Why should I care about my Sweat Rate?
Dehydration decreases power output which means LESS CALORIES BURNED!
Dehydration and Performance
Dehydration decreases exercise performance, including maximal aerobic power
The greater the dehydration level, the greater the performance decrement
Dehydration reduces anaerobic performance
Dehydration and Core Temp
Dehydration causes increase in core temp
For every 1% drop in body weight due to dehydration, core temp elevates ~ 0.2°C
How much do we sweat?
Average person sweats between 0.8 to 1.4 liters (roughly 27.4 to 47.3 oz.) per hour during exercise.
Smaller bike water bottles typically hold 0.6 liters (20 oz.)
Larger bottles hold 0.7 liters (24 oz.) of fluid
Most of us do not even empty the water bottle we bring during the class. Even if we drank the full 24 oz water bottle, we would still not have replaced what the average person loses in sweat.
The Sweat Rate Test
Take your nude weight before exercise
Complete your exercise session (30 min – 1hr sufficient)
Take your nude weight after exercise
1 kg body weight lost = 1 Liter
1 lb body weight lost = 16 oz
Must add any fluid consumed and subtract any fluid excreted
Be sure to record the heat and humidity conditions in your sweat test.
Repeat the test in cool and hot conditions.
Repeat the test for swimming, running and cycling
Sweat rates vary with each sport and environmental conditions.
Knowing your sweat rates:
Drinking enough fluid will help replace the fluid lost in sweat
Maintain hydration -->Maintain your power! --> Burn more calories! -->Maintain intensity! -->Top of the leaderboard!
Calculate Sweat Rate
L/hr = [(Weightpre(kg) – Weightpost(kg)]/exercise duration (hr)
Example of a 30 minute test:
L/hr = (56.69 kg – 56.24 kg)/0.5 hr
L/hr = 0.9 L/hr
Convert liters to ounces = L/0.02957
0.9/0.2957 = 30.44 ounces per hour
How much to drink?
30.44 ounces per hour
Divide by 15 minute intervals
30.44/15 = 2.03 or 2 ounces every 15 minutes
8 ounces in 1 cup
2 ounces = ¼ cup
2 ounces = 2 full gulps
3 ounces = 3 full gulps
Example in pounds
145.6 lb Start Weight
143.5 lb End Weight
2.1 lbs = 33.6 ounces (2.1 lb x 16 ounces)
Drank 20 oz + 20 oz + 14 oz = 54 ounces consumed
54 oz consumed +33.6 ounces lost = 87.6 sweated / 2.25 hours = 39 ounces per hour
39 oz per hour/15 minutes = 2.6 ounces every 15 minutes
What do I need to drink?
< 60 min workout, WATER is sufficient
Drinking a Sports Drink increases your caloric intake. If weight loss is your goal, you are adding calories when you are trying to burn calories
> 60 min workout, Water and Carbohydrate/Electrolyte drink is necessary to replace lost sodium in sweat and to supply carbohydrates to maintain the work output.
TIME YOUR DRINK INTERVALS
Now that you know your sweat rate, be sure to set a timer or reminder to drink your specified amount every 15 minutes. It's easy to forget to drink during class. And it has been proven that if left to our own voluntary rehydration, no one ever drinks enough.
Replace any weight lost after your workout
Once your workout is over, if you have still lost weight, that weight lost needs to be replaced with fluids post-workout. So, if I did my best to rehydrate during the workout, and I still lost 1 lb. I will need to replenish with 16 ounces of fluid post-workout.
KEEP YOURSELF HYDRATED DURING AND AFTER WORKOUTS AND YOU WILL FIND YOUR ENERGY INCREASE DURING THE CLASSES AND YOU WILL BE LESS FATIGUED POST-WORKOUT OR FOR THE NEXT DAY'S WORKOUT. DEHYDRATION CAN BE A COMMON CAUSE OF FATIGUE.
Heather Flebbe, M.S., ACSM holds her Master's Degree in Exercise Physiology and is a lecturer at California State University, Los Angeles. Heather also presents for the American College of Sports Medicine certification workshops. She may be reached at firstname.lastname@example.org.