Negligible epimuscular myofascial force transmission between the human rectus femoris and vastus lateralis muscles in passive conditions

Purpose There have been contradictory reports of the effects of epimuscular myofascial force transmission in humans. This study investigated the transmission of myofascial force to the human vastus lateralis muscle by determining whether vastus lateralis slack angle changed with hip angle. Since the distance between the origin and insertion of the vastus lateralis muscle does not change when hip angle changes, any change in vastus lateralis slack angle with hip position can be attributed to epimuscular myofascial force transmission. Methods Nineteen young adults were tested in hip flexed (80 degrees) and neutral (0 degrees) positions. Ultrasound images of the vastus lateralis muscle were obtained as the knee was passively flexed at 5 degrees/s. The knee angle at which vastus lateralis muscle fascicles began to lengthen was used to identify muscle slack angle. Results Overall, there was a negligible effect of hip position on vastus lateralis slack angle (0.6 degrees [-0.7 to 1.9]; mean [95% confidence interval]). However, a small and variable effect was noted in 3/19 participants. Conclusion This result indicates that, over the range of joint angles tested here, there is little or no epimuscular myofascial force transmission between the vastus lateralis muscle and neighbouring bi-articular structures under passive conditions. More broadly, this result provides additional evidence that epimuscular myofascial force transmission tends to be small and variable under passive conditions in healthy human muscle.