Author(s): OZAWA, Y., SHIMIZU, M., MIYAZAKI, S., UCHIYAMA, S., YAMADA, H., Institution: TOKAI UNIVERSITY, Country: JAPAN, Abstract-ID: 986

INTRODUCTION:
The Electromechanical Delay (EMD) is caused by 1) the propagation of action potential on muscle membrane, 2) the excitation-contraction coupling processes, and 3) the stretching of the series elastic component (SEC) by the contractile element (Norman RW and Komi PV, 1979, Alexander RM and Bennet-Clark HC, 1977). The time for the last factor is considered a major portion of EMD time (Cavanagh PR and Komi PV, 1979).
The effect of SEC stretching on EMD had been examined in tendons of the lower limb however it had not been examined in that of the upper limb. The tendon slack length would be more affected for motor control on the upper limb because its joints especially require more precise control than the lower limb joints. Therefore, there is the possibility that the upper limb tendons have different behavior. In addition, a tendon on the lower limb is too long to be captured by one prove of ultrasonogram. The tendon length on the triceps brachii (TB) is 10-15 mm (Keener JD et al., 2010) and it could be captured by one probe. In the present study, we focus on the changing behavior during the stretching slack length of the tendon on TB.
METHODS:
Six healthy subjects were recruited. The trials were elbow concentric contraction for 30, 60, and 90% of maximal voluntary contraction (MVC) with a seated position. The distal tendon of TB was captured by using B-mode ultrasonography. Each trial was tested three times, and before the test trials, the MVC trials were tested for two times. The electromyography was recorded from biceps brachii (BB) and TB. The percentage of tendon stretching length was calculated by dividing the tendon length during muscle contracting by relaxing. The mean ± standard deviation of all data was calculated. The effect of contraction levels on tendon length changes was examined by using paired one-way ANOVA. Statistical significant level was set at a level of p < 0.05.
RESULTS:
There was no significant difference in the tendon length in 30% MVC between relaxation and contraction (p = 0.052). In the 60 %MVC and 90% MVC trials, the tendon length at the contraction condition was significantly longer than that of the relaxation condition (60% MVC: p = 0.002, 90% MVC: p = 0.002). The percentage of tendon stretching length in 30% MVC was shorter than that of 60% MVC (p = 0.010) and 90% MVC (p = 0.013).
CONCLUSION:
When the tendon loads the tension, during the weak load the tendon stress increases non-linearly, however, the load tension through the transition point, the tendon stress increases linearly (Connizzo et al., 2013). In the previous study, the Achilles tendons transition point was around 60% MVC (Muraoka T, et al., 2004). In the present study, the percentage tendon stretching length change was significantly different between 30% to 60% MVC and 60% to 90% MVC. From these results, the upper limb muscle tendon has the slack length as well as lower limb tendons, and the behavior has a similar pattern with the lower limb tendon.