Time to stabilization in single leg drop jump landings: An examination of calculation methods and assessment of differences in sample rate, filter settings and trial length on outcome values

Abstract

Time to stabilization (TTS) is the time it takes for an individual to return to a baseline or stable state following a jump or hop landing. A large variety exists in methods to calculate the TTS. These methods can be described based on four aspects: (1) the input signal used (vertical, anteroposterior, or mediolateral ground reaction force) (2) signal processing (smoothed by sequential averaging, a moving root-mean-square window, or fitting an unbounded third order polynomial), (3) the stable state (threshold), and (4) the definition of when the (processed) signal is considered stable. Furthermore, differences exist with regard to the sample rate, filter settings and trial length. Twenty-five healthy volunteers performed ten 'single leg drop jump landing' trials. For each trial, TTS was calculated according to 18 previously reported methods. Additionally, the effects of sample rate (1000, 500, 200 and 100 samples/s), filter settings (no filter, 40, 15 and 10 Hz), and trial length (20, 14, 10, 7, 5 and 3s) were assessed. The TTS values varied considerably across the calculation methods. The maximum effect of alterations in the processing settings, averaged over calculation methods, were 2.8% (SD 3.3%) for sample rate, 8.8% (SD 7.7%) for filter settings, and 100.5% (SD 100.9%) for trial length. Differences in TTS calculation methods are affected differently by sample rate, filter settings and trial length. The effects of differences in sample rate and filter settings are generally small, while trial length has a large effect on TTS values.

The effect of the stability threshold on time to stabilization and its reliability following a single leg drop jump landing

“…Time to stabilization (TTS) is a frequently used outcome measure, but widely different calculation methods to establish TTS following a single leg jump landing test have been identified in the literature (Fransz et al, 2015). For instance, these calculation methods differ with regard to the input signal that is used.…”

“…For instance, these calculation methods differ with regard to the input signal that is used. The GRF's can be assessed in vertical (V), anteroposterior (AP) or mediolateral (ML) direction, resulting in substantially different TTS values, ranging from 1.3 to 6.1 s (Fransz et al, 2015). Secondly, four essentially different signal-processing methods have been employed.…”

Postural stability and lower leg muscle activity during a diagonal single-leg landing differs in male collegiate soccer players with and without functional ankle instability

“…These were separately analyzed from peak GRFs to 20 seconds later using the TRIAS data analysis system (Biometrics, UK). The last 10 seconds of GRF components in the control group, which were divided by the body weight of each participant (N), were averaged for calculating an overall mean range of variation variables 30) . Three SDs of the overall mean range of variation variables were calculated and added to the variation variables to create a normalized range-of-variation variable.…”

Time series of ground reaction forces following a single leg drop jump landing in elite youth soccer players consist of four distinct phases

“…The TTS aims to quantify the transition from an instable situation to a stable situation. Large differences exist in TTS calculation methods, therefore studies should be interpreted and compared with caution [10,11]. Calculation of the DPSI is straightforward and quantifies the fluctuation of the resultant ground reaction forces (GRF) around the origin (mean value) for 3 s following impact [12].…”

“…This resulted in large variation in outcome values (0.5-6 s) and low correlations between calculation methods applied to the same measurement [10,11]. Therefore, distinct information may be available within the dynamic phases as well.…”