Effects of Lower Extremity Alignment During Barbell Squat Training on Muscle Volumes

Area of Science:

• Biomechanics
• Exercise Physiology
• Musculoskeletal Adaptations

Background:

• Barbell squat training is known to increase hip and knee extensor muscle size.
• Biomechanical analyses suggest differing hip muscle demands between "knees in" and "knees out" squat variations.
• The influence of these variations on hip extensor muscle hypertrophy and safety remains unclear.

Purpose of the Study:

• To investigate whether "knees in" versus "knees out" tibiofemoral alignment during barbell squat training differentially affects hip extensor muscle size.
• To assess the safety and tolerability of these squat variations in novice female trainees.

Main Methods:

• Eleven healthy women completed 6 weeks of barbell squat training.
• Participants were assigned to either a "knees in" (n=6) or "knees out" group.
• Muscle volumes were quantified using magnetic resonance imaging (MRI), and knee health was assessed via the Knee Injury and Osteoarthritis Outcome Score (KOOS).

Main Results:

• Both groups demonstrated significant increases in lower-body strength and vasti muscle volumes.
• No significant increases in hip extensor muscle volumes were observed in either group.
• The "knees in" group experienced a decrease in gluteus maximus volume, suggesting potential muscle atrophy or altered loading.

Conclusions:

• Neither squat variation led to differential hip extensor muscle hypertrophy over 6 weeks.
• The observed decrease in gluteus maximus volume in the "knees in" group warrants further investigation into its loading effects.
• Both "knees in" and "knees out" squat variations appear safe and tolerable for novice women, though longer interventions may reveal distinct adaptations.