Differences in lower limb co-contraction calculations vary clinical interpretation of aquatic treadmill walking in typically developing and children with cerebral palsy.

Objective: The purposes of this study were to (1) investigate muscle co-contraction during aquatic (Wet) and conventional (Dry) treadmill walking at various speeds in typically developing (TD) and children with cerebral palsy (CP) and (2) explore how the clinical interpretation of co-contraction, using co-contraction indices (CCI), may vary depending on the method employed. Methods: Fifteen TD children (30 limbs, 7 M | 8F, 11.3 ± 4.1 yrs., 1.46 ± 0.18 m, 44.2 ± 16.8 kg) and 10 children with CP (20 limbs, 6 M | 4F, 13.1 ± 3.5 yrs., 1.54 ± 0.18 m, 53.2 ± 26.2 kg, 7 GMFCS I and 3 II) participated in this study. Muscle activity of the tibialis anterior (TA), rectus femoris (RF), medial gastrocnemius (MG), and semitendinosus (ST) was recorded during three 3-min walking trials on a Dry treadmill followed by a Wet treadmill. Muscle co-contraction was calculated using three common CCI calculation methods for the RF/ST and TA/MG muscle pairings. Separate linear mixed-effects models examined the influence of population (TD vs. CP), walking speed (Slow, Normal, Fast), and treadmill environment (Dry vs. Wet) on CCI for each equation and muscle pairing. Results: CCI Conclusion: This study shows the potential of aquatic treadmill walking to reduce muscle co-contraction; however, caution is recommended as clinical implications can vary due to the computation method. Future studies should aim to report values from multiple methods to account for the variability within methods and validation of results.