Mental overload: can it harm your quality of movement?

The indivisibility of mind and body has long been understood, and so it’s hardly surprising that the mind can and does have a big impact on physical performance. In a number of previous SPB articles, we have explored evidence showing that the brain is the master controller of the fatigue your muscles experience when performing exhaustive exercise. We’ve also seen how certain types of music can enhance performance and lower perceived effort levels^(1,2), and even how different expectations of an exercise session can impact how much effort can be sustained⁽³⁾.

Mental demand and sports performance

Given the powerful link connecting brain to exercise performance, it would be incredible if mental and psychological demands experienced by athletes didn’t affect performance, and this indeed is what we find. In a recent SPB article, Andrew Sheaff highlighted a recent review of all the research investigating whether performing resistance training while mentally fatigued would result in worse performance compared to performing exactly the same resistance training without prior mental fatigue⁽⁴⁾. As Andrew explains, the results were very clear: the inclusion of mentally fatiguing activities prior to intense resistance exercise significantly reduced the number of repetitions subjects were able to achieve during a set. Indeed, the presence of mental fatigue, even in the absence of physical fatigue, negatively impacted performance.

In the study above, the impact of pre-existing mental fatigue on exercise was assessed. But what about the impact of mental demands during exercise itself – so-called ‘dual tasking’? The research on this topic is fairly unambiguous: adding extraneous cognitive loading (ie mental demands) during a motor task will typically lead to worse performance, as compared to normal or single-task conditions⁽⁵⁾. Good examples of this include:

·        Worse performance in soccer players who try to solve arithmetic problems while juggling a ball⁽⁶⁾.

·        Poorer time trial performance in cyclists asked to monitor multiple forms of feedback⁽⁷⁾.

·        Reduced accuracy, balance and smoothness when performing exercise requiring good motor coordination^(8-10).

Coping mechanisms

How is it that performing mental tasks or being mentally fatigued while exercising affects physical performance? The most likely explanation stems from the fact that each of us has a limited capacity to attend to task-relevant stimuli. That explains why becoming mentally distracted – eg having an argument with your spouse while driving along the highway - is not recommended for safety! Even if your eyes never leave the road, the cognitive processing that results due to a mental distraction takes away from the processing required to execute the action of driving in the safest possible manner.

When extra cognitive demands do occur, research shows that humans adapt to that extra load by trying to free up attentional resources through alterations of behaviour. A very common way of accomplishing this is to reduce the quantity or complexity of ongoing motor execution⁽¹¹⁾. This effect is illustrated by the finding that healthy individuals walk with shorter stride lengths in dual-task conditions (ie when performing mental tasks), as compared to a single-task condition (ie just walking with no mental demands)⁽¹²⁾.

Regression of movement patterns

Interestingly, this method of coping fits with the ‘progression-regression hypothesis’, where under adverse conditions, people tend to regress in their movement patterns in order to cope. To illustrate what this means, let’s take walking as an example. After years of progression and learning how to walk, our gait is typically characterized by long and confident strides. However, when we are stressed by increased cognitive demands, we tend to regress towards previously learnt patterns that involve less sophisticated movement patterns. In the case of walking, this means that we revert to the relatively short and less fluid steps that are typical of children learning how to walk (or an adult re-learning to walk after suffering from a stroke)⁽¹³⁾.

Interestingly, anxiety-inducing stimuli ,which also divert attentional resources away from motor tasks (thus affecting movement patterns), can produce a similar effect. In golf for example, research shows that when players are in presence of an audience or facing the pressure of missing out on prize money and status rewards, movement patterns can regress to those seen in less experienced golfers. In this case, the regression is evidenced by shorter backswings or reduced follow-through) when putting^(14,15).

Tighter coupling

Regression is one way of reducing movement complexity when facing cognitive demands, but another is via a phenomenon known as ‘tight coupling’. In tight-coupling, movements in different limbs tend to take place simultaneously, which reduces movement complexity⁽¹⁶⁾. Because tightly coupled movements are less complex and easier to learn, it’s a common observation that when athletes take up a sport and develop specific sports skills, the movement patterns tend to start in a tightly coupled manner and become progressively uncoupled as the skill level increases.

Taking rowing as an example, the ideal (uncoupled) rowing action sequence usually progresses from proximal (near the body center) to distal (away from the body center) areas. This allows the larger muscles (the glutes, and the quadriceps) near the body center to initiate the rowing action, resulting in effective power development⁽¹⁷⁾. However, novice rowers typically employ a more tightly coupled movement, extending their legs and pulling the oar at the same time (until the stoke technique is mastered). Following skill practice, athletes in general typically progress from tight coupling to a more uncoupled action, which allows more nuanced and sports-specific movement.

Figure 1: Ideal rowing technique