Combined Cardio and Strength Training Reduces Muscle Growth

Cardio & Strength Training

Over the last few years, there has been much debate about whether performing cardio after resistance exercise blunts muscle growth.  Concurrent (strength plus endurance) training has traditionally been assumed to lead to less muscle growth in comparison with strength training only. Researchers have called this phenomenon the “interference effect.” Basically, the “interference effect” results from a blunted increase in anabolic signaling pathway due to combining aerobic and resistance exercise at the same time.  The research to date has used “untrained” subjects and has shown that aerobic exercise does not interfere with anabolic signaling when performed after resistance exercise.

Cardio After Resistance Exercise

The latest study in Scientific Reports suggests that trained athletes may want to avoid performing cardio after resistance exercise.  Participants first completed 8 weeks of either : Resistance training (RT) alone, or RT combined with cardio/interval training (HIT+RT).

The researchers took muscle biopsies, and also measured muscle growth before and after each group.  Trained individuals, greater anabolic signaling responses are observed after workouts involving only strength training, compared to concurrent (strength and endurance) workouts. Post-workout levels of the anabolic signaling pathway AMPK, mTOR, and p70S6K1 phosphorylation were increased solely after strength training only. In particular, mTOR was increased more after resistance exercise compared to resistance exercise with cardio. The p70S6K response after a single workout has previously been associated with long-term muscle growth and it provides a good indicator of mTOR signaling activity.

Strength training only group had a greater increase in muscle growth compared to Combined Training.  Type I muscle fiber CSA increased (by 22%) and type II muscle fiber CSA tended to increase (by 22%) after strength training only. Changes after concurrent training were non-significant and numerically smaller. In sum, individuals looking to maximize increases in lean muscle mass should avoid doing cardio after resistance exercise.

Enhanced skeletal muscle ribosome biogenesis, yet attenuated mTORC1 and ribosome biogenesis-related signaling, following short-term concurrent versus single-mode resistance training. Fyfe, J. J., Bishop, D. J., Bartlett, J. D., Hanson, E. D., Anderson, M. J., Garnham, A. P., & Stepto, N. K. (2018). Scientific Reports, 8(1), 560.