Nutritional Considerations for Ultra-Endurance Runners


Ultra-endurance sports have been classified by a winning time ≥6-hours (Zaryski and Smith, 2005; Tiller et al., 2019), however, some authors suggest that any event ≥ 4-hours can be defined as ultra-endurance (Hoffman and Krouse, 2018; Hoffman, Ong and Wang, 2010; Knoth et al., 2012). Thus, for the purpose of this critical essay, ultra-endurance running (UER) performance will be defined as any event ≥4-hours or those in excess of a distance of a traditional marathon (>42.2-km) (Millet and Millet, 2012; Nicolas, Banizette and Millet, 2011; Best et al., 2018). These events take place over single or multiple-days and involve prolonged bouts of demanding physical effort (Costa, Hoffman and Stellingwerff, 2019), which may or may not incorporate scheduled periods of respite (Brown and Connolly, 2015). Thus, it’s imperative that athletes carefully and correctly manage their nutrient and hydration requirements, to achieve and sustain peak physiological and psychological performance (Costa, Hoffman and Stellingwerff, 2019). Furthermore, these events take place in differing and challenging environments like altitude or in extreme weather conditions (desert, jungle or artic) and can be classified as trail, track or road events (Figure 1) (Costa, Hoffman and Stellingwerff, 2019; Costa et al., 2019; Best et al., 2018). Consequently, these events generate large energy demands due to the energetic cost of UER, inducing a negative energy balance which may lead to energy depletion if the athlete is not sufficiently fuelled (Williamson, 2016; Nikolaidis et al., 2018; Lazzer et al., 2012). This large energy demand upregulates thermoregulation leading to increased sweat-rates and possible dehydration (Chiampas and Goyal, 2015), resulting in reduced performance (Kruseman et al., 2005; Machefer et al., 2007; Stuempfle et al., 2011; Shirreffs and Sawka, 2011; Goulet, 2013).


Figure 1: Schematic definition of the multifactorial nature of UER reproduced from Costa et al. (2019).

Physiology and Training Demands

Success in UER is defined by one’s ability to achieve and maintain a greater mean running velocity for the set event distance, above that of the competition (Zaryski and Smith, 2005). This is governed by a plethora of physiological determinates of endurance and ultra-endurance performance (Bassett Jr and Howley, 2000; Joyner and Coyle, 2008) which consists of, but is not restricted to: a greater maximal oxygen consumption (VO2max) and velocity at VO2max (vVO2max), delayed lactate response to exercise, running economy (RE), substrate availability and utilization, thermoregulatory demands and gastrointestinal (GI) robustness (Knechtle and Nikolaidis, 2018). Additionally, some psycho-physiological demands also play an important role in successful performance including: technical proficiency and race experience (Knechtle, Knechtle and Rosemann, 2010; Knechtle et al., 2011; Knechtle et al., 2009), pacing strategy over the entire event (Micklewright et al., 2015), availability of ergogenic aids, preparation characteristics such as food and fluid preparation, equipment backpack weight and sleep, mental resilience and cognitive ability under fatigue (Gucciardi et al., 2015; Hoffman, 2014; Knechtle and Nikolaidis, 2018), pain threshold (Best et al., 2018; Hoffman et al., 2007), acclimatization if racing at altitude (Millet and Jornet, 2019) and sleep deprivation (Martin et al., 2018). Important anthropometric and training characteristics associated with successful performance include a lower body fat percent (%BF) and body mass index (BMI) (Hoffman, 2008; Hoffman et al., 2010), greater weekly training mileage and a faster training running velocity (Knechtle, Knechtle and Rosemann, 2010; Knechtle et al., 2012; Rüst et al., 2012).

Training for the ultra-endurance consists of several aspects including: physiology, biomechanics, sports psychology, racing and pacing tactics and injury and illness (Zaryski and Smith, 2005) and applies the same training and general adaptation principles, like training for any other sport, requiring the application of frequent and progressively overloading stressors to the athlete to stimulate adaptation and supercompensation so that the following training sessions are completed at a higher intensity or a longer duration (Selye, 1956; Zaryski and Smith, 2005; Verkhoshansky and Siff, 2009; Haff and Triplett, 2015). Additionally, relationships between training and performance decrements, and sub-optimal nutritional intake are well supported (Thomas, Erdman and Burke, 2016; Burke et al., 2019) and the necessity of applying strategic nutritional intake to meet the energy demands of the sport has recently been emphasized (Costa et al., 2013a; Costa et al., 2019; Costa, Hoffman and Stellingwerff, 2019). Therefore, it’s imperative that these performance and training demands are accompanied by key principles of nutrition to support the metabolic and recovery demands of the sport.

Nutritional Demands for Training

The most challenging aspect in performance nutrition for the ultra-runner is to meet their daily energy requirements to augment performance and recovery (Nikolaidis et al., 2018). These daily energy requirements are governed by several factors including basal metabolic rate (De Lorenzo et al., 1999), physical activity levels (Ainsworth et al., 2011), training volume and intensity, body composition goals, and the thermic effect of food (Tiller et al., 2019). The total amount of energy expended during a single training session is inversely proportional to the duration of that session (Costa, Hoffman and Stellingwerff, 2019), however other factors including fitness level, training intensity, environmental conditions and training course landscape (Costa et al., 2019; Costa, Hoffman and Stellingwerff, 2019; Costa et al., 2013a) also play a role. In terms of the metabolic pathway, UER places extensive demands on the aerobic metabolism to efficiently utilise stored muscle and liver glycogen along with fat-oxidation, with a substantial increase in the utilisation of free fatty acids for ATP production with increasing running distance, mainly due to the decreased availability of carbohydrates and stored glycogen as duration increases (Alcock et al., 2018; Bergman et al., 1999; Davies and Thompson, 1986; Scrimgeour et al., 1986; Waskiewicz et al., 2012). Tiller et al. (2019) has recommended that any training program should be supplemented by a nutritional intervention that maximises the capacity for fat-oxidation, sparing glycogen for the latter periods of running distance. This is an important factor as glycogen stores and circulating blood glucose availability are key limiting factors of ultra-endurance performance (Costa, Hoffman and Stellingwerff, 2019; Jeukendrup, 2011).

Current evidence recommends that, to support successive and progressive training sessions a daily energy intake of ~50-80 Kcal/kg/day (Potgieter, 2013) depending on the duration and intensity of training should be consumed, with 60% of energy coming from carbohydrates, 15% from protein and 25% from fat (Burke et al., 2019; Burke et al., 2001; Thomas, Erdman and Burke, 2016). For ultra-runners, carbohydrate intake relative to body mass should be in the range of 7–10 g/kg/day, this is also dependant on the metabolic flexibility, training load and the ability of the athlete to oxidise fat during training (Kerksick et al., 2018; San-Millan and Brooks, 2018). Protein intake relative to body mass is recommended to range between 1.6–2.5 g/kg/day to support recovery between training sessions (Kato et al., 2016) and my also play a role in providing energy during endurance exercise where glycogen stores are depleted (Tarnopolsky, 2004; Tarnopolsky, 1999). Protein distribution is also an important aspect for endurance athletes, with regular (every 3-hours) moderately sized (20g) feedings augmenting muscle protein synthesis more efficiently than other methods (Areta et al., 2013). This intake of protein can be supplemented with carbohydrates (1.0–1.5 g/kg every 2-hours for the first 6-hours post-exercise) to aid the recovery process and replenishment of glycogen (Burke, van Loon and Hawley, 2017), however, if a train-low, compete-high or ketogenic protocol is in place this should be managed accordingly. Similarly, ingestion of casein protein prior to sleep may also facilitate better recovery for athletes (Snijders et al., 2019).

With regards to fat intake, unless targeting the optimisation of fat-oxidation through a ketogenic diet, ultra-endurance athletes should consume between 1.0–1.5 g/kg/day of fat (Tiller et al., 2019). However, the main nutritional goal of training for ultra-endurance athletes needs to be increasing their ability to oxidise fat, thus preserving glycogen stores during ultra-endurance performance (Tiller et al., 2019). This can be achieved in two ways: train-low, compete-high and ketogenic dietary preferences (Mata et al., 2019; Stellingwerff, Morton and Burke, 2019; Baar and McGee, 2008; Volek et al., 2016). The concept of train-low, compete-high is essentially based on manipulating glycogen stores by performing endurance exercise either fasted or with low glycogen availability (Burke et al., 2018) to alter metabolic pathways and augment substrate utilization and adaptations to endurance performance (Baar and McGee, 2008). This low-glycogen availability activates key signalling pathways which control glucose transporter-4 (Glut4) and mono-carboxylate transporters, which are key glucose transporter proteins that facilitate endurance exercise performance (Baar and McGee, 2008) resulting in metabolic adaptations which augment fat-oxidation-gene-transcription resulting in improved endurance performance (Yeo et al., 2008; Hansen et al., 2005).

Altering nutritional preferences to a ketogenic diet (>70% daily energy from fat) has also been shown to increase fat-oxidation during ultra-endurance exercise (Volek et al., 2016). This is due to a reduced rate of muscle glycolysis and may facilitate a metabolic shift towards fat-oxidation (Cox et al., 2016). However, the effects of this shift on performance is unknown and caution should be taken (McSwiney et al., 2018) as performance at intensities ≥60% VO2max may be inhibited due to diminished oxygen-economy (Burke, 2015; Burke et al., 2017) resulting from reduced conversion rates of pyruvate into acetyl-CoA as a function of the suppression of pyruvate-dehydrogenase (Zinn et al., 2017). Thus, unless experimenting, athletes should stick to intakes as recommended by Potgieter (2013), Thomas, Erdman and Burke (2016), Burke et al. (2019) and Tiller et al. (2019).

Nutritional Demands for Competition

UER places extremely large energetic demands on the athletes during competition …

UER places extremely large energetic demands on the athletes during competition (Stuempfle and Hoffman, 2015; Knechtle and Nikolaidis, 2018). Although energy demands are unique to each individual and the duration and environment of event, the general observations of energy expenditure during competition ranges from 3,831–4,999 Kcal/day in hot racing environments (Costa et al., 2013a), 4,764–5,654 Kcal/day in cold to mild environments (Britton et al., 2011), 6,000–8,000 Kcal/day in a lab simulated multistage competition (Alcock et al., 2018), and up to 18,000 Kcal/day during a 24-hours trail event (Costa et al., 2014). The ability of the athletes to replace these energy demands has been associated with more successful performance (Glace, Murphy and McHugh, 2002; Wardenaar et al., 2015; Stuempfle et al., 2011) and reduced physiological maladaptation’s (Alcock et al., 2018; Costa et al., 2013a; Costa et al., 2014) during the event. The optimal planning of energy and fluid intake is of upmost importance to successful performance (Eden and Abernethy, 1994; Wardenaar et al., 2015; Costa et al., 2019).

The energy demands of UER can be met with intricate planning as per the guidelines of Thomas, Erdman and Burke (2016). The consumption of up to 12 g/kg/day of carbohydrate and 1.2–2.0 g/kg/day of protein are recommended to meet the demands of UER (Thomas, Erdman and Burke, 2016; Kato et al., 2016; Burke et al., 2019; Costa, Hoffman and Stellingwerff, 2019; Costa et al., 2019). As glucose is the most favourable source of fuel (Burke et al., 2019), with ~88% of energy derived from carbohydrates (Fallon et al., 1998; Martinez et al., 2018) carbohydrate consumption is of upmost importance, to preserve glycogen stores (Noakes et al., 1988; Tiller et al., 2019) and perform at higher intensities of exercise (> 60% VO2max) (Burke, 2015; Burke et al., 2019; Burke et al., 2017).

Enhancements in performance can be observed with the consumption of intra-race carbohydrate (2:1 glucose-fructose ratio) supplementation (Stellingwerff and Cox, 2014; Smith et al., 2013) following the guidelines of Burke et al. (2019), Thomas, Erdman and Burke (2016), Costa et al. (2019) and Casa et al. (2019) (Figure 2) and should be consumed as tolerated (Costa et al., 2019). It’s also recommended to partake in carbohydrate loading (10–12 g/kg/day) 36–48-hours prior to the event to super-compensate glycogen stores (Burke et al., 2019; Thomas, Erdman and Burke, 2016; Costa et al., 2019). Although carbohydrate should be the focus of competition fuel, for longer ultra-endurance events there is an increase in the proportion of fat and protein contribution to ATP production (Knechtle and Nikolaidis, 2018), with a proportional relationship between increasing distance and fat-oxidation (Martinez et al., 2018). It’s possible that this intake in fat can assist in decreasing the negative energy balance that occurs during ultra-running events (Dempster et al., 2013; Knechtle and Bircher, 2005; Nikolaidis et al., 2018) and may be an important consideration.


Figure 2: Nutritional strategies for fluid and carbohydrate (CHO) before and during ultra-running events adapted from Burke et al. (2019), Thomas, Erdman and Burke (2016), Costa et al. (2019) and Casa et al. (2019).


During UER, a reduction in body mass of >2% due to perspiration can have negative effects on performance (Goulet, 2013). Specifically, dehydration results in an increase in cardiovascular strain, core temperature, heart rate, rate of perceived exertion and an increased emphasis on carbohydrate as the predominant fuel source, resulting in the depletion of glycogen (Barr, 1999). However, the recommendation of 2% is not a precise marker for assessing hydration status for ultra-running (Hoffman and Stuempfle, 2014), with the risk of hyper-hydration evident during ultra-endurance events (Speedy, Noakes and Schneider, 2001) leading to hyponatremia (Arnaoutis et al., 2020). To prevent this, it’s recommended that ultra-runners drink to thirst during performance as its most suitable to maintain euhydration (Costa et al., 2013b; Hoffman and Stuempfle, 2016; Hoffman and Stuempfle, 2014; Noakes and Speedy, 2006; Costa et al., 2019). Figure 3 offers practical recommendations for hydration adapted from Costa et al. (2019). The supplementation of fluid loss with sodium supplements is discouraged and may cause hyper-hydration and decrements to performance (Costa et al., 2019; Williamson, 2016), thus drinking to thirst coupled with carbohydrate enriched (6–12% CHO concentration) drinks are recommended (McCubbin et al., 2020; American College of Sports et al., 2007; Williamson, 2016). To achieve euhydration prior to performance, it’s recommended to sip 5-10 ml/kgbm of water between 2–4-hours prior to the event (Thomas, Erdman and Burke, 2016; Williamson, 2016).


Figure 3: Practical recommendations for hydration for ultra-runners adapted from Costa et al. (2019).


In summary, UER is highly physiologically and psychologically demanding where the nutritional and hydration demands are dependent on course distance and terrain, environmental conditions, event characteristics (single or multi staged), degree of supplemental support and a host of individual athletic characteristics (VO2max, training age, racing experience, metabolic flexibility, etc). It’s imperative that ultra-runners meet their daily energy requirements to augment performance and recovery (Nikolaidis et al., 2018), with current evidence recommending a daily energy intake of ~50-80 Kcal/kg/day (Potgieter, 2013) depending on training duration and intensity, with 60% of energy coming from carbohydrates, 15% from protein and 25% from fat (Burke et al., 2019; Burke et al., 2001; Thomas, Erdman and Burke, 2016). This, however, may be altered depending on the training nutritional strategy in place for the athlete train-low, compete high or a ketogenic diet which may alter metabolic pathways and augment substrate utilization and adaptations to endurance performance (Mata et al., 2019; Stellingwerff, Morton and Burke, 2019; Baar and McGee, 2008; Volek et al., 2016). Although UER results in a large energy demands during performance (Stuempfle and Hoffman, 2015; Knechtle and Nikolaidis, 2018) the these can be met with intricate planning of competition nutrition (Figure 2), with athletes also being recommended to drink to thirst and supplement with a carbohydrate-enriched drink to aid hydration (Figure 3). These practical, evidence-based recommendations outlined in this essay are aimed to prepare an ultra-runner for optimal performance.


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