The Effects of Either a Mirror, Internal or External Focus Instructions on Single and Multi-Joint Tasks
Halperin I, Hughes S, Panchuk D, Abbiss C, Chapman DW
Evidence is still building up
Summary
In a crossover trial with 28 resistance-trained adults, elbow flexion maximal voluntary contractions (single-joint) and countermovement jumps (multi-joint) were compared across four conditions: mirror, internal focus (on arm muscles), external focus (on pulling a strap), and neutral. For the single-joint task, external focus produced the greatest force output; the mirror condition was statistically equivalent to neutral and significantly higher than internal focus. Surface EMG showed no significant differences across the four conditions, indicating that looking in a mirror did not itself increase muscle activation.
Key findings
- 1
In the single-joint task (elbow flexion MVIC), external focus produced the greatest force output (significantly higher than mirror, P=0.017, and internal focus, P<0.001)
- 2
The mirror condition was statistically equivalent to neutral (P=0.392 for single-joint force; ES=0.01 for multi-joint jump height) but significantly higher than internal focus (P<0.001)
- 3
Surface EMG (biceps brachii, triceps brachii, co-contraction ratio) showed no significant differences across the four conditions (P≥0.588) — looking in a mirror did not itself change muscle activation
- 4
This was a single-session crossover design without full randomization of condition order or extensive familiarization; it measured acute force output and EMG, not long-term training adaptations, so extrapolation to chronic training effects should be cautious
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