Measuring Force vs. Pressure

Author: Chelsea Cornelius – Product Development Manager/Biomedical-Mechanical Engineer

In using force sensing technology, the PeriCoach System® has introduced a brand new way of detecting and presenting pelvic floor movement.  Historically, one of the most common methods of biofeedback has used pressure as the means of measurement, and I am often asked the difference between the two technologies and why we have veered from the usual path.  In our kick off clinician blog post, I though it an ideal time to share the key differences and insights we gathered during development.

Imagine a pressure perineometer as a balloon filled with thousands of little “balls”, and as an external force is applied to the outer surface of the balloon, this drives some of the balls out of the balloon, up the tube, and into the measuring device/handset – indicating that something has occurred to cause a change in ball arrangement and number.  This action is the same regardless of where the force is applied; at the end of the balloon; at the mid-point; at the base.

red balloon illustration

Balloon filled with “balls” that represent the change in pressure.



It is also dependent on the surface area of the force being applied –> if a finger pokes into the surface of the balloon, it will displace more balls than the same force applied by the whole hand.

finger poking balloon

Using a finger or a larger surface to apply the force can make a difference to the measured pressure.



When the applied force is removed, the balls return to the balloon as before.

Using pressure as a way to measure pelvic floor squeeze may lead to some confusing results – the pressure measured is higher when a force is applied using a smaller applicator (the gauge readout showing higher output) than when using a larger surface area of application.  Also, the readout will display a change in pressure when the “balloon” is pressed in at any point along its surface.

pressure against device in uterus

Pressure measurement showing potential force actions affecting the readout.

What the PeriCoach is measuring on the other hand, is direct force.  It uses Force Sensors, strategically placed along the body of the probe to pick up the direct squeeze of the pubococcygeus and lift of the puborectalis as the top sensor is pressed against the urethral wall.

PeriCoach sensors


PeriCoach without the silicone outer, showing force sensors.

These force sensors will pick up muscle activity acting against the sensors themselves, and can determine both magnitude and speed of force application.  In this way, PeriCoach can offer women the “full picture” of muscle activity.

Offering users and clinicians more information on what is happening with a pelvic floor squeeze and relax is the key to using force sensors, and the technology is such that we can adjust sensitivity to suit the user, measure squeeze force improvements over time, measure speed of contraction, provide a record of compliance, and more.  I will discuss these extra features in more detail in future blog posts.  Feel free to email requests for blog content if there’s something you’d like to know more about – send details to

Until next time – Happy Holidays, and many happy returns!