‍Purpose: 

To examine the effects of flywheel Bulgarian squats across 8 weeks on quadriceps function (rate of force development (RFD), maximum voluntary isometric contraction (MVIC) and central activation ratio (CAR)) on athletes that are rehabbing an ACL reconstruction.   

Methods: 

11 collegiate athletes with unilateral ACL reconstruction (≥ 6 months post-op) participated in this study.  The training intervention consisted of one set of flywheel Bulgarian split squats to exhaustion on their injured leg only, 2 times per week for 8 weeks.  The initial loading (week 1) for females was .025 kg m² and .05 kg m² for males.  Load increased by .025 kg m² in the proceeding session if the athletes were able to successfully complete 20 “strong” repetitions.  RFD_{0–50 ms}, RFD_{0–150 ms}, MVIC, and CAR were measured bilaterally on a custom-made leg extension machine the week before and after the intervention. 

Results: 

There was a significant improvement in both RFD_{0–50 ms} and RFD_{0–150 ms} in the injured limb (30.6% and 20.6%, respectively).  In addition, the between-leg difference (injured vs uninjured leg) in MVIC was significantly reduced.  

Key Takeaways: 

• The changes in RFD indicate that the athletes improved their ability to generate maximal force at a quicker rate, which is a strong indicator of sport performance.  In addition, the improved RFD does suggest that motor unit behavior improved (i.e., firing rate). 

•  The between-leg difference changes in MVIC suggest that limb symmetry improved and that the injured limbs MVIC was returning to baseline measurements.  Limb symmetry is a common metric monitored throughout the return to sport process and is thought of as a criterion in advancing athletes through the stages of ACL rehab. 

• Altogether these finding suggest that 1 set of flywheel Bulgarian split squats to exhaustion can be utilized to improve quadricep function among athletes who are recovering from an ACL reconstruction.  This study provides the efficacy of utilizing flywheels in a return to sport program.  However, it is likely that more overall training volume and a wider range of exercise selection on the flywheel is needed to fully drive adaptation, specifically in reference to MVIC and CAR.