Cardio Isn’t Going to Kill Your Gains. Need More Evidence? You Got It.

Does cardio kill gains? No. In fact, a recent study adds more evidence suggesting cardio and lifting make for a stronger, more jacked athlete.

Ever since I published my first article on this subject about a month ago, my inbox has been flooded with questions about it.  Half of them were asking if I was crazy, and the other half were asking me how to implement some cardio in their training (which my friend Alex already covered here).

If you’re in the former group of people, I’ve got something just for you today.  A study in January covered this topic, and did so on the molecular level.

By necessity this post is pretty science-heavy.  I’ll do my best to explain things as we go along, but if gene expression and protein phosphorylation aren’t your schtick, feel free to skip to the “Takeaways” section at the bottom.

Without going too far afield (and putting most of you to sleep in the process), there are two major cellular pathways that largely govern aerobic and hypertrophy responses to training.  The AMPK pathway is activated by essentially anything that depletes cellular energy – low calorie intake, aerobic exercise, etc.  The mTOR pathway is activated by food intake (especially leucine-rich protein sources) and resistance exercise.

The two are typically thought to be essentially antagonistic.  For our purposes here, it’s commonly believed that activating the AMPK pathway is going to shut down the mTOR pathway and the hypertrophy response.  It’s much more complicated than that, but most people still assume that aerobic training –> AMPK phosphorylation  –> mTOR inhibition –> small and weak.

A new study flips that assumption on its head.  The study is titled (spoiler alert!) “Exercise-induced AMPK activation does not interfere with muscle hypertrophy in response to resistance training in men” (Lundberg et. Al, 2013).


The recent meta-analysis I linked to in my first post on this subject essentially said that you can absolutely get stronger while doing some aerobic training.  Cycling is better at running for this purpose, and duration is a key factor.

However, the question remains:  If you have to do aerobic work and then train directly after, can you still get jacked?

This is an important question to answer because it’s putting the muscles in catabolic conditions from the outset.  The same authors showed that strength and hypertrophy could coexist with aerobic training if there were 6 hours between sessions, but for this study, the participants did their strength training a mere 15 minutes after cycling – when the muscles were already fatigued and glycogen depleted, and when the AMPK pathway was already activated.

The subjects

The subjects selected could be a little more relevant for out purposes.  They were young (mostly between 20 and 30) and healthy, performing recreational activities ~3x/week.  None of them were currently active in strength training.

I’d like to see trained subjects (some strength trained and some aerobically trained would be awesome), but these people were in decent shape, and with a fairly short study period (5 weeks), untrained subjects are more apt to see noticeable changes.

The training protocol

This protocol was a little strange, but certainly creative for ensuring the results were from the training itself and not differences between groups.

The subjects acted as their own controls.  With one leg, they performed aerobic exercise followed by resistance exercise, and with the other leg they only performed resistance exercise.

The aerobic training was cycling with one leg, and the resistance exercise was knee extensions – 4 sets of 7 reps at maximal effort.

The one legged cycling sounds pretty freaking hard – 70% of maximal work load at 60RPM for 40 minutes, and then, to ensure fatigue of the “aerobic” leg, work load was increased further and the subjects cycled until failure.

Then, after only a 15 minute break, it was on to leg extensions.

Aerobic training was 3x per week for a total of 15 sessions, and strength training alternated 2x per week and 3x per week, for a total of 12 sessions (but always occurring after an aerobic session).

The results

After 40 minutes of pretty challenging aerobic training, eventually going to failure, peak power in the subsequent leg extensions was 10-20% lower in the aerobic leg vs. the strength training only leg.  That was to be expected

Contrary to other studies where strength increased but power output decreased or remained unchanged with strength+aerobic training, both legs increased in power output to a similar degree.

Endurance improved in the aerobic leg but not the strength training only leg.  That was to be expected.

Peak knee torque increased for both legs, but while only eccentric increased significantly for the aerobic leg, both eccentric and concentric increased for the strength only leg.

Hypertrophy was twice as great in the aerobic leg vs. the strength only leg!  A 6% increase in quadriceps area vs. 3%.

The aerobic leg had more glycogen (stored carbohydrate) at rest after training, but glycogen stores were about 32% less than the strength-only leg after the single leg cycling, heading into the knee extensions.

There were a lot of gene expression changes.  I won’t bog you down with all of them, but two worth noting were PGC-1a, which has been implicated in a wide range of health benefits, and myostatin, which inhibits muscle hypertrophy.  Increases in PGC-1a were significantly higher in the aerobic leg (10.3-fold increase vs. 2-fold increase), and myostatin reductions were significant in the aerobic leg (65% decrease), but not in the strength only leg (31% decrease).

AMPK phosphorylation was greater in the aerobic leg compared to the strength only leg, but there were no changes in p70S6K phosphorylation (a downstream protein in the mTOR pathway).


As stated, it would be awesome if this study was performed on trained athletes.

While the study design was cool in that it let the subjects function as their own controls, it’s hard to know for sure whether single leg cycling and knee extensions will translate to regular cycling and squats.

I’d also like to see this study repeated with higher resistance training volume.  28 reps is pretty low for a workout, especially if hypertrophy is the goal.  It could simply be that the added training volume from the cycling was the determining factor for the different hypertrophy responses.


The AMPK-mediated effects of aerobic exercise probably aren’t going to negatively affect hypertrophy, even if the aerobic training is performed directly before strength training.  Protein synthesis is elevated for 24-48 (perhaps even up to 72) hours post-resistance training which means, to quote the authors, “the very short-lived AMPK activation induced by AE most likely evokes minute, if any, impact on the net protein balance accumulated between exercise sessions.”

At least based on this study, hypertrophy was enhanced by preceding strength training with aerobic training, but improvements in strength were somewhat decreased.  This may simply be due to the fact that performance was hindered by the preceding aerobic work – the volume was sufficient for a larger growth response, but the inability to train at maximum strength hampered improvements in concentric knee torque.

So, to broaden our scope just a little bit, when combining strength and aerobic training –  the hypertrophy benefits may occur regardless of when you do your aerobic training relative to your strength training (and due to decreased myostatin without changes in mTOR signalling, cycling before leg training may actually be better for hypertrophy.  Counter-intuitive for sure, but that seems to be what this study is suggesting – at least for untrained people), but cycling to exhaustion right before strength training probably isn’t the best idea if you’re trying to get stronger.

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