Paisley Park Soundstage, Chanhassen, MN
Many dancers “mark” their steps for much of their rehearsal time, meaning they do slight movements to mimic the choreography until it is time to rehearse the full choreographed number. Prince, however, often rehearsed just as rigorously as he performed.1 This type of over-training is the most common risk factor for fatigue, impaired movement and increased risk of injury.2,3 Especially in the earlier years of his career, Prince did not seem to have a half-speed. For his fans, Prince was always willing to give his all. The key to performing at this level of intensity night after night requires not just the mind, but the body to be both WILLING AND ABLE.*
The most famous of Prince’s dance moves is also the one that likely did the most damage to his body — the splits. There are many ways to do the splits: right-front splits, left-front splits, side/middle/straddle splits, straddle jump splits, right-front jazz splits and left-front jazz splits.
Prince had a dance habit or preference of a left-front jazz split. In a jazz split, the back leg is flexed at the knee and slightly externally rotated at the hip. Prince took it a step futher by ending with a slide to stand and often performed with repetitive bouncing jazz splits either staying with the left front or bouncing back and forth from left-front to right-front split. In all of the videos I have seen of Prince doing a jazz splits to stand, rarely did he ever do a stand alone right-front jazz split. When he did, it was usually in transition from a left-front jazz split. His slide to stand was always weighted on the left foot at the top of his slide, even the few times his slide-to-stand was from a right front position.5
6 We all form habits, whether consciously or subconsciously, that effect our body and how it functions or dysfunctions. If we become consciously aware of our habits we can understand what is causing our pain and start forming healthier habits. The jazz split and slide to stand was arguably made famous by the Nicholas Brothers, but even these tapper brothers each had a side they favored. Harold preferred a right-front jazz split while his brother Fayard preferred a left-front jazz split. Likely, this is because the brothers performed together and the aesthetic required symmetry, so they mirrored each other.7
But why did Prince develop a left-front jazz split to stand habit? It is well known that James Brown had a large influence in Prince’s music and style. In my observation, James Brown had the exact opposite habit of Prince. James Brown habitually performed a right-front jazz split to stand. It’s conjecture, but I like to imagine preteen Prince watching James Brown on television and trying to imitate his moves in his living room, the same way I did with my favorite performers when I was child. It would explain why Prince had an exact mirrored habit to James Brown.8 Therefore, it is possible that this analysis could also apply to the pain James Brown felt in his later years. It is very possible that Prince and James Brown had the exact same injury on opposite sides.
To explain WHAT that injury is, first we have to understand HOW different tissues of the body behave so that we can understand WHY they fail. For this post, I want to introduce you to some of the concepts you will need to understand in order to understand the injury analysis. In my next post, we will analyze the splits and the injury I believe it caused our dearly beloved Prince.
Before I was a chiropractor I was a civil engineer. Instead of analyzing the structure of buildings and bridges, now I analyze the structure of the human body. The basic understanding of mechanics of materials crosses over from one field of science to the other almost seamlessly because the physical principles are mostly the same. The main difference is the materials. Instead of comparing steel to cast iron or adamantium to vibranium, we are comparing bones to muscles and ligaments to tendons. The properties of each tissue determine its function and how quickly it can recover from injury.9
Tendons and ligaments are considered viscoelastic materials. “Viscoelasticity” is a property of a material that demonstrates both characteristics of a liquid and of a solid. Viscosity is the thickness of a liquid and elasticity is a solid material’s ability to return to its original shape after being subjected to an applied force.10 Hence, “viscoelasticity”. Scientists love squishing words together! Viscoelasticity is what allows tendons and ligaments to withstand the various forces that are placed on them such as tension (pulling), compression (pressing) or shear stress (2 types: torsion/twisting and transverse/frictional, like scissors).9
Deformation is a term we use to describe how the shape and size of a material changes after a force has been applied to it — in other words, how the material “deforms”. Any force applied to a material within its “elastic range” implies that the tissue will return to its original size and shape once the applied force is removed. In the elastic range, the tissue undergoes temporary deformation. When a material enters the “plastic range” (in true Mean Girls fashion), that implies that enough force has been applied to it to cause some level of permanent deformation of the tissue even after the applied force is removed. To visualize this concept we use a graph called an stress-strain curve. In viscoelastic materials, strain is dependent on the time over which the force is applied. This simply means that how a tissue deforms, depends on the how quickly and for how long a force is applied to the tissue. The yield point is where the material moves from the elastic range (healthy motion) into the plastic range (injury—strain/sprain). The failure point is considered rupture where the tendon or ligament is torn.10
So first, let’s identify, define and compare the properties of each tissue involved in an articulation (joint) of the body.
The chart below gives a comparison of ligaments which attach bone to bone and tendons which attach muscles to bones. I have highlighted the most relevant information for our purposes here. The main takeaways from this comparison are that the primary function of ligaments is to provide stability to a joint while the primary function of tendons is to allow for movement of the joint within the muscle’s natural range of motion. That means that an injury to a ligament results in instability of the joint while injury to a muscle results in a loss of mobility and/or loss of strength. In comparison to tendons, ligaments act as a static (non-moving) restraint for motion and are therefore are at a disadvantage when they are put under highly dynamic (moving) stresses.
Another major difference is that because tendons are attached to muscle which is a contractile tissue, they have more elastin than ligaments thus a higher yield point for tensile stress (tendons are more flexible than ligaments).
Warning! This part gets a little “mathy”. No worries! The concept here is more important than the math. So if you’re not interested in this section, just scroll to the pictures and get an idea of what motion is happening. You can otherwise skip the parts in gray.
For my mathletes… I know how satisfying formulas involving Greek letters can be!
You’re welcome! 😉
From our stress-strain diagram, stress (normal stress, sigma,σ) is the intensity of the internal force within a material at a perpendicular cross-sectional area (A) when it is subjected to some external tensile force (F), so that:
In order to understand Prince’s splits injury you need to be aware of another type of stress called shear stress. There are two types of shear stress — transverse (frictional) stress and torsion (twisting) stress. Transverse shear stress (tau,τ) is the intensity of the internal forces acting parallel to a cross-sectional area (A) of a material when it is subjected to some external force (F), so that:
Torsion shear stress is …
Strain (epsilon, ε) is a measure of the degree or intensity of deformation. In others words, how little or how much the material has changed shape and/or size. Normal axial strain is the ratio of the change in length of a material (delta l) to the original length of the material (l), so that:
Welcome back! The next topic you’ll need to know is the major anatomical structures that are stressed during the splits, specifically Prince’s left-front jazz splits and slide to stand.
The structures we are most concerned with in this analysis will be: sacroiliac joints (SI joints), femoroacetabular joints (hip joints), anterior and posterior sacroiliac ligaments, the hip extensors and their tendons including gluteus maximus and hamstring muscles (biceps femoris, semitentinosus and semimembranosus) the hip flexors and their tendons (psoas major/minor and iliacus), the hip abductors and their tendons (gluteus medius and gluteus minimus), the lumbar nerves (L4, L5), sacral nerves (S1–S4) and the sciatic nerve. Most of the muscles we have already identified in previous posts. Below are images to identify the joints, ligaments and nerves/nerve roots listed above.
Now you have been introduced to the main concepts and anatomy involved. Based on the movement of the jazz splits, the properties of tendons and ligaments and the different forces we discussed, can you guess what the injury is? In the next post, I will do the analysis and explain what I believe Prince’s injury was. We will discuss symptoms, some of the differential diagnoses for the injury, how to prevent this injury and how to treat it.
*Willing and Able https://youtu.be/3Apk2Qr9yVc
Rehearsal video: https://youtu.be/buYwLgmP7lQ
Lin CF, Lee WC, Chen YA, Hsue BJ. Fatigue-Induced Changes in Movement Pattern and Muscle Activity During Ballet Releve on Demi-Pointe. J Appl Biomech. 2016 Aug;350(358):350-8. doi: 10.1123/jab.2014-0263. Epub 2016 Mar 8. PMID: 26955753.
Li, F., Adrien, N., & He, Y. (2022). Biomechanical Risks Associated with Foot and Ankle Injuries in Ballet Dancers: A Systematic Review. International journal of environmental research and public health, 19(8), 4916. https://doi.org/10.3390/ijerph19084916
Nicholas Brothers with Cab Calloway: https://youtu.be/IoMbeDhG9fU
James Brown jazz splits: https://youtu.be/Ke34BuxR6_w
Özkaya, Nihat & Goldsheyder, David & Nordin, Margareta & Leger, Dawn. (2012). Fundamentals of biomechanics: Equilibrium, motion, and deformation, third edition. 10.1007/978-1-4614-1150-5.
Nordin, Margareta & Frankel, Victor H.. (2013). Basic Biomechanics of the Musculoskeletal System, fourth edition.