Research Review: Proper loading for sled pulls
Whether you want to make like Rocky IV or Rudolph the Red-Nosed Reindeer, sled pulling is a great way to help you run faster and improve your performance in many sports. But if you want to improve your sprints in particular, how fast should you run, and how heavy should the sled be?
We know that adding resistance to movements makes you stronger and faster.
Adding resistance to some movements is obvious. To jump higher, for instance, you can squat with weight. To push harder, you can do presses or explosive pushups.
But how do you add resistance to activities where you’re moving through space instead of sitting on a bench? For instance, how do you add weight to sprinting?
Well, cement shoes or running piggyback are two possible options. Another one is dragging a sled.
The idea of pulling a sled isn’t completely out of the blue. One of the all-time great movie training montages, from Rocky IV, features Rocky pulling a sled through the snow.
If you want to run faster to improve your performance in a given sport, or a change of pace from your regular workout routine, you can try pulling a sled.
Now, sled pulling isn’t fancy or complicated. Load a bunch of stuff on a sled and run. (Or try.)
However, if you want to improve your sprint speed specifically, then there’s a little more to it.
Goldilocks and the Three Sleds
Just like the children’s bedtime story Goldilocks and the Three Bears, there is a “just right” to how much weight you should pull.
Too little weight and the sled slides past you when you stop running – meaning you’re not getting much of a training effect. Another sign you don’t have enough weight on the sled is that it becomes airborne during your sprint. And considering it’s moving towards you, that’s probably not such a great idea.
Too much weight and you’re nearly parallel to the ground when you “run”. Shockingly this running pattern doesn’t translate into a “normal” load free running pattern.
Thus, with too light a load there isn’t enough of a stimulus. With too heavy a load your running pattern becomes sub-optimal.
But if the load is “just right” then you have a training overload and proper running pattern — I’m calling this the Goldilocks phenomenon.
The 90% rule
So how do you figure out what’s the “just right” weight to use?
It turns out that three separate studies have already figured out what the optimal loaded sprint speed is. Since there are three separate studies coming up with the same conclusion I’m pretty confident in their findings.(1-3)
They agreed that with the loaded sled, you want to slow down by 10% of your normal sprint speed.
Thus, if you can run 30 metres in, say, 10 seconds then the optimal loaded sprint speed for you is 30 metres in 11 seconds. (10% of 10 = 1, thus 10 + 1 is your ideal time.)
If you can run 30 metres in 50 seconds, then your loaded sprint speed is 55 seconds. And you obviously really need that sprint training.
In other words, if you keep the distance the same between loaded and unloaded sprints, you should take 10% longer to finish your sled sprint — no more and no less.
OK, that’s the speed. But how do you figure out your “optimal load”? Well there are two ways:
- Trial and error: simply try different loads until you hit the magical 90% speed.
- Use an equation that somebody already figured out.
Luckily this week’s review is on a study that figured out an equation for optimal load when sprint training with a sled.
Alcaraz PE, Palao JM, Elvira JL. Determining the optimal load for resisted sprint training with sled towing. J Strength Cond Res. 2009 Mar;23(2):480-5.
The study included 26 male university sprinters, jumps or decathletes as participants. All weight trained twice a week for two months before the study and could squat close to twice their body weights. So, these guys were in pretty good shape and had a solid base of strength training.
All sprints were on an outdoor track (Rekortan M99 synthetic track to be exact – who knew).
The participants wore sprinting attire: spiked sprint shoes and athletic training clothing.
The participants warmed up with:
- 8 minutes of running at a heart rate of 140 beats per minute
- 8 minutes of dynamic (or active) stretching
- 10 minutes of running technique exercises
- 2 to 4 sub-optimal sprints
Then they were off to the races. (Geddit?)
They started standing and sprinted for 50 meters, but their time was recorded for only the last 30 meters with electronic timing gates at the beginning and end of the 30 meters.
There were four sprints in total:
- 6% of their body weight
- 10% of their body weight
- 15% of their body weight
There were 6 minute breaks between sprints.
Oh and by the way they used a radar gun to measure max speed, which I think is a bit of overkill, but I guess they had a cool toy they wanted to use.
As you probably could have guessed, the greater the load on the sled the slower the speed of the sprinter.
Table 1 is a summary of all the results.
Using statistical analysis (regression analysis) they figured out the following equation:
-0.8674 X % velocity + 87.99 = % body weight
In English, this equation calculates what percent of your body weight you need to add for a given percent of velocity. Clear as mud, right?
Okay, how about you look at it this way? If you want to sprint at 90% of your max (which is optimal sprint training load) you put it into the equation.
% of velocity
% of body weight
-0.8674 X 90 +87.99 = 9.92
You get 9.92% bodyweight. So, for optimal sprint training you just use that number.
To simplify it for optimal sprint training load all you need to do is multiply your body weight with 9.92/100.
If you weigh 50 kg then you load 4.96 kg (50 x 9.92/100).
If you weigh 200 pounds then you load 19.85 pounds (200 x 9.92/100). You don’t even need to convert to metric!
To make the math even simpler you can just go with 10% of your bodyweight; it won’t matter that much.
This study figured out that for sprint training, the optimal sled load was about 10% of participants’ body weight.
While 10% is a good place to start, it may not work out for you. Why? Because this was a very specific group, using a specific track, shoes and sled. The closer you are to the experimental methods the better the 10% load will likely work for you.
So what to do? An experiment! On yourself! Really, it won’t hurt — I do it all the time.
Your own Mini Experiment
- A participant
- An experimenter
- Three pylons or anything you could use to mark three spots: standing start, timing start and finish
- A sled (duh)
- Some weights (2.5 lb or 1.25 kg increments should work)
- A calculator
- Radar gun (optional… and if you have one, why?)
To do the experiment, follow these steps.
- Have the experimenter time the participant sprinting the last 30 metres of the 50 metres without the sled (see above for the setup).
- Add the sled and weight based on the equation (10% of your weight).
- Time the participant’s sprint over the last 30 metres.
- Did it take you 9-11% longer to sprint with the sled?
- If yes, that is your optimal load.
- If not, add (if <9% longer) or remove (if >11%) more weight from the sled.
- Take 6 minute breaks or longer if need be.
Have fun experimenting!
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