Hydration for Indoor Cycling Sessions

Written by Aitor Viribay from Glut4science, nutritionist and scientific advisor to UCI professional cyclists in collaboration with Crown Sport Nutrition.

Why is Hydration important on the indoor trainer?

Thermoregulation is one of the human body's most complex challenges during exercise because the body converts energy inefficiently. Around 75-80% of energy production is released as heat, so one of the body's priorities is to dissipate this heat to keep thermal homeostasis within physiological levels. Beyond understanding core temperature as one of the main limiting factors of physical exercise, we currently know that this increase entails secondary physiological effects such as increased cardiac output and blood pressure, increased perception of effort, increased catecholamines, and increased glucose consumption (4). All are directly related to the loss of a euhydrated state, which is accelerated in hot environments because the lack of airflow (convection) reduces sweat evaporation (2). This leads to severe dehydration that is determined by a high loss of fluid and electrolytes.

During indoor trainer sessions, the fluid and electrolyte imbalance is far greater than during outdoor exercise, even at high temperatures and relative humidity. Likewise, the relative intensity of the sessions increases due to the particularities of indoor trainer exercise (greater muscular and thermal stress). In this sense, we have been able to document dehydration of more than 7% in professional cyclists during a 1,5h session on the indoor trainer, with a significant increase in urine density and a threefold loss of minerals (especially sodium and chloride) in sweat (unpublished data, personal observations), which allows us to get an idea of the high hydroelectrolyte demands of this type of session.

How should you approach an indoor trainer session?

The importance of not underestimating the demands of an indoor trainer session is decisive when it comes to optimizing the adaptations of these workouts, especially if they are prolonged over time and consecutively.

In terms of hydration, starting sessions in a slightly hyperhydrated state supports better thermoregulation and sports performance (2). In fact, severe losses in performance during exercise lasting <1 h have been documented when starting in a hypohydrated state (5). The two most important factors in hydration during exercise are the following (6).

1. 1. Sugar composition of beverages.
2. 2. Amount of sodium in drinks.

In this sense, an intake of around 7-10 ml/kg of body weight is recommended through a Hypotonic Drink in the 2-3 hours prior to exercise (2). Osmotic agents such as sodium, glycerol or creatine may also play an important role, although creatine's effects in this context remain to be determined. The most widely recommended and studied is sodium, which can be obtained from commercial salt capsules. The approximate amount could be around 300-500 mg/L (7,8).

Figure 1. Absorption of monosaccharides Glucose and Fructose in the intestine. The combination of sugars increases gastric emptying and the intestinal transport rate (9).

Likewise, during exercise it is recommended to ensure a greater fluid intake than during road training. This amount can be around 750-900 ml/h depending on the intensity and duration of the session, through Isotonic Drinks with different types of sugars such as Glucose or Maltodextrin and Fructose (10). Along these lines, beyond an increase in gastric emptying and transport of sugars in the intestine, a significant increase in net water absorption has been documented through the joint intake of different sugars with respect to a single monosaccharide (7).

Similarly, the intake of osmotic agents such as sodium increases the absorption and retention of ingested liquid, limiting internal losses. During indoor trainer sessions, therefore, a high intake (750-900 ml/h) is recommended of a beverage containing sugars (6-9% or 30-45g per 500 ml) that use different intestinal transporters, with approximately 600-700 mg/L of sodium (2,10,11). Regarding the rate of intake, recent studies show that a higher frequency of intake (15 min vs 30 min) offers benefits in sports performance, coinciding with previous knowledge about greater gastric emptying every 20 minutes (12). Therefore, an intake frequency of 15-20 minutes is recommended. Drink temperature is also important, as it directly influences thermoregulation. An approximate temperature of 8-12ºC is recommended.

Figure 2. Net absorption of water in relation to the osmolality of beverages. F and E drinks, with a combination of sugars, also improve passive water transport (7).

After an indoor trainer session, fluid and electrolyte replacement is a priority. Although body weight and urine color are not sufficiently reliable or precise research measures, they appear to be useful practical tools for monitoring hydration status (12). In this sense, fluid intake is recommended at around 150% of the weight lost during the session (if 1 kg has been lost, intake of 1,5L)(11,13). To this end, it is important to drink slightly isotonic drinks (5-6%) that provide sugars with different intestinal transporters, as well as a minimum amount of sodium close to 500 mg/L. The effect of possible ergonutritional aids such as creatine, whose effects on fluid retention have been demonstrated, on hyperhydration after exercise remains to be determined.

Recommendation with Crown Sport Nutrition products:

• Pre-hydration with 2 scoops of Isodrink & Energy dissolved in 1L of water.
• During the exercise:
  • Light sessions: 500 ml/h + 1 scoop of Isodrink & Energy + 1 PRO Salts Caps tablet
  • Moderate sessions: 500 ml/h + 2 scoops of Isodrink & Energy + 1 PRO Salts Caps tablet
  • Intense sessions: 750-900 ml/h + 2 scoops of Isodrink & Energy + 2 PRO Salts Caps.
• After exercise: 2 scoops of Isodrink dissolved in 1L of water + 3 PRO Salts tablets depending on the weight lost.

AUTHOR

Aitor Viribay Morales – Nutritionist and Scientific Advisor to UCI Professional Cyclists. Founder and Director of Glut4Science (www.glut4science.com)
Instagram: @glut4science
Facebook: Glut4Science
Twitter: @glut4science

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