Speed and strength are physical qualities every athlete needs. Traditionally, these qualities are improved through resistance training. Multi joint movements like squats, lunges, deadlifts, and cleans are a few examples of movements that can be used to progressively overload the body and stimulate greater speed and strength adaptation. Similar to resistance training, sprinting and jumping need some sort of overload stimulus to elicit a greater adaptation. An easy and effective method to achieve this is by doing resisted sled sprints.
In a nutshell, resisted sled sprints are exactly how they sound. A maximal effort sprint with an external load in the form of a weighted sled. The sled makes a mechanical overload possible while the athlete is able to simulate sprinting. This method targets many of the physical determinants that affect sprint performance (i.e. force production, sprint specific musculature, stride length and frequency, kinematics and neurological activation). The resisted sled sprints consist of two phases: acceleration and maximal velocity. The acceleration phase on average takes place from 0-30 meters depending on the athlete's ability and is characterized by horizontal force production, causing an increase in speed until maximal velocity is reached. Maximal velocity phase refers to the highest possible velocity that an athlete reaches. This phase can only be maintained for a brief period until some deceleration begin to occur and it characterized by vertical force production as opposed to horizontal.
Below are the key areas Resisted Sled Sprinting Improves:
Muscle Size and Strength
Resisted sled sprinting has a high degree of transferability to sprinting. Due to this dynamic correspondence, much of the same musculature is targeted. Hip flexors and extensors (i.e. iliopsoas, pectineus, rectus femoris and glutes and hamstrings) and knee flexors and extensors (quadriceps and hamstrings) are all targeted to increase in size and strength. A larger and stronger muscle is able to produce a greater force resulting in a more powerful movement. This increase will allow the athlete to propel themselves further each step, thus in turn increasing their stride length.
Resisted sled sprinting can also improve neurological aspects. It has been shown to have an effect on decreasing inhibition throughout the nervous system. This decrease allows a faster transmission of impulses to muscles, which helps increase firing rates and rate coding. This can directly relate to how fast an athlete is able to create stride frequency. Resisted sleds have also been shown to have a potentiation effect going from an overload to unresisted. Though exact potentiation mechanisms are still unknown, but the benefits are likely caused by an increase in motor unit recruitment and an increase transduction site sensitivity.
Kinematics have reportedly been shown to be altered while performing resisted sled sprinting. Qualities affected were torso angle and hip/knee angles. Torso angle was shown to increase along with hip flexion angles. These kinematic differences can benefit sprint acceleration, specifically by the torso lean and knee drive, which will help transmit force horizontally. In theory, the changes in kinematics can transfer over to unresisted sprinting, which can help increase sprint performance and speed.
All in all, resisted sled sprinting can produce many positive adaptations in the areas of kinematics, nuerological activity and muscle size/strength and can be beneficial for increasing sprint performance in athletes.