Ultra-endurance record-breaking attempts place significant metabolic, cardiovascular, and mechanical stress on the athlete. This research explores the personal experience and physiological responses of a non-professional athlete attempting the Guinness World Record of covering 620 km on foot across the United Arab Emirates in 7-days or less. The participant wore a smartwatch throughout the challenge to collect heart rate, activity, and environmental temperature data. Anthropometric, body composition, and inflammatory, haematological, and endocrine biomarkers measurements were completed pre- and post-event. A pre- and post-event interview was conducted to collect data on training and preparation, and self-reported experiences during the challenge. Despite episodes of diarrhoea, vomiting, and muscle cramps due to hypohydration during the first days of the challenge, the participant successfully completed 619.01 km in six days, 21 hours, and 47 minutes (average pace 10.11 min/km) achieving a new Guinness World Record. Body mass remained unchanged, fat mass decreased, and fat-free mass especially in the legs increased over the seven days, most likely due to water retention. Biomarkers of stress, cell damage, and inflammation increased. Haematological markers related to red blood cells decreased probably due to exercise-induced increases in plasma volume with the participant classified with mild anaemia post-event. This case study reinforces the importance of amateur athletes attempting similar ultra-endurance events adhering to a pre-planned hydration and nutrition strategy to maximise performance and minimise the risk of injury.

• This study assessed the personal experience and physiological responses of a non-professional athlete attempting the Guinness World Record of covering 620 km on foot across the United Arab Emirates in 7-days or less.

• Despite a well-defined nutritional and walking pace plan, the participant suffered from gastrointestinal pain and diarrhea during day 1 and physical pain from day 2 due to failure of adhering to the nutrition and pacing strategy.

• The athlete experienced changes in biomarkers that indicate stress, cell damage, and inflammation including a 30-fold increase in c-reactive protein, an 81% increase in creatine kinase-MB (CK-MB) and 102% increase in ferritin from pre- to post-event.

• The participant was borderline anaemic prior to the event and his haemoglobin levels decreased by 9% by the end of the challenge to 12.2 g/dL classifying him with mild anaemia; however, this may be due to post-exercise haemodilution.

• This case study observations reinforce the importance of (i) consulting a sports medicine physician in the pre-planning stage; (ii) adhering to a pre-planned hydration and nutrition strategy and training the gastrointestinal tract to tolerate high glucose intakes during prolonged physical exertion; (iii) complementing endurance training with sport-specific strength and conditioning; and (iv) psychological skills development, especially to cope with physical pain, discomfort, sleep deprivation, and injury.