Analysis Of Rectus Femoris And Vastus Lateralis Muscle Thickness In Response To Different Training Volumes

PURPOSE: The purpose of this investigation was to examine changes in muscle thickness (MT) of the rectus femoris (RF) and vastus lateralis (VL) following eight weeks of high- and low- volume resistance training. METHODS: Twenty-six resistance-trained males and females participated in supervised, progressive lower body resistance training twice a week for eight weeks. Participants were randomly assigned to a high- (HV; M/F = 7/7) or low-volume (LV; M/F = 7/5) training group of eight (LV) or 16 (HV) sets of lower body exercise consisting of leg press and RDL each week. The weekly volume for each group was split over two sessions separated by ≥48 hours. The final set of each exercise was completed to volitional failure. Ultrasound images of the VL and RF were taken at pre-, mid-, and post- timepoints to assess for changes in MT. Prior to analysis, ultrasound images were blinded and measured by a separate investigator. Testing commenced after an eight hour fast and 48+ hours after the previous exercise bout. RESULTS: There were no significant (sig.) time × muscle × sex × group interaction effect (p = 0.873). There was a sig. time × sex × group (p = 0.033) interaction. No other sig. 3-way or 2-way interaction effects were present (p = 0.500-0.898). Post-hoc analyses indicated that when collapsed across muscle, LV males and HV females had sig. greater MT at MID and POST compared to PRE (p = 0.01-0.013). LV Males changed PRE to MID (+0.08 ± 0.08 cm2) and PRE to POST (+0.18 ± 0.136 cm2); HV Females changed PRE to MID (+0.13 ± 0.19 cm2) and PRE to POST (+0.17 ± 0.19 cm2) with no sig. changes over time in HV males or LV females (p = 0.218-0.516). There were no within sex differences between groups at any timepoint (p = 0.343-0.806). There was also a sig. muscle × time interaction (p = 0.011). Post-hoc analyses indicated that when collapsed across sex and group, VL MT was sig. greater at MID (2.49 +/- 0.60 cm2) and POST (2.47 ± 0.61 cm2) compared to PRE (2.30 ± 0.58 cm2). RF exhibited no change in MT across time (p = 0.393-0.844). Consequently, RF had sig. greater MT than VL at PRE (p = 0.014); 2.57 ± 0.48 cm2) but not at MID (2.56 ± 0.46 cm2) or POST (2.60 ± 0.50 cm2), (p = 0.168-0.541). CONCLUSIONS: The present data suggests that biological sex and training volume may play a role in changes in muscle thickness of the quadriceps following 8-weeks of RT.