Ever since the invention of the wheel, technology has evolved to enhance the training of modern human beings. While much of the current interest in flywheels is the result of the resurgence of eccentric training, the reality is that flywheels are about redirecting momentum, not providing a true eccentric overload. Isoinertial training is old news, but the new companies providing equipment are also providing fresh ideas that dramatically improve the outcomes of training. The promise of this article is simple: We outline the necessary components of a great flywheel product and list the companies in the industry who are leading the way.
Before the Space Race: A Very Brief History of Flywheels
Usually the story of flywheel training starts with Per Tesch and NASA, but the truth is it’s likely somewhere between the first potter’s wheel and the 1970s when isoinertial exercise machines were invented. Flywheels are used today in other industries outside of sports equipment, so they are not unique to exercise. Sports training flywheels are simply disc-based machines that spin and provide an efficient way of conserving energy, usually through squatting or pulling motions.
Flywheels are not eccentric overload machines that increase the force beyond the concentric contribution from the athlete. The machine does not create eccentric overload; it’s the exercise technique in receiving the load that is truly an increased eccentric muscle action.
Several companies provide flywheel training devices, and some have taken the equipment to new levels with their designs, but the evolution is only a refinement, not a quantum leap. The reason is obvious: Flywheel technology is primitive and exercises are, for the most part, ancient. So why the increased popularity of flywheel systems? The answer is simple: The science is gaining (pardon the pun) momentum. The proponents of loading the body to assist in rehabilitation—usually with more aggressive approaches than in the past—are driving interest in flywheel training. Today, we see about a half-dozen international providers with flywheel equipment, and this is likely to grow with the American companies starting to spring up now.
The Biology Behind Flywheel Muscle Contractions
What do flywheels do uniquely to muscles and the nervous system as compared to conventional gravity-based options like barbells and bodyweight exercises? Recent investigations using tensiomyography indicate that flywheels provide a specific stimulus that challenges the neuromuscular system differently, and those differences have shown up in other research studies that include performance testing.Flywheels challenge the neuromuscular system differently than barbells or bodyweight exercises do. Click To Tweet
Flywheels resemble an old lawnmower start, and finish with a rapid eccentric rebound. A barbell squat begins with the bar lowering until the athlete redirects the load up concentrically. Each rep usually includes a rest period of a second or more, then the work continues again with another eccentric to concentric pattern. Flywheels have no break in the work being done, as the repetition constantly cycles from concentric to eccentric activity. Additionally, the work being done on the eccentric portion experiences a redirect of velocity from the peak velocity of the concentric side. Thus, the rate of the early eccentric work is dramatically different because free weights respond to muscle tension and gravity.
Peak eccentric forces are about how the body receives the redirected energy from the flywheel, not about the machine in any way boosting the force. True eccentric overload occurs when the total work done is greater than what was either volitionally provided by the preceding concentric action or what could be done if the athlete was to evoke a maximal concentric action. Researchers are exploring muscle architectural changes or morphological adaptations to muscles that favor performance and injury resilience benefits.
So far, we do know that any eccentric overload that creates a lengthening of the muscle is more resilient to injury, especially in the hamstring group. Hamstring curls using flywheel training do provide a lot of torque, but only when a partner assists the concentric portion does the eccentric work become very interesting to coaches and researchers. Classic approaches like two legs up and one leg down are examples of eccentric overload without the need for a flywheel, and are back in use due to the Nordic hamstring exercise becoming popular in sport again.
Generally speaking, most of the techniques using flywheels are about generating a larger-than-possible force into the machine, such as a partner-assisted motion or bilateral concentric to unilateral receiving exercise. What coaches are trying to do is train the body differently eccentrically or overload it more by using an exercise pattern that exploits the ability to transition to a different motion after the flywheel redirects the forces. An example of this is a squat to Romanian deadlift, where the athlete is squatting concentrically and fighting the eccentric action early with the Romanian deadlift action.
Common Design Choices of Flywheel Training
Flywheels usually come in two options: a platform with a disc wheel or a cube with a cone-shaped mechanism. Most flywheel training platforms are for squatting movements, while the cube options are for total body movements and rotational patterns. Both options can be used for leg training, but the squatting platforms are popular because they are a portable lower body option for soccer teams. Due to the culture of the sport, getting athletes to train before they leave the pitch is a needed benefit for teams.
Platform systems are the most popular in the industry, and nearly every company has a “squat” device of some sort. Most systems are about 1 meter long and half a meter wide, and resemble a table saw. Most of the systems have the flywheel outside and on the top of the platform, but the kBox has the system on the bottom of the platform and uses small legs to keep the flywheel free. The cables are mainly either straps or rope-like materials, and the discs are alloy metals with a hexagonal hole in the middle. Companies usually provide harnesses for squatting, similar to a vest or backpack.
Cube systems are mainly conic-shaped flywheels, so the cables can wind and unwind smoothly. Cube or box systems provide opportunities for exercises that require more movement, like upper body exercises that use rowing motions. Cube systems are also solid solutions for squatting and lunging motions, and many American coaches are familiar with the VersaPulley popularity of the early 2000s.
Due to the portability of the machines, coaches tend to use them outdoors or bring them out in the weight room. Some of the companies allow for mounting for clinics and therapy rooms, but for the most part these systems are more mobile in design.
Quantifying the Loading of Flywheel Training
A lot of high-level math is needed to get precise work transferring through a flywheel, as countless variables can interact with energy creation, storage, and redirection. Due to safety considerations, training flywheels collect energy, but don’t enhance the energy or speed they receive. So, treat flywheels like a rubber ball rebounding off a surface, not an underhand softball throw to a home run monster, creating more energy than it receives. Coaches have to trust the companies that build the machines to have valid measurements, since small details like weight and radius must be very precise or the estimations will be inaccurate. Additionally, other details, like the materials used, angular velocity, and additional weights near the edge, require a lot of development time and effort to ensure the calculations are accurate.
Video 3: The video above shows the instant feedback using the Desmotec system. If you are serious about flywheel training, you’ll want and need the quantification of peak forces throughout the workout.
The estimation of work done with flywheels can be made with different instruments, but for the most part the calculations are done from RPMs of the crankshaft or the use of a positional transducer. The kMeter was already reviewed, and systems like GymAware have been used to help display and record flywheel training work in the past.
Rotational energy is the consolidated work calculated from all of the sensors and instruments available and, while that is a fair summary, it doesn’t tell much beyond the work performed. Coaches and therapists at first want to know how much work is done per repetition of an exercise, but as they become more experienced, they are likely to want more specific context such as the time frames involved and the distance of motion of each repetition. Unfortunately, most of the problem with flywheel equipment is that the sensors are on the machine instead of the body. While it’s fine to see how a human interacts with a machine for the purpose of quantify output, we also need to know how athletes create the forces to understand how training is trending up or down. Coaches and therapists must be careful to not rely on one metric or score, as a number in isolation usually doesn’t tell much beyond the result of an action.
While slightly oversimplified, the sports training flywheel is a cable-driven machine that can quantify the work from the pulling action and the work receiving the redirected energy. The challenge is that, in general, stroke distance provides a better way to create force. However, receiving the load quickly usually decreases the distance of work and makes it difficult for the next rep to have the same concentric output. Also, if the athlete can lower their body to a deep receiving position, they may not be strong enough to handle the abrupt forces on their joints. The unique back-and-forth motion of the flywheel systems are a challenge to perform and quantify, as the need to see specific work done on parts of the body is far different than on the body as a whole.
Top Systems in the Flywheel Market
The top seven systems providers are all selling equipment to coaches and physical therapists for performance and rehabilitation. More companies exist in Spain than are listed now, as the market is extremely saturated in that country for some reason, but those companies are not selling enough and have not been around long enough to be considered. Expect a very dramatic change in the U.S. market at the end of 2017, as some creative coaches are likely to get involved in the flywheel space.
A good test to see the quality of a machine is spinning the flywheel with the disc and timing the duration of the rotation period. The longer the spin, the better the flywheel machine. Also, welding is more durable than using brackets, but most systems will last for nearly a decade, save the rope or strap system. Each system must be maintained though, so like cable or selectorized machines, physical maintenance is required. All of the companies offer accessories, but third-party vendors are important to consider, as they can provide very specialized harnesses, bars, and handles.
VersaPulley – Heart Rate Inc., the American company that makes the VersaClimber and other products, was founded in 1978. Known for their VersaPulley product line, the company has three models of conic isoinertial products, and they range from a portable to a platform to a cube hybrid system for more specific leg exercises. The mid-range product is a wall-mount system, and the company offers a rep counter and a display, but it’s not a tool that indicates actual force or power. Many strength coaches in the U.S. will remember VersaPulley was endorsed by Mark Verstegen before he transitioned to Keiser. Phil Wagner, the founder of Sparta Science, endorsed the product more recently.
Exxentric – Founder of the kBox, this Swedish company provides a series of platform options that use a band- or strap-based flywheel. The cardinal difference with the kBox is that it has a flat top; the flywheel crankshaft is under the platform, but it requires legs to keep the flywheel disc from hitting the ground. The product provides an excellent opportunity for those wanting to do deadlift movements and deep squatting, as no machinery is near the foot area. The kBox series has an oversized pro option, as well as a lite option for maximum portability. The strongest feature of the product, besides the flat foot area, is the kMeter, the sensor that transfers the RPMs of the crankshaft to useable data on iPads and iPhones.
Proinertial – This Spanish company has been in business for 10 years and is growing internationally. They provide multiple machines besides platforms, and can also customize for a very small fee. Their systems use Chronojump technology to calculate work performed by the user in training, and feature a rope-driven flywheel. Their products are very popular in soccer clubs and training facilities, and just entered the U.S. market this year. Proinertial’s product line includes a platform option with oversized boards for tall athletes, and their slant boxes are permanently fixed for lateral lunges and squats. The cube products are portable and can be mounted to walls, and they even have a leg press.
Desmotec – Similar to Proinertial, this Italian company has two primary models. Each model has customized features that are optional, like sliding mounts and a specialized platform option for therapists. The system is popular in soccer, and it has been on the professional market in the U.S. for years. The products are well-crafted, and their attention to detail makes them the sports car versions of flywheels. Several professional athletes have their own home systems and, like the previously mentioned companies, Desmotec offers a complete line of accessories. They also offer perhaps the most developed software, and data is captured via a linear positional transducer.
Space Wheel – The Space Wheel system is a combination product that is one part platform and another part pulley option. The Space Wheel doesn’t currently offer any sensor to calculate output, and the system is very barebones. The one strong area of note is that the product is arguably the most portable of all of the platforms, after the kBox lite. The Space Wheel is known for its spiral decorated disc that nearly hypnotizes the viewer due to the design. Space Wheel is a very small Italian company and has some traction in the market, but they’re not as visible as Desmotec.
nHANCE – nHANCE is known for their collaboration with Dr. Per Tesch, and their product line includes other options, like a leg press and hamstring machine. The squat platform system offers a connection to a third-party sensor for output measures, and has a long history with teams. One of their most popular products is the YoYo Leg Curl machine, which elicits a high amount of EMG activity. It is known to place a lot of strain on hamstrings—enough to create adaptations beyond typical curls. The company has not innovated in years, and is likely feeling the impact of competition.
RSP – The final company is from Vigo, Spain. The company has three systems: a pure conic option, a wall system, and squat system. Its products are very contemporary and they don’t have any sensors: all are conic-shaped flywheel systems except for the platform. Because they provide a smooth experience, the products are known for their rehabilitation benefits, likely for early shoulder strengthening post-operation.
These flywheel systems range from about $2,000-$5,000 USD, and accessories are all priced differently. Most of the time coaches want the waist belts, as the torso harnesses are more expensive. The sensors for quantifying work range from $500-$1000 USD, and connect to either a laptop or tablet. One major factor in the purchasing decision is the shipping cost, which adds at least $200 to the equation.
Educational videos and articles are the lifeblood for the products, since most sports training courses and textbooks don’t mention flywheels, except in passing. Some courses and conference exist, but they are usually extended infomercials and focus on the benefits of the product instead of deeper science. So far, the Exxentric company is the leader here, with other companies soon to be following suit.
What to Expect in the Future With Flywheel Training
Don’t hold your breath for a radical change in the market. Most of the cost of flywheels is the cost of materials, not the development needs. The real innovation is on quantification of the energy created and received, as well as nuances such as accessories and refinement to the construction.
It’s safe to say that flywheels are not going away soon. Several other technologies can provide isoinertial experiences, but they are more expensive. Although the price of motorized resistance is currently very high, they do provide true eccentric overload and the user experience and exercise options are better. Flywheels are going to be around for a while, due to the fact they don’t require much to work, and are a staple in many training programs.
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