I have two words to unlock your untapped speed potential.
Resisted. Sprints.
What is it?
It’s all in the name.
Resisted sprinting is sprinting while being resisted.
Common methods used include sled sprints, prowler pushes, parachute sprints, and weighted vest sprints.
Why does it matter?
Sprinting faster is a cheat code in team sports.
Sprinting has two phases to it, acceleration and max velocity.
Acceleration is the beginning of a sprint while you’re building up speed.
Max velocity is the point where you’ve stopped gaining speed and now you’re trying to not slow down (think about the back half of a 100 meter dash).
Acceleration is critical to team sports that have a lot of stopping and starting.
Resisted sprinting has long been thought to help skyrocket acceleration capabilities.
How does it work?
At the end of the day, accelerating just comes down to physics.
Specifically, Newton’s 3rd law: For every action there is an equal and opposite reaction.
When we push into the ground, the ground pushes us back.
However hard we push into the ground, the ground pushes us back just as hard.
Whatever direction we push into the ground, the ground pushes us back in the exact opposite direction.
Acceleration comes down to three factors:
1) How much force can you push into the ground
2) How quickly can you you push that force into the ground
3) How horizontal can you orient that force
Resisted sprinting can help with two of those elements, #1 and #3.
Amount of force
Think of resisted sprints as a super sprint-specific version of lifting weights.
If you’re moving heavy weight as fast as you can, you’re going to get stronger.
The stronger you are, the more force you can put into the ground.
Direction of force
When we accelerate, the direction that we want to go is out, not up.
We want to push backwards into the ground, so that the ground pushes us forward.
We want the ratio of ground reaction forces to be much more horizontal than vertical.6
Resisted sprinting allows you to achieve a much more horizontal angle than you would be able to achieve without the weight pulling you back.
With the weight essentially holding you up, you can have a steeper lean without falling over.
The theory here is that this allows your body to feel what it’s like to put force into the ground horizontally and carry it over to regular sprinting.
How can you use it?
Heavy or light?
The answer is: yes.
Both have a place and time to be useful.
You’ll hear people say that you shouldn’t have a greater than 10% reduction in sprint speed, because anything heavier than that will alter your sprinting technique.
Don’t listen to them.
Read the “Fun facts” section below for an interesting lesson on how peer-reviewed research is often no different than elementary school kids playing telephone.
Heavy and very heavy sled sprints have been shown to have no negative impact on sprint mechanics.
Does resisted sprinting alter sprint technique?
Yeah, that’s kind of the whole point.3,4,7
We want to alter sprint technique to put more force backwards into the ground.
But, there’s no evidence to suggest that using resisted sprinting has any negative carry-over to long-term sprint mechanics.2,3,5
Heavy loads (80% BW, 50-60% velocity decrement) have been shown to improve acceleration qualities.1,2,3
So, how do you choose a load?
Practically speaking, there is no universal answer.
There’s some evidence that different loads correspond to different phases of acceleration, with the heavier loading (>50% velocity decrement) corresponding to the first steps and the lighter loading (10% velocity decrement) corresponding to the later steps.9
Body weight % or velocity decrement?
Some studies use a percentage of body weight, while others use velocity decrement (meaning how much does that resistance slow you down compared to your unresisted velocity).
Which is better?
Velocity decrement probably has more universal utility.
If we go back to the lens of viewing sled sprints as a sprint-specific weight lifting exercise, it gets a little more clear.
You don’t go in the weight room and tell every athlete to throw on 80% of their body weight on the bar for reverse lunges.
Some people are strong.
Others are not.
Body mass does not dictate what weight they can move.
Sled sprinting is no different.
What type of equipment is best?
Ideally, you’ll want something that pulls you backwards and can be loaded heavily or lightly.
Running with a weighted vest is lowkey useless when trying to learn how to put force backwards into the ground. A weighted vest pulls you down, not back.
Being heavier is not the same as being resisted.
Pushing a prowler sled can be useful. While it doesn’t pull you backwards, it does resist you horizontally, so it helps you develop backwards force.
It’s super specific for collision sport moments, like an offensive lineman coming off the ball.
But, it’s less specific for pure speed development, because it removes your arm-swing from the equation.
Parachutes pull you back and allow you to have free arm swing. Also, they look cool for training montages.
Is it a winner?!
Sadly, no. The resistance is the equivalent to my toddler trying to pull me back with a resistance band.
It’s not a heavy enough load to make a meaningful difference. Nor is it scalable.
Enter tow sleds.
– Horizontal resistance? Check.
– Allows organic sprint form, including free arm swing? Check.
– Scalable from light to heavy? Check mate.
Furthermore, I prefer using a waist belt attachment over a shoulder strap.
The waist belt sits right in line with your center of mass, so it provides the most natural kinematics.
My thoughts
Resisted sprinting falls in line with my strength levels used for the weight room.
When you’re young, untrained, and weak, sled sprints probably don’t change the game a whole lot.
When you’re in the middle of getting stronger, you can scale up and down from relatively light loads to heavy loads to work all phases of acceleration.
When you’re “strong enough,” you can dial in on specifics and focus in on a certain aspect of loading that corresponds to your weak point in acceleration.
We don’t operate in a universe where I have to pick one singular tool to help athletes get faster.
But, if we did, I’d choose sled sprints.
Fun facts
“Chase the citations” with 10% velocity decrement
So, where did this 10% figure come from?
I played a game of “chase the citations.”
Where a study cited the detrimental effects of loading greater than 10%, I went to the cited study.
Each study was just just referencing an earlier study that cited the same thing.
Eventually, I came to a 2003 study that was the earliest experimental, peer-reviewed evidence that people cited: Effects of Resisted Sled Towing on Sprint Kinematics in Field-Sport Athletes7 by Dr. Robert Lockie and his team.
However, my reading of the article gave no indication that the authors concluded that heavier sled sprints are detrimental or should not be performed. It was just a summary of what happens at different loads.
So, I reached out to Dr. Lockie to see if I was missing something.
Turns out, I wasn’t.
Prior to his study, there were some coaches who anecdotally stated they thought heavy sled sprints had detrimental carryover.
Dr. Lockie the first to run a study to actually see what happens and there was no conclusion that heavy sled sprints should not be done.
Somehow, people continue to cite a myth with no foundational evidence in peer reviewed journals today.
Don’t believe everything you read.
PAP
Post-activation potentiation is the concept that after you do something heavy, you can be faster or more explosive.
There’s evidence that sled sprints can do just that.
Research has shown improved acute sprinting velocity at following a 50% velocity reduction sled sprint.2
While that’s cool and all, but is it really useful?
It’s not like you can do a sled sprint right before you step in the batter’s box and run to 1st base.
Maybe if you have a lot of freedom before running the 40 at a combine that could be helpful, but I’ve never seen that be logistically feasible.
Puberty matters
If you haven’t hit puberty yet, resisted sprinting probably doesn’t move the needle forward.8
There are a million other ways to get pre-pubescent kids faster, so saving sled sprinting for later in the pipeline is a good idea.
That’s it!
Best,
Zach
References
1) Morin JB, Petrakos G, Jiménez-Reyes P, Brown SR, Samozino P, Cross MR. Very-Heavy Sled Training for Improving Horizontal-Force Output in Soccer Players. Int J Sports Physiol Perform. 2017 Jul;12(6):840-844. doi: 10.1123/ijspp.2016-0444. Epub 2016 Nov 11. PMID: 27834560.
2) Zisi M, Stavridis I, Agilara G-O, Economou T, Paradisis G. The Acute Effects of Heavy Sled Towing on Acceleration Performance and Sprint Mechanical and Kinematic Characteristics. Sports (2075-4663). 2022;10(5):77. Accessed April 18, 2023. https://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=157237297&site=eds-live
3) Lahti J( 1 ), Morin J-B( 1,5,6 ), Huuhka T( 2 ), Häkkinen K( 2 ), Romero V( 3 ), Bezodis I( 4 ). Changes in sprint performance and sagittal plane kinematics after heavy resisted sprint training in professional soccer players. PeerJ. 2020;8. doi:10.7717/peerj.10507
4) Zabaloy, Santiago1,2; Carlos-Vivas, Jorge3; Freitas, Tomás T.3; Pareja-Blanco, Fernando2,4; Loturco, Irineu5,6,7; Comyns, Thomas8; Gálvez-González, Javier2; Alcaraz, Pedro E.3,9. Muscle Activity, Leg Stiffness, and Kinematics During Unresisted and Resisted Sprinting Conditions. Journal of Strength and Conditioning Research 36(7):p 1839-1846, July 2022. | DOI: 10.1519/JSC.0000000000003723
5) Petrakos G, Morin J-B, Egan B. Resisted Sled Sprint Training to Improve Sprint Performance: A Systematic Review. Sports medicine (Auckland, NZ). 2016;46(3):381-400. doi:10.1007/s40279-015-0422-8
6) Hicks, Dylan Shaun MSc1; Schuster, Jake George MSc2; Samozino, Pierre PhD3; Morin, Jean-Benoit PhD4. Improving Mechanical Effectiveness During Sprint Acceleration: Practical Recommendations and Guidelines. Strength and Conditioning Journal 42(2):p 45-62, April 2020. | DOI: 10.1519/SSC.0000000000000519
7) LOCKIE, ROBERT G.; MURPHY, ARON J.; SPINKS, CHRISTOPHER D.. Effects of Resisted Sled Towing on Sprint Kinematics in Field-Sport Athletes. Journal of Strength and Conditioning Research 17(4):p 760-767, November 2003.
8) Rumpf MC, Cronin JB, Mohamad IN, Mohamad S, Oliver JL, Hughes MG. The effect of resisted sprint training on maximum sprint kinetics and kinematics in youth. European Journal of Sport Science. 2015;15(5):374-381. Accessed April 23, 2023. https://search.ebscohost.com/login.aspx?direct=true&db=s3h&AN=102715458&site=eds-live
9) Cross MR( 1,2 ), Samozino P( 1 ), Brown SR( 2 ), Morin J-B( 2,3 ). A comparison between the force–velocity relationships of unloaded and sled-resisted sprinting: single vs. multiple trial methods. European Journal of Applied Physiology. 2018;118(3):563-571-571. doi:10.1007/s00421-017-3796-5