[Evaluation of the effect of external load activation of periarthicular shoulder muscles]

In new prospect of motor control, the effect of muscle force is considered important not only in producing movement but also in inducing stability and control of activity. The aim of present study was to evaluate the electrical activity of periarthicular shoulder muscles by surface EMG in order to identify the muscular activity during series of static and dynamic pattern of movements. This Quasi experimental study was performed on 30 healthy male and female volunteers with age of 20-30 years and mean age of 23.2 +/- 2.9. The subjects were enrolled into this study by simple non-probability sampling and were exposed to different movement patterns randomly. During the experiment the surface EMG of every muscle was recorded. The external load applied to shoulder was assessed at three levels in static as well as dynamic situations. According to the results of this study, increasing the external load on the scapulothoracic muscles caused a significant increase in the activity of the muscles; except for upper trapezious muscle in descending phase of the movement [p<0.05]. After increasing the external load on shoulder in ascending phase, most of the investigated muscles showed significant differences in their activities. [p<0.05]. In static situation by application of external load only teres major muscle showed significant difference in its activity compared to the reference position [p=0.01]. It can be concluded that application of external load during ascending phase of push up is more effective than its application during descending phase. It can be claimed that during ascending phase slight increase in external load as low as 2% of body weight, would induce more alterations in muscular activity compared to higher external load such as 4% of body weight, but in static situation no significant change could be detected

[ short term effects of one-session of whole body vibration training on isokinetic strength of rotator cuff and shoulder proprioception in young healthy subjects]

The aim of this study was to determine the effect of onesession of whole body vibration training on isokinetic strength of rotator cuff and shoulder proprioception 32 students experienced three positions including control [no vibration], push up with straight elbow and push up with semi flexed elbow [two vibration positions] for 2 minutes with 30 minutes interval between positions. After control position, vibration positions were tested on a random basis by means of a power plate device [Freq: 30Hz and Amp: low]. The isokinetic strength of rotator cuff and shoulder proprioception were measured in angle repositioning test in 3 target angles of 0°, 45° and 90° by means of Kin-Com dynamometer before and after each position. Then the results of 3 positions were compared with one another. Despite decreased dynamic strength of medial rotators after 3 positions, this decrease was significantly less in push up with straight elbow than that in control position [p=0.03]. Also there was a significant difference in concentric MPT of lateral rotators between 3 positions so that, control position caused the greatest decline in lateral rotators strength [p=0.01] and push up with straight elbow was more effective than push up with semi flexed elbow [p=0.03]. Moreover, There was a significant improvement in angle repositioning in 3 positions but only in zero degree a significant difference was detected between the push up with semi flexed elbow position and the control position [p=0.03]. No significant change in muscle strength was found between push up with straight elbow and semi flexed elbow positions. Conclusions: The results of this experiment show that a two minute single-session of whole body vibration is relatively a good stimulation for neuromuscular system in young and healthy individuals

[ feed-forward effect of pretibial muscles on quadriceps femoris during stance phase of gait]

An excitatory pathway is reported to link the pretibial muscles to quadriceps motoneurones. It has been suggested that the interneurones in this reflex pathway relay the supraspinal inputs to quadriceps motoneurones. This may suggest an important role of this neural pathway in the motor control of knee during activities such as walking. In this regard, the pattern of modulation of this short latency reflex was investigated in normal subjects during walking in order to find its role in the motor control of quadriceps muscles. The reflex was elicited in 12 subjects by stimuli applied to common peroneal nerve at several points of gait cycle during walking on treadmill. The reflex magnitude and the intensity of the contraction were calculated from the surface EMG recorded in vastus medialis, rectus femoris and tibialis anterior and was normalized as the percentage of the maximum voluntary contraction in related muscles. The reflex showed the significant correlation with the intensity of contraction in quadriceps, mainly during the early stance phase. The correlation was weak during transition period from stance to swing, where rectus femoris showed a small peak of activity in half of the subjects and it was not accompanied by any reflex. The average peak activity in tibialis anterior was 69 ms preceded that of quadriceps. The precedence of activity in anterior tibial muscle and the strong presence of the reflex during the early stance phase may indicate a positive feed-forward effect from ankle dorsiflexor afferents to quadriceps muscle. Stimulation and activation of this neural connection may have clinical application in the improvement of the motor control of quadriceps muscles as an antigravity muscle in patients with gait disorders

[ effect of cold on the strength of anterior forearm muscles]

Cryotherapy has long been introduced as a common method for preventing and reducing edema caused by traumatic injuries. Many studies have been conducted regarding other effects of cold such as its effects on muscle strength which provided controversial results over the past decades. The aim of this study is to investigate whether cold is capable of changing the muscle strength. The research was conducted on 30 volunteers with the mean age of 22 years. In a standard situation, the volunteers were asked to make their maximum grip force. Cold was applied over their anterior forearm using an ice pack for 15 minutes. The maximum grip force was measured before and within 0 to 120 minutes after cold application. The strength of the anterior forearm muscles decreased rapidly after cold application. The maximum reduction of muscle strength, in average 18%, was observed after 10 minutes. This was followed by a gradual increase of grip force. After 120 minutes the force was increased to about 5% above the baseline force that was before cold application. Regarding the slight increase in the muscle strength and its long delay, cryotherapy of muscles cannot be considered as a practical method in rehabilitation of patients. However, this method would be of great importance for athletes