“High-resistance sprint training will increase injury risk”: another training myth?

This post will address misconceptions about high-resistance sprint training (HRST) in the form of heavy sleds or high-resistance set with robotic devices such as the 1080Sprint, i.e. loads that slow down the athletes by 50% of their maximal running speed, or more. To be clear, I do not think this type of training stimulus is the magic stick: I think it is key in some contexts to develop some features of sprint acceleration performance (which is also supported by research results). I also think it is not recommended in other contexts, and so as always in training, it is not YES or NO, it is “IT DEPENDS”.

What’s the problem?

I have been training as an athlete, learning athletics as a coach, and studying it as a researcher. Surprisingly, and contrary to gym-based heavy (sometimes super heavy) resistance work, HRST has never been a popular training stimulus, at least within my training and coaching environment. Over the last 5 years, I basically discovered that it was a bit like the dish kids “hate” but have never really tasted. For example, I was one day teaching about our research to elite sprint-hurdles coaches and asked the very simple “skin in the game” question: “raise your hand if you have already (yourself, or your athletes) performed a session of HRST”. Simple question, about 20 coaches in the room, two hands raised, including mine. However, many of them had a clear and assertive view on the fact that “HRST was not recommended because it would increase injury risk in athletes”. Never used, but convinced about risks. Another part of the problem is that this statement is also echoed by some sport science researchers, based on very far-fetched, and unsupported arguments, as we will see. Funny enough, and paradoxically, some of the same coaches or scientists who recommend against HRST due to injury risk and lack of sprint-specific feature of this stimulus, advocate using heavy gym-based work (squats variations, press, etc…) to develop force capability. I find this illogical since these exercises are even less sprint-specific, and at least equally “risky”, in my opinion.

This whole context, and lack of published data observed in our seminal review of litterature on the topic pushed my group and I to run some studies and know more. We also started reaching out to high-level practitioners over the world who have been using HRST for long, and may provide significant and insightful practice-based evidence, where research evidence is lacking. 

What does academic research say?

Nothing. Peer-reviewed research does not say it will increase the injury risk, it does not say it will decrease it, and it does not say injury risk is unchanged. Nothing. There has not been any publication, to my knowledge, supporting the statement that HRST is associated with a higher risk of injury, all other things being equal. In addition, some data under review show that the acute changes in running form that occur while performing HRS (which have never been shown to correlate with higher injury risk) clearly do not transfer to unloaded sprinting in the long term, in the professional soccer players we studied. In other terms, you don’t sprint with an altered running pattern after using HRST as a training stimulus. However, consistent results show that you may very likely improve your acceleration key mechanical outputs, and in particular your horizontal force output, via a more efficient (i.e. forward-oriented) force transmission onto the ground, and the associated mechanical power. This might be very useful in acceleration-based sports. I will not address arguments related to EMG activity in acute HRS studies, since (i) EMG activity is a questionable indicator of muscle force (see here), which makes injury risk extrapolations even more speculative and (ii) acute studies use comparisons without control for the effect of running speed, so no surprise EMG activity is different under heavy resistance, since running speed is markedly lower. 

Absence of evidence is not evidence of absence, but one thing that people need to keep in mind (especially “evidence-based” absolutists) is that other sources of evidence should be considered, not only academic, peer-reviewed, ivory-tower research. Many recent examples show that it is a reference source of information, but as any other human activity, it is subject to bias, limitations, politics and manipulation. As researcher and elite physical coach Alberto Mendez-Villanueva discussed in a recent Football Science Institute online Congress, an efficient, comprehensive “evidence-based approach” should not only be limited to “academic research evidence”, but also include practitioners expertise and athlete’s feedback and expertise. 

What do experienced HRST users say?

Lack of “skin in the game” is a major issue in the field of sport sciences, like in many other scientific fields with clinical applications. So, to have a more balanced view of things, I’ve tried to gather information from people actually using HRST in real life sports performance scenarios. They have collectively much more experience and long-time retrospective view on the topic than any published researcher myself included, so this is, in my opinion, very important information. I thank all the coaches who answered my Twitter poll and individual request for comments.

Twitter Poll

Although such a poll may easily be manipulated, and is biased by the fact that it was mainly viewed by my personal followers, it is interesting to see that among the 130 responses sent from (let’s admit) experienced HRST users, only 19% reported increased soft-tissue injury risk they attributed to HRST. 37% answered the risk was likely unchanged, and interestingly, 45% reported a likely protective effect of HRST. This poll should be taken for what it is: an anonymous online survey (10k views, 130 votes) but the outcome is interesting: just as ANY other intense training method (gym-based heavy work, high-volume endurance running, high-intensity interval training) or ANY sport performed with wrong dosing-programing, it might be associated with injury risk. I interpret this “20% negative – 37% neutral – 45% positive” result as indicative of any type of training stimulus: unwanted side effects are possible. But in my opinion, they are not due to the stimulus itself, but to the overall programming, periodization, progressivity of use, in short, to the “deciders”. It is a tool and tools don’t cause issues, users do. One interesting result (that will be corroborated by some practitioners comments below) was that the majority of votes confirmed a likely positive, “protective” side effect of HRST.

Our own experience

So far, my research group has completed and published three experimental studies in real-life training scenarios involving HRST. Because these studies were performed within the training scheme of competitive (amateur and professional) soccer and rugby teams, we were able to track the performance consequences of HRST, but also, potential injuries in the following weeks-months. This was possible thanks to the close collaboration with staffs, that went beyond “just an experiment”. Before detailing each study and the associated anecdotal evidence, it is important to mention that systematically, the players involved were taught and progressively introduced to HRST over at least 6 to 8 sessions (sometimes more) of increasing load and volume. Their feedback was carefully checked and the familiarization to the HRST stimulus was part of the training plan. This is important since yes, I agree, HRST might be harmful in athletes who transition abruptly from never-did-that to two sessions a week with heavy resistances. Just like for ANY other type of training stimulus. A 10km-a-week jogger shifting directly to 50km-a-week runs will likely get injured. Should we recommend against running? No, wrong programming is the cause of injury, not running.

The very first experimental study we ran used 80% body mass sled loads in amateur soccer players (please see this post for my points about the fact that using %BM to set the HRST load is misleading and should be abandoned as a standard). The training program was integrated to their typical training week (2 training sessions) and in parallel to the improvements of maximal force, power, and “ratio of force” during the early acceleration, no abnormal hamstring or other types of injuries were reported during the rest of the season.

The second experimental study was made in competitive amateur soccer and rugby, in-season, and the feedback from players and coaches (physical and technical staff) was positive on the overall sprint performance side, but also on the injury side. The rugby S&C coach reported to me a total (>30 players) one or two injuries in three seasons that he thought might have resulted from the use of HRST. However, he clearly admitted that it was likely due to his own programming and dosing choices over the season. Since the first and second study (he was the same S&C coach for the amateur soccer and then rugby team), he kept on using HRST as a regular stimulus (yet with lower weekly doses than during the specific studies protocol). This time, the load was individualized and used to target a 50% decrease in maximal running speed, instead of an absolute mass in kg or percent body mass. Within the soccer team involved, the physical coach maintained HRST due to the demand of the players who felt this was positive for them. He also observed something that we are currently investigating: accelerating heavy loads is an interesting stimulus for the “ankle strength”, stiffness, and foot strength. It is also a unique way to show “technical and energy leaks” as detailed in this video. Some step mechanics can only be observed under high loads…

I thank S&C coaches and former Master students Satya Veysseron and Mehdi Chedati for their collaboration to these studies and this post. 

The recent works of Johan Lahti include two more experimental studies, this time with highly-trained professional rugby and soccer players. In the first study (pre-print here), we observed improvements in early acceleration mechanical outputs with no associated changes in early acceleration or top speed running pattern (Figure above). Since this study was a part of a larger collaboration with these professional clubs, we could keep track of all soft-tissue injuries and especially hamstring strains. Within the team that did the pre-season HRST protocol, only one hamstring strain was observed over the rest of the season (19 players monitored). In the control team that played within the same championship, 5 hamstring injuries were observed over the same season. The 1 athlete that got injured from the intervention team happened 16 days after the testing and it was to the semimembranosus in an overstretch COD situation. In the control team, 5 injuries all happened within 3 months of testing.

Of course, this is not a solid comparison, but my point here is to show that the number of injuries reported after HRST was not greater, it was in this very small sample case example, in fact smaller. To emphasize this point, we had the unique opportunity to collect injury data from a total of 9 teams within this professional league (as a part of Johan Lahti’s ongoing Ph.D. project, see video here). A total of 39 hamstring strain injuries were reported during the 2019 season (including re-injuries). Two teams managed impressively to only have one hamstring strain injury during the entire season, one of which was the HRST intervention team. The other team completed systematic acceleration training three times per week, including heavy and light RST. All teams within this League performed Nordic hamstring exercises on a regular basis, except two that used sliders exercises.

The other experimental study involving HRST was published (read here) a few weeks ago, and performed within the professional rugby club of FC Grenoble, France, during their Top14 elite season. The results confirmed the improvements in early acceleration mechanical outputs (see the paper for detailed discussion, especially about the highly individual response pattern). The head of S&C Patrick Chassaing (PhD student under my supervision) and the S&C coach in charge of speed development Ben Simond-Cote kindly sent me their comments on the injuries that occurred after the protocol. They open a list of stories that elite coaches agreed to share with us. I selected them based on their extensive experience with HRST in high-level athletes from various sports, and hope you will find their input insightful.

Benjamin Simond-Cote and Patrick Chassaing, FC Grenoble Rugby

“During the 2018-2019, in the elite professional league, we used 3-week blocks with contrasted work: HRST and blocks of unloaded sprints (no overspeed). During the 2019-2020 season, we used contrasted HRST and overspeed work every week. Comparing the two seasons on the same period, we observed a 20% decrease in muscle injuries (16 versus 11 injuries on a 30 weeks basis).“ 

Scott Salwasser, S&C coach, South Carolina Football

“While many methods of speed development have their value, in regard to risk, in my personal experience with my athletes, resisted sprint training has proved to be even safer than non-resisted in terms of soft tissue injuries. In fact, so much so that after an extended break in training, resisted sprinting is my go-to modality for re-introducing speed development protocols. The reason for this is that it encourages correct acceleration mechanics and reduces contractile velocity to a safe range while still promoting specific force production and a high level of effort. I have used resisted sprinting at multiple locations in the training calendar and at multiple loads, ranging from 50% speed decrement (heavy) to 10% speed decrement (light) and anecdotally speaking, have experienced an environment with reduced soft tissue injuries when compared to non-resisted maximal speed or particularly, over speed methodologies.”

Read a detailed article by Scott here, and listen to his podcast here.

Carlos Balsalobre-Fernandes, S&C coach, app developper and researcher, Autonomous University Madrid

“We started playing with sleds in the 2015-2016 season. Our middle- and long-distance runners never did sled pushing before (as a matter of fact, they didn’t do much strength training either), and that season we used around 30-50%BW loads once a week. We have included heavy strength (80%1RM squat/deadlifts and things like that) and heavy/very heavy sleds ever since and the feelings have been great. We never had an injury derived from that heavy sled training and, as a matter of fact, last season we used the highest load since we started using sleds (90%BW) until July. 

That season, while training at 70-90%BW once a week, Fernando Carro broke the Spanish National 3000m steeplechase with 8:05.69 and performed really well in the World Championships in Doha. Adrian Ben, another athlete from our team, ended 6th in the 800m at the World Champs, being the Spaniard with the best World ranking on 800m ever. When analyzing these great performances, the main coach of the team (Arturo Martin) told us that he thought that the “continuity” (i.e., being able to train without periods of rest due to injuries) was the key. Of course, this is not scientific evidence, but we have been using heavy sleds for 5 years now, with great performances, low injuries and great sensations perceived by the athletes, and this is very important IMO. They just love to pull heavy sh*t.”

Follow Carlos here.

Cameron Josse, Athletic performance coach, Indiana Football

“In my experience, the use of HRST can be a potent stimulus to help develop horizontal force capabilities associated with acceleration performance. I have measured and seen first-hand how sprint kinetics can be improved from this type of training, specifically the magnitude of horizontal force capability (N/kg), the ratio of force application (RF), and the minimization of the decrease in the horizontal ratio of force as speed increases (DRF). In addition, I have also measured and seen how sprint times can be improved as a result of these adaptations, sometimes substantially.

While performance improvements are great in their own right, I am also cognizant in my attempts to reduce the risk-to-reward ratio of incorporating certain activities in my training programs. Along these lines, the use of HRST must be understood in context. It is, after all, a very specialized form of strength training for the horizontal plane. Therefore, I treat it no differently than I would a loaded activity in the weight room. I would not take a novice athlete and immediately have him/her perform a barbell back squat with 150kg of load. First, I would develop the skill of squatting with bodyweight and light loads before proceeding with the principle of progressive overload. Further, I would not load the system in ways that would drastically violate biomechanical laws of safe movement. I apply the same logic to prescribing resisted sprint training. The resisted loads must be introduced in a progressive manner to help the athlete become gradually familiarized to sprinting against heavier loads. If this is not done, then inherent risks become evident. So, sound and logical training progressions can easily avoid these risks.

Sprinting is a complex neural activity requiring high levels of neuromuscular coordination. In this way, sprinting differs tremendously from basic barbell lifting. Sprinting is a skill that must be practiced and developed through routine technical training in order for an athlete to perform competently and safely. Resisted sprint training should never exist in the absence of unloaded technical sprint training. If an athlete has only performed resisted sprinting and then has to perform an unloaded high-speed effort in a game or practice, the risks of potential injury or performance disruption become obvious. All in all, when following basic principles of familiarization and progressive overload, I have only seen positive training effects from incorporating heavy resisted sprinting.”

Read some very interesting articles by Cameron on HRST here and on running pattern here.

Pedro Jimenez-Reyes, athletics coach and researcher, University Rey Juan Carlos, Madrid

“Here I write about athletes with whom I have worked with heavy sleds and some of their results and sport level.

Natalia Romero – Spanish Champion 800m (no injury in hamstrings from the time she started with this type of training)

Sergio López – Spanish Champion 60m (no injury in hamstrings from the time he started with this type of training)

Sprint Group in Barcelona and Madrid – many of them are finalists and medalists in Spanish Championships (I have worked as strength consultant with them and injuries in hamstrings reduced considerably from they started with this training) (before this training, usually they had many injuries)

Spanish R7 Team – I also worked as strength consultant and they reduced considerably hamstrings injuries. 

Madrid Hockey Team (champions for first league) – I also worked as strength consultant and again they reduced injuries and we only registered one in the season. 

Jaen Futsal Team (champions of Spanish Cup and competing at first league) – I also worked as strength consultant and they did not registered injuries.

Follow Pedro here.

Carlo Buzzichelli, professional coach, Director of ISCI

I began using the heavy sled in my periodization of strength for sprinters and jumpers in 2014. The first athlete I used it with was Paolo Serranti, an Italian Master sprinter (M35). He hired me to prepare the 2015 season. I started right away by choosing the load according to the time increment over the acceleration training distance of 30m. My definition of the heavy sled is a “special strength training mean, that teaches the angles of application of horizontal forces during the acceleration”. After one preparation, Paolo went from not entering the final, to win the 2015 Italian Indoor Championship M35, with a .34” PB over 60m. Of course, I changed his training pretty radically compared to his previous coach, also introducing other new training means in his program, different overall volume and mean training intensity, but the improvement is consistent with the experience of Scott Salwasser with his players. In 2017 I introduced the heavy sled to the jump coaches of the Cuban T&F National team. To make the story short, all the Cuban jumpers that had used the heavy sled periodization PBed within one year, including the 2018 long jump World Indoor Champion Juan Miguel Echevarria, and Maykel Massò, 4^that the 2017 World Championship by 1cm at 18 years of age, who had the fastest take-off velocity in the final. In 2018 I started using it with the Filipino sprinter Kristina Knott, who in December 2019 won the South-East Asia Games in the 200m, setting her PB, the National record, the Games record and the South-East Asia record. On top of that, she ran at PB pace 6 times in three days (collecting two gold medals, and two silver medals) in the 100m, 200m, 4×100 and 4×100 mixed. If anyone would ask me what are the probability of injury running 6 times at PB pace in three days for a sprinter, I would answer “pretty high”, but it did not happen. The last time we used the sled was 10 days from the start of the Games. In the fall 2019 I was also hired by the Italian sprinter Irene Siragusa, Olympic qualifier with the Italian 4×100 relay (NR) and 2014 100m and 200m Italian Champion; this past winter she won the Italian 60m Indoor Championship for the first time and set her PB in the 60m by 0.02”, 0.07” faster than the previous year, which was the standard time to qualify for the 2020 World Indoor Championships, that did not take place because of the Covid situation. Also with her I use the sled periodization, going from heavy to moderately heavy from mesocycle to mesocycle, according to the time increment over 30m. With all these athletes, in all these years, we did not experience any sled related hamstring injury. It does not make much sense to postulate that HRST might favour the incidence of hamstring injuries because a) the velocities that are reached do not stress the knee flexors as much as max speed, and b) during the acceleration phase there is a shared propulsion role between knee extensors, hip extensors and plantar flexors. For instance, more progressive physiotherapists in high level sport know that very short accelerations can be resumed pretty quickly after a grade 1 hamstring strain, because the forces the hamstrings have to withstand in very short sprints are pretty low due to the low velocities that are reached. With a heavy sled those low velocities are maintained for 20 or 30 meters. The same way, we know that the vast majority of hamstring injuries occur at max velocity or near max velocity when the forces the hamstrings have to withstand are much higher compared to the acceleration phase, the propulsion role is almost completely on the hip extensors, and the knee flexors transition from shortening to lengthening to shortening again very quickly. 

Read the famous textbook on training periodization by Carlo here.

Jonas Dodoo, Head coach, Speedworks and consultant to pro football and rugby

I must be honest, I am extremely biased when it comes to resisted sprint training. Over the past 10 years of coaching developmental and elite sprinters, long jumpers and team sports players, I have looked for training systems and exercise progressions to simply address my main training goals. In planning I aim to create phase potentiation and essentially prepare my athletes for the peaks of the season in a seamless manner. The puzzle that we are trying to solve is always how to best blend teaching of our key skills with the training or physical preparation for these key skills. In my naivety I have created paralysis through analysis, over-focused on intrinsic feedback, made athletes strong in the gym but not fast on the field, made athletes aerobically fit but not fit for purpose and essentially built work capacity of things and then “hoped” they would transfer to performance and health. 

The past seven years I have been a big proponent of using resistance sprints of all types of loads. I have never witnessed an athlete get hurt using resistances sprinting, in fact I believe it’s a great tool for building physical robustness as well as technical efficiency.  Trunk discipline and shin discipline during initial acceleration is as much a skill as it is underpinned by mechanical properties. Heavy and moderately heavy resistance sprinting can be a great exercise for all, but is just one tool in the coaches tool box. The discussion should not be on its relevance as the evidence is clear, at least to me. Instead I am more interested about where and when it goes in the program how much to do and best progressions for transfer to the competitive event. Further to maximize the learning effect I am interested in what type of equipment suits each phase/goal i.e prowler, exergenie, sled, hip harness, shoulder harness etc. Injuries are always multifactorial and in my experience usually due to programming error. If people are getting hurt using this tool, blame the marksmen not the riffle. 

Read a key article on sprinting by Jonas here.

Finally, you may also read the detailed, 3-part discussion of how ALTIS coaches used HRST, here.

Conclusion: Dosis sola facit venenum(the dose makes the poison)

Overall, the content of this post suggests that at least, HRST is not the devil, and at best, it is a useful method to improve some parts of the force-velocity spectrum, and other key mechanical components of sprint performance, if the context and player individual profile indicate it is necessary. Also, some anecdotal evidence tends to support the fact that if done properly, it may help building more robust athletes to face the high-constraint sprint actions in sports like athletics, soccer, American football or rugby. 

The major mistake coaches and scientists with no practical experience make is that it is not the HRST itself that is “dangerous”, but people who use it incorrectly. Like for any other training stimulus, doing too much, without familiarization progressivity and well-designed periodization, may increase injury risk. If heavy sleds are inherently dangerous, then any type of gym work and heavy leg press is, plyometrics are, high-intensity interval training is, altitude training is, and drinking too much water is. After all, if you drink five liters of water in one go, you’ll have issues. Should we recommend not drinking water?

Resisted sprint training in the form of pulling or pushing heavy sleds is in fact very old, despite the first international paper about a controlled training study was published recently. I do not have any personal bias in favor of HRST, but I’m observing facts and listening to real-life, long-time users with extensive experience and skin in the game. I’m afraid most coaches and researchers who advocate against using HRST because of injury risk have a much less objective and documented approach. 

When I was myself a middle-distance runner 20 years ago, strength training was almost forbidden because it was thought to “wreck athletes’ running pattern” and “cause tendonitis and other injuries”. Today we know it was a training myth and meta-analyses show that strength training is a key variable for endurance running performance. Practice confirmed these studies, with many top-level endurance athletes adding strength work to their training routine. For example, Elite marathon runners like Paula Radcliffe, Mo Farah or Eliud Kipchoge reported they added strength and gym work to their training plan, which was very likely one piece of their outstanding performance puzzle. Same goes for strength training for kids, and many other “training myths” shown wrong by evidence: academic-research and experienced practitioners’ evidence. At some point in time, they were “new ideas” and then followed the classical path of new ideas synthesized by Schopenhauer: “Every original idea is first ridiculded, then vigorously attacked, and finally taken for granted”.