Hypertrophy Science: Concurrent Training

Resistance training combined with aerobic exercise in a single program is known as concurrent training (1). 

Wilson et al. did meta-analysis of 21 studies with a total of 422 effect sizes. Concurrent training results in decrements in strength, hypertrophy and power (although overall power is the major variable affected), however while some individuals experience strength decrements others experience substantial gains. The interference effect may be a result of overreaching and overtraining and stimulates competing adaptations over a long-term training program. The longer the endurance activity the greater the interference. 

Specific signals imposed by variations in the duration, modality, and type of exercise are recognized by muscle tissue (2). The adaptations for each modality are vastly different and in most cases conflict one another, and are primarily body part specific. Endurance exercise preferentially increases net protein synthesis in the mitochondrial subfraction (2,3) whereas resistance training preferentially increases net protein synthesis in the myofibrillar subfraction (2,1).

Another example, endurance exercise can decrease the speed of contraction in fast-twitch fibers (5 times faster) and increase the contraction speed in slow-twitch fibers after 10 days of training, interestingly they return to baseline after a detraining period (4).

There’s also fiber conversions, Kraemer et al. observed that concurrent training can cause a conversion from Type IIB to type IIA, in terms of percentage; and in terms of area it was found a significant increase in Type IIA (5). This data suggests that type I increases, and also type IIA at the expense of Type IIB decrease (conversion).

In the endurance only group, type IIa and IIc increased in percentage with a decrease in IIB; areas for type I and IIC decreased, resulting in some muscle loss (this group did long duration cardio and also HIIT, HIIT may have played a role in increase in the percentages observed). In the strength group only, the increase in Type IIA was greater, at a greater expense of conversion from Type IIB, and all areas for Type I, Type IIc and Type IIa increased (5).

Endurance exercise before resistance training impairs the upregulation of translation initiation via the PI3K-AKT-mTOR signaling (1,6,7); and inhibits important elongation factors (eef2) responsible for increasing protein synthesis and maintains this inhibition for the duration of the activity (1,8).

In concurrent training, running, but not with cycling, results in significant decrements in both hypertrophy and strength (1), possibly because cycling is more biomechanically similar to the exercises performed for strength and resistance training. Running has also a high eccentric component, as opposed to cycling consisting primarily of concentric actions. Eccentric actions create greater damage, increasing muscle damage in long distance running. 

Moreover, sprinting (cycling) or HIIT (running) mimics the exercises and intensities often performed for strength and resistance training, and should be used on non-training days, if necessary for some reason.


1. Wilson, JM, Marin, PJ, Rhea, MR, Wilson, SMC, Loenneke, JP, and Anderson, JC. Concurrent training: A meta-analysis examining interference of aerobic and resistance exercise. J Strength Cond Res 26(8): 2293–2307, 2012
2. Sarah B. Wilkinson, Stuart M. Phillips, Philip J. Atherton, Rekha Patel, Kevin E. Yarasheski, Mark A. Tarnopolsky and Michael J. Rennie. Differential effects of resistance and endurance exercise in the fed state on signalling molecule phosphorylation and protein synthesis in human muscle. J Physiol 586.15 (2008) pp 3701–3717
3. MacLean, DA, Graham, TE, and Saltin, B. Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise. Am J Physiol 267: E1010–E1022, 1994.
4. R. H. Fitts , D. L. Costill , P. R. Gardetto. Effect of swim exercise training on human muscle fiber function. Journal of Applied PhysiologyPublished 1 January 1989Vol. 66no. 1, 465-475
5. W. J. Kraemer , J. F. Patton , S. E. Gordon , E. A. Harman , M. R. Deschenes , K. Reynolds , R. U. Newton , N. T. Triplett , J. E. Dziados. Compatibility of high intensity strength and endurance training on hormonal and skeletal muscle adaptations. Journal of Applied PhysiologyPublished 1 March 1995 Vol. 78no. 3, 976-989 
6. Creer, A, Gallagher, P, Slivka, D, Jemiolo, B, Fink, W, and Trappe, S. Influence of muscle glycogen availability on ERK1/2 and Akt signaling after resistance exercise in human skeletal muscle. J Appl Physiol 99: 950–956, 2005.
7. Hawley, JA. Molecular responses to strength and endurance training: Are they incompatible? Appl Physiol Nutr Metab 34: 355–361, 2009.
8. Ogasawara R, Loenneke JP, Thiebaud RS, and Abe T. Low-load bench press training to fatigue results in muscle hypertrophy similar to high-load bench press training. International Journal of Clinical Medicine 4: 114–121, 2013.