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Recently, while discussing the testing indicators related to the force platform with peers, a question arose: why does DSI use CMJ PF instead of SJ PF?
Questions:
1) CMJ includes SSC, so the PF will definitely be higher, but how much higher compared to SJ PF is uncertain.
2) CMJ consists of squat-braking-jumping, while IMTP and SJ actions are closer, at least without a reverse action phase.
In response to this question, research by Paul Comfort and others explains why DSI recommends using CMJ PF.
Research data results:
DSI-SJ
Showed moderate reliability (ICC=0.419) and high variability (CV%=15.91) in the first phase of testing.
Showed higher reliability (ICC=0.948) and low variability (CV%=4.03) in the second phase of testing.
DSI-CMJ
Both phases of testing showed nearly perfect reliability (ICC = 0.920-0.952) and low variability (%CV =3.80-4.57)
Additionally, the results of DSI-SJ showed a small but significant increase between tests (P=0.01, d=0.37), while the increase in DSI-CMJ between tests was negligible and not significant (P=0.796, d=0.07).
The greater variability and lower reliability observed in DSI-SJ may be due to subjects struggling to jump as high as possible from a static squat position without any reverse action.
In CMJ, the effect of SSC results in PF (3.6%) being higher than SJ, but this difference is actually negligible and not significant. The jump height in CMJ is also significantly higher than SJ (12%).
Coaches who have conducted SJ tests know that not everyone can perform the SJ test well, partly due to unfamiliarity and partly because it differs from their usual movement patterns.
If it’s firefighters, most can complete a high-quality SJ test, and careful observation reveals that their daily training items (like rope climbing) involve a preparatory position that is a slight squat or half-squat, while they are noticeably uncoordinated during CMJ testing, leading to less than ideal results (the table below: test data from a certain rescue unit in Southwest China shows that SJ height is significantly higher than CMJ height).
In practice, using CMJ PF or SJ PF is feasible, but it is essential to fully consider the familiarity of the tested personnel with both types of jumps, and whether there is a need to assess other force characteristics and performance features in sports tasks.
For most sports, CMJ is the appropriate choice, as it not only offers higher testing reliability and lower variability but also provides complete jump force characteristic information, which helps obtain comprehensive performance results.