Ultra-running (UR) comprises running events longer than a marathon (>42.2km). Due to the prolonged duration of UR, decrements in most or all physiological parameters are to be expected, and include a decrease in body mass and dehydration, loss of skeletal muscle mass and increased total body water. Purpose: to present data on a female multiple world record holding ultra-runner, examining haematological and physiological perturbations, as well as nutritional strategies throughout a successful treadmill world record attempt for total distance completed in seven days on a treadmill (833.05km). Methods: Sharon Gayter (SG) 47 years, 162.5cm, 49kg, V̇ O2max 48 ml/kg/min-1 ran continuously for 7 days on a treadmill located at Teesside University, UK. 3-hours of running were followed by 30-minute breaks, and night-time rest from 1am-5am. Heart rate (HR), oxygen uptake (V̇ O2), weight (kg), blood lactate (La; mmol.L-1), haemoglobin (Hb; g.DL-1), haematocrit (hct; %), glucose (G; g.l-1), and nutrition were recorded. Results: SG ran at approx. 7km/h for 17.5 hours/day, covering an average of 120km. Mean V̇ O2 1.2 ± 0.1 L.min-1/ 24.7 ± 3.2 mL.kg.min-1, RER 0.80 ± 0.03, HR 125 ± 5 b.min-1. Weight increased from 48.6 to 49.5kg. Hb decreased from 13.7 to 11 g.DL-1, and hct decreased from 40% to 33%. Average G was 6.3 ± 1.6 g.l-1, (range 2.65-9.14 g.l-1), and average blood lactate was 1.0 ± 0.5 mmol.L-1, (range 0.4-3.3 mmol.L-1). Energy expenditure (EE) for each 24-hour period was 6878 kcal, and energy intake (EI) was 2701 kcal. Hourly EE was 382 kcal, with 66.6% and 33.4% of the energy coming from fat and carbohydrate oxidation, respectively. 7-day EI was 26,989 kcal and EE was 48,147 kcal, resulting in a total energy deficit (ED) of 21,158kcal. Conclusion: The previous record of 753.24km was extended by 79km to a new world record of 833.05km. SG exhibits an enhanced fat metabolism through which she covered the large daily ED. The increase in body weight could be the result of protein catabolism. The corresponding development of hypoproteinaemic oedema, and increased plasma volume, likely lead to the reduced Hb and hct. Her success can be attributed to a combination of physiological and psychological factors, as she remained upbeat throughout the event and stated that she felt that the attempt was easy but became a bit ‘tedious’ towards the end.