Mind-muscle connection: does thinking about the muscle make it grow larger?

Does thinking about the working muscle make it grow? A little, perhaps. Focusing on a muscle increases its electrical activity at a moderate load, and the only study lasting several weeks made the biceps thicken almost twice as much. But to lift heavier or perform more reps, it is better to think about moving the load. Here is what twenty studies measure.

Two ways to focus

Researchers contrast two instructions. An internal focus, is the "mind-muscle connection" of gyms: thinking about contracting the targeted muscle. An external focus, is thinking about the result of the movement: pushing the bar, pushing the floor away. This is the definition used by the only long-term trial on the matter, and most subsequent studies compare these two instructions to a set done without any particular instruction.

Thinking about the muscle activates it more, up to a point

In 18 trained men, focusing on the chest or triceps during the bench press increased the electrical activity of the target muscle between 20 and 60% of the maximum load, but not at 80%. The gain did not come at the expense of the other muscle: thinking about the triceps even increased chest activity at 50 and 60%. The authors place a threshold between 60 and 80% of the maximum load.

The threshold is not absolute. In 13 trained men, the instruction to isolate the triceps on the bench press increased its activity at 50% and also at 80% of the maximum load; the instruction to isolate the chest, on the other hand, changed nothing. During push-ups, in 18 trained men, thinking about the chest increased their activity by 9 points (as a percentage of their maximum activity); for the triceps, nothing on average, and the ability to activate it at will increased with years of training.

Beginners are not left out. In 31 untrained individuals, on the machine shoulder press, thinking about the deltoid increased deltoid activity, thinking about the triceps increased triceps activity, and the trapezius did not move. The instruction therefore hit the mark, without spilling over onto a neighboring muscle. In 17 experienced men who were contracting the biceps and triceps at the same time, thinking about flexing or extending the elbow also modified biceps activity.

Where the effect fades out

In 18 young men, thinking about the chest or triceps increased chest activity by 6% and 4% on the bench press performed at a controlled speed. When pushing explosively, no effect remains. Yet pushing fast has its own advantages for strength, as shown in the article lifting slowly or fast.

The effect also disappears with fatigue. On the seated row, in 20 moderately experienced practitioners who went to muscular failure, the instruction to contract the back increased latissimus dorsi activity by 15% and reduced rear shoulder activity by 14% on the first reps. In the middle of the training set, the effect faded; on the last reps, the ones that matter most, it had disappeared.

And it is not always found. In 13 volunteers, successive bench press sessions with a focus on the chest changed neither their activity, nor that of the triceps, nor perceived effort, compared to a session without instructions. In 21 trained men, both internal focus and external focus increased the activity of six upper body muscles compared to a set without instruction: it is perhaps having an instruction, rather than its content, that matters.

At the squat, the instruction shifts the work rather than increasing it. In 15 trained men, internal focus increased glute and hamstring activity on the ascent, but reduced that of the vastus lateralis, a muscle at the front of the thigh, at both 50 and 80% of the maximum load.

Over eight weeks: a thicker biceps

A single study followed practitioners long enough to measure the muscle. Thirty untrained men did the same weight training for 8 weeks (3 sessions per week, 4 sets of 8 to 12 reps), some thinking about the muscle, others about the result of the movement. The thickness of the elbow flexor muscles increased by 12.4% with internal focus versus 6.9% with external focus. For the thighs, no difference.

In terms of strength, nothing significant: elbow strength leaned toward the internal focus side, knee strength toward the external focus side. This is a single trial, on beginners: it supports the idea that thinking about the muscle helps it grow, without proving it.

To lift heavy: think about the load

On strength, studies lean in the other direction. A 2021 meta-analysis of 10 studies finds that external focus increases strength on the spot (effect size of 0.34, small but clear). Long-term, no overall difference between the two focuses; on lower body exercises alone, the advantage goes to external focus (0.47).

In 18 trained athletes, during the mid-thigh isometric pull (pulling with all their might on a locked bar), external focus yielded 9% more strength than internal focus. And a set with no instruction at all already yielded 5% more than internal focus.

Same thing for the repetitions. Another 2021 meta-analysis finds that the external focus makes you last longer than the internal focus (effect size of 0.58) and than a set without instruction (0.42), for both upper and lower body; the internal focus does no better than the absence of instruction. In 17 experienced practitioners, during the bench press and squat at 75% of the maximal load, the external focus resulted in more repetitions to muscular failure than the other two conditions. A 2019 review on the bench press, curl, squat, and leg extension also concludes on a more economical and higher performing movement with the external focus.

What about imagining the movement while doing it?

In 100 national-level CrossFit athletes, 5 weeks of squatting (3 sessions per week) while mentally representing the movement during its execution improved the 5-repetition load and power more than the same training without imagery. Imagining the descent performed better than imagining the ascent for the load, at the cost of a higher perceived effort. This is one trial, on confirmed athletes.

In summary

In practice, the mind-muscle connection has its place on moderate isolation sets, and focusing on the load on heavy sets. To build a workout that mixes both, the workout generator suggests exercises, and the 1RM calculator tells you what percentage of your maximum you are working with. To know how far to push each set, the article sets, repetitions, or time under tension reviews the matter.

Every figure in this article comes from a study you can open: the underlined mentions lead to the summary of the work it is taken from, written solely from the abstract. The trials are small and mostly involve young men. Informational content, which does not replace the advice of a healthcare professional.