Background and Aim: Sports such as baseball, volleyball, and racquet sports demand skills that place substantial load upon the athlete's shoulder when his or her arm is in an overhead or abducted position. Athletes who participate in these sports are consequently at higher risk for overuse injuries of the shoulder. Infraspinatus syndrome is defined as a condition of frequently painless atrophy of the infraspinatus muscle caused by suprascapular nerve neuropathy. The syndrome typically causes symptoms that mimic those of rotator cuff tendinopathy, and the diagnosis is often overlooked until the condition fails to respond to a traditional rotator cuff treatment program.

In this study muscle timing and activities of shoulder rotator cuff compared between normal athletics and volleyball players with infraspinatus syndrome.

Materials and Methods: Thirty voluntary male professional volleyball players (20 healthy and 10 patient) in the range of 20 -30 years contributed in this study. Patients group in base of electroneurography had injury of suprascapular nerve at right side. Subjects lied prone on table and their shoulder were 90 degree of abduction and medial rotation with 90 degree of flexion in elbow with vertically position of forearm at the lateral side of table. Electromyographic activities of maximum voluntary contraction of infraspinatus, middle trapezius and teres minor . Muscles were recorded three times with monitoring of dynamometer for normalization of dynamic activities. Activities (RMS) of above muscles were recorded during three dynamic motions similar to spark skill and onsets of their activities determined by external synchronized apparatus.

Results: There was significant difference between normalized RMS of infraspinatus,. and middle trapezius of patients in dynamic motion (p<0.05). Whereas healthy subjects showed significant difference between infraspinatus. and two other muscles (p<0.05). Comparison of normalized RMS indicated different in all three muscles between two groups (p<0.05).  

The sequence of onset three muscle activities were different between two groups significantly (p<0.05). This sequence in patients was middle trapezius, teres minor and infraspinatus whereas in healthy subjects was middle trapezius, infraspinatus and teres minor. Duration of above muscle activities were different in two groups (P<0.05). In patients infraspinatus were active less than other two muscles.       

Conclusion: Professional volleyball players are candidate of suprascapular nerve and infraspinatus muscle weakness. Synergic and stabilizer muscles after this condition with more activities contribute and caused reduce of accuracy of motion and early muscle fatigue.

Background and aim:The role of thoraco-lumbar muscles is important in spinal column stability. Following fatigue due to constant activity, these muscles encounter with variable control pattern and variations of median and mean frequencies are little in relation to torque of force. However these parameters are useful in the literatures, but due to complexity of neuromuscular interaction and variety of motor control, signal processing can determine a wide range of changes and measurements.     

Signal processing nonlinear techniques exploit in biologic signals. Variables of nonlinear techniques are recurrence, determinism, entropy and so on.

The purpose of this study was to determine changes of entropy as nonlinear parameter in comparison with linear parameter and applicability of entropic measurements of the erector spinae muscles during fatigue.   

Materials and methods: Ten healthy women and 6 women with nonspecific low back pain (NSLBP) with a range of 20-30 years old patticipated in this study. Surface electromyography of isometric activities recorded from trunk (T12), lumbar (L3) and biceps femoris muscles during modified Sorenson isometric fatigue test. Median and mean frequency and also nonlinear parameters such as entropy and trend measured in one second of muscles activities before and onset of fatigue. 

Results:  Following fatigue in healthy group, median and mean frequencies reduced at a range of 12-20% (p<0.05). This decrement in LBP group was little (4 - 20%, p<0.05). Entropy increased 120-200% and trend reduced 800-2000% in normal subjects (p<0.05), whereas subjects with LBP indicated increment of entropy 65-220% and decrement of trend 240-500% (p<0.05). Before and after fatigue there was a significance difference between two groups in entropy parameter (p<0.05), whereas median and mean frequencies differences were not significant.

Conclusion:Following static positions, fatigue occurred in three levels of above muscles particularly at lumbar region. Traditional fatigue indicators showed good differences, but percentage of variability was low in comparison to nonlinear parameters. It suggests that nonlinear variables especially entropy are more sensitive than traditional indicators and can explain these stochastic behaviors