Hamstring injury: spinning the wheel of fortune

If you’re a regular SPB reader, you’ll already be well aware that adding strength training to an athlete’s routine does more than boost strength. It can also help to develop speed and power – an important attribute in many sports – and improve body composition by increasing lean muscle mass. Another key benefit of strength training is an improvement in something called muscle economy, which is how efficiently your muscles use energy to produce motion while exercising⁽¹⁾. This is important for endurance athletes because research has found that when muscles are regularly exposed to heavy loads, for example lifting weights - they become better at turning energy into movement, which means you can run, swim, cycle, or row at the same pace using less energy and oxygen. The result? You feel less tired and have more in the tank for when it really matters—like the final push in a race.

Get going with inertia!

Most athletes are familiar with strength training using weights, gym machines, resistance bands, or even bodyweight exercises. Some might have tried plyometrics (jump-based training) or machines that use air or hydraulics for resistance. But fewer athletes know about a different strength-training method called ‘inertial training’. n this method, resistance comes from a spinning flywheel. When you pull or push against it, the flywheel spins and creates resistance. This training concept is based on a basic law of physics known as ‘conservation of angular momentum’ (see the video clip below for a simple explanation). Flywheel training was first developed in the 1990s to help astronauts maintain strength in space, where they can’t rely on gravity. Since then, many studies have shown how effective it is for improving strength and performance^(2–4).

The beauty of angular momentum

Basically, every spinning object has angular momentum, and doesn’t want to change its velocity or change direction unless an external force is applied. To change angular momentum of a flywheel, YOU have to apply that force. You will have encountered this phenomenon if you’ve ever played with a spinning gyroscope! In flywheel training, the concentric (muscle shortening) action is initiated by pulling the strap connected to the shaft of the device, spinning (accelerating) the flywheel/cone. Once the strap rewinds around the shaft, an eccentric (muscle lengthening) action is performed to decelerate the flywheel/cone rotation. If executed correctly, this enables a greater application of force during the eccentric action, resulting in a mechanical eccentric overload.

Using a spinning flywheel for resistance training might sound an odd approach compared to simply lifting some weights, but it actually some big benefits. First, the resistance to change of angular momentum of the spinning flywheel adjusts automatically; the harder and faster you execute a strength training movement, the more the flywheel pushes back. It also provides resistance in all directions, which means it’s great for training movement patterns used in real sports. Another big advantage of flywheel training is how easily it allows for eccentric training movements, ie when your muscles work while lengthening (akin to lowering a weight slowly). Eccentric training is known to be very effective for building strength, generating larger gains than concentric training movements per unit of energy invested⁽²⁾. In flywheel training, as you spin the wheel faster during the pushing (or pulling) phase, you also need to control that force during the return, which is what gives your muscles a powerful eccentric workout.

Boosting athletic performance

In recent years, sports scientists have studied how flywheel training can help athletes perform better. One 2017 study looked at national-level swimmers who added just four weeks of flywheel training to their routine⁽⁵⁾. They saw a 12.8% boost in muscle force, 14.2% more muscle power, and swam faster - 0.76% faster in freestyle and 1.86% faster in butterfly. A year later, researchers carried out a systematic review of multiple studies on flywheel training and confirmed more benefits in athletes employing this training mode⁽⁶⁾. These were as follows:

·        Muscle mass gains of 5–13%.

·        Strength gains of 21–90%during eccentric movements.

·        Muscle power gains of 10–33%.

·        Over 15% better jumping performance.

·        Increases of 2–10% in top running speeds.

Other sports like soccer⁽⁷⁾, rugby⁽⁸⁾, and basketball⁽⁹⁾ have also shown solid results using inertial flywheel training—especially for improving speed, power, and agility.

Harness the healing power

One big benefit of strength training (and reason that many athletes strength train) is to reduce the risk of injury, or rehab after injury. When it comes to the best type of strength training for injury prevention and rehab, a large body of evidence has accumulated that strength training exercises that emphasize eccentric muscle contraction are particularly effective, especially for recurrent and troublesome injuries like hamstring strains^(10-12). It stands to reason therefore that if flywheel strength training is a very efficient of delivering powerful eccentric loadings to muscles, it might be an excellent strength tool for athletes whose main goal is to prevent or recover from injury.

It’s certainly the case that training programs incorporating eccentric-focused resistance exercises have been shown to be very effective at developing eccentric hamstring contraction strength, and improving hamstring muscle fiber length (thereby increasing elasticity in the muscles), and that flywheel training is a good way of developing these attributes^(13,14). But can a regular flywheel training program help athletes to develop more resilient muscles and lower the risk of injury, particularly when it comes to reducing the risk of a re-injury following an initial injury?