What is BWS and what does it do?

Updated: Sep 14

(Pt. 1 of 2)

Here at LEVER Running, we are committed to not only making body weight support (BWS) technology available to all runners, but the science behind it more digestible too. Our goal is to take a moment to help YOU, the everyday athlete, and the Comeback Legend, understand what is going on with your body when you run with body weight support. We also want to help you understand what isn’t changing when you run with LEVER.


This week’s blog starts with a question. What is body weight support (BWS) and how exactly does running with body weight support help you - an athlete - run, recover, and heal faster?


Body weight support is any method of suspending part or all of your body weight. It can be done by overhead harnesses, outdoor bicycles, water, air pressure, or here at LEVER - a frame with an elastic cord. At LEVER we use our devices to allow runners and walkers to move on treadmills under partial body weight support - currently any amount of weight between 0 and 45 pounds (0 to 20 kilos) reduced.


The major way that body weight support acts upon your body is to offload the impact on your bones and joints. It does this by reducing the percentage of weight that is interacting with the ground as you run or walk. This “impact” is called a ground reaction force (GRF) and it is the measure of the force exerted by the ground when your body interacts with it. GRF is made of both vertical and horizontal components. To help better explain GRF we will address vertical and horizontal in separate paragraphs.


When you stand, your vertical GRF is equal to the weight of your body. When you run, vertical GRF can increase up to 3x your body weight. This massive increase in vertical GRF is a significant factor leading to pain and overuse injuries during running (see photo of runner in a downstep - this is when your GRFs are the highest!).

It’s no surprise that you and many runners experience pain and injury at higher rates than many other sports - you are loading your body thousands of times each run with 3x your body weight. This is where body weight supported running and LEVER enter the equation. Body weight supported running and the LEVER LV1 reduce vertical GRF during running and walking - reducing the force impact upon your hips, knees, and ankle joints and bones. But, by how much? Well that depends upon the amount of weight you are reducing. The more weight you take off with the elastic cord of the LV1, the lower your vertical GRF will be during running. Why should you care? Because whether you’re coming back from injury, having knee pain, or just trying to maximize your training volume, having less impact on your bones and joints can help you recover or heal faster.


Horizontal GRF is the component of GRF that is defined by forward or backwards movement. When you stand, your horizontal GRF is equal to zero, as you are not moving. When you run or walk, your horizontal GRF goes to non-zero and is defined by the speed of your run or walk. Horizontal GRF is thought to be a major contributor to muscle firing patterns and gait mechanics during both running and walking (see photo of muscle pattern activation during running). Most importantly, regardless of weight horizontal GRF remains exactly the same at any percentage of body weight supported running. What does this mean? It means you can run or walk with the same gait on a LEVER device as you can when you run on any other treadmill! If you compare this to other rehabilitation methods, the same cannot be said. Deep water running must be performed in a specific high-knee style in order to elicit comparable muscle firing patterns. With LEVER, you are able to run or walk in the same gait without even having to think about it.

In summary, LEVER Running helps you recover and heal faster by reducing the amount of load that your bones experience during running, and by allowing you to move in the same gaits that you would for any other normal run! We hope that we have armed you with the scientific knowledge to feel informed and confident about the training tool that is the LEVER LV1. Pt. 2 of this series will explore some of the cardiovascular benefits of training with body weight support!


Nell Crosby, M.S.

Brennan, Christopher T., David G. Jenkins, Mark A. Osborne, Michael Oyewale, and Vincent G. Kelly. “Can Anti-Gravity Running Improve Performance to the Same Degree as over-Ground Running?” Journal of Sports Sciences 36, no. 20 (October 2018): 2273–81. https://doi.org/10.1080/02640414.2018.1449092.


Jensen, Bente R., Line Hovgaard-Hansen, and Katrine L. Cappelen. “Muscle Activation and Estimated Relative Joint Force During Running with Weight Support on a Lower-Body Positive-Pressure Treadmill.” Journal of Applied Biomechanics 32, no. 4 (August 1, 2016): 335–41. https://doi.org/10.1123/jab.2015-0075.


Mercer, John A., Bryon C. Applequist, and Kenji Masumoto. “Muscle Activity during Running with Different Body-Weight-Support Mechanisms: Aquatic Environment versus Body-Weight-Support Treadmill.” Journal of Sport Rehabilitation 23, no. 4 (November 2014): 300–306. https://doi.org/10.1123/jsr.2013-0032.

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