Hi LanEvo - Lengthy reply, (apologies) but really only three main points. I've listed and bolded the main issues for a hopefully easy read or skim. Honestly, not trying to score any victory points here. As a former 2012 PD+ user, and former Kevlar user (in a flexible Volkl mid 1990's) I just feel the need to speak up about putting Kevlar in a PD. IMHO that's just crazy talk, akin to getting down on your hands and knees and begging the tennis Gods for injury.
Point 1. Putting poly, and especially a Kevlar string into a very stiff frame like the PD is risky business for sure, by any measure of arm safety.
I think most people, yourself included, already know this. Of course technique is a huge factor. But you'd have to be living under a rock to not see the overwhelming correlation btwn stiff frames, stiff strings and arm issues. When a player falls in love with a particular stiff frame or string, they might engage in something like wishful thinking, or willful negligence. Alternately a player might look the obvious health risk square in the face, acknowledge it, and decide that they will go ahead and try this stiff string+ stiff racquet combo, and will see if it works for them, see first hand if it causes injury or pain. The player might be thinking if it does cause pain, then they will deal with that in one way or another: IE lower tension, change strings, change frame, use ice and advil, stop playing for a while, do physical therapy, lay off tennis for a while etc.
Point 2. What most players don't consider, is three things:
2A - Just how difficult it can be to recover
from elbow, wrist or shoulder problems once they occur. You might be in for a battle, the length of which you didn't sign up for. Often these issues take months or years to resolve.
2B - That 100% recovery from injury is never guaranteed.
One might be thinking, "If this string or racquet causes me pain, I will just stop using it". That's a good place to start, but understand that previous injuries leave you vulnerable to future injuries, and you might not ever get back to pre-injury health.
2C - That pain is a often lagging indicator that there is physical injury. I know this sounds counter-intuitive, let me expand on that.
There's two classifications of sports injuries, chronic and acute. Often, the athlete has no idea which is occurring, just knows that something hurts. With acute injuries such as, you miss the nail altogether, and hit your thumb with the hammer, it's easy to see a connection, to connect the dots.
2C - With overuse injuries, chronic conditions
that last, and evolve over the course of weeks or months, the pain is not immediate. Often the pain is a lagging indicator of tissue damage. Tissue is being stressed into building itself back back, is being stressed into repair mode, but is somehow failing at the task. by the time you feel pain, often the underlying damage has been done. There is now real tissue damage to the arm, elbow or shoulder in the same way that there is real damage in the thumb hit by the hammer, it's just that the cause isn't as clear, and the pain might show up long after the damage has occured.
Quote: " In most cases, it is easy to classify an injury as acute or overuse, but in some cases it may be less obvious. This is particularly true when the symptoms have a sudden onset, although the injury may actually be the result of a long-term process. For example, an athlete with a stress fracture in the foot will often report that the symptoms originated during a specific run, perhaps even from a specific step. This means that the injury could be classified as an acute injury. Nevertheless, the actual cause of the stress fracture is overuse over time. These types of injuries should be classified as overuse injuries. As illustrated in fig 2, the pathological process is often under way for a period of time before the athlete notices the symptoms. It is believed that repetitive low-grade forces exceeding the tolerance of the tissues cause overuse injuries. In most cases, the tissue will repair without demonstrable clinical symptoms. However, if this process continues, the ability of the tissue to repair and adapt can be exceeded, resulting in a clinical overuse injury with symptoms."
- Professor R Bahr, Oslo Sports Trauma Research Center
Published in the British Journal Of Sports Medicine, October 2009
Also Illustrates the same point, additional source:
Point 3. Kevlar (even as a hybrid) is off the charts stiff
. Gut is the softest, and most arm safe. Then there is nylon, which is the major material for the construction method we casually call "multi". Then there is Poly. Then there is a long walk to the outfield, over the fence, out of the stadium, and down the street. That's where you will find where Kevlar lives in the measure of arm safety. It is 2-3 times stiffer than the stiffest poly. See below. The full table is found at the USRSA, and in the freely available non-member section.
3A - Kevlar And Ball "Pocketing"
. I'll never argue against what somebody says they feel on the court, but as a former user of Kevlar myself, and observer of all things geeky, the idea that Kevlar offers "ball pocketing" is a puzzler to me. Just consider how dynamic stiffness is measured. The string is impacted in a way designed to simulate the impact of a 120 per hour serve. The sideways and lengthwise distance of string movement is measured, as well as the tension changes before, during and after impact. Stiffer strings deflect less, softer strings deform more.