The Effects of Either a Mirror, Internal or External Focus of Attention Instructions on Single and Multi-Joint Tasks

Background. A substantial amount of research indicates that instructing participants to focus on bodily movements (internal focus, IF) hinders performance, whereas instructing them to focus on the movement outcome (external focus, EF) improves performance. However, despite the popularity of training in front of mirrors, it is unclear how mirrors influence performance.

Methods. Experiment 1 compared IF, EF, neutral and neutral-mirror instructions on maximal voluntary contractions (MVC) and EMG activity of the biceps and triceps of 28 resistance-trained participants (14 males). Participants completed two MVCs in each condition, two minutes apart. In Experiment 2 the same participants repeated similar testing procedures as in Experiment 1, but performed counter-movement jumps on a force plate.

Results. Experiment 1: EF led to greater normalized force production compared to all instructions (P≤0.02, effect-size [ES]=0.46-1.31). No differences were found between neutral and neutral-mirror (P=0.15, ES=0.15), but both were greater than IF (P<0.01, ES=0.79-1.84). EMG activity was comparable across conditions (P≥0.1, ES=0.10-0.21). Experiment 2: Despite not reaching statistical significance (P=0.10), results followed a similar pattern to Experiment 1 wherein greater jump heights were detected with EF compared to IF (ES=0.51). No differences were observed between neutral and neutral-mirror conditions (ES=0.01), but both were greater than IF (ES=0.20-22).

Discussion. Performing in front of a mirror has a neutral effect on performance during both isometric single-joint and dynamic multi-joint tasks. The mirror condition led to superior performance compared to IF, inferior performance compared to EF, and was equal to neutral conditions.