Vastus Lateralis and Vastus Intermedius as Predictors of Quadriceps Femoris Muscle Hypertrophy after Strength Training

The aim of the present study was to investigate which of the four musle heads of the quadriceps femoris is the best surrogate of quadriceps hypertrophy, following resistance training, evaluated by ultrasonography. Forty three physical education students (age: 22.1 ± 3.1 years, height: 175.2 ± 9.3 cm, mass: 75.3 ± 8.0 kg, BMI: 22.8 ± 2.8 kg·m⁻²) participated in the study. Participants followed an 8-week resistance training program in order to enhance quandriceps muscle hypertrophy. Before and after the training period muscle ultrasonography was used to evaluate: total quandriceps (T), vastus lateralis (VL), vastus intermidius (VI), vastus medialis (VM) and rectus femoris (RF) cross sectional area (CSA). Total quadriceps’ as well as VL, VI and VM, CSAs were significantly increased after training (changes ranged between 10.9 ± 9.9% and 18.6 ± 10.8%; p < 0.05). No significant changes were found for RF CSA after training (p > 0.05). Agreement analyses revealed high values for VL and VI (e.g., ICC = 0.879–0.915; p = 0.000), and low values for VM and RF (e.g., ICC = 0.132–0.526; p = 0.000). These results suggest that training-induced changes in muscle hypertrophy in VL and VI measured via muscle ultrasonography may be significantly predict the whole quadriceps hypertrophy in response to lower body resistance training. Consequently, VL and VI may considered as valid surrogates of whole quadriceps muscle hypertrophy.