Concurrent Training: Can aerobic exercise limit strength/hypertophic gains? Or vice versa?

People work hard in the gym every day with specific goals in mind. Endurance athletes want to run as long as they can or keep their pace under a certain time….Resistance-training (Strength training) athletes want to get big and strong… Some people may not know how engaging in concurrent training (aerobic exercise + weight lifting) could affect their performance. Today I will be talking about the effects of concurrent training on endurance athletes vs. resistance-training athletes.

       Endurance athletes could benefit from adding resistance-training in their endurance-training program. Resistance training has shown to decrease running times (people run faster) with a positive effect on running economy (Paavolainen et al., 1999). The greater muscle stiffness and cross-sectional area from resistance training increases the efficiency of each step without a change in cardiovascular capacity, as measured by VO2 max (Storen et al., 2008). There is also no “interference effect” when incorporating resistance exercises into an endurance athlete’s program, such as the Akt/mTOR pathway, which promotes protein synthesis and does not affect the AMPK/PCG-1α pathway, which promotes mitochondrial biogenesis (Fyfe et al, 2014). It would be most beneficial to add resistance-training on endurance-training rest days in order to prevent overtraining.

 Athletes who engage in resistance-training and wish to gain strength, muscle mass, and power should not incorporate a lot of endurance-training to their resistance-training program because there is a large amount of evidence supporting the detrimental effects of concurrent training on resistance trainers. Strength and power are greater in resistance training only groups than they are with concurrent training (Docherty et al, 2000, Hakkinen et al, 2003, Souza et al, 2013, Mikkola et al, 2012). Endurance exercises activate the AMPK pathway, which inhibits the mTOR signaling by the secondary messenger tuberous sclerosis complex (TSC) (Nader et al, 2006). Concurrent training also increases the fast-to-slow fiber types transition (Putman et al, 2004). Type IIx fibers are converted to the more efficient type IIa fibers during concurrent training instead of a shift away from type I, which is more beneficial to the endurance athlete (Aagaard, 2007). Hormones also play an anabolic and catabolic role in muscle protein synthesis. Cortisol is decreased with any form of acute exercise, but after extended bouts, cortisol builds up, therefore increasing muscle breakdown (Chatard et al, 2002, Tsai et al, 2012). With concurrent training in the same day, testosterone is only increased and maintained if resistance training is completed after the endurance portion…however it is inferior to maximize strength and hypertrophic gains compared to a no-endurance program (Cadore et al, 2012). Surprisingly, there is no evidence that the levels of testosterone and growth hormone with their anabolic properties are increased with concurrent training over time (Bell et al., 2000). These hormones all have many variables that determine their secretion such as sleep, diet, and stress, and research has yet to be done that covers them extensively. Satellite cells are also an indicator of muscle growth. Resistance training has shown the most satellite cell density and activation compared to concurrent and endurance training (Roth et al, 2001, Lyle et al, 2012). The problem with concurrent training is the amount of stimuli to the muscles and body. There is research that the interference between strength and conditioning could be from fatigue from overstimulation of the muscles, or overtraining (Docherty et al, 2000).

      In conclusion, it may be beneficial to engage in resistance-training throughout an endurance-training program. However, endurance-training may have detrimental effects on athletes that want to maximize increases in strength, hypertrophy, and power. If a strength training athlete MUST engage in a cardio program, it is best to do cardio after resistance training so that they can be fresh for their lifts and thus, lift more volume and get better results. For endurance athletes, it is best to complete endurance training first, and then focus on weightlifting. The same idea applies here. Whatever your main goal is, you’ll want to focus on that first so that you have more “in the tank” and can perform best at what you are trying to get better at. 

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