One on the most received messages as an athlete is to consume carbohydrates, pre, during and post exercise to aid with adequate fuelling, support athletic performance and optimise rates of recovery.

Carbohydrate provision and its role in enhancing exercise performance are well documented, where carbohydrate availability through glycogen stores and diet are a key indicator for sustaining prolonged exercise performance. In this instance, carbohydrates are still considered to be ‘king’ and the most important nutrient for optimising athletic performance.

Competition Nutrition

This is primarily through maintaining muscle and liver glycogen stores which become compromised during the latter phases of exercise – however is dependent on the type, intensity and duration of the exercise session or event. For example, continuous endurance exercise sessions under 60-90 minutes or intermittent higher intensity exercise (team sports) less than 45-60 minutes would not require additional carbohydrates through drinks or gels during as muscle and liver glycogen stores will most likely be adequate. In comparison, untrained individuals who follow a balanced diet would have glycogen stores ~ 80-90mmol kg−1 w.w., where exercising endurance athletes have higher stores ~150mmol kg−1 w.w., and even higher following a 3 day carbohydrate load in excess of 200mmol kg−1 w.w.. Since the availability of glycogen stores drives exercise performance, higher glycogen stores prior to an event or training sessions would be more favourable in reducing fatigue and improving exercise performance. In some instances, a carbohydrate load can improve exercise performance by 2-3% over set distances and reduce fatigue by 10-20 percent in long duration endurance events before reaching critically low levels of muscle glycogen ~ 25mmol kg−1 w.w.. Therefore during longer duration events, the higher the starting point, the better.

Exercise sessions over ~60-90 minutes may require carbohydrates during to ‘spare’ glycogen stores and offset a decline in work rate, fatigue and exercise capacity. Therefore, longer exercise sessions or events become more reliant of carbohydrate provision during. As carbohydrate intake is paramount for increasing longer duration exercise performance, it should be stressed that competition strategies utilise carbohydrate rich foods in order to supercompensate muscle and liver glycogen stores prior to an event whilst consuming carbohydrate drinks and gels during an event to sustain performance.

Exercise Nutrition: ‘Train Low’

The aim of competition and exercise sessions are different, therefore nutrition and fuelling practices will adjust accordingly to maximise the outcome. In recent years, emerging evidence of the concept ‘train low’ has demonstrated significant improvements with regards to enhancing the endurance training adaptation. Train low involves training on reduced carbohydrate availability, where both dietary and stored carbohydrates are reduced to bring about favourable training adaptations; enhanced signalling pathways, oxidative enzymes, whole body and intramuscular lipid oxidation in return improving exercise capacity. The aim of any training session is to adapt in order to have improved performance for subsequent training sessions. Research appears to consistently show that manipulating carbohydrate intake around endurance type training sessions (3-10 weeks) increases mitochondrial biogenesis, which results in increased mitochondrial mass. Increasing mitochondrial mass allows for the athlete to train at higher absolute intensities for a longer period of time by maintaining metabolic homeostasis, such as; smaller decreases in ATP, phosphocreatine, muscle glycogen, lactic acid and smaller increases in ADP and AMP.

Some Mechanisms

To keep the mechanistic side brief, low levels of muscle glycogen increase signalling enzymes known as AMPK and p38MAPK, in return activates the downstream transcription coactivator; PGC-1alpha which stimulates mitochondrial biogenesis. Therefore, in order to further increase the end goal of mitochondrial biogenesis, carbohydrate restriction appears to be favourable.  It’s worth noting that the endurance training adaptation with a traditional carbohydrate fuelling strategy also yields a training adaptation through increases in VO2max, however not to the same magnitude of carbohydrate restriction as many of the muscular adaptations become blunted when carbohydrates are consumed.

The Downside

As with any intervention, a trade-off or compromise will become apparent – this is no different to the ‘train low’ paradigm.  The favourable components of ‘train low’ have been mentioned above, however with any positive approach, comes some negatives. Below outlines the main concerns with training for long periods of time without the provision of carbohydrates.

  • It’s been well documented and previously discussed in a previous post; Low Carbohydrate dieting for Sports: On its Last Legs? that the provision of carbohydrates drives exercise performance. Therefore during periods of carbohydrate restriction, maintaining training performance and workload will be reduced. This may result in a lower training impulse (training volume x training intensity) and in some cases may result in the ability to hit a desired workload set by a training programme or staff.
  • Carbohydrate restriction during higher intensity exercise may compromise the immune system and increase susceptibility to illness and infection. Given carbohydrates role in reducing exercise induced immunosupression, this is a trade off worth being mindful of if the occurrence of illness is frequent. 
  • Prolonged low carbohydrate availability in the absence of dietary protein can cause elevated rates of muscle protein breakdown, which may lead to muscle mass loss if repeated on a continual basis. With muscle mass loss, decrements in strength, power and muscular endurance will be observed – which are not favourable attributes for an athlete to have.
  • Continuously training with low carbohydrate availability can impair carbohydrate utilisation when consumed through the diet. This is a negative adaptation to chronic low carbohydrate training and may decrease competitive performances when consuming carbohydrates to fuel the race or event.

A misunderstanding occurs with ‘train low’ as it is often believed to be a low or zero carbohydrate diet, which simply isn’t the case. Training low involves carbohydrate manipulation on a daily basis, where total daily carbohydrate intakes are still met through withholding carbohydrates in some meals; before, during and after training sessions and compensating in other meals. For example, Marquet et al (2016) compared a three week carbohydrate equated diet (6 grams per kilogram of bodyweight ~ 420g from a 70kg athlete), however one group manipulated carbohydrates timing over the course of the day for low and high intensity training sessions, where the control group consumed an equal amount of carbohydrate spread throughout the day. At the end of the three week period, the group that manipulated carbohydrate intake around their sessions improved submaximal cycling economy, as well as supramaximal cycling capacity and 10-km running time. Therefore, manipulating the timing of a high carbohydrate diet (6g per kilogram of bodyweight) can improve exercise performance and highlights that the ‘train low’ paradigm is not a low or zero carbohydrate diet.


Training with low carbohydrate availability is still in its infant stages where many unanswered questions remain with regards to an optimal approach and best practice. With this in mind, here are strategies to implement ‘train low’ into a training programme and offset the likeliness of any of the negative factors mentioned prior.

  • Many different approaches appear to work, such as; fasted state exercise ~6-10 hours after previous meal, double day training where carbohydrates are not consumed post A.M. training which results in the evening session being performed in a carbohydrate reduced state. Furthermore, a ‘sleep low’ approach can be taken where higher intensity/glycogen depleting exercise is performed in the evening without replenishment in the post exercise period which is followed by training the following morning in a carbohydrate restricted state. More simplistic approach such as restricting carbohydrates in the hours post exercise is also a simple and pragmatic approach.
  • It is still unsure which method is superior, however identifying lower intensity training sessions to adopt a ‘train low’ approach may be warranted as it may not compromise exercise performance due to the lower intensities. Opting for lower intensities should also help with managing immunosupression associated with carbohydrate restriction at higher intensities.
  • As mentioned, carbohydrate restriction impairs exercise performance. Interventions such as caffeine consumption and carbohydrate mouth rinsing pre training can offset decrements in performance whilst achieving the desired outcome of training low. Therefore, implementing this strategy will be useful for individuals who struggle with sustaining exercise performance during ‘train low’ sessions.
  • To reduce muscle protein breakdown and potentially muscle loss, consume a protein meal or shake pre and post training without adding any additional carbohydrates or fats. Consuming protein only will not interfere with the signalling pathways; therefore this is an essential area to consider mitigating losses in strength, power and muscular endurance.
  • Plan and implement sessions where carbohydrate provision is undertaken alongside training sessions that replicate competition intensities and duration. Therefore, these sessions should follow ‘normal’ carbohydrate intakes, such as; carbohydrate loading, pre and post exercise carbohydrate rich meals. Therefore, a periodised training and nutrition plan will bring about the best possible results from both elements of training and competition. I.e. some sessions will aim to drive and test exercise performance with a high carbohydrate provision, where some sessions will aim to drive the training adaptation with a restricted carbohydrate approach.

In closing, carbohydrate intake should not be considered as linear or universal approach where all training sessions require the same nutrient provision. Therefore, an individualised and periodised nutrition approach may be required to maximise the outcome of each and every training sessions by following the motto;

‘Fuel the work required’




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