Fabio Comana by Fabio Comana

Refuel and Rehydrate - Fitness FrontlinesThe unfortunate reality for many of us is that the post-exercise period is perhaps the most neglected component of our exercise program, yet possibly the most influential in determining how effectively our body adapts to the exercise stress and recovers. The objective of this blog series therefore is to share various post-exercise refueling and rehydration strategies that will help your clients maximize their training goals and performance.

However, the strategies you ultimately select should always mirror your client or athlete’s specific training goals and consider the amount of recovery time available prior to their next workout. We will classify the strategies under rehydration (most important), glycogen re-synthesis or muscle synthesis. While varying scientific opinions exist on the efficacy of commercially-available recovery agents or specific nutrients like Omega-3 fatty acids, zinc and vitamin C that potentially accelerate recovery, our discussion in this blog will focus upon water and sports drinks for rehydration. Part two of this series will address strategies for glycogen re-synthesis and protein synthesis.

Regardless of the amount of fluid consumed during exercise, it is inevitable that rehydration of body water is critical in recovery, but how much should one consume? A simple method to determine your fluid needs involves measurement of pre-exercise and post-exercise body weight. Before exercise, go to the bathroom (void), then weigh yourself naked or while wearing dry clothes, and repeat this same process after your workout. The weight differential represents your fluid deficit. For example, if Mary’s pre-exercise weight (voided) is 145 lbs. and she weighs 142 lbs. post-exercise (voided), her fluid deficit is 3 lbs. or 48 oz. Does this imply she requires 48 oz. of fluid to rehydrate? Unfortunately not, as some of the ingested water will be lost to urine during the process, but the losses to urine from water versus sports drinks will differ.

Body water exits within two compartments in our body; intracellular fluid (ICF) - fluid located within cells and extracellular fluid (ECF) - fluid located outside cells (e.g., blood, interstitial fluid, tears, etc.). While body water is lost from both compartments during sweating, the majority lost originates from the ECF initially. While both need refilling during recovery, they do so at different rates.

Consuming plain water may eliminate unneeded calories, but it is a slower process. Ingested fluid first enters the ECF and once that compartment is filled, any excess fluid passes to urine before it really has the chance to move into the ICF. Over the ensuing few hours, fluid will slowly shift back into the ICF, partially dehydrating the EFC again. Further water consumption simply repeats this cycle until both compartments are re-hydrated, a process that may take between 6 to 10 hours, and up to 24 hours to complete. Consequently, the guidelines for water consumption recommend 19 – 24 oz. of water for every 16 oz. lost (120 – 150 % of lost fluid volume) to account for urine losses.

Commercial sports drinks on the other hand, being slightly more concentrated than our blood (due to carbohydrates, electrolytes, etc., contained in the product) force the body to retain excess fluid rather than passing it out to urine given the drink’s effect on increasing blood concentration. This in turn pushes fluid more rapidly into the ICF, resulting in faster rehydration rates of both compartments with less urine output. Consequently, rehydration guidelines with sports drinks recommend only 16 – 20 oz. of fluid for every 16 oz. lost (100 – 125 % of lost fluid volume). Sports drinks rehydrate the body more rapidly, an important consideration when time is of essence.

When deciding between water and a sports drink, fitness professionals should consider the need for calories against the urgency in rehydrating. Water is a good thirst quencher, but not as effective as sports drinks when time is important. For most clients who exercise at moderate intensities in moderate climates, and do so every 24 – 48 hours, they are probably better suited drinking water (or some non-caloric flavored water) and sparing themselves the unneeded calories. Any depleted glycogen or lost electrolytes (to sweat) will be adequately replaced with their regular diet.

A lesser concern with rehydration pertains to hyponatremia, a condition defined by inadequate sodium levels within the ECF (blood) attributed to water consumption with inadequate electrolyte replacement. While potentially harmful, inducing altered cognitive function (confusion, loss of consciousness, etc.), it is rare, affecting only 0.6 % of a marathon or endurance-type population and almost zero % of the general population. If individuals sweat profusely, participate in extreme environments (hot and humid) or exercise beyond 60 minutes, fitness professionals should consider using a sports drink over water and avopid any risk, however small of hyponatremia.

Read Refueling and Recovery (Part 2 of 2) where we cover glycogen re-synthesis and protein synthesis.