Let's rethink the performance foot. Good morning. Happy Monday. I have neuro coffee in hand and it is perfect. All right, almost as perfect as the Intensive 12 went this weekend. It was fabulous. Had a great group of people in there. The neural coffee was flowing. Questions were great. The model evolved. We talked about things that we'd never talked about before at any previous Intensive, so that was really, really cool. I am looking forward to Intensive 13 so much. I think we had about five weeks. We're about five weeks out from that. So again, looking forward to that. We'll probably get one done in August. I'll let you guys know about the dates on that one. Quick housekeeping. IFAS University. We have a Q&A call on Zoom at 1pm Eastern Standard Time. So don't forget about that. If you are not signed up for IFAS University, I suggest you do it very, very quickly so you can join us on that call. So over the weekend, obviously very busy with the intensive, dug into the Q&A email and there was a foot question in there and we talked about feet over the weekend. So I thought it'd be really cool to do an encore presentation of the performance foot video that we did way back in November. Very, very useful in regards to perspective and some really good information to sort of get you to look at feet just a little bit differently. So we're gonna cut away to that here in just a second. If you would like to participate in a 15 minute consultation or you have a question, go to askbillhartman at gmail.com and leave me a question there or put 15 minute consultation in the subject line and we'll arrange a call at our mutual convenience. Everybody have an outstanding Monday. We will cut away to the performance foot video here in just a second and I will see you tomorrow with a little bit of perspective on the performance related foot because I think it's still a little bit of a challenge for people because of some of the biases that have been created over time and some of the perspectives as to what constitutes a good performance foot versus one that is interference. And so I want us to look at this thing differently. Now, let me preface everything that I'm about to say is that performance is multifactorial. There are so many potential influences here. It's not just a foot thing. The foot is one part, but we're gonna talk about it in isolation to give you a little bit of perspective. So the things that you also probably need to consider is like, okay, what kind of an archetype are we dealing with? What are some of the proportional issues in physical structure. So the size of your thorax relative to the size of your pelvis is an influence in performance. Your proportions as far as you know the length of your axial skeleton to the length of the appendicular skeleton is an influence. Your force-to-weight ratio etc etc etc. So so again let's let's keep this in perspective, okay? The first thing we want to do then is we want to review a little bit about the simplified foot model. So we're going to go through the phases of this foot position. So our traditional heel rocker would represent this early propulsive phase. So as I bring the medial calcaneus to the ground and I get the forefoot to the ground and the toes are extended, the tibia is still behind the foot. So this is an ER position. So I still have an arch and I've got an ER tibia relative to the foot. And so that's my early propulsive foot. As I move through middle, this is where the arch is going to move down towards the ground. So this is your traditional pronation. This is tibial interrotation. So this is a lower arch. Now, here's the key element of this that I want you to understand is that the maximum force into the ground is that maximum pronation. And where that is, max propulsion is just as that medial calcaneus re-brakes from the ground and so this is actually a low position of the arch because right after that I'm going to get a bunch of concentric orientation on the plantar aspect of the foot. This is what they traditionally call that windlass effect and I'm going to crank that sucker back into an externally rotated position right and that is traditionally considered this high propulsive foot with the force application came just prior to that. And so this is the demonstration of what happens after that force production. And so when we talk about a performance related foot, this is why we're going to see lower arches on a lot of these really, really high performance. And so people look at these feet, and they go, oh, these are really crappy feet because pronation has always been described as this accommodative foot position, which is not untrue. But the highest force production also happens in maximum pronation. So that's where our max propulsion is. So when we look at feet like this, it can be a little confusing as to why we would see these low arches. But what they're actually doing is it's a time saver that allows these athletes to get to maximum propulsion much faster than what we would consider our non-athletic population. So that's what they're representing. Now, we've got some subtle differences between these low arched feet as well that we can talk about. If we have someone that is closer to maximum propulsion than, say, another athlete, what you're typically going to see under these circumstances is you'll see, if we were to make a comparison in performance, we would see a better broad jump than vertical jump. So it doesn't mean they're bad vertical jumpers, it just means that as a representation of where they perform the best, they are better at horizontal projection because they are so much closer to maximum propulsion than another athlete would be. And so they'll have the quicker first step. They'll have great acceleration. But what you're going to measure, to throw them on the table, they're going to be biased more towards external rotation. So remember, as I break that foot, I get this concentric orientation that's going to move me quicker towards the ER. So what happens is they have a reduced yielding strategy, which again, that dampens their ability to produce a vertical jump, but it also improves their horizontal projection. They're going to have limited hip flexion. They'll probably have a limited straight leg raise, et cetera, that's associated with this extra rotation bias and a reduced yielding strategy. If I move you back just slightly from max propulsion, I have now just increased the amount of time that you have between where you are as a representation of your center of gravity and maximum propulsion. So in doing so now, I've actually increased the time that you have to produce a yielding strategy. These are the people that will have a better vertical jump than broad jump as a representation. But they're going to be a little bit slower in regards to change of direction. But they're going to have better top speed because their vertical projections are better. They're going to have slightly less external rotation bias. So they're going to have a little bit more of an internal rotation capability than, say, our guys that are better horizontal projectors. And so they'll have a little bit better hip flexion, a little bit better straight leg raise. So if we look at a couple representations of feet, I'll try to show you the subtle little difference. So what we have right there is a pair of feet that can run a 4-4-40. So he is very, very good at acceleration. He is very, very good at change of direction. So this is a Division I football player, and he played four years of high level Division I football. This other representation right here it looks very very similar but this is a better vertical jumper than a horizontal projector and so this is actually a very very high level basketball player and so he's got a better vertical jump than horizontal projection and and so again subtle differences as to how close these guys are to to their maximum propulsion phase. Now, let me show you another pair of feet that don't jump very well and not very fast, but also on a very high level basketball player. So this individual has a much higher arch. He has positioned much more into an earlier phase, so he's a little bit slower. He doesn't jump as high and he's not as fast. It doesn't mean that he can't play high level basketball. It just means that he's going to rely on other things. This person also happens to be exceptionally tall. And so again, we have all of these representations. So again, everything's multifactorial from a performance perspective. There are many different ways that these people can perform. But what we want to start to think about is like, okay, I have these different feet. They're going to be better at different things. And it is one element that supports this high level of performance. Now, let's take this into the clinic. So I can take these same concepts and I can start to look at my, quote unquote, normal people from a very, very similar perspective. So when I see a pair of feet that might be more pronated, so the arch is lower to the ground, I might have this person that is struggling with gravity. And so they're in a situation where they're constantly producing a higher force into the ground because they're just not managing gravity as well. He will have the compensatory strategies that we'll typically see. He'll have a lot of concentric muscle orientation, and therefore a lot of limitations in range of motion. Under those circumstances, we probably want to move him away from maximum propulsion to give him the capacity to move through his extra rotation to intro rotation strategies, and this allows him to move away from the ground to reduce the concentric orientation and then restore a lot more of the active range of motion that he's missing. So again, it's just a matter of perspective of what we're looking at, but feet are always a great representation of this. They're very confirming as far as some of your measures that you're going to find up the chain, so to speak. So some of your top-down influences are going to be represented in the feet. If you can't manage this from a top-down influence, then it may be it is time to do something about this at the foot. So maybe this is your manual therapies for the foot. Maybe this is selecting activities that are specifically designed to improve the representation of sensation from the ground up. Maybe this is the person that you put in an orthotic as a solution to give them the capacity of adaptability. Performance is an intentional reduction of adaptability to create a higher level of output. Whereas when we're trying to make people more adaptable, such as the rehab situation, now we need to take away some of that reduction in adaptability, restore it to give them the ability to rest, reduce concentric orientation and then restore ranges of motion.

So it doesn't mean they're bad vertical jumpers, it just means that as a representation of where they perform the best, they are better at horizontal projection because they are so much closer to maximum propulsion than another athlete would be. And so they'll have the quicker for a step. They'll have great acceleration. But what you're going to measure, to throw them on the table, they're going to be biased more towards external rotation. So remember, as I break that foot, I get this concentric orientation that's going to move me quicker towards the ER. So what happens is they have a reduced yielding strategy, which again, that dampens their ability to produce a vertical jump, but it also improves their horizontal projection. They're going to have limited hip flexion. They'll probably have a limited straight leg raise, et cetera, that's associated with this extra rotation bias and a reduced yielding strategy. If I move you back just slightly from max propulsion, I have now just increased the amount of time that you have between where you are as a representation of your center of gravity and maximum propulsion. So in doing so now, I've actually increased the time that you have to produce a yielding strategy. These are the people that will have a better vertical jump than broad jump as a representation. But they're going to be a little bit slower in regards to change of direction. But they're going to have better top speed because their vertical projections are better. They're going to have slightly less external rotation bias. So they're going to have a little bit more of an internal rotation capability than, say, our guys that are better horizontal projectors. And so they'll have a little bit better hip flexion, a little bit better straight leg raise. So if we look at a couple representations of feet, I'll try to show you the subtle little difference. So what we have right there is a pair of feet that can run a 4-4-40. So he is very, very good at acceleration. He is very, very good at change of direction. So this is a Division I football player, and he played four years of high level Division I football. this other representation right here it looks very very similar but this is a better vertical jumper than a horizontal projector and so this is actually a very very high level basketball player and so he's got a better vertical jump than horizontal projection and and so again subtle differences as to how close these guys are to to their maximum propulsion phase. Now, let me show you another pair of feet that don't jump very well and not very fast, but also on a very high level basketball player. So this individual has a much higher arch. He has positioned much more into an earlier phase, so he's a little bit slower. He doesn't jump as high and he's not as fast.

Hopefully that gives you a little perspective on what we're talking about regarding the performance-related foot and how it might relate to what we're measuring on the table or what we're seeing on the court or on the field. Yesterday we talked about the low arch performance foot. Apparently it's turning into foot week. We're going to talk about the higher arch representations. Remember, we have two positions of the foot where we see this higher arch. So in our early propulsive foot where the toes are in line with the first metatarsal, we have first contact with the first metatarsal medial heel. This is where we start to superimpose internal rotation on top of the external rotation field, so we have an externally rotated foot, but this is our first representation of IR. What we're going to see mostly in the hip is preservation of a straight leg raise, access to early hip flexion, and partial availability of internal rotation up into the hip. When we look at the later representation, where the heel is off the ground and we're moving back into ER but now we have extended toes under this circumstance, we're going to see all those measures start to drop off. We're going to lose straight leg raise, lose early hip flexion, and start to lose internal rotation. This is really important when we see this high arched foot because we have a couple of representations; we have to figure out where people are. If you'd like to ask me a question, go to askbillhartman@gmail.com. If you'd like a 15-minute consultation, make sure you put 15-minute consultation in the subject line, and we'll arrange that at our mutual convenience. We're going to cut away to a YouTube video where we talked about this high arch foot representation. We'll see compensatory strategies and strategies on how to deal with that. If you're interested in catching up on the videos, they're all up on YouTube. Don't forget to subscribe, and I'll see you guys tomorrow.

So go there. Don't forget to subscribe and I will see you guys tomorrow. And then I had a great mentorship call almost immediately after that, and that's where today's Q&A questions is gonna come from because it was a really neat, really neat presentation a little bit off the beaten path and initially a little bit confusing as to what my mentee was really looking at, and then it just, it becomes clear once you sort of put the pieces together. So we're gonna use that, like I said, to drive to today's Q&A. So let me give you this scenario. The confusing presentation was that the client that he was working with had a limited straight leg raise, limited hip flexion, limited hip IR, but a really high arch in the foot, which again, that looks like a combination of a very late propulsive strategy in the pelvis and the hip, but an early propulsive foot. And so again, there's a little bit of confusion there, but if we break this down, there was one telling representation in the foot that sort of gives it away as to what's really going on. First and foremost, let's talk a little bit about airplane wing physics because if we can understand a little bit about an airplane wing, so bear with me here, if we understand a little bit about an airplane wing, we're gonna understand a little bit more about an arch. So that the way that an airplane wing works is as the air passes over the airplane wing, it creates a low pressure above the wing and a high pressure below the wing and that's what creates a lift. If we look at the arch of the foot we're going to see a very similar representation here. So if I look at my early propulsive foot, I have an arch. And so what I actually have is I have a lot of concentric orientation underneath the foot in this early propulsive strategy. So this is a concentric yielding strategy on the bottom of the foot, which means that I have this eccentric strategy on top. So eccentric is high volume, low pressure. Underneath we have concentric orientation, which is low volume, high pressure. So this is literally just like an airplane wing. And so again, low pressure on top, high pressure on the bottom. And that's what's gonna help me maintain that arch as I move through the three rockers so so I have my early propulsive phase which is my my heel rocker and then my ankle rocker so to have a normal ankle rocker what I have to be able to do is I have to be able to flip flop the pressures so I have to be able to create the eccentric orientation on the bottom so the low pressure strategy here and the high pressure on top and so if I can't create the transition in pressures, I can't translate the ankle over the foot. And so it looks like I might be stuck here.

This is also going to help you sort of diagnose what kind of an orthotic you might need, what kind of a shoe you might need. That's a different story for a different day. Bilateral symmetrical exercises by design stop rotation. So they are for max propulsion. Good morning. Happy Wednesday. I have neuro coffee in hand and it is perfect. All right. So today is Wednesday, that means tomorrow is Thursday, which means 6am tomorrow morning. Coffee and Coaches conference call. Please join us for that great group of people, great questions, always got new people coming on. So this thing is growing and I'm having a blast doing it, so we're going to keep doing it. So again, please join us for that. This week has been sort of about the foot, and we talked about early and late phases of propulsion. So why not capture middle today? So we're going to talk a little bit about middle propulsion today, a little bit about max. I got two segments for you that we've done in the past. One was actually a conversation with Drew and Dusty Keele, the quarterback docs. And I got to hang out with Drew for a few days over the weekend at the intensive. So we had a great time there. But this was a question in regards to some rotational athletes and how we want to influence the extra rotation capabilities, middle propulsive capabilities of these athletes by exercise selection. So I think it'll be a very useful Q&A for you. And then we slide into a max propulsion question that we've answered in the past. Again, that goes into the details of that. So again, really good Q&As for you for this week. And if you would like to participate in a 15 minute consultation, please go to askbillhartman at gmail.com, askbillhartman at gmail.com, put 15 minute consultation in the subject line and we will arrange that at our mutual convenience. If you have any other questions, go to the same email askbillhartman at gmail.com and I will try to answer those for you as well. Alright, everybody have a great Wednesday and I'll see you tomorrow morning, 6 a.m. Coffee and Coaches Conference call.

If I'm teaching a young quarterback, I love what you teach about compression on one side and expansion on the other side through unilateral work. So if I was starting with a younger quarterback who is learning basic skills and is novice in the weight room, what should I start with in that unilateral motion to create expansion and compression, to really maintain the external rotation fields that I want to keep versus starting them on bilateral lifts like a bench press, squat, or deadlift? I want to conserve that external rotation field as long as possible while avoiding internal rotation.

So a compressed athlete that we know is lacking some rotation in areas where we want rotation would he ever perform an exercise with his foot flat? Would we want him to do that? If he knew he was compressed. Sure. Okay. So would that be interference stuff? Because in my mind, that's mid-medical.

But in the split stance representation, look where the tibia is going to fall. So the tibia is going to fall behind or it's going to fall in front. And so now I'm playing with terms, right? What you might want to reorganize your little question is that, do I want their feet symmetrical? So Slasha says, assuming mid propulsion falls in this propulsion phase, would mid be an exhalation bias? And I would say absolutely it is. So as we move through the phase of propulsion, we're going to be landing in an ER inhalation strategy, we have to move through this middle phase of propulsion where we're going to increase that IR gradient, exhalation bias gradient, and then as we leave and we go into this late propulsive phase, we're going to re-extrally rotate, and we're going to move towards that inhalation bias again. Now, Slasher continues, he said, I would think that late propulsion would be a max propulsion stage of gate, and then that would be biased towards an exhalation moment, but based on the way that the propulsion is presented, it's an E-R orientation, is this correct? Or is it externally rotating from a state of interrotating that gives me my late propulsion? Okay, so here's what we gotta understand first and foremost, and I think this is the point of your confusion, Slasher. is that the implication that the late propulsion is max propulsion and that is not true. So what we want to do is we want to look at where maximum force is being produced. And so what we'll find is that the maximum propulsion is going to occur as the calcaneus breaks from the ground. So if I have my foot, my reposition of the foot, so I landed early, I've got a high arch, I'm ER'd, I got a plantar flexed first ray, and as I move the tibia over the foot through this middle face, the belief is that that is going to be the late stage of propulsion. Now it's late in regards to how we designate the segmentation of propulsion, but it's not the highest force. The highest force actually comes right as I break the calcinius from the ground, because this is the point where from a traditional standpoint maximum pronation actually occurs. So here's what we want to do. We want to think about this from an evolutionary standpoint, okay? So we were swimmers before we were walkers and so our biases towards inhalation to float, okay? And external rotation because we didn't have to produce force against a fixed point and so we used a lot of external rotation as swimmers. So just watch a frog swim and you'll get the idea. When we come up on land and we have to deal with gravity, this is where we started to learn how to internally rotate and produce force. So the point of maximum internal rotation is actually the point of maximum force production. And this occurs at the very end of this middle propulsive phase where traditional pronation is at a maximum. Where else will we see this? Well, we're going to see this in any rotational sport where we have to stop our turn to create some sort of forward momentum into an implement. So if I'm throwing a baseball, if I'm swinging a golf club, if I'm swinging a tennis racket, All of these these sports will demonstrate the same element where I will have a maximum Propulsion where actually have to stop motion and I translate that into the implement and that is the point of max propulsion during those activities So if we think about a baseball pitcher, it's when the lead leg that's stepping towards home plate is hits its point of maximum propulsion as they're landing through the heel because they never get towards this end propulsive phase except through follow through which is actually an external rotation moment which is actually a re-inhale if you will as they're following through. So again maximum propulsion is not not in this late phase of the propulsive continuum, regardless of what activity that we're talking about, whether we're talking about gay or whether we're talking about sport. It's actually at the point of the maximum pronation that is an IRD strategy that is an exhalation bias. you're going to have to get AP expansion, but, but start driving like true internal rotation from, from proximal to distal.

And this occurs at the very end of this middle propulsive phase where traditional pronation is at a maximum. Where else will we see this? We're going to see this in any rotational sport where we have to stop our turn to create some sort of forward momentum into an implement. So if I'm throwing a baseball, if I'm swinging a golf club, if I'm swinging a tennis racket, all these sports will demonstrate the same element where I will have a maximum propulsion where I actually have to stop motion and I translate that into the implement and that is the point of max propulsion during those activities. So if we think about a baseball pitcher, it's when the lead leg that's stepping towards home plate hits its point of maximum propulsion as they're landing through the heel because they never get towards this end propulsive phase except through follow-through, which is actually an external rotation moment that is actually a re-inhale if you will as they're following through. So again, maximum propulsion is not in this late phase of the propulsive continuum, regardless of what activity that we're talking about, whether we're talking about gait or whether we're talking about sport. It's actually at the point of the maximum pronation that is an IR strategy that is an exhalation bias. You're going to have to get AP expansion, but start driving like true internal rotation from proximal to distal.

How are you?

Out of the car, waiting for the train. Yeah. Um, so I've, uh, an older brother who is currently dealing with a situation that one would normally diagnose or self-diagnose as carpal tunnel syndrome. And he plays a lot of piano. He's a very good piano player and obviously he loves to do it and something he wants to keep doing. So I've been trying to help him out. because I think he, he went to his doctor and his doctor wants to start giving him steroids and I was like, really trying to want to, you know, want to stay away from that if he can. But it's not, you know, it's not debilitating to the point where he can't play obviously, but it is getting to the point where It is interfering with what he's doing. So from a conceptual standpoint, I kind of wanted to know how you viewed it from the lens of your model, and then maybe some things to go after or pay special attention to in regards to interventions.

So, there's a very, very good chance that he is lacking internal rotation in his shoulders, is it both sides? Both sides, more so the right. Okay, yeah. So it's very likely that he is lacking the capacity to internally rotate approximately. Right. So, upper thorax, scapula, shoulder are probably lacking a great deal of internal rotation. And so what you end up with is you end up with a lot of compensatory pronation strategy. So internal rotation strategies, because he's got to get his hands into a pronated position to play. And so you'll get a whole bunch of muscle activity. So like pronator teres, pronator quadratus, you're going to get a bony twist in the radius. You're potentially going to get a twist in the distal humerus. He's going to get a pronated hand relative to the radius. And so all of those things reduce the amount of space. And if it's traditional median nerve symptoms that he's getting and not like a global thing, if it's median nerve symptoms, the way that the median nerve tracks through the arm, it's going to get compressed potentially in multiple places, not just here. Okay. This is a biggie. This is a biggie because the last compensatory strategy to get your hand into pronation is pronation of your hand. And so then, then that closes the carpal space there where the ligament goes across the hand. And that's why they do the surgery. They just go in and they go, 'Oh, we just go in there. We slice the hand open. We slice the carpal ligament. We sew it back up. Everything's all fine and wonderful.' But that's the basic issue that you run into typically with that type of a situation is you've got just internal rotation compensations all the way down, literally into the hand. And so you've got to kind of undo that.

Both sides, more so the right.

Okay, great. Yeah. He's definitely one of those people. He's super, super narrow, really tall. And his shoulders are just pulled way, way forward, like no arm swing when he walks.

And then so some of this can be, if he modifies his seat height a little bit, he's actually going to make it a little bit easier for him to get his hands into position. So he might be actually sitting low. Have him elevate the seat just a little bit and see if that prolongs his ability to tolerate the position. But ultimately, I think that what you're going to end up doing is you're going to have to get AP expansion, but start driving like true internal rotation from proximal to distal. Because like I said, chances are he's already pronated down into his hand if he's getting hand symptoms.

Okay, great. So I just wanted to make sure I was kind of going after the right things. I've been, he's also pretty compressed dorsal rostral as well.

Cool. Thank you, Bill.

I had a question regarding heavy sled pushes or sled pulls about the ER-IR relationship. When using a very heavy load for squatting, you make external rotation seem very small while internal rotation becomes much larger. Is this effect minimized with sled pushes when using heavy loads because it's more ballistic? I'm not sure how to explain it, but is it less compressive since you're pushing all the way through with the extremity, or is it still the same?

The same rule applies. So anytime the load is magnified. So the heavier the resistance, the harder I have to push into the ground. The longer I push into the ground, which means that you're going to bring the ERs in. So think about this for a sec. So let's put 10 kilograms on a sled. Okay. And we'll drag that. How big a step can you take? Pretty big. Okay. Now I want you to put 100 kilos on the sled. And what happens to your step length? Yes, shorter. Exactly. Why does it get shorter? Because you don't have ERs anymore. So the rule applies. So when you're using sled work to try to create relative motions, the load matters. We can go back to Matt's question. So the position matters. The load matters. The extremity behavior matters. And so you just have to decide what it is that the intention right? It's like, I can create more emotion with resistance, but the resistance has to be to such a degree that I still have access to compression expansion because that's what's turning is. The minute I ramp up where compression becomes the predominant behavior, I've just narrowed my cones, so to speak, into the IR representation.

Yes. Shorter.

The same rule applies. So anytime the load is magnified, the harder I have to push into the ground, the longer I push into the ground, which means that you're going to bring the ERs in. So think about this for a second. So let's put 10 kilograms on a sled and drag it. How big a step can you take? Pretty big. Now I want you to put 100 kilos on the sled. And what happens to your step length? Exactly. Why does it get shorter? Because you don't have ERs anymore. So the rule applies. So when you're using sled work to try to create relative motions, the load matters. We can go back to Matt's question. So the position matters. The load matters. The extremity behavior matters. And so you just have to decide what it is that the intention. Right? It's like, I can create more emotion with resistance, but the resistance has to be to such a degree that I still have access to compression expansion because that's what's turning is. The minute I ramp up where compression becomes the predominant behavior, I've just narrowed my cones, so to speak, into the IR representation.

Okay. And then as far as the difference as far as I understand between like a squat or a deadlift or a sled push is that you're not as—during the push-through, you're not stopping the movement right—you're pushing all the way through and then your foot comes off the ground. So is that anywhere, for example, we're talking about like running, sprinting, or jumping? Is the sled a little bit more transferable to those kind of dynamic movements than a deadlift or squat, or is it still all the same if you're going heavy?

You see the difference?

Yeah. So like a sled push is a lot closer to acceleration. As far as force production goes, then the upright high box step up, which is more top speed mechanics. So if I'm working on very specific mechanics with an athlete, I kind of know where I'm going to go. Right? Yeah.

Does that make sense? Yes. I'm just trying to figure out where heavy training fits into more like court and field athletes. They need to accelerate and change direction.

That would have these four. Yeah. So my approach is that most people I'm working with don't really have enough range of motion to get into good positions to accelerate or change direction. So I'm getting away from heavier training. But I'm still trying to figure out when I can still use it, like when it's still useful.

You can still use heavy training when force production is the limiting factor, right? Or if I'm trying to maintain the ability to produce force, but that's a volume-based decision. So if I'm trying to increase someone's force capabilities, and if I do 10 sets of three in a deadlift, that's a lot of volume for force production. If I do two or three sets, that might be enough to maintain that force production. You see the difference? So I'm making a volumetric change. So the strength of the stimulus is magnitude and the volume of that. And then that's what's going to drive the outcome. So it's not that you can't use heavier stuff with people that you're trying to make changes with. You just have to decide how much volume can I do that doesn't interfere with what I'm trying to capture otherwise.