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I'm going to be running in the London Marathon in two weeks. Initially my target time was to run sub 4 hours. Its my first marathon and my training had been going quite well until the last two weeks.

I've been doing a long run every Sunday. The longest I've done is 29 KM (18 miles) and my time was 2 hrs and 34 mins with an average pace of 5:19 per km (8:34 per mile). I also did a half marathon two weeks ago and my time was 1 hr and 45 mins.

Both my half marathon and 29k times indicate that I should be able run a sub 4 hour marathon (if not quicker according to some calculators).

My biggest run was meant to be last Sunday, 35k (22 miles). As I set off, I did feel like it was a litte bit tougher than normal but just thought it would be a rough patch so tried not to pay too much attention to it. At the 21k mark, I started struggling. It was like nothing I've ever experienced before on a long run, I couldn't run anywhere near my target pace, my effort levels felt quite high yet my km splits were >6 mins/km. At 25.6 km I gave up and ended my run. I realised afterwards, that I must've hit the notorious 'wall'. I didn't have a very good pre run breakfast. I had three High5 ISO Gels throughout the run (aim was to have one every 10k).

After the disastrous run last Sunday, I decided to attempt a 35k again today. This time I had a substantial breakfast around three hours before my run; 4 weetabixes and half a banana around an hour before I set out. Also sipped on water in the hours leading upto it. I knew I was well hydrated based on pee colour.

I set off with the aim of going at an easier pace than my previous long runs. Kept the effort level relatively low and I felt quite good after an opening rough 5k. Had gels every 10km and overall I felt a lot better at the 21K stage than last week.

However I started experiencing the same problems as last week at the 25k mark. I could feel the pace slipping away and it became physically and mentally very tough just to keep running regardless of the pace. I gave up at the 27k mark :(

The weather has picked up in London in the past week or so. These are the first long runs I'm doing in the sun and slightly warmer weather, they seem to have a massive impact on my performance. My half marathon PB and 29k were ran on cold, cloudy days.

After every long run, I evaluate my target marathon time based on how the long run felt and the pace I did it at. My initial target time was sub 4:30, this was based on before I did any training. Over the weeks its been mostly at sub 4, but after my half marathon I was entertaining sub 3:45. My last two runs have put to bed any of those target times and I think I'm back to my initial target time of sub 4:30.

Based on my situation, my questions are:

  • How can I deal with the effects of hot weather and minimise any impact on my performance during the marathon?
  • What fueling strategies would folks recommend? I'm toying with the idea of using Zipvit gels too as they have 51 grams of carbs per sachet.

closed as off-topic by Ale, rrirower, Don_Biglia, Fillet, user10632 Aug 18 '16 at 16:29

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There are many factors that cut your marathon short. Firstly, the heat dissipation is better in a shorter runner than in a tall runner (the area-volume ratio larger to transfer heat if shorter). Secondly, the warm environment requires extra effort from your body like running extra miles. The ideal solution is to get used to the warm environment weeks before the competition. Lastly, the worrying thing is the inexperience in warm weather that can result to lack of consistency. To run marathon in warm weather, you need to get used to such climate and distances.

Just two weeks until the warm marathon race

Extra heat must transferred somehow away because your body is not yet used to it. Either you need to cut your goals (less heat from muscles generated) or cool down your body other ways such as run-showers, cooling body in aid stations and more hydration. The risks contain overhydration and hyponatremia where you start to feel fatique and heavier body can result to more pain in joints such as knees.

Strategies to tackle the extra heat in warmer race environment

  1. water yourself in aid stations

  2. drink more during the race: extra weight requires more effort from your legs, your front thighs/shins may fail. Relax calves, shins and front thighs before the race: backwards walking/running etc, more here.

  3. plan your hydration on aid stations such as more gels and watering pre 20km while more cold watering later

More about aid stations planning in https://sports.stackexchange.com/questions/13718/how-to-manage-hydration-in-aid-stations-during-marathon is covered in terms of the opposite hydration levels where dehydration versus overhydration analysed.

Long term

It seems that the distance is not your main problem but the consistency. The inconsistency is probably due to the lack of experience in warm runs. 2 weeks before race should be more intensive training and you have little time to do major changes. Just 1 week before the race it is important to build up the glycogen reserves and work particularly on the front thighs and knees -- particularly if your plan is to do major changes in hydration. Your body cannot adapt in a split second to more hydration and watering can also be an obstacle. In long term, overhydration can drain important trace minerals. In next run, train in warmer weather or simulate it with clothes.

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