Fluid and Electrolyte Replacement in HOT Temperatures
One thing we can all agree on is that it is HOT HOT HOT and will be for at least a couple more months! Whether you are an early morning or late afternoon exerciser, you are likely to experience much larger fluid losses during this time of year as evidenced by squishy shoes and drenched clothes. In order to receive optimal benefits from each workout, it is vital to properly replace lost fluids and, for some, electrolytes in order to recover fully before your next scheduled training session.
There is no other nutrient as essential or needed in as great an amount as water. Water makes up 45-75% of our body weight. Every body system requires water for function. It is essential for proper regulation of body temperature, elimination of waste products, regulation of heart rate, digestion of food, and lubrication of joints. When we exercise outside during warm summer months and our core body temperature increases, we will begin to sweat as a cooling mechanism. We are not only losing fluid through sweat, but also vital electrolytes, including sodium, potassium, magnesium and calcium. Concentration of sodium in sweat is much greater than that of potassium, calcium and magnesium. So, when we think about fluid loss, we must not forget about electrolyte loss, specifically sodium, as well. Recommendations for daily fluid intake for the standard adult can depend on a number of variables, but most health organizations agree that on average females require 9 cups and males 13 cups of water per day.
Those exercising to maintain normal fitness levels (30-60 minutes of moderate exercise 3-4 days per week) can meet daily fluid and electrolyte needs through normal food and beverage intake and probably do not require deliberate replacement. However, athletes who train outdoors during hot summer months may struggle with dehydration and large sodium losses if not focusing on proper replacement following workouts. When attempting to train even mildly dehydrated, an athlete may experience muscle cramping and fatigue, frequent headaches, and lethargy.
Fluid and electrolyte needs for athletes are individualized based on various factors including, a person’s size, activity level, metabolic rate, makeup of the diet, losses during activity, weather conditions, etc. Relying on thirst to trigger drinking is not wise as mild dehydration could already be taking place when thirst is stimulated. Rather, measuring sweat losses and monitoring urine color and frequency are better assessment tools. To properly assess fluid and electrolyte losses it is recommended to know your individualized sweat rate. As soon as you wake up in the morning and use the restroom, weigh yourself nude and note the weight. After exercising, weigh again and note the difference, or your sweat rate. Once you know your sweat rate, you can refer to the below formula for fluid replacement before, during and after exercise:
16-20 fl oz 4 hours prior to activity; 5-10 fl oz 10-20 min prior to activity based on tolerance.
Drink to prevent dehydration; defined as < 2% loss of body wt using your sweat rate.
2-3 cups of fluid for every pound lost using your sweat rate as a guide.
Many athletes will be able to properly replace electrolytes with a normal daily intake of wholesome foods. However, if you limit your sodium intake on a daily basis, have a high sweat rate, or workout in the heat up to 2 times per day, it is recommended to consume 250-500 mg sodium per hour during exercise, the amount in approximately 20-40 fl oz of common sports drinks or electrolyte tablets. A healthy diet rich in fruits, vegetables and minimally processed whole foods should replace calcium, magnesium and potassium without the need for deliberate replacement.
Ideally, it is best to replace fluids throughout the course of a day, rather than consuming large amounts at one time. Pre-loading large amounts of fluid and electrolytes prior to workouts is not recommended because your body can only utilize so much at one time. Rather, consistently drink throughout the day in preparation for the next scheduled workout.
As an athlete wanting to maintain strength and fitness during the long summer months, it is vital to assess your fluid and electrolyte losses and replace as necessary. In doing so, you will be able to not only maximize each workout, but recover much faster. If you are wanting a more individualized assessment of your daily fluid and electrolyte needs for your specific training goals, contact a Registered Dietitian and stay cool!!!
Rosenbloom, C. Coleman, E. Sports Nutrition A Practice Manual for Professionals. 5th Edition
Clark, N. Nancy Clark’s Sports Nutrition Guidebook. 4th Edition