To the naked eye, professional athletes appear to display repeatable and consistent movements, yet variability in movement is an inherent feature of successful performance.
The key question then becomes – what is good variability and what is bad variability?
The Uncontrolled Manifold Hypothesis
The uncontrolled manifold hypothesis offers a statistical method to measure movement variability when performing an action, such as throwing a ball. Importantly, it offers a way to measure whether movement variability is “good” or if variability is “bad”.
However, this statistical technique is not practical for many applied environments. For instance, this measure can only be used when the action is performed from the same location (i.e., the same start and same end location) every time. This is often not feasible when working with athletes (although it is possible to analyse some sports actions with this technique, such as the golf swing or running on a treadmill).
Nonetheless, its use in controlled ‘lab’ environments has advanced theory and, consequently, has helped us further understand movement variability.
Think of a Roger Federer forehand. More specifically, think of his hitting arm as he is swinging the racket towards the ball. His remarkable timing – which is extremely consistent – is the product of his wrist, elbow and shoulder joints (amongst the rest of his body) working in unison.
In other words, variability in the shoulder joint is counteracted by variability in the elbow and wrist joints, and vice versa. This coupling of joints – which produces (good) variability in movements – allows precision in execution. It also allows the body to adapt to different scenarios, which is also a hallmark of skilful performers.
Think of anyone first learning to throw a ball. They will probably look uncoordinated, meaning the body’s segments are not working together – certainly not fluently. This is bad variability!
Implications for coaching?
Obviously the aim in coaching is to promote good variability. Studies examining the effect of practice on developing good variability in sport skills are scarce. Nonetheless, there appears to be at least two strategies that might be effective:
- Encourage exploration of technique (as opposed to being overly prescriptive), which can be facilitated by promoting variability in practice. This also applies when an athlete is aiming to change their technique.
- Use appropriately sized equipment (more relevant in children’s sport)
Scholz, J. P., & Schöner, G. (1999). The uncontrolled manifold concept: identifying control variables for a functional task. Experimental brain research, 126(3), 289-306.
Wu, Y. H., & Latash, M. L. (2014). The effects of practice on coordination. Exercise and sport sciences reviews, 42(1), 37.