https://bleacherreport.com/articles...or-non-contact-injuries-occur-in-nfl-workouts
How and Why Non-Contact Injuries Occur in NFL Workouts
DAVE SIEBERT, M.D.
How do these types of injuries occur, and why do they occur? To come up with an answer, let's use some anatomy and a bit of physics to analyze two of the most serious kinds of non-contact injuries: The ACL tear and the Achilles tendon rupture.
Soft-tissue injuries occur when the ligament or tendon in question stretches beyond a critical point, beyond which damage, tearing or rupture occurs. A number of factors determine that critical point, such as flexibility and tensile strength.
Movements that cause injury are tissue-specific. For example, ACL injuries occur when something forces the knee to twist down and inward—one of the types of motion it tries to prevent.
To create the sensation of the ACL limiting such internal rotation, stand with both feet planted on the ground with both sets of toes pointed forward. Then, bring one knee inward and slightly down—toward the body's midline. It can only move so far, largely due to the ACL.
In the case of direct contact ACL injuries, a blow to the outside of the knee is frequently to blame. On the other hand, non-contact ACL injuries often come as a result of a perfect storm of positioning, momentum and direction change. Often, subtle contact elsewhere on the body also plays a significant role.
That said, the relative roles of anatomical and biomechanical factors leading to non-contact ACL tears remains a subject of research. However, some basic anatomical knowledge provides insight into the underlying mechanisms of two recent examples of minimal-to-no contact ACL tears in the NFL.
The GIF below—courtesy of Fox Sports via AOL's
Sporting News—makes it clear Sam Bradford's knee did not receive significant contact.
As shown, a slight nudge to Bradford's side—while he simultaneously turned to his left at least partly on his own accord—created a mismatch between his momentum and the direction his knee faced relative to where his toes pointed. As a result, his knee collapsed inward without direct contact—a moment that becomes painfully clear with the following screenshot.
Immediately after the above moment, Bradford dropped the football seemingly suddenly—possibly a reaction to the onset of extreme knee pain.
In addition to preventing internal over-rotation of the knee, the ACL also keeps the lower leg from moving forward with respect to the thigh.
Knee hyperextensions—or over-straightening, leading to a bending of the leg in the opposite direction—can cause the lower leg to shift forward with respect to the thigh. If it does so suddenly and sharply enough, the ACL may not be able to keep up.
A number of scenarios—such as landing from a leap onto a forcefully straightened leg—can result in a knee hypertension and ACL injury. Hyperextensions can also damage other knee ligaments.
Elsewhere, sudden stops, plants and cuts may injure the ACL if the momentum and direction imbalance mentioned in the previous section results. For example, running forward and planting the right foot—with the toes pointed to the right—before attempting to cut to the left can cause the injury.
Despite the relative safety of non-contact OTAs, injuries remain a threat. Relative deconditioning may play a role in some, while a combination of unfortunate positioning and bad luck reigns supreme in others. Regardless, whenever a motion, plant or cut stretches tissue beyond its capacity, a sprain or strain becomes a possibility.