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

Standing still in chest-deep water, a hip carries a fraction of its land load. Kick fast with a fin on the foot, and the same hip can carry about three times body weight.

Here is why “the pool unloads joints” is only half true.

Want to go deeper? Explore the 12 Ways to Progress Any Aquatic Exercise course →

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 one lab study, jumps in water cut peak landing forces by 33% to 54% compared with land: lower, but still real.²

• 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.

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. In one study with instrumented implants, fast leg movements with fins raised hip and knee forces by up to 59%, to as much as about 300% of body weight.¹

• 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)?

Other References:

1. Hoogenboom, B. J., & Lomax, N. E. (2024). Aquatic therapy in rehabilitation. In Rehabilitation techniques for sports medicine and athletic training (pp. 379-404). Routledge.

2. Abadi, F. H., Sankaravel, M., Zainuddin, F. F., Elumalai, G., Choo, L. A., & Sattari, H. (2020). A perspective on water properties and aquatic exercise for older adults. International Journal of Aging Health and Movement, 2(2), 1-10.

For education only; not a substitute for individual clinical judgment.