Sled Training

In a new investigation on very heavy sleds (VHS), a group of great researchers created an experiment to see if sprint training with VHS would improve horizontal force production with amateur soccer players. They compared the forces and times of loaded and unloaded players after a short eight weeks. The results were not surprising. The loaded group, using loads that were 80% of body mass, improved horizontal force more than the unloaded group.

Is this exciting and revolutionary? Will this change the sport of soccer? Of course not. The study design was an important milestone because it presented a framework for coaches to think about how loads affect short (5m) and longer (20m) acceleration distances.

The use of heavy sleds in sprinting to develop acceleration is hotly debated. For years, I’ve sprinted with loads that are very conventional while other coaches have gone far lighter and far heavier with success. Recently some proponents of VHS work have pushed us to rethink sled work in more detail.

I have read all of the research, listened to both sides of the argument, and share my thoughts in this article. I delve deeper into sleds with a smart and wise perspective; not to test groups of athletes for a few weeks and then draw conclusions. Rather than rehashing old rebuttals about why one way is better than others, I will start backwards, examine the best accelerators, and ask the obvious questions.

Recent Controversies: We Can Calm Down

Every time a new study appears with a surprising or different conclusion, social media loses its mind and coaches go into a frenzy. The VHS study created waves of fever among coaches who love ultra-light sleds and emboldened the heavy-is-better coaches who only view the world in progressive overload.

After reading the VHS study a few times, I noted obvious questions most coaches will ask:

• Does the improvement in going from point A to point B excite anyone?
• Is the population of athletes even relevant for those who work at high levels?
• What are the limitations of the study, including other variables?

The answers to these are simple. Amateur athletes are likely less talented and perhaps less well-trained. An elite athlete who is talented isn’t necessarily in great shape nor participating in an amazing speed program.

It’s fair to ask: What about talented athletes who are in a well-constructed training system for all parts of training? Do resisted sprints have as much impact when many other factors are involved?

The core lesson from the VHS study is that we must juggle a lot of sub-variables carefully to truly understand how small decisions factor into a program’s results—not that one technique or method is better. When most programs address speed through a multitude of factors, is it safe to say that one ingredient is never as effective as an entire recipe?

We must juggle many variables to understand how small decisions influence a program’s results. Click To Tweet

Rarely, if ever, has anyone created a hierarchy of interventions based on impact that satisfies both the statistical and scientific needs of real world application for which most coaches are searching. It’s a bold proposition, but ducking it is cowardly. To innovate, we must explore with risk.

Improving Speed without Resisted Sprints

I am a huge fan of sled sprints. While adding resistance to a specific motion is straightforward and effective, however, there are other valuable training methods. Different benefits come from various loads, ranging from microdosing one or two kilograms to loading more than 50% of bodyweight.

The most common mistakes I see with a majority of training modalities are not seeing the big picture when deciding what something is worth and looking at what athletes in the past have done to improve. I will explain how to look at all the methods in one program without bias and let time serve as the judge.

The fastest athlete wins the 100m dash, not the one with the best buzz metric. If the buzz metric of choice was the key to running faster, why are we not seeing everyone getting faster progressively? To develop speed, most power athletes lift weighted loads, sprint, and do some jump exercises. If they didn’t do any sled work, would they miss the opportunity to get faster?

Several studies have compared different lifting exercises and speed, and the range of motion in the same exercise, and found improvements. With all of the options, do any sled loading options make that much difference?

Many athletes fail to improve consistently, indicating the community doesn’t have a perfect blueprint for getting faster. Since improvements in a 30m acceleration can be as little as.05 seconds over a year, coaches have no choice but to be very meticulous when choosing training options based on a needs analysis of the athlete’s abilities and current development.

Force, power, and velocity profiling are growing in popularity, but so far, not too many Olympic medalists in the last fifty years can show how they used sled loads in this fashion. With the increasing proliferation of equipment as well as the improved ease of use, I think we might see something in Tokyo.

Many variables interact in sports training, so segregating or isolating variables isn’t easy, especially when they develop at different times. For example, an athlete who improved lower body strength and power may not improve speed the same season. Theoretically, however, they could learn to use their acquired strength the following season.

An athlete with a plyometrics program may improve their jumps but still have problems with race modeling and tapping into their jump enhancements, even though practice times improve. Some athletes improve dramatically just by working on technique and sprint repetitions at different intensities and distances. They need little else to support these changes.

Look at the greatest first 10m splits by Greene, Bolt, Stewart, Fredericks, Johnson, and others. Does anyone believe that just squatting heavy got them to where they were? That they would have run faster with heavy sleds? If we see a lot of 1.65s (taking out reaction time) in the next ten years by sprinters who do reach over 12 m/s, I would be beyond shocked.

Team sports may need sled work because of the lack of specific speed development. Click To Tweet

It’s safe to say that team sports may need sled work because of the lack of specific speed development, but the NFL Combine times don’t seem to show systemic and remarkable improvements based on the last ten years of data.

Overcoming Inertia, Technique, Specificity, and Repetition Arguments

Speed

Speed is a vague term, and acceleration is not clear either. When resisted sprints are performed with sleds, it’s interesting to see what distance is measured and at what point during the sprint the athlete’s time and velocity improve. Technically, acceleration occurs most of the time in sport. But in the 100m, acceleration happens all the way to about 50-60m. Any research on 120% of body weight improving 40-50m segments?

The likely reason that many programs use weight exercises that overload the body is to help overcome inertia which usually happens in the first few steps. Beyond 5m, maximal horizontal forces don’t matter as much as how athletes can create body speeds.

The fastest men in the world express amazing power at high speed but don’t have squats that would place them on the weight room record board. We can say the same for sled times; many stronger athletes who do great speed work may have faster times with the same body weight load percentage.

When testing an athlete’s speed, it’s always difficult to judge technique. If you read any of the papers, even the information on kinematic changes with sleds and sprints, the data is rarely shown in its entirety to allow us to tease out the right information.

Many athletes can improve technique and speed without sled loads if they have proper coaching. Click To Tweet

Sled loads may change things acutely, and perhaps chronically, but we lose the specific context. Many athletes can improve both technique and speed without sled loads if they have proper coaching. I believe that loading sprints allows athletes to become comfortable, and heavy sleds are necessary to prop up an athlete with very aggressive angles.

Noted researcher JB Morin shares the point that, without heavy loads, mechanical exposure to very acute angles is not possible compared to light sleds. Falling sprints and other activities can expose athletes to brief periods (a few steps) of aggressive and deep accelerated running. Ramps and hills have a similar influence on developing deep acceleration. Sleds are more of a staple, though, because they are more controllable. Also, access to ramps and hills with some facilities can be hit or miss.

Specificity
Specificity is another heated topic. Some coaches hate anything general. Others may respect general changes but believe specific work elicits a better transfer from the capacity of biomotor ability to use that change.

My concern with any specificity debate is that pattern overload is the bane of the common and effective way to improve, working on direct measures by replicating them in practice over and over. It’s fair to argue that lighter loads are specific. We can also argue the benefits of progressive overload.

The specificity discussion includes the subject of repetition because rehearsing performance is usually specific in nature. Global ability with speed and power gives athletes a chance to be better, but demonstrating the ability to repeat performance is a stronger indication of what is probable in the future. Coaches are comfortable when athletes perform tasks in practice that are very similar to what they need to do in competition.

As Nick Saban says, don’t practice something until you get it right, practice it until you can’t get it wrong. Clearly, we can argue about how much volume to use before an athlete hits diminishing returns or fatigue causes poor practice. The point is that rehearsal and skill development take time and multiple repetitions. Reducing errors and getting to optimal form are indeed the goals, but they can’t happen magically overnight.

Thoughts on Fatigue and Loading Patterns

One emerging idea is to stop profiling athletes for optimal sled loads and, instead, come up with a model that allows coaches to select progressions of resisted sprints in conjunction with weights, plyometrics, and other variables. Progress in training is easy with time and health. Unfortunately most coaches don’t have time, and they have to work around an athlete’s past and present injuries and impairments.

Many of the protocols for sled sprints are based on blanket prescriptions, arbitrary designs based on unknown influences, and repeating past studies. I don’t fault any researcher for doing this; a study can’t be perfect, and for scientific purposes, it needs to be artificially designed to see a cause and effect with what is often one variable.

The VHS study (coauthored by SimpliFaster guest writer George Petrakos) included 16 sessions of 10 x 20 sled sprints. I’ve used higher volumes and seen improvements in unloaded times with a similar protocol. But the fact that I used loads that were considerably less may explain that total work output is a better measure of volume. VHS should follow the general recommendations for acceleration volumes, but with one difference—looking at how force drops off during training.

I attempted to push how I started using indices of velocity, force, and power with the 1080 Sprint in my earlier article, High Resolution Programming for Acceleration. Some speed training theories cut sessions off when the time drops, but this could mean that the athletes did not perform enough repetitions. Some athletes are great at creating a fast time early. Other athletes often find technique and rhythm starting to click after performing many repetitions, settling into a groove later, especially early in the general training season.

Velocity and power can be allowed to drop slightly, but be cautious when force falls. Click To Tweet

I believe coaches may want to allow velocity and power to drop slightly but should be cautious when force falls. Although I may miss a huge rebound by pushing harder or doing too much and moving into the acute fatigue regions of the nervous system, as long as athletes are getting faster or returning to best speeds faster, it doesn’t hamper development.

VHS work, meaning loads that are 80% or greater, is likely to fatigue athletes more than light loads when the distances (short) are the same. Not much theory exists along with research as to how different sled loads and programs create fatigue and adaptations. The only solid variables we have as guides are time, the actual sled prescriptions, and results over time.

In a 2016 study, improvements in sprint performance were similar to what we’d find in a squat program. The lifts went up, but the times didn’t budge much at all. In the VHS study, the 5m improvements matched nicely to the force characteristics of the sprints; the results from the 20m, less so.

It would be interesting to see a study with heavy squatting or hip extension exercises without loaded sprints to make a fair comparison since many coaches spread the distribution of load among various options. Would a lifting and no-sled program perform as well as a heavy sled program? What about more advanced athletes? What about a mixed program of different loads based on conventional periodization strategies?

A lot of unanswered questions. This is why coaches get frustrated when conclusions are pushed on them as gospel based only on a few studies.

Some Theoretical Ideas for Heavy Sled Use

I decided to go heavier than normal to see if I missed anything special with heavier than conventional (30% of body mass) protocols. The confusion over much of the research is that we don’t know the horizontal resistance forces applied by athletes (instead of sled weight). This provides a very shaky indication of what is actually occurring, even when you’re timing.

Part of the equation when timing sprints is effort. So I’ve tried using intensity as a percentage of all-time best performances, with some success. But the true load that takes into account friction would contribute to more universal conclusions.

Matt Cross authored a wonderful paper recently about this challenge but, again, how practical is this when working with large groups? Even with a backroom full of sport scientists, the workflow of setting up loads and workouts isn’t easy. Coaches usually will reduce a more elegant string of progressions to the safety net of 10% body weight. Even without load, athletes get faster in the 5m distance, and with a slew of other variables and light loads, results are showing up on the timing watch.

I like using heavy sleds to improve posterior chain recruitment without much equipment and to get athletes comfortable with their faces closer to the ground while feeling relaxed and powerful.

I don’t count early acceleration of the first 5 meters because other studies show that this can be accomplished without sleds. When most coaches want to improve speed potential, 20-30m distances are more interesting. It’s also important to note that athletes with great maximal speed rarely have poor 10m times; global velocity and coordination abilities can be directed to early speed using few resources.

Many programs work speed and force from both ends by driving maximal power and strength in the weight room and doing long accelerations with light loads. They don’t seem to be missing out from not using the VHS approach. So why bother?

I’ve had a few athletes who benefited from going heavy, even when they had great weight room numbers and great top speed. One would assume that given these two solid abilities, early acceleration would be a non-issue.

Most elite sprinters are great out of the blocks due to practice, not because they have better numbers in the squat and clean (even pound for pound). Otherwise, powerlifters and Olympic lifters would have at least 1.50-10m dashes given their body mass and maximal weight performances.

Sometimes overloading sport specific actions can work, as it did for three or four athletes who didn’t respond to a general outline. Profiling works, but most variables wash out with beginners and intermediate athletes. At higher levels, it may become essential to get force-velocity profiles. Time will tell.

I find that heavy sleds represent an opportunity for athletes to get into a deep acceleration angle, deeper than they can get on their own, and become comfortable producing high levels of force behind them. It’s not magic, but I like this far better than wall drills. In fact, I haven’t had an athlete do wall drills for ten years.

Heavy sleds let athletes get into a deeper acceleration angle than they can get on their own. Click To Tweet

Currently, I don’t use the bullet belt. I do feel, however, that heavy resisted sprints are great teaching tools for some athletes. I like staying with light sled loads and longer reps, for the most part. I only experiment with going heavy when athletes have well-rounded profiles; in my program, we do a lot of repetition and get faster from specificity.

Every coach and athlete should do what works for them. Practically, this means athletes improve as fast as, or faster than, their peers, and they’re not putting all their eggs in one basket. Or in this case, all their plates on one sled.

Find What Works and Experiment

Heavy sled sprints are overrated only because they are one option of one variable of one method. Because I favor speed, I’ve questioned the 10% of body weight rule. I’ve never seen an athlete with a “sled stride” because they went heavy for a few weeks. I have witnessed a national champion do sled work late in the competition phase when preparing for the 100m and 200m, so anything is possible.

Heavy sled sprints are overrated only because they are one option of one variable of one method. Click To Tweet

It’s sound to use heavier than normal loads for very early and short acceleration changes. Remember, however, that other methods may address that need. Don’t be too biased either way. Plenty of options exist to get better, so I suggest mixing methods to address multiple areas.

I’m discovering that, as I become more experienced, my prescriptions are becoming more individualized, and going heavy might be good for some athletes.

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