Posted on September 09 2018
What is your favorite type of training? Do you live to lift? Maybe you love to run trails on a beautiful day, or maybe it’s a combination sport like Crossfit.
Regardless of what type of training you prefer, the positive health benefits that you get from exercise are enormous. And many of these benefits can be attributed to hormone production. These positive hormonal changes apply to both strength training and endurance/cardio training.
More specifically, both methods of training have been shown to cause favorable changes in ergogenic (physique enhancing) hormones such as testosterone, growth hormone, IGF-1, and fat burning catecholamines (adrenaline/nor-adrenaline). For both men and women, optimizing these hormones via exercise is a key component of building a lean, healthy body.
In the lab, and in the gym, both resistance and endurance training build lean muscle and burn fat, but it is common knowledge that resistance training will build more muscle than endurance work.
This brings up an interesting question when it comes to fat loss. If resistance training builds more muscle than endurance training, and both methods of training burn calories, then why do cardio at all? Wouldn’t it be most efficient to simply resistance train while in a caloric deficit?
The answer may lie in a discovery made by a team of researchers at the University of Copenhagen.
Boosting FGF21, The Body's Own Fat Burning, Anti-Obesity Drug
Their study sheds light for the first time on a positive fat burning hormonal response seen in athletes after endurance/ cardio training, but not after resistance training. 
According to the study, training on an exercise bike causes a three fold increase in the production of the hormone FGF21 than strength training with weights. This is significant because FGF21 has a lot of positive effects on metabolism such as:
- increased fat loss
- reduced inflammation
- increased insulin sensitivity
- improved liver health
- increased health span
The fact that FGF21 produces these results with no known side effects is why it is currently being researched as a new drug against diabetes, obesity, and other similar metabolic disorders.
Mimicking the Study
In order to replicate the results from the study, it is important to try to mimic the conditions in the study as closely as possible.
It is important to note that the endurance exercise method used in the study was cycling at 70 percent of maximum oxygen intake (Vo2 max) for 1 hour, so this wasn’t a leisurely pace.
Cycling is a very lower body dominant form of endurance/cardio training, so if you chose not to cycle, ensure that you do chose a lower body dominant form of exercise, with some resistance, such as jogging on a low incline of 1.5 percent or so, or running trails in the foothills (this will vary depending on your fitness level).
The participants in the study cycled for 60 minutes, which may be a very long cardio session for many of us. In order to accommodate hour long sessions, you may need to simply perform fewer cardio/endurance sessions per week, with each session elongated to reach that 60 minute mark.
While it is highly likely that shorter sessions will still result in significantly elevated FGF21, we will need more studies to verify.
And therein lies one of the most frustrating parts of exercise science. As science and technology progress, studies reveal more and more about what the optimal training method for a specific goal looks like.
But for each study that answers one question, we are often left with several more questions that will have to wait for further studies to answer.
Key Takeaways from Current Study
- Endurance/cardio training for 60 minutes, but not resistance training for 60 minutes, increased FGF21 300 percent for 4 hours after training
- Cycling at 70% Vo2 max for 60 minutes was the specific exercise performed
- Endurance training has at least one key hormonal metabolic response not seen with resistance training
- FGF21 is a powerful metabolic hormone which may be responsible for many of the health benefits of endurance/cardio training
- - This study lends validation to the common practice of a mixed routine that includes endurance/cardio training in addition to resistance training for optimal fat loss