Lukus Klawitter M.S, CSCS

Hello all, I apologize for the delay in training blogs recently, as most of you can likely relate to, it has been a hectic year.  You may think that a discussion of core body temperature regulation would be a topic for the warmer of months of the year, being that it is -6 degrees Fahrenheit in Fargo currently…  However, indoor cycling does not get the benefits of wind for cooling and drying, as we do when riding outdoors.  When riding indoors overall body temperature increases at an exceptional rate and therefore, a higher sweat rate as sweat is the body’s main source of cooling.  And no, fans just are not the same.  Right, I know, if it is soooo (insert Minnesota accent) cold why not just open a window to cool the room down and cool body temperature.  The window is likely frozen shut and some of us have dexterity issues, that’s a different topic for another time. 

Optimal hydration for individuals differs greatly, but for the purpose of this post, it is necessary to emphasize the physiological implications dehydration has on exercise performance.   During exercise our working tissues need blood flow to maintain intensity.  Blood flow during exercise is mainly delivered to the muscle and skin, which in turn, creates a battle of blood flow to the skeletal muscle and skin counterparts.  It is also important to know that elevated body temperature leads to a reduction in the amount of blood the heart can pump out each minute (Cardiac Output).  Reducing cardiac output during periods of high heat stress or hyperthermia could therefore impact performance because less blood is available to be delivered to the working muscles.  For an endurance athlete a reduction in blood flow can be detrimental as our blood carries the needed oxygen to the muscle in order to maintain exercise and energy output.  Therefore, prolonged exercise at submaximal intensities in heat will lead to dehydration and a reduction in cardiac output, impacting the ability to maintain intensity.

Understanding how heat stress affects our abilities to maintain exercise intensity while cooling the body is essential for endurance performance.  Dehydration is often a precursor to heat related stresses on the body.  Hydration strategies in endurance sport is quite technical.  Many factors can influence how much volume of fluid and the electrolyte contents your body needs.  Some research has stated that drinking ad libitum or drinking to the perception of thirst is enough to maintain adequate hydration levels, which reduces the risk of under or overdrinking.  It is also important to understand that previous hydration status, food consumption, caffeine consumption, and environmental variability all can have an affect on how much fluids is needed during prolonged exercise.  This makes drinking to thirst or ad libitum maybe not the best route.  Another rather simple method of addressing hydration status is measuring total body weight before and after exercise. To do this record your pre- and post-exercise weight in kg.  Multiply post-exercise body weight by 100 and divide it by pre-exercise weight and subtract by 100.  One kg of body weight lost is equivalent to roughly 1l of fluid.   

One study sought to determine the influence of this personalized hydration strategy compared to drinking to thirst in a timed to exhaustion indoor test.  The personalized hydration strategy led to greater time to exhaustion, lower skin temperature, and lower heart rate compared to the drink to thirst group.  This study only utilized water for the purposes of their experiment.  If you are mainly cycling indoors during the winter months, environment is rather consistent.  However, if implementing this strategy for race preparation, then you want to try to mimic race environment as best as possible, which makes things more difficult.  When training or racing we also need to take into account duration/intensity/skill level/environment/etc. and optimal carbohydrate and electrolyte percentages for best possible performance. 

The major takeaways here is that adequate hydration is essential for training in all environments indoors and out.  In order to keep skin temperature controlled and oxygen filled blood flow to the working muscles, fluid intake should not be taken for granted.  The blog posts to come will discuss adequate carbohydrate and electrolyte intakes for endurance performance. 

Pleasant training.

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