In summer, on the shooting line, the heat is the first thing people talk about and the last thing they think they can do anything about. You drink, you look for shade between ends, you keep your hat on, and all the while it is taken for granted that at thirty-five degrees you shoot worse. The question I hear most often is whether anything is worth changing, in preparation or in how you handle the competition, or whether the heat simply has to be put up with.
On the score, the research has a single answer, but a well-built one: a study that followed Chinese professional archers for seven years and set each of their competitions beside the weather of the day. It says what heat costs, where the loss begins, who pays most and what reduced the loss. Around that study there is one experiment on water and little else, so it is worth looking closely at what was measured and how.
What was measured
The study gathered the qualifying results of 460 contests, each made up of the arrows shot at a single distance, within 57 competitions held in China between 2010 and 2016: 35,954 performances by 3,196 professional archers, men and women in roughly equal numbers. For each performance the authors had the mean score per arrow, which averages 7.91 across the sample, and the share of arrows in the ten. The weather came from stations within 150 km of the venue, weighted by distance, and for contests spread over more than one day it was the average over their whole duration.
Heat is not measured with a thermometer but with the heat index, which combines the day's mean temperature with relative humidity and describes how hot a person feels. The strength of the design is the comparison: each archer is set against themselves on different days, so differences in level between athletes stay out of the calculation, and the model also holds wind, rain, distance, bow type and number of arrows constant. It remains an observational study, with the limits that brings, but it describes competitions actually shot rather than laboratory trials.
What heat costs
As their reference the authors took days with a heat index between 18 and 22 degrees. Above that band the score always falls, and not only on scorching days. With no wind the average arrow loses 0.25 points between 22 and 26 degrees, 3.2%; 0.42 points between 26 and 30 and 0.41 between 30 and 34, just over 5%; then, above 34 degrees, the loss jumps to 1.07 points, 13.5%. At the sample's mean wind of 2.35 metres per second the losses between 22 and 34 degrees shrink to 0.19 to 0.29 points, while above 34 they stay at 0.82 points per arrow, 10.4%.
Days above 34 degrees were no exception: they made up 14.2% of the observations, and more than 32% were above 26. For anyone who thinks in thermometer readings, the study also gives a version closer to the opening question. In the specifications that use the day's maximum temperature instead of the index, a competition day with a maximum above 34 degrees costs 0.66 points per arrow with no wind, 8.3%. The authors note that these estimates are slightly lower than those based on the index, because temperature on its own does not capture how much the humidity weighs.
In the registry this reading sits under the claim that extreme heat lowers competition scores, and it is reported: the study is large and well built, but it is one study, on one federation, and on its own it cannot support anything stronger.
Humidity and wind
What counts is the combination of temperature and humidity, not either one taken alone. When the authors separate the two, relative humidity is never significant, and the coefficients for temperature are smaller than those for the heat index. That is why the claim that rain, humidity and temperature make no measurable difference to the score is contested in the registry: on the day's rainfall and on humidity alone the study supports it, while on temperature combined with humidity it points the other way.
Wind enters the picture in two ways. On the one hand it lowers the score in its own right, which is the reported claim that the more wind there is, the lower the score, once temperature is accounted for. On the other, in the heat it softens the loss, as the step from no wind to mean wind shows: between 22 and 34 degrees the loss goes from 0.25 to 0.42 points per arrow down to 0.19 to 0.29, while above 34 it stays large, 0.82 points rather than 1.07. In the sample, moreover, wind never goes above 5.38 metres per second, because events are postponed in strong wind, so the figures hold for the conditions archers normally shoot in.
Who loses most
The part of the study closest to the experience of a mid-level archer is the one on how scores spread out. With a heat index above 34 degrees the gap between the highest and lowest mean score in a contest grows by 79.1%, and the coefficient of variation of scores by 105.2%. To find where the gap came from, the authors built an index of each archer's results at earlier competitions: those who had done better in the past lost less in heat above 30 degrees, and the top 10% handled extreme heat significantly better than everyone else. Extreme heat therefore lowers everyone's score, though the best archers' by less, and widens the gap between the leaders and the rest of the field.
Two other divisions, on the other hand, make no difference. There is no difference between men and women: the interactions between sex and heat bands are not significant, with a single marginal exception for the share of tens between 26 and 30 degrees. Nor does the length of the contest change the picture, because a 72-arrow contest suffers no more from the heat than a 36-arrow one. It should be said, though, that 72% of the 36-arrow contests were completed in one day, while 65% of the 72-arrow contests were spread over two or more days, so the comparison is not between two identical days.
What reduced the loss
The same study looked for what protected archers from the heat, and found two things. The first is competition experience, measured as the number of arrows shot at all previous events: more experience softens the loss above 26 degrees, and the effect is largest above 34. Simply moving out of the least experienced quarter of the sample means the average arrow loses 0.33 points less in extreme heat, about 40% of the 0.82 lost on average, which the authors read as a sign that adapting through experience becomes effective quickly.
The second is long-term familiarity with the climate. Chinese archers rarely move between provinces, and scorching days are far more common in the south of the country than in the north: archers who train in the south lose 0.296 points per arrow less in extreme heat, and those competing in their home province 0.348 less, about 30% of the loss. Home events, however, make up only 5.6% of the observations, and at home a shorter journey and the support of family and friends also count, as the authors themselves note, so the share due to climate may be smaller.
The most useful result for anyone preparing for a summer of competition, though, is the negative one. For the archers whose training city was known, 21,251 observations, the authors counted the hot days experienced one, three and twelve months before the event and crossed them with the heat on competition day: the coefficients are small and almost never significant, and within less than a year, they write, the scope for acclimatisation is limited. That is why the registry's claim speaks of years rather than weeks: competition experience and years of training in the heat reduce the effect of heat on scores. It is reported, because it comes from a single observational study, and the authors' total of more than 70% of the loss offset adds experience and climate together from two different models.
Water
On hydration there is an experiment with a different design, and that is exactly what makes it useful. Ten Cypriot national-level archers shot the same 72-arrow round at 70 metres twice, in 36 or 37 degrees and 81 to 83% humidity, a week apart: once hydrated and once after twenty-four hours of reduced fluids, which had taken all of them past the threshold for dehydration. The score did not fall, 550 points hydrated and 562 dehydrated, a difference that was not significant, and the archers who were most dehydrated were not the ones who lost most points. In the registry this is the reported claim that one study found that arriving dehydrated at a competition in the heat does not lower the score.
It does not contradict the Chinese study, because it compares the same archer in the same heat, hydrated or not, rather than a hot day with a mild one. Nor does it say that water makes no difference: when dehydrated, the archers started the round thirstier, more tired and feeling less focused, and their heart rate was higher at rest and in the second half of the round. The alertness they reported, on the other hand, did not change, which is another reported claim: dehydration does not change how alert the archer feels in competition. The sample is ten people and the round lasted one morning, from 8:20 to 10:50, so the answer holds for that situation and not for a tournament over several days. I have written about what and how to drink in competition in the article on hydration and nutrition on competition day.
And the cold
The Chinese study also looks at the other end of the scale, and here the result depends on the model. In the one the authors choose as their main model, which includes the interaction between heat and wind, days with a heat index between 14 and 18 degrees and those below 14 cannot be told apart from the reference band; in the model without that interaction, however, they lose 0.31 and 0.22 points per arrow. That is why the claim that moderate cold does not lower competition scores is contested. Severe cold has not been tested: the lowest heat index in the sample is 4.6 degrees, only one observation in ten falls below 14, and what is measured is the air, not the archer's hands.
Where the research stops
Almost everything known about heat and scores comes from a single study, on one federation in one country, and its limits are those of data collected for other purposes. The weather is that of stations within 150 km, averaged over the day or days of competition, rather than measured beside the shooting line; the score is an average for the contest, and there is no way to tell in which end, in the morning or early afternoon, the points went. Experience, too, is measured in arrows shot in competition, and does not separate archers who have often competed in the heat from those who have simply competed often.
Some questions have not been put to the test by anyone. Heat in the preceding months was counted from the weather in the training city, so the study says nothing about a block of training in the heat planned specifically before an event. Nor have the summer habits of every venue, shade between ends, water, a hat, the way time between arrows is managed, been compared with the score: whether they reduce the loss has not been measured.
What I take to the shooting line
My answer to the opening question is this: part of the heat simply has to be accepted, and the measurements say that part is larger than most people believe and begins before the scorching days. What can be changed has little measured support, and I keep that in mind in the four points I draw from it.
The first concerns how to read your score. If above a heat index of 34 degrees the average arrow loses 10% even with some wind, a July competition should not be compared with an April one. It makes more sense to set it beside the other hot competitions of the season, and all that takes is noting temperature, humidity and the timing of the rounds in your competition diary. The same goes for the rankings: in extreme heat the gaps widen, and a placing on a scorching day says something different from one on a mild day.
The second concerns experience. In the study, what protected archers was accumulated competition experience, and moving out of the least experienced quarter was enough to cut the loss considerably, which means that those just starting out pay more for the heat than everyone else. I would not conclude from this that you should seek out the hottest events, because the study does not separate experience gained in the heat from experience in general; what I take from it is that the first summer competitions of an archer with few events behind them should be judged by a different yardstick from the rest.
The third concerns preparation and wind. Heat experienced in the preceding months gave no protection, and a block of training in the heat built for the purpose has not been tested on archers, so I could not say what it adds to the score. In the same way, I would not count on the wind: in moderate heat it softens the loss, but above 34 degrees the loss stays large, and wind costs points in its own right.
The fourth concerns water and shade. The experiment on dehydration in the heat did not see the score fall, but it did see the archers feel worse, with more thirst, more fatigue, less perceived focus at the start and a faster heart in the second half of the round. In that experiment, then, arriving hydrated helped the archers feel better during the round. Whether water and shade change the points lost to the heat, though, nobody has measured. Anyone who wants to understand how they respond to the heat has the same tool as in the first point: a few summers of competitions logged with the conditions of the day say more about one archer than an average across more than three thousand.