Cardio or weights, which should we do? The simple (and correct) answer is both; since cardiovascular/aerobic fitness AND muscle strength are significant predictors of healthspan and longevity. A consistent aerobic exercise routine paired with several days per week of strength and resistance exercise is probably one of the best “life hacks” that exist.
However, some people want to optimize one fitness realm over another — prioritizing either aerobic endurance or strength and muscle growth, depending on their performance or physique goals.
There is a long-running debate on whether one can perform high-level endurance and resistance training while simultaneously maximizing the benefits of both. The debate stems from the physiology behind how each exercise stimulates our body to adapt.
Aerobic exercise activates its own unique signaling pathway and, specifically, a “master regulator” protein known as AMPK — leading to mitochondrial biogenesis and an improved ability to generate energy aerobically.
Resistance/strength exercise activates a different unique pathway and specifically, another regulatory protein known as mTOR — leading to muscle growth and protein synthesis, among other effects.
These pathways are theoretically “incompatible,” leading to what is known as the “interference effect.” This states that if one performs both strength and endurance training, especially if performed in close proximity (known as concurrent training), then the benefits of one type of exercise (or perhaps both) will be down-regulated. This is often why strength athletes claim that running and other types of endurance exercise can “hurt your gains.”
Some studies have shown evidence of this effect, but very few have investigated whether the interference effect is actually taking place at the molecular level. It is also unknown whether the intensity of aerobic exercise may uniquely affect strength training-related anabolic signaling. How does high-intensity training compare with moderate intensity training in regard to their effects on anabolic signaling in muscle?
This was the question investigated by a new study published in Nature Scientific Reports.
Brief study methods
8 male participants with an average age of 32 years participated in this study. All participants had a fairly long history of competitive cycling experience and were quite fit — with an average VO2 max of 55 mlO2/kg/min.
In a random order, participants completed three differnet experimental conditions. 1) a resistance exercise only condition that involved 6 x 8 repetitions of back squat exercise at 80% of their estimated one-rep maximum, 2) the same resistance exercise session followed by a 45-minute bout of moderate-intensity cycling (65% of VO2 peak), and 3) resistance exercise session followed by a 40-minute high-intensity cycling session (alternating intervals of 3 minutes at 85% and 45% of VO2 peak).
Before and 3-hours after each session, a muscle biopsy was taken from participants’ vastus lateralis muscle (large muscle in our quadriceps). This tissue sample was analyzed for primary outcomes related to anabolic and endurance training-related signaling pathways. Specifically, the phosphorylation (i.e. activation) of the mTOR pathway (and related proteins) and the AMPK pathway (and related proteins).
- There was a greater phoshorylation of the AMPK pathway in the resistance exercise + moderate intensity cycling condition compared the resistance only and resistance + high-intensity cycling condition
- There was a greater phosphorylation of mTOR following resistance exercise + moderate-intensity cycling compared to the resistance exercise only condition
Overall, the findings of this study suggesting a few very interesting things about the interaction between endurance and strength training.
For one, there was NO evidence of an interference effect. Performing endurance exercise after a strength training session — regardless of the intensity — did not “lessen” the anabolic signaling response in the muscle.
In fact, adding the endurance exercise bout to the resistance training session enhanced the anabolic and endurance-related protein signaling pathways — both mTOR (strength) and AMPK (endurance) phosphorylation was enhanced in the resistance + moderate intensity cycling conditions.
It is important to note that this was an acute study, and the results may not exactly translate to a long-term training program. However, for recreational and competitive athletes who prefer to perform strength and endurance activity within a single session, it appears there may be no harm in doing so.
Would performing exercise in the opposite order (endurance exercise followed by resistance exercise) elicit the same effect? We can’t say for certain given these results, but there are some studies that suggest it may be better to perform concurrent training in this order. Preference definitely matters — I always do my endurance work before hitting the weights at the gym.
Jones TW, Eddens L, Kupusarevic J, et al. Aerobic exercise intensity does not affect the anabolic signaling following resistance exercise in endurance athletes. Sci Rep. 2021;11(1):10785.
Perez-Schindler J, Hamilton DL, Moore DR, Baar K, Philp A. Nutritional strategies to support concurrent training. European Journal of Sport Science. 2015;15(1):41–52.