Effects Of Various Contraction Modes With Equivalent Exercise Volume On Muscle Mtor Signaling

Abstract

Although muscle contraction type (i.e. eccentric, concentric, or isometric contraction) affects the magnitude of mTORC1 activation and subsequent muscle protein synthesis, its regulatory mechanisms are still unknown. Previous studies have shown that eccentric contraction induced the highest mTORC1 activation and muscle protein synthesis as compared with other contraction modes. Although the magnitude of exercise volume (torque × contraction time) is critical in mTORC1 activation and muscle protein synthesis, no previous study was able to match the exercise volume between various contraction modes. PURPOSE: To investigate the effect of different contraction modes with equivalent exercise volume on mTOR signaling in rat skeletal muscle. METHODS: The male SD rats aged 11-week were randomly assigned to three groups designated as eccentric (ECC), concentric (CCN), or isometric contraction(ISO) groups. After a 12-h overnight fast, muscle contraction was performed on right gastrocnemius muscle by percutaneous electrical stimulation (100Hz, ∼30V, 3 sec stimulation × 10 contractions, with a 7 sec interval between contractions, per set, with 3 min rest intervals) by changing ankle joint angle (ISO: at 90°, ECC: 60°∼105°, CCN: 105°∼60°, with joint angular velocity at 15°/sec for ECC and CCN). To standardize to an equivalent exercise volume, the number of sets were modified between contraction modes (i.e. ECC: 3sets, CCN: 4sets, ISO: 5sets). Left gastrocnemius muscle served as the control. Animals were sacrificed and muscle samples were taken immediately and 3 hours after exercise. Western blotting analysis was used to measure phospholyration status of mTORC1 signaling. RESULTS: Erk1/2 and Akt phosphorylation significantly increased at immediately after contraction in all groups as compared to the control leg (p < 0.05), without significant group difference between groups. Furthermore, significant increase in p70S6K phosphorylation (∼11-fold above control) was observed in all three groups at 3h after the contraction, but no significant group differences were observed. CONCLUSIONS: Differential activation of mTORC1 by the electrical stimulation-induced divergent muscle contraction mode seems to be determined by the exercise volume and not by the contraction mode itself.