According to the jokela and hanin (1999) izof meta-analysis, athletes who were within their individually optimal state anxiety zones performed almost of a standard deviation unit better than athletes who were outside their optimal zones.

They performed 1/2  of a standard deviation unit better than athletes who were outside their optimal zones.
The study was being done in order to find the correlation between anxiety and performances in athlete. Due to strong correlation between the two, almost all olympic teams today always accompanied with personal psychologist to give them with psychological assistance.

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Recordings of musical performances