History of heat-related symptoms and heat illness

The history of a previous diagnosis of EHI was not dependent on gender (p=0.509) or race category (p=0.885). The cyclists’ history of heat-related symptoms is presented in table 1. Most notably, the prevalence of symptoms was higher in men (75%) than women (28%) (p<0.001). This was mainly associated with a higher rate of cramping (58% vs 12%) (p<0.001). Junior athletes reported fewer heat-related symptoms (p=0.018). Seventeen per cent of the cyclists reported having been previously diagnosed with EHI (table 1). While self-reported data regarding clinical diagnoses may be inaccurate, cyclists were encouraged to discuss the questions with their medical staff if necessary. Overall, these data suggest that heat is a common issue for elite cyclists.

Pre-existing illness in the 10 days preceding the race

Twenty-two per cent of the respondents reported (any) illness symptoms in the 10 days preceding the World Championship (figure 1). This prevalence is higher than the IAAF World Championship where 13% of the athletes reported illness symptoms, especially considering that the IAAF questionnaire included the 4 weeks prior to the championship.5 It is important to note that the IAAF championships included a mixed profile of athletes (eg, track and field disciplines), whereas cycling can be considered as an endurance sport. In this context, the prevalence of illnesses before the UCI World Championships is similar to a large scale study on 7031 amateur long-distance runners where 19% reported pre-race illness symptoms.6 Thus, almost a quarter of respondents were symptomatic with the most common being headaches (56%) and minor gastrointestinal symptoms (32%).

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Figure 1

Prevalence of illness symptoms in the 10 days preceding the World Championships.

Training in the heat

Sixty-one per cent of the respondents had some form of heat exposure prior to the World Championships (table 1), following the recommendation that training in the heat is an important countermeasure to adopt before competing in the heat.4 Some riders adopted a strategy of between 1 and 4 days only; that is, a procedure likely too short for optimal adaptations.4 Thirty-eight per cent of the riders performed a dedicated HA period of at least 5 days. Of note, this proportion was more prevalent than in athletes participating in the IAAF Athletics World Championship (15%).2 This might be partly explained by the fact that the IAAF championships were held in August, with most athletes already experiencing summer conditions whereas the UCI championships were held in October; and the IAAF athletes included jumpers, throwers and sprinters who may not need to acclimate from a performance perspective.

The 2015 IAAF athletes with a previous diagnosis of EHI were seven times more likely to train in the heat.2 However, the present study found no association between the HA strategy and a previous diagnosis of EHI (table 1). However, the pre-travel acclimation strategy in the current study depended on race category (p<0.001) with most elite cyclists spending at least 7 days training in the heat before travelling to Qatar (31%) or living in a hot environment (23%), while most juniors performed fewer than 7 days (80%), and U23 had either none (57%) or fewer than 7 days (21%) only. This reinforces the need to inform non-elite (non-professional) categories about the importance of HA. Elite categories should also be aware of the benefits and limits of living in a hot environment as heat acclimation is not solely achieved by living in hot ambient conditions, but by training in the heat to induce an increase in core and skin temperature, as well as profuse sweating.4

Of note, the cyclists in the current study arrived in Qatar on average 5.4±2.5 days before competing in their event, affording most of them a heat acclimatisation stimulus, whether intended or not. Indeed, it has been shown that cyclists experience significant adaptation to the heat after training for only 1 week in Qatar, even while living in air-conditioned environments during the rest of the day.7

Travel arrangements

Only 6% of the respondents arrived in the 48 hours preceding their first race, while 58% arrived 3 to 6 days before and 23% arrived 7 to 10 days before their first race. The number of days between travel and the first race did not depend on the country travelled from, as most cyclists travelled from a European country at the end of their race season and crossed only two time zones (table 1) without considering jet lag in their travel plans. The combined management of jet lag, heat acclimation and tapering may however be more challenging during other events, such as the upcoming 2020 Tokyo Olympics.

Environmental conditions

A total of 247 measures of ambient temperatures, 228 of relative humidity and 248 of WBGT were recorded from different locations along the course during the 8 days of the World Championship. The American College of Sports Medicine (ACSM) guidelines recommend to cancel all training and competition when the WBGT reaches 32.3°C.8 This threshold (commonly characterised by a black flag) was reached in 1% of the measurements during the UCI World Championships. However, those measurements were from the car park and this threshold was never reached on the course or from the car following the race. As such, the UCI expert panel did not advise cancelling or shortening any of the races. Of note, the ACSM also suggests to cancel competition for continuous activity from a WBGT of 27.9°C (commonly characterised by orange and red flags), a threshold that was reached in 35% of the measurements. However, the expert panel considered the cooling effect of the relative wind velocity while cycling at high speeds, which helps evaporative heat loss by removing the layer of saturated water vapour from the skin.9 10

Although the UCI expert panel did not recommend any race cancellations, it did recommend increases in feeding and hydration opportunities. This recommendation was implemented by the local organisers and UCI commissaries, for example, by allowing car feedings during the ITT. Unfortunately, it was logistically not possible to increase the number of feeding stations on the race course lap circuit, a situation which was criticised by some cyclists. Such countermeasures should therefore be planned ahead of time as they may require additional resources and preparation.

Heat exhaustion

The AMC assessed 46 injuries and 26 illness with six cyclists being transferred to the hospital for surgery (n=3) or further examination (n=3). In addition, three other cyclists were directly transferred from the road to the hospital following a crash (one head trauma, one knee trauma and one elbow trauma) without being assessed at the AMC. Only three cyclists were assessed for heat exhaustion, a mild form of EHI. They were treated with normal saline while receiving oral rehydration (n=2) and oxygen (n=1). Another cyclist was assessed for exhaustion and received oral rehydration only. Although several finishers and medallists had a core temperature >40°C,3 none of the athletes assessed for heat exhaustion had a rectal temperature >40°C, showing that no case of exertional heat stroke (the most severe form of EHI) was diagnosed by the AMC, although the time frame for assessing temperature is unknown. One rider was assessed for dehydration and potential arrhythmia, and was referred to the hospital for further examinations. The three recorded heat exhaustion cases over the 982 race starters at the UCI Cycling World Championships might appear lower than the five cases reported during the IAAF Athletic World Championships representing 1.6% of the athletes participating in the study.2 These numbers should however be treated with caution as the AMC was not located at the finish line and a larger proportion of injury and illness complaints might have been managed by the national team doctors without reporting to the AMC. As such, the current figure represents the number of encounters by the AMC facility to help future organisers plan for the necessary resources, rather than a true reflection of the illness burden associated with a World Championship event. Organiser should also aim to locate the AMC immediately after the finish line.

Pre-cooling strategy

In line with recent meta-analyses concluding that pre-cooling can improve subsequent performance in the heat,11 12 most cyclists utilised a pre-cooling strategy. However, this was dependent on the event, with 96% of the respondents planning some form of pre-cooling before the TTT and ITT, versus 74% before the RR (p<0.001). There were also differences in cooling strategies (eg, fanning, ice vest, ice neck collar, whole body cold water immersion (CWI) and ice slurry) (all p<0.05, table 2). This wide-spread use of pre-cooling call for event organisers to provide the necessary facilities such as fan, fridge to accommodate cold vest or power supply for ice slurry machine. This may appear as beyond the duties of the organiser but this would help ensuring equities between countries with and without a strong logistical support.

Eight per cent of the respondents planned on having ice slurry during the races itself, irrespective of the event (p=0.597). The prevalence of leg CWI was 9%, irrespective of the event (p=0.913). Leg CWI requires some logistical planning and it is likely not suitable before a time trial as decreasing muscle temperature limits sprint performance and likely power output during the first minutes of a time trial.4 12 An easily applicable pre-cooling strategy is the use of cold towels,4 which were used before all race types. The differences in strategies between the TT and RR are likely due to the event duration and warm-up type. Cyclists typically perform an intense stationary warm-up before starting a TT during which cooling strategies such as wearing an ice vest and ingesting ice slurry might attenuate the rise in core and skin temperature.11 More cyclists planned on using ice vests and cold towels (ie, two portable solutions) before the ITT than TTT, whereas more planned CWI and ice slurry (ie, two solutions requiring logistical supports) before the TTT than ITT. The differences between the TTT and ITT may relate to the TTT being a professional trade team event where the athletes were benefiting from their usual sports science support team.

The different prevalence of pre-cooling strategy used between the RR and TT was specific to men. In women, 96% of respondents planned on using pre-cooling before the RR, versus 57% of men (p=0.001). This result showed a different trend in cyclists than observed during the IAAF Athletics World Championships where more men (52%) than women (42%) planned to use pre-cooling.2 This gender difference may be due to the limited sample size and the main results remain that most cyclists pre-cool before a cycling race in the heat.

Hydration strategy

The elevated thermal strain associated with exercising in hot and humid environments increases fluid and electrolyte losses. It has been reported that athletes may tolerate up to 4% of body mass loss during real-world time trials without experiencing a performance impairment,13 but dehydration is well known to exacerbate heat strain.14 A recent meta-analyses demonstrated that fluid ingestion is the most efficient countermeasure to attenuate the rise in core temperature when exercising in the heat and is the third most effective countermeasure, after aerobic fitness and heat acclimation, to improve endurance performance in the heat.15 Different hydration strategies were observed between events; partly explained by the fact that cyclists used only one bottle during the time trials (electrolytes for most riders), whereas they used several bottles during the RR (electrolytes and water) (table 2). Furthermore, 66% of the respondents planned to include carbohydrate in their drinks during the RR, but only 42% and 32% during the TTT and ITT (p=0.007). It is important to note that this figure does not include additional consumption of energy bars, gels or other sources of food or fluids.

Post-race recovery strategy

Ninety-two per cent of respondents planned on using one or several recovery strategies (table 1). This high prevalence is in line with the 89% reported during the IAAF Athletics World Championships.2 Despite limited research, massage was the most frequently utilised recovery strategy (77%), likely as it is anecdotally believed to have numerous benefits.16 Stretching (55%) and active cool down (48%) were also prevalent. Thirty-nine per cent of respondents planned on utilising compression clothing, with indications that it may improve recovery after a cycling time trial.17 One-third of the respondents (34%) planned on using water immersion, mainly cold (CWI, 28%), but also hot (4%) or contrasted (6%). While being superior to passive recovery or rest, there are no clear differences between the benefits of these different immersion techniques.18

The proportion of cyclists planning on using a recovery strategy was equivalent in men and women (p=1.000), but the nature of recovery differed between genders. Only 31% of women planned to actively recover compared with 60% of men (p=0.026). Conversely, 60% of women cyclists planned to use compression clothing while this percentage decreased to 29% in men (p=0.023). The prevalence for the other recovery techniques was equivalent between genders. This observation partly contrasts with a previous report showing that women athletes during the IAAF World Championship were planning recovery strategies more frequently than men, with a greater use of massage.2 This difference is likely due to the fact that massage is the primary recovery technique in cycling, independent of gender.