Load Carrying Cardio Doesn't Affect Muscle Protein Flux While Intra-Workout EAA Reduces Protein Breakdown and Bumps Nitrogen Balance From Zero to Plus 50µmol/kg/h

While this picture shows loaded cardio in its most beautiful form, the study investigated loaded cardio on the treadmill and compared it (for questionable reasons) to non-loaded cardio on a stationary bike and guess what: Both burn the same amount of muscle - NET: Zero!

Carrying a (heavy) load during cardio? Sounds dumb? Well, that's however, how the real world looks like. Not just soldiers who are carrying armor and a heavy backpack in the field, but also hikers will attest to the fact that doing "cardio" with a weight on your shoulders or elsewhere is more natural than running around in the park with your mobile and ear-plugs as the only load you're carrying on top of your ultra-light runners clothing.

With that being said, it is actually quite astonishing that Stefan M. Pasiakos and colleagues from the Military Nutrition Division at the US Army Research Institute of Environmental Medicine in Natick are the first to take a look at the muscle anabolic and catabolic effects of regular (unloaded) and loaded cardio training in 40 free-living healthy, physically fit (peak oxygen uptake, VO2peak 40/60 mL/ kg/ min), adults (37 males and 3 females), normal weight men and women between the ages of 18–39 years.

HIIT is the ideal complement to classic "cardio" training!

Never Train To Burn Calories!

Tabata = 14.2kcal /min ≠ Fat Loss

30s Intervals + 2:1 Work/Rec.

Making HIIT a Hit Part I/II

Making HIIT a Hit Part II/II

HIIT Ain't For Everyone

In said study, the volunteers were then randomly assigned to one of four experimental groups, each
of whom performed a single 90 min exercise bout.

• Two groups performed CE and the other two performed LC. 
• One of each of the exercise groups received EAA drinks to consume during exercise, and the other groups received control (CON) drinks. 

To determine the effects on skeletal muscle, the subjects' individual muscle protein synthesism (MPS) was assessed during exercise and recovery and whole protein turnover was determined in recovery only. What may be a bit surprising in this context is the fact that a resting MPS measure was not included in the study. The authors, however, have a good argument to neglect this, when they say that (a) the MPS responses to endurance-type exercise (i.e.,as they relate to resting MPS) are well established and that (b) their ...

"[...] intent was not to determine temporal changes in MPS within an exercise mode (with or without EAA), but to examine MPS responses between LC and CE during exercise and recovery independently" (Pasiakos. 2015).

Another thing that was just like in any other study, though, was the standardization of diet and physical activity, the scientists describe as follows:

"Volunteers completed 3 d diet and activity records at baseline, and similar to our previous work (Pasiakos. 2011), these records were used to individually prescribe 7 d lead-in diets to maintain body weight and to limit the potential confounding effect of diet on outcome measures. Compliance was confirmed by 24 h dietary recalls conducted every two days during the lead-in phase (Food Processor SQL1, version 10, ESHA Research, Salem, OR) (Table 1). Volunteers were also instructed to maintain activity levels reported at baseline for the first five days of the lead-in phase. All resistive and endurance-type activity was prohibited 48 h before data collection to minimize any potential residual effects of previous exercise on protein turnover" (Pasiakos. 2015).

The actual news is however not the dietary standardization what you are (rightly) interested in is probably the exercise protocol which is - and I will get to that in the bottom line - not ideal: While the LC, i.e. the load carriage training, was performed by walking on a treadmill while wearing a weighted vest equivalent to 30% of baseline body mass, the CE, i.e. the control endurance exercise, was non-weight bearing and performed on a cycle ergometer (Lode, BV, Netherlands), of which the scientists say that they used it to "allow for comparisons with our previous studies" (Pasiakos. 2015).

Illustration 1: Graphical overview of the study design (Pasiakos. 2015) | EAA = 10g of EAAs, CON = non-nutritious control drink; LC = load carrying cardio on a treadmill, CE = control endurance exercise on a stationary bike.

What's unquestionable a strength of the study, though, was the fact that the baseline VO2peak and associated heart rates at maximal and submaximal levels were used to establish target exercise intensities for the LC and CE trials. In addition, speed and grade for LC and power (watts) for CE were adjusted to match the absolute exercise intensity (intended oxygen uptake was 2.4 L /m) and
to elicit a similar energy cost (intended energy expenditure was 1050 kcal /90 min) between
LC and CE. Lastly, ...

"[m]atching the intensity and energy cost was done to isolate the effects of the possible differences in mechanical force and contractile properties of LC and CE from the relative intensity and energy cost of the exercise bout [and a] familiarization trial was conducted to ensure the accuracy of the exercise prescription and the ability of the volunteer to complete the prescribed exercise bout" (Pasiakos. 2015).

As previously alluded to, the intra-workout beverage the subjects consumed was either a high EAA drink (10 g EAA: 0.7 g histidine, 0.7 g isoleucine, 3.6 g leucine, 1.2 g lysine, 0.3 g methionine, 1.4 g phenylalanine, 1.0 g threonine, and 1 g valine) or an identically looking placebo drink (non-nutritive).

Figure 1: Overview of protein fluxes (synthesis vs. breakdown and oxidation) and subsequent net protein balance in the four treatment groups, i.e. loaded and control cardio with and with out EAA (Pasiakos. 2015)

Interestingly enough, the latter, i.e. the 10 grams of EAA drink that was consumed in four small doses (i.e., 350 mg of phenylalanine and 900 mg of leucine per serving), over 90 min to minimize "any isotopic dilution that may have occurred if the EAA drink was consumed as a bolus" (Pasiakos. 2015) was the only treatment that made a difference to the protein flux parameters illustrated in Figure 1. In that it is worth mentioning the tthe difference in protein oxidation alone does not fully explain the conservation of skeletal muscle protein even if we assume that all the amino acids that were oxidized during the EAA supplementation trial came from the EAA supplement. This is curious in view of the lack of effect of BCAAs on exercise (learn more) induced protein breakdown and points with a finger to other EAAs as potential motors of this effect.

Figure 1: Protein synthesis. Mixed-muscle (A), myofibrillar (B), and sarcoplasmic (C) muscle protein synthesis (MPS) during exercise and mixed-muscle (D), myofibrillar (E), and sarcoplasmic (F) MPS in recovery from a 90 min, metabolically matched load carriage (LC) or conventional endurance (CE) exercise bout, with and without (control, CON) essential amino acid (EAA) supplementation. Data are mean ± SD, n = 10 per group. †Mode main effect; LC different than CE, P < 0.05. *Drink main effect; EAA different than CON, P < 0.05 (Pasiakos. 2015).

The fact that the loading didn't make a difference in either direction, i.e. that it did neither increase nor decrease the breakdown or synthesis of muscle protein may be surprising, but it's not the only result worth mentioning before we evaluate the results in the bottom line. In addition, it should be noted:

1. The EAA-mediated decrease in muscle breakdown was complemented by both enhanced mixed-muscle and sarcoplasmic MPS during exercise.
2. During the recovery phase, the mixed muscle and sarcoplasmic protein synthesis in response to loaded cardio training were higher than they were in the control group.

Of these results, finding #2 is of most interest as it puts the alleged uselessness of loaded cardio into perspectives. Muscles do after all grow during rest and if the muscle protein synthesis during the recovery phase is increased compared to the control non-loaded exercise this clearly suggests that loaded endurance exercise is more anabolic than non-loaded endurance exercise.

Yes! You can use whey or even regular milk protein, as well and benefit. Better don't eat a steak during your workout though. Learn more in this SV Classic  "23g of Dairy Protein + 5g of Leucine Turn Cardio Sessions Into Muscle Building Workouts"

So, loaded endurance exercise is not much, but a little better? Well, in this study it appears to be as if the former was the correct conclusion to be drawn. Generalizations, however, must be made with utmost care. Especially in view of the unfair comparison of walking on a treadmill with cycling on a bike, of which you could argue that it is naturally less anabolic than walking - irrespective of whether you're carrying an extra-load or not. Thus, the researchers have weakened the generalizability of their results by making the (imho unnecessary) decision to rely on a tried and proven method, i.e. cycling, only to (as I suspect) make it easier to standardize the workload in numbers. This, however, is bogus: I mean, you all have probably worked out for say 500kcal on an exercise bike and for 500kcal on a treadmill. Now tell me: What did you feel was more exhausting and had a subjectively significantly larger impact on your metabolism? You answer probably is 'treadmill'.

Eventually, the most practically relevant information you can draw from the study at hand are thus: (A) You can do both 90 minutes of loaded cardio on the treadmill and 90 minutes of classic cardio on an exercise bike without any muscle loss (at least from the exercised muscles) even if you consume only water (see net balance = 0 in Figure 2). (B) If you bring 10g of EAA and consume them over the course of your workout you may even hop off the treadmill or bike with a few micrograms extra muscle on your legs. And (C) if you chose the treadmill and loaded cardio this will trigger a better post-workout anabolic response than the bike. How meaningful all that is - in terms of gains, I mean - will yet have to be seen in future long(er)-term studies | Comment!

References:

• Pasiakos, Stefan M., et al. "Leucine-enriched essential amino acid supplementation during moderate steady state exercise enhances postexercise muscle protein synthesis." The American journal of clinical nutrition 94.3 (2011): 809-818.
• Pasiakos SM, McClung HL, Margolis LM, Murphy NE, Lin GG, Hydren JR, et al. "Human Muscle Protein Synthetic Responses during Weight-Bearing and Non-Weight-Bearing Exercise: A Comparative Study of Exercise Modes and Recovery Nutrition." PLoS ONE 10.10 (2015): Online only.