Effects of 8 Weeks of Moderate- or High-Volume Strength Training on Sarcoplasmic Reticulum Ca²⁺ Handling in Elite Female and Male Rowers

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.