Pacing + Hydration advice needed for sprint event in heatwave

What have been temps during the bulk of your training?  

If you're reasonably acclimated to the heat, consider racing but...

slow down
cover up
hydrate, hydrate, hydrate.

If you're not acclimated, you'll have to decide if you can recognize and heed the early warning signs or things get dangerous in a hurry.  

Only you can answer the question of whether you should race or not. 

As to pace, this is where having an accurate RPE-O-meter becomes very useful.  Your HR is going to be elevated because of the heat and your pace is going to be slower for the same reason.  RPE "takes into account" environmental conditions.  Listen to your body - it will let you know if you are going to hard.

Take in a good breakfast before the race, maybe a gel half-an-hour before and you should be good unless you are going to be on-course for more than 90-minutes or so.  If you expect to be on-course for more than 90-minutes, take a gel in towards the end of the bike and you'll be fine,  If you're using a sport drink (Gatorade, Infinit, etc.) for hydration you likely wouldn't need the gel on-course.

For hydration, you need to know your sweat rate in as close to race conditions as possible.  Just taking in massive amounts of hydration with no thought to volume can lead to problems - specifically Hypernatremia.

The first step in developing a proper race day fluid replacement plan begins with understanding your body’s true hydration requirements – knowing your sweat rate and understanding what it means.

Hydration is very important to race day performance.  Water makes up over 60% of our body and is involved in everything from energy production in the cells to transporting oxygen through exercising muscle.  Even slight de-hydration can slow you down, cause overheating, and lead to serious gastrointestinal problems. The other side of the coin – over hydrating – can increase your risk of developing hyponatremia, an abnormally low level of blood sodium that can be serious and even fatal.

GETTING STARTED

To find your personal race day hydration sweet spot – not too much and not too little – begin by setting up a program to regularly check your sweat rate for both the run and cycling throughout your training season (obviously since the race is only a few days away you aren't going to do repeated tests, next season, you'll be served well by testing frequently in different conditions).  Yes, your sweat rate will likely be different for running and cycling.  Regularly testing your sweat rate will indicate changes brought by weather/humidity, your acclimation and changing fitness levels.  Record the collected data in a spreadsheet or flowchart.  Looking back at your data prior to a race will allow you to fine tune your hydration plan for expected conditions at the race venue.

SWEAT RATE TEST

Make sure you are properly hydrated before beginning the test.

1. Weigh yourself nude before a ride/run.
2. Ride/run for one hour keeping track of your fluid intake in ounces.
3. After the ride/run, towel off, and weigh yourself nude again.
4. Subtract your post-run/ride weight from your pre-run/ride weight and convert to ounces. To that number, add the number of ounces you drank during the test.  For example, if you lost one pound and drank 16-ounces, your total fluid loss was 32-ounces.
5. To calculate a hydration plan, divide the fluid loss by the number of times you will drink per hour. For example, if you will drink every 15-minutes, divide 32 by 4.  You will need to drink 8-ounces every 15-minutes.

ELECTROLYTES

Using the results of this test will replace most of the fluid you lose through exercise.  It may not be accurate for everyone so use caution and verify the results in training.  Only replacing fluid with water will NOT replace important electrolytes so you should consider a sports drink such as Infinit for your fluid replacement.