The effects of knee and hip joint angles on patellar tendon loading during quadriceps neuromuscular electrical stimulation

Quadriceps neuromuscular electrical stimulation (NMES) may stimulate patellar tendon remodeling and recovery, but it is unclear if hip and knee joint angles during NMES affect patellar tendon loading. Therefore, the purpose of this study was to evaluate the effects of hip and knee joint angles on patellar tendon properties during quadriceps NMES. Twenty healthy men performed quadriceps NMES in supine with 60º of knee flexion (SUP60), seated with 60º of knee flexion (SIT60), supine with 20º of knee flexion (SUP20), and seated with 20º of knee flexion (SIT20). Patellar tendon mechanical and material properties were determined during maximum quadriceps evoked contraction. Patellar tendon force, stress, and stiffness were greater for SUP60 and SIT60 compared to SUP20 and SIT20. Young's modulus was greater for SUP60 and SIT60 compared to SIT20. Tendon elongation, strain, resting length, and average CSA were not different between conditions. In conclusion, during quadriceps NMES, the patellar tendon is loaded more when the knee is flexed to 60º compared to 20º. These findings suggest that clinicians should favor 60º of knee flexion over 20º during NMES when the goal is to load the patellar tendon. Further research is needed to determine optimal positioning for maximal patellar tendon loading.