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Weekend recap - physiology of the heart by training in the heat



Some people have no trouble training in the heat whereas others think it is just brutal and not welcomed. I'd like to think that most athletes prefer the ideal temperature of 50-65 degrees for running and around 70-75 degrees for triathlons but everyone has their preferences....just like their style of training.
As I prep for Kona which is 6 weeks away, I am not training in the hottest part of the day for I feel there is no need to lose form or risk dehydration/exhaustion from the heat. Instead, I will train when I feel the best and that is in the morning but of course, it is to be expected that as my training volume progresses, I will be training in the heat whether I like it or not. Gotta love living in Florida for it is a sweat fest everyday.....and I love it!
For this weekend's training, I'd like to explain a little about my workouts and to also explain a little about the physiology of the body (the heart) in the heat to better help with your training/working out.
For my cycling, I go by power which measures my watts on the bike. My zones are determined from a max sustainable power test but I also with all my interval training and past Ironman, I have a very good idea as to what I can sustain (watts) for different intervals. I love training with my power meter because it takes the guessing away from training and also allows me to run stronger off the bike because I can pace myself on the run. I do believe in perceived exertion and keeping a steady cadence but I do not get hung up on speed...but it is nice to see that since IM Lake Placid I am riding much faster and stronger than before.
For my runs, I have to be smart with my running, not only for my past history with hip/back issues but to maintain consistency with my  training and now, Kona prep. I do not do long hours of working out each day but instead, I do  a lot of intervals at various paces. This allows me to recover better from working out because although I stress my body everytime I train (thus why I value recovery days off from structured training), I do not risk the gradual fatigue that occurs due to running out of oxygen or not getting enough nutrients to support metabolism during training by training high volumes (relative to many athletes in my sport of choice).
For my run off the bike on Saturday, I choose to go by RPE and only monitor my HR as I feel the HR should be focused on but it is not the best way to train 100% of the time. I am more of a RPE and pace kinda of endurance athlete and I feel that by understanding the physiology of the body, it is easier to get in a quality workout when you are not 100% focused on the HR, especially in the heat. However, you must always be smart with training and listen to the body - whether it is speaking to you with pain or it is showing you something unhealthy with your training data on your Garmin.
On Saturday, knowing it was 11am and 95 degrees out, my body was limited by my core temperature increasing and thus my HR increasing and not because of lactic acid buildup. Because running will naturally cause an increase in HR over the course of the run due to "cardiac drift", the smartest strategy for me was to walk each mile in order to help control my HR. As you can see from mile 5-6, my body was compromised by the heat as my HR was elevated but I was running much slower and perceived effort felt the same. I always run with sport nutrition but also water for cooling my body. Anytime you workout, your cardiovascular system is stressed. This is why I am not a fan of long workouts for Ironman training because this also dampens the immune system. I realize you must properly prep for the distance ahead but I believe it can be done by getting faster before you go longer and then adapting with the least amount of training stress. 

The heart is a powerful muscle and not always appreciated. Not only does it need to deliver oxygen to the working muscles but it also needs to help transport heat to the skin and to help ensure that the GI system is working to digest and absorb nutrients to fuel the body/brain during exercise. The stroke volume of the heart (volume of blood delivered by each beat of the heart) increases when you exercise to help circulate blood to your metabolic systems so that you can continue to have a great workout.
Eventually when you workout, there is going to be a plateau in stroke volume. Unlike anaerobic exercise which is limited by your ability to tolerate and flush lactic acid due to lack of oxygen (thus the need to slow down when you can't breath anymore and your legs are burning), we all have a limit as to how much blood our body can pump during exercise and eventually you are going to notice that your HR will not increase and your body will not go any faster. 
As you train, remember that working out and getting faster/stronger is not just about motivation. You have to be smart with your training in order for your body to actually respond favorably to training stress. Secondly, your main limiters with longer distance exercise is lack of oxygen and nutrients. If you are pushing too hard without adequate recovery and/or not supplying your body with nutrients (ex. fluids, electrolytes, carbohydrates) to support the metabolic demands of your body (or not able to properly digest and absorb those nutrients), you are sabotaging yourself for performance gains. Many athletes feel frustrated when the workout doesn't go as planned and then blame the body for having a bad day. With smart, quality training, you should find yourself consistently improving, recovering well from working out and having your mind as the only limiter and constantly thanking your body. This equation is not always perfect so keep in mind, you must NEVER give up by finding the perfect balanced training plan to help you move closer to your racing goals.
Saturday: 
3:45 bike + 50 minute run
Time started: 7:45am

Bike:
1 hour warm-up (building to upper Z2)
Main set:
20 min Z3 w/ 2 min EZ
25 min Z3 w/ 2 min EZ
30 min Z3 w/ 4 min EZ
3 x 10 min low Z4 w/ 4 min EZ
Steady upper Z2 until time is complete. 

Run (off the bike):
Mile 1: steady, perceived effort 7/10, walk 1 minute
Mile 2- 4: steady 90% effort, walk 1 minute in between
Mile 5-6: Comfortable (get it done)

Garmin 910XT data:
54 minutes (6.12 miles)
Average pace 8:49 min/mile (with walking)
Average HR: 152
Mile 1: 8:07 min/mile, 136 HR
30 sec walk: 137 HR
Mile 2: 7:56, 150 HR
30 sec walk, 147 HR
Mile 3: 8:03, 154 HR
30 sec walk, 150 HR
Mile 4: 8:02, 159 HR
30 sec walk 155 HR
Mile 5: 8:50, 155 HR
30 sec walk, 150 HR
Mile 6: 8:35, 157 HR

Sunday: 2 hour run (or 15 miles) - whichever feels "right"
Time started: 8am

Total time: 2:10
Distance: 15.11
Average pace 8:38 min/mile (including walk breaks, not including a 3 minute stop for bathroom at mile 10 and to refill handheld flask bottles w/ nutrition)
HR 142 average

Set for today: hold around 8:15 min/mile (give or take 5-10 sec) which is my "ideal" run off the Ironman bike in a marathon but haven't yet accomplished that...but I still have it as my goal with training to see where I can take my body overtime and I am not afraid to work hard for it. I typically go by RPE on the marathon run in an IM based on my current level of fitness and bank these great workouts for mental strength on race day. Especially when my body is hating me around mile 20 of a 140.6 mile race.
My plan was to walk 30 sec after each mile and every 40 minutes to walk 1 full minute to help postpone fatigue. I have to be very careful of my body to not overdo it and since my longest run before Placid was 15 miles, I was using this as a confidence builder but also to assess my endurance and fitness. Let's just say I was very impressed with my body and thanked it about 15 times this morning. 
I have my watch set on auto lap each mile and then I hit lap to start a new interval.
I monitor lap time, current HR, lap pace and current pace.

Mile 1: 8:48 min/mile, HR 126 (warm-up)
30 sec walk: HR 116
Mile 2: 8:16 min/mile, HR 131
30 sec walk: HR 123
Mile 3: 8:10 min/mile, HR 137
30 sec walk: 125 HR
Mile 4: 8:07 min/mile, HR 141 + 5 minutes at 8:19 min/mile, HR 144
1 min walk, 124 HR
Mile 5.5 (ish): 8:13 min/mile, HR 143
30 sec walk: 133 HR
Mile 6.5: 8:15 min/mile, HR 143
30 sec walk: 129 HR
Mile 7.5: 8:14 min/mile, HR 146
30 sec walk: 138 HR
Mile 8.5: 8:10 min/mile, HR 149
30 sec walk, HR 142
Mile 9.5: 8:11 min/mile, HR 150 + 2 min walk 8:30 min/mile, 150 HR
3 min break
3.5 minute ease back into running, 8:38 min/mile, HR 134
Mile 10.5 (ish) - 8:17 min/mile, HR 146
30 sec walk, HR 142
Mile 11.5 - 8:14 min/mile, HR 148
30 sec walk, HR 143
Mile 12.5 - 8:13 min/mile, HR 148
30 sec walk, HR 143
Mile 13.5: 8:16 min/mile, HR 148
30 sec walk, HR 147
Last 5 minutes with Campy - 8:45 min/mile (he wanted to go faster...I didn't), HR 138