Does combined endurance and strength training limit adaptations in muscle strength and size?

The last years more and more people are going to the gym to get fit and the Norwegian people are training like they never have before. At the same time there has been a shift in focus where more and more people care not only about the health, but also the performance aspect of training. Many want strong and big muscles, while simultaneously having a good cardiorespiratory fitness. This leads to some worry and questions about whether endurance training alongside strength training can limit the adaptations in muscular strength and size.

A meta-analysis in the Journal of Strength and Conditioning Research has looked into this question. This kind of analysis gathers all the previous research of a high quality and analyzes it together. This gives them a lot of data that makes them able to draw some conclusions the individual studies might not have been able to, such as if the effect of different endurance training modalities matter.

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Overall, they found no significant differences between strength training alone and combined strength and endurance training on adaptations in muscular strength and size. However, when looking at the data for cycling and running alone, it looked like running could have a small negative effect on these adaptations in the lower body, whereas cycling did not. In addition, the shorter the endurance training bouts were, the less likely they were to hamper strength and size gains. Maybe short, intense interval training on a bike is the way to go to increase cardiorespiratory fitness alongside muscular strength and size?

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On the ability to develop maximal power, which is needed in sports that require jumping, fast sprinting, etc. the researchers found a negative effect of incorporating endurance training in a strength training program. Therefore, they think athletes in power sports may need to be careful when incorporating endurance training into their programs.

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The researchers also found no difference between endurance training alone and combined strength and endurance training on adaptations in the maximal oxygen consumption (VO_2max)

Fredrik Hjulstad Bækkerud, PhD Candidate at CERG

1. Wilson, J.M., et al., Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. J Strength Cond Res, 2012. 26(8): p. 2293-307.