I am sat at my desk as I write this looking at data and feedback from athletes I coach on their weekend's training and racing and one factor stands out above everything else - the hot weather!
As runners in the UK we tend to be pretty bad at adapting to changes in the weather. We have our plan, or the run we have intended to do and regardless of whether its 30 mile an hour headwinds, 30 degree heat or knee deep snow we judge our success or failure on whether we have hit the paces or intensity we had planned for. Running in hot weather feels hard because your body pumps more blood to the skin to cool you down and increase sweat rates. This in turn reduces stroke volume and the availiblity of oxgygenated blood to the muscles. Whilst the heat we have experienced over recent days has been more of a 'dry heat' we can expect plenty of more humid hot days to come. Humidity represents an bigger challenge because with a high 'dew point' with humidity in excess of 65%+ it's very hard for sweat to evaporate in the saturated air - and you therefore lose your most important method of regulating body temperature whilst training.
Running in very warm weather requires planning, adapting and realism but whilst you might find some of your runs tougher than you might be used to there are a number of key advantages. Whilst I have referred to runners in the main in this post the physiological benefits are the same for cyclists.
* The Increased blood plasma volume created by training in hot weather is similar to the increase in red blood cells from living and training at altitude. When blood plasma expands it increases cardiac output and therefore increases Vo2 max. Studies have shown increased power output at lactate threshold and peak power as a result of these changes when training in back in cooler weather - more so than training at altitude. Check out https://www.ncbi.nlm.nih.gov/pubmed/20724560 and https://www.ncbi.nlm.nih.gov/pubmed/21915701
* Vitamin D - OK so this is less 'heat' and more 'sunlight' but still getting a healthy dose of vitamin D (actually it's a hormone not a vitamin) is important to maintaining bone health as it improves the absorption of calcium.
* UVA exposure triggers nitric oxide pathways (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427189). Nitric Oxide is a vasodilator meaning it helps expand your blood vessels and can increase blood flow and oxygen to your muscles as you run, increasing performance.
* Heat dissipation - In warm weather your key method of staying cool is through sweating. The Oregon research I have already linked to suggests that your body adapts to hot conditions by sweating earlier (thus becoming more effective at heat dissipation) and even by developing a cooler core body temperature. As thermo-regulation is a key performance factor even in temperate climates this can be a very useful effect of training in the heat.
* Mental Gains - Whilst harder to quantify one of the most obvious benefits is that gradual exposure to the stresses of training in the heat is an increased tolerance of a wider range of future training and racing conditions. Many runners worry a great deal about racing in hot weather, there is no better way to get your head ready for that challenge than to train in the same, or harder conditions.
Training adaptations and considerations
It's a pretty basic evolutionary concept that animals adapt to stress and external stimulus. Runners can sometimes tend towards doing all they can to avoid stresses that take them out of their comfort zone. I mentioned that some of the training effects of heat can be even more pronounced than altitude training but differently to altitude simply 'living' in the heat and not training in it will not help you adapt. I would strongly advise still getting out and training and training well in these conditions because your body will adapt to these stresses, but there are considerations and adaptations you can make to make this more sustainable, it's about balancing making training and racing sustainable without shielding yourself totally from the conditions.
* Approach with caution. Whilst above I have highlighted some of the benefits of heat adaptation you also need to be mindful that if you get it wrong training in the heat can reduce performance but also be potentially dangerous. An overall lift of about 1-1.5 degrees in core body temperature over what you might normally experience in training will help your body adapt, much more than this and hyperthermia can occur which can reduce your training effect and in extreme cases, kill you. Take our advice below to help adapt to the heat but staying safe and training well;
* The obvious. Light, and frankly minimal clothing is clearly the way to go in the heat. I appreciate that for a range of reasons some runners will always wear longer sleeved or legged kit but where as little as you can get away with and crucially make sure it's breathable to allow for sweat to be wicked away and heat to be dissipated. Wear water resistant sun protection.
* Top down. When racing or even in hard long sessions a baseball cap can be very useful - it will keep some sun from your eyes but if you pour a little water on top it will help you feel cooler. Sunglasses are also a must and can make a surprising difference to how relaxed you feel in bright conditions.
* Compression. Some compression garments have been shown to aid heat dissipation. We work with CEP. Check out their video on how compression using the right fabrics can help keep you cool in hot conditions (when you might be thinking they would have the opposite effect)
* HR over GPS. Heart rate can really come into its own in these conditions. I adapt all my own sessions to HR using my Polar M430 working within 5 heart rate zones I have determined for myself through lab testing (you can do your own max HR testing to help get your zones more accurate without a lab test). Don't get too hooked up on your paces during those really hot sessions. Likely for the same heart rate and perceived efforts you will be running a bit slower than you might be used to, and that's OK. This is also a case of you becoming more mentally resilient as an athlete. If you cannot cope with the idea that in these temperatures some of your GPS stats might not be what you want them to be...then turn the GPS off and just keep HR on or work to perceived effort. If you still want to monitor all your speeds and cannot accept that in this weather your paces will be down and you end up losing confidence as a result then as a coach my sympathy is limited as you are cutting your nose off to spite your face ;)
* Give it time. Be patient and allow your body to adapt without putting undue mental pressure on yourself. In conditions that we are seeing at the moment with 25-30 degree heat your body will adapt pretty quickly. With regular enough training 7-10 days will be plenty to start to see your body acclimatise and eliciting some of the benefits listed above. If you are training to HR you could try following this simple protocol for how well you are adapting to the heat. Run for 5 minutes at around 70% of you maximum HR and check the pace it takes to reach this (very light) heart rate. Now continue to run at the SAME PACE over a flat route and notice that your heart rate gradually drifts up despite the pace staying the same. Keep going until you get to around 15 beats off your maximum HR. In temperatures of 25-30 degrees + this is likely to be after about 45-60 minutes. Over time you should be able to conduct the same test and notice the HR 'drift' upwards occurs at a slower rate.
* Time your sessions. Whilst I strongly believe that getting out and training in warm weather has many benefits for athletes and that I would not recommend routinely taking all of your sessions indoors into air conditioned environments obviously there is a balance to be struck. If its so hot that you lose all the quality sessions that's not ideal either. Be sensible and avoid the middle of the day. The temperatures between 6am and 9am and 6pm and 9pm are likely to be still hot enough to get a good adaptive response but will take the edge off those peaks in the middle of the day and this is when I would be looking to complete my harder interval sessions. You might also think about mixing sessions in your week. If you have a really easy, recovery focused day - make sure that you aim to complete this in cooler conditions. Your general easy and steady running are the sessions which will give you the best opportunity to adapt to heat and try out the protocol above.
* Adapt your sessions - If it's super hot (and the athlete isn't specifically preparing for a hot race) I prefer to work on sessions that allow athletes to our their legs over quickly but in relatively light volumes. Big engine building hard efforts over 1km, 1200m, mile reps etc can make it hard to stay controlled and can often see sessions tailing off in very hot weather. Slightly shorter reps, runs with control, from shortish recoveries can be useful on days when its hotter than expected. Tonight for example I cut back a planned 6 x 1200m session to 5 x 400m + 2km threshold + 5 x 400m....it's lighter but recovery will be easier and the athlete in question came out with more confidence than clinging on to pace which was unrealistic in 28-30 degrees. I know quite a few coaches read these blogs. Your athletes will need time to acclimatise to sudden increases in temperature - as they adapt (as above) so you can start to increase the volume of the sessions and reps. You might even consider changing the training environment to take athletes out of a less measurable setting (on grass or running reps to time for example) to allow them to focus on effort or even in areas which provide more shade.
You will of course still want to be doing longer blocks of threshold and tempo running though and this is where I would turn to your heart rate monitor to ensure you are achieving the stimulus you want from the session and remaining at the correct effort levels in that 80-85% max HR zone.
* Pre-cooling. Pre-cooling, particularly before races and key hard sessions can be a great option if possible for you because this is when you are focused on performance, not acclimatization and adaptation. Cold water immersion, ice packs or even a cold shower can help to lower the core body temperature before then completing a short and specific warm up to target key muscle groups without elevating HR unnecessarily. At the very least it doesn't make sense to be stood around in the blazing sun waiting for sessions or races to start...
* Adapt warming up, cooling down & mid session rest protocols before hard sessions. Again it seems obvious but it's an area often neglected by coaches and athletes who are used to having a routine and sticking to it. Your key hard sessions and races are about performance, not so much heat adaptation (this can be more of a primary goal of easier sessions, and a secondary goal of quality sessions). The goal of your warm up before hard sessions and races should be to get the muscles warm enough to perform with the speed and strength required for the session without seeing core body temperature go up to the point where it will inhibit the session. If it's super hot I will tend to include more active stretching and mobility work and whilst I will still obviously include drills and strides I'll carefully monitor the volumes of plyometric elements of the warm up to ensure athletes heart rate isn't rising to the point that I feel hyperthermia might be induce early in a session as a result. Mid session having reps finishing in a shaded area where cold drinks and even ice on hand can be a great option and again for the coaches be aware that different athletes will respond differently to heat and some may require in-session adaptation of rep or interval duration to maintain session quality. The cool down needs to be active enough to get re-oxygenated blood to the muscles and prevent blood pooling enough maintaining an unnecessarily high HR - slow the paces right down and if you're newer to running a walking cool down before stretching in the shade could be a great option. Science on ice baths post session is mixed, but some say they feel a benefit after sessions in very hot weather.
* Hydration - Obviously training and racing in the heat results on higher sweat rates as your body tries to cool down, the key is getting the your hydration balance right without becoming very dehydrated and experiencing high levels of electrolyte loss. 500-1000ml per hour with electrolytes (e.g. High5 Zero or Energy Source) can be a good general rule but experiment as different for different athletes and some will be more prone to salt and electrolyte loss. If you find that you regularly have a chalky residue on your clothes after sessions consider looking ad some additional salt supplementation. Some elite level performers experiment with not drinking fluids during some sessions whilst heat acclimatising in order to generate Heat Shock Proteins (HSP) and stimulate greater blood plasma production. Certainly a level of dehydration (2-3%) appears to support great blood plasma increases, and can even help elite performers at the end of races through a reduction in bodyweight. This is not recommended for those of use who do not have methods of accurately measuring core body temperature - stay safe and well hydrated when training in hot weather. Measuring bodyweight before and after sessions can give you an idea of fluid loss. Some overall weight reduction is actually OK because your body is capable of 'metabolic water production' (water created inside your body from oxidising food) - for example a weight reduction of perhaps 1-1.5kg in a male athlete from a 2 hour long run would be normal.
* Recovery - I am sure there is a direct relationship between warm weather and beer and coffee consumption, I am also sure there is an inverse relationship between warm weather and the number of hours sleep athletes get. Just be aware that hot weather can also affect your recovery between sessions - stay well hydrated between sessions, pick a up fan and change your bedding to keep you as cool as possible at night and make sure you drink well on first waking as you will be losing more fluid at night than normal.
In train safely, and hydrate well particularly for your key sessions and races, but also give your body the chance to adapt and acclimatise to the heat in your easy and steady runs and get out there and enjoy the sun - we get precious little of it! Tom