How hydration status is measured?

In the world of mixed martial arts achieving the goal to make weight on time is the difference of being classed as “professional” or “unprofessional”. There has recently been a few MMA athletes who have not made weight and if they have it has been seen as controversial but we’re not here to talk about that stuff. We’re here to talk about hydration status and how it is measured. This is the first of three articles which looks at how hydration can be measured, the different signs of dehydration and the effects of dehydration on performance.


The human body is made up of 60-70% water and is vital for a number of physiological functions such as biochemical and metabolic reactions, substrate transportation across cellular membranes, temperature regulation and other regulatory functions which help maintain homeostasis (L. E. Armstrong, 2005). It is also important to understand where fluid is lost from the body and how it affects total body water (TBW).

Hydrations Status

Hydration status is a measurement of fluid balance in the body. There are three classifications (L. E. Armstrong, 2005; Kavouras, 2002).

  • Hydrated – When the body is in optimal fluid balance.
  • Dehydrated – When the body is in a negative fluid balance. (during weight cut)
  • And over hydrated – When excess fluid has been consumed. (water loading)

How hydration is measured

There are a number of different ways in which hydration status can be measured.

Isotope dilution is seen as the gold standard for measuring hydration status because it is able to occupy intracellular and extracellular spaces which accounts for 63.3% of total body water (TBW) (Lawrence E. Armstrong, 2007; Sawka et al., 2005). Isotope dilution involves the use of either radioactive, stable or non-radioactive solutions. The term gold standards refers to mainly laboratory conditions where exercise, dietary and environmental factors can be under control compared to the real life or field environment. Isotope dilution is expensive, requires a high level technician to carry out the tests and results are best when body fluids are stable (Lawrence E. Armstrong, 2007). During fight camp training or competition body fluids are rarely stable and with a number of interval tests required to analyse the data this can be an impractical way to measure hydration status for most MMA athletes.


Bioelectrical impedance analysis (BIA) is a non-invasive procedure which uses resistance from electrical current to determine total body water and body composition. The key principles for BIA is based around water as a conductor of electricity. It works with electrodes being placed on the hands and feet to create a circuit.


As fat free mass (FFM) contains water and ions, electrical current will predominantly travel through FFM compared with fat mass which acts as a resistance to the electrical current.


Overall BIA uses a number of equations of anthropometric measurements and data for both weight and height. It is widely used in large population studies as it is portable and relatively inexpensive compared to other methods. It has been tested as a reliable source for measuring total body water (Shanholtzer and Patterson, 2003) and with the high volume of physical activity MMA athletes participate in each week it is important to make sure hydration status is balanced both pre and post workouts. It also has the benefit of body composition readings which I will cover in another article.

The most common method used to measure hydration status is urine. A number of different variables or metabolic waste products such as nitrogen, potassium (Na+), ketone bodies, sugars and both red and white blood cells can be identified from a urine sample (Williams et al., 2010). Armstrong (2000) concluded the relationship between urine colour, specific gravity and osmolality and is why we use urine colour chart to help identify hydration status.


Changes in body mass mainly occur due to water loss from sweat, respiration and increase urine production. Sweat rate in athletes is very important to know and understand as it can range from 2-3 litre/hour and can vary due to temperature, duration, intensity, humidity, heat acclimatisation and body mass changes. I now see a lot of MMA athletes on their Instagram promoting the “real work”, “hard work” and “man’s work” with images of their sweat pools on the floor. This is all good but when the sweat rate exceeds fluid replacement the body is unable to cope. Skin blood flow slows down and there is a reduction in sweat rate which causes an increase in core body temperature. This is why there is a need for MMA athletes to regularly assess their pre-post exercise body weight in order to determine sweat rate in order for correct fluid replacement to be achieved as well as being able to customise an individual hydration program based around training. During exercise you should minimise body weight losses to around 1-2%. When rehydrating it is vital that water is consumed alongside a drink containing sodium (sports drink). Sodium aids in the absorption of water increasing the process of hydration as well as helping to plasma sodium concentration and osmolality. A reduction in these can have increase stress and pressure on the cardiovascular system such as increased heart rate.


So we know that hydration status can be measured in different ways but what is important is that you also understand the signs of dehydration before you become dehydrated. If you are an athlete or just really into fitness finding the correct method to measure your hydration status is vital and being hydrated will help enable you to perform to your maximum as well as aid in recovery during training and competition.

(by Daniel Hendrick Bsc)



  • Armstrong, L. E. (2000) Performing in Extreme Environments. [Book] Champaign, Ill: Human Kinetics.
  • Armstrong, L. E. (2005) ‘Hydration assessment techniques.’ Nutr Rev, 63(6 Pt 2), Jun, 2005/07/21, pp. S40-54.
  • Armstrong, L. E. (2007) ‘Assessing Hydration Status: The Elusive Gold Standard.’ Journal of the American College of Nutrition, 26(sup5), 2007/10/01, pp. 575S-584S.
  • Kavouras, S. A. (2002) ‘Assessing hydration status.’ Curr Opin Clin Nutr Metab Care, 5(5), Sep, 2002/08/13, pp. 519-524.
  • mfony, A. (2015) Woah-termelon. wordpress: [Online] [Accessed on 19/04/2017]
  • Sawka, M. N., Cheuvront, S. N. and Carter, R. (2005) ‘Human Water Needs.’ Nutrition Reviews, 63(s1) pp. S30-S39.
  • Shanholtzer, B. A. and Patterson, S. M. (2003) ‘Use of bioelectrical impedance in hydration status assessment: reliability of a new tool in psychophysiology research.’ Int J Psychophysiol, 49(3), Sep, 2003/09/26, pp. 217-226.
  • Williams, G. J., Macaskill, P., Chan, S. F., Turner, R. M., Hodson, E. and Craig, J. C. (2010) ‘Absolute and relative accuracy of rapid urine tests for urinary tract infection in children: a meta-analysis.’ Lancet Infect Dis, 10(4), Apr, 2010/03/26, pp. 240-250.


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