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5 Facts: Muscle Size vs Strength

The relationship between Muscle Size and Strength has been argued and debated for a very long time. This is because the results of individuals who train with weights vary on such a large scale that it can be hard to determine what exactly solicited anyone's results. Introduce chemical warfare (Anabolic Steroids) and you can be sure the entire subject will become much more clouded than it even was before. The truth is your genetic potential for muscle size from a particular stimulus is different from almost every other individual. The key and the 'Holy Grail' is to find the common ground by which everyone can benefit. Hopefully in this article we can outline the main differences between physiological changes in your body for Muscle Size and that of Strength, and maybe make you think differently about your goals, and how to address achieving them.

1. Motor Units

'Motor Units' is a fancy term used to describe the nerves that are connected to your muscle fibres. Everyone is born with their fixed number of Motor Units. Motor Units are turned on either at a few at a time, in a sequence or in a big bunch. They are the nerves that are responsible for Muscle Recruitment. Why is this relevant to us? Well, when we lift weights or use our muscles, our Central Nervous System is switching Motor Units on in a way that is appropriate for the task they are performing, e.g. Less muscle will be recruited for standing up from a chair then if say, we were performing weighted squats in the gym. Our brains can learn to switch on more muscle fibres in a particular path way if we provide enough stimulus, and this is the main theme of what is happening when someone is getting stronger; The heavier the task, the more muscle recruitment needed to complete it.

NOTE: Since averagely (even for heavy gym lifting) a lifter will only recruit approximately 30% of the target muscle fibres to perform an exercise, there is a whole lot of strength the individual can gain while not increasing muscle size (from the 70% remaining fibre not switched on). E.g. A well trained Olympic Lifter may be able to recruit upwards of 70-80% for a one rep max.

2. Muscle Damage

The word 'damage' in this term isn't actually implying any long term injury, but the microscopic muscle tears that occur in muscle fibres while performing tasks. Ever felt stiff or sore from a workout? Most likely it is related to the micro-tears in the muscle tissue due to performing a new task or stimulus. It is normally a temporary feeling, lasting only a few days. However, what is happening in your body is very important with regards to understanding how the muscle grows. Micro-tears are the beginning of the process known as the 'Over-Compensation Phenomenon', named in the sense that we cannot fully define what actually happens at the microscopic level yet. All we know is that our bodies, when given adequate rest and nutrition will repair these micro-tears to be slightly bigger or more adaptive, in the effort to perform that stimulus both more effectively and without further damage.

3. The Training Stimulus

When the muscles are provided with a stimulus, e.g. a heavy object to move, your central nervous system recruits what it thinks is the right amount of muscle fibre to move it. However, if not enough muscle is recruited then the object cannot be moved. What do we do then? Well, we can either do two things: 1. Teach more Motor Units to turn on, recruiting more muscle - in the hope we can then progress our strength further and further. OR 2. Cause more muscle micro-tears for growth, so the motor units that currently turn on are attached to larger/stronger fibres, so they can perform the movement better. Both ways provide more muscle fibres for the task, but only one way actually increases your current muscle mass/ size. Moreover, they happen to require two entirely different training approaches, one being strength focused (motor unit recruitment), the other mass building (muscle damage).

4. Recovery

As stated, increases in muscle size from micro-tears can only occur when given adequate amounts of Rest and Nutrition. So what happens when we don't give damaged muscle these things? Well, it still eventually gets repaired, but it could be at the sacrifice of existing tissue, which will have a kind of 'size-exchange' effect, leaving you exactly the same size as before OR if your Recovery is especially bad - smaller than you were before. But say you ate enough good quality nutrition to stay exactly the same as before, what happens then? Your motor units were still stimulated in part, so they could provide you with more strength next session, despite your muscles not increasing in size. So, you can be increasing in strength a lot, but not actually increasing your muscle size. This would be the goal for say, Olympic lifters - where body weight is also relevant to strength in competition.

5. Crossover

There is plenty of crossover between Strength Training and Bodybuilding, and it is a major contributor to how confusing the entire relationship between the two subjects is. It is mainly to do with individual biomechanics and the exercise approach. Increased time under tension potentially causes more micro-tears long-term than low rep, high weight training. But, low reps (1-5) can still produce micro-tears, and therefore cause potential muscle size increase - but as the motor unit recruitment becomes better over time, this will decrease dramatically. Also, a sudden change in stimulus from either training style to the other will cause a huge spike in Micro-tears as well, purely because the body is not used to performing the different task; Strength trainee's muscle won't be conditioned to prolonged time under tension (8-15 reps), and Bodybuilders won't be used to the increased resistance their muscles must handle for a lower rep range found in strength training.


Weight Training produces different results for every individual, and what results you get from any training style depends on your genetics. Think of strength increases as a Central Nervous System response, and Muscle Size as a micro-tear repair phenomenon. Sometimes, each training style can benefit from the other in order to improve and progress long term. Recovery and Nutrition can be used to control muscle mass gain, and if held at maintenance level can limit the body's adaptation to just a Motor Unit response. Although more muscle mass can give you the potential to get stronger, it is much more effective to stimulate the nervous system and motor units if your only goal is to be strong.

Happy Lifting!


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