The Validity and Reliability of a Smartphone Application for Break-Point Angle Measurement during Nordic Hamstring Exercise.
Toshiaki Soga, Shota Yamaguchi, Takayuki Inami and 6 others
PMID 37547835WHAT IT FOUND
In seven healthy men, a smartphone app's break-point angles during the Nordic hamstring exercise were close to motion analysis values, but the match was not conclusive.
The app was consistent within sessions, but the small sample means use with caution.
Key findings
01The app's average break-point angle was very close to the motion analysis average, but the match was not conclusive.
02The mean difference between the app and motion analysis was 0.4 ± 2.1°, and the limits of agreement ranged from -3.9° to 4.6°.
03The app showed perfect reliability across repeated same-day trials, ICC = 1.00, while motion analysis showed nearly perfect reliability, ICC = 0.97.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only seven healthy male volunteers were tested, so the results cannot be applied confidently to female athletes, older adults, injured athletes, or people with different hamstring strength. The sample size was based on a previous study's effect size, but the effect size here was smaller, so the validity of the app may be overestimated. The agreement analysis was performed on data that were not normally distributed, so the limits of agreement may not be exact. The app was compared only with two-dimensional motion analysis, not three-dimensional motion analysis. Reliability was checked only across repeated trials on the same day, not across separate testing sessions. The study did not test whether the app's break-point angle reflects eccentric knee flexion strength or hamstring injury risk.
Declared interests
The Nordic Angle app was developed in collaboration with S-CADE Co., Ltd. and the Athletic Training Laboratory at Waseda University. The first author collected and analyzed the data. The authors state they received no fees from S-CADE, and the app installation is free.
The easy way to misread this
Do not read this as proof that the app predicts hamstring injury risk. The study only compared break-point angle with motion analysis in seven healthy men, did not test the app against eccentric knee flexion strength, and the correlation did not reach significance.