It sounds so logical that it must cost more energy to lift your feet and knees higher when running compared to not lifting your feet so high. For example, it costs more energy to lift an arm than to....eeee....not lift an arm. But that's not how it works, which I show in this video as I use my 3D cameras to measure how much energy it costs to move my body parts and how having higher feet and knees can be more energy efficient than having your feet close to the ground when you run.
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Fredrik Zillén has over the years helped thousands of runners to a more efficient running technique - from the slowest beginners to members of the Swedish national team in running and triathlon who have participated in the World Championships and the Olympics. Fredrik also writes articles on effective running technique for Runner's World magazine.
Following the success of Fredrik Zilléns online course in Swedish, he has now produced an updated and improved version in English. You can find it here: www.fredrikzillen.com
You find the Swedish version at: www.fredrikzillenonline.se
"Fantastic running course. Fredrik is an excellent teacher with a unique approach. I highly recommend this course to runners of all levels."
Kevin, UK
"The best money I have ever spent. Great mix of humour, practical technique and theory. It’s brilliant and I have been telling all my friends about it. I’ve knocked 30 secs off my average pace to 4:30 and at 53 I’m absolutely astonished how relaxed I feel running. It’s also really helped my cycling my adapting similar techniques and visualisation. Thanks so much.
Paul, UK
Read more testimonials here: fredrikzillenonline.newzenler...
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The course in Swedish: www.fredrikzillenonline.se
Another advantage. I recently caught my foot on a small reflector in the road and did a spectacular and public faceplant. Definitely takes more energy to faceplant than to lift your feet.
Does it take energy to faceplant? I'd have thought it just happens effortlessly once you've caught your foot on something.
Takes energy to recover from a faceplant, both physically and emotionally hah
@@adrien5834 you lose a lot of potential energy by faceplanting 😂
@@markopolic9964 Ah, but then, strictly speaking, it's picking yourself up that takes energy. Lying down is very energy efficient.
Well said sir
I was one of those who was unconsciously stopping his legs. I knew my form is not good but always thought that I will eventually get faster and move my legs. I watched this video yesterday. Tried to ‘relax’ and just let my legs flow. My easy run was much faster and I felt that my effort was much less. I cannot explain how just relaxing could cause such a huge difference that too on first try! 😮
Like driving with the E-brake on.
whoever you are, your comment has contributed to my running epiphany. Time to try this!
A really good runner knows how to feel their muscles getting tired and adjust to different types of strides to distribute the load better and make you able to run further.
Excellent description of the force characteristics of the gait cycle in running (at various speeds, even!). I've been coaching for a long time and have never quite thought about it in that way.
Solid gold, this video has made a significant instant improvement in my running. Thanks FZ!!
Great video and excellent analysis with a concise explanation! You just changed my mind. Subscribed.
Whoa! This actually seems useful! In an age of tepid, and at the same time, noisy running advice videos I am quite surprised to find a video with some REAL INFORMATION 👍
Finally somebody who explains the body mechanics for running! I love the Metronome example, that one works beautifully. When playing with high kick towards the back I find that the front landing has quite a bit more impact on the knees. Have you measured the front landing in your experiments?
It depends on pace. There's a certain pace that very much is more efficient without lifting. There's a break even point that's somewhere between a quick walk and a slow run that depends on the runner. Sprinting will always benefit from lifting because of the pendulum effect.
Exactly.
Sort of the difference between jogging and running then…
I think it depends very much on one's body physique as well. Even in the pendulum effect, the period of oscillation is proportional to the length of the pendulum, while the mass of the pendulum determines the amplitude of the oscillation. So for running, depending on the mass of the runner's legs/body as well as the length of the legs, there's got to be a most energy efficient stride to take to ensure we spend the least energy to run the same distance within the same amount of time. But It should be different for everyone because everyone's body is made differently. So in summary: the correct stride (which includes how high the legs should be lifted) depends on these few factors: 1) body physique such as mass of body, length of legs etc. 2) the target distance to be covered . and 3) the target time to finish running the distance. If any of the above factors are changed, the most energy efficient stride would change as well.
He's a running technique specialist; what are you?
@@runspace He’s thrown a kettle over a pub
Yes you are Correct you actually save energy picking your feet up when u run. I noticed my feet and glutes getting tired when i didnt pick my feet up enough while running then when I started picking them up the pain went away. Thanks for the Video 👍🏻 👍🏻👍🏻👍🏻
that doesn't sound right. he's saying NOT to expend energy to pick up your feet. that you need to relax your legs and just let the movement happen
@@longebane read it again big bro
Great video! I did try and it worked well. I did knee drive forward and my feet naturally lifted up, I ran faster with less effort. Thank you so much for what you are coaching!
Elite runners are having their feet swing higher in the back because they are running faster. Any discussion of this topic needs to point out that the foot is always traveling at ZERO speed during the stance phase, while the hip is moving at 10 mph at 6:00 pace and 15 mph at 4:00 pace. Another way to look at it would be that the feet are moving at 15 mph slower ground speed than the hips at 4:00 pace. The knees also need to move forward after toe-off and in front of the hips to get ready for the next footstrike. Basically, elites are mostly neither lifting or resisting the height of their foot while it's behind the hip. It's just the physics of pulling the knee forward at pace with a lower leg attached.
Thank you for saying exactly the same thing as me but in a more complicated way 😀
Thanks. That was very interesting and helpful. I’ve been working on form but have got a bit stuck when it comes to cycling legs: I’ve been actively thinking about pulling my feet/knees up and through but I can feel that using extra energy. I have not tried intentionally relaxing to pull through so I’m looking forward to giving it a go. I would be interested to see an HR overlay to this experiment. I’m assuming that the relaxed method would also give a lower heart rate that the higher energy, low feet method.
Thanks for this! Nice to have it explained so well. Great video!
Fantastic! The moment I read the title, I understood the mechanism.
This video is life-changing. Thank you very much coach Fredrik Zillen.
This seems to explain why it's so tiring to run with together someone who is slower than me! I chalked it up to having longer legs and it being more tiring to run in smaller strides, as well as having to hit the ground more frequently, but this explains a lot! I might have been using energy to resist my legs going higher in order to maintain the slower pace, which may just have caused more fatigue
I’ve felt the same thing!
I never thought of this but yes, I don't understand why I'm hurting on long runs with slower people and this makes sense!
@@georgepagotelis doesn't make sense to me and i have long legs. I can run at a slow pace forever it's just extremely boring and frustrating
I know this theory and try to use it. But my breath can not effort the faster of the cadence that cause by kicking the leg higher. Can some one explain it to me pls.
That's why when I run with friends, we all agree that we'll run at our own pace and not at someone else's
This misses to most important reason why lifting your feet higher is more efficient. Lifting your feet is just a tiny fraction of the work you do when you-re running, the majority of work is done lifting the body when the feet is in contact with the ground. That's the part of the step you need to optimize, you do that by swinging your leg in a larger circle so you can activate large muscles in the contact phase, and direct the forces in a more optimal direction.
Thank you for explaining this. I always wondered about the energy use from higher heel lift.
I knew it! Thank you for confirming what I felt intuitively. I've had so many casual self-proclaimed "experts" tell me how I should run, and when I took their advice, it just felt so forced and bogged down. I've been running the way that feels good for years, and I have yet to encounter the injuries these weekend warriors claim I will if I don't follow their preferred method. Funny thing is that I run way more often than they do, yet they seem to think they know my body better than I know myself haha. The confidence is admirable!
I suppose you experienced the Dunning Kruger effect in real time
I never used the close to the ground technique until I went to get my running techniques analysed and they told be it was too bouncy and I needed to stay low. Basicllaly, use the glide technique. They said it is good for the knee. I use this glide technique from time to time just to rest other muscle group for short period but I usually don't use for more than a few minutes. I prefer natural running. Thank you for you point of view. It is nice to need that it isn't white or black.
Frederik- you blew my mind. Thanks!
Excellent video as always. I also find if I relax and let me knees naturally drive up, your back kick will increase as well, as your pace increases, effortlessly. It’s like magic….watch the elites, as they effortlessly run at 4 min/mile, with negative splits toward the end of a marathon.
Thank you for your work. It would have been interesting to give more details on the spent energy comparison. For exemple an oxygen comsumption comparison would have been interesting (of course it would have been more costly and difficult to realize). Thank you !
First time I watch this man. I love your attitude, Fredrik!
Really glad for this insight! I have to keep this in mind!🏃♀️🌿🙏
Just getting into your channel and binging the videos and love them! Great advice and backs up a lot of things from Shane Benzie and Lawrence Van Lingen work. I think if everyone follows you and those 2 then gives everything they need to improve run form 👏
I litteraly did this this week for the last six miles of a marathon! You litterally just relax after ground contact and it just happens! It was the fastest final 6 of a marathon and my 5th fastest 10k? Bonus* also my hips and anterior tibs not being total garbage the next day! Take away* running form is actually a thing! Great vid, sub too! Tq
I am going to try this today. My feet stay so closely to the ground when I run that it looks like I’m skating 🛼.
❤❤
@@jamstar876hopefully the result was great for you 😊.
Ok you got me intrigued. I've subbed. Hopefully you've got vids that show how to move from one to the other
Many thanks for explaining concepts!!! Now you have a new subscripter from Argentina, cheers!
Wow. I am a slow runner (or jogger I should say) and always struggled to run faster. The explanation here is very well done and makes total sense. I am going to try it.
So did u try and what was the outcome?
Great explanation. Will certainly try this on my next run. I do wonder if this technique inflicts more strain on the joints. I’d think the landing impact is bigger when your feet are higher off the ground. However, I could be totally wrong about this, so I hope someone could inform me about this
I am 65 yrs.Just a beginner in running.I hv done three 10km runs. I will try to follow your tips in my coming 10kms run.
Hopefully, it went well 😊.
Thank you for the insight and information! Great video
3 miles into a run. I had to stop and thank you! Its amazing what a difference it makes and its so easy to do! Plus, ive had some nagging knee pain and even that is not hurting!
Thanks Fredrik, I'll try this next run!
This is so interesting. I always find I run easier and faster when I focus on relaxing, especially when I’m tired.
This has always confused me. When I do my speedwork I have to lift my legs to get the numbers I aim for but when racing i revert back to the small steps thinking of preserving energy. Thanks for the key point which is to relax after pushout. Will test this out. More power!
Amazing video. Great examples to explain his point
I try It today! And yes it’s faster easier ! Thanks 🙏🏼
Love the science behind it! Way to back it up!
Thank you Fredrik! Very useful info 👍🏼
Thanks for this! I've been wondering about this. Sometimes it seems that running a bit more faster gives me a better running form and "roll" while the heart rate stays pretty much the same.
I'm afraid of getting injured so I always start from the back and get faster and more confident over time, should start like that from the getgo
More faster? So, to win a race, you have to run most fastest? Sorry, not sorry.
I don't believe heart rate stays the same if you're running faster no matter the form unless you're talking about 1-3 seconds per kilometer difference.
@@siemniak Heart rate is a function of your fitness and how hard you're working. With a more efficient technique, you can cover more ground with the same effort. I'm now running 12.5% faster with the same heart rate.
Great analysis. What about for those of us trying to approximate an east african type gait with high butt kicks? By mile 6 of a half marathon my knee angle is 90 degrees or more. Though still decent running economy, not ideal. Should I be focusing more on hamstring/post strength, or correcting pelvic tilt?
Ingenious explanation! Thank you very much.
Wow what a gr8 explanation / analogy whatever you want to call it - this all makes sense now - oddly enough I used to run with higher legs / knees but over recent yrs Iv gotten kinda lazy and Iv started running with low long straight legs which I’m finding absolutely exhausting ! So I actually went back to picking my legs up abit higher from the hip and bingo I’m not getting as fatigued as quickly !! I’m so glad I stumbled across you - I think u are fab I really enjoy listening to you - you make it make sense ! 🫶
This might be true, but another thing to consider is wear and tear. A higher leg lift means more impact force with each foot down stroke. Minimizing wear and tear is a factor for longevity. Everything is a tradeoff. What a higher leg lift does do is train the body to take longer strides, and for racing longer strides = faster times, for me at least. It's interesting to note that in a race, my stride length goes down over time due to fatigue. Training with a higher leg lift would help with this, as well as hip flexor strengthening exercises...... Run for your life.
Another simple point is that if you lift your heel while the other foot is on the ground, this raises your centre of gravity unless you bend the knee on your grounded leg more (and increases the vertical force needed in the grounded foot to achieve the raised centre of gravity). This may increase stride length (loosely speaking, the higher your centre of gravity when both feet leave the ground, the longer it is before you hit the ground again, everything else being the same). This point also (correctly) suggests that raising your lower leg more while running outside tends to be associated with using more power in a useful fashion, making more sense when running fast. If you don't believe this then do an experiment. Run comfortably outside, then at some point focus on tucking your heel as you lift the back leg and move it forward, still running comfortably. I predict you will go faster, but not for free (power and heart rate rise).
the one and only thing this whole video proves is that u need you lift your heel higher when u wanna run faster. and as you pointed out: ofcourse this requires more energy. as well as not raising it higher and still running faster by just increasing frequency is using even more energy and increases further the faster you go. but all this is nonsense for slower speeds. just run and let your legs do their thing without forcing them anything. your body optimizes your running form just by running alone.
Nice piece of information. Thanks for the Enlightenment May you discuss about vertical oscilation in its relationship with pace and running efficiency Thanks Sir
Great video! I liked it a lot! Your explanations are clear to the point! In any case I t is not safe to run with the feet close to the ground. It make sense to lift your feet high from the ground specially while running in tall wet grass!
Great video!!!
Eye opening for me. I’ve always tried to keep my feet as close to the ground as possible! MIND BLOWING!
Yes, I think that is a lot easier on the knees and ankle too.
The way you explain it certainly makes sense, and it does match up to how I feel when I run. I mean I quite often force myself to keep my feet closer to the ground and it feels like it's more straining on my muscles to do so. However, both my heart rate and my running power (measured by Stryd footpod) seem to disagree. They are the reasons why I run like that in the first place, because it seems to be the only way for me to stay in zone 2 in either the watts or the HR. It is odd, because it might feel harder on my legs, but easier on my heart. But it is probably something else with my running form that causes this, then.
Same here. When my feet go higher up, so does my HR, which in turn makes it much harder to stay in Zone 2.
Because if you are doing any movement beyond what your automatic nervous system does, you are exerting your muscles for no gain. Think about this: is the ancient locomotion system of the brain efficient, evolved over billions of years, or did it need the much newer sapient layer to finally become efficient? Of course not. The ancient systems have been honed over millions of years into efficiency. We would never have been successful organisms if we had needed the conscious parts of the brain to control basic functions such as movement efficiency. It's total nonsense. You don't need to think about how you pick up a cup from the table. Running "right" is no different. Does your dog think about its running form?
Thanks so much for this amazing video 😊
Wouldn't you be increasing the impact of each foot strike by lifting your feet more? In a marathon, I think minimizing the impact (and injury) would be more beneficial, especially for heavier runners?
Nice one. I'll try it out with my hips forward technique
6:57 - 7:08 - " and of course I would like to add that exactly how high the foot and the knees should be depends very much on how fast you run... the faster the pace the bigger the movement." This is the only correct statement in this video and voids the entire premise of the video.
Yep... pretty much. I think he is confusing conservation of effort with energy expended. In other words, more vertical movement equals less efficient running but can be compensated by using momentum through muscular relaxation to compensate.
Great explanation! Where were you 30 years ago when I needed this the most.
I was probably standing at a track here in Sweden. Where were you? 😃
@@SpringSnabbare Running cross country and track in Philadelphia. I love Sweden.
@@SpringSnabbareIf your claims were correct, one could simply make perpetual motion machine based on your measurements and diagram. The machine would create more energy by extending a rotating arm while it's coming down and getting pulled by gravity than it loses when the arm is moving up if it was retracted. You are confusing energy expenditure, force and torque. Your logic is an oversimplification because it doesn't for example account for the addition of forward momentum: when you accelerate the leg that is not touching the ground, you add to the forward momentum. So if you use more force to accelerate that leg forward, you need to use less energy of the planted leg to achieve the same speed and vice versa. You might be able to analyse the energy spent of those motions if the person was only swinging their legs that way while hanging from the ceiling, but to analyse the situation while the person is actually moving forward is much more complicated.
it was nonsense..... I could easily prove it the way this guy has or I could say there is a reason sprinters lift their feet higher than marathon runners...but I will let you think why that is.
It’s also about maintaining momentum.
I never really noticed this until I was able to run an 8-minute pace consistently for a few miles. I definitely save energy for a faster time no doubt about that. I was 280 in July of '23, and now im 205. It took a long time before my body felt comfortable or I should say authentic to be able to pick my feet up more because I always trained like I was walking or slow jogging while losing weight. Once I started stretching more and doing sprints, that all changed.
Very clearly explained. For slow running also, around 10km/h speed, I was dragging my feet closer to the ground. I think I need to kick them up a little, or maybe let them do their thing. Because I've realized, I put in energy to drag them forward and I can very realistically feel that effort. Kudos to you!
10km/h is not slow, 90% of my run are below 9km/h
@@JohnSmith-rr8hp that's great. do you also mean to say that even in runs less than 9km/h, you lift your feet higher? For the last week I've been experimenting a higher kick for runs anywhere from 6km - 10km/h speed, (higher kick depending on the speed). What do you think about it?
@@VishalVishal-pf4nu I think you need to have a strong core to do that naturally, i'm almost 40 now and that's still a work in progress for me, mind you, I'm a beginner runner
@@JohnSmith-rr8hp It'll happen my friend. I'm nearing 40, but have been running for many years now.~15yrs, but still haven't got the heel kick integrated into my running. 😇
@@JohnSmith-rr8hp10kmph is Slow I am beginner I can run at 12.5 kmph for 10 km
Every advice video should end, "Do what you want. I don't care!" It's the kind of attitude I can relate to. Five stars. Subscribed.
You also recruit more muscles in the back of your legs and glutes to do the motion as opposed to using your quads and hip flexors.
Physiologically speaking, the amount of individual differences in muscle fiber types/distribution (muscle fiber type I,IIa, IIb, IIx) would help determine the precise amounts of adenosine triphosphate(ATP) used when running. This could also vary depending on the VO2 max of an individual-> more cardiovascular endurance could mean more ability to perform easier under conditions such as lifting legs higher.
You really think this know it all spaz understands any of that? lol
I am not a runner, never seen your channel but this is super fascinating to me.
The two best things that you can do to improve your biomechanics while running are first, to keep your body fully erect and to control speed by hinging ONLY at the ankles NOT at the hips. (Your foot merely stops your fall.) Second, practice skipping. Running is actually a vertical jump (coupled with a forward fall). The jump is achieved by flexing the calf and driving the knee upward. The first, the lean, moves your center of mass forward and hence your body forward thus controlling forward speed. The second, the jump, moves your center of mass upward and hence your body upward, thus controlling your air time. A fast lift increases airtime and makes you run faster. That is why a higher leg lift uses less energy, because of increased air time. But it is not the height of the leg that is critical it is the velocity at which you raise it to that position that matters. Run then practice skipping for a week then run again. See what happens.
thanks so much for this video it was so insightful
Very well explained - thank you!
Is the bar at 4:22 in the video per stride? If so the higher cadence movement could potentially cost more energy over time, depending on the total number of strides taken to run the same distance.
personally, I think there's probably a sweet spot in speed and length of stride where one takes over from the other in respect to energy used, where the momentum of the pendulum has a better transfer to lift the foot naturally, the faster you go the more the lifting effect is productive, slower you go then more likely it's using more energy than is needed. so lifting your feet higher costs less energy when running... as long as you're not activating muscles to do the lifting.
there definitely is, and it's determined by the momentum of the limb. From a physics perspective, you need to consume energy to fight against momentum - so relaxation is key. Newton's 2nd Law, in short. Apply force with all the relevant musculature to propel your body through the stride until it feels awkward and inefficient. Then stop applying force and relax once while the foot is turning over, letting the weight of the leg guide the movement. The rest will work itself out according to pace because the limbs have more momentum at higher paces and less momentum at lower paces.
It's true, running a natural movement must be more relevant than trying to awkwardly apply physics.
First off..I love the counter argument to most runners that say, ' I need to increase my cadence so i will lift my foot less'. I knew this couldn't be correct. Kipchoge said there's a difference between jogging and running
This video alone improved my pace from 5:30min/km to 4:30min/km! Excellent explanation! Thank you for this Fredrik :)
You are a great young man for trying to be nice and express gratitude, but this video alone did not improve your pace like this. You are in your teens and it is absolutely natural that you improve if only you train. Changing techniques can give you 2 or 3 or MAYBE 5 % improvement, and all these numbers are huge anyway.
Thank you for the great video. Very interesting and informative indeed. I am guilty of trying to keep my feet closer to the ground to "save energy". Now, the question is, how do I go about "relaxing" while running to take advantage of what you’ve just taught me? One tip: The vertical vooden beam background isn’t too great. I got motion sickness while watching you explain things. It would be great if you could use another background.
This one is a great video! 🎉
Heel height is connected with the size of angle between legs. If the angle is larger, the back leg can swing more and its heel will get higher. Such mechanics spends less or more energy proportional to the BMI.
You have a nice, enthusiastic voice
Wow, good information, I tried it on short runs, it felt good. I have to work on it to get all other things to go with this form of running, it changes everything. For sure you need to do lots of home exercise to be able to support this form of running, strong lower and upper muscles specially lower back muscles Thank you👍👍👍
thank you. I used to fun a lot but I barely worked on my form. seems like good form can lead to significant gins rather quickly lol and it'll keep me safer. thanks
Would you say that this is an advanced approach to running or also just good to do for beginners as well? I would think it should benefit all but just wanted to get your thoughts on it.
I've always instinctually known this. It's nice to finally have an explanation to go with it! 🙂 I've never understood why people who are trying to be intentionally lazy, want to make more work for themselves... But such is the plight of all laziness - in the end, you always end up working more.
Hi Fredrick. My own running is in agreement with your idea. The faster I run my leg just sort of lifts up higher. It just feels more natural. I am by beginner runner. I just follow your explanation. It doesn't make sense to me. But if it works who cares why.
What about the force of the impact on the ground when comparing these two types of running ?
Thank you! :)
Very userful. Thank you very much 👍
Amazing info. Thank you sir
Maybe that works for some people. I find lifting my knees higher takes more effort. Sure it makes me faster, but increasing my cadence also makes me faster but without additional effort.
If you can get best cadence with higher knees it is ok. But at lower speed, cadence is more important and lower knees bring better cadence and less energy.
I know very little about running, so apologize if this is a stupid question: I notice that you do all the measurements on movement and energy on a treadmill. Do you get the same results when running on a track? I know that treadmill vs. track feels different to me, so trying to understand if the physics are the same in both instances. Thank you!
Your content is so rich! Congrats, love the science in it
Thanks I actually tried this, expected my stride length to increase but to my suprise, cadence increased.
The hamstring is contracting already to achieve hip extension, let the contraction spill over into knee flexion when the rear foot breaks contact with the ground.
great video, but i agree it deepends on pace, if i run 6-7 or 8 min\km we can not lift our knees up and the motion differs from faster jogging. thanks
Amazing thank you. This information is free
I’m such a nerd. I just love learning about this!
Fred...Thanks for the prudent explanation. I would like to know, when I try to left my legs (as adviced) , it increases my HR. What's your view on that ?
Fascinating!
Great demonstration thanks
Great video and explanation.
Great explanation 😊
I have had very good results on running economy/speed with a certain effort, when actively trying to relax more. But a negative consequence I have experienced is a little more tendon pain in low back towards hips, and maybe some more pain in knees etc. I probably experience more pendulum or longer steps with less effort when relaxing. But more speed leads to higher shock value. I would choose to use the total relaxation more on race day than in training. Especially downhill.
Without having seen you run, I would guess that your relaxation causes the foot to continue a little too far back once it has left the ground. It is not entirely unusual and usually produces exactly the symptoms you describe. When the foot leaves the ground, it should swing up and forward almost immediately. If the forward movement of the foot begins a little too slowly, you tilt the pelvic bone forward (which causes pain in the lower back) and more likely lower knee lift, which causes the foot to have a little too much forward movement when it goes down to the ground, which exposes the knees and thighs to great strain. Of course, it can be hard to constantly work on getting your foot/leg/knee forward. That movement should actually come from how the hip, core and shoulders work together, but that is a bit too complicated to explain in a comment. But if you keep working on your relaxation while making sure your feet come forward a little faster after toe off, I hope it works out for you.
I've been on a journey to get back up to speeds I was at before COVID lockdown and having many similar thoughts to you on relaxation to help get more miles in. This video impacted me because my attempt at relaxation caused increased tendonitis in my Achilles and soreness in my hip flexors. The opposite of what I expected. When I was relaxing I didn't perform almost any knee drive and my hip flexors would ache severely mid run. I wonder if the "longer pendulum" of sweeping my feet put extra weight at the top of my hips. And possible recruit less muscles with the knee drive. In the last 3 weeks I've maintained at least some knee drive up to lengths of 10 mile runs and I'm almost completely pain free while running comfortably at a faster pace than before.
Thanks for this!