Spring vs Bungee Rebounders: The Science

We’ve already spoken about the longevity, reliability, and general benefits of spring versus bungee rebounders. Now let’s get right into the science of rebounding and how these two types of systems compare.

G-Forces

A g-force (gravitational force) is the force applied to mass – a stationary object on Earth, for example, experiences 1 g-force. So when anyone moves up or down against gravity, they are experiencing varying degrees of g-forces on their body. A positive g-force is experienced when someone is landing and therefore the stress is placed on the lower extremities (blood flow to the legs). A negative g-force is applied when someone is decelerating upwards, and the stress is then placed on the higher extremities (blood flow to the brain).

Longer G-Forces are Bad for the Body

Ironically, extended g-forces are generally considered destructive for the body while momentary g-force exposure can stimulate the body in healing ways. This is why astronauts, race car drivers, skiers, and even basketball players often have to manage the effect of destructive g-forces and how they affect the body. This includes both landing and jumping, as both forces can cause destructive effects to different parts of the body. Rebounding, likewise, applies varying degrees of g-forces on the human body when landing and being pushed upwards. The destructive effects can include muscle degeneration (atrophy), neck and back pain, loss of consciousness, joint issues, and even bruising due to capillary ruptures (petchiae). Finally, these destructive forces are directly proportional to the amount of time the body is exposed to them – the shorter, the better, the longer, the more destructive. Many humans can experience extremely high g-forces for brief moments, but even one millisecond longer and damage then begins.

Rebounding & The Goldilocks Zone

Despite the fact that negative and positive g-forces are generally bad for the human body, there is a thin “goldilocks” zone whereby the right combination of g-force and time exposed to these g-forces actually flips the switch and stimulates the body in highly beneficial ways, triggering healing, muscle regeneration, and lymph node flushing. These benefits can be further explored here. The most important consideration when contemplating whether these movements are destructive or productive is the amount of time spent experiencing these g-forces. Generally, the longer they are experienced, the more destructive they become. So, although it may seem good for a single bounce to last longer, it is actually damaging to the body and can in fact create musculoskeletal and joint problems in months or even years.

Bungee Rebounders

In general, rebounders apply between 2-4 g-forces on the human body during bouncing – this means anywhere from double to quadruple your weight is forced onto your body. That is a lot of g-forces! By their very nature, bungee cords do not store a huge amount of potential resistance, and likewise, as they are used, one can actually feel them heat up as they stretch and contract. This results in a bounce that is elongated – ie, the curve of resistance as you land is quite long. This increases the amount of time you are exposed to these strong g-forces – this includes all of your joints and muscles.

As you land on a bungee rebounder, your feet, knees, back, and neck, and all the muscles in between, are exposed to a flatter curve, meaning your body is experiencing these extreme g-forces for extended periods of time comparatively, even if it may only seem momentary.

Spring Rebounders

Springs, unlike bungee cords, are made of steel – they store huge amounts of static resistance, and so, when the weighty 2-4 g-forces of an individual’s body hits them, they react by stretching and contracting with a great deal more explosive energy than bungee cords do. This can, of course, be equally destructive for muscles and joints if that resistance is too high, as then we lose the benefits of rebounding – one can achieve a similar effect simply by jumping off a bed and landing on the ground. But in doing so, we put all of our joints and back at risk, making it just as bad for our bodies as long exposure to g-forces would be. Also, poor quality springs may initially provide sufficient resistance, but as they stretch and contract, may become so malleable due to weak materials that they may provide too little elasticity and remain extended.

However, when we then look at high-quality springs made of high quality materials, such as the Needak springs, we now enter the goldilocks zone. With high quality steel springs, the maximal amount of resistance is released with every bounce, and due to having high-quality materials, this does not change even on the hundredth or thousandth bounce. The static energy is stored to a much larger degree than bungee cords or cheap springs, and this provides a gradual bounce curve, but one that is just right for the human body to experience maximal benefits with minimal damaging stress.

What’s the Actual Difference?

A bungee rebounder will, on average, force 2-4 Gs on the human body for approximately 3-5 times the length of time a high-quality spring rebounder such as the Needak will. This is not good for the human body as only short bursts of exposure to these g-forces result in the benefits of rebounding without damage to the organs, joints, and muscles in the body. Short bursts of exposure allow muscles and joints to build and recover and adapt in a continuous, steady pattern, emulating normal movements. However, extended exposure, such as that found on bungee rebounders, simply does not provide the body enough time to recover while increasing the stress and damage those extreme g-forces apply to the body. This results in an exponentially more destructive effect on the body, as with every session the body will get more and more “indebted” to this damage, and over an extended period of time, this damage will begin to manifest in tangible and potentially irreversible manners.

In the end, Milliseconds Matter

When we see videos of people jumping on bungee rebounders versus spring rebounders, it may look indistinguishable. However, if one compares the two bounces side by side, there is a clear difference: bungee rebounders sink more, allowing approximately 30% of the number of bounces in the same amount of time as a spring rebounder. This means we spend a significantly longer amount of time decelerating on a bungee rebounder, and therefore, are placing extended stress upwards of 4 times our body weight on every organ and joint. This is highly destructive over the long term. High-quality springs, in contrast, explode on every bounce, capturing all of those g-forces, providing just the right amount of feedback and resistance to ensure joints are protected on landing, but the body is not unnecessarily exposed even a millisecond longer. Milliseconds matter when it comes to 4 times your bodyweight, as when you bounce on a bungee rebounder for even 5 minutes, you’ve exposed every system in your body to 300-500 more fractions of seconds of unnecessary stress than a high-quality spring rebounder. And that adds up, just like anyone can twist an ankle in one misplaced moment.