# Mechanical Focal Vibration Therapy for Muscle Injury Recovery in a Runner
## 1 Introduction  
Vibration therapy (VT) is a low-magnitude high-intensity physical agent modality representing a proper way to safely deliver relevant mechanical stimuli as an option to improve musculoskeletal strength and physical performance in the rehabilitation field [1, 2, 3, 4]. Two wide categories of vibrating devices are available: the whole-body vibration (WBV) approach and vibration devices locally applied, i.e., the mechanical Focal Vibration (mFV). Both modality applications exploit a mechanical stimulation defined by a frequency (in Hz) and by the amplitude of the oscillation generated by a peak-to-peak micrometer shift, but the modality applications differ in area and application [5, 6, 7, 8, 9]. WBV appears to increase muscle spindle activity, thus lowering the muscle activation threshold and providing greater background tension and less disruption of excitation-contraction coupling [10]. The mFV is able to activate single muscle fibers, selectively stimulating the Ia and IIb fibers as well as the Golgi tendon organs with respect to a selected application frequency, thus ensuring an improvement in proprioceptive response as well as in muscle trophism [11]. Regarding the sensitivity of proprioceptors to low-amplitude vibrations applied to muscle tendons, Ia fibers were found to be the most sensitive, responding in a one-to-one fashion up to 180 Hz, thus firing harmonically with vibrations up to 80 Hz and then subharmonically at higher frequencies [12]. In this scenario, with tonic contraction of the receptor muscle, the sensitivity of the Golgi tendon organs increased in response to the vibratory stimulus [12]. [PERSON] et al. [13] demonstrated the positive effect of mFV on balance and gait in the elderly; the administration of vibrating insoles in conjunction with limited ankle and foot mFV application provided reliability. Among other things, the mFV approach might deliver mechanical stimulation to the bone and muscle-tendon structures, thus reproducing motion and exercise as well as influencing muscle functioning and recovery [14]. In this scenario, numerous applications of mFV diverge based on the body areas considered, the parameters set, the amplitude and frequency of administration, as well as, in part, the therapist coordinating the physical therapy and any considerations subsequent to the follow-up of short- and long-term outcomes [5]. Further, there are widespread differences between protocols in the characterization of conceivable advantageous application properties and thus of the most active vibrational features [15]. Muscle injuries are the most prevalent type of injury encountered in sports, presenting a significant challenge for primary care physicians and sports medicine specialists [16]. The general process of injury and subsequent repair is remarkably consistent across various muscle injury types; nevertheless, this process is characterized by three distinct phases: The destruction and inflammatory phase, with a breakdown of muscle tissue and the activation of the body's inflammatory response, which lasts up to a maximum of 3 days. The next phase is the repair phase; the body focuses on regenerating the damaged muscle fibers and forming new connective tissue, which lasts for 3 to 4 weeks. Lastly, we have the remodeling phase, which can take 3 to 6 months and involves a gradual strengthening and reorganization of the repaired muscle tissue [17]. In elite athletes, [PERSON] et al. reported that the time to return to training for grade II rectus femoris injuries ranges from 26 to 42 days [18]. The scar tissue shaped during the healing process is structurally inferior to the original muscle fibers, making it less capable of performing the same functions and more susceptible to re-injury. To minimize disability and promote a full recovery, current conservative treatment focuses on limiting bleeding and inflammation through compression, elevation, and local cooling.