Hydration status is measured by monitoring changes in body mass, assessing urine color, and measuring the osmolarity of body fluids. Using several methods together produces a more reliable assessment than relying on one measurement.
Hydration status reflects the balance between water intake and water loss. In IB SEHS A.2.1, each method provides different evidence about water and electrolyte balance.
| Method | Interpretation and procedure | Main limitation |
|---|---|---|
| Body weight | Measure body mass before and after exercise using the same scales, similar clothing, and consistent conditions. A short-term loss of approximately represents about of water loss. | Food, drink, urine production, clothing, and measurement conditions can affect the result. |
| Urine color | Compare urine with a standardized color chart. Pale urine generally suggests good hydration, while dark yellow or amber urine indicates more concentrated urine and possible dehydration. | Foods, supplements, medication, and recent fluid intake can alter urine color. |
| Osmolarity | Measures the concentration of dissolved particles per litre of solution. Higher urine osmolarity indicates concentrated urine and greater water conservation; lower urine osmolarity indicates more dilute urine. | Laboratory equipment is required, and results depend on whether urine or plasma is tested. |
Percentage body mass loss can be calculated as:
For example, an athlete falling from to has lost , equivalent to of initial body mass. Fluid consumed and urine produced during exercise should also be considered.
A common misconception is that clear urine always proves optimal hydration. It may instead indicate excessive recent fluid intake, so it should be interpreted alongside body mass and osmolarity.
In an IB response, describe the procedure, explain what a high or low result indicates, and state one limitation. Do not simply list the three methods.