Case example of a female solo sailor competing in the Vendée Globe reveals extraordinary biological demands

ABSTRACT

The Vendée Globe is a non-stop, unassisted, single-handed round the world sailing race. It is regarded as the toughest sailing race, requiring high cognitive functioning and constant alertness. Little is known about the amount of sleep restriction and nutritional deficit experienced at sea and effects that fatigue have on sailors’ performance. This report aimed to investigate these aspects by monitoring one of the female participants of the latest Vendée Globe. Sleep, food intake and stress were self-reported daily using specific app. Cognitive assessments were digitally completed. Heart rate and activity intensity were measured using a wrist-worn wearable device. Mean self-report sleep duration per 24 h was 3 hours 40 minutes. By the end of the 95 race days, the sailor reached a caloric deficit of 27,900 kcal. On average, the sailor spent 50 minutes per day in moderate-to-vigorous activity. Cognitive assessments did not show any effect of fatigue or stress on completion time or performance. Recent technological and communication advancement for offshore sailors, enabled continuous data to be monitored in near real time, even from the Southern Ocean. Moving forward this will enable greater understanding of when sailors will be at risk of poor decision making, illness or injury.

KEYWORDS:

• Sailing
• single-handed offshore sailing races
• sleep
• extreme conditions
• food inventory
• cognitive performance

Introduction

Offshore ocean sailing is considered to be one of the most strenuous endurance sports, subjecting the sailors to prolonged extremely demanding physical and mental efforts (Allen & De Jong, 2006). At the competition level, ocean sailing requires navigating through exceptionally challenging conditions, in seclusion and self-sufficiency, with restricted availability of outside assistance or rescue while spending extended durations at sea on a racing boat designed to be performant with minimal to no onboard comfort (Sjøgaard et al., 2015). The energy expenditure is substantial during offshore sailing, making it difficult to sustain sufficient nutrient intake onboard, particularly in adverse weather conditions (Fearnley et al., 2012; Myers et al., 2008). Important weight loss and diminished muscle strength are often observed as a negative energy balance and dehydration (Allen & De Jong, 2006; Bigard et al., 1998; Lafère et al., 2020). Effective sleep management is crucial for maintaining optimal performance (Léger et al., 2008). Sailors sleep in multiple short bouts and experience significant sleep deprivation during competitions, leading to decreased cognitive performance and alertness (Hurdiel et al., 2014).

The Vendée Globe is a single-handed (solo), unassisted, non-stop round-the-world sailing race via the three capes, first held in 1989. A physically demanding challenge compounded by sleep deprivation and psychological stress from continuous alertness to changing weather and risk of damage and/or collision.

The Vendée Globe is considered an extreme quest of individual endurance and the ultimate test in ocean racing for which appropriate nutrition should maintain energy balance and ensure optimum performance focusing on an assessment of daily nutritional intake, heart rate (HR), sleep patterns, during the race using a multimethod approach.

There is a dearth of research into the impact of extreme endurance sport on female athletes, in terms of impact on hormones, menstrual cycle, sleep, stress and cognitive function (Fearnley et al., 2012; Ireland et al., 2020).

Findings published in 2012, reported data from 16 sailors during a two-leg transatlantic race reported significant functional impairments experienced throughout the race including technical errors, mood changes and hallucinations (Hurdiel et al., 2012). These impairments were found consistent with the typical effects of substantial sleep loss. The paper concluded that “single-handed sailors could benefit from the development of innovative tools to help them to manage sleep and fatigue and thereby improve safety and effectiveness”.

This is an account of a professional and experienced female racer that completed the 2020–2021 Vendée in 95 days, 11 hours, 37 minutes and 30 seconds on her first attempt, becoming the eighth woman to have ever completed the race (12 February 2021). The aim of this study was to monitor an elite female sailor taking part in a competitive race using a consumer-grade wearable device, digital app assessments and digital sleep diary. The purpose of the study was to gather valuable insights into the impact of extreme endurance on elite female sailors participating in single-handed sailing racing in terms of nutrition, sleep, stress and cognitive function which help the racer in improving their nutrition strategies and sleep and stress management.

Methods

The sailor was a 47-year-old white Caucasian female with height of 173 cm (5 ft 8 inches). One aspect of the sailor’s preparation for the Vendée Globe was an injury prevention programme, working on regular stretches and strength and conditioning exercises to ensure optimum physical performance. This was also matched with increased caloric intake in the build up to the race to support weight gain, and muscle mass. Her usual body weight is 71 kg but by the start of the race the sailor had a weight of 74.2 kg. Based on her height and weight a daily energy intake calculation of 3257 kcal on average was recommended. The menu plan was calculated to provide a balance of nutrition and considering her vegetarian-based diet preference, as detailed in Table 1. Daily food rations were packed into a 10-day cycle and marked. Fluid intake (three litres per day) was a combination of water and tea and targeted to maintain hydration and avoid energy depletion and decreased brain function. Medical advice was sought via direct link on the Satellite phone to her medical team and logged by them.

Table 1. Contents of 10-day food bag.

Brand	Product	Quantity	Energy (kcal)	Carbo hydrate (g)	Fat (g)	Protein (g)	Fibre (g)
Day 1
Nakd	Lemon Drizzle bar	2 × 35 g	266.00	36.20	10.80	4.20	3.60
TentMeals	Subtly Cinnamon Breakfast	1 × 182 g	800.00	100.90	37.90	18.30	13.50
Tesco	Dried Fruit – Apricots	1 × 250 g	475.00	106.00	0.00	5.00	14.50
TentMeals	Italian Inspired Main Meal	1 × 198 g	800.00	112.70	28.20	29.10	12.70
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Trek’n Eat	Chana Masala	1 × 180 g	610.20	122.40	4.50	16.92	10.26
Day 2
Nakd	Carrot cake	1 × 35 g	148.00	16.20	7.60	2.80	1.60
Expedition Foods	Porridge with Blueberries	1 × 170 g	806.00	100.10	34.00	20.10	9.40
Tesco	Dried Fruit – Raisins & Cranberries	1 × 300 g	1005.00	231.30	3.00	5.70	14.70
REAL	Field Meal Couscous with lentils and spinach	1 × 165 g	706.00	92.40	23.10	28.10	3.00
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Expedition Foods	Macaroni and Cheese	1 × 180 g	804.00	101.00	30.40	28.60	5.60
Day 3
Nakd	Strawberry Sundae	1 × 35 g	130.00	19.00	4.60	2.50	1.40
TentMeals	Cashew & Goji Berry Breakfast	1 × 196 g	800.00	107.60	34.00	24.90	15.80
Tesco	Dried Fruit – Mango	1 × 200 g	660.00	149.40	1.60	3.80	16.20
Trek’n Eat	Chana Masala	1 × 180 g	610.20	122.40	4.50	16.92	10.26
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
TentMeals	Almond Jalfrezi Main Meal	1 × 174 g	800.00	96.60	41.00	18.70	11.90
Day 4
Nakd	Bakewell Tart	1 × 35 g	137.00	17.60	5.90	2.60	1.70
Expedition Foods	Granola with Raspberries	1 × 190 g	800.00	129.00	44.60	23.60	17.50
Tesco	Wholefood Luxury Fruit & Nut Mix	1 × 300 g	1452.00	136.20	81.90	33.30	18.00
REAL	Turmat Chili Stew with Beans	1 × 132 g	567.00	51.50	25.10	26.40	16.50
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Expedition Foods	Fish & Potato with Parsley Sauce	1 × 144 g	800.00	55.40	55.00	21.20	4.60
Day 5
Nakd	Banoffee Pie	2 × 35 g	258.00	37.20	9.20	4.80	3.20
TentMeals	Subtly Cinnamon Breakfast	1 X 182 g	800.00	100.90	37.90	18.30	13.50
Tesco	Dried Fruit – Apricots	1 × 250 g	475.00	106.00	0.00	5.00	14.50
Firepot	Dal and Rice with Spinach	1 × 200 g	750.00	142.60	8.20	29.00	21.00
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Trek’n Eat	Potato Stew with Fried Onions	1 × 150 g	592.50	73.35	24.30	16.35	1.80
Day 6
Nakd	Lemon Drizzle bar	2 × 35 g	266.00	36.20	10.80	4.20	3.60
Expedition Foods	Granola with Raspberries	1 × 190 g	800.00	129.00	44.60	23.60	17.50
Tesco	Chewy Banana	1 × 300 g	918.00	201.60	1.80	13.20	21.90
LYO Expedition	Nettle Curry by Sean Villanueva O’Driscoll	1 × 110 g	530.00	56.32	27.06	11.11	5.00
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Firepot	Posh Baked Beans	1 × 200 g	695.00	118.80	5.00	43.50	29.70
Day 7
Nakd	Carrot cake	1 × 35 g	148.00	16.20	7.60	2.80	1.60
TentMeals	Blueberry burst breakfast	1 × 198 g	800.00	126.80	22.80	21.40	20.00
Tesco	Dried Fruit – Apple	1 × 300 g	846.00	189.00	0.90	5.10	31.20
Trek’n Eat	Mexican-style Quinoa	1 × 140 g	597.00	63.00	29.40	15.40	10.78
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Firepot	Dal and Rice with Spinach	1 × 200 g	750.00	142.60	8.20	29.00	21.00
Day 8
Nakd	Strawberry Sundae	1 × 35 g	130.00	19.00	4.60	2.50	1.40
TentMeals	Cashew & Goji Berry Breakfast	1 × 196 g	800.00	107.60	34.00	24.90	15.80
Tesco	Unsalted Mixed Nuts	1 × 100 g	649.00	5.00	58.80	20.40	9.30
Expedition Foods	Fish & Potato with Parsley Sauce	1 × 144 g	800.00	55.40	55.00	21.20	4.60
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
TentMeals	Almond Jalfrezi Main Meal	1 × 174 g	800.00	96.60	41.00	18.70	11.90
Day 9
Nakd	Bakewell Tart	1 × 35 g	137.00	17.60	5.90	2.60	1.70
TentMeals	Subtly Cinnamon Breakfast	1 × 182 g	800.00	100.90	37.90	18.30	13.50
Tesco	Fruit & Seed Mix	1 × 150 g	823.50	51.90	58.20	17.55	10.95
REAL	Turmat Chili Stew with Beans	1 × 132 g	567.00	51.50	25.10	26.40	16.50
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Expedition Foods	Fish & Potato with Parsley Sauce	1 × 144 g	800.00	55.40	55.00	21.20	4.60
Day 10
Nakd	Banoffee Pie	1 × 35 g	129.00	18.60	4.60	2.40	1.60
TentMeals	Cashew & Goji Berry Breakfast	1 × 196 g	800.00	107.60	34.00	24.90	15.80
Tesco	Dried Fruit – Raisins & Cranberries	1 × 150 g	502.50	115.65	1.50	2.85	7.35
Firepot	Dal and Rice with Spinach	1 × 200 g	750.00	142.60	8.20	29.00	21.00
Alpro	Long Life Oat Milk	1 × 200 ml	88.00	13.60	3.00	0.60	2.80
Expedition Foods	Fish & Potato with Parsley Sauce	1 × 144 g	800.00	55.40	55.00	21.20	4.60

Throughout the 95-day voyage the sailor wore a wrist-worn Garmin vívosmart^Ⓡ4 wearable linked with Bluetooth to an app, Atom5^TM, designed specifically for the race by Aparito, a digital health company. Daily self-reported data were recorded in the app and transferred back in real time via satellite phone along with the Garmin data. The app was configured to match the daily food rations and the sailor recorded if she had not ingested certain planned rations on certain days, or if she had eaten extra food not on the planned ration. The sailor’s basal metabolic rate (BMR) was estimated from the Harris-Benedict formula (Harris & Benedict, 1918). Her daily activity energy expenditure (AEE) was estimated from the wearable data using the following formula (Keytel et al., 2005):

$\mathit{AEE}=\frac{-20.4022+0.4472\ast \mathit{HR}-0.1263\ast \mathit{W}+0.074\ast \mathit{A}}{4.184}\ast \mathit{ACT}$

Where:

HR = mean HR (in beats/minute) for the day

W = weight (in kilograms) at race start

A = age (in years)

ACT = Activity duration of light to vigorous intensity (in minutes) for the day

The daily total energy expenditure was then estimated as the sum of BMR and AEE.

Physical activity intensity was estimated from HR measures derived from the wearable. A percentage of maximal HR (HRmax) indicates intensity. Very light activity intensity (rest) threshold was estimated as a percentage of HRmax evaluated from the average resting HR prior to race start. Moderate and vigorous intensity thresholds were computed based on the American College of Sports Medicine’s guidelines for aerobic exercise testing and prescription (Schulz et al., 2020). The athlete’s resting HR was monitored with the wrist wearable in the week preceding the race while she was in the race village where boat safety inspections and final testing took place.

The sailor maintains good sleep hygiene and sleeps on average 8 hours per night while on shore. The sailor has a long experience of competing and solo training, she learned over the years how to adopt polyphasic sleep. Her preparation for the competition in terms of sleep management consisted of banking sleep while on shore. The sailor used the app to report sleep periods and restfulness. Available restfulness categories were: Very well-rested, Well-rested, Somewhat rested, Slightly rested, Not at all rested. Sleep debt was estimated based on the average value of eight hours of sleep per day, which is the sailor’s personal average on shore. Sleep debt was computed by subtracting the actual sleep duration from the amount of eight hours of daily sleep, required by the sailor to maintain her performance.

The racer was prompted to complete a daily stress assessment using a 1–5 Likert scale (calm to stressed, respectively). Every three days, the sailor took part in cognitive assessments modified from the Montreal Cognitive Assessment (MoCA) (Nasreddine et al., 2005). Namely the sailor was alternatively asked to complete forward and memory number tasks and answer a set of trick questions (Table 2). The assessments remained available for 24 hours in the app for completion and were meant to assess the sailor’s memory and alertness.

Table 2. Cognitive assessments.

Assessment type	Task	Outcome Measure
Forward Memory #1	For each of the 4 sequences of numbers, read the numbers and repeat them in exactly the same order. 1 *** 6 *** 9 *** 2 *** 5 3 *** 0 *** 1 *** 2 *** 6 *** 4 7 *** 1 *** 1 *** 9 *** 8 *** 4 *** 6 2 *** 0 *** 5 *** 6 *** 9 *** 7 *** 3 *** 8	Assessment completion time Number of errors
Forward Memory #2	For each of the 4 sequences of numbers, read the numbers and repeat them in exactly the same order. 3 *** 5 *** 6 *** 9 *** 8 2 *** 6 *** 4 *** 2 *** 7 *** 1 2 *** 7 *** 5 *** 8 *** 3 *** 1 *** 6 4 *** 2 *** 8 *** 5 *** 7 *** 8 *** 9 *** 1	Assessment completion time Number of errors
Backward Memory #1	For each of the 3 sequences of numbers, read the numbers and repeat them in reverse order. 4 *** 7 *** 0 *** 9 6 *** 5 *** 2 *** 8 *** 1 5 *** 9 *** 0 *** 3 *** 7 *** 4	Assessment completion time Number of errors
Backward Memory #2	For each of the 3 sequences of numbers, read the numbers and repeat them in reverse order. 9 *** 2 *** 4 *** 7 2 *** 4 *** 2 *** 1 *** 3 6 *** 7 *** 3 *** 4 *** 5 *** 1	Assessment completion time Number of errors
Problem Solving #1	Answer the following questions. How are a watch and a ruler similar? Write down how they are alike. They both are… what? How many hours are there in 3 days and 4 hours? You are buying £13.45 of groceries. How much change would you receive back from a £20 note?	Assessment completion time Number of errors
Problem Solving #2	Answer the following questions. Write down the names of up to 12 different animals (minimum of five) How many hours are there in 4 days and 18 hours? You are buying £3.45 of groceries. How much change would you receive back from a £10 note?	Assessment completion time Number of errors
Problem Solving #3	Answer the following questions. Write down the names of the seven dwarves in Snow White How many hours are there in a week? You are buying three pints at £2.45 each. How much will it cost you in total?	Assessment completion time Number of errors

Analyses were done in R version 4.2.2. Regression analyses were performed to test the relationship between two variables. Statistical significance level was set at 0.05.

Results

On the first day into the race, the reported nutrition intake represented 29% of the intake goal. Over the course of the race, the sailor consumed on average 95% of the expected daily intake. She complimented her daily nutrition intake with extra food that were not included in the food bags such as apples or high protein snacks (Long Range Fuel, Resilient Nutrition). On average, this extra food intake represented 32% of the sailor’s daily nutrition intake. In total the racer usually reached or nearly reached her intake goal due to the high nutritive value of her snacks. However, her energy expenditure was most of the time higher than the daily energy intake goals resulting in a mean daily caloric deficit of 294 kcal. Consequently, by the end of the race she was in a cumulative caloric deficit of ~ 27,900 kcal (Figure 1).

Figure 1. Cumulative caloric deficit. Oceanic phases are reported on top. D = doldrums.

Over the course of the race, the sailor was physically active between 4.6 and 18.5 hours in a day (13 hours on average). On average, she spent 50 minutes per day in moderate-to-vigorous activity. During the most strenuous phase of the race, in the South Pacific, the average time spent in moderate-to-vigorous activity reached 1 hour 25 minutes per day. Her physical demands were particularly high on three consecutive days where her HR was in the moderate-to-vigorous intensity zone for two to four hours a day (Figure 2).

Figure 2. Physical activity duration and intensity. Oceanic phases are reported on top. D = doldrums.

The average HR 64.1 bpm recorded during the week preceding the race was quite high as compared to her usual resting HR of 59 bpm and reflected her high stress levels in the run-up to the race. The racer’s HR pattern at the time of significant race events such as mast climbing, and rudder change are presented in Figure 3.

Figure 3. Heart rate patterns at the time of significant events. A: Mast climbing to fix tie back elastics. B: Sailor informed that boat immediately before hers hit a whale. Tack line snapped with a loud bang. C: Rudder change. D: Jellyfish sting. Oceanic phase is reported on top of each panel. When known, the exact timing of the events is shown by a vertical dotted or dashed line.

On her 95-day voyage, the sailor completed 75 (79%) stress assessments (Figure 5). Most of the time, she reported feeling calm (75%). She experienced some stress self-reported as being of level two in 9% of the days and a stress of level three in 16% of the days at sea. Sailing in the South Atlantic was the most stressful race phase. The sailor reported a stress level of three for 24% of the days spent in this ocean. The highest rate of non-responded stress assessments (38%) was in the last portion of the race in the North Atlantic on the way back to Les Sables-d’Olonne.

The sailor’s sleep was polyphasic with sleep periods ranging from 10 minutes to four hours (Figure 4). Her sleep duration per day varied from 35 minutes to 8 hours 30 minutes, with an average of 3 hours 40 minutes per day. The sailor recorded a total of 348 sleep periods. Out of these, she reported feeling well-rested after 4% of the sleep periods, somewhat rested after 27% of those, slightly rested after 30% of those and not at all rested after less than 1% of those. Restfulness was not captured for 38% of the sleep periods. The sailor’s sleep debt per day ranged from 15 minutes to 7 hours 25 minutes, with an average of 4 hours 20 minutes per day. On three occasions, she slept through or over her average sleep duration of eight hours per day while on shore. In the strenuous phase of the South Pacific, her average sleep duration per day dropped to 2 hours 40 minutes and her average sleep debt per day increased to 5 hours 19 minutes.

Figure 4. Reported sleep duration and estimated sleep debt. A: Sleep duration. B: Sleep debt. Oceanic phases are reported on top. D = doldrums.

Figure 5. Reported stress level. Oceanic phases are reported on top. D = doldrums.

During the race, a total of 30 cognitive assessments were sent out to the app for the sailor to complete. She completed 26 of these assessments (87%). The sailor completed the assessments in 56.8 seconds on average (range: 27–123 seconds). It took more than twice as long to complete the problem-solving assessments than to complete the memory tasks (79.5 seconds vs 37.3 seconds on average, respectively). The sailor seemed more comfortable with repeating the sequences of numbers backward than repeating them forward as reflected by the average completion times of 30.7 seconds and 43.9 seconds, respectively. Overall, the maximum completion time for the backward memory assessment (35 seconds) was shorter than the minimum completion time for the forward memory task (37 seconds). The responses were all correct for the seven backward memory assessments while five out of the seven forward memory assessments were 100% correct and two were 75% correct. Errors or incomplete answers were more frequent for the problem-solving tasks (53.8% of the assessments contained an error) than for the memory assessments (11.8% of the assessments contained an error) (Figure 6). Overall, the sailor demonstrated a good memory and alertness level. Indeed, the assessments with errors contained no more than a single error. Errors happened throughout the whole race and not at a particular phase. No relationship was found between the correctness of the responses and the completion time of the assessments.

Figure 6. Cognitive assessments. A: Backward Memory. B: Forward Memory. C: Problem solving. Oceanic phases are reported on top. D = doldrums.

Relationships between continuous variables (sleep duration, moderate-to-vigorous activity minutes, calories) were explored as well as between these variables and categorical stress levels. No relationships were statistically significant except for the relationship between moderate-to-vigorous activity minutes and burned calories (adjusted R2 = 0.51; p-value <0.0001) and between moderate-to-vigorous activity minutes and sleep duration (adjusted R2 = 0.05; p-value = 0.034).

Discussion

Nutrition and hydration

According to the self-reported food diary, the sailor‘s energy intake met on average 95% of the expected daily energy intake, largely higher than the 72% of energy consumption reported by Fearnley et al. (2012). The lowest energy intake reported throughout the race was 29% of the day intake goal and was reported on the first day. It was the only occasion that the reported energy intake reached levels below 45% of the recommended intake. The sailor reported that she was unable to find time to eat due to bad weather conditions at the beginning of the race and the effort required to sail. Snacks were not included in the daily food bags, however they represented on average 32% of the daily food intake and up to 56%. Snacks did not require any preparation, thus were easier to consume than the freeze-dried meals, especially when the sailor was being absorbed in challenging weather fronts, fixing and maintenance of the boat. Since snacks represented a large proportion of the total food intake, these should be planned more carefully for future voyages. Food fatigue of the repetitive food provided was also experienced by the sailor. Wider variability of food that avoids too many repetitions in food bags could have a positive impact on the sailor’s nutrition, thus should be considered in the future. In general sleep always took precedence over food and the racer had to force herself to eat at times. The sailor evidenced a 9-kg weight loss during the voyage as a consequence of caloric underconsumption and dehydration. This represented around 10% body loss over the race. Although the sailor was regimented about consuming three litres of fluid every day, she suffered periods of dehydration where her urine output signification decreased, as reported by her medical team. Few studies reported the hydration status in competitive sailors (Arnaoutis et al., 2018; Fearnley et al., 2012; Lewis et al., 2013). Lewis et al. reported significant body mass losses in elite Olympic class sailors even in cold conditions despite ad libitum fluid intake (Lewis et al., 2013). Arnaoutis et al. demonstrated a progressive dehydration and body weight (−5.8 ± 0.2%) loss over a 4-day race in elite young sailors (Arnaoutis et al., 2018). Her menstrual cycle also stopped after the second month at sea. Amenorrhoea is a common symptom in elite female athletes (Berz & McCambridge, 2016; Coelho et al., 2021; The Female Athlete Triad, 2007). These results shed light on the specific energy needs of a female athlete involved in specific tasks of a single-handled ocean sailing regatta, a critical result given the importance of assessing energy balance and food habits for sailors (Bernardi et al., 2007).

Physical activity

Over the course of the race, the sailor was physically active for an average of 13 hours per day and spent on average 50 minutes per day in moderate-to-vigorous activity. The physical activity amount reflected the constant effort and endurance required in ocean racing. The high time spent in physical activity was consistent with the low amount of sleep. Physical activity duration was estimated from the sailor’s wearable-derived HR. The sailor’s usual resting HR of 59 bpm is typical of the low resting HR observed in endurance athletes. Endurance athletes typically demonstrate better cardiac autonomic function than non-athletes, with lower resting HRs (Carter et al., 2003).

Stress

The increased and prolonged elevated HR levels at the time of significant race events showed the sailor’s physiological and emotional response to physical effort and stress. Stress is inevitable in such incredibly demanding sailing races. The lack of control over factors like injury, equipment breakages or stormy weather can generate high levels of stress. Stress can also be exacerbated by poor performance. In 75% of the daily stress assessments, the sailor reported that she was feeling calm. Her self-reported stress levels may differ from her overall stress levels during the whole day. In the most strenuous moments, stress levels were often not reported. Thus, her stress levels at the time she was able to complete the assessments may have been lower than the stress levels she experienced during the whole day. Correlation analysis between resting heart rate and self-report stress levels were not statistically significant. The findings of this study can help sailors manage their stress and sail more effectively as they become more trained to recognise the manifestation of high levels of stress. Devices that provide real-time feedback could be used to inform about high stress and prevent poor decision making.

Sleep

The sailor slept in short blocks whose duration ranged from 10 minutes to four hours (Figure 4). Her accumulated sleep duration per day varied from 35 minutes to 8 hours 30 minutes, with an average of 3 hours 40 minutes per day. Although the sleep data were only self-reported, confidence in the accuracy of the sleep amounts can be inferred from the fact that comparable average sleep amounts were reported by other solo sailors (Hurdiel et al., 2012). Sleeping on average less than four hours a day is substantially less than what would have been recommended to maintain a good level of alertness and optimal cognitive functioning (Belenky et al., 2003; Dinges et al., 1997; Van Dongen et al., 2003). Out of the 95 days of the voyage, the sailor reported her sleep for 86 days (91%). The very low amount of missing sleep data was indicative of the high engagement of the sailor and commitment to this case report. No technical issues in logging sleep data were reported. Sleep setting while at sea was not optimal. The equipment considerably limited the space for sleeping, thus the sailor was not able to properly lay down. She slept on a beanbag which may not have provided the comfort required for restful sleep. She indicated that she felt somewhat rested after 27% of the reported sleep bouts and slightly rested after 30% of those. Single-handed sailors need to achieve an optimal optimal balance between time awake for high-performance sailing, and time asleep for maintaining optimal performance capability. As technology and connectivity evolves, future opportunities for real-time analysis and feedback are.

Exhaustion did not have an evident effect on memory/alertness assessment. This may be due to the appropriateness of the cognitive assessment scale used, which was a modified version of an in-clinic scale, and therefore possibly not sensitive enough for the environment and likely high variability observed from hour-to-hour. Based on the extreme environment endured, and the stressors on the athlete, the effort required for logging food, sleep and completing cognitive tasks are not to be underestimated. The total number of missed assessments (13%) and daily reports (21%) are therefore considered to be relatively low, demonstrating the high motivation of the sailor. Regression analyses were conducted to explore the effects of stress, sleep deprivation and physical exhaustion. However, none of the tested relationships were statistically significant except for the positive relationship between moderate-to-vigorous activity minutes and burned calories which was physiologically expected and between moderate-to-vigorous activity minutes and sleep duration. Although the latter relationship was statistically significant, the low R² value (0.05) indicated a poor fit. More data, especially objective sleep data, would be required to further explore the sailor’s recovery process after intensive activity.

Wearable technology

Wearable technology has been increasingly used to improve monitor sport performance through real-time tracking (Rana & Mittal, 2021; Seçkin et al., 2023; Seshadri et al., 2019), including in outdoor sports (Noonan et al., 2012). The choice of Garmin vívosmart^Ⓡ4 was comfortable to use, with long battery life, and Garmin Health SDK allowed access to the raw sensor data for analysis. Although the Garmin vívosmart^Ⓡ4 provided activity and energy expenditure metrics, these are based on 3-axis acceleration signals which are processed with proprietary algorithms. In sailing conditions, boat movement would need to be accounted for when processing the acceleration signals in order to distinguish the sailor’s activity. Thus, energy expenditure was estimated from the heart rate measurements in this care report. The chosen device is a consumer-grade device which uses photoplethysmography to derive the user’s heart rate from the changes in blood volume. While consumer-grade devices provide less accurate heart rate measurement than medical-grade devices, they are more affordable and more widely used. Studies demonstrated that wrist-worn consumer-grade devices provide heart rate measurements that are within an acceptable error range of 5% as compare to the gold-standard electrocardiogram (Chow & Yang, 2020; Shcherbina et al., 2017), which we considered reasonable for the purpose of this study. This case report demonstrated that wrist-worn wearables can accurately monitor HR response to stress. Their use in managing sailors’ stress could be further explored.

Digital self-reporting

Questionnaire answers were received in real-time, but the data was not actionable, and in keeping with the Vendée Globe race rules on outside support. Descriptive studies based on self-reported data collected through questionnaires have been as adequate solutions for studying adventure sports such as offshore ocean racing (Feletti & Brymer, 2018). In our study, subjective self-reports were complemented with objective data monitored with the wearable device. This is considered to be the first of its kind in terms of innovative, endurance monitoring during extreme sports and extreme conditions. Such insights should be considered for preparing athletes for such environments. Future races would benefit from such monitoring across the fleet, to allow for comparability of the results, but also overall monitoring of the sailors’ physical and emotional well-being while at sea.

Limitations

One of the limitations of the study is that the food intake measures solely relied on self-reported food consumption. Although the sailor rigorously completed the food diary, a postrace inventory of non-consumed food items would have been more accurate especially for listing consumed snacks which were not pre-programmed in the app. Fluid intake and hydration were not measured due to the difficulties in getting precise measurements without adding burden to the sailor. Precise measurements require, at a minimum, insight into the sailor’s sweat rate and urine concentration which would be difficult to obtain in such harsh conditions experienced by the Vendée Globe sailors. It is widely acknowledged that proper hydration is crucial for enhancing performance, preventing injuries, and aiding recovery in competitive athletes. Sustained consumption of fluids enriched with carbohydrates and electrolytes during activities lasting more than one hour has been shown to prevent declines in endurance, strength, blood volume (Costill, 1977; Coyle & Montain, 1992; Sawka et al., 2007), and cognitive function (Adam et al., 2008). More insight on hydration status of sailors competing in extreme conditions should be gained to determine optimal fluid intake and develop hydration recommendations for elite sailors.

Another limitation is that no notifications were sent to remind the sailor to log her sleep in the digital diary. The days with missing data were essentially at the beginning of the race where the weather conditions were strenuous and on the last race day, where reminders to log the data would have been helpful to the sailor. The Garmin vívosmart^Ⓡ4 used in this case report did not integrate the on-device sleep feature that the newest generation of the wearable offers. As a result, sleep tracking was not available for this case report. Some algorithms have been developed to predict sleep cycles using wearable data (Liu et al., 2020; Walch et al., 2019), however they are based on accelerations derived data which were not used in this case report for the reasons stated above. Sailors could benefit from using a newer generation of wearables that integrate sleep tracking as they provide valuable insight into sleep cycles and restfulness which could help the sailors to better manage their sleep while at sea.

We did not consider the impact of bright light on sleep in our study. The potential sleep disruptive effects of bright light as reflected on water have been discussed by Postolache and Oren (Postolache, 2005).

Conclusion

This case report provided valuable insights into the impact of extreme endurance on elite female sailors participating in single-handed sailing racing in terms of nutrition, sleep, stress and use of wearable technology. The study demonstrated that further work is required to improve the sailor’s nutrition strategy for future races and prevent considerable weight loss. Sailors could benefit from wearable-based sleep and stress measurement and real-time analysis training them on recovery and sleep deprivation induced stress management. Wearable technology is rapidly evolving and could become more effective in improving the performance of elite athletes taking part in competitions in extreme conditions.

Acknowledgments

We would like to thank the sailor for her commitment to this case report and for providing valuable data.

Disclosure statement

SK is employee at Aparito. LA is employee at Pip Hare Ocean Racing. EHD is employee at Aparito and holds shares.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.