Every once in a while a study comes along and alters my understanding of biomechanics and sports science. Effects of weighted sled towing with heavy versus light load on sprint acceleration ability by Kawamori et al. was published ahead of print earlier this year in March. It’s an excellent study that supports what many strength coaches have been saying for quite some time (and refutes what many track & field coaches have been saying) – that heavier sled towing is effective in improving acceleration ability. In the past, many T&F coaches believed that using sled loads of greater than 10% of bodymass (or loads that reduced speed by greater than 10%) would alter sprint mechanics too much and negatively impact speed.
I’ve been a proponent of heavier sled towing for quite some time. However, prior to this study, I’d have told you that an progressive training cycle of heavy sled towing would increase speed production by increasing hip extensor strength which would produce larger horizontal ground reaction forces and therefore greater stride lengths. Now I attribute the increases to different mechanisms, which I’ll explain below.
The Study
The study examined 8 weeks of 2X/wk training of light sled (around 13% of bodymass) towing versus heavy sled (around 43% of bodymass) towing on 10m acceleration times. These loads reduced speed by approximately 10% and 30%, respectively.
Results
The heavier sled towing group significantly increased 5m acceleration by 5.7% and 10m acceleration by 5%, whereas the lighter sled towing group only increased 5m acceleration by 2.8% (not significant) and 10m acceleration by 3%.
Mechanisms
Here’s where it gets interesting. The heavier sled towing group significantly decreased resultant GRF impulse (impulse = force x time) by 4.3% and vertical GRF impulse by 11.5%, which wasn’t the case with the lighter sled towing group. The horizontal GRF impulses didn’t show any significant changes in either group. The heavier sled towing group also significantly increased step frequency by 8.1%, which wasn’t the case with the lighter sled towing group.
To reiterate, heavier sled towing created favorable sprint adaptations that led to sprinters producing less vertical impulse and less resultant impulse so that a greater percentage of the GRF impulse production was directed horizontally, which led increased stride frequency and acceleration.
To quote the authors:
“Based on such findings, it seems necessary to revise our understanding of potential mechanisms of weighted sled towing to improve sprint performance; that is, weighted sled towing especially with heavy loads improves sprint acceleration performance by teaching athletes to direct GRF impulse more horizontally, not necessarily by allowing athletes to produce larger horizontal or resultant GRF impulse.”
I’d like to mention that this research jibes perfectly with prior research I’ve mentioned on this blog two years ago HERE which examined the technique of ground reaction force application. I also touched on this same line of reasoning three years ago HERE, and last year HERE and HERE.
Here’s another important quote from the authors:
“If this new hypothesis regarding the potential mechanism of weighted sled towing is correct, then weighted sled towing could be regarded as a skill practice exercise more than a strengthening exercise. That is, it does not necessarily strengthen the neuromuscular systems involved in sprinting in a specific manner, as many believe, but rather it teaches a more efficient/effective way to apply GRF impulse while sprinting, which has more to do with motor control than muscular strength improvement per se.”
Conclusion
Heavier and lighter sled towing both significantly improve 10m sprint ability, but only heavier sled towing improves 5m sprint ability. Coaches should abandon the “10% Rule” and start implementing heavier sled towing with their athletes.
Future research needs to continue along these lines and examine even greater towing loads on acceleration and maximum speed sprinting.
Bret,
Were the test subjects trained sprinters or untrained general population guinea pigs?
Do you think the % improvement in acceleration would be any different if the test subjects pushed rather than towed the sled?
When calculating sled load, did the researchers include the empty sled weight or just the additional weight plates? Reason I ask is that my sled, the Sorinex Root Hog, weighs 67 lbs. empty which would be over the 43% load used in the experiment if one weighed < 156 lbs. and that may pose a problem for younger sprinters, especially females.
What brand / type of sled was used in the study?
What about surface friction? Were the sprints on real grass, artificial turf, rubber track?
Patrick
Patrick:
excellent questions. maybe rather than load, they should have measured resistance. then again, this study would be very hard to reproduce without the same sled and surface.
Good review Bret, I’ve just read the whole paper.
Patrick ~ See these quotes below from paper…..can’t find anything about what sled it was though.
Twenty-one physically active men who had experience in team sports such as soccer, basketball, field hockey, and Australian Rules football were recruited for this study. Their performance standards ranged from recreational performers to regional-level athletes. When this study was conducted, the subjects were either in their off-season or pre-season preparation period, and none of them were in the competition period.
Outside grassed field
Note that we use the terms “light” and “heavy” in this study to describe the magnitudes of the two added loads in a relative (rather than absolute) sense. During weighted sled towing, the participants were connected to the sled via a shoulder harness that was in turn connected to the sled by a connecting lead.
Regards
Nicholas Jones
Bret,
Did the research study reveal the towing length in meters for each training session?
What about the number of tows per session?
Thanks again!
Patrick
Patrick, I just emailed you the paper.
I’d be interested in the difference(s) between heavy sled pushing (aka Prowler or Root Hog) and heavy sled pulling for acceleration or overall speed.
Me too! I think they’d be similar but the kinematics and kinetics are slightly different.
I know Joe DeFranco loves doing heavy sled drags with the prowler and says there one his favorite methods for developing speed for his athletes. I think a better study like you said would be using a heavier load such as 70-80% of a persons bodyweight.
I agree. And even higher than that. Need multiple studies on this topic.
21 physically active men, in that case I guess truck pulling would have an even better effect, the heavier, the more focus on strength (longer contacttimes, so not too bad for acceleration in beginners. But a bold conclusion to use heavier sledge pulling for “real” sprinters, leave alone elite sprinters. Since the movement patterns is so far from sprinting (take contacttme only, one could have done squats and get the same effect on acceleration in this group.
But I am pretty sure this going to have a great impact in the US….. and soon we’ll see the pulling of heavy sledges, loaded supermarket trolleys, light cars, heavy cars, trucks and Boeings 747….. the heavier the better, guys… proven by science. At least it will make the physical therapists, chiropractors and orthopedic surgeons happy 😉
Damn Henk! How do you really feel? I’m not in agreement that the mechanics throw the sprinter off as long as it’s programmed properly. And sleds are just one tool to aid in sprint development. The point is not to overvalue sleds but to utilize them along with free sprints, weights, and plyos for a sound overall program.
Why not just squat and sprint? People keep coming out with all these methods and it seems like overkill. As a whole, people don’t seem any faster than they were 20 years ago.
Bret,
I’d like to
Eat jelly from your tip.
I think adding sleds without specific protocols for specific parameters is a problem. The athletes couldn’t break 2 seconds in the 10m and that shows they are beginners, even at the early 20s. The research does show that kinematically technique does become altered and the motor learning research. I also believe that all of this washes out if done right but 5m sprint times are also influenced by squatting. I think we need to look at are we trying to influence 30 or 60m or get the first 3 steps faster? The level of athlete doesn’t matter in studies, so long as we are not extrapolating to a different subject population.
One place that’s been getting this right is Sparta Performance Science. They use heavy sled pulls to teach “proper shin angles” in their lingo. The reduce most athletic ability to GRF and shin angles.
http://spartascience.blogspot.com/2012/10/speed-training-drillsif-you-could-only.html
Nice in theory but shin angles are not an adaptation quality. I hate if you had to do only one exercise posts since we are not living in that society. Holistic please.
So what would you recommend for programming these? Distance, reps, rest, etc.?
Bret,
Appreciate you sending me this study. However neither the sled brand nor any details if the total weight sled load included the empty sled weight or just the added weight. How can these looming questions be answered…inquiring minds want to know?
Thanks,
Patrick
Patrick – look at chart A on page 31. Shows relative sled mass. Heavy appears to fluctuate between 40-45% of bodymass, light around 12% of bodymass.
Table 2 on page 27 shows the training schedule.
Table 1 on page 26 shows bodymasses between groups: heavy was 77.5 kgs, light was 82.7 kgs.
If you multiply 77.5 by 40-45% you get 31-35 kgs (or 68-77 lbs).
If you multiply 82.7 by 12% you get 10 kgs (or 22 lbs).
Bret,
Where did you find the % of the subjects’ body mass that was loaded into the sled for this study? I see where they describe the reduction in running velocity these loads produced, but cannot find an estimation of load as a percentage of body mass.
PS thanks for the blog post! I follow you on many sites and observe your training methodologies. I am glad that I came across this study on your site. I will be presenting it to my graduate kinesiology class.
Bret,
As I re-read, I found the portion of the study mentioning the load relative to body mass.
Thanks again!
hi, old post i know, but can someone tell me the protocol used in terms of distance and reps in training? Thanks.
I have openathens thru work but still cant get the whole article