Steadiness training improves the quadriceps strength and self-reported outcomes in persistent quadriceps weakness following nine months of anterior cruciate ligament reconstruction and failed conventional physiotherapy

Effects of 8-Week Exhausting Deep Knee Flexion Flywheel Training on Persistent Quadriceps Weakness in Well-Trained Athletes Following Anterior Cruciate Ligament Reconstruction

Persistent quadriceps weakness after anterior cruciate ligament (ACL) reconstruction is a common hurdle to efficient rehabilitation. Therefore, we evaluated a new treatment strategy for athletes with ACL reconstruction. Eleven athletes with unilateral ACL reconstruction performed one set of flywheel Bulgarian split squats to exhaustion with a maximum knee extension of 60°, over 16 sessions, on their reconstructed limb. Quadriceps rate of force development (RFD) 0-50 ms (RFD_{0-50 ms}), and 0-150 ms (RFD_{0-150 ms}), maximum voluntary isometric contraction (MVIC), and central activation ratio (CAR) were measured bilaterally on the week before and after the intervention. In the reconstructed limb, the RFD_{0-50 ms} (p = 0.04; Cohen's d = 0.8) and RFD_{0-150 ms} (p = 0.03; d = 0.9) increased after training. Before-after changes in MVIC and CAR were not significant (p > 0.05), but the lower the baseline MVIC, the greater the gain in MVIC (r = -0.71, p = 0.02). The between-leg difference in MVIC changed from large before (p = 0.01; d = 0.8) to small after training (p = 0.04; d = 0.4). One set of deep knee flexion flywheel Bulgarian split squats to exhaustion improved quadriceps deficits in well-trained athletes with ACL-reconstruction, particularly those with relatively low quadriceps force production.

Dispersion of Knee Helical Axes during Walking after Maximal versus Resistant Strength Training in Healthy Subjects

Knee joint stability can be estimated during functional tasks through the analysis of the helical axes (HAs) dispersion. The study aimed at investigating (1) the test–retest reliability of knee HAs dispersion during walking and (2) the effects of maximal versus resistant strength training on knee HAs dispersion during walking. Thirty healthy subjects (age: 22.6 ± 2.1 years) randomized into a maximal training (MT) group and a resistance training (RT) group underwent a 2-week quadricep–hamstring strength training at 90% or 30% of the maximum voluntary contraction, respectively. Participants walked on a treadmill with clusters of retro-reflective markers placed on thighs and shanks to detect knee kinematics with an optoelectronic system. Knee HAs dispersion was assessed using mean distance (MD) and mean angle (MA) at 1 week before training start, before and after the first training session, and before and after the last training session. Moderate to excellent reliability was found for MD and MA on the sagittal plane (ICCs ≥ 0.70). No differences over time were found for MD and MA between MT and RT. HAs dispersion indexes resulted in reliable parameters for the quantification of knee stability on the sagittal plane during walking. Maximal and resistance strength training induced no knee HAs dispersion changes during walking.