The Science of Stretching: Snap, Crackle, Pop

Spoiler alert: Your bones don’t actually pop!

A student recently asked me why her bones popped while practicing yoga. Technically, I told her, her bones weren’t popping. The sounds she’s most likely hearing aren’t actually from the bones themselves popping or cracking but rather from a number of other sources that are occurring at the joint such as tendon and ligament movement, inadequate vitamin supply, dehydration, or—most commonly—crepitation/cavitation.

Anatomy 101

A joint is the site where two or more bones meet. Joints are essential in helping humans perform various ranges and degrees of locomotion. Some joints are immovable [such as the sutures that connect the various bones that form the collective skull] while others have a slight degree of motion [such as those that comprise the vertebral column]. However, most joints in the human body are capable of a high degree of movement and flexibility. These are called synovial joints. They’re often the places that are most susceptible to injury, and the exact places where most people hear those “popping” and “cracking” sounds. Its important to note that while these sounds are a fairly common phenomenon, they can over time be precursors and warning signs to wear and tear of the joint and articular cartilage [arthritis]. So what exactly causes these sounds?

Tendon/Ligament Movement

When you move a joint and change its shape the tendon (a form of connective tissue that connects muscle to bone) also moves to accommodate this shift and sometimes makes a snapping or clicking sound as it returns back to its initial position. The same holds true for ligaments, which connective bone to bone. This occurs often for people at the knee and ankle joints.

Inadequate Vitamin Supply

The body needs the appropriate amount of vitamins and minerals to function optimally and properly. Of these Vitamin D in particular is vital to health of the joint. While getting a limited amount of natural sunlight (15–20 minutes) is one of the prime ways of obtaining Vitamin D those that do not should obtain through other naturally occurring sources (fatty fish and various dairy products) or through supplements (4000 IU/daily or Omega 3s). Think of these elements like the motor oil that you put in your car. Without the necessary lubrication provided by the oil your cars gears and component parts begin to wear and tear and ultimately stop working. The same is true for the human body and especially due to the inherent repetitious nature of most yoga classes (Plank/Chatturanga/Up-Dog/Down-Dog).


The average human body is roughly 50–65 percent water. Because water is one of the primary components (80 percent of its weight and 65–80 percent of its mass) of cartilage when the body is not properly hydrated its lubricating and cushioning properties decrease dramatically. In a nutshell drink copious amounts of water post yoga class, especially in the summer and especially if you take “hot” style yoga classes.

Crepitation and Cavitation

Crepitation is defined as a dry, grating, crackling sound or sensation. Cavitation is the formation of an empty space within a solid object or body. Applied to the human body small air pockets or bubbles often get created (cavitation) when joints are bent (flexion) and/or straightened (extension). When this air gets trapped and then moves a popping or crackling sound occurs (crepitation). Because this action of bending and straightening is what happens in most yoga poses and classes this is exactly why people hear these sounds more often than not while practicing yoga. Most common examples are lunges where the front knee is straightened then bent and in the transition from Chatturanga to Upward-Facing Dog.

Our bodies can be like old houses making all sorts of sounds like popping, cracking and snapping. Begin to take notice when these sounds occur. Are they in the same place? Do they occur when making the same movement? Is there any pain or discomfort preceding the sound and sensation? The good news is these bodily sounds are quite common and, if you don’t feel any pain when the sound occurs, can be quite harmless. If, however, these sounds become more frequent in nature and you begin to experience pain or discomfort, it might be time to schedule that appointment with your health care professional.


Chad Dennis has been teaching yoga since 1998. He is certified in numerous schools of yoga and brings this knowledge and insight to both teachers and practitioners at Wanderlust. He is also the co-leader of the Teacher Intensives and the curator of Yoga Workshops and Teacher Residencies. Follow him on Instagram @ChadDennisYoga