Does Endurance Training Promote Muscle Building From Strength Training?
Title: Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR
Author: Kazior et al
Journal: PLOS One
Objective: To examine whether endurance training, with session of high-intensity intervals, influences the response to a subsequent session of resistance exercise with regard to strength development, muscle fiber composition, and fiber size, as well as total level of proteins in the Akt-mTOR pathway.
Endurance training is commonly performed among athletes of all types, from pro to recreational. The question is, does this help or hurt muscle building?
Early studies suggested there was a negative relationship between endurance and strength training, meaning that endurance training could blunt the effects of strength and power from resistance training.
However, not all studies have been consistent and some more recent studies suggested a positive relationship.
The AKT-mTOR pathway is an intracellular signaling pathway involved in regulating much of all cellular activity, including myocytes or muscle cells and makes a major contribution in development of muscle mass. This pathway is known to be activated by various types of exercise.
So the authors wanted to know if endurance training combined with strength training had any effect on strength , muscle fiber composition and protein levels of the AKT-mTOR pathway.
They included two groups of male subjects who performed 7 weeks of resistance exercise alone (n = 7) or in combination with preceding endurance exercise, including both continuous and interval cycling (n = 9).
Muscle biopsies were taken before and after the training period.
Similar increases in leg-press 1 repetition maximum (30%; P<0.05) were observed in both groups, whereas maximal oxygen uptake was elevated (8%; P<0.05) only in the combined endurance and resistance exercise group.
The combined group training enlarged the areas of both type I and type II fibers, whereas the resistance exercise only group increased only the type II fibers.
The mean fiber area or hypertrophy increased by 28% (P<0.05) in the combined group group, whereas no significant increase was observed in the resistance exercise only group.
Expression of AKT-mTOR protein was enhanced in the combined endurance and resistance exercise group, however, only the level of mTOR was elevated following resistance exercise only group.
Training-induced alterations in the levels of both Akt and mTOR protein were correlated to changes in type I fiber area (r = 0.55–0.61, P<0.05), as well as mean fiber area (r = 0.55–0.61, P<0.05), reflecting the important role played by these proteins in connection with muscle hypertrophy.
Both training regimes reduced the level of MAFbx protein (P<0.05) and tended to elevate that of MuRF-1. These are two enzymes that regulate protein muscle breakdown.
This study provides support that endurance training increases hypertrophy in strength training or resistance exercise training.
This appears to be more due to stimulation of anabolic activity than inhibition of catabolic activity, thus providing more data that endurance exercise does not inhibit the anabolic stimulus of resistance training.
Endurance exercise showed advantages to Type I and Type II muscles fibers as well as expression of the AKT-mTOR protein axis.
Kazior, Z., Willis, S. J., & Moberg, M. (2016). Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR. Plos One, 11(2). doi:10.1371/journal.pone.0149082