In hotter temperatures during summer races, it is important to keep your core temp as low as possible for as long as possible. Long warm ups are likely to be counterproductive.
Having tried different warmups over many years, and working with a top coach who had advantage of testing a bunch of decent masters amateurs, what seemed to be best for me and many others, is a short 15-20 minute “priming” warm-up. The “world tour” warm-up routines are too much and just spinning for 10, 15, or 20 min is not enough.
The trick is to “prime” your body for the effort to come by eliciting a high heart rate for a short period. You aren’t doing a work-out or inducing fatigue, you are simply opening up and getting ready for the hard effort (race).
To do this, just do a quick ramp. Here is my basic warm-up protocol:
(1) 5-10 min easy spinning. This just gets the legs moving and also lets you shift the bike and make sure everything is working with the bike, your power meter and HR strap.
Start very easy and every few minutes ramp up a gear. My target wattage for a 40km event is 235-240w so will start around 125-130w and end the easy warmup segment around 185-200 watts.
(2) 1-2 min spinning. Have a drink. Check your start time and go through your final mental checklist.
(3) Priming step. Short ramp of 3-4 min duration. Start around 150 watts and shift up every 20-30 seconds. 150-180-210-230-250-275-300w progression. For me that gets my HR within 5-10 BPM of HR max. That’s what you are looking for. Adjust as needed for your FTP and HRmax.
(4) 3-5 min easy spin. Another drink. Slam final nutrition if that’s your thing. Hop Off the bike. Final nature break if needed on way to start. Get to the start line.
(6) Cool down. I always spin 20-30-40 min after a short race. After a 40km, am generally shattered and just roll around for 10-15 then pack up. Drink and eat. Especially hydrate in hot summer races.
The longer the event and the hotter the temperature, the shorter the warm-up.
Good luck and if folks try the above report back how it worked for you.