Historically, many bodybuilders championed the importance of implementing a “mind-muscle connection” during strength training.
Using a mind-muscle connection refers to focusing our attention on the muscle that is working during a set of strength training exercise.
While this may not seem like an obvious area for researchers to investigate, the effects of where we focus our attention during physical activities has been of great interest to scientists. This wider literature, as well as some recent studies into attentional focus during strength training, allows us to assess whether using the mind-muscle connection could help or hinder us on our quest to achieve greater muscle growth.
What is attentional focus?
Two key types of attentional focus have been identified: (1) internal, and (2) external.
An external focus of attention involves thinking about the environment, such as the weight or the ground. An internal focus of attention involves thinking about the body, such as the contraction of the working muscle or the movement of the limbs around a joint.
Researchers have found that when individual employs an external focus of attention during a physical movement, this allows them to achieve greater maximum force production, greater performance on tests of athletic ability, and more reps in tests of muscular endurance. These benefits all likely occur due to greater movement efficiency.
Consequently, it is hardly surprising that using an external focus of attention has also been associated with superior gains in motor learning over a long-term training period.
In contrast, researchers have found that using an internal focus of attention leads to greater muscle activation (as measured by surface electromyography) in conjunction with reduced joint torques measured by a dynamometer. This finding also been reported when researchers have examined the mind-muscle connection during conventional strength training, at least when using lighter loads and when the subjects have some strength training experience.
Even so, using the mind-muscle connection to produce an internal focus of attention has been associated with superior gains in muscle size over a long-term training period. Researchers have generally explained this finding by reference to the greater activation of the working (agonist) muscles that is usually observed during reps done with an internal focus, compared to with an external focus.
How could an internal focus of attention enhance muscle activation?
During strength training, muscle activation is affected mainly by the level of motor unit recruitment, although it can also be influenced by the motor unit firing frequency, as well as other factors. When muscle activation is higher, this indicates that more motor units may have been recruited to carry out the task. Additional motor units are recruited when the central nervous system identifies that the existing levels of force production are insufficient to carry out the movement as intended.
More motor units are recruited in any of three scenarios: (1) load increases, and therefore the requirement for external force production increases, (2) movement speed increases, and therefore the force produced by each muscle fiber decreases, and (3) fatigue occurs, and therefore the force produced by each muscle fiber decreases.
Given that an external focus of attention often involves superior performance in athletic movements, it is unlikely that an internal focus of attention would cause greater agonist muscle activation than an external focus of attention due to increased movement speed. Consequently, in unfatigued conditions, it is likely that an internal focus leads to increased motor unit recruitment due to a need to produce a larger agonist muscle force at the same (or perhaps even at a slower) movement speed.
Exactly *why* there is a need to produce a greater agonist muscle force when using an internal focus of attention is rarely discussed.
Some possible explanations for the increased agonist muscle force include: (1) an increased antagonist muscle force, (2) altered synergist muscle force, and (3) the activation of regions of the agonist muscle that are less effective for the movement being performed.
An increase in antagonist muscle force will necessarily require the agonist to produce more force in order to achieve the same joint torque, since the joint torque is the net effect of the agonist muscle less the antagonist muscle forces. Alterations in synergist muscle force (due to impaired coordination) will also require the agonist muscle to exert more force in order to achieve the same joint torque, since the synergists contribute positively to joint torque, usually by making the joint more stable. Activating regions of the muscle that are not normally activated to perform the specific exercise would be very inefficient. In such cases, these regions might simply contract in isolation, while not contributing to force production at the joint in any meaningful way.
Ultimately, since it is probably not possible to alter the amount of motor unit synchronization, the greater agonist muscle activation for the same amount of external force or joint torque must arise due to one of these factors.
How could an internal focus of attention enhance muscle growth?
Although an internal focus of attention does increase muscle activation, and it is likely that this leads to increased agonist muscle force in a given exercise for the same amount of external force or joint torque, how might this translate into increased muscle growth?
The answer may depend on the mechanism by which muscle activation is increased with an internal focus of attention.
#1. Increased antagonist muscle activation
However, hypertrophy only occurs when the muscle fibers of high-threshold motor units shorten at slow speeds (and therefore produce high forces and experience high levels of mechanical loading). The circumstances that lead to force being exerted by those muscle fibers are largely irrelevant.
In other words, it should not matter whether those muscle fibers produce force in response to an external load, or to antagonist muscle activation. Indeed, this is why we can produce high levels of muscle activation (and subsequently also hypertrophy) by simply flexing muscles.
Consequently, it seems unlikely that differences in the level of antagonist muscle activation between an internal and an external focus of attention could be responsible for the greater hypertrophy that occurs when using an internal focus of attention.
#2. Altered synergist muscle activation
Similarly, it should not matter whether the muscle fibers controlled by high-threshold motor units produce greater force in response to altered synergist activation or increased antagonist muscle activation.
This is why training using unstable (free weights) and stable (machine) implements generally involve similar levels of agonist muscle activation and probably also cause similar amounts of muscle growth, when using similar exercises. Even though the unstable conditions require much greater contributions from the synergist muscles in order to stabilize the joint, the resulting hypertrophy is not that different.
#3. Regional muscle activation
Muscle growth does not occur evenly in all parts of a muscle after strength training, but rather occurs in specific regions. This likely occurs for at least two very different reasons.
Firstly, it happens when muscle fibers increase in either length or diameter, since increases in length tend to lead to greater increases in distal muscle size, while increases in fiber diameter tend to cause greater hypertrophy in the proximal and middle regions of a muscle.
Secondly, it happens when specific functional regions of the muscle are activated in order to perform certain movement. This can involve force production at specific muscle lengths, or in different directions at a joint. Researchers have found that these regions are controlled differently by the central nervous system in much the same way as different muscles are themselves controlled.
When we perform a movement with an external focus of attention, we likely only produce force with those regions that are optimally structured to contribute to that movement. In contrast, when we perform a movement with an internal focus of attention, we may well produce force with additional regions as well, and these regions may not contribute particularly effectively to the movement. This would cause greater overall muscle activation without substantially increasing the external force or joint torque (which is what we observe) and could also lead to greater overall hypertrophy, because of muscle growth in additional regions of the muscle that are not trained when using an external focus of attention.
What does this mean in practice?
In practice, the use of an internal focus may be helpful for some groups of lifters who are training for hypertrophy, but not others.
Complete beginners may find that using an internal focus of attention is helpful during certain exercises, to make sure that they are using the exercise effectively to train the target muscle. Indeed, researchers have found that asking people to focus on certain muscle groups does allow them to activate those muscle groups
Intermediate lifters may find that using an internal focus of attention can interfere with progressive overload. Unlike complete beginners, intermediates cannot always easily increase the number of reps in each set or the weight on the bar from one workout to the next. And yet, achieving progressive overload is essential for hypertrophy to continue over a long period of time. Since using an internal focus of attention leads to fewer reps being performed on a set, it can be tempting to temporarily stop using the internal focus of attention towards the end of a set purely in order to achieve the target number of reps for a set for the day. This can lead to the appearance of progressive overload being achieved, without actually achieving it.
Advanced lifters who are able to employ exactly the same focus of attention on every rep of every set may find that they can use an internal focus of attention effectively, but this may take a lot of time and practice.
What is the takeaway?
The mind-muscle connection is an internal focus of attention, which involves directing our attention to the working muscle during strength training. An internal focus of attention likely increases muscle force for the same level of external force or joint turning force due to either increased antagonist muscle force, altered synergist muscle forces, or the activation of additional regions of the agonist muscle that would normally not be used for that particular movement. However, it is most likely that only the activation of additional regions of the agonist muscle contributes to the greater hypertrophy that is observed when training using an internal focus of attention.