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Weight Bearing during Immersion: Start to Move and All Bets are Off

Many therapists count on the use of buoyancy to reduce joint load. But is it possible that the pool is not a safe place for everyone, always? Let's investigate.

Does immersion in the pool produces a reduction in joint load? Absolutely! Here is a useful article that tells more about this reduction of load and how you can ballpark how much load is reduced based on the level of immersion on each person.

  • Stuart, A. R., Doble, J., Presson, A. P., & Kubiak, E. N. (2015). Anatomic landmarks facilitate predictable partial lower limb loading during aquatic weight bearing. Current orthopaedic practice, 26(4), 414-419.

But while it is true that load is reduced in water, the piece often forgotten by therapists is that this study (and similar studies) quantified load while standing still. And while it is possible to have dramatic decreases in joint loading in the pool because of buoyancy, you have to understand that all bets are off once you add movement.

  • Haupenthal, A., Ruschel, C., Hubert, M., de Brito Fontana, H., & Roesler, H. (2010). Loading forces in shallow water running in two levels of immersion. Journal of rehabilitation medicine, 42(7), 664-669.

And what of jumping and leaping and other vertical translation activities like plyometrics? Aquatic-based plyometrics are beloved because they product much lower joint compression forces than land-based jumping, but they don't produce "none". In fact, they can produce double (or more) the amount of load as standing still on land does.

  • Held, N. J., Perrotta, A. S., Buschmann, L. K., Bredin, S. S., & Warburton, D. E. (2019). A systematic review of the efficacy of lower body aquatic plyometric training: the development of evidence-based recommendations for practitioners. The Health & Fitness Journal of Canada, 12(1), 17-33.a

To complicate things, once you start rapidly moving limbs against water, especially if you have a resistive device like a fin on their foot, drag now creates a new force. And drag can create 300% of the load of movement on land.

  • Kutzner, I., Richter, A., Gordt, K., Dymke, J., Damm, P., Duda, G. N., ... & Bergmann, G. (2017). Does aquatic exercise reduce hip and knee joint loading? In vivo load measurements with instrumented implants.PloS one,12(3), e0171972.

So, the question that therapists have to ask when looking to the pool for load reduction is: How deep, how fast, how high (out of the water), and how hard (resistance)?

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