Increasing FATMAX despite 90g/hour carbs intake!

WHAT WAS STUDIED?

This was a interesting investigation of twelve elite cyclists performing a 6 hour race simulation in a laboratory & field setting (1). This study aimed to investigate "durability" of the athletes. Namely repeated sprint and time trial performance. Surprisingly, it also investigated FATMAX of the athletes. This was surprising given the high intensity work of the cyclists and not a marker that would typically be associated with work of this nature. The participants were  instructed to consume 90–100 g/h of carbohydrates every 2 h, which included energy drinks, gels, bars, and chews with a 2:1 glucose to fructose ratio. The authors highlight the limited knowledge in this space and thus hoped to shed some light on the impact and effect of a extended race simulation on riders.

WHAT DO WE KNOW ALREADY?

"Durability” is defined as “the time of onset and magnitude of deterioration in physiological characteristics over time during prolonged exercise” [2]. This concept alongside "capacity" are frequently used as markers of successful outcomes for athletes to aspire to improving in order to maximise performance in races and events.

In cycling, the best sprinters and best climbers are able to maintain peak numbers despite accumulation of work through repeated efforts. Resistance to fatigue is going to be a KEY determinant for endurance exercise performance (1). The ability to resist fatigue is highly individualised and will relate to experience, fitness, strength, the environment and nutrition.

WHAT DID WE LEARN?

Top level cyclists fatigue! Always good to know. Variability did exist between the riders as to the extent of fatigue which was also expected. Saying this, all but one athlete declined. in power output across the 6hr testing period.

TESTING

(a) These athletes had very high predicted MFO at the start. 0.9+/-0.3g/min is on the upper end of fat oxidation for athletes. Especially for athletes who regularly consume carbohydrates. Their FATMAX was 236+/-26 which is 84% of their FTP values. Fairly high as well. So, these athletes were fat adapted to begin with.

FATIGUE

(a) Peak sprint power dropped after the first 2hrs of racing and then was maintained over the next 4 hours in the subsequent sprint efforts. Authors hint at neuromuscular or neural drive as a potential cause of this.

(b) Progressive loss of TT power numbers may be explained by glycogen depletion. It is unclear what status the athletes were in leading into the testing as carb loading was not outlined in the "Methods" section. It would have been great to see a full carbohydrate loading protocol for athletes of this ability and see if that impacted fatigue and also the FATMAX numbers.

(c) Time accumulated above the first lactate threshold correlated closely with individual reductions in TT power output. This makes sense. Time spent above or repeatedly going over threshold has been shown to increase fatigue compared to keeping consistent power and being under that threshold.

‍

WHAT WAS SURPRISING?

The rate of max fat oxidation (MFO) might be surprising to many given the intake of carbs during the 6 hour simulation. However, we have seen in other studies (3) and Fuelin athletes including Holly Lawrence. This was discussed in detail on the Triathlon Hour Podcast between Holly and me. Despite moderate intakes of carbs at 5-5.5g/kg/day and additional in session carbohydrate fueling of 60g/hr, we saw Holly bump her MFO from 0.6g/min to 0.9g/min in the post-season period. The biggest driver being duration of training rather than intensity of training. I also wrote about Hollys results here.

FATMAX

(a) There was a significant increase in MFO over the six hour period from the fasted state to finish. An initial drop occurred between the fasted state to the start of testing in ten of the athletes. It would have been interesting to see what happened from ) to two and two to four hours. I suspect they may have been a drop due to intake of carbs over the first two hours and then a graded increase in MFO over the remaining three to four hours.

"The physiological measurement revealed increased fat oxidation from pre- to posttest at the intensity eliciting MFO in fasted conditions, although the riders ingested high amounts of carbohydrates. Interestingly, the FATMAX intensity was similar to the mean power output during the periods with paced peloton riding, indicating that fat metabolism, even in conditions with very high glucose ingestion, as practiced in competitions, may cover a substantial part of the energy turnover in certain phases of prolonged races."

(b) The athletes took in on average 90g/hr (360 kcal/hr). Their accumulated work (kJ) for the 6hrs was estimated at 4610kJ (1102 kcal). This appears to be very low for estimated work completed at this intensity. The authors do mention that the work completed during the peloton ride correlated. to the power output at MFO. What the authors hint at is, that fat oxidation contributes to a significant portion of fuel availability for these types of riders & racing. Thus, being fat adapted is important. The caveat to this is perhaps the intake of carbs was not high enough to offset the dip into stored glycogen. The contribution of exogenous carb intake can offset and delay fat oxidation and endogenous glycogen use. This may have changed the results seen by reducing MFO yet preserving TT power numbers and time.

(c) The question about their starting glycogen status is important. If the riders were not fully loaded at the start of the race then that can impair exercise capacity.

SPRINT POWER

(1) Despite an initial drop in sprint power after the first 2hrs of racing, it showed no further reductions for the repeated efforts. This was a surprise to me.

THE PRACTICAL TAKEAWAYS

What this study revealed was that fatigue will occur despite high levels of training and relatively high levels of carbohydrate intake. It also demonstrated that MFO is possible despite moderate to high intakes of carbs.

The keys for me are these:

(A) Are you aiming for high MFO? If so, the duration of the training will impact that rate. Even if consuming 90g/hr carbs, you can see that over a six hour session that fat oxidation is very high. Don't skimp on carbs even if the intensity is not super high. This was demonstrated by the correlation between average watts by these riders at peloton pace being the same as their MFO power. You will be using fat and carbs to power your efforts.

(B) Are you are more interested in offsetting fatigue in a race or high intensity session? Then ensure you are loaded up on carbs before hand (Carbohydrate Loading). Glycogen availability can offset initial fatigue. Secondly, intake of carbs needs to be high. 90g/hr intake is not 90g/hr absorption due to metabolic efficiency factors. In order to have a rate of 90g/hr, you need to ingest 120g/hr (0.75 efficiency average). This might have been a reason for fatigue with these riders, as it may not have been enough carbs.

At Fuelin we plan carbs around your training sessions. The lower intensity sessions get arbs and mixed macros (fat & protein) whilst the higher intensity sessions get the carbs they deserve. It is why we have "Carb Colours" and it is how athletes know what and how much to consume to reach their desired goals and outcomes. Easy, and effective,

I would love your feedback on this study and your insights if you have them.

Thanks for reading,

Scott

REFERENCES

1. Klaris, Magnus Bak et al. “Performance and Fatigue Patterns in Elite Cyclists During 6 h of Simulated Road Racing.” Scandinavian journal of medicine & science in sports vol. 34,7 (2024): e14699. doi:10.1111/sms.14699

2. Maunder, Ed et al. “The Importance of 'Durability' in the Physiological Profiling of Endurance Athletes.” Sports medicine (Auckland, N.Z.) vol. 51,8 (2021): 1619-1628. doi:10.1007/s40279-021-01459-0

3. Ørtenblad, Niels et al. “Substrate utilization and durability during prolonged intermittent exercise in elite road cyclists.” European journal of applied physiology vol. 124,7 (2024): 2193-2205. doi:10.1007/s00421-024-05437-y