Validity and Reliability of Two Field-Based Leg Stiffness Devices: Implications for Practical Use
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Bibliographic record
Abstract
Leg stiffness is an important performance determinant in several sporting activities. This study evaluated the criterion-related validity and reliability of 2 field-based leg stiffness devices, Optojump NextR (Optojump) and Myotest ProR (Myotest) in different testing approaches. Thirty-four males performed, on 2 separate sessions, 3 trials of 7 maximal hops, synchronously recorded from a force platform (FP), Optojump and Myotest. Validity (Pearson's correlation coefficient, r; relative mean bias; 95% limits of agreement, 95%LoA) and reliability (coefficient of variation, CV; intraclass correlation coefficient, ICC; standard error of measurement, SEM) were calculated for first attempt, maximal attempt, and average across 3 trials. For all 3 methods, Optojump correlated highly to the FP (range r = .98-.99) with small bias (range 0.91-0.92, 95%LoA 0.86-0.98). Myotest demonstrated high correlation to FP (range r = .81-.86) with larger bias (range 1.92-1.93, 95%LoA 1.63-2.23). Optojump yielded a low CV (range 5.9% to 6.8%), high ICC (range 0.82-0.86), and SEM ranging 1.8-2.1 kN/m. Myotest had a larger CV (range 8.9% to 13.0%), moderate ICC (range 0.64-0.79), and SEM ranging from 6.3 to 8.9 kN/m. The findings present important information for these devices and support the use of a time-efficient single trial to assess leg stiffness in the field.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it