Are Resisted Sled Sprints Effective?

Sled sprints are a great training tool to help with acceleration. But it is often misunderstood and implemented incorrectly. We often see developing athletes towing a sled that makes the athlete look like they are moving through mud – slow!! And if trying to improve speed, moving slow doesn’t mean moving fast!

We know speed is king when it comes to athletic performance. Whether it’s soccer or track and field, getting to the ball or to the finish line first, it’s a matter of being faster than your competition. But what is speed? Our previous article, Sprinting is Art, provides a more in depth anatomy of a sprint.  But essentially, it’s the rate at which an athlete covers distance. Whether it’s the 40yd dash or the 100m dash, how fast the athlete covers any particular distance, depends on executing the different sprint phases just right – the start with acceleration, max speed and deceleration. With a good acceleration phase, it can mean the difference between running the fastest 40yard dash at the 2020 Scouting Combine with a 4.27s 40 yard dash and the 18^th ‘slowest’ 40yard dash with a time of 4.45s. Therefore, a good start/acceleration phase is important. This is why coaches spend countless training sessions trying to improve every phase of the sprint, in particular the start. However, it isn’t just the track or football athletes that need to perfect their sprinting phases. Soccer, baseball, volleyball, basketball – all these team sports require an athlete to try to get from the starting point to the next point faster than the competition.

Acceleration Phase of a Sprint

Acceleration is the rate of change of velocity. And when talking about velocity, it’s the rate of change of position in a given direction. What all this is saying is that when accelerating, a person is making every effort to move away from the starting point as quickly as possible. Although speed and acceleration are oftentimes used interchangeably, they are not the same thing. As we stated before, speed is the rate at which an object covers a certain distance – how fast someone is running.

Why are these distinctions important? When attempting to improve any portion of a sprint, knowing what every phase of the sprint entails – from the acceleration and top end speed phase – helps identify the appropriate training protocols for each phase. Each phase demands and requires different training to make improvements along the sprinting continuum.

Improving Acceleration

Did you know that a soccer athlete can do on average 150 accelerations in a game? But it’s a good thing that those are only 2-3 second burst of energy because accelerating takes a lot of power and strength. Accelerations are a lot of work – it taxes the body a lot! When you start your sprint or take off, during the acceleration phase, you are overcoming inertia – trying to get your body to move forward and fast. Pushing your body forward fast requires a lot of strength and power. Positioning your body in a horizontal position can help overcome inertia, but the angle has to be just right. Therefore, the stronger and more efficient you are with your mechanics, the better your acceleration phase will be.

A common and effective training tool to help improve the acceleration phase is resisted sled sprints. Resisted sled sprints are typically performed using a vest or a belt around the waist. But executing the proper sled sprint is more than just adding weight to the sled and trying to pull it forward. With the appropriate weight and implementation, resisted sled sprints enforces a chest lean angle necessary to efficiently overcome inertia. With this chest lean angle, it cues the legs to apply large amounts of ground force to propel the body forward, explosively and quickly. But having more weight on a sled isn’t necessarily better when trying to improve acceleration. In fact, it can actually attenuate any speed improvements and change running mechanics. Too much of a chest lean angle beyond the acceleration phase can negatively impact stride length and stride frequency as well as power output. As we know from our previous article, the longer the stride length and  higher stride frequency, the faster the athlete can sprint. Trying to tow too much weight for too long has the opposite effect, decreases stride length and frequency and changes overall mechanics trying to pull the sled by all means necessary.

Loading the Sled

How much weight is ideal for resisted sled sprints? Research has identified that the best amount of weight to provide any significant improvements in acceleration is between 10-43% of body mass of an athlete. This is dependent on the athlete’s experience and whether they have been strength training, sprinters or team sport athletes. For undeveloped athletes, having a sled weight at 10% of body mass showed an improvement but using unresisted sprint training is best to improve acceleration. For developed athletes, 10% is too light. In fact, research indicated that a load less than 20% of body mass didn’t have any significant benefit. Regardless of the amount of load, it should not change running mechanics and it should not decrease an athlete’s speed by more than 10%. This means you would need to have accurate times for 10m to 30m.

It’s always impressive seeing strong men and women pulling cars or heavy sleds down the field. While this is quite a feat, when the goal is to improve accelerations, it may not be the best strategy. Sled sprints are great for improving acceleration, but more weight is definitely is not better. As research has indicated, to ensure resisted sled sprints are implemented properly to make improvements in the acceleration phase, there are a couple of guidelines to follow:

1. Make sure the load isn’t decreasing speed by more than 10%; and
2. The load is enough to enable the athlete to apply greater force with every stride, without changing their running mechanics.

A program that achieves these elements in addition to a comprehensive stregth program will inevitably lead to improvements in acceleration.