Background The break-point angle (BPA) obtained during the Nordic Hamstring Test (NHT) can be used for preventive purposes to identify individuals with low eccentric hamstring strength. Video analysis is the preferred standard method, but there lacks an easily accessible and highly reproducible method for field use.

Objective To establish the reproducibility (reliability and agreement) of the smartphone application ‘DrGoniometer’ (DrG) for measuring BPA in healthy adults.

Design Diagnostic study.

Setting Clinical setting.

Patients (or Participants) Five volunteers and four raters (two physiotherapists and two physiotherapy students).

Interventions (or Assessment of Risk Factors) Ten NHT videos per subject were obtained by smartphone camera (total=50 videos). Raters independently measured the BPA, first using DrG app set in blind modality on two separate occasions (one week apart), then by standardized video analysis software on a PC.

Main Outcome Measurements Intra- and inter-rater reliability of DrG was calculated with ICC_(2,1) (95% IC). Longitudinal standard error of measurement (SEM) and inter-rater agreement within 5° and 10° were also calculated. The agreement of DrG with video analysis was expressed as 95% limits of agreement (LoA) with the Bland-Altman method.

Results Intra- and inter-rater reliability of the DrG were excellent, with ICC=0.885 (95% IC=0.836–0.918) and .821 (95%IC=0.738–0.885), respectively. The SEM was 2°. All four raters had substantial inter-rater agreement within the limits of 5° (68% and 78%) and 10° (94% and 100%) for the DrG and video analysis methods, respectively. The agreement between the two methods was good, with 95% LoA equal to 13.4° (mean difference=1.0±6.7°).

Conclusions DrG proved to be a highly reproducible method for measuring the BPA in the NHT in healthy subjects. Given its wide availability, low cost, and ease of use, the DrG app can be considered a good resource for field-based BPA measurement.