If you have an upcoming race at altitude and don't have the ability to to prepare at elevation, don't sweat it! Including some heat training is a decent alternative. Research supports heat acclimation as a way to reduce physiological strain and improve performance in hypoxic environments. Basically, your system is more tolerant to higher altitude after you are acclimated to the heat.
The process of heat acclimation may also be a less stressful way to induce adaptations in a shorter timeframe compared to altitude training involving hypoxic exposure. The average amount of time required for adaptations is 7-10 days, possibly less for men than for women. Physiological adaptations from heat acclimation include increased plasma volume and sweat rate, in addition to lower exercising heart rate and core temperature.
So how do we actually heat train? There are two main ways: active and passive heat exposure. Both have pros and cons.
Active heat training
Complete your training sessions in the heat.
Pros:
Ninety minutes of training in a hot environment for ~7-10 days appears sufficient to induce adaptation without additional equipment, tools, or time commitment.
Cons:
Interval workout quality and performance is impacted, so active heat training is best suited to easier endurance rides.
Passive heat exposure
Complete training sessions in a normal, comfortable environment and utilize heat exposure in a sauna or hot water bath post-workout.
Pros
30-40 minutes of hot sauna or immersion in 104 degree F water ASAP after training for ~7-10 days appears sufficient to induce adaptation without compromising workout quality and interval training.
Cons:
Requires additional tools (sauna, hot tub or hot bath) and additional time required to complete the protocol, above and beyond training hours.
As always, discuss the options with your coach, and with your doctor if you have any medical issues. Make sure to drink plenty of fluids when undergoing heat training and rehydrate with sodium containing fluids.