If you have ever heard stories of Mothers hurling vehicles off of their children trapped beneath, then you may have found that such yarns set off your ‘cynicism alarm’. Can there really be any truth to behind them?
As it happens, the answer may just be yes. These stories are examples of what some researchers refer to as ‘crisis strength’ and there’s actually a very reasonable explanation as to how something of this nature might occur.
Your muscles are made from muscle fibers, which in turn are grouped together as bundles called ‘motor units’. These motor units can contain different numbers of muscle fibers, as well as different types – some will contain more fast twitch explosive muscle fiber, while others will contain more slow twitch endurance muscle fiber.
When you contract a muscle, your brain sends signals via nerves and the ‘neuromuscular junction’ to the muscle fibers. This action potential then causes those fibers to fire. What’s key to understand here though, is that when this happens, it causes the muscle fibers in that motor unit to contract entirely. There is no such thing as a ‘partial contraction’. Instead, they act in a binary fashion and either fire all the way, or not at all.
Thus, the power of your movements is not controlled by how ‘much’ a fiber contracts. Rather, it is modulated by the number and type of motor units that fire.
When you’re eating your cereal and lifting a spoon to your mouth, your brain will send signals to the smallest motor units comprised of largely slow twitch muscle fibers. This ensures that you’re not exerting too much force and at the same time, it means that you can continue to repeat the same motion over and over again without tiring out.
On the other hand, any movement that requires you to accelerate very quickly, or to exert a large amount of force suddenly, will require you to use motor units comprised of large amounts of fast twitch muscle fiber. These wear out very quickly though and are demanding in terms of their energy expenditure, which is why you can only perform 10 reps of bench press for example.
The more you have to move and the faster you have to move, the more motor units you will recruit and the greater the proportion of fast twitch muscle fiber will be used.
Limitations and Overcoming Them
Even when trying to lift the heaviest object we can though, our body will still only recruit around 20% of our motor units at once. An athlete might do a bit better and could recruit as much as 50% of their muscle fiber but we will never use 100%.
So what’s the reason for this cap? One possible explanation, is that if we were able to use 100% of our muscles, we would risk injury by tearing ligaments and connective tissue, impacting our joints or even fracturing our bones.
Another theory is that it makes sense for the body to conserve some of its strength and to hold some back. Imagine if you could use 100% of your muscle fiber at the gym and thereby exert all of your fast twitch muscle fiber. If you did this, you would then be left with only your relatively weak slow twitch fiber after a training session. The heaviest thing you’d be able to lift would be a spoon!
Now imagine that you’re in the wild and following this exertion you were attacked by a lion. You’d be completely unable to run away, never mind defend yourself! As you can see then, it simply doesn’t make sense for us to engage our full strength potential in any single movement and this may be another reason for the limit in strength.
Crisis Strength and Berserker Rage
But there are potential exceptions to this rule. One, as you guessed, is what happens in situations where we’re facing life or death, or where someone very close to us is. In another tale of crisis strength, a rock climber is said to have managed to throw a rock off of themselves that weighed several times their bodyweight. In such scenarios, it seems that the body can temporarily ‘override’ the normal cap on strength, thereby giving us access to a much greater percentage of our strength and power.
We may see something similar in cases of ‘berserker rage’ – where intense anger provides us with momentary increases in strength. It’s often commented that certain types of mental disability can also lead to heightened strength.
The survival value of such a provision is obvious as it allows us to escape from situations that otherwise might prove fatal. In terms of the mechanism of action, it’s generally agreed that the fight or flight response is responsible and that stress hormones are what can unlock this type of stress. Indeed, it has been shown that taking stimulants (which trigger a ‘faux’ parasympathetic nervous system response) can increase max strength during weight lifting (1).
Right now, there’s no way for us to access this kind of latent strength at will – and it’s not necessarily something that we should gain access to either. Nevertheless though, it’s somewhat comforting to know it’s there and it’s definitely a fascinating example of just how amazing the human body really is.