OBJECTIVE To evaluate the muscle response in order to determine the mechanism of neuromuscular adaptations with Forsus Fatigue Resistant Device which has greater elasticity and flexibility; allows greater range of movement of mandible; is available in prefabricated assembly of springs, tubes and rods and is a simple, effective and reliable corrective appliance that benefits not only growing patients but also malocclusions that previously required extractions, headgears and surgery. METHODS Bilateral EMG activity from anterior temporalis and masseter muscles was monitored longitudinally on 10 young growing females with Class II Division 1 malocclusion to determine changes in postural, swallowing, and maximal voluntary clenching over an observation period of 6 months. RESULTS There was a significant decrease in the muscle activity at one month after Forsus Fatigue Resistant Device insertion during swallowing of saliva and maximal voluntary clenching which gradually returned to pre treatment levels at the end of six months. CONCLUSIONS This study suggests that Forsus Fatigue Resistant Device should be given for at least six months to allow for adequate neuromuscular adaptations to occur for long-term stability of the result.