporating exercises for each of them in your regular workouts will help you establish and maintain a balanced fitness plan that promotes muscular balance.

  • Frontal

The frontal plane divides your body into front and back halves. However, despite the plane's name, the exercises you perform on the frontal plane consist of side-to-side -- rather than front-and-back -- motion. Movements of abduction and adduction occur on the frontal plane. Side leg lifts and lateral raises are resistance training exercises you can try on the frontal plane. Jumping jacks and side-to-side gallops are examples of cardiovascular exercises on the frontal plane of motion.


  • Sagittal

The sagittal plane divides your body into right and left halves. Exercises that involve flexion and extension and forward and backward movement happen on the sagittal plane. Biceps curls and squats are both examples of strength training exercises on the sagittal plane. A simple forward or backward step, walking, or running are all cardiovascular exercises that you can try on the sagittal plane of motion.


  • Transverse

The plane that divides your body into top and bottom halves in the transverse plane. When you perform movements of rotation, you are working on the transverse plane of motion. Exercises that involve twisting happen on this plane. Try alternating oblique crunches or alternating cross jabs to include exercises in your routine that require you to work on the transverse plane of motion.


With regards to any movement we always try to start by placing the body into a neutral position ready for each one to commence.

  • Putting It In Neutral

Before you get started with exercises on the different planes of motion, it is important for you to understand the universal starting position, which is called "anatomical neutral" or "anatomical starting position." 

To assume this position, stand up or lie on your back with your knees straight but not locked out, your legs hip distance apart, your toes forward, and your arms by your side.


  • The Stretch Reflex

The stretch reflex is very important in posture. It helps maintain proper posturing because a slight lean to either side causes a stretch in the spinal, hip and leg muscles to the other side, which is quickly countered by the stretch reflex. This is a constant process of adjusting and maintaining. The body is constantly under push and pull forces from the outside, one of which is the force of gravity.

Another example of the stretch reflex is the knee-jerk test performed by physicians. When the patellar tendon is tapped with a small hammer, or other device, it causes a slight stretch in the tendon, and consequently the quadriceps muscles. The result is a quick, although mild, contraction of the quadriceps muscles, resulting in a small kicking motion.


  • Anatomy of The Stretch Reflex

Located within the belly of the muscle, between and parallel to the main muscle fibers, are muscle spindles. These muscle spindles are made up of spiral threads called intrafusal fibers, and nerve endings, both encased within a connective tissue sheath. These spindles monitor the speed at which a muscle is lengthened and are very sensitive to stretch.

If a muscle is stretched (lengthened) too far or too quickly the muscle spindles are excited and the stretch reflex is activated, which causes the muscles to contract, thereby protecting the muscle from being over stretched or torn.

These impulses travel from the spinal cord to the muscle and back again in a continuous loop. Conscious movement comes from impulses in the brain travelling down the spinal cord, over this loop, and then back to the brain for processing. The stretch reflex skips the brain portion of the trip and follows the simple loop from muscle to spinal cord and back, making it a very rapid sequence.

The gamma efferent cells in the loop work to keep the muscles ready for the stretch reflex, even when inhibited or contracted. This is important because if the muscle is working against a load and shortening during contraction and an additional load is added, the muscle recognizes the stretch immediately and can compensate with a stronger contraction. This also protects the inhibited antagonist muscles from being injured from excessive stretching.


  • So, What Activates the Stretch Reflex?

The stretch reflex is activated (or caused) by a stretch in the muscle spindle. When the stretch impulse is received a rapid sequence of events follows. The motor neuron is activated and the stretched muscles, and its supporting muscles, are contracted while its antagonist muscles are inhibited (relaxed).

The stretch reflex can be activated by external forces (such as a load placed on the muscle) or internal forces (the motor neurons being stimulated from within.) An example of the former is a person holding an empty tray in their outstretched arm and then having a plate of food set on it. The stretch reflex would kick in to keep the tray at the same height and balanced. An example of the latter would be the shivering of a cold muscle. The motor neurons are stimulated from an internal “stretch” to warm the muscles.

Any abrupt, forceful stretch on the muscle causes the stretch reflex to fire, in a healthy person. Delays in or absence of the stretch reflex are signs of possible neurological or neuromuscular compromise.


  • Avoiding the Stretch Reflex

Many people have never learnt how to stretch properly. Maybe you have done this yourself: You watch other people stretch in the gym and try to imitate what you see. But who is to say that the person you are watching is doing it right? Here are some of the most common mistakes made while stretching:

  • Bouncing. Many people have the mistaken impression that they should bounce to get a good stretch. Bouncing will not help you and could do more damage as you try to push too far beyond the stretch reflex. Every move you make should be smooth and gentle. Lean into the stretch gradually, push to the point of mild tension and hold. Each time going a little further, but never forcing it.

  • Not holding the stretch long enough. If you do not hold the stretch long enough, you may fall into the habit of bouncing or rushing through your stretch workout. Hold your stretch position for at least 15 to 20 seconds (and up to 60 seconds for even better results) before moving back to your original position.

  • Pushing the stretch too hard. Stretching takes patience and finesse. Each move needs to be fluid and gentle. Do not throw your body into a stretch or try to rush through your routine. Take your time and relax.

  • Forgetting form and function. Think about your sport or activity. Which muscles will you be using? A routine for a marathon runner will be very different from a routine for an hour of lifting weights. Pay attention to the muscles you will need to use in your program and make sure your form for each stretch is attained properly. Consider the range of motion you will be putting that particular muscle through. The whole point of stretching is getting your muscles accustomed to moving through a specific range of motion, so if the muscle is not used to going that far, you may end up with an injury.


So, to avoid the stretch reflex and potential damage to your muscles and joints, avoid pain. Never push yourself beyond what is comfortable. Only stretch to the point where you can feel tension in your muscles. This way, you will avoid injury and get the maximum benefits from your stretching.



Types of Stretches

  • Static Stretching

Static stretching is most often recommended for general fitness. With this type, you slowly ease into the position and hold for 10 to 30 seconds before slowly releasing the stretch. Static stretching should be performed with warm muscles, such as after a warm-up or at the end of a workout. There are two forms of static stretching.

  • Active Static: This form of stretching is used in yoga and martial arts. The stretch is held by the strength of agonist muscles (muscles responsible for the movement). Think of the stretch across the upper body during the Warrior II pose in yoga. Your arms are extended as your back, chest, and shoulders are stretched. The muscles of the arms and shoulders are the agonist muscles that allow you to hold this stretch.

  • Passive Static: During this type of stretching, you hold the limb to perform the stretch without any assistance such as a bar or bands. Think of a standing quadriceps stretch in which you bend your leg behind you and hold the foot, pulling the heel in close to your bottom, which stretches the front of the upper thigh.


  • Dynamic Stretching

Dynamic stretching is stretching with movement. The body transitions gradually into a position and this movement is repeated as you increase your reach and range of motion. If you have ever taken a group exercise class, you have likely engaged in dynamic stretching. Movements such as alternating knee lifts repeatedly stretch the hamstrings while keeping the body in motion. Research has found that dynamic stretching is less beneficial than static stretching for increasing range of motion, but unlike static stretching, it is ideal during the pre-workout phase because it gently warms muscles while also stretching them.


  • PNF Stretching

PNF stands for Proprioceptive Neuromuscular Facilitation. This type of stretching is often referred to as partner stretching because two people are needed to perform the movements. There are many forms of PNF, but most involve an isometric hold followed by a static stretch of the same muscle group. An example of PNF is a hamstring stretch where one person lies on her back with the right leg extended straight up into the air. The second person grasps the ankle and gently presses the leg towards the other person’s head to stretch the hamstring. The pressure is released and then the stretch is repeated.

While PNF is as effective as static stretching for improving range of motion, it is less practical because of the necessity of a partner. It is most often used in clinical and fitness settings for training and rehabilitation.


  • Ballistic Stretching

This type of stretching uses bouncing movements to create momentum which moves the muscle into the stretch. For example, instead of holding a hamstring stretch you would quickly reach towards your toes and release repeatedly in short bursts of movement. Fitness trainers have long been warned about the dangers of ballistic stretching because it can cause a stretch reflex that injures the muscle. Current recommendations from the ACSM state that ballistic stretching can improve flexibility as well as static stretching when it is performed properly. It is best considered for those participating in ballistic exercises such as basketball and other athletics.

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