• Mark Turnbull

Fitness Components and Human Physiology

To prescribe the correct variables (reps, intensity, rest etc) to suit our goals and abilities you need to consider how the fitness components relate to our physiology. In this post we look specifically at the relationship with the energy, nervous and musculoskeletal systems.


Fitness Components and the energy systems Each of the fitness components has a duration and intensity that can be linked to the energy systems that allow our body to complete the work.  A high duration and low intensity activity will mainly use the aerobic energy system.  A moderate intensity and moderate duration will use a mix of anaerobic glycolysis and the aerobic system.  A short duration and high intensity activity will predominantly use the ATP-PC system. Each fitness component is plotted below against the energy systems which fuel it. 

1 =  Power, speed, max strength, agility

2 =  Sub max strength

3 =  Hypertrophy, anaerobic fitness

4 =  Muscular endurance, aerobic fitness


You can see here that the fitness components of power, speed, agility and maximal strength (i.e. very high load, very low reps(s)) are all supplied primarily by the ATP-PC system (number 1 above).  They are fundamentally done at close to 100% effort (meaning a rapid rate of ATP production is required).  The ATP-PC system supplies ATP very quickly to fuel maximal or near maximal intensity exercise, but it also fatigues quickly which is why training for such components is short in duration.


Sub max strength and hypertrophy are supplied by a mix of the ATP-PC and Anaerobic Glycolytic systems with strength being more ATP-PC based (number 2 above) and hypertrophy being more anaerobic glycolysis based (number 3 above) - remember “feel the burn!”.  Anaerobic fitness falls into the Anaerobic Glycolytic system (number 3 above).


Muscular endurance (to a degree) and aerobic fitness especially, fall into the aerobic system (number 4 above) although it’s important to remember that the anaerobic systems will make some contribution as the aerobic system ‘gears’ up to supply ATP.  This is because for any activity ATP is needed immediately and the aerobic system takes time to start developing ATP. So while the aerobic system is ‘gearing up’ most activity will be supported by the anaerobic systems. 


So, we are now left with the fitness components of balance/stability and flexibility to look a little more closely at.  We’ll do that by discussing what all of the fitness components require of the nervous and musculoskeletal systems.


Fitness components and the musculoskeletal and nervous systems

When we use our bodies to do something we must have ATP for energy and the rate at which we need ATP dictates the energy system that will be used to supply the ATP.  We also need to control our movement which happens through the nervous and musculoskeletal systems. 


Each fitness component requires these systems to respond in a certain way in order for the exercise to occur.  Some adaptations can therefore be expected in both the nervous and musculoskeletal systems as a result of training a particular fitness component.


The following table summarises some of the requirements placed upon these systems when training each of the fitness components listed.  You will see that balance/stability and agility require programming of the reflexes related to the movement (i.e. are movement specific) as well as good awareness within the brain (i.e. a strong map of what ‘balanced’ feels like or what the ‘change in position’ should feel like) in terms of the map it carries of the movement and what it knows is important in terms of departures from that map.


You should also note that in almost all cases a nervous system that is primed up for the job ahead and a musculoskeletal system that is warm and pliable is a must.

Speed

Nervous system

We need to generate nerve signals at high rates to many muscles with very low delay times. The brain needs a well rehearsed motor pattern, priming of the pathways it will use, reflexes to control / correct the movement as it happens, and a nervous system without fatigue. In other words we will be fastest when we are doing something we are familiar with, have warmed up for, and when we are fresh.

Musculoskeletal system

We need muscles that can contract quickly and take the shock (of foot strikes for instance) without tearing, connective tissue (tendons, ligaments) that can withstand rapid and repeated loading, joints that are well lubricated with synovial fluid and have good joint space, and bones that are strong and rigid in the lines of force we will repeatedly expose them to.


Power

Nervous system

We need to generate nerve signals at high rates to many muscles with very low delay times all at once. The brain needs a well rehearsed pattern with optimal sequencing of the movement to allow the most force to be generated quickly, have practiced firing all of the motor units it can at once, priming of the pathways it will use, reflexes to control / correct the movement as it happens, reflexes that don’t limit the muscle activity that can happen, and a nervous system without fatigue. In other words we will be most powerful when we are doing something we are familiar with, have warmed up for, when we are fresh, when we have done it enough before that the spinal reflexes don’t limit our contractions.

Musculoskeletal system

We need muscles that can contract quickly and very forcefully without tearing, connective tissue (tendons, ligaments) that can withstand rapid and forceful loading, joints that are well lubricated with synovial fluid and have good joint space, bones that are strong and rigid in the lines of force we will expose them to.


Flexibility

Nervous system

We need the nerves to decrease their activity (frequency of firing to the muscles), a brain that does not perceive risk in the position (e.g. it’s familiar with the position and the joint(s) is healthy), spinal reflexes which have been conditioned to not fire in the range of motion we adopt, a generally relaxed nervous system in a low stimulus environment (think waterfall music and dark room)

Musculoskeletal system

We need muscles and fascia (remember the coating around the muscle tissue) that isn’t damaged, torn, rigid. We need tendons and ligaments that are not damaged. We need the muscle and fascia to be warm as this enhances its pliability. We need to be stretching across a healthy joint where no injury is present (otherwise the muscles may be ‘bracing’ the joint in position to protect it).


Balance/Stability

Nervous system

We need the spinal reflexes to be finely tuned and responsive so that balance can be quickly restored, we need the brain to have been programmed on how to detect and correct changes in position of the body (including not over correcting). We need the nervous system to be alert (i.e. the pathways involved primed and ready).

Musculoskeletal system

We need the muscles to be warm and previously fired to enable contractions to happen quickly. In cases where high loads may result we will need the muscles and connective tissues able to tolerate rapid and significant forces (e.g. if we were tackled in a game of rugby or football and put off balance as a result)


Agility

Nervous system

We need the brain to have been programmed how to create and execute changes in the position of the body quickly and efficiently. We will likely need to be able to fire many muscles at once to overcome momentum in one direction and shift it to another. We need the nervous system to be alert (i.e. the pathways involved primed).We need the spinal reflexes to be finely tuned and responsive so that slight modifications to position can be made rapidly (external forces such as the ground will mean the reflexes will have to quickly modify positions).

Musculoskeletal system

We need the muscles to be warm and previously fired to enable contractions to happen quickly. High loads may occur with momentum changes so we will need the muscles and connective tissues able to tolerate rapid and significant forces (e.g. if we were going to side step someone in a rugby match). We need the bones to be strong in the lines of force that may eventuate. We need the joints to be healthy and well positioned/lubricated so rapid position changes can happen smoothly.