Effects of 8 Weeks of Moderate- or High-Volume Strength Training on Sarcoplasmic Reticulum Ca²⁺ Handling in Elite...

While acute exercise affects sarcoplasmic reticulum (SR) function, the impact of resistance training remains unclear. The purpose of the present study was to investigate SR Ca²⁺ handling plasticity in response to moderate- and high-volume strength training in elite rowers. Twenty elite male (n = 12) and female (n = 8) rowers performed three weekly strength training sessions for 8 weeks and were randomly allocated to either perform 3 sets (3-SET) or progressive increase from 5 to 10 sets (10-SET) of 10 repetitions during the training period. Skeletal muscle biopsies were collected before and after the intervention period and analyzed for SR vesicle Ca²⁺ handling, SR related proteins, and myosin heavy chain (MHC) composition. Muscle strength was determined by isometric midthigh pull (IMTP). Training increased both the overall SR Ca²⁺ release (19%) and uptake rates (34%), with no differences between groups. SR protein analysis revealed a high variability but suggests an increase of RYR1 and SERCA1, while SERCA2 decreased, corroborating changes in SR function, with no differences between groups. Regardless of training volume, a 9% higher relative MHCIIa proportion and a 7% decrease in the MHCI isoform was observed. There was an overall 8% increase of IMTP. Males exhibited higher SR Ca²⁺ uptake and release rates compared to females, likely explained by a higher proportion of MHCII. These findings suggest that 8 weeks of moderate- or high-volume strength training enhances SR vesicle Ca²⁺ uptake and release rates in elite male and female rowers, accompanied by a shift toward a larger proportion of MHCIIa fiber type.