Changes of flexion relaxation pattern following rhythmic motion and fatigue during neck flexion

Cognition of fatigue effects on motion response can improve treatment approaches. Determination of mechanism (maximal voluntary contraction and repetition of movement) that cause change of central responses and neuromuscular transmission have specific emphasis in evaluation and treatment of patients. Following fatigue it is arguable which is more important, neural or osteo-ligamental components. Behavior of para spinal muscles due to their roles in control of posture and spinal alignments are more importance. Gesture and motion pattern of neck and lumbar column following fatigue is due to accession of disorder in neuromuscular junction (NMJ) or limitation in reflex response at this system. Reflex influence is not just for muscle fatigue but also it appeared in synergic muscles. It is clear that stimuli and inhibitory ways have important role in this process. Twenty normal subjects (10 female and 10 male) contributed in this study. Tests were including: 1- Training and warm up 2- Placement of recording electrodes on neck extensor muscles at second and forth spinal vertebra of dominant side. 3- Five motion of neck flexion and extension in sitting position at full range without external load. 4- Fatigue test, contain; A- Maximal isometric contraction at middle range about 3 minute, which were controlled by a dynamometer until onset of fatigue. B- Fifty dynamic and cyclic motions of neck flexion and extension in full range of it. 5- Perform five motions similar stage 3 immediately after muscle fatigue. Three middle cycles were chosen for evaluation. Degree of off activities in flexion, degree of onset of activities in extension, silent period and mean of muscles activities (RMS), before and after fatigue selected for analysis. Comparison of two type of fatigue indicated that there are significant differences between them. Range of motion and eccentric activity were similar for two conditions. Isometric fatigue showed more effect than cyclic condition. In neck motions flexion relaxation occurred. Dynamic motion and isometric activities caused muscle fatigue and changed silent period. This period reduced and it means that onset of extensor muscle activities occurred very soon and moved to middle and outer ranges. In this manner, naught privilege mechanical of non contractile elements in neck region is cause of this reduction. On the other hand extensor muscles have more responsibility for control and preservation of posture. Comparison of two approaches indicated that isometric activity produce more fatigue and spectral indexes such as median and mean frequency reduced markedly.