Physiological changes occur as we train and race in the heat and some considerations should be made. Many Durata athletes’ have been bringing this up with their coaches here in the first real week of hot Texas weather and if you’re not in TX don’t worry it’ll be hot where you are or are racing soon enough, so read up
Fatigue has been shown to develop in an athlete once a core temperature of ~40deg Celsius is reached. Interestingly it does not matter how well trained the athlete is, what there acclimatization is like, body size, starting temperature or relative intensity. The only thing that these variables may influence is the amount of time it takes to reach the 40deg mark. For example someone that is acclimatized to TX summers or has better fitness may be able to go longer at a relative workload before reaching 40deg core temperature than someone that is not acclimatized. Unfortunately the larger the athlete the more heat seems to negatively affect their performance. The good and bad news is that heat affects everyone, so if you have properly prepared for it and can tolerate it more effectively then you will triumph over your competition.
During training a few key points should be noted. It has been shown that the rating of perceived exertion (how hard you are working) increases exponentially as the temperature rises. This is true at the same relative workloads; in fact RPE rises faster in warmer environments at lower power outputs than it does in cooler environments at higher power outputs. This is to say that you’re not a wimp it indeed does feel harder to do those intervals at 250 watts or 6:30/mi pace when it’s hot out. Your body is also working to protect itself when exercising and once the core temperature rises, or possibly even when the body anticipates that the core temperature is going to rise it begins to decrease the activation of skeletal muscle. So, your brain is not telling your body to slow down, it’s simply stops sending signals to the muscles for contracting and you have to slow down. Typical of anything there are many levels at which these two control mechanisms operate but as an athlete what you are concerned with is how you can get the most out of your training and racing.
As ambient temperatures increase the body begins to compete for blood flow. Blood flow must get to the skin in order to permit cooling through sweat, but while exercise blood flow must still make it to the working muscle to supply it with the needed oxygen and nutrients for contraction. This shift in blood distribution forces the heart to beat faster in order to maintain the same cardiac output (Heart Rate x Stroke Volume) because less blood is being returned back to the heart (venous return). Dehydration also plays a role in this increased heart rate as blood volumes fall due to fluid loss the volume of blood that is pumped by the heart/beat decreases, in order to compensate heart rate speeds up. This is known as cardiac drift.
One of the most important things to do is to pace you training efforts and racing accordingly. If you know that you have until your body temp hits 40deg before you start to fatigue then it does you no good to exert yourself more than absolutely necessary early on in a workout or race. If working out in warm conditions, plan to get the entire workout by starting off a little easier than you normally may, hold the lower end of your power or pacing range if possible. Also if racing, especially in triathlons or time trials do not start off so hard that you bring your core temperature up so quickly that the 2nd half of your effort or your run off the bike suffers dramatically, start off a little easier and slowly go harder.
Interestingly exercise in heat has been shown to shift substrate utilization. Notably carbohydrate use goes up, with that it’s important to make sure you are taking in an appropriate amount of carbohydrate day to day as well as during your workouts. For more information on how you should structure your diet specific to your own needs consult a registered dietician. Amazingly much of our nutrition work with athletes shows that nearly 70% of them under eat! Even those that are trying to loose weight restrict caloric intake too much, to a point of undermining their own weight loss, training goals and general health.
Stay cool for as long as possible. There is some evidence to suggest that if you can keep the core temperature lower prior to a race you in effect buy more time while racing or training before hitting that 40deg mark. This is a reason ice vests were so popular in the Sydney, Athens and Beijing games. If you can drop you core temp even marginally it might allow you to exercise a little longer before fatigue. This could mean the difference in a Gold or Silver, that hard earned Kona spot or sticking a break all the way to the finish. Ice vests are not readily available but what you can do is try to time your warm up to be in the shade or even inside and possibly even reduce the intensity or duration of your warm up in hot environments.
There have been some reports on wattage and pace being significantly lower when exercising in the heat with or without fans or in warm environments. Many of the typical responses occur in these situations decreased workload, increased RPE, increased heart rate and a decreased time to fatigue. In the real world our consultants report that athletes tend to be about 5-15 watts lower or 5-10 seconds/mi slower for a given RPE. The effort feels he same but the athlete just cannot recreate the effort. This is where communication with your coach is critical, if you have very specific workouts that demand an absolute power output or paces it might be best to do those in a cool controlled environment or adjust appropriately. You’ll still get the acclimatization affects from doing your other training in the heat but you are more likely assured the specific workout you need if done inside or during the cooler parts of the day…if you are so lucky as to have those…
In the heat your heart rate will likely be higher by 5-10bpm than when training indoors or during cooler times of the year. With that heart rate becomes even less significant as a training tool (it’s not very good to begin with) and more attention should be placed on power and pace.
Some athletes also report that they feel like recovery is delayed after training or racing in the heat. If you can typically bounce back from an overload workout in 24-36hrs but are finding that even at 36-48hrs you just cannot achieve the intensity necessary for a quality workout, let your consultant know. You may need more time to recover or you may need to address your recovery techniques more specifically, such as hydration status or nutritional intake.
For those that do not train in typically hot environments it’s important to try and acclimatize to the heat as best as possible. Literature suggests that this is most effectively done by arriving in the environment with 5-8 days of exposure prior to the event. It is also suggested that mild to moderate exercise is best for acclimatization, so no need to do killer hard workouts when you arrive to your toasty destination, instead just walk around or go out for a recovery workout.
There seems to be additional evidence that it is the cumulative exposure to heat that causes a robust acclimatization, with some reports suggesting that it takes up to 14 consecutive days of exposure before complete acclimatization. It is also best to stick to mild to moderate exercise during this acclimatization period. Simply taking walk or doing yard work can help your body adjust to the effect of heat.
It’s also very important to remember your hydration status during the summer months. This needs to be a full time commitment. If you are just remembering to hydrate for your workout 60-90min prior it’s probably too late. Instead make it habit to hydrate throughout the day. Athletes should have clear to lightly straw colored urine all of the time, no exceptions, if this is not you then you need to discuss your hydration strategy with your consultant. Often times though you simply need to set a goal of carrying a water bottle around and refilling it every 60-90min. During the evening you should get up to go to the bathroom at least once. This is especially important if you workout first thing in the morning, also keep a glass beside your bathroom sink and drink some water down before returning to bed. This way you wake and start your day hydrated.
Listen to your body in the heat, note any trends or abnormalities you might experience and discuss these. All athletes are unique and respond in their own way, it’s important to figure out what works for you in training so that you can race to your potential.
