Evaluation of ultrasound data from the MARES Sinusoidal Perturbation Protocol for the analysis of vibration-induced changes in fascicle length and pennation angle as a function of vibration frequency and muscular preload

Kurzfassung

Background: Vibration exposure has proven to be a useful training method and examination method in a variety of contexts. Nevertheless, not much is known about the mechanical properties of muscle tendon unit during vibration exposure. Therefore, the main aim of this study was to get an insight into vibration-induced changes in fascicle length and pennation angle at different frequencies and levels of contraction. Methods: 23 subjects performed the sinusoidal perturbation protocol before and after 60 days of bed rest. Ultrasound videos of gastrocnemius medialis were recorded during vibration exposure at 10 different frequencies (4 – 16 Hz) and 4 levels of contraction (0, 25, 50 and 75% MVC). Excursion of fascicle length (FL) and pennation angle (PEN) was evaluated using an ultrasound tracking software. Results: Excursion of FL and PEN was significantly smaller when muscle was contracted. For the range from 7 to 10 Hz there was a significant increase in excursion for pre-tensioned muscle, especially for FL. After bed rest, excursion was significantly greater at 9 Hz and 10 Hz vibration for FL and at 8, 9 and 10 Hz for PEN, respectively. Conclusion: Fascicle excursion decreases as the muscle contracts. However, no further correlation between the level of contraction and the decrease in excursion could be found. The main finding of this study was a significant resonance effect at 7-10 Hz vibration and contracted muscle. Resonance was even more evident after bed rest.