###### Abstract  
Pathologies in neck and masticatory muscles affect muscle tone and biomechanical and viscoelastic properties, necessitating precise assessment for treatment. This study evaluated the impact of two guided interventions--relaxing exercises targeting the neck and masticatory muscles (\"Exercise\") and heavy chewing using six chewing gums (\"Chewing\")--on the masseter and upper trapezius muscles. Twelve participants (aged 19-40 years) underwent myotonometric assessment pre- and post-intervention, measuring tone, stiffness, decrement, relaxation time, and creep. The results showed significant changes in the masseter muscle after exercise, with increased stiffness (14.46%, \(p<0.001\)) and tone (7.03%, \(p<0.001\)) but decreased creep (\(-9.71\%\), \(p<0.001\)) and relaxation time (\(-11.36\%\), \(p<0.001\)). Conversely, chewing decreased stiffness (\(-8.82\%\), \(p<0.001\)) and tone (\(-5.53\%\), \(p<0.001\)), while it increased creep (\(9.68\%\), \(p<0.001\)) and relaxation time (\(9.98\%\), \(p<0.001\)). In the trapezius muscles, tone decreased after both interventions (Exercise: \(-7.65\%\), \(p<0.001\); Chewing: \(-1.06\%\), \(p=0.003\)), while relaxation increased (Exercise: \(1.78\%\), \(p<0.001\); Chewing: \(2.82\%\), \(p<0.001\)). These findings reveal the distinct effects of exercise and chewing on muscle properties, emphasising the complexity of their therapeutic potential and the need for further investigation. Maseter muscle stiffness and tone are elevated in patients with myogenous or mixed TMDs and those with self-reported bruxism [7; 9; 11; 12]. Increased masseter stiffness has also been reported in individuals with forward head posture, particularly due to smartphone usage [13]. Tension, acting as a self-reinforcing loop within the pain cycle by linking muscular tension, emotional distress, and behavioural responses, has been notably associated with an increased prevalence of TMD symptoms [14; 15]. Moreover, because of the interconnectivity of mandibular and neck activities, prolonged nociceptive input from Myofascal Trigger Points (MTrPs) in the trapezius may contribute to central sensitization, amplifying peripheral pain and disrupting stomachite system function [16]. Stretching and coordination exercises for the neck and orofacial muscles have already been proposed as a non-pharmacological therapeutic option to treat TMDs [1; 2; 17], significantly reducing pain and muscle stiffness in the targeted region [18]. Moreover, similar exercise interventions have been used in patients with obstructive sleep apnoea [3], preventing oropharyngeal injuries due to intubation [19], improving mastication, and increasing muscle stiffness in older adults [20] and after orthodontic or surgical treatments [2]. On the other hand, chewing exercises can be used as strength training for the masseeter muscle and, when adopted regularly, can increase bite force and muscle stiffness in healthy populations [21; 22]. Moreover, chewing exercises have been used to increase muscle stiffness as post-operative treatment following orthognathic surgeries [23] and in patients with orofacial muscular diseases [24]. It is important to recognise that various pathologies and dysfunctions can significantly affect muscle tone and biomechanical and viscoelastic muscle properties [25; 26; 27]. These conditions necessitate the precise assessment of methods to monitor and treat the changes in muscle properties effectively. Historically, evaluations of muscle tone and stiffness have relied on manual palpation. This traditional assessment method relies heavily on expert assessment and is subject to significant bias, particularly in detecting small changes over time. The limitations of this approach have triggered the development of objective tools like myotonometric and tensiomyographic measurement devices. Myotonometry has proven valid and reliable in various conditions [28; 29], and different muscle groups and subjects of different age groups [30; 31].