The Fallacy Of The Force-Velocity Spectrum & How Jump Testing Impacts Programming w/ Paul Comfort

Paul Comfort0:24

And now, luckily, there's a small team of us at the University of Salford actively involved in research, supervising PhD students. And some of those students are based at the university. The majority are aligned with sports teams or work full-time in professional sport, but also are doing their PhDs part-time. That's both a blessing and a curse. They can collect data on a daily basis, that's easy, but then they have to find time to write up their PhDs, which is a little bit more of a struggle.

James de Lacey2:32

For sure. Your early research was in rugby league, correct?

Paul Comfort2:32

Some of it, yes. So I suppose the early stuff was in rugby league or looking at all the different weightlifting derivatives.

James de Lacey2:57

I cited your strength, speed, and power characteristics in elite English rugby league in my strength, speed, and power characteristics paper I published a few years later, but in the NRL.

Paul Comfort2:57

Oh yeah, that's awesome.

James de Lacey2:57

Rugby league was my first love within strength and conditioning.

Paul Comfort2:57

It's a good space to be in.

James de Lacey2:57

But it'll be interesting to kind of go into, you mentioned weightlifting derivatives as well, we'll definitely touch on that. But some of, I think probably strength, speed, power characteristics is probably where a lot of your research really lies. It'll be interesting to kind of maybe start around testing and what tests you find applicable and how that can influence programming. That's a very broad question, but I'll let you take that kind of where it goes.

Paul Comfort3:27

Yep, no problem. So we've kind of refined what we do compared to certainly compared to that paper back in the day. So we'll definitely make sure we've got sprint performances in there and ideally change of direction performance, 505 change of direction, and sprints, 20 up to 30 meters with 5, 10, 20 meter splits, because obviously that's one of the things that athletes and coaches want to know: who's the fastest, who can perform this task both efficiently and effectively?

We'll have jump tests in there as well. We stopped doing squat jumps. It's fine if you're doing a squat jump on a contact mat or an Optojump or something, calculating jump height from flight time, and you generally don't notice that athletes cheat, and they will actually perform a slight countermovement. As soon as you get them on a force plate, it's terrible trying to get them to perform a squat jump without them performing that countermovement.

And actually what you find is, we've used in the past, I think in that paper we might have reported eccentric utilization ratio, so the difference between jump height from a countermovement jump and jump height from a squat jump, with the assumption being that the difference is due to better utilization of the stretch-shortening cycle in the countermovement jump and you don't use it in the squat jump. It doesn't appear to be due to that.

All it just appears to be a complete difference in posture and depth that you squat to. In fact, you can allow your trunk to fall forward quicker and gain more momentum, and the joint configurations when you're jumping are completely different in a countermovement jump to a squat jump. So it doesn't necessarily appear to be stretch-shortening cycle utilization.

James de Lacey5:11

Do you still use that eccentric utilization ratio but with different jumps?

Paul Comfort5:11

No, we pretty much just abandon it and don't bother, because there's no really good way of standardizing it and comparing. Because you can't say, well, let's do a countermovement jump, let's look at the depth you squatted to, and then let's make sure you squat to the same depth on a squat jump, because as I said, people just cheat all the time and it takes too much time in that sort of applied setting. So we generally don't bother with the squat jumps there.

So what we'll normally do is something like an isometric mid-thigh pull to get maximum strength or maximum force production. And if the athletes are familiar with it, we can also get rate of force development or force at specific time points with the isometric mid-thigh pull. We'll then do a ballistic task of slow stretch-shortening cycle, like the countermovement jump, and then normally a fast stretch-shortening cycle task, like some type of rebound jump.

Most commonly recently, we've been using a countermovement rebound jump: a countermovement jump that is comparable to their countermovement jump height, followed immediately by that reactive rebound, get off the floor in under 250 milliseconds, to make sure it truly is fast stretch-shortening cycle and reactive.

Now we've been doing that because we've been traveling around a whole host of football teams, teams at different levels of competition, different age groups, and also a few rugby league clubs as well. And because we're traveling in, taking six or seven sets of force plates with us plus three isometric mid-thigh pull rigs, there's just not room for boxes to do drop jumps. And also, there's limitations with every reactive jump.

If you do a 10-5 test, the best jumps are the last five jumps, so what's the point in doing the first ones? It's almost a waste of time. So we've reduced that down to a countermovement jump followed by a rebound. If you do a drop jump, nobody falls from the height of the box. If they're confident, they plant their feet and go from a higher height. If they're not confident, they step down.

It's only, if you look across the research, it's about a 20% difference from the box height, but that means one day an athlete could jump from, if it's a 40-centimeter box, they could jump from or drop from 32 centimeters. The next time it could be 48, so not comparing like with like, which is a bit of a problem.

So we've actually found if we set a threshold on the countermovement rebound jump of being within 10% of their countermovement jump height for the countermovement jump that precedes the rebound, we've halved that error. It's not perfect. You can't say it must be exactly the same height as your countermovement jump, because getting that level of consistency and not being within a centimeter or two is quite difficult, but it tends to work quite well.

On the odd occasion, you'll get, especially with some of the bigger rugby league players, they can't make 250 millisecond contact time no matter how much you coach them. I've had people say that they struggle to do that with most athletes. That's just poor coaching in most cases.

In fact, we had a student who went and did some testing doing the countermovement rebound jump. We looked at all the data when they got back and made them go back and recollect all the data because it was terrible. No contact time was sub-250. So I don't know what they'd been obsessing over, but it certainly wasn't the contact time. We went back in a couple of days later, retested, and every single person got below 250 milliseconds.

James de Lacey8:12

What was the cue you ended up giving to get there?

Paul Comfort8:12

Just to be, get off the ground as quickly as possible on that rebound and stiffen up. So what we found, we have to do is...

Because they've done counter movement jumps first, they're quite compliant with those. The first counter movement rebound jump, they always do a compliant strategy. So what we basically get them to do is some pogos, maybe five or 10 pogos, before they do the counter movement rebound jump. You cue them faster, higher, and then make them do the counter movement rebound jump. Suddenly they can do it.

So it doesn't take a huge amount. It's just adding that reactive, almost familiarization and warm-up for them, and then they can normally nail it within the first four or five trials. And that's still then less fatiguing than doing the 105 task, because you've only done five rebound jumps. Not that it is fatiguing, but some athletes or some of the medical staff will complain that it may be fatiguing if they're doing too many trials.

So yeah, we do the counter movement rebound jump together. Use that reactive component. If they can't do it, and as I said, some of the much heavier rugby union and rugby league forwards struggle with it a little, but that's fine. That tells us something. If they've had 10 trials and they still can't get a short contact time, that tells us they need to train that reactive component.

But then we can also go back and see, well, speak to the performance analyst: how do they play in the game? Do they ever cover more than 20 meters? Because if they don't, do we really need to focus on that really, really short reactive and ground contact time? Or are they the person who's a battering ram and only ever goes 10 to 20 meters and that's it? In which case, that probably explains why they can't do the reactive jump.

Then we do the counter movement jump, so we've got that slow stretch shortening cycle. And then that gives us a nice profile: how strong are they, what's their counter movement jump like, what's their reactive jump performance like, and how balanced are they in that? And how does that compare to the normative data that we've collected over the last few years?

I'm going to generalize now. In general, soccer players are weak. Jump height can be great, reactive capability can be great, but they're weak. What that tells us is, if you look at their training, that's not surprising. But the only way they're going to get better at those reactive and plyometric components is to actually just get stronger in general, because they're very efficiently using the force they can produce, but they can't produce much force.

However, if you look at the goalkeepers, the goalkeepers you sometimes flip that. Sometimes you've got the goalkeepers who have got a really high relative strength level on isometric mid thigh pull, can produce force quickly in doing that task, great on the counter movement jump, not very reactive. Again, their generalizations, there are a few differences in there.

If we look at rugby league, they tend to be more balanced and quite good across the board. But then you've got those who are phenomenal rugby league players, and you look at their performances and go, wow, why can't they perform on an isometric mid, counter movement jump, and a rebound jump? That's a bit worrying. But they should sign when you watch them. They read the game so well, but they're the person that covers the least distance on the pitch because they were always in the correct position.

And then you get some anomalies. We had one guy with an isometric mid thigh pull relative peak force, and this is net peak force of subtracting his body mass, that was up at about 55 Newtons per kilogram. So pretty high, one of the highest we seem to get when it's expressed as net force. Over two and a half times body weight is a back squat, and that's a full depth back squat.

Counter movement jump height 65 centimeters, so pretty good. So we're looking at this going, what does he need to do? He's 120 kilos, he's got low body fat, what does he need to work on?

And in that example, we looked in more detail at the isometric mid thigh pull and found that the rate of force development was relatively low, certainly at the early time points. Looked at the counter movement jump, and while he was jumping 65 centimeters, it was taking him 1.2 seconds. So time to takeoff was huge. I think the average for the squad was just under 750 milliseconds.

So he was taking half a second longer, which means that if you're the average person in that squad, you've jumped, caught the ball, landed, and started to sprint before he's left the ground. That's not a good situation to be in.

So for him, he had to work more on producing force as rapidly as possible. And actually, I think the strength coach after about six or seven weeks of preseason had him at the point where he dropped about 2 centimeters off that counter movement jump height. So that's well within measurement error. No one would know. But he got his time to takeoff down to about 750 milliseconds, so it was similar to the rest of the squad.

The isometric mid thigh pull performance was the same in terms of his relative peak, but actually his rate of force development, the curve was much steeper. So that improved quite dramatically. But it's rare that you get those anomalies like that where you look and go, wow, what do we do with this person? And then you have to really start interrogating the data more to figure those things out.

Most cases, you can go relative peak force in the isometric, jump height and time to takeoff on the counter movement jump, jump height and ground contact time on the rebound jump, and that gives you a good profile of which you can program from. But it's only once you get those anomalies where they're either not very good at anything or they're phenomenal at everything that you go, wow, okay, we need to look and really identify the priorities.

James de Lacey13:27

That's awesome. And for some examples, it would be interesting I think for the audience as well. You mentioned that player, okay, his rate of force development wasn't so great. So what would be something that would be programmed, or how would the program generally look to improve that quality for him? And you mentioned obviously his counter movement jump came down a bit, so I'm assuming then they also put some other stuff on the back burner to be able to prioritize that.

Paul Comfort13:54

Yeah, so he ended up focusing a lot more on, still do some heavy strength work, but they'd reduced the volume of heavy strength work. So if he'd been doing five sets of five reps at 85% or one rep max, it was dropped to three sets of three, just to try and maintain strength at that point.

Some heavy weightlifting, pulling variations, to really focus on producing high force but as quickly as possible. And then loaded counter movement jumps and unloaded counter movement jumps with him being cued to basically be as explosive as possible. And it was nothing particularly fancy. Some of those loaded jumps were hex bar jumps. Some was a barbell on the shoulders to give some variety. A little bit of low-level plyometrics. Those were just pogo type tasks.

I said he was 120 kilos, was never running more than about 30 meters, so it didn't really need to focus on that aspect. And yeah, it was basic stuff that was done consistently. And again, making sure that the volumes weren't too high. This was the start of preseason, so he'd come back from the off-season doing a lot more hypertrophy type work. So part of that could have just been residual fatigue.

And we know that rate of force development or rapid force production is impaired by high volumes of training. So just reducing that volume of the very high load at first and focusing on other tasks seemed to create those improvements. And yeah, like I said, 2 centimeter drop in your counter movement jump, that's within measurement error. So you're happy to take that when you've taken 500 milliseconds off your movement time.

James de Lacey15:13

Awesome. We've also talked about their counter movement jump and breaking down or looking deeper into their data, because obviously you can look at jump height, but jump height doesn't give you how they got to that height. And so we've talked about some of their force time stuff. So it'd be interesting, I think, there was a company, right, it was a Sparta that was profiling athletes just off one counter movement jump.

I'm not sure if you're familiar or not. I don't know if that's even possible to be able to take a counter movement jump and be like, okay, you need to work on this. But it would be interesting to hear your take on force time curve and what you're looking at there. And can you influence programming or get a sense of an athlete's power profile from that, just from a couple of trials?

Paul Comfort16:00

You probably can't get a huge amount because you need to, like I said, you can have somebody who's got good jump performance, and we've seen this within soccer players. Really good counter movement jump height, short time to takeoff, so they look like they're a really good athlete. But they could be really weak and the reactive capability might not be great. So you definitely need a profile of those sorts of tasks to really identify what they need.

In terms of the force time curves, it's starting off keeping it simple. So if you've got time to takeoff and you've got jump height, that gives you a good indication of their strategy. If they're taking a long time, like the example I used, over a second, you know they've got quite a compliant strategy. They're unweighting relatively slowly. They're not hitting the brakes particularly hard. They might be going for a big counter movement.

I think, if I remember correctly, that one athlete that I referred to that the 65 cm countermovement jump was going through about 55 cm of countermovement depth on the way down. The average around about in that squad was around about 40 cm. So he's squatting a lot deeper, going to take longer.

Now what you want is not necessarily somebody not to squat as deep, but you want them to do it quickly. And if you look at some of the early work that Cormie did back in 2007, 2008, they found actually just getting people stronger—people that were, I think there was people squatting less than 1.4 times body weight trying to back squat—if you just train them for strength, they improve their countermovement jump performance more than doing loaded jump training at the load to optimize their power output.

Now that actually makes sense once you look in that study at the force-time data. They actually found that they unweighted quicker. That means you got a higher momentum on the way down. If you're moving quicker on the way down, your momentum's higher, so you have to hit the brakes harder. You have to generate more force or it's going to take a lot longer to stop.

So what happened, they referred to it as eccentric forces or eccentric rate of force development was higher. Now we shouldn't refer to it as eccentric necessarily because you don't know what each individual muscle group is doing during a countermovement jump just from force-time data. And you could have gone through max dorsiflexion so that you've gone isometric with the tricep surae complex, you'll still be flexing through the knee so your quads might still be eccentric, but we don't know exactly what's happening.

Now that is semantics, but it's important. We really need to be thinking about it as the unweighting and the braking phase, because that's what the force-time gives us, and then propulsion at the end. But Cormie basically demonstrated that that unweighting phase decreases in duration, which means you move at higher velocity on the way down because they still squatted to a similar depth. So to achieve that same depth in a shorter time, you've got to go at higher velocity.

The braking characteristics improved dramatically, and that was—this was just from getting stronger. So your ability to hit the brakes and decelerate quicker improved, which removed time, to reduce time to takeoff substantially. And they also resulted in a higher propulsive phase impulse which caused a high jump height. And that was just from getting people stronger.

Which still surprises me now that when people say, "Oh, this person's jump height isn't great, let's do loads of jump training." Well, again, that might be the solution, but actually are they just weak? Are they not able to unweight quickly? Because if you cue an athlete to try and be as quick as they can on the way down, sometimes they get stuck at the bottom. You see them hit the brakes, stop, pause, you've just suddenly lost that utilization of the stretch-shortening cycle.

So they almost need to adopt that faster strategy once they've developed the capability, and that's what tends to happen. So if you keep it simple and go time to takeoff, jump height, how do they both look, you can then break it down if you want to. You can break it down to the unweighting, braking, and propulsion phases if you want to. And if we do that, we can then start to interrogate that data a lot more. But you're probably not going to feed that back to the coach or the athlete because that's probably too much information.

James de Lacey20:19

For sure. I'm going to ask you the question around—you mentioned obviously just get stronger to jump higher—what is there a too strong in that regard or a point where you revisit maybe, hey, we don't need to push that squat up any further, we need to look at the other stuff?

Paul Comfort20:19

Yeah, I wouldn't say you can be too strong because from experience and the different PhD students we've had that have gone on and worked in different clubs, it varies dramatically. Never seen a soccer player with a particularly impressive squat, you know, kilograms per kilogram. Rugby players—Rugby League and Rugby Union—seeing them up at over two and a half times body weight and still getting stronger.

Whether it's through British Cycling or one of my PhD students who works at Hong Kong Sports Institute, you've got people doing well over three times body weight back squat. And that's full depth. You see it and you think, have they stopped halfway through? But they're grinding so slowly and their performances are fantastic.

But again, it is some of it is sport-specific. I think if you're weak, you definitely need to get stronger. But then that's where, if we've got this profile, so if you've got the tests or similar tests to what I've mentioned—if you've got something for maximum force production, we've got a slow stretch-shortening cycle task and a fast stretch-shortening cycle task—it's really easy to look. If you've got somebody who's generating huge forces on the isometric task but they're not great on the ballistic and plyometric, it's obvious they need to focus on those more.

And you wouldn't just—somebody who's who is you would class as weak—you wouldn't just focus on strength training. You're still going to do a bit of ballistic and a bit of plyometric training, but you'll just change that balance. And once you've got somebody who's really strong, you know that it's going to take longer to get them stronger because if you're weak, you improve rapidly without any major issues. But if you're strong, it takes a lot longer to increase that strength, so you end up with a law of diminishing returns.

And you might get more bang for your buck enhancing other characteristics. But again, after a while, if your strength's here and then your performance in those ballistic and plyometric tasks is there, once it starts going up, you've got to suddenly shift that ceiling up again. Otherwise, if you're being really efficient with using your force, you can draw those ballistic and plyometric tasks—can you improve them further without increasing that strength?

Now that is slightly different. You know, I think if you look back to some of the information that used to be put out there about plyometric tasks where people would say you've got to do a one and a half or two times body weight squat before doing high-intensity plyometrics—if you're talking about true plyometrics with short contact time—I think that's complete rubbish. Because you don't really flex knee and hip, you end up with a stiff strategy, and it's very, very ankle-dominant. So why would you have to squat to a decent depth with a high load?

The plyometric tasks are very ankle-dominant. If it's more that shock jump training where you're doing a depth jump, not a drop jump, so you're much more compliant movement, much more flexion through the knees and the hips, and you're dropping off a box a meter high or higher, yeah, in that situation you need to be strong. Because if you think about it, you've got to generate an impulse sufficient to decelerate you when you land, and that impulse is equivalent to your momentum.

So if you're heavy and you're falling from over a meter, you're going to hit the ground at high velocity, so your momentum is pretty high at that point. So you've got to be strong enough in that position. But that's with something like a depth jump with a very compliant strategy where you go through a large angular displacement of your knee and hip, lots of flexion. That's not a reactive plyometric task.

But then again, flip that—if it is something like shock training, drop off a one, 1.5 meter high box, have a compliant strategy, jump as high as you can—yeah, you need to be pretty strong at that point or you'll just get buried at the bottom. We've all tried it, if not as an adult, as a child. You jump off something too high, think you're going to land it, and you end up in a heap on the floor because your legs just give way. And that's not what you want when you're training your athletes.

James de Lacey24:12

Ideally not. I think Verkhoshansky actually classes that depth jump as a maximum strength exercise anyway, that variation that you mentioned. So yeah, there you go.

And regarding around the force-time curve as well with the jump, what do you see when an athlete is, say, fatigued, like from week to week, playing or whatever it is, or just training? Do you see large changes in that unweighting phase? Maybe they're going deeper just to change that strategy to maintain that jump height?

Paul Comfort24:36

Yeah, there's a few things that tend to change. Jump height tends to stay pretty constant. You've got to really beat somebody up to change or decrease jump height. And they'll normally change their strategy, certainly if they're sore. And you see this sometimes with the rugby players—they will unweight much more cautiously, go through a bigger range of motion. They don't have to hit the brakes as hard, and then it gives them more time for that propulsive phase and a greater range of motion to go through. And that way they can maintain jump height, but the total time to takeoff increases.

And if we break it down, most of that comes from that unweighting and braking phase increasing. Acutely, there's a really nice study by one of our previous students, Ryan Spencer, which Dr. John McMahon sort of supervised him on, John, his, I think it was John, his master's degree. So they looked at changes in jump performance in soccer players post-match. And actually their strategy didn't change dramatically, but what happened was they, on average, they'd lost just over two kilos in mass. So the relative net impulse, which then determines your velocity at takeoff—

Takeoff and therefore your jump height had decreased. So there was time from what I can remember was similar, but the forces are dropped. But they still maintain jump height because they're now 2 kilos lighter. So it's important if you're acutely monitoring that, or even longitudinally over time, has the person actually lost body mass, or in some cases have they increased body mass? And therefore you might see that's why their jump height has decreased.

You've done a big hypertrophy phase with them, or they've come back from the offseason and they've overindulged a little bit. Is that what's really then starting to affect their jump performance? Again, one of the easiest ways, if someone's carrying extra body fat, one of the quickest and easiest ways to increase their jump height is get them to lose some body fat.

It's like if you put a weighted vest on at 10 kilos now and you do a jump, take that weighted vest off, you're going to jump a hell of a lot higher. Not that you can lose 10 kilos like that, but it's still the same principle.

You've got to identify, well, where's the biggest bang for your buck on this and what's going to improve your performance the most? I think more practitioners probably need to understand that interaction between the force time characteristics and body mass and what actually causes jump height, which is the relative net impulse. So if you change that impulse from force or duration, or you change your body mass, you're going to get a potential change in jump height.

And it's a bit of a blessing and a curse when you look at all of the different manufacturers of the automated Force plate systems and they'll instantaneously give you all of these variables. I think pretty much everyone will give you 100 variables or more. That's great because it's really easy for people to use. The problem is you look at the education of a lot of people, they don't fully understand the force time characteristics, how the data has been analyzed, how cuing them differently will change their strategy.

Simply, if you put up a leaderboard and on your leaderboard to try and get them competitive you've got jump height, people start doing a more compliant strategy, go through a bigger range of motion and take longer to jump higher. Put time to take off up there, everyone tries to get a shorter time, jump height starts coming down. So what do you do? What do you give them feedback? Do you not give them feedback? Do you put up something like contraction time flight time ratio, or modified reactive strength index, so that's a combination of the two?

But actually, when you do that, we've done it with students and athletes, and they don't really understand it. So they don't know what they're chasing after really, it doesn't help to motivate them. So that's really interesting and I think we need to try and make sure, and we do it with our students on our undergraduate, Master's programs and our PhD students, but we need to make sure people have a much better understanding of these things.

And there's still a lot of information that we don't know in terms of how some of those variables may interact, how do they change with certain types of training? Because a lot of the research out there is acute: if we do this now, what happens? Because if you do a study that takes 8 to 12 weeks in an applied setting, it's really difficult.

You wouldn't believe the amount of studies we've started with local teams where we've got official partnerships with through the university and the teams, or maybe even the coaches come in and said, "Right, we need to know this." You get four weeks into a study, they're on a losing streak, everything gets changed, and then you're like, "We haven't got enough data yet." "No, give it a few more weeks, it's not down to this intervention." So those studies are much harder to do.

There's more and more being published now, which is nice, but we just don't have enough information to be able to fully unpick all of that. Although at the same time, there are some metrics out there which we know are meaningless, aren't going to tell us anything.

James de Lacey29:17

Perfect. Then for anyone who wants to visualize some of that, if you just search impulse momentum relationship, it might help some people with just a visualization. Actually, I have a question here in the live chat, we ended up getting this live. Yan, he's saying he's found it interesting what you're saying about plyometrics. He wanted to ask, would plyometric training or jump training help prevent patella or Achilles tendonitis, or develop it? Is there something there for me?

Paul Comfort29:40

If you did a really, really high volume which wasn't progressive and the athlete wasn't prepared for it, yeah, that could cause problems. So be like with anything, if you overload a structure too much, too quickly, you're going to get an adverse response. So yeah, overloading the Achilles or the patella tendon too quickly rather than doing it progressively could be problematic. It could definitely help to reduce the injuries, but actually the one thing to bear in mind is that for tendons they adapt based predominantly on the magnitude of strain that's applied to them and the duration of that strain.

So with plyometrics, the strain's not there for a long time. Now, you can train people to be better at their plyometric performance, but in terms of creating those adaptations, you're going to get a muscular adaptation but probably not huge tendon adaptation. You probably need to do more high load or hypertrophy type loads through the patella tendon and the Achilles tendon to really get adaptation.

That's also really safe then, compared to the very high strain rates you get with plyometrics. So you need to make sure you've appropriately preconditioned them, and that would probably be a block of hypertrophy training focusing on those structures being stressed. So some heavy calf raises, some heavy knee extensions, which a lot of people tend to avoid the single joint, but that's really going to load the patella tendon as well as your normal squatting patterns and everything else.

And then you can move on to a strength dominant period of training and then progress on to a greater emphasis on those plyometric tasks. Now, you'd never completely drop out the strength training, you'd need to maintain some of that to maintain the tensile strength of tendons and the force production capability of the muscles. But you just decrease the volume of it and then slowly increase the volume of the plyometric and ballistic type training.

But it has to be, like with everything, has to be progressive. We've always got to go back to the two key principles: progressive overload, and if we're trying to get a hypertrophic response, increasing volume generally is the most effective. If it's strength, increasing load is the most effective way to optimize force production. But it's got to be progressive overload. And we also need to think about specific adaptations to imposed demands. And if we're specifically loading a structure or tissue in a certain way, we should get the appropriate adaptations.

James de Lacey32:05

Perfect. Hopefully that answers your question, Yan, and if there's any more of them in the chat. But I wanted to go into as well on Olympic lifts versus jumps, because this honestly, this is pretty much like the social media panacea for strength and conditioning coaches to argue over every damn month. So I want to know, regarding the kinetic variables of these two, like waves and derivatives and jumps or loaded jumps, can you match them one to one?

Can you just take out one and the other and you're going to get very similar adaptations? Or is there something very different about these two where both can and potentially should be?

Paul Comfort32:34

It depends predominantly on the loading. So if you perform them at a comparable load, you end up with, it depends on the weightlifting variation, but if you looked at something like a loaded countermovement jump with the barbell on your back, hex bar jump, or a jump shrug that Dr. Tim Suchomel has made popular, you get very, very similar kinetics and kinematics. There's minimal difference between those three exercises if performed at the same load.

One of the benefits you get with something like the jump shrug is you hip hinge down to the knee, so you're getting a bit more of a stimulus in that braking phase at the bottom for the hamstrings as well. But overall, kinetics, kinematics similar. The issue is you can't use particularly high loads safely with jumping tasks. So we can go moderate to low load or unloaded for some of those jumping tasks, and if we're doing those moderate or very low loads, like I said, they are comparable in terms of the kinetics and kinematics.

You wouldn't want to do, it's been done in the research, one of Tim's studies they went as low as about 30% of one rep max for hang high pulls and hang power cleans. And you'll see that the force and velocity and power is much lower than a jump shrug. Well, that's not surprising, is it? Because let's be honest, if you did a hang high pull or a hang power clean at 30% max intent at 30%, yeah, you could snatch that comfortably.

You wouldn't even have to drop into that power position to snatch that load. So if you did it with max intent, that's hitting you in the chin and you're losing some teeth.

So you won't go through weightlifting variations where you have to catch the barbell with any real intent with a maximal load. But what that means is then if we go to those higher loads, if we go above sort of 60, 70% of your one rep max, you don't want to be jumping with that. But if we're doing 60, 70% of your one rep max in hang power snatch...

Hang power clean, those sorts of movements. The ideal loads tend to be between about 70 and 90% of your one RM power clean or one RM power snatch. And I'm saying power snatch rather than snatch, or clean rather than power clean rather than clean, because most people can perform those more competently unless they're a weightlifter. So 70 to 90% tends to be the most effective at enhancing the kinetic and kinematic outputs, and there's not a huge amount of difference between 70, 80, and 90% of one RM.

So if your athlete's technique is a bit ropey, maybe keep them down at the 70 to 80% where they can focus a little bit more on technique. If the technique's really good, then you can play about across that spectrum and load them up a little bit more.

And then you've also got the weightlifting variations, the pulling variations where we don't catch, which can be used at those lighter loads. But it doesn't always drive intent. Some people you just see with 80% of the water RM and they just do a hang pull, they just go through the motions on it. There's no intent there because they haven't got to displace the bar high enough to catch it, in which case definitely use the catching variations because we want to drive maximal intent.

If you go back to Behman Sale's research from, what would that be now, 30, 40 years ago, it clearly illustrates that it's not movement velocity that drives adaptation, it's the intent to move as quickly as possible. And that's also one that recruits those high threshold motor units.

But then with those pulling variations, we can go above your one RM hang power clean or hang power snatch because we don't have to displace the bar to the height of the sternum to be able to catch it, because there is no catch. So you can go up as high as 120, 140% of one RM. You generally wouldn't go that high if it's a clean pull or a snatch pull from the floor because if you look at the time it takes, the first pull to the knee takes about 50% of the full clean pull motion, so it becomes more fatigue and limiting factor.

So with if it's clean or snatch pulls, normally you'd go up to about 120% of one RM. If it's hang power cleans, power clean, sorry, hang hang clean pulls, clean pulls from the knee, mid thigh, pulls whether it's with a clean or a snatch grip, you can go up as high as about 140% of your one RM.

And interestingly with that, you can actually do high volumes if you want to. I'm not suggesting that you do necessarily go and do it. One of my previous PhD students, Dr. David Mein, has published a couple of studies, one with the comparing the hang power clean, one with the counter movement shrug going up to 140% of one RM doing six reps, and then tried using rest redistribution to see if we need that in inter-repetition rest to enhance power output, enhance velocity and force.

And actually six reps, you don't fatigue, you maintain your performance throughout six. As long as you're using lifting straps so you don't lose your grip, you can maintain performance across six reps. We don't know how many more you could do being cruel enough to subject anyone to that. The only caveat to that is, it's performing those tasks at those loads for those reps if you can maintain technique and performance. If you're losing posture, you need to go lighter.

But what it means is we've got the loaded ballistic jumping tasks, however you're doing them, whether it's a barbell, weighted vest, hex bar, etc., dumbbells, light to moderate loads work really, really well. You could do a jump shrug as well. Soon as you want to go up to those heavier loads and train a higher force aspect to the force velocity continuum, we're probably looking at using hang power cleans and those sorts of variations or hang power snatches up at about 70 to 90% at one RM.

And then if you want to go really heavy and really push the force aspect, pulling variations where we exclude the catch and you can go up to 120, 140% at one RM as long as the technique's really good. So it allows us to train that full sort of full continuum.

But I suppose to go back to your original question, if we're doing jumps or weightlifting variations, if the weightlifting variation is a jump shrug with a light load, they're comparable. It's only once we start to load them more that we start to see notable differences. And it's certainly a lot more, you get more ballistic intent with those weightlifting pulling variations as the load increases.

And you can take that load way beyond what you can do with jumping tasks. For example, one of the studies we did with hang hang clean pulls, 140% of the one RM was equivalent to their one back squat for most people. So you're really then driving true maximal intent with a high load, whereas if it was a back squat, you're not going to try and jump with a one RM load or close to a one RM load because everyone gets inhibited just because you've got to land the bloody thing.

But it allows you to accelerate almost through the full range of motion, whereas we know that with squatting, there's a top end of that range of motion, 40% of the duration is actually deceleration.

James de Lacey39:53

That was a great answer. I love that as well. There's a couple of things I want to go into a little deeper on that too. Let's start with you mentioned about the intent to move the bar, right?

So I guess we're all kind of told, hey, just move the bar as fast as possible. There is, I think probably in terms of just general strength training programs, Jody Willness, 5-3-1 is probably most famous for not pushing intensity but never really going too heavy, low intensity, but get stronger through max speed and effort for every rep that you're doing.

So in that sense then, you obviously mentioned around high threshold motor unit recruitment, etc., which you can also get from heavy loading. So can we, is there a potential for not actually having to load heavy as an athlete and just moving moderate loads faster and we're still going to get these similar adaptations, or that heavy load is going to give us other adaptations that we're not going to get just from moving things quickly?

Paul Comfort40:49

I suppose you're certainly going to get some good adaptations using those moderate loads and managing with max intent. We are going to hit the high threshold motor units. But what you also end up with is a reduction in the total volume of work performed with lighter loads, a reduction in time under tension, although that's only a small component of what drives adaptation.

So I think you're always going to be missing out on some of those muscular, hypertrophy adaptations if you don't go heavy. That doesn't mean you should be maxing out all the time, but we know if you do very heavy load training that improves your performance at those high loads most effectively.

If you do moderate load training, and with all of these you're aiming to move at the highest velocity possible, move with max intent, moderate load training, you'll improve most at those loads. You'll get some strength gains and you'll improve slightly at the unloaded ballistic and plyometric tasks, but you improve most at the load that you train at.

So what we need to do is then identify what does our athlete need to be able to do, and it's not necessarily what do they need to be able to do in their sport. Because you could say, well, sport like soccer, there's minimal collisions apart from, it's very gentle. I know they fall on the floor and roll about, they'd be shocked, but it's not any real big collisions most of the time. It's not like watching American football or rugby.

So you're really only accelerating your mass. But if you can accelerate your mass really effectively doing ballistic and plyometric tasks, but your ability to get off the marker with the first five, ten meters is limited, that's going to hold you back. You need to focus on strength. So it's really just evaluating with your athlete, where are you going to get most bang for your buck?

And training across that continuum and regularly evaluating, well, how well do they perform in each of those? Are they performing best with a low load, best with a moderate load, best with the high load? And if you suddenly go, well, you know, high load, they're phenomenal, but the rest they're not great, we need more of this type of training.

But then you can flip that. If they're great, like the example I give with a lot of soccer players that we've tested, great at accelerating their mass during ballistic and plyometric tasks, but they're really weak, just chasing after those ballistic and plyometric tasks with low, moderate, isn't going to dramatically improve their performance any further. Because we need to increase the muscle's ability to generate higher force.

And if you're generating 90% of your maximum force in a short duration, well, there's only one way you can improve that any further, because you're not going to be able to generate 100% in a really short duration. So the only thing to do that is push that ceiling up.

But again, we can flip that. If you're really, really strong, but it takes you two seconds to produce that force, that's no good at most sporting tasks. We need to be able to produce something much quicker. So we've got to train across that continuum and identify what's most effective for the sport, what's going to give you the most benefit for that individual.

James de Lacey43:16

You mentioned that force velocity kind of spectrum or continuum. I don't know if you're a Twitter user.

You mentioned that force velocity kind of spectrum or continuum. I don't know if you're a Twitter user. Did you see Dan Cleather post the other day on his take on the force velocity? I'd love you just to kind of, just for the audience who are probably not familiar with it, just kind of a quick brief summary of what it was and then maybe your take on what he wrote there.

Paul Comfort43:42

Well I think the problem is with force velocity profiling and force velocity curves in general is most people don't go back to the original research, so they misinterpret things. So sometimes it's referred to as a force velocity curve and it's really a load velocity curve. Most of the time people only evaluate velocity and make assumptions about the force which is produced.

But we don't know how long that force was produced over, so we are making assumptions about the actual force itself, because to achieve a set velocity you've got to generate a certain inputs. And if we don't know the time that force was applied, we're struggling with it.

If you go back to the very early research from A.V. Hill back in the '30s, in the 1930s—and the reason people don't do this is it's not always easy to access those articles and some of them are really difficult to read. I think one of them is about 58 pages and it'll probably take you a month to figure out some of the equations and calculations in there as well.

But if you look at that, they were looking at the original research, there was looking at individual muscle fibers, how you can lengthen them so you've got that eccentric component, how temperature affects it, how stimulation affects them. And to summarize it quickly: to make a muscle shorten quicker, it has to produce a higher force; to lengthen it quicker, you have to pull harder on it. Of course you do.

You look at that, then if we look at something like isokinetic testing, if we want to increase the angular velocity during isokinetic testing single joint, we have to generate a higher force. Because what we're doing when we sit on an isokinetic dynamometer, we're generating a maximal isometric force trying to hold it, and the machine is basically pulling on your shank and trying to straighten or flex the knee, because it's normally the knee with testing.

And the only way you're going to do that and accelerate it faster to generate a higher force against your isometric force that you've initially started producing. So that holds true with A.V. Hill's model of that sort of force velocity relationship.

But then what most people do then is confuse the load velocity relationship and the force velocity relationship. And the force velocity relationship that A.V. Hill demonstrated and the force velocity relationship we get on an isokinetic dynamometer is completely different to what we see with whole body movements. So that suddenly brings into question: well, what are we really looking at? Are we really looking at a force velocity relation? Have we assessed force and have we assessed velocity? Most of that research, it's a case of no. Have we assessed velocity and we've predicted force? Most of the time, yes.

What I'd like to see is then somebody where you do some of this load velocity profiling is they'll put the approximate force or the predicted force at zero velocity. Why don't we just go and test it at zero velocity and do an isometric test? And then you're predicting maximum velocity. Well, that would be completely unloaded. How do we achieve? Well, we can go up onto the moon and reduce gravity if we want, but that's going to be—well, might not be too expensive soon with the way things are going. But so we can't test that full profile.

We also know that if we do that, it is sort of that—it is curvilinear if we look at the single muscle fibers and if we look at isokinetic testing. Whereas we know if we progressively and incrementally increased load, and I know Dan Cleather posted a figure of this, if we go from 10 to 20 to 30 to 40 to 50, 60, 70, 80% or 80 kilos, just that incremental increase, we see an incremental decrease in velocity with an increase in load. But again, then that's now a load velocity relationship, not a force velocity relationship.

So I think part of the problem is is that people confuse a term. Dan fully understands it. He's got fantastic knowledge and understanding of biomechanics but also of the underpinning physiology as well. And I've discussed this with him a few times. In fact, I've actually got—and you're probably going to motivate me to spend some of Christmas now trying to do this and Dan to assist me with it—I've got a part written manuscript on my desktop purely about this, the force velocity relationship, load velocity relationship, where most people get it completely wrong.

Actually, without naming any institutions, I know there's a lot of institutions where students are told, "Don't reference anything more than five or 10 years old." Really? Yeah. And I think sometimes that's because some of the academics haven't read stuff that's that old because they're very new in their careers and they don't want to go back any further, which is completely crazy, because you need to look at that seminal work that was done originally.

And a lot of it still holds true. Yeah, there's technological advances which may allow us to tweak and fine-tune certain things, but one person I can think of in particular that asked me a question about this: "I've been told I shouldn't reference anything more than 10 years old. I'm looking at the force velocity profile. I've found some of this work by A.V. Hill. What do I do?" Like, reference it!

Then actually go through that journey of: this is single muscle fibers, this is isokinetic, this is whole body or this is multi-joint dynamic tasks, this is why it's different. Actually you might educate your tutor. However, be warned, they might not like it. They might think you're being patronizing or whatever, but ultimately they can't fail you for it.

And I think that's part of the problem, is people don't fully understand a lot of these different concepts, or things get used interchangeably. And some of it is down to as simple as semantics and the terminology might be used slightly differently to mean the same thing. And that does create a lot of confusion.

As we mentioned earlier: braking or eccentric phase, jump, eccentric movement, jump, concentric or propulsive? Well, they should be identified in the same way, so it could just be the terminology. But actually if you look across the research, some people have gone the bottom of the force-time curve to the top as being the eccentric or braking phase. You don't start braking until you apply a force equivalent to body mass, so that's definitely not braking, is it? Eccentric? Well, the muscle could be lengthening, but we haven't put an ultrasound probe on there to figure that out, so can we really say that?

And then other researchers will have classified from the point that force returns to body weight back to the peak. What if the peak actually occurs during the propulsive phase, which it does in some people? So you're not comparing like with like. And again, it's down to—it's probably—like I said, I've got this half manuscript that's probably been on my desktop for about three or four years now, so probably partly my fault.

I could have educated, published information. I need to finish writing it. But as I said, read some of those papers that are 50 pages long, go back in, go back through the equations again to double check you've got things right. Takes some time.

James de Lacey50:38

Perfect. I can imagine that as a headache to go through that, too. But honestly, this is the perfect place to end this podcast. This was really good. Hopefully a lot of good information for people listening. Where can people find and follow you and keep up with what you're doing?

Paul Comfort51:00

You can either find me on ResearchGate if you want to find some of the research that's on there. Anything that I'm allowed to share does get shared on there. If I'm not allowed to share it, it doesn't, so don't ask for an entire textbook because we can't share that. Or if you look on Twitter or Instagram, it's Paul Comfort 1975. That gives away my age as well.

Follow me on—I'm not necessarily that active on there. It varies. It fluctuates depending on how busy I am with other things. Or otherwise, just search for me at the University of Salford if you want to drop me an email and ask me any questions, and you'll find me on there as well.

James de Lacey51:24

Perfect. I appreciate this, Paul. Thanks for coming on.

Paul Comfort51:24

No problem. Thanks, we've enjoyed it.