Why Bigger Riders May Need More Carbohydrate During A Ride?

Here at Fuel The Ride Academy, we always like to keep abreast of the latest advances in sports nutrition science to help ensure that you, as an athlete, can stay competitive and ensure our advice is up to date and the best it can be.

A recently published study has caught our eye as it turns our existing understanding of a key area of performance nutrition on its head; let me explain…

For most cyclists riding for extended periods, i.e. 90minutes+ at moderate to high intensities, fuelling (i.e., taking in carbohydrates on the bike) is a critical nutrition strategy for maximising performance. Fuelling can significantly improve a rider's performance compared to not (By as much as 10-15% in some circumstances, as we’ve covered previously). This is by maintaining blood glucose levels late into exercise, helping to maintain muscle function and through helping to maintain carbohydrate use late into exercise. 

The current sports nutrition guidelines for rides longer than 2.5 hours suggest that athletes should to aim to consume 90 grams of carbohydrates per hour, using a combination of glucose and fructose. However, gut training is essential for an athlete to tolerate this much.

A key theory behind why this guideline is 90grams an hour is that it is believed that our digestive system is a key limiting factor in terms of how much of the carbohydrate we ingest during exercise from a sports drink can be used by the muscle (referred to as exogenous oxidation). Generally, it is assumed that if there is a big difference between the rate of intake of carbohydrates and the rate of exogenous oxidation (which we can measure in a lab using some cool techniques), then it likely means there is carbohydrate that isn’t being absorbed that is accumulating in the gut and over time, particularly during stressful situations like competition, will result in significant stomach upset.

Of particular note is that the guidelines for fuelling during exercise are currently expressed in absolute terms, so regardless of how big or small an athlete you are, the intake guidelines are the same. As such a 50kg is given the same carbohydrate intake target as a 90kg athlete. This is in contrast to an athlete’s daily carbohydrate needs, which are relative to an athlete’s body weight.

This is because previous data has suggested that regardless of size, athletes appear to be able to use the same amount of carbohydrates, meaning that size has little influence over an athlete’s ability to use carbohydrates, as shown in the figure below. 

However, from a logical perspective, an athlete who is larger in size is likely also to have a larger digestive tract and greater muscle mass, both of which could theoretically increase the athlete's ability to absorb carbohydrates during exercise and also give them a greater ability to use it.

Limitations with the data outlined above warranted further examination and a team at the University of Bath in partnership with other academics at the University Of Birmingham set about designing a study to better test this hypothesis. 

They looked to measure exogenous carbohydrate oxidation in two groups of athletes who were distinctly different in size: a small group at around 66kg in weight and a larger group of athletes at around 87kg in weight. They got the athletes into the lab and had them cycle at a fixed intensity for 2 hours whilst consuming 90 grams an hour of glucose. They also used clever techniques to measure how much of the ingested drink the athletes were able to use.

The key finding of the study was that the large group where able to oxidase, on average, an additional 13 grams an hour compared to the smaller group of participants. Suggesting that there is in fact an influence of body weight on how much carbohydrate an athlete can use and as such, we may need to individualise fuelling strategies with a consideration for their body weight.

Of significance was that the two groups had exogenous carbohydrate oxidation tested whilst riding at the same relative intensity (this was based on a preliminary fitness test); they also had an additional trial where the large group of athletes rode at the same absolute intensity as the small group, even when riding at the lower intensity, the large group still oxidised more of the glucose from the drink, suggesting the difference between the groups wasn’t down to exercise intensity alone.

This finding, whilst may sound small, in a practical sense, is pretty significant given athletes want to balance both maximising the exogenous oxidation of carbohydrates whilst also limiting any negative effects that come from consuming more carbohydrate than they can absorb and utilise.

Coach Ben