To solve this problem, a statistical parametric mapping (SPM) procedure that enables an analysis of continuous signals is promising. However, all of the previous studies, which have applied a data reduction of continuous torque-time curves to single values (e.g., peak torque, HQ-ratio), potentially loss important information. When taken together, the findings indicate that more research is needed. Also, conflicting results exist regarding the effects of the movement velocity on the HQ-ratio. Thereby, one study found a more pronounced increase of the eccentric compared to the concentric peak torque. At greater hip flexion, knee extension and flexion peak torques during isokinetic eccentric and concentric testing at different velocities increased, while the HQ-ratio did not change. Moreover, an extended hip joint was recommended for sport-specific testing (e.g., sprinting). It was shown that an extended hip joint has an impact on isokinetic results due to the potential influence on the stretch-tension relationship, relative contribution of active contractile components, and neuromuscular control of the muscle. In previous studies, peak torque values for knee extension and flexion as well as hamstring/quadriceps (HQ) ratios were typically calculated. Frequently, quadriceps and hamstring strength is measured during concentric and/or eccentric muscle contractions in a sitting position at different velocities (e.g., 60°/s and 180°/s). Isokinetic dynamometers are commonly used to evaluate knee muscle strength in athletes and patients. Within these topics, the interaction between quadriceps and hamstring muscles and the contribution of mono- and bi-articular muscles remain complex and are not fully understood. However, after return-to-sport, strength deficits and imbalances may persist and potentially cause further injuries. Consequently, prevention and rehabilitation procedures focus on strengthening and balancing the muscles that surround the knee joint. Muscle strength and imbalance between quadriceps and hamstring muscles are discussed as risk factors for non-contact anterior cruciate ligament as well as hamstring injuries. Therefore, angle-specific analyses are recommended to obtain supplemental information and consequently to improve knee strength testing. The angle-specific effects cannot be mirrored by the conventional parameters. Maximum knee strength is lower in supine position, which should be considered for training and testing. Therefore, a seated position during testing and training is questionable, because the hip joint is rarely flexed at 90° during daily life and sporting activities. Isokinetic knee strength is influenced by the hip flexion angle. The torque values were greater at the lower velocity and eccentric mode, but the influence of the velocity and contraction mode were lower at shorter and greater muscle lengths, respectively. Thereby, in comparison to the knee extension, the torque values decreased to a greater extent during knee flexion but not consistent over the entire ROM. Generally, the angle-specific and conventional torques and HQ-ratios were lower in the extended hip compared to a flexed hip joint. The effects of hip angle, contraction mode, and velocity on angle-specific torques and HQ-ratios as well as conventional parameters (peak torques, angles at peak torque, and HQ-ratios) were analyzed using statistical parametric mapping and parametric ANOVAs, respectively. Twenty recreational athletes (10 females, 10 males 23.3 ± 3.2 years 72.1 ± 16.5 kg 1.78 ± 0.07 m) were tested for isokinetic knee flexion and extension at 10° and 90° hip flexion with the following conditions: (i) concentric at 60°/s, (ii) concentric at 180°/s, and (iii) eccentric at 60°/s. Limited information concerning the influence of hip angle, muscle contraction mode, and velocity on the isokinetic knee strength over the entire range of motion (ROM) is available. Additionally, the hip flexion angle during seated testing diverges from that in the majority of daily life and sporting activities. During isokinetic knee strength testing, the knee flexion angles that correspond to the measured torque values are rarely considered.
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