This study analyzed the influence of competition stress on the psycho-physiological state of a group of swimmers. The CSAI-2 inventory was used and a spectral analysis was conducted to relate precompetitive state anxiety with heart rate variability (HRV). Results showed that with a higher level of pre-competitive anxiety, HFms2 and HF nu. parameters related with parasympathetic activity decreased significantly (p < 0.05), whereas LF/HF% parameters related with sympathetic activity significantly increased (p < 0.01). Performance was significantly enhanced under these conditions (p < 0.05). An HRV analysis can be used as a quick, non-invasive technique to assess objectively competitive stress and its related performance. The determination of the profile of each individual's psycho-physiological state is proposed in terms of the IZOF model (Hanin, 2003).