Most people are aware that our body mass is composed of roughly 50-70% water (1). Yet very few people pay direct attention to their individual hydration requirements. Here are a few facts that should make you reconsider the significant role of hydration in athletic performance.
- 1% reduction in hydration can result in up to 10% reduction in strength (2)
- 4% reduction in hydration can result in 20-30% reduction in physical work capacity (2)
- 50-90% of people fail to meet water consumption guidelines (2)
Based on the above figures, it’s easy to see the strong association between hydration and athletic performance. And probabilistically, it’s likely you fall into the category of not meeting the water consumption guidelines. But I want to be clear about something, proper hydration is not about water consumption alone. Although that is an important part of the equation, there are several other components that determine whether or not the water you drink will hydrate you or actually have a negative effect on your hydration status. This article will offer a basic overview of hydration, as well as give practical guidelines to ensure optimal hydration status is reached for your individual goals and circumstances.
The role of hydration is significant. water acts as a transport medium, lubricant for joints, it facilitates chemical reactions, acts as a thermoregulator and a solvent. There are various factors that impact an individuals hydration status such as the sport being played, bodyweight, climate, exercise, individual physiology, diet composition, lifestyle etc. It’s been observed that individuals at higher bodyweights sweat more. Food composition also has a role. Sources of water are typically 50% water from food, 30% fluid (coffee, sodas, etc) and 20% actual water. Highly processed foods are dehydrated through cooking and often have added salt which further disrupts hydration balance. The image below details some of the factors influencing hydration:
I had previously mentioned a 4% reduction in hydration can result in a 20-30% reduction in physical work capacity. This is for several reasons including reduction in blood volume, decreased skin blood flow, decreased sweat rate, decreased heat dissipation, increased rate of muscle glycogen utilization, increased core temperature, increased perception of difficulty and so on. There is no shortage of papers demonstrating significant performance degradation when dehydrated (3)(4)(5)(6)(7)(8). Which gives rise for concern since most athletes will only rehydrate approximately 50% of the lost fluid post exercise.
One paper looking at endurance capacity found “Run time for the NF-trial (no fluid trial) was 77.7 +/- 7.7 min, compared to 103 +/- 12.4 min for the FR-trial (fluid replacement trial) (P < 0.01). Body mass (corrected for water ingestion) decreased by 2.0 +/- 0.2% in the NF-trial and 2.7 +/- 0.2% in the FR-trial (P < 0.01), while plasma volume decreased by 1.1 +/- 1.1% and 3.5 +/- 1.1% in the two trials respectively (N.S.). However, these apparent differences in circulatory volume were not associated with differences in rectal temperature. Respiratory exchange ratios indicated increased carbohydrate metabolism (73% vs 64% of total energy expenditure) and suppressed fat metabolism after 75 min of exercise in the NF-trial compared with the FR-trial (NF-trial, 0.90 +/- 0.01; FR-trial, 0.86 +/- 0.03; P < 0.01). Blood glucose concentrations were similar in both trials, while blood lactate concentrations were higher in the NF-trial at the end of exercise (4.83 +/- 0.34 vs 4.18 +/- 0.38 mM; P < 0.05)” (9). Essentially what they found is fluid replacement enhanced endurance capacity.
But as I mentioned previously, hydration is not as simple as drinking more water. Hydration balance refers to the actual volume of water as well as the concentration. We know that the water distribution throughout our body is approximately ~66% intracellular, ~27% extracellular, and ~7% in blood (1). Roughly 98% of potassium is in our cells, and most sodium is in the extracellular compartments. Sweat consists of sodium, potassium, chloride, magnesium, and calcium which makes up roughly 1%. While the remaining 99% of sweat is composed of water. We lose water and minerals from extracellular fluid when we sweat. Intracellular compartments then transfer water to preserve the balance between intracellular and extracellular volume and concentration. This reduction in intracellular and extracellular fluid volume increases the mineral concentration which disrupts hydration balance. So optimizing hydration isn’t as simple as drinking more water, instead we need to balance total fluid volume with concentration.
Practical Applications To Optimize Hydration
So in order to optimize hydration we need an operational definition. In their 2016 paper Kenefick and colleagues stated “Adequate fluid intake can be dually defined as a volume of fluid (from water, beverages, and food) sufficient to replace water losses and provide for solute excretion” (10). Broadly speaking what this paper also highlights are three primary recommendations to ensure hydration is achieved (11)(12):
- Beginning exercise in a hydrated state (euhydration)
- Preventing dehydration beyond 1.1% of body mass during exercise (hypohydration)
- Replenishing minerals and water lost during exercise
Kenefick mentions three primary indicators to determine your hydration status.
- Bodyweight. Measured in the morning to increase precision.
- Thirst first thing in the morning.
- Colour of urine using the 8-color scale urine hydration chart
If diet is relatively consistent, fluctuations in body weight can be indicative of fluctuations in your body’s fluid volume. Evaluating thirst on a scale of 1-10 and observing the colour of your urine are also good observational tools to evaluate your hydration status. The venn diagram below gives you an idea of how these three metrics are related. No metric in isolation is an indication of dehydration. But if two metrics line up it’s likely you are dehydrated, and if all three line up it’s very likely you are dehydrated.
The image below is an 8 colour scale urine hydration chart. It’s part of the subjective evaluation of hydration status first thing in the morning.
As mentioned previously in order to ensure hydration balance we need to balance fluid intake with mineral concentration. Sodium and chloride are the primary constituents that balance the concentration. Potassium, calcium and magnesium are also important but less so. Additionally, losses in calcium and magnesium are not large and optimal levels can be maintained through consumption of specific foods. Below is a short list of foods rich in these minerals. You’ll notice spinach is high in all three (potassium, magnesium, and calcium):
- Sweet potatoes
- Leafy greens
- Spinach and leafy greens
- Bread made with fortified flour
- Sardines and pilchards
- Whole meal bread
Ideally you want a 4:1 ratio of sodium to potassium. Mixing a pinch of sodium chloride (table salt) in a litre of water is an excellent way to replenish sodium and chloride. If you’re inclined to increase precision of water intake beyond the subjective scale mentioned above you can use more advanced instrumentation which may not be
Carbohydrates can also play an important role in the hydration process during post-exercise recovery. Since carbohydrates trigger the release of insulin which drives nutrients into cells it also aids in cellular hydration. This is also one of the reasons many sports drinks contain some form of carbohydrate. Products like ceralyte, drip drop, and LMNT can also be an effective supplement to assist in rehydration during and post exercise. They have good concentration profiles and you can use more or less depending on your individual needs. They are low in carbohydrates which may or may not be a drawback depending on the users goals and diet. One thing to be mindful of is fluid consumption during exercise may make gastric emptying more difficult (13). And although your body does adapt to this, it’s likely not a good idea to chug a bunch of fluids at one time during exercise. Rather, take periodic breaks to consume smaller portions of water to minimize GI distress.
Hopefully by this point you understand that hydration is more nuanced than simply drinking more water. Ideally you can take some of these guidelines and apply them to see better results with your hydration and sports performance.