There are times when we as movement assessors are asked why we rate something as dysfunctional.
We always have a criteria. Even the vaguest criteria has been used, such as..."I'm not quite sure what I don't like about it, but there's something about it I don't like."
That "something" can be qualified. It's loss of motor control or excessive effort. The assumption is we can define what good motor control looks like. We can. Come to any SFMA course and you'll learn that quickly. Come to my own course and you'll learn that quickly.
Within the "loss of motor control or excessive effort" criteria for rating movement as dysfunctional is a concept well known in motor learning research called the "performance bandwidth" (Schmidt and Lee, 1999).
A movement that has a mistake deemed undesirable or unacceptable is one that
Look at this still of a hit, (link to the video can be seen here (Warning – the athlete lands awkwardly and suffers a knee injury) you’ll notice the angle of the trunk and shoulder— lateral flexion of the trunk away from the ball. We can hypothesize why this is the case, or I can tell you why. This athlete had a coexisting left shoulder pain, affecting shoulder elevation range of motion. If shoulder abduction and external rotation is painful, laterally flexing the trunk is the only option to get away from pain and still reach the height of the ball. Inevitably the center of mass moves so far laterally, and a double-leg landing is impossible.
From my article on bulletproofing the volleyball shoulder, “pain in the shoulder can lead to problems moving through the trunk, which can lead to pain in the low back, which can predict injury as far away as the knee (Zazulak et al, 2007a, 2007b). It’s no wonder the top three injuries in volleyball are the shoulder, back and knee.”
Whilst hitting an overhead volleyball at abduction angles is within the performance bandwidth, an athlete who uses abduction angles because of pain and a strategy to get away from full elevation is moving with a mistake, brought on by pain, mobility restrictions or motor control deficits. The keen-eyed professional recognizes this and aims to break the mistaken pattern, particularly if it increases the risk of injury. In the case of less-than-full-elevation, it isn’t a mistake for success of the hit, or efficiency, but could be an increased risk of injury.
The keen eye of the professional uses the process of training movement to look for mistakes that are outside the realm of acceptable. This should be a “performance bandwidth” based on performance parameters of population and task specificity (where they exist) or safety ranges.
The presence of pain or mobility restrictions is evaluated and addressed.
Where these don’t exist, moving with a mistake requires reactive neuromuscular training, or creating a task where the mistake can’t happen. The simplest way to envisage how RNT works is to note the mistake, then exaggerate it/feed it. That is the meat and potatoes of the Mobility, Stability and Motor Control for Rehabilitation, Exercise and Sports Performance 2-Day Course.
Zazulak, B.T., et al., Deficits in neuromuscular control of the trunk predict knee injury risk: a prospective biomechanical-epidemiologic study. Am J Sports Med, 2007. 35(7): p. 1123-30.
Zazulak, B.T., et al., The effects of core proprioception on knee injury: a prospective biomechanical-epidemiological study. Am J Sports Med, 2007. 35(3): p. 368-73.
Schmidt RA, Lee TD. Motor control and learning : a behavioral emphasis. 3rd ed. Champaign, IL: Human Kinetics; 1999. xvi, 495 p. p.