This article is the second part of a mini-series on resisted sled sprint (RSS) training. Please read Part 1 first. This article will not deliver the ’best resisted sprint sessions for your athlete’, or ‘how to periodize your sprint program’. Instead, the article provides the basis for you to construct resisted sprint sessions based on the requirements of your athlete.
A Requirement for RSS Training?
A sprinting performance model contains a myriad of factors. However, we can generalize physical factors into two broad categories:
- Physical output
- Efficiency of physical output
Increases in physical output for improvements in sprint performance can be achieved through both ‘non-specific’ [1, 2] and ‘specific’ methods [2, 3]. Non-specific methods, such as general maximum strength and power training, may provide an efficient transfer to sprint performance for less-trained individuals. Less-trained individuals may require a foundation of general muscle force and power production that is best acquired by non-specific means. Non-specific means are also vital for improvements in lean muscle mass, training resilience and injury prevention. Specific means, such as sprinting, will likely have the greatest impact on the sprint times of well-trained athletes .
Improvements in the efficiency of physical output must be obtained by specific methods. Application of ground reaction force, rather than the magnitude of ground reaction force production, is a significant determinant of sprint performance [5-8]. In a mix of top-class (World or European medallists) and national level male sprinters, acceleration and maximal velocity performance were strongly related to horizontal force and the angle of force application . Performance was not related to total nor vertical force, suggesting that maximal and vertical force production are key determinants of sprint performance in high-level sprinters.
Conversely, in physical education students, the vertical force at maximal velocity is a determinant of maximal velocity during a treadmill sprint . Furthermore, many will quote Weyand et. al.  regarding the relationship between total ground reaction force and sprint performance. In this study, the fastest athlete produced 1.26 x the force of the slowest athlete, with total force predicting 39% of the variance in maximal velocity on a treadmill . However, this study used male and female participants of whom produced maximal velocities of 6.2 – 11.1 m/s during a treadmill sprint. The large range in participant ability questions the validity of the argument that maximum sprint velocity is significantly related to the production of large ground reaction force. However, both studies demonstrate there is a certain level of force production, required for improved sprint performance, but it does not provide evidence that total force differentiates sprint performance between high or elite level athletes [5-7]. Although every athlete has individual requirements, traditional strength training for general or vertical force production has a significant role in speed development in untrained, novice or slower athletes. This is a general comment as each individual has their own requirements for improved sprint performance.
To continually chase vertical gains beyond a certain threshold with high-level athletes may provide a polish to the gym records board, but with little positive effect on the stopwatch.
Horizontal-based exercises provide a mode of resistance training that can develop both sprint specific force production and application. Resisted sled sprint (RSS) training emphasises the skill of sprinting, movement-specificity, horizontal force production and application. RSS training can be accurately manipulated by changes in intensity, volume and concurrent exercise selection. Therefore, there is a real opportunity to periodize and program RSS training with the same level of detail and accuracy that we commit to squat, deadlift, jump squat and Olympic lift variations. Sled load can be manipulated to influence horizontal force production and application, whilst sprint distance and number of repetitions will affect the ‘practice’ time of the sprinting skill. Simply, RSS training can be classed as both a skill and strengthening exercise, increasing the level of transfer efficiency to sprint performance from traditional strength and power training.
Physical output, Efficiency of Physical Output and RSS Training
Many RSS studies prescribe load as a % of body mass (%BM). However, I will attempt to interpret these data to provide RSS training recommendations for volume, intensity and concurrent training.
Figure 1 provides a general overview of the potential adaptations to RSS training. As always, general findings should be applied with caution – know your athlete, know what they have and what they require. Decide upon an adaptation and chase it.
A load of 10%BM does not provide a stimulus for enhanced explosiveness in the acceleration phase [10-13]. Horizontal ground reaction force is greater at RSS loads of 20%BM than unresisted sprinting (URS) and 10%BM , while a load of 30%BM provides a greater horizontal impulse than 10%BM . Therefore, we are looking at heavier sled loads for enhancements in physical output.
The efficiency of physical output following RSS training may involve changes in foot-strike position, braking forces, ground contact time and angle of ground reaction force [11, 14-16]. It is hypothesised that RSS training may eventually decrease braking forces (vertical force), providing a foot strike more under the center of gravity and thus increasing the time for propulsive force production [15, 16]. Therefore, RSS training does not cause adaptations for longer ground contact times but teaches the athlete to use more of the ground contact time to create propulsive force. Compared to light sled or URS training, heavy sleds provide the athletes with more practice of horizontal force application . There are two common coach issues with heavy RSS training, and I have attempted to provide a resolve for both of them in Table 1. Heavy RSS loads may also improve sprint specific rate of force development (RFD) . Using heavier RSS loads to improve RFD for sprint performance may be superior to traditional vertical methods (Olympic lift variations, concentric jumps) due to the horizontal application of force in RSS training. The specific intermuscular coordination required for rapid horizontal force production in RSS training may have a greater efficiency of transfer to sprint performance than, say, the mid-thigh clean pull. Further research is required on the relationship between the development of resultant RFD, vertical RFD, horizontal RFD, horizontal force application and sprint performance.
|Heavy sled sprinting will change sprint mechanics and will therefore be detrimental to sprint performance.||From a recent review of 11 studies, not one found conclusive evidence of a reduction in sprint performance following RSS training. In fact, studies using ‘heavy’ or ‘very heavy’ sleds found marked improvements in sprint performance [3, 21, 22]. It is possible that the acute change in sprint mechanics during RSS repetitions provides the overload required for an improvement in long-term sprint mechanics and sprint performance. In the same vein, loaded jump squat and back squat mechanics are different to those of a vertical jump. However, we know that heavy strength and power training improves jump height.|
|Heavy sleds increase contact time and create a ‘slow’ feeling for the athlete.||I agree. Heavy sleds do increase ground contact time, allowing for a greater potential for increased force production and horizontal propulsion [10, 11, 16]. Thankfully, programming for speed is not black and white. We can create sessions where we combine heavier work (heavy sled) and work designed to improve contact time and reactive strength. We can add heavy RSS training into a program founded on URS and plyometric work. Use complexes, contrasts and supersets!|
While RSS training can overload the force component, RSS force production is significantly less than that of unloaded jumping, loaded jumping or heavy back squat exercises . I do not recommend RSS training to improve maximum triple extension force production. RSS training has many uses, but there are more effective tools to improve maximum force production [2, 17]. Regarding the ‘horizontal versus vertical’ argument, one may discuss the use of extremely heavy horizontal exercises (sled push for strength, prowler push) as a replacement of traditional compound lifts. Although training programs are never so black and white, I’d like to see a research group really probe the difference in performance outcomes following either horizontal- or vertical-dominant training programs.
Force-velocity curve and RSS training
The balance between how load influences force and velocity can determine long-term adaptations to RSS training. Figure 2 proposes a force-velocity (FV) curve for resisted and assisted sled sprinting.
I have a problem with FV curves that are built without a ‘specific’ action in mind. The terms ‘strength-speed’ and ‘speed-strength’ are meaningless when used in isolation. ‘Strength-speed’ pertains to: “higher force, lower velocity than X”. ‘Speed-strength’ is the opposite: “lower force, higher velocity than X”. Without X, we have nothing. I believe an FV curve should revolve around the ‘specific’ sporting action one is trying to improve. In this case, our sport-specific action is sprint acceleration.
The proposed force-velocity curve centres on unresisted sprinting. ‘Strength-speed’ and ‘acceleration-speed’ involves an overload of the force component and reduces movement velocity. ‘Speed-strength’ and ‘speed’ work increases the velocity component and does not challenge peak force production. In agreement with previous FreelapUSA articles (The Sled: Resisted Sprint Training Considerations and Resistance Run Training: Thoughts, Observations and Guidelines), to run fast, you must train fast – likely > 90-95% of the best time for a given distance. As aforementioned, I do not believe RSS training with light loads adds a sufficient stimulus above that of URS training alone. Why go to the hassle of adding a sled when a standard URS session will do the trick? Therefore, true sprint speed training takes place below the threshold line. Speed training is not prescribed above the proposed threshold. Above the threshold, we are prescribing skill-practice and strength/ power training. As with the majority of sporting movements, performance can be enhanced by training at varying parts of the curve depending on individual athlete requirements.
Acute Program Variables
I wish to be conservative with recommendations when discussing intensity, volume and rest periods. Unless one has an excellent understanding of the athlete, the concurrent training and program goals – it is difficult to prescribe effective acute variables. Therefore, I have provided a range of options in Figure 3. These options are based on 11 peer-reviewed papers  and three years of UCD High-Performance Gym data.
Long-term improvements in sprint performance following RSS training likely requires >2 sessions per week for > 4 weeks . Acute variable selection for RSS training (Figure 3) differs little from that of traditional power training. Higher intensities require lower volumes and vice versa. An athlete may initially experience neural adaptations such as improvements in trunk lean during URS and a subsequent improvement in the angle of force application during URS – although more research is required to test this hypothesis. Given the high importance of horizontal force application to sprint performance, neural adaptations may be the most favourable benefit of RSS training.
Sprint training adaptations are distance-specific . For example, if sprint acceleration is the goal, I’d recommend working between 10 and 20 m with the appropriate sled load. UCD athletes have shown an ability to maintain 0-20 m sprint acceleration for 5-8 repetitions at 80% maximal resisted sled load (MRSL) and 10-12 repetitions at 30% MRSL. I generally prescribe RSS volumes based on these data as once an athlete begins to decelerate, the movement quality and power output have already declined.
If improvements in sprint speed are the key goal, I recommend never to ignore true speed training i.e. unresisted sprinting. Adaptations are specific. Heavy sled sprints will not make you slower, ignoring true speed training will make you slower! I truly believe that the most efficient transfer of RSS training to URS performance is achieved when both variations are performed within the same session. RSS efforts allow the athlete to understand exactly what trunk lean and horizontal application can feel like. Successive URS efforts allow the athlete to (a) attempt to physically transfer the feeling of RSS trunk lean to URS and (b) run fast and feel fast. RSS training may a potentiating effect on URS performance, but this is still in debate [18-20]
Your coaching eye is vital to RSS training. Like any exercise, a complete breakdown in RSS form and movement quality is unlikely to provide an effective motor pattern or speed/ power stimulus. Adjust your acute variables accordingly and don’t be afraid to swerve away from the planned session. Be a coach.
RSS training provides the opportunity to continue emphasising your usual technical sprint cues. Whether you prefer internal or external cues, they can be directly applied to RSS training. As heavy RSS efforts are slower than traditional sprinting, athletes may find the ‘slow-motion’ of RSS useful to practice a specific cue. Cueing an athlete to “explode” from the start may be useful, especially given the extra effort required for initial acceleration at heavy RSS loads. This type of cue during heavy RSS efforts may also help increase long-term peak total and horizontal RFD and peak power. If the athlete understands RSS training is about trunk lean or horizontal force application, the athlete may try to exaggerate their forward lean during the sprint. This often leads to miss-stepping and a stutter-like sprint. I often ask these athletes to “allow the lean”, rather than “force the lean”. Finally, it goes without saying that athletes should be encouraged to provide maximum effort to RSS training.
- Resisted sled sprint training is a ‘specific’ method for improvements in sprint performance.
- Depending on sled load, long-term adaptations to RSS training range from decreased braking forces, an increased trunk angle, greater horizontal application of force and improvements in the rate of force development. These adaptations combine for greater sprint speed.
- Although RSS training is effective for improvements in sprint performance, it is just one very small tool in the toolbox. General or ‘non-specific’ exercises, lifts for maximum vertical force/ power and true speed training are vital elements of an athlete’s physical training program.
- If the goal is to improve sprint performance, do not forget to program for true speed work i.e. unresisted sprinting.
- When planning RSS sessions, coaches must manipulate load, repetition distance, session distance, cues and concurrent training to achieve eventually the desired adaptations.
- Unresisted sprint coaching cues can be used directly with RSS efforts.
All papers mentioned in this article can be found here.
Thank you to Dr Eamonn Flanagan and Dr Brendan Egan for providing feedback for this article. A huge thank you to Maria Monahan of whom continually researches, applies and challenges RSS work at UCD High Performance.
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