Parts of the rear-foot-elevated split squat repetition with high force demands show good-to-excellent kinetic waveform reliability in healthy young adults, whereas the start and end of the repetition show high uncertainty in reliability and relatively large smallest detectable change thresholds.
The middle portion of the rear-foot-elevated split squat repetition (25-75%) was the most reliable region for joint kinetic waveforms.
Reliability was poor and uncertain at the onset and end of the repetition.
Within-session variance was substantially larger than between-session variance in the mixed-effects models.
Reliability (ICCJ) and SDCJ could be improved by collecting more repetitions, with diminishing returns beyond about 10 repetitions.
A pointwise linear mixed-effects modelling approach can be used to assess test-retest reliability of entire kinetic waveforms rather than only discrete outcomes.
This study looked at how consistent measurements of joint forces are when people perform a heavy lower-body exercise, the rear-foot-elevated split squat, on two different days about a week apart. Twenty-one healthy young adults did 2 sets of 5 repetitions at 80% of their maximum load. Instead of looking at single peak values, the researchers examined the whole force curve across the repetition using a statistical method that evaluates each point on the curve. The middle part of the movement (roughly 25-75% of the repetition), when force demands are high, gave good-to-excellent consistency between days. The very beginning and end of the repetition were much less certain, with results ranging from poor to excellent and larger changes needed before a real difference could be detected. Most of the variability came from repetition-to-repetition differences within a session rather than differences between days. This research suggests that averaging more repetitions can improve reliability, although gains level off after about 10 repetitions. These findings may help researchers decide which parts of a movement curve to trust and how many repetitions to collect. Results apply to healthy young adults and this specific exercise.
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Upload Your LabsPalamarcukas I, Zhu T, Kong P. (2026). Reliability of multilevel functional data in resistance training biomechanics - a pointwise mixed-modelling approach.. Journal of biomechanics. https://doi.org/10.1016/j.jbiomech.2026.113587