Researchers recommended that NeuroMuscularControl (NMC) training should not begin immediately after an acute Lateral Ankle Sprain(LAS) because of pain and weight-bearing restrictions. So, there is a need for an alternative way by which we can begin NMC retraining sooner. By training the non-affected ankle (Cross education), clinicians can begin NMC retraining before the individuals can bear weight on the affected ankle, in the acute stage of healing, or even if there is any other precautions or contraindications to exercise due to the injuries. Athletes with more chronic injuries may be able to perform NMC and functional retraining at higher levels than otherwise would be possible by initiating the training on the non affected ankle. Initiating these activities on the non-affected ankle will result in earlier improvements in postural control and function in the affected ankle.

By this way, the rehabilitation times will be short, athletes can return earlier to sport participation or work, health care costs will decrease. Up to the knowledge of the author, there is a gap in research investigating cross education effect of balance program in patients with ankle instability. So, the current study was conducted to reveal the role of this phenomena in such cases and add this phenomenon on the physical therapy field to manage patients with ankle instability (If Cross Education phenomena is effective, this phenomena will be used in rehabilitation).

Thirty five females with Chronic Ankle Instability will be recruited from the Faculty of Physical Therapy, Cairo University by announcements to participate in this study. They will be randomly assigned into three groups; (A) Cross Education (balance training for the non affected side )(n=10), (B) Traditional training(balance training for the affected side) (n=10), (C) control group (no intervention) (n=15). stability indices measured by the Biodex Balance system , Single Leg Stance Test and scores of Star Excursion Balance Test will be assesssed before and after six weeks of Single Leg Balance training.

Inclusion Criteria:

• At least 1 ankle sprain, with the initial sprain occurring more than 1 year before the study
• A feeling of ''giving way'' (at least 2 episodes in the 6 months before the study).
• At least two ''yes'' answers on questions four to eight on the Modified Ankle Instability Instrument (MAII)

Exclusion Criteria:

1. - A history of previous surgeries or fractures in either limb of the lower extremities.
2. - Acute injury to musculoskeletal structures of other joints of the lower extremity in the previous three months, which impacted joint integrity and function (ie, sprains, fractures) resulting in at least one interrupted day of desired physical activity.
3. - Balance deficits due to vestibular disorders, such as vertebrabasilar insufficiency and/or visual disorders.
4. - Neuropathies and diabetes