By Carl Valle
The Dynamic Strength Index (DSI), a measurement that compares maximal force with ballistic force, is one of the most underrated metrics in strength and conditioning. It’s a straightforward measurement that forces coaches to ask how well their athletes apply their strength in the weight room to activities that matter, such as jumping.
While other activities like sprinting and cutting have yet to show as clear a relationship, coaches still need to respect the measurement. It provides a direct and simple way to design training based on the testing outcomes. Coaches want to know if the weight room makes a difference and, more specifically, if time with heavy barbells transfers efficiently to faster sporting action. In this article, we’ll cover why the DSI is a great option, and how to use it to make athletes better.
Why the Dynamic Strength Index is Important
The ability to use maximal strength efficiently is the heart of nearly every training program in sport–success requires the ability to apply force. Sport science, a vital resource for coaches, is part of the process of seeing how methods work as well as the value of interventions like training programs and exercises. DSI is a composite metric showing the connection, or lack of a relationship, between an athlete’s absolute strength to a more ballistic action, typically a jump.
Earlier I talked about the Isometric Mid-Thigh Pull (IMTP) as a safe and effective way to capture maximal strength, but other options are good as well. These include isometric tests like quarter squats and deeper position variants along with traditional 1-repetition max tests. In fact, an array of tests usually paints a more complete picture of what’s going on with training. More testing isn’t always an option, however, so coaches are looking for better tests, not necessarily more tests.
A measure that evaluates the absolute strength carryover to higher velocity contractions with similar movements is valuable, especially since most programs include strength training to reduce injuries, increase performance, and extend careers. DSI research spans a few decades with solid science showing that the measurement is worth using. And because most coaches already perform jump and strength tests, the theoretical burden is a non-issue.
The Origin of the Dynamic Strength Index
Although the metric is not new, it became more popular in the 1990s when Vladimir Zatsiorsky outlined its definition and family of measures. But it didn’t take off until ten years later. In his book, Science and Practice of Strength Training, Zatsiorsky introduced the concept of a specific transmission gap of what he called the explosive strength deficit (ESD).
While coaches and other sport scientists recognized the two qualities and their relationship, Zatsiorsky identified the points on superimposed force-time plots and used calculations to explain their interaction. This was still rather abstract, as the relationship between short time frames and maximal strength is more complicated than how much one squats compared to how much force they put into the ground while jumping or running.
Any coach worth their salt will agree that many qualities and factors create success in sport, and it’s up to the support staff to construct the right plan. The ESD was a nice formal, organized step forward in understanding the relationship between strength and the expression of force at higher speeds.
In the following years, the term Dynamic Strength Index, not to be confused with the Reactive Strength Index, became more prevalent in the strength and conditioning community due partly to the rise of isometric pull strength tests and force plates used in the weight room. As technology and science increased in use and practice, coaches started looking at weight training with a sharper view. In the past, strength-to-weight ratios and speed or jump height was a quick and dirty way to get a ballpark idea, but now a tighter estimation is possible.
How to Calculate the Dynamic Strength Index
A true calculation for DSI doesn’t exist; it’s a relationship between two qualities, not two exercises. Because DSI is a ratio between maximal force and a ballistic force score, most coaches use two force plate tests to compare neuromuscular system performances properly.
DSI is not a dirty metric, meaning there’s too much baggage to be valid and reliable. But it also doesn’t fully represent what’s going on with an athlete regarding maximal strength in high-speed activities like jumping and running. To say that peak forces in squat jumps and maximal squats give a perfect summary is a longshot. It’s best to consider the DSI as a rough guideline for starting weight room evaluation.
To compare apples to apples based on current standards, coaches and sport scientists use peak force values from two tests to create a ratio and typically calculate the percentage between ballistic and maximal strength. The current challenge with this calculation is not the math but figuring out the best way to gather information on the two qualities.
The exercises we use to collect the data must be practical and show a strong relationship. Usually max strength has less value for maximal speed than for acceleration. It’s a challenge to compare similar motions or patterns of muscle action, and most coaches and sport scientists default to comparing bilateral squats and bilateral jumps with the countermovement jump. As long as the exercise pairs are validated by research, or they demonstrate enough similarities worth comparing, it’s fair to use them in a team setting provided the protocol is easy to reproduce over time.
What are the Limits of the Dynamic Strength Index Measurement?
Calculating DSI won’t solve all mysteries as to why an athlete is not winning or is constantly hurt, but it does answer important questions. It demands testing maximal strength and teasing out a force value, which is highly useful by itself. Just answering the question of how strong an athlete is begins the process of tailoring a training program; adding the relationship to field tests with ballistic exercise is even better.
Unfortunately testing only two field tests won’t be enough to give predictions and identify talent. DSI is not a performance predictor nor a screen. It’s a tool that reveals who has been naughty (not training) and who has been nice (putting in an honest effort). Although DSI reveals strength qualities, part of what makes up performance, it does not represent total performance unless you compete in powerlifting.
DSI helps a coach manage strength training trends. It’s not a lock for determining success in sport, where outside variables exist such as skill and other athletic characteristics as well as less objective qualities like passion. Consider DSI as a measurement of two tests that can be revealing, not a performance summary. If coaches use it to see an athlete’s ability to tap into their strength qualities relatively, the metric will be enough to have value in both the score and process.DSI helps a coach manage strength training trends. It’s not a performance summary. Click To Tweet
Look at the proposed approach by Sheppard and colleagues and consider not only the percentage bracket but also the absolute value of maximal strength compared to an athlete’s weight. A good DSI ratio doesn’t matter if the scores are not respectable, so it’s important to focus on maximizing output instead of optimizing resources of low performances. When maximal strength is low, optimizing power is only going to come by raising the ceiling of absolute force.
Does the Dynamic Strength Index Matter Now that F-V Profiling is Popular?
Many strength and conditioning coaches will point out that the explosive strength deficit of absolute strength and basic strength is similar to Force-Velocity (F-V) profiling and provides hints about the Load-Velocity (L-V) relationship. This is true, but an important difference exists.
F-V profiling with speed or jump testing is an inspection of the test data rather than a comparison of two different tests. Most coaches who’ve read the research from France and New Zealand conclude that, while DSI is not the same as an L-V relationship evaluation, it is eerily similar to F-V profiling. I love that DSI confronts maximal strength directly instead of arbitrarily recommending more strength. DSI doesn’t replace F-V profiling or L-V applications, it contributes to stronger conclusions and different perspectives.
I’ve written two controversial articles that were misinterpreted–one as attacking the value of F-V profiling and the other as unnecessarily hyping it because it’s trendy. Taking the middle ground (where most reason lives) can appear contrarian, but in the world of sports performance standing on either end of an argument’s spectrum is a bad idea.
Obviously the rate of force development (RFD) has a connection to both F-V profiling and DSI, and perhaps additional metrics are superfluous. But if I want closure on a challenge, I’d rather nail the coffin shut then leave it ajar. RFD measurements are not easy to work with and are sometimes so prone to artifacts (defects) they could be bogus. It’s better to work with tests that provide higher levels of confidence like speed and jump tests, which extract impulse and height scores.
In conclusion, many measurements produce similar findings. This means an athlete needs to address conventional strength or do activities that express force in very short or narrow time frames. Before changing a program, most coaches know they need to look at how the athlete got to where they are in the first place. If an athlete is advancing in a program and making progress, ride that horse as long as they’re improving.
Profiling an athlete’s F-V ability in different field tests may help you come to conclusions that jive with the DSI or prompt you to add more specificity such as how they accelerate. For the most part, focusing on speed from day one and patiently adding complementary modes of training is the best path to success.
Why I Like to Combine Squat Testing and Isometric Strength Assessments
Another issue that commonly comes up is the difference between maximal strength tests that are dynamic and non-ballistic compared with isometric testing. Based on the law of specificity, we assume that a moving test will represent an athlete better than a static test such as IMTP. A dynamic test that assesses maximal strength might represent athletic force production better than an isometric measurement, but it comes with a risk and requires a sufficient training background to be effective.
At the professional level, many athletes roll into pre-season as unknown entities because of their off-season strength training. Requesting a maximal strength performance may give great information. But it also places the team in a bind with the risk of injury, and actually getting good data can be a problem.
If I were to add one point to the IMTP blog, it would remind coaches that it’s not recommended that athletes train isometrically, it’s that testing isometrically is useful. Most of the time low maximal force production scores mean an athlete should head to the weight room and focus on the tried and true path of progressive overload.Testing isometrically is useful while training isometrically is not recommended. Click To Tweet
The opposite strategy is recommended when an athlete is not performing well with 1-repetition maximum testing. They may need to focus on clusters or very low volumes and push through a plateau by dramatically decreasing assistance exercises and provide even more rest to ensure quality is high and recovery is maximal. Overload is not just about higher poundage, it’s about modifying resources by removing volume and throttling up recovery anywhere possible.
While beyond the scope of this article, I’ll note that some athletes are great performers on the IMTP because the movement requires less skill and has a specific joint angle that favors those who aren’t squatting at traditional low depths.
We could argue that another deficit exists—the difference between maximal dynamic strength and isometric peak force in a pull or squat position. Currently some normative data is emerging, but no calculation or test is strong enough to pass the high standards of scientific scrutiny. In my observations, those with great talents and less exposure to training will have a noticeable gap, and time usually bridges the highly gifted athlete who has escaped training because of their abilities.
How to Use the Information to Train Athletes More Efficiently
Coaches most value the application of DSI. Any metric that is not actionable can be interesting but not useful. Earlier in the calculation section of this article, Sheppard’s research suggested that based on the index, coaches could assign athletes to three distinct groups for training prescription purposes. The first group was maximal strength, the second was a mixed or balanced group, and the third was rapid force.
Similar to the considerations proposed by JB Morin and colleagues, either you’re not training heavy enough, you need to use your strength better, or you should continue using both training modes and try to improve. It’s not that complicated from a strategic standpoint. The challenge comes from the day-to-day tactical needs in the real world. Travel, practices, illness, nagging injuries, and athlete compliance derail plans no matter how great the sport science is.
I offer one word of caution. If an athlete falls on either end of the DSI, none of the research recommends that a coach should put all of their eggs in one basket. If an athlete is strong and needs more speed or higher velocity work, neglecting the barbell isn’t a wise idea either. Athletes who are fast and need more strength work should progress slow and steady. Any changes to an athlete’s development, while well intended, may backfire if rushed or forced. Two examples are doing far more strength work than is reasonable or adding more speed and jumping sessions while reducing time under the bar. Most cases require an adjustment, not a radical abandonment of what got the athletes where they are.
Some athletes score well in strength tests from their years of sprint work. They respond favorably to the stimulus and make systemic adaptations that raise the potential to express maximal strength. I thought the idea that sprinting helped maximal strength was coach’s lore, like wishful thinking or fuzzy theory. But twenty years of watching this happen has convinced me that something is going on that we have yet to understand fully.
Coaches worry about two things in training—that the plan will cause injury or will not work well and waste time. The DSI helps ensure that coaches know the resources they are working with and keeps them from overthinking the process. It’s easy to get seduced by more esoteric needs, like special exercises and advanced protocols. But if the primary responsibilities are not changing, nobody cares if contrast training looks good on video or if the drills seem creative.DSI helps coaches know their resources and keeps them from overthinking the process. Click To Tweet
When designing a training program, be honest with the session’s goal and commit to creating a program that will fulfill the athlete’s needs. I’ve lost touch with simple goals when advanced training ideas focused too much on majoring in the minor when a bread and butter program would have been far more effective. Coaches think efficiency is about how much work gets done in an hour by supersetting workout components. Efficiency actually refers to how well an athlete taps into their talents and training.
Finally, the athlete who has a well-balanced ratio will likely still need to advance further in both speed and strength if they aren’t pushing the envelope with maximal force production and speed and jumping prowess. The evenly distributed athlete who has good strength and good power qualities is sometimes the most challenging. They don’t have a big deficit, but they’re not excelling anywhere. This means coaches have to decide to either:
- sequence areas by periodizing their program differently, or
- divide resources and allocate each need by alternating between energy and time without having too much emphasis on either
If I were to make an educated guess about the distribution of the three types of DSI groups, I’d say two-thirds belong on the even splitters, followed by the strong but slow and finally the fast and untrained in the weight room.
Add the Dynamic Strength Index to Your Testing Battery
The interventions for improving DSI are long-term training programs, not exercises or a blockbuster workout. DSI is humbling as it can only reflect objective changes from testing. It doesn’t reflect hard work or good intentions. Changes will not be seen quickly unless the athletes are young or severally undertrained, so don’t copy research study protocols like they are recipes for success.
Many good published papers describe programs that can be used as viable outlines for training, which can be restructured and learned from. Find what works and retest a few times a year. It takes months to improve and could take weeks to decay if injuries arise or if athletes stop training.
DSI is great because you’re likely already intuitively looking at the relationships between basic activities and maximal force. Or you’re testing an explosive movement and a slower maximal force exercise. Comparing the two tests or exercises doesn’t add time, and it targets how maximal strength training shows up in maximal dynamic performance.
As maximal strength hits the diminishing returns seen with many programs, DSI also can help decide if it’s necessary to fight the stubborn limits of a genetic ceiling. Using DSI a few times a year in training provides a compass for coaches. We can fast track performance results knowing how the training is either working or failing to capitalize the weight room.