Dizzy triathlete–evidence supporting vestibular etiology

Dizziness during or after the swimming leg is a common complaint among triathletes. We hypothesized that the dizziness is caused by asymmetrical cooling of the vestibular organ. This caloric response is characterized by involuntary eye movements called nystagmus. Altogether, 125 triathletes completed an electronic questionnaire. Fifteen triathletes who had frequently experienced dizziness during the swimming leg agreed to take part in a cold water swimming test. The test comprised two cold water swimming legs, first without earplugs and then with earplugs to prevent a potential caloric response. Eye movements and possible nystagmus were recorded immediately after the swimming legs. A majority (87%, 109/125) of athletes had experienced dizziness during triathlon races or training. Of these, almost all (97%, 106/109) experienced it during or after swimming. Dizziness affected the triathlon performance in half of the athletes with dizziness (50%, 51/102). Fifteen athletes participated in a cold water swimming test. During the first leg (without earplugs), 11/15 athletes (73%) experienced dizziness. Of these, six had nystagmus (55%), four had uncertain nystagmus (36%), and one did not have nystagmus (9%). Only one of these athletes experienced dizziness during the second leg with earplugs. The prevalence of dizziness among triathletes is notable. A large part of the dizziness is likely to be caused by caloric reaction of the vestibular organ. We recommend earplug usage for triathletes suffering from dizziness during the swimming leg.


| INTRODUCTION
Triathlon is an endurance sport consisting of swimming, cycling, and running. Due to the nature of the sport, medical complaints are common during races. Dizziness comprises 20% of all medical contacts during half-or full-distance triathlon. 1 In addition, dizziness especially during or after the swimming leg is a common topic in various triathlete Internet forums, eg, Facebook groups. The etiology of dizziness during swimming is unknown: benign paroxysmal positional vertigo, cervicogenic dizziness, and caloric reaction (after mastoidectomy) have all been suggested as the cause of dizziness. [2][3][4][5] In addition, motion sickness, orthostatic hypotension, and caloric reaction are common hypotheses in Internet triathlon forums.
Caloric response is caused by asymmetrical warming or cooling of the external auditory canal. This produces stimulation or inhibition of the same-side vestibular organ, resulting in dizziness. 6,7 Caloric response as the cause for dizziness Dizziness during or after the swimming leg is a common complaint among triathletes. We hypothesized that the dizziness is caused by asymmetrical cooling of the vestibular organ. This caloric response is characterized by involuntary eye movements called nystagmus. Altogether, 125 triathletes completed an electronic questionnaire. Fifteen triathletes who had frequently experienced dizziness during the swimming leg agreed to take part in a cold water swimming test. The test comprised two cold water swimming legs, first without earplugs and then with earplugs to prevent a potential caloric response. Eye movements and possible nystagmus were recorded immediately after the swimming legs. A majority (87%, 109/125) of athletes had experienced dizziness during triathlon races or training. Of these, almost all (97%, 106/109) experienced it during or after swimming. Dizziness affected the triathlon performance in half of the athletes with dizziness (50%, 51/102). Fifteen athletes participated in a cold water swimming test. During the first leg (without earplugs), 11/15 athletes (73%) experienced dizziness. Of these, six had nystagmus (55%), four had uncertain nystagmus (36%), and one did not have nystagmus (9%).
Only one of these athletes experienced dizziness during the second leg with earplugs.
The prevalence of dizziness among triathletes is notable. A large part of the dizziness is likely to be caused by caloric reaction of the vestibular organ. We recommend earplug usage for triathletes suffering from dizziness during the swimming leg.

K E Y W O R D S
caloric vestibular reaction, dizziness, nystagmus, open water swimming, triathlon during triathlon is supported in Internet forums by the reports of numerous athletes who experience dizziness only in cold water and describe the preventive effect of earplugs.
Caloric response, or any other vestibular cause of vertigo, causes dizziness clinically characterized by involuntary eye movements called nystagmus. 6 Nystagmus may be detected without any equipment, but prevention of gaze fixation makes nystagmus easier to detect. The prevention of gaze fixation is usually achieved by Frenzel's goggles and/ or darkness. The prevalence of nystagmus without gaze fixation prevention is 40% in patients with vestibular vertigo. The prevalence increases to 66%-83% with Frenzel's goggles and 100% in total darkness. 8 The direction of nystagmus (defined by the fast phase) correlates with the stimulation or inhibition of the vestibular system. 6,9 We evaluated the prevalence and etiology of dizziness among triathletes, using a questionnaire to examine the former. We explored the etiology of dizziness utilizing a cold water swimming test with nystagmus recordings; selected athletes were analyzed for nystagmus after a cold water swim with and without earplugs. Our hypothesis was that earplug usage would prevent dizziness by obviating the caloric reaction.

| MATERIALS AND METHODS
The Ethics Committee of Helsinki University Hospital (HUS/3494/2018) approved the study protocol. All participants were voluntary adults and gave their informed consent. Patients or the public were not involved in the design, execution, reporting, or dissemination of our research.

| Questionnaire
We distributed an electronic questionnaire through the Finnish triathlon clubs. The questionnaire consisted of questions concerning training history and possible dizziness during triathlon training or competition. Participants with dizziness were asked about the prevalence, inconvenience, and type of dizziness. They were also asked whether they had experienced dizziness during or after swimming, cycling, or running, and whether swimming in indoor pools or open water makes any difference. Alleviating and exacerbating factors of dizziness, visits to a doctor, and details about their swimming technique were also recorded.

| Cold water swimming test
Triathletes who had frequently experienced dizziness during the swimming leg were asked to participate in a cold water swimming test. Fifteen triathletes consented to participate. The test consisted of two cold water (max 20°C) swimming legs for a minimum of 5 min each. Average swimming time was 9 min 12 s (SD ± 4 min 18 s) during the first leg and 7 min 30 s (SD ±1 min 48 s) during the second leg. Eleven athletes swam in small lakes, 3 in a sea water pool, and 1 in the Baltic Sea. Average water temperature was 17.4°C (SD ± 2.6°C). The first swimming leg was without earplugs or swimming cap covering the external auditory canals, followed by an identical leg with earplugs. We recorded the eye movements and possible nystagmus immediately after each of the two legs with a mobile phone camera (see supporting information file). The mobile phone was attached to specifically designed swimming goggles that allowed the recording of eye movements and hindered gaze fixation ( Figure 1). In addition, the athletes were asked about the sensation of dizziness. Three of the athletes did not experience dizziness or had definite nystagmus after the first leg and did not swim the second leg. One athlete dropped an ear plug during the second leg and was excluded from the second leg analyses.

| Nystagmus analyses
A total of 27 eye movement recordings were evaluated by two experienced neurotologists blinded to the sensation of dizziness, use of earplugs, and each other´s evaluations. The neurotologists independently classified the recordings for nystagmus as yes, no, or maybe and its direction as right or left. At least, five beats were considered as F I G U R E 1 Mobile phone attached to specifically designed goggles was used to record eye movements after cold water swimming legs nystagmus. Each recording was shown twice in a random order. Every recording was thus reviewed four times. Four "yes" answers or three "yes" answers and one "maybe" were classified as nystagmus.

| Statistics
An independent professional consulting statistician from Elisa Appelsiini Oy (Helsinki, Finland) completed all statistical analyses.

| Questionnaire
We contacted 23 triathlon clubs by e-mail, 15 of which agreed to distribute the questionnaire electronically to its athletes. Thus, we do not know the number of athletes who received the questionnaire. The questionnaire was filled out by 125 triathletes. Some questions were not answered by all of the athletes. Background data of the participants are presented in Table 1. A majority (87%, 109/125) of athletes had experienced dizziness during triathlon races or training and 65% (80/124) had experienced dizziness often or always. Almost all (97%, 106/109) of those with dizziness experienced it during or after swimming, 7% (8/109) during cycling and 6% (6/109) while running. Dizziness was more common in open water (76%, 80/105) than in indoor pools (1%, 1/105). One-fourth (23%, 24/105) of the participants reported dizziness in both milieus.
Of those with dizziness, the dizziness affected the training or race performance in half of the athletes (50%, 51/102) (Figure 2). One-third of athletes with dizziness (31%, 32/102) needed to slow down and 13% (13/102) needed to stop for a while. Three athletes (3%) had fallen, one (1%) had interrupted a race, one (1%) had vomited and interrupted a race, and one (1%) needed to change swimming technique.

| Cold water swimming test
Fifteen triathletes participated in the cold water swimming test. During the first leg (without earplugs), 11 athletes (73%) experienced dizziness. Of these, six had nystagmus (55%), four had uncertain nystagmus (36%), and one did not have nystagmus (9%). A majority (91%, 10/11) of these athletes did not experience dizziness during the second leg (with ear plugs) and dizziness was more common during the first swimming leg (p = 0.0039). Results of the swimming test are presented in Table 2.
Each of the 27 eye recordings was analyzed four times. Concerning the presence of nystagmus "yes/maybe/no", the four analyses were unanimous in 65% (17/27) of recordings. The agreement in the direction of nystagmus was 100% (10/10) for recordings with a definite nystagmus. Intra-rater reliability was 0.81 (95% confidence interval 0.63-0.99) and 0.81 (0.66-0.96) for the two neurotologists. Six athletes experienced dizziness and had definite nystagmus after the first swimming leg. In these six athletes, the direction of nystagmus was opposite to the breathing side in five athletes (83%) who used unilateral breath. One athlete (17%) used bilateral breath and had a rightward nystagmus.

| Dizziness is a common concern among triathletes
Our study reveals that dizziness is a prevalent complaint among triathletes. The vast majority (87%, 109/125) of the questionnaire respondents had experienced dizziness at least once during triathlon training or racing. Even though there is probably a selection bias, as athletes with dizziness were more likely to participate, the prevalence of dizziness among triathletes is notable.

| Caloric reaction has a major impact on dizziness among triathletes
Almost all respondents (97%, 106/109) with a history of dizziness had experienced it during or after swimming. Several respondents (36%, 39/109) reported cold water as an exacerbating factor and some (15%, 16/109) had noticed alleviation with ear plugs. We consider these significant findings since the question was open-ended and we expected that all athletes had not tested earplugs during swimming.
Our hypothesis was that by preventing the caloric reaction, earplug usage prevents dizziness during cold water swimming. This hypothesis was supported by the cold water swimming test since the prevalence of dizziness and nystagmus was high during the first leg without earplugs (40%, 6/15) compared with the second leg with earplugs (9%, 1/11, p = 0.13). Almost all triathletes with dizziness (91%, 10/11) reported alleviation with use of earplugs in the cold water swimming test, and dizziness was less common with earplugs (p = 0.0039).
Our study demonstrates that a large part of the dizziness among triathletes is aggravated by caloric reaction of the vestibular organ. However, dizziness is often multifactorial and additional factors may have a role. These include high-intensity training with possible hyperventilation and motion sickness with visual-vestibular mismatch, as waves were reported as exacerbating factors and visibility is poor in open water swimming.

| Perspective
Dizziness accounts for one-fifth of medical visits during half-or full-distance triathlon. 1 Dizziness clearly affects the triathlete's performance, especially in cold and open water conditions. A major part of the dizziness is aggravated by caloric reaction of the vestibular organ and ear canal protection seems to prevent it. Earplug or swimming cap usage is an easy and affordable way to improve triathlon performance and swimming safety. In addition, they may prevent the formation of exostoses. 10 We recommend ear canal protection for all triathletes suffering from dizziness during swimming.