External focus instruction using a soft paper balloon on muscle activation patterns in isometric hip abduction...

This study investigates a novel isometric method utilizing an external focus instruction technique with a soft paper balloon. By emphasizing control to avoid crushing the balloon, this method promotes co-contraction of muscles without exerting pressure on the object. We aim to evaluate differences in muscle activation patterns during isometric hip abduction exercises between the paper balloon task and tasks using external resistance (hard plastic, non-elastic, and elastic bands), and further determine their influence on the contralateral side.

Thirteen healthy adult males aged 20-28 years were recruited. Six trunk muscles (transversus abdominis [TrA], internal oblique [IO], external oblique, rectus abdominis, multifidus [MF], and lumbar erector spinae) and five lower-extremity muscles (gluteus maximus [GMax], gluteus medius [GMed], adductor longus, rectus femoris [RF], and biceps femoris [BF]) were measured using surface and fine-wire electrodes to compare the different isometric hip abduction exercises.

The muscle activity did not differ between the abduction sides except for GMax and GMed with the elastic band and RF and BF with the hard plastic (p > 0.05).

The trunk muscles (TrA, IO, and MF) were similarly activated with the paper balloon and external loading tasks; however, the paper balloon task activated trunk muscles without bearing weight, potentially avoiding pressure on the spine, knee, or hip joints. Moreover, all tasks showed muscle activation on the opposite side of the body.