Author(s): BERSINER, K., JACKO, D., SCHAAF, K., BLOCH, W., GEHLERT, S. , Institution: UNIVERSITY OF HILDESHEIM, Country: GERMANY, Abstract-ID: 2036

INTRODUCTION:
Phosphorylation of the ribosomal protein S6 (rpS6) is indicative for muscle anabolism and is acutely regulated by resistance exercise (RE), while phosphorylation of HSPB5 is indicative for mechanical stress in myofibers. Furthermore, HSPB5 Ser59 and rpS6 Ser235/236 phosphorylation is fiber type-specific in dependency of volume and intensity. Whether different volumes of high intensity RE over an extended period of time will reduce and re-increase prpS6 Ser235/236 and pHSPB5 Ser59 has not yet been investigated, especially when a reduction of RE in terms of detraining is applied. It is also unknown whether HSPB5 and rpS6 will display a corresponding phosphorylation pattern in single muscle fibers. We analyzed prpS6 Ser235/236 and pHSPB5 Ser59 in Western Blot and fiber type-specifically by means of immunohistochemistry in two groups with different training volumes.
METHODS:
Participants (14 male, 4 female; 24 ± 3.4 yrs.; 179 ± 10 cm; 75,9 ± 12,3 kg) were assigned to two groups, differing in training volume (1 set=VOLx1; n=8, or 2 sets=VOLx2; n=10) for 14 RE sessions within 6 weeks, followed by 3 weeks without RE and one final (15th) training session. Training consisted of one or two sets at the respective 4, 8 & 16 RM on the leg extension machine as well as at the 4 and 8 RM on the leg press. Vastus lateralis biopsies were taken before and 1h after the first (R1, S1), 14th (R14, S14) and final (R15, S15) training session. Training before biopsies was carried out with equal volume in both groups (2 sets). prpS6 Ser235/236 and pHSPB5 Ser59 were analyzed in Western Blot and immunohistochemically. Two-way repeated measures ANOVA were performed to detect differences between groups and time points, and linear regression for fiber type-specific differences at S1. A statistical level of p<0.05 was accepted.
RESULTS:
prpS6 Ser235/236 was increased after the first training session and after the detraining phase in both groups, but only in VOLx1 after the 14th session. Values at S14 differed significantly between groups (p<0.05). A similar regulation was observed in pHSPB5 Ser59, where S14 was significantly lower than S1 and S15 only in VOLx2 (p<0.05). Co-staining of pHSPB5 Ser59 and prpS6 Ser235/236 at timepoint S1 revealed a significant negative correlation in type 1, but none in type 2 fibers.
CONCLUSION:
In dependency of the volume, repeated high intensity muscle contractions exceed a yet undefined adaptive threshold which reduces the acute anabolic and proteostasis-related signaling within skeletal muscle fibers, indicating sarcomeric desensitization to mechanical stimulation. Although temporarily activated, acute RE-induced chaperone activation does not correspond with the magnitude of single muscle fiber anabolism, indicating a vastly independent regulation of damage and anabolism in skeletal muscle.