Lifestyle & Training

Does Xendurance Xtreme Endurance Work?

Extreme Endurance by Xendurance is a popular supplement in the sport of CrossFit.  It's popularity is due to its claim that it can reduce lactic acid and muscle soreness after bouts of high intensity training.  We put the supplement and its claims to test by running our own open label study.


Efficacy of Xendurance’s Extreme Endurance on Increasing Performance and Recovery During High Intensity Exercise


An athlete’s ability to maintain high levels of performance during high intensity exercise can be limited by metabolic acidosis due to the accumulation of hydrogen ions in the working muscles.  It is the goal of this study to determine the efficacy of Xendurance’s Extreme Endurance in increasing performance and recovery during high intensity training.

Fourteen well-trained CrossFit athletes were randomly assigned to either a placebo or test group.  Each athlete completed a three minute max effort assault bike test for calories followed by ten days of supplementation following the dosing recommendation from Xendurance.  At the end of the ten days, participants re-tested their three minute assault bike test and completed an exit survey to gauge recovery.

Our findings show no meaningful increase in performance in the test group versus the placebo group.  However, participants in the test group reported on average feeling faster levels of recovery than the placebo group.


Increasing an athlete’s performance during bouts of high intensity exercise has been the subject of much scientific research.  Additionally, with the rise of high intensity training and competitive CrossFit, many athletes are looking for ways to sustain near maximal work capacity for longer durations of time.

It is well known that the acidification of the blood during high intensity exercise ultimately causes a decrease performance.  It is hypothesized that introducing an alkalizing agent, like calcium bicarbonate, may be effective in buffering blood acidosis.  Extreme Endurance by Xendurance is an alkalizing agent and has been previously shown to reduce lactic acid levels and creatine kinase during and after intense bouts of exercise.  

Our study aimed to test whether a buffering of lactate concentrations would allow an athlete to increase their performance during high intensity training.



Fourteen well-trained athletes—training CrossFit for at least one year—were randomly assigned to either a placebo or supplement group.  Participants were unaware of whether they were taking the placebo or supplement and were instructed to not talk to each other about the experiment until its completion.

The trial administrator, Michael Verdi, did know which participants were a part of the placebo group vs the supplement group.  Although not ideal, this was necessary due to limited resources.


Participants used assault bikes by Assault Fitness for both test pieces.  Each participant received a ten day supply of supplements with a sheet of paper instructing them on how and when to take the supplements.  Finally, an exit survey was sent to each participant upon completion of their re-test.

Copies of both the exit survey and the supplement instruction sheet can be found in the appendix.


Participants gathered on day one of the trial to complete a three minute max effort assault bike test for calories.  Each participant used the Target Time function on the bike to ensure no calories were counted after the completion of three minutes.  No advice was offered on how to pace or prepare for the test.

Assault bikes were chosen because they require little to no skill and all participants had familiarity with using the equipment previously.  Additionally, assault bikes allow for a high rate of turnover which is important for exposing the desired metabolic pathway. The time duration of three minutes and intensity level were chosen because together they target a participant’s anaerobic threshold.


The first data set for analysis is on performance, i.e. whether they had an increase or decrease in total calories from their first to second test.

The second data set is qualitative and was gathered via the exit survey.  The goal was to gauge how the participant felt during and after the re-test.


Averages were found from the above data.

Excluded Results

Of the 14 participants, three were excluded from the final results.


Extreme Endurance by Xendurance has been previously shown to reduce lactic acid concentrations by 15-26%.  The goal of this study was to determine if lactic acid buffering could account for a measurable increase in performance and recovery.  

Our findings show that the drug group had an average increase in performance of 2.48 calories or 3.87% versus the placebo group which had an average increase of 4.48 calories or 8.81%.  Therefore, our findings suggest that the drug in question does not provide a significant increase in performance over a placebo.

Due to limited resources, we were unable to test actual blood lactate levels throughout the experimentation, however, we did use an exit survey post re-test to evaluate participant’s perceived level of pain and recovery.  Across the board, participants in the drug group felt that they could push harder for longer and stated they believed to have recovered faster than after their first test. Rate of recovery was rated 1 through 5 and took into account the degree of local muscle soreness and burning.

This lends support to previous research which showed reduce oxidative stress and creatine kinase levels following intense exercise.  This may suggest that Extreme Endurance may provide benefit to athletes who participate in repeated bouts of high intensity exercise where recovery windows are small.  However, more testing is needed.


Supplementation with athletic performance formula decreases lactate concentrations in trained athletes after exhausting incremental cycle ergometer test:

The Effects of 10 Days of a MultiIngredient Supplement on Performance Lactate during Exercise and Post Exercise Muscle Damage, Oxidative Stress and Inflammation:

Extreme Endurance Takes On “Fran”:

April 7, 2020
Danette Gleason, General Manager
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