By Carl Valle
In the last 20 years, enough research has confirmed that isoinertial resistance from flywheel training is not a gimmick, but perhaps one of the most potent ways to train and rehab athletes. I was skeptical and cautiously optimistic at first, but after years of experimenting I came to the realization that not only does the modality work, it works better than I imagined. In this article, I dive into the essential science of how the body remodels from specific flywheel training and explain how to use your flywheel system better.
Breaking Down the Physics of a Flywheel Repetition
If you skip to the coaching goodies, or all of the adaptations that are possible with flywheels, you must understand how they work in great detail. SimpliFaster’s Buyer’s Guide to Flywheel Training Equipment touched on the different options on the market, but didn’t break down the mechanics into enough detail to fully explain what is happening on the physics side. Too many coaches skip through the details and wind up holding their athletes back because the details matter more than you think.
Flywheels are about leveraging an exchange or transition of force, not performing an exercise in isolation. The best way to understand a repetition of flywheel training, besides actually trying it, is to contrast it with barbell training, something we are all comfortable with experience-wise.Flywheels leverage an exchange or transition of force; they don’t perform an exercise in isolation. Click To Tweet
Generally speaking, a flywheel workout is constant work, with no rest between reps. For the most part, each repetition bleeds into the next, so rest only occurs when an athlete stops working, which is something very foreign to an athlete starting off.
The most brutal or rude awakening to the unique value of flywheels is the dramatic difference between squatting with a barbell and squatting with a flywheel. While there is an opportunity to rest at the top or completion of a barbell squat repetition, flywheel squatting has no available rest period. There is usually a bit of breathing room at the top period of a barbell squat, but the top part of a flywheel repetition is like the peak point of a rollercoaster—meaning the brief instance before the gut-wrenching plunge down.
Note: The rapid descent of a flywheel can feel like it’s jerky, but don’t be deceived. The reason you feel like you are yanked uncomfortably is because the rapid rate of descent is uncoordinated for many athletes who can’t create fast rates of eccentric force to manage the high-velocity force.
While gravity does interact with the repetition, the primary force is the momentum created from the legs driving through the platform and creating a high spin of the disc or flywheel. Thus, the resistance back is faster and more demanding than conventional barbells. Flywheels were created to provide a form of resistance that didn’t need gravity, and the forces that athletes can generate internally are massive. The major difference athletes feel is not the concentric pushing that is like barbell squatting; it’s receiving the momentum eccentrically, the prime stimulant to adaptations that coaches desire.
In summary, here are the ways that flywheels differ from barbells:
Constant Tension: Generally, the repetitions are without pauses or rest at any part of the movement, meaning the muscle is constantly working.
Momentum over Gravity: While gravity is part of the equation, the speed of the eccentric action results from the concentric effort before the cam changes direction, not the weight of the bar.
Concentric and Eccentric Speed: Jumping actions and explosive lifting are not possible with flywheels, but the descent rate eccentrically is usually much faster and more aggressive than barbells.
Eccentric Emphasis: The eccentric force is applied uniquely to the body, far differently than with the barbell, thus creating an advantage over conventional free weights.
Skill Demand: On average, the performances of the flywheel versions of common exercises done with dumbbells and barbells require more skill. It is inappropriate to do jumps or Olympic-style weight lifts on a flywheel device.
Free weights and flywheel training have similarities and differences. It is important to be aware of the subtle and large differences because, as a coach, you need to eventually teach something that isn’t natural to the body at first. Athletes need to experience flywheels because they can’t be explained by just words and videos, but the information above should help coaches articulate the sensations and how flywheels work better than a casual summary.
Do Flywheels Have Advantages over Free Weights?
Recently, researchers in Spain and Sweden completed a comprehensive meta-analysis on flywheels, and the findings were extremely compelling to anyone who cares about athlete performance. I highly recommend that you not only read the summary of the studies, but also read each study mentioned to truly understand the impact of the training method. It’s easy for coaches to absorb the conclusions of a study, especially a meta-analysis that has more weight than a single study.If you are not using flywheels now, you are missing an advantage. Click To Tweet
The problem is that the studies use just weeks of interventions, not entire athletic careers. The controls or comparisons were conventional programs and not robust, hardcore training programs, so it wasn’t a true competition between the best free weight programs and flywheels. My point is that it’s an oversimplification to suggest that just replacing conventional free weights with flywheels will be a better option for athletes, but it’s not a stretch to say if you are not using flywheels now you are missing an advantage.
Most of the advantages I have seen in the research help with two key needs: the ability to increase force production and the ability to improve injury resilience.
Strength Changes: The greatest number of studies defending the stance on flywheels as superior to conventional training have to do with strength. Strength is one of the most plastic adaptations to muscle, and flywheels seem to perform better than other options for early gains in strength or ability to express force maximally.
Power Development: Power requires adequate strength levels, so it’s not surprising that power from flywheel training does appear to be higher than in controls. Power blooms in a soil of strength, but from the rapid contractions eccentrically the use of flywheels for developing power does make sense here.
Muscle Hypertrophy: Due to the constant tension on the body, it’s no mystery that rapid gains in muscle mass are common with flywheel training. My own personal experience saw dramatic differences by just adding two finisher exercises twice a week to athletes; I witnessed a major jump in muscular development far faster than ever before.
Jumping Performance: While improvements in jumping performance are available in the research, absolute changes like record-level heights or distances are not known at this time. Like early levels of strength change from flywheels, jumping responds favorably at early periods of training. There have been no studies using advanced jumpers or athletes who can jump with impressive abilities, so the results of flywheel training later in development are not yet known.
Improvement in Speed: The least-tested benefits of flywheels are speed and change-of-direction abilities, but the results are promising. So far, I have not seen anything more specific, like where in the speed continuum flywheels exhibit their effects—e.g., peak velocity or early acceleration. Also, many of the research studies use different machines, so it’s hard to know how they are helping.
In every area of transfer, flywheels have an advantage over the control. The issue is that the control is not a fair comparison because most of the studies have been with rudimentary programs and not with advanced trainees. So, while the research shows great promise, it’s still a bit premature to have any conclusive belief in the superiority of flywheels.
What Eccentric Adaptations Are Possible with Flywheels?
As of today, the review of skeletal remodeling of eccentric training by Martino Franchi is perhaps the most illustrative document on how tissue adapts down to the molecular level. Along with his colleagues, Dr. Franchi really paints a clear picture of the morphological, metabolic, and molecular adaptations from eccentric training compared to concentric changes. While flywheels do elicit a unique eccentric response, many of the adaptations are not as clear as conventional strength training.
The theoretical list here is just an outline, and in time we will know from research whether flywheel training meets, falls short of, or surpasses the adaptations. Perhaps there are other unknown adaptations unique to isoinertial training that we have yet to observe in the research. Coaches may not know the exact reasons or biology for what happens from eccentric training yet, but the benefits show up in the injury rates and performance testing enough to confidently say something good occurs.
Below are three main responses to eccentric training that the current evidence strongly supports as an argument for flywheels. The base review done by Franchi covers the science in a far more comprehensive light, but here is the best of the studies.
Neuromuscular Patterns: Differences between eccentric and concentric do indicate that eccentric training has special changes to the nervous system, but placing eccentric training on a pedestal is a dangerous mindset. Concentric training has adaptations that you should not overlook, such as rate coding and other benefits to athletes.
Muscle Architecture: Eccentric lengthening of muscles, usually the hamstrings and perhaps other muscle groups, is the target goal. Nearly any coach worth their salt wants a muscle to be “long and strong.” I have seen the ultrasonography of hamstrings from flywheel training and the results are just as impressive as the Nordic hamstring studies. Unfortunately, the exercises done with flywheel training require more preparation and coaching, but over time this should not be a problem.The results of flywheel training on hamstrings are just as impressive as Nordic hamstring studies. Click To Tweet
Fiber Type Recruitment: Based on the small set of research studies, explosive fiber types tend to be more recruited with eccentric training than concentric training. The prime responsibility is the real-world application of adding eccentrics to a program when most of the training in sport includes concentric actions. The truth is that concentric and eccentric training are a natural sequence most of the time, and isolating contractions is not the primary way to train and prepare for performance. Rehab may be a time when isolated eccentric training is a potential method, but for now there needs to be a lot of eccentric-only training to influence the fiber type composition. Maybe elite athletes can create favorable shifts in fiber composition from intense blocks of eccentric training, but for now nobody has long-term training biopsies except a few elite coaches like Henk Kraaijenhof.
The coaching world is less familiar with mechanisms and cellular responses, but the nuts and bolts of what happens at the microscopic level are paramount.
Satellite Cell Activity: Eccentric training shows more satellite activity than concentric training, even when the load is equalized. Based on the current evidence, it seems that satellite cells are one of the possible mechanisms for some training programs inducing more growth than others, but for now the precise pathway is unknown. In a study done on ice baths, satellite cell activity decreased when athletes used cryotherapy. The way eccentrics can modulate satellite cells is currently uncharted, because the frequency of training is lower for more maximal training.
Extracellular Matrix Remodeling: Connective tissue and its assembly with remodeling is an observation in the research, as well as my own personal experience with athletes. When dealing with pathologies of the tendon, I have seen the revival of athletes in extremely short periods of time. Many of the studies done with flywheel training are on performance, but I think we should further investigate the area of rehab, especially during short off-season periods.
Gene Responses and Cellular Signaling Pathways: A growing area in sport science is the response of genes to exercise and nutrition. Based on the research available, it seems that genes respond similarly in both concentric and eccentric training, besides the time course of activities such as protein synthesis. Based on the lack of research specific to flywheels, as well as eccentric training as a whole, no clear pathways exist to explain what is going on with isoinertial training that could be unique.
Obviously, the eccentric research does shed light on what is possible with flywheel training, but it will be about 10 years before we will know if anything special happens to the body beyond what we see now. My bet is the flywheel adaptations are similar to the general eccentric changes, but the primary differences are neuromuscular enhancements. Perhaps more intense or rapid adaptations occur with isoinertial training, but only time will tell here.
Who Can Benefit Most from Flywheel Training?
Those who can benefit from flywheel training range from youth athletes to elderly patients. While it seems almost too good to be true, using a flywheel is something anyone can do with just a few learn-by-doing sessions. However, elite athletes are the population that benefits the most from flywheel training. The reason? As an athlete becomes more explosive or competes longer, their available time must be more productive. Eccentric training is not only very effective, it’s very time-efficient as well.
To narrow down the specific subpopulations, I think tall athletes as well as athletes with poor strength training histories seem to benefit from flywheel training. Using a waist harness allows those with poor lumbar strength to train aggressively, and this is the reason many soccer players benefit tremendously from flywheels. Taller athletes who have disadvantages in maximal strength tend to do well because they are able to use waist harnesses to overload the body, too.
Getting even more specific, the areas on athletes that I see adapt the best from flywheel training are the legs and torso muscle groups. Conic or rotational systems tend to target the congested areas of the hip and groin, and platform options prepare the knee and hamstrings thoroughly. Some programs have used flywheels for upper body, but those approaches are beyond my experience. We should use flywheels for specific purposes, not as a panacea or cure-all.
Finally, you can do flywheel training year-round without problems, provided you do both the intensity and exercise selection right. My program is about 5-10% flywheel training now, and I have yet to have a single athlete with a non-contact injury who uses isoinertial training religiously.
What Are Some Training Limitations of Flywheels?
Flywheels are excellent tools, but they’re not without some limitations and challenges. Since they are machines, they need to servicing and they are not a perfect fit for everyone. Some exercises are awkward and don’t translate well from simple dumbbell or barbell versions, like calf raises, for example. Additionally, athletes can’t do some movements that they enjoy—like the snatch, clean, and jerk—with flywheels. While the contractions are faster than normal on the eccentric portion of flywheel movements, they are not plyometric or reactive in nature, and so are not ideal candidates for advanced jumping or similar.
Flywheels are not just for squatting, but for pulling in many different ways and angles. However, they are still limited. With flywheels, you must also be aware of the torque and force during movements like squatting and deadlifting. You don’t drop the weight like a barbell, so from a safety perspective, they have the same risks and hazards of traditional weights.
In the last 20 years, there have been very few documented cases of injuries, so the accident rate and severity is unknown. Still, anything that creates an overload is a risk. The demand of flywheels is not foolish because the forces are what the athlete creates, not what the coach or athlete estimates. For the most part, because flywheels are useful in injury prevention, the problems with isoinertial training haven’t been notable.
Flywheels also have limits because we simply don’t have much available knowledge on how to best program them into training. While plenty of research shows how they work with adaptations and results, not much comprehensive information exists on placing them into training properly. The lack of information with flywheels is not going to be a problem forever, but as of 2017, very little peer-supported education exists outside of a handful of experts in the field.
Unleash the Monster Inside Your Athletes
Flywheel training isn’t something that you jump into without doing your homework, but it’s not something to fear either. A healthy viewpoint with flywheel training is to respect the modality and learn what it can provide and how to implement it into a comprehensive program. Some coaches are huge fans of flywheel training and dedicate their entire strength training time to isoinertial training, but not every repetition needs to be done that way.
Flywheel training is not going away anytime soon, and it’s a great vehicle to learn about other methods of training as well, such as isokinetics and accommodating resistance. Training with flywheels works scientifically and you can place it into a program practically. Even if you add one exercise a few times a week, the benefits are potent and rapid.