Fast off the Ball: Revisiting Heavy Resisted Sprinting for American Football

A short while ago, I wrote an article overviewing a small case study I performed using heavy resisted sprinting for my American football players. I based the case study on a recent paper by Matt Cross titled, “Optimal Loading for Maximizing Power during Sled-Resisted Sprinting.”¹ Specifically, I wanted to monitor changes in the players’ 40-yard dash performances with the inclusion of heavy resisted sprints. I described my methods using the 1080 Sprint machine and provided the data to show what happened with each athlete.

I used four football players training for potential scouting combines and/or pro days: two running backs and two linebackers. One of the linebackers left our program before recording his post-test sprint times, but the other athletes saw improvements of 0.10-0.33 seconds in their 40-yard dash times after four weeks of training that included heavy resisted sprinting.

The Case Study Weekly Training Template

While the split times at the 10-, 20-, and 40-yard segments improved, the cause of these improved times is less clear. This is the template for the training week:

The NFL combine and NFL pro days contained a battery of tests, including the 40-yard dash, pro agility shuttle, L- or three-cone drill, vertical jump, broad jump, and 225lb bench press for maximum repetitions. The case study took part while my clients trained for these tests. Although I wanted to see the effect of heavy resisted sprinting on their 40-yard dash times, I ensured that it stayed “business as usual” and did not deviate from the overall training program. Thus, the training template was broad and focused on many different stimuli simultaneously. This is an obvious limitation that I will expound upon later.

The training on Day 2 did not feature any sprint work, but did include maximum intensity jump training. Between the total volume of horizontal and vertical jump training, the day featured 30-40 jumps performed as explosively as possible. I used a jump mat to measure vertical jump variations and a measuring wheel and markers to measure horizontal jump variations to ensure that intent was maximal on each repetition. The focus of the weight training was on using heavy resistance (slightly below maximum effort) in the primary lift, followed by auxiliary training.

Day 4 was the designated “case study day” where athletes performed unloaded short sprints of 10-20 yards before progressing into sprints against the individualized load of maximum power. Lighter resisted sprints followed this and then athletes headed back to the weight room for auxiliary training. We timed all sprints and kept records, ensuring that each sprint was high intensity with full recovery periods.

Video 1. A look at three athletes sprinting against individual loads of maximum power. Lighter resisted sprints followed this and then athletes headed back to the weight room for auxiliary training.

The variety of training stimuli may have affected each athlete differently even though they all ran faster times. They were all getting back into power and speed training after spending the past several months in-season. Therefore, their baseline 40-yard times may have reflected a diminished readiness state. It may have taken them the length of the case study (four weeks) to “get back” their pre-existing strength, power, and speed capabilities, and this may not have been a direct result of the heavy resisted sprinting. However, due to the broad array of training stimuli, it’s not easy to assume what helped each athlete the most.

Changes in Force and Velocity

In the previous article, I showed that both running backs saw improvements in their velocity output with virtually no change in their horizontal force outputs, while the linebackers saw the opposite effect. In Figure 3 (also featured in the previous article), we can see changes in theoretical maximum relative force (F0), theoretical maximum relative velocity (V0), and theoretical maximum relative power (P_max). “Relative” indicates the outputs as they relate to body mass.

While all players showed increases in relative horizontal power, they each did so differently—some by improvements in force and others by improvements in velocity. The training template featured a full spectrum of resisted sprint training: unloaded sprints, light resisted sprints, and heavy resisted sprints. It is likely that each athlete underwent an individualized adaptation due to their current state and the exposure to each sprint, jump, and resistance training variation.

Horizontal Force and American Football

In the absence of a fully controlled study isolating a single variable, it is tough to determine the full impact of the heavy resisted sprinting. However, the research by JB Morin and Matt Cross shows promise for heavy resisted sprints improving horizontal force production. I provide a detailed explanation of the scientific background of my case study in my previous article, but I will briefly review some of the important concepts.

Sprinting fast is based upon applying force onto the ground, in the right direction, at the right time, consistently over a designated distance (e.g., 40 yards). Force can be applied onto the ground with greater horizontal emphasis (like starting the sprint motion and propelling forward at a low angle) or with greater vertical emphasis, as seen during maximum velocity where flight time is increased. Horizontal and vertical force application are both always present.

The total force applied in each step is referred to as the resultant force, which is the combination of net vertical and horizontal force application.

The effective ratio between horizontal and vertical force will differ depending on the stage of the sprint: The ratio of horizontal force should be greater when starting a sprint and the ratio of vertical force will consistently rise during acceleration and achieve the highest ratio when running at maximum velocity. Since maximum velocity is attained once acceleration is no longer occurring, the ratio of horizontal force will inevitably drop in favor of a higher ratio of vertical force. This is referred to as the decrease in the horizontal ratio of force (DRF).

Once at maximum velocity, there is a limited window to hold top speed before deceleration starts to occur. For track and field sprinters, it is logically advantageous to spread out acceleration as much as possible, minimizing the risk of decelerating by achieving maximum velocity too early. Top-level sprinters can continue accelerating for over 60 meters: Usain Bolt has shown the ability to accelerate up to 80 meters.³ These distances are much longer than 40 yards, which is equivalent to 36.58 meters. Yet, we constantly see American football players at the NFL Combine start to decelerate before hitting the finish line.

As pointed out in the research by JB Morin and his colleagues, top-level sprinters display high ratios of force in the horizontal direction (RF = horizontal ratio of force) and show great ability to maintain this horizontal force as they continue to accelerate (DRF). The DRF is therefore viewed as a measure of sprinting efficiency, exhibiting the ability (or lack thereof) to prolong the acceleration period. However, American football players do not have the same acceleration strategy.

When a running back sees an open hole through the line of scrimmage, his only concern is being able to gain as many yards as possible RIGHT NOW. There isn’t much time to spread out his acceleration. It’s even more interesting when we consider that a 10-20 yard gain is a decent offensive play. In fact, football coaches often refer to plays over 20 yards as “big plays” and try to minimize them as much as possible from a defensive perspective.

So, while a 100-meter sprinter knows 100 meters will be covered during the sprint, the running back pats himself on the back any time he gets a 20-yard gain. Longer distances are substantially harder to come by, especially at the professional level. Acceleration requirements are very different between the two sports, which can help explain why football players may decelerate before reaching the finish line in a 40-yard dash.

Despite the differences in sport requirements between American football and the 100-meter sprint, the 40-yard dash is, without question, closer in task to a 100-meter sprint than it is to playing football. Understanding how to improve 40-yard dash performance can start by taking pages out of track and field training methodology.

Acceleration Strategies in the 40-Yard Dash

While the NFL Combine doesn’t require football players to sprint 100 meters, the 40-yard dash is a true “make or break” testing measure whereby the best performers have a much higher possibility of getting a contract and a career in the NFL. Football players should put themselves in the best position to accelerate steadily over the course of 40 yards. At the very least, they should develop the ability to not decelerate before the finish line.

The goal is to maximize the RF and minimize the DRF as much as possible. Share on X

They can accomplish this in one of two ways. The first way is to develop the ability to accelerate at each 10-yard split, where the split between 30 yards and 40 yards is the fastest. The second way, which is more common for bigger-bodied players, is to accelerate and achieve top speed before the 40-yard line and then maintain this speed until the finish.

Regardless, the goal is to maximize the RF and minimize the DRF as much as possible. Translation: maintain the acceleration phase for as long as possible. As exemplified in my case study, JB Morin and his colleagues proposed that improving RF can result from sprinting against the resistance that maximizes horizontal power production. When sprinting without resistance, maximum power is typically reached within one second, which is the point at which velocity starts becoming significantly higher than horizontal force.¹ Finding the load of maximum power indicates finding a load that optimizes the product of horizontal force and velocity.

Since unloaded maximum sprinting power is typically achieved within one second, we can assume that it occurs somewhere between 5 and 10 yards, as it takes closer to two seconds to reach the 10-yard mark (e.g., 1.55-second 10-yard split). When aiming to find the load of maximum power, we basically try to find the load that will allow the athlete(s) to remain in a similar environment to the first 5-10 yards and spread it out for longer distances. In my experience, and based on Matt Cross and JB Morin’s work, 20-25 yards seems like a nice distance range for sprinting against the load of maximum power.

Determining the Load of Maximum Power in Resisted Sprinting

How do you determine the load of maximum power? In my previous article, I went into the details of the paper by Matt Cross, JB Morin, and colleagues, where they determined that the load equivalent to the highest point on a power curve occurred between 69% and 91% of body mass (load on the sled, including the sled) for mixed sport athletes and between 70% and 96% of body mass for sprinters. So, they imply that a 205lb NFL safety would have to sprint with a sled load of 141-187lbs. These recommendations are significantly higher than traditional sled sprinting guidelines, which indicate sled loads should be less than 40% of body mass.

We must keep in mind that these recommendations are based upon a very specific approach to improving sprint performance. Namely, we may use maximum power sled sprinting to improve the potential to generate high levels of horizontal force from the sprint start and on through the rest of acceleration. I see it as a tool that helps athletes feel the sensation of propelling forward in the acceleration position. If they do not generate sufficient force in this exercise, they will go nowhere in space.

The sled load may be variable due to friction of the surface being trained on. For example, when using sleds, the sled may slide differently on a turf surface than on concrete or rubber surfaces. For this reason, it’s likely safer to use other measures to determine the load rather than just percentage of body mass. The Cross paper found that the load of maximum power occurs between 48% and 52% of maximum velocity, with 50% being a good aiming point. The paper focuses on average velocity achieved rather than peak velocity, as average velocity gives a better indication of what’s happening over the entire distance rather than at one point in the sprint. This is NOT the same as split time.

Velocity is typically measured in meters per second (m/s) and represents a kinematic quality of physics, not a time taken to complete a distance. For example, if a football player has a maximum sprinting velocity of 9.00 m/s, then it’s likely his load of maximum power will occur at a velocity of 4.50 m/s (50%). Therefore, we may determine that his range of maximum power is 4.32-4.68 m/s (48-52%). Once the football player can consistently sprint faster than 52% of his maximum velocity with a given load (e.g., 4.68 m/s), his sprinting power has improved and he will have to use heavier loads to continue to push his sprinting power higher.

You can calculate velocity with proper measurement devices such as radar, video analysis software like the My Sprint App, and machines like the 1080 Sprint. The 1080 Sprint instantly displays both peak and average velocity after each sprint. However, without these tools, many coaches may not know how to determine their athletes’ maximum sprinting velocity.

One very simple way of determining an athlete’s average sprint velocity is to divide a distance covered by the time taken to reach it. For example, if an athlete ran a 40-yard dash in 4.50 seconds, then you would do: 40/4.50 = 8.89 yards per second (yd/s). Since football is a game of yards, it is appropriate to keep the velocity in yd/s, but it may be worthwhile to also convert it into meters per second (m/s), which is more universally understood. Converting 8.89 yd/s into meters per second would yield 8.13 m/s.

The problem with using this approach is that the coach must ensure that the athlete has sprinted far enough to reach maximum velocity if the numbers are to be valid. In the case of football, the primary test of speed is, of course, the 40-yard dash. But it’s possible that smaller athletes like wide receivers and defensive backs can keep accelerating farther than 40 yards, while some bigger athletes like offensive linemen may reach their top speed before 40 yards.

If a coach plans to figure out average velocity by dividing distance over time, they may be well-served to test their athletes at 30-, 40-, 50-, and 60-yard distances to be certain they found the right distance that yielded the fastest average velocity. To that point, there is structural risk associated with bigger athletes (i.e., over 275lbs) testing at distances over 40 yards, so those distances may not be necessary for linemen or large big-skill players like tight ends or outside linebackers.

My Proposed Simple Field Measure

For sake of observation, I have started using the 40-yard dash time and finding the average velocity of that distance for each player as a proxy to determine a time range for individualized loading for heavy resisted sprint training in a very time-efficient manner. If we use the example above where the player runs 40 yards in 4.50 seconds and yields an average velocity of 8.89 yards per second, then taking 48-52% of 8.89 yd/s would yield a range of 4.27-4.62 yd/s, with 50% being 4.45 yd/s.

If we apply the 50% velocity over 20 yards (which is the distance I used in my case study), then we would have to load the athlete until he sprinted 20 yards in 4.49 seconds. The 48-52% range would indicate that the athlete has a goal range of 4.33-4.68 seconds. Notice any pattern? It appears that the 20-yard split time of 4.49 seconds at 50% velocity would be very close to the 40-yard unloaded time of 4.50 seconds. The 48-52% range is also very close to being within 0.20 seconds above or below the unloaded 40-yard time.

I am experimenting with having athletes run the 40-yard dash and using that split to determine the time range for heavy sled sprinting. In the hypothetical case of a 4.50-second 40-yard dash time, I would load the athlete until he ran 20 yards between 4.30 and 4.70 seconds. If the athlete showed the ability to run faster than 4.30 with a given load, I would then make the load slightly heavier.

I should immediately state that I do NOT have any research to back this up. My objective is simply to try and find a simple way for coaches to get the adaptive benefit of heavy sled sprinting with minimal equipment. Time will tell if research will support this idea.

Justifying a Simplistic Approach

I must express a couple of thoughts unequivocally. First, as stated previously, using a 40-yard dash time as a proxy to determine maximum average sprinting velocity has obvious flaws from a validity standpoint. If it is NOT a distance where maximum velocity is reached, then inevitably the loads used for heavy sled sprinting will be heavier than what you may have used if calculating the velocity with a more valid measure. However, I don’t believe it is as much of a worry with American football players. I say this because football requires the athletes to possess high levels of early acceleration ability to cover short distances as fast as possible. Not to mention, collisions occur on nearly every play. Therefore, sprinting against slightly heavier loads may prove beneficial for the most force-dominant scenarios in football, such as a running back breaking through tackles or a safety trying to take down a tight end.

Again, this simplistic approach has no scientific validation and is only my attempt to simplify the process for coaches who may lack the equipment to successfully measure maximum velocity. I certainly still encourage coaches to consider products like the 1080 Sprint, which instantly provides force, power, and velocity data after every sprint repetition.

Everything Has Its Place in Training, But Take Nothing Out of Context

In his book, The Science of Running, Steve Magness describes the concept of the hype cycle,⁴ which he explains as: “when an idea is new or gains popularity, it follows a cycle of initial overemphasis before eventually leveling off into its rightful place.” The work of JB Morin and Matt Cross explains that heavy resisted sprinting has a specific purpose: maximizing horizontal power to increase the magnitude of force and the efficiency of its application during acceleration. It is not meant to be a one-size-fits-all model of training.

It is simply not logical to assume that those training to be fast need only do heavy resisted sprint training. You must use unloaded sprint training if you truly expect anyone to get faster. JB Morin and Matt Cross consider heavy sled sprinting as strength training, not speed training. To only train with heavy resisted runs is like only squatting heavy and expecting to jump higher without ever jumping.

There appear to be two broad strategies to training for power: increase the magnitude of force and/or increase the rate at which it is applied. When examining long-term training structure, both variables should always be present in the mind of a coach. It may not matter how quickly force can be applied if there isn’t much force to begin with. It has also been accepted that increases in the magnitude of force may result in a shift of the force-velocity relationship such that force of muscle contraction will be greater at any given velocity of muscle shortening.⁵

However, we must keep in mind that increases in force without specific context cannot guarantee any improvement in performance.⁶ While a barbell squat may start to lose its positive adaptation effects on sprint performance, heavy resisted sprinting may still have a large window of opportunity to improve sprint acceleration through greater specificity and context to the sprinting motion. Diving in further, the context of resisted sprint training may determine which phase of sprinting we are ultimately developing.

Increases in force without specific context cannot guarantee any improvement in performance. Share on X

The use of heavy resisted loads in sprinting may specifically target the sprint start and early acceleration (force at low velocities), but may not be as potent for targeting the later phases of sprint acceleration (force at high velocities) or maximum velocity. In developing maximum velocity, you can logically assume that you should not use resistance and all exercises aimed at improving this phase should be unloaded or even assisted. The following table briefly lays out potential options for when to use resisted loads and when not to:

For help using the table above, I strongly suggest reading George Petrakos’ articles on sled sprinting guidelines: “Resisted Sled Sprint Training – Part 1 – Methods of Sled Load Prescription” and “Programming for Resisted Sled Sprint Training.” Also read the overspeed sprint training articles by Carl Valle: found “Hacking the Brain with Assisted Speed Training,” “The Science of Assisted Speed in Sport,” and “Overspeed—4 Ways to Overclock Your Nervous System.”

Video 2. Football players running unloaded and loaded sprints. The use of heavy resisted loads in sprinting may specifically target the sprint start and early acceleration (force at low velocities), but may not be as potent for targeting the later phases of sprint acceleration (force at high velocities) or maximum velocity.

Exploring the Entire Force-Velocity Spectrum

Ultimately, improving power output in sprinting comes down to improving force, velocity, or both. We may expect exercises like heavy resisted sprinting to improve the magnitude of force in the sprinting motion, but we certainly can’t expect it to improve the velocity of muscle contraction. While heavy resisted sprinting may improve the ability to apply greater force with each step, it is safe to assume it will not help an athlete contract his/her muscles faster.

The coach determines which part of the force-velocity relationship is essential for each athlete. Share on X

Training to improve velocity with drills much closer to maximum sprinting velocity (or, in the case of assisted training, surpassing maximum sprinting velocity) may be necessary if an athlete is unable to apply force in a rapid manner. It is the responsibility of the coach to determine which parts of the force-velocity relationship are important for a given athlete at variable times throughout the training year. I encourage you to look to the work of Carmelo Bosco, JB Morin, and Pierre Samozino, and their references, to learn more about force-velocity profiling to help guide the programming process in favor of enhanced power performance.

As it relates to training American football players, sprinting distances are significantly shorter than those found in track and field. If we exclude the over-reliance on the 40-yard dash combine test, many players literally make their money on how well they can burst within 10-30 yards. Big plays are relatively rare, especially at the professional level. Additionally, football is a collision sport requiring players to collide with opponents of all different sizes. Consequently, horizontal force and maximum power are vital attributes for all positions, and force becomes even more important the closer the player lines up to the ball (e.g., offensive and defensive linemen).

Training with the use of heavy resisted sprints may have a desired adaptive influence on motor performance for football players, but it is certainly not the be-all and end-all! While certain individuals need to develop specific areas depending on their current physical preparation or their positional requirements, athletes must do themselves a favor and explore the entire force-velocity spectrum if they want to truly maximize their power potential.

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References

1. Cross, M. R., Brughelli, M., Samozino, P., Brown, S. R., & Morin, J. B. (2017). Optimal loading for maximising power during sled-resisted sprinting. International Journal of Sports Physiology and Performance, 1-25.
2. Smith, J. (2014). Applied Sprint Training.
3. Berry, N. (2013). Usain Bolt: World’s Fastest Man. Datagenetics.
4. Magness, S. (2014). The Science of Running. Origin Press.
5. Cormie, P., McGuigan, M. R., & Newton, R. U. (2010). Influence of Strength on the Magnitude & Mechanisms of Adaptation to Power Training. Medicine & Science in Sports & Exercise, 42(8), 1566-1581.
6. Harris, N., Cronin, J., & Keogh, J. (2007). Contraction force specificity and its relationship to functional performance. Journal of Sports Sciences, 25(2), 201-212.