What’s up everybody?
Today we’re doing a biomechanics video.
We’re gonna talk about something called gait.
And gait analyses are something I used to do all the time when I was working in sports
medicine, but because I’ve been a teacher for so long now, I haven’t actually done
one in a while.
So I decided to bring in a little bit of help on this one.
(Maren) Helloooo.
I’m so glad you’re here.
Come in come in come in.
(Patrick): So I recruited my fabulous friend Maren because she’s a YouTuber, she’s
a runner in her own right (something I would want to do).
And she’s done the personal trainer thing.
So what do we need to know about this?
(Maren) Well there’s a lot to cover including some musculoskeletal anatomy, the normal gait
cycle, lots of info which we’ll get to but we’re gonna start with the big picture like
Pat always does — which is the fact that do get anywhere, you need to take multiple
steps.
P: Cool, alright let’s get into it.
P: If you do anything thousands and thousands of times a day, a pattern starts to emerge.
And as it turns out, all healthy, able-bodied humans follow almost exactly the same pattern
for walking.
We care so much because walking is crucial to our independence, so when something goes
wrong with walking, we want to know exactly where things are going wrong.
M: And if someone isn’t walking correctly or is running with poor form, they can end
up with injuries.
This is kind of the exercise equivalent of desk ergo nomics.
We’re taking an activity that you do for big chunks of the day and making sure it’s
not going to hurt you.
While we’re not going to talk about in this video, your footwear plays a role in how you
walk, which I made a video about.
So if you’d like to learn more about that, click on this icon here.
P: So let’s get right into the normal gait cycle.
It may seem like unnecessary detail to get into, but we’re going to such depth because
small tweaks repeated hundreds of thousands of times can rear their ugly heads /hard/.
One full gait cycle starts when the heel of one foot strikes the ground, and it ends when
that same heel strikes again.
That might be counterintuitive that the gait cycle includes two steps, but that’s how
people walk.
They don’t take a step with their left foot then take another step with their left foot.
M: Okay, we can divide gait into two main phases, the stance phase and the swing phase.
To do that, we need to choose one foot to be the star of the show — we’ll choose
the left foot — and that’s what we refer to as either standing or swinging.
Like we said earlier, the stance phase starts when that heel strikes the ground and throughout
this time, this foot is going to be weight-bearing while the other foot is swinging.
Stance phase can be further divided into three periods that focus on what part of the foot
is in touch with the ground.
We start stance phase with the contact period is when your heel contacts the ground.
Once again, great naming work kinesiologists.
That’s followed by midstance where your heel and forefoot are on the ground, then
the propulsive period where you’ve transferred your weight onto your forefoot and you’re
barely putting weight on the left foot anymore.
At this point, your other heel has touched the ground and is starting its stance phase.
This means your left foot is off the ground, ready to swing forward and keep you moving.
P: This one can be divided further also, but we generally give this one less attention
since the foot isn’t weight-bearing, so it’s less likely to be the /cause/ of pain.
One thing that is interesting is that when that food is swinging forward, most people
have about a /centimeter/ of clearance between them and the ground.
So if you scuff your feet every now and then, don’t worry about it.
There’s not much wiggle room.
Now this whole process take anywhere from 0.98 seconds to 1.07 seconds on average, but
a lot can change that.
Things like stride length, age, how competitive of a walker you are can all impact gait speed,
but in general, this whole thing takes about a second.
It makes sense that we’d focus on the lower body when looking at gait, but clearly other
joints move too.
Your arms swing, your head bobs up and down, and everyone sways side to side at least a
little bit.
And we’re not even getting into pronation and supination.
Believe me, once you learn that stuff, you’ll never be able to watch people walk in flip
flops the same again.
M: Apart from anatomical similarities, everyone follows a predictable physics pattern too
— what are called ground reactive forces.
Remember that whole equal and opposite reaction law from physics?
Well as you strike the ground with your foot, the ground pushes back on you.
M-VO: And a graph of that force looks something like this: ground forces are highest when
you first land on your heel, they go down a little in midstance when you spread your
weight between your fore and hindfoot, then increases again as you roll onto your forefoot.
Then when you lift your foot off the ground, the force goes down to zero since ya know,
/it’s not on the ground/.
P: Now, all of that, the stance and swing phase, the ground reactive forces, that all
describes your gait 99+% of the time.
When we transition from /normal/ gait to /abnormal/ is when its multiplied by tens of thousands
of steps per week forever and ever.
A limp because you stubbed your toe?
Not /really/ an abnormal gait.
Even after breaking your leg, spending some time on crutches, and returning to walking,
you can probably return to a normal gait.
So most of the time in young, otherwise healthy people, any abnormal gait is short-lived.These
gaits become an issue when they either lend themselves to greater injury like a fall,
or when they’re the result of an underlying problem like the Parkinson’s gait.
What makes a lot of these abnormal gaits so unique is that every aspect of the nervous
system is involved, both sensory and motor
While there are a ton of different gaits that we could go through, I picked two that represent
different causes of abnormal gait: one musculoskeletal and one neurological.
M: There’s a pattern called the Trendelenburg gait looks like this, a kind of clunky, side
to side sway that comes down to a weakness in the gluteus medius muscle, one of the muscles
on the side of your hip.
You can actually feel it contract if you put your hand on your hip / side butt area, and
swing your leg out to the side.
But the glute medius matters during this gait because it keeps your hips level while you
walk.
So if someone has a very weak glute medius for whatever reason, it won’t support their
body weight while they’re in stance phase, and the other hip will dropdown.
Quick example, if it’s the right side that’s weak, when they stand entirely on their right
foot, their left hip will drop.
And as they’re walking, their hips will drop with each step, making it look like a
little sway.
P: Now, while this gait is ultimately due to weak muscles, remember that all kinds of
things can influence even /that/ from neurological issues to muscle imbalances.
But some abnormal gaits are entirely due to neurologic conditions.
Like if you know anyone with Parkinson’s, you know just how badly the brain affects
their ability to control movements.
But we would be colossal jerks if we acted out a Parkinson’s gait on camera, so we’ll
choose something else.
Something you might see this weekend if you go to the right bar.
Ataxic gait results from loss of motor control — that could mean from alcohol, or from
different places in your nervous system that affect balance.
For instance, someone could have sensory ataxia because of a lack of bodily awareness /somewhere/.
Say they’ve lost sensation in their leg for instance, kind of like when you’ve been
sitting criss cross applesauce for too long and you can’t feel your feet.
Your stance gets wider, slower, and relies on your other sensory inputs that still work
well.
So to assess this kind of gait, you’ll make your observations and usually test balance
with things like single leg stance or tandem walking.
This is all still an extremely simplistic way of looking at gait, but if you’re going
to dedicate years of study to this, you’re going to have to learn how to study these
things.
And we actually did a video on Maren’s channel all about how to study.
All about studying so if you’ve ever found yourself in an exam situation and been like
“holy crap, how did I not study this?
How could I have prepared for this better?” then I think that our video that we made together
over on my channel might be really helpful.
We’ll link it at the end of this one, it’ll be down in the description.
Everybody, have fun, be good, I’ll see you next time.
Thanks for watching.
Nice to meet you.