How is a pistol squat functional? What do you do in your everyday life that needs you to be able to move like that? There is a way to answer that question, but there’s also a way to challenge whether that’s the right way of looking at “functional”.
I’ll give the short answer. But the longer answer is going to compare a “naive” understanding of functional fitness against the CrossFit model, to see which more elegantly reflects what functional fitness is and its benefits.
part of what you want to be fit for is taking on the unusual; having some fun
Short answer
We’re talking about transferable skills
The short answer is that “functional” training is training that develops basic principles or skills of fitness. So, if there’s a reason you can’t do Pistols, then practising them will help you develop whatever fitness skills are holding you back. Those skills are then transferable into other movements inside and outside the gym.
The Naive Answer
The 1:1, training:life answer
You could define “functional” training as training that replicates movement you’ll do in everyday life, and then at a higher level finds a way of scaling that movement up. I’m going to call this answer the Naive Answer because - although I can see where the thought comes from - it misses some fundamental points about CrossFit and functional fitness. Here’s an example of how the Naive Answer might think about exercise: the movements from a late '90 Mr Motivator step class replicate walking up stairs; larger steps for box steps scale that up as a harder version of walking up stairs; then - there it is - pistol squats are scaling it up again by making the single-leg movement even harder. The idea is that the movement has some 1:1 relationship with an everyday movement.
By the same reasoning, deadlifts are a self-scaling way of replicating picking up shopping by just changing the weight on the bar; cleans are then a way of scaling up the act of picking up shopping to put them on the counter; snatches, then, are… I’m not really sure…
And ring muscle ups are… errr…
There are strengths in looking at it this way: training the squat so that you have high-level (surplus, even) getting-out-of-a-chair functionality sets you at a high-level for when things might start going the other way later in life; you’ll retain the ability to get out of a chair for longer and into older age.
But the definition has its drawbacks. For one, it can’t really explain why anyone other than penguins would do double unders and it’s not at all clear what thrusters are for. Its second major drawback is that it only really assumes that you’re preparing for the everyday, even if part of what you want to be fit for is taking on the unusual; having some fun.
The CrossFit answer
I’m not biased, but this is the correct answer
The real answer for why Pistols are functional is because training to do pistols will progress your balance, strength, flexibility and coordination (and at high-volume, also stamina). That’s 4 (or 5) of the 10 physical skills of fitness.
cardiovascular/respiratory endurance, stamina, strength, flexibility, power, coordination, agility, balance, and accuracy
Unlike the Naive Answer, where all everyday movements would need a progression ladder and every gym movement would need an everyday referent, the Fitness Skills answer says there are 10 physical skills which can be trained by exercise. Those skills, then, can be applied to everyday movements and be used to increase your ability to take on the more unusual challenges; the skills have reach into all movement.
a regimen develops fitness to the extent that it improves each of these 10 skills
With this answer, you can explain why we do double unders (and it’s not to jump and flap like a penguin; it trains endurance, coordination, agility) or muscle ups (power, strength, flexibility, accuracy); you can understand how your fitness goes beyond the everyday; you can still talk about having high-level functionality that can protect against decrepitude due to ill-health or old age, but without having to explain all movements in terms of single movements in the gym.
But… I can’t do a pistol
Fitness neither begins nor ends with any one movement
This doesn’t mean that Pistols are some essential movement and that you should worry if you can’t do them. Quite the opposite: if you can’t do them, then there is something apparent and obvious to work on - but the simple fact that you’re on that journey at all puts you so many steps ahead of other people.
I could go on - there’s CrossFit’s Sickness-Wellness-Fitness Continuum that has gone unmentioned for yet another answer - but that is probably enough to let you explain to your friends why getting upside down and doing handstand push ups - or, at least, trying to - is “functional”.
If you have any thoughts about this, or any other questions you want me to tackle, drop them in the comments