Reliability and validity of the Stryd Power Meter during different walking conditions

Background: The Styrd Power Meter is gaining special interest for on-field gait analyses due to its low-cost and general availability. However, the reliability and validity of the Stryd during walking on positive slopes using different backpack loads have never been investigated.Research question: Is the Stryd Power Meter reliable and valid for quantifying gait mechanics during walking on positive inclines and during level walking incorporating load carriage?Methods: Seventeen participants from a police force rescue team performed 8 submaximal walking trials for 5 min at 3.6 km.h(- 1) during different positive slope (1%, 10% and 20%) and backpack load (0%, 10%, 20%, 30% and 40% of body mass) conditions. Two Stryd devices were utilized for reliability analyses. Validity of cadence and ground contact time (GCT) were analyzed against a gold standard device (Optojump).Results: The Stryd demonstrated acceptable reliability [mean bias: < 2.5%; effect size (ES): < 0.25; standard error of the mean: < 1.7%; r: > 0.76] for power, cadence, and GCT. Validity measures (mean bias: < 0.8%; ES: < 0.07; r: > 0.96; Lin's Concordance Coefficient: 0.96; Mean Absolute Percent Error: < 1%) for cadence were also found to be acceptable. The Stryd overestimated (P < 0.001; ES: > 5.1) GCT in all the walking conditions. A significant systematic positive bias (P < 0.022; r = 0.56-0.76) was found in 7 conditions.Significance: The Stryd Power Meter appears to produce reliable measurements for power output, cadence and GCT. The Stryd produced valid measurements for cadence during walking on positive slopes and during level walking with a loaded backpack. However, the Stryd is not valid for measuring GCT during these walking conditions. This study adds novel data regarding the reliability and validity of this device and might be of particular interest for scientists, practitioners, and first responders seeking reliable devices to quantify gait mechanics during walking.