(21) THE EFFECTS OF SET STRUCTURE ON RECTUS FEMORIS AND VASTUS LATERALIS ADAPTATIONS IN TRAINED INDIVIDUALS

Purpose: The purpose of this study was to compare traditional (TR) and cluster (CL) set structures on rectus femoris (RF) and vastus lateralis (VL) adaptations following 4 weeks of resistance training. Methods: Seventeen resistance-trained individuals (9 males, 8 females; age range: 18-33 years) completed this 4-week resistance training intervention. Participants underwent 8 (2x/week) supervised lower-body resistance training sessions, each separated by at least 48 hours. Each participant’s legs were randomized to one of two training conditions: (1) TR, which consisted of 4 sets performed to volitional failure; (2) CS, which was equated to the TR leg for workload and time. Muscle thickness of the RF and VL was assessed at baseline (PRE) and post-intervention (POST) via ultrasonography. Separate three-way (condition × time × sex) repeated-measures ANOVAs were used to analyze differences in RF and VL muscle thickness, with post-hoc comparisons performed for significant interactions and/or main effects. Results: A significant condition × time × sex interaction was observed for RF thickness (p=0.020). Post-hoc analyses indicated that in the CL group, RF muscle thickness significantly increased in both males (PRE: 2.06 ± 0.42 cm; POST: 2.19 ± 0.26 cm; p= 0.004) and females (PRE: 1.93 ± 0.37; POST: 2.10 ± 0.22 cm; p= 0.024). However, in the TR leg, RF muscle thickness only increased in males (PRE: 2.10 ± 0.34 cm; POST: 2.33 ± 0.28 cm; p< 0.001) but not females (PRE: 1.98± 0.34 cm; POST: 1.99 ± 0.28 cm; p= 0.961). There were no significant differences in RF muscle thickness between TR and CL legs within each sex at any timepoint (p= 0.067-0.463). There was no significant 3-way interaction effect for VL muscle thickness (p= 0.889); however, there was a significant time × sex interaction effect (p< 0.001). Post-hoc analyses indicated that when collapsed across condition, VL muscle thickness significantly increased in males (PRE: 1.94 ± 0.52 cm; POST: 2.28 ± 0.34 cm; p< 0.001), but not in females in females (PRE: 2.10 ± 0.34 cm; POST: 2.12 ± 0.271 cm; p= 0.263). Conclusions: These findings suggest that both traditional (TR) and cluster (CL) resistance training elicited increases in RF and VL muscle thickness in males. In females, however, only the RF in the CL exhibited significant increases in muscle thickness, with no changes in the VL or RF of the TR leg. Thus, the present data suggests that both muscle and set structure may influence the hypertrophic responses, particularly in females. Practical Applications: Based on the present data, strength and conditioning professionals should tailor training to account for muscle and sex-based differences in adaptation, particularly for female trainees. However, these findings should be interpreted with caution until the underlying mechanisms of these findings can be determined. Acknowledgements: None