The magnitude of applied manual force is defined as the amount of force applied by the practitioner on a body [1]. The Force–Velocity Relationship explains how the force of fully activated muscle varies with velocity [2]. Applying oscillatory Posterior anterior mobilization techniques or Vertical Oscillatory Pressure, the maximum magnitude of applied force is usually reported as the mean of the force peaks that occur during a specified period [3,4]. Studies by [5], Harm et. al., (2010), and [6] all quantified mobilization force in terms of magnitude of force applied, frequency of oscillation, and duration of treatment.

Force magnitudes have been measured for mobilization techniques applied to the lumbar spine and, to a lesser extent, the thoracic and cervical spines [5]. Mobilizations are quantified by measurement of both the applied force and the displacement (movement) that occurs as a result of the applied force ([3], Harm et. al, 2010).

The magnitude of a mobilization or how hard the Physiotherapist pushes on the spine is usually reported as the magnitude of force ([5], Harm et al, 2010). However, the sensations felt by a patient during mobilization will be affected by the concentration of the applied force (namely, the pressure). Studies have noted that pressure is defined by force, the surface area where the force is applied can affect the pressure measured and likely the sensation of pressure felt by the patient (Maitland et al., 2005, [7]). For example, a person receiving mobilization will feel a different sensation if the force is applied over a smaller compared with a larger surface area, such as when a Physiotherapist mobilizes with a thumb grip vs a pisiform grip. In previous research and clinical trials on mobilization techniques, researchers have usually reported the force applied without measuring the surface area upon which it is applied (Matyas et al., 1985)

In some previous studies, Force applied during mobilization has been measured in connection with different parameters such as frequency of oscillation [5,8,9] also explained that the magnitude of force applied can be categorized in terms of the frequency of oscillation and the force amplitude ([4], Petty et al., 2001). The frequency of the oscillating force during mobilization is another potential source of variation between Manual Therapists or when Physiotherapists repeat techniques on subsequent occasions, which may be subject to the Physiotherapist’s skill level ([7], Maitland et al., (2001)] recommended applying mobilizations at a rate ranging between 1 oscillation every 2 seconds and 2 to 3 oscillations per second, depending on patient factors ([5], Cormdie et al., 2004, Lee et al., 2005). And research indicated that Physiotherapists apply digital pressure forces at a rate of 1 to 1.5 Hz (ie,1-1.5 oscillations per second) regardless of the grade of mobilization [6]. Moreover, [7] indicated that oscillatory movement can be applied on the spinous during mobilization about twice or thrice for about 15-30 seconds depending on the acuteness of the pain. [7,10] also noted that oscillatory movement is dependent on the somatotype of the patient. According to [7], a good and effective oscillation can be characterized by smoothness of the movement, amplitude, velocity, and rhythm. Another factor is the amplitude of force. Amplitude of Force amplitude is the difference between the minimum and maximum forces applied during mobilization; that is, the difference between the force recorded at the trough and the force recorded at the peak of an applied oscillatory force on a force-time curve. [7] noted that patient anthropometric makeup could interfere with force applied during VOP, however, other factors such as pain intensity, number of oscillations and frequency of treatment were not considered as determinants to predict the magnitude of force applied. Also, the average force applied has not been expressed in terms of these parameters such as pain intensity and somatotype.

In view of the above, this study predicted the digital pressure force applied on the body tissue with pain intensity and somatotype. Also, expressed the average force that can be applied in terms of pain intensity, somatotype, and age of the participant.