Hamstring Activity Before and After Break-Point Angle Calculated By Smartphone Application During the Nordic Hamstring Exercise.
Toshiaki Soga, Shota Yamaguchi, Takayuki Inami and 9 others
PMID 39282209WHAT IT FOUND
The Nordic Angle app closely tracks motion analysis for hamstring break-point angles, but reads slightly higher on average.
Biceps femoris activity stays high until 20 degrees past this break point, then drops sharply. Clinicians should use multiple trials to average out small measurement errors.
Key findings
01The smartphone app's break-point angle correlated nearly perfectly with motion analysis, though the app read 3.0 degrees higher on average.
02Biceps femoris muscle activity peaked near the break-point angle and dropped significantly once the knee flexed 20-25 degrees past it.
03Because the standard Nordic Hamstring Exercise break-point angle is usually around 50 degrees, the muscle activity often falls off before reaching the 15-35 degree range where hamstring injuries occur.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study only included 13 young, healthy male participants, so results may not apply to older adults, females, or injured athletes. Measurements were taken in a single session, so it is unclear how consistent the app is from day to day. The app showed a systematic bias, reading 3.0 degrees higher than motion analysis, and the range of agreement was wide (-5.5 to 11.4 degrees), meaning single measurements can vary significantly. EMG electrodes were placed without ultrasound guidance, which raises the possibility of signal crosstalk from nearby muscles.
Declared interests
The Nordic Angle app was developed in collaboration with a company (S-CADE Co., Ltd.) and the authors' university. The authors state they receive no fees from the company, but the first author collected and analyzed the data for this study evaluating the app.
The easy way to misread this
Do not assume the Nordic Angle app provides a precise, single-use measurement. While it correlates well with motion analysis, it reads 3.0 degrees higher on average and has a wide limit of agreement (-5.5 to 11.4 degrees). A single trial may be misleading; multiple trials averaged together are necessary for accurate clinical decision-making.