Submaximal fatigue of the hamstrings impairs specific reflex components and knee stability

Abstract

Rupture of the anterior cruciate ligament (ACL) is one of the most serious sports-related injuries and requires long recovery time. The quadriceps and hamstring muscles are functionally important to control stability of the knee joint complex. Fatigue, however, is an important factor that may influence stabilizing control and thus cause ACL injuries. The objective of this study was therefore to assess how submaximal fatigue exercises of the hamstring muscles affect anterior tibial translation as a direct measure of knee joint stability. While 15 test participants were standing upright with the knees in 30 degrees of flexion, anterior tibial translation was induced by a force of 315 N. Two linear potentiometers placed on the tibial tuberosity and the patella recorded tibial motion relative to the femur. Reflex latencies and neuromuscular hamstring activity were determined using surface electromyography (EMG). Muscle fatigue produced a significant longer latency for the monosynaptic reflex latencies, whereas no differences in the latencies of the medium latency component were found. Fatigue significantly reduced EMG amplitudes of the short and medium latency components. These alterations were in line with significantly increased anterior tibial translation. Our results suggest that hamstring fatigue is effectively associated with mechanical loss of knee stability. This decrease in joint stability may at least in part explain higher risk of ACL injury, especially in fatigued muscles. Furthermore, we discuss why the present findings indicate that reduced motor activity rather than the extended latency of the first hamstring response is the reason for possible failure.

An Extensive Evaluation of Different Knee Stability Assessment Measures: A Systematic Review

“…For example, the sensitivity and specificity of the Genucom knee analysis system have been reported to be low, at 60% and 65%, respectively [42].On the other hand, the KT-1000 sensitivity at maximum manual force is 93%, and it has a specificity of approximately 93% [16]. Despite the existing studies on the use of the hamstring-stretch reflex [26,[73][74][75], the literature lacks evidence on whether the reflex latency can be a valid objective clinical knee stability measure.…”

“…The reflex has been investigated intra-operatively by direct traction under arthroscopic visualization and in a research setting by instrumenting a laboratory-based rig [11]; thus, its clinical usefulness is doubtful. Three studies by Schoene et al [11], Friemert et al [26] and Melnyk et al [73] revealed that the ACL-hamstring reflex measurement could be elicited, specifically for injured ACLs. Previous work by Friemert et al [26] has shown that a prolonged reflex was present in patients with a ruptured ACL.…”

“…It has been evaluated in several studies to assess muscle fatigue, knee stability [73] and knee proprioception [74]. It is used in operative theatres through a direct pull of the ACL to differentiate short and long latencies [75].…”

“…The longer reflexes corresponded with patients who had instability symptoms even though mechanical testing with the KT-1000 showed no difference. On the other hand, Melnyk and Gollhofer [73] concluded that it was hamstring muscle fatigue during submaximal isometric exercises that was the reason behind the longer latencies of the hamstring stretch reflex and not the existing ACL injury. Despite the argument in the literature on its usefulness for detecting the aforementioned variables, the authors suggested that this technique has room for improvement in terms of its applicability in a clinical setting to guide rehabilitation protocols [3,11,74].…”

The risk factors for rupture of the anterior cruciate ligament of the knee: The neuromuscular state

“…In addition, the hamstring muscles are activated by the ACL receptors when the ACL is subjected to stress, providing further evidence for the agonist effect of the hamstring muscles on the ACL 32 . A protocol of muscle fatigue alters both the latency and the extent of the re lex response of the hamstring muscles and therefore would have potential repercussions for tibial translation in women [33][34][35][36] . A decrease in the re lex response of the hamstring muscles, and consequently an increase in tibial translation in relation to the femur, increase the instability of the knee and could contribute to the pathomechanics of ACL injuries, especially in women [33][34][35][36] .…”