Reliability of video-based identification of footstrike pattern and video time frame at initial contact in...

Two-dimensional video recordings are used in clinical practice to identify footstrike pattern. However, knowledge about the reliability of this method of identification is limited.

To evaluate intra- and inter-rater reliability of visual identification of footstrike pattern and video time frame at initial contact during treadmill running using two-dimensional (2D) video recordings.

Thirty-one recreational runners were recorded twice, 1 week apart, with a high-speed video camera. Two blinded raters evaluated each video twice with an interval of at least 14 days.

Kappa values for within-day identification of footstrike pattern revealed intra-rater agreement of 0.83-0.88 and inter-rater agreement of 0.50-0.63. Corresponding figures for between-day identification of footstrike pattern were 0.63-0.69 and 0.41-0.53, respectively. Identification of video time frame at initial contact ranged from five frames to 12 frames (95% limits of agreement).

For clinical use, the intra-rater within-day identification of footstrike pattern is highly reliable (kappa>0.80). For the inter-rater between-day identification inconsistencies may, in worst case, occur in 36% of the identifications (kappa=0.41). The 95% limits of agreement for identification of video time frame at initial contact may, at times, allow for different identification of footstrike pattern. Clinicians should, therefore, be encouraged to continue using clinical 2D video setups for intra-rater identification of footstrike pattern, but bear in mind the restrictions related to the between day identifications.