INTRODUCTION: The assessment of the respiratory frequency (fR) has practical importance in monitoring training progress in competitive athletes, especially during exercise. This study aimed to validate a new wearable chest-strap (wCS) device to measure fR against ergospirometry as a criterion device in healthy adults. The gold standard for performance evaluation remains the cardiopulmonary exercise test. However, it remains a test that cannot be applied in daily training practice METHODS: A total of 26 elite professional soccer players (23.6±4.8 years; 180,6±5.7 cm; 77.2±5.4 kg) from three Italian Serie A League teams participated in this cross-sectional study. The sample included attackers, midfielders, and defenders. All participants were free of injuries at the time of testing. Participants were equipped with a heart rate sensor (Polar H10, Polar, Kempele, Finland); they wore a face breathing mask connected with a fast-responding gas analyzer (Vyntus Vyaire medical, Chicago, ILL, USA). In addition, they wore a wCS equipped with sensors to read HR and RF and with the newly designed device that tests breath frequency and heart rate, i.e., a belt strap (similar to Polar or Garmin) made of elastic and inelastic materials, and with two internal electrodes, to check the heart rate and with a strain gauge sensor, only with resistive functions, that is used to record the breathing act; it is mechanically and electrically connected, through four snap contacts to a device; hardware cyclically reads the analogic signals created by the internal sensors of the belt and transmit them, after an appropriate collecting filtering to a remote station. The subject underwent an incremental symptom-limited exercise test wearing gas analyzer and chest band simultaneously RESULTS: A total of 16529 comparisons were performed after collecting data in the maximal incremental exercise test. No significant differences were found for both methods (P<0.05). Correlation among devices was statistically significant and very large (r [95% CI]: 0.970 [0.970, 0.971], P<0.01; aR2 [95% CI]: 0.942 [0.942, 0.943], P<0.01). Similarly, a high concordance was found (*c [95% CI]: 0.970 [0.969, 0.971], bias correction factor: 0.999). However, the VyntusTM CPX, as a standard criterion, showed moderate agreement with wCS after Bland-Altman analysis (bias [95% lower to the upper limit of agreement]; % agree: 0.170 [-4.582 to 4.923]; 69.9%). A strong association between measurements (rrm [95% CI]: 0.960 [0.959, 0.961]), a high absolute agreement between methods (ICC [95% CI]: 0.970 [0.970, 0.971]), and a high inter-rater reliability (rF: 0.947) was found CONCLUSION: The new wCS device is an in-field valid and reliable method to evaluate fR compared to a breath-by-breath gas exchange analyzer. The statistical parameters analyzed show a high correlation between the two methods. We are already testing the device in a larger sample. Notwithstanding, caution is advised if methods are used interchangeably while further validation occur
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