In the field of neuroscience and human physiology, a reflex is an automatic, involuntary response to a stimulus. In the context of reflexive relaxation induced by vibrations, we're particularly interested in a specific reflex called the "stretch reflex."

Muscle spindles, small sensory organs located within the muscle, are key players in this reflex. They are sensitive to changes in muscle length (i.e., stretching) and rate of change in length. In a way, muscle spindles act as the muscle's own surveillance system, keeping the central nervous system informed about what's happening in the muscle at any given moment.

Let's delve deeper into how vibrations can trigger this reflexive relaxation response:

1. Vibrations and Muscle Spindle Activation:

When vibrations are applied to a muscle, the repetitive, rhythmic oscillations can cause micro-stretching of the muscle fibers. This stretching is detected by the muscle spindles, which promptly generate nerve impulses or signals. These signals travel along sensory nerve fibers to the spinal cord, providing information about the muscle's state of stretch.

2. Modulating the Stretch Reflex:

Usually, when a muscle is rapidly stretched, the stretch reflex kicks in to contract the muscle – a protective response to prevent overstretching and potential injury. However, the high frequency of vibration leads to a sustained activation of the muscle spindles. This persistent activation can lead to the adaptation of the muscle spindles, reducing their response.

In other words, the muscle spindles get "used to" the vibratory stimulus and lessen their signaling, which can modulate the stretch reflex and lead to muscle relaxation. This is akin to entering a room with a strong smell; initially, the smell may be overwhelming, but if you stay in the room for a while, your sensory system adapts, and the smell becomes less noticeable.

3. Reflexive Relaxation and Fascial Tension:

As the muscle relaxes reflexively, there is less pull or tension exerted on the associated fascia – the connective tissue sheaths that envelop muscles. Because muscles and fascia are interconnected in a continuous network (the myofascial system), changes in muscle tension can directly influence the state of tension in the fascia. Thus, by reducing muscle tension, vibrations can also help reduce fascial tension and stiffness, thereby improving tissue mobility.

This reflexive relaxation response and its impact on fascial tension is one of the mechanisms through which vibration therapy may help improve flexibility, range of motion, and reduce muscle and fascial stiffness. It's worth noting, however, that the effectiveness of this approach can vary among individuals and may depend on the specific parameters of the vibration (e.g., frequency, amplitude), the individual's overall health status, and the targeted muscle group.

References:

1. Aminian-Far, A., Hadian, M. R., Olyaei, G., Talebian, S., & Bakhtiary, A. H. (2011). Whole-body vibration and the prevention and treatment of delayed-onset muscle soreness. Journal of Athletic Training, 46(1), 43-49.
2. Lau, W. Y., & Nosaka, K. (2011). Effect of vibration treatment on symptoms associated with eccentric exercise-induced muscle damage. American Journal of Physical Medicine & Rehabilitation, 90(8), 648-657.
3. Marín, P. J., Hazell, T. J., & García-Gutiérrez, M. T. (2013). The response of muscle spindle afferents to vibration during isometric contraction of the plantarflexors in humans. European Journal of Applied Physiology, 113(11), 2857-2867.
4. Tozzi, P. (2015). A unifying neuro-fasciagenic model of somatic dysfunction – Underlying mechanisms and treatment. Part I. Journal of Bodywork and Movement Therapies, 19(2), 310-326.
5. Zhang, J. T., Clark, B. C., & Mo, X. (2020). Acute Effects of Whole-Body Vibration on Trunk and Neck Muscle Activity in Consideration of Different Vibration Loads. Journal of Sports Science & Medicine, 19(2), 362-368.