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Kathy Liu and Gary D. Heise

Dynamic stability is often measured by time to stabilization (TTS), which is calculated from the dwindling fluctuations of ground reaction force (GRF) components over time. Common protocols of dynamic stability research have involved forward or vertical jumps, neglecting different jump-landing directions. Therefore, the purpose of the present investigation was to examine the influence of different jump-landing directions on TTS. Twenty healthy participants (9 male, 11 female; age = 28 ± 4 y; body mass = 73.3 ± 21.5 kg; body height = 173.4 ± 10.5 cm) completed the Multi-Directional Dynamic Stability Protocol hopping tasks from four different directions—forward, lateral, medial, and backward—landing single-legged onto the force plate. TTS was calculated for each component of the GRF (ap = anterior-posterior; ml = medial-lateral; v = vertical) and was based on a sequential averaging technique. All TTS measures showed a statistically significant main effect for jump-landing direction. TTSml showed significantly longer times for landings from the medial and lateral directions (medial: 4.10 ± 0.21 s, lateral: 4.24 ± 0.15 s, forward: 1.48 ± 0.59 s, backward: 1.42 ± 0.37 s), whereas TTSap showed significantly longer times for landings from the forward and backward directions (forward: 4.53 ± 0.17 s, backward: 4.34 0.35 s, medial: 1.18 ± 0.49 s, lateral: 1.11 ± 0.43 s). TTSv showed a significantly shorter time for the forward direction compared with all other landing directions (forward: 2.62 ± 0.31 s, backward: 2.82 ± 0.29 s, medial: 2.91 ± 0.31 s, lateral: 2.86 ± 0.32 s). Based on these results, multiple jump-landing directions should be considered when assessing dynamic stability.

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Tai T. Tran, Lina Lundgren, Josh Secomb, Oliver R.L. Farley, G. Gregory Haff, Robert U. Newton, Sophia Nimphius, and Jeremy M. Sheppard

The purpose of this study was to develop and evaluate a drop-and-stick (DS) test method and to assess dynamic postural control in senior elite (SE), junior elite (JE), and junior development (JD) surfers. Nine SE, 22 JE, and 17 JD competitive surfers participated in a single testing session. The athletes completed 5 drop-and-stick trials barefoot from a predetermined box height (0.5 m). The lowest and highest time-to-stabilization (TTS) trials were discarded, and the average of the remaining trials was used for analysis. The SE group demonstrated excellent single-measures repeatability (ICC = .90) for TTS, whereas the JE and JD demonstrated good single-measures repeatability (ICC .82 and .88, respectively). In regard to relative peak landing force (rPLF), SE demonstrated poor single-measures reliability compared with JE and JD groups. Furthermore, TTS for the SE (0.69 ± 0.13 s) group was significantly (P = .04) lower than the JD (0.85 ± 0.25 s). There were no significant (P = .41) differences in the TTS between SE (0.69 ± 0.13 s) and JE (0.75 ± 0.16 s) groups or between the JE and JD groups (P = .09). rPLF for the SE (2.7 ± 0.4 body mass; BM) group was significantly lower than the JE (3.8 ± 1.3 BM) and JD (4.0 ± 1.1 BM), with no significant (P = .63) difference between the JE and JD groups. A possible benchmark approach for practitioners would be to use TTS and rPLF as a qualitative measure of dynamic postural control using a reference scale to discriminate among groups.

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Lina E. Lundgren, Tai T. Tran, Sophia Nimphius, Ellen Raymond, Josh L. Secomb, Oliver R.L. Farley, Robert U. Newton, Julie R. Steele, and Jeremy M. Sheppard


To develop and evaluate a multifactorial model based on landing performance to estimate injury risk for surfing athletes.


Five measures were collected from 78 competitive surfing athletes and used to create a model to serve as a screening tool for landing tasks and potential injury risk. In the second part of the study, the model was evaluated using junior surfing athletes (n = 32) with a longitudinal follow-up of their injuries over 26 wk. Two models were compared based on the collected data, and magnitude-based inferences were applied to determine the likelihood of differences between injured and noninjured groups.


The study resulted in a model based on 5 measures—ankle-dorsiflexion range of motion, isometric midthigh-pull lower-body strength, time to stabilization during a drop-and-stick (DS) landing, relative peak force during a DS landing, and frontal-plane DS-landing video analysis—for male and female professional surfers and male and female junior surfers. Evaluation of the model showed that a scaled probability score was more likely to detect injuries in junior surfing athletes and reported a correlation of r = .66, P = .001, with a model of equal variable importance. The injured (n = 7) surfers had a lower probability score (0.18 ± 0.16) than the noninjured group (n = 25, 0.36 ± 0.15), with 98% likelihood, Cohen d = 1.04.


The proposed model seems sensitive and easy to implement and interpret. Further research is recommended to show full validity for potential adaptations for other sports.

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Kristof Kipp, Michael T. Kiely, Matthew D. Giordanelli, Philip J. Malloy, and Christopher F. Geiser

.1519/JSC.0b013e3181e72466 20634740 5. Flanagan EP , Ebben WP , Jensen RL . Reliability of the reactive strength index and time to stabilization during depth jumps . J Strength Cond Res . 2008 ; 22 ( 5 ): 1677 – 1682 . PubMed doi:10.1519/JSC.0b013e318182034b 18714215 10.1519/JSC.0b013e318182034b

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Paul A. Solberg, Will G. Hopkins, Gøran Paulsen, and Thomas A. Haugen

class only once, and a plausible reason for the smaller effect of going up could be that the lifter needs time to stabilize in the new weight class. Athletes participating in weight-restricted events typically train at a body mass 5% to 10% above their required competition weight class. 30 To “make

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Niall Casserly, Ross Neville, Massimiliano Ditroilo, and Adam Grainger

measuring jump height . Int J Sports Physiol Perform . 2017 ; 12 ( 7 ): 959 – 963 . PubMed ID: 27967279 doi:10.1123/ijspp.2016-0511 10.1123/ijspp.2016-0511 27967279 21. Flanagan EP , Ebben WP , Jensen RL . Reliability of the reactive strength index and time to stabilization during depth jumps

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José R. Lillo-Bevia and Jesús G. Pallarés

and Passfield, 5 only PO and cadence values from the 10th to the 70th second of each 75-second steps were analyzed, to allow the ergometer enough time to stabilize the assigned breaking load. During each test, PO (W) and cadence (rev·min −1 ) of Hammer Cycleops were recorded at a frequency of 1 Hz

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Sean J. Maloney, Joanna Richards, and Iain M. Fletcher

, Dugan E . Application of strength diagnosis . Strength Cond J . 2002 ; 24 ( 5 ): 50 – 59 . doi:10.1519/00126548-200210000-00014 10.1519/00126548-200210000-00014 16. Flanagan EP , Ebben WP , Jensen RL . Reliability of the reactive strength index and time to stabilization during depth jumps

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Paul J. Read, Jon L. Oliver, Gregory D. Myer, Mark B.A. De Ste Croix, and Rhodri S. Lloyd

. PubMed doi:10.2478/hukin-2013-0005 10.2478/hukin-2013-0005 23717354 9. Ebben WP , VanderZanden T , Wurm BJ , Petushek EJ . Evaluating plyometric exercises using time to stabilization . J Strength Cond Res . 2010 ; 24 : 300 – 6 . PubMed doi:10.1519/JSC.0b013e3181cbaadd 10.1519/JSC.0b013e3181

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John R. Harry, Max R. Paquette, Brian K. Schilling, Leland A. Barker, C. Roger James, and Janet S. Dufek

reactive strength index and time to stabilization during depth jumps . J Strength Cond Res . 2008 ; 22 ( 5 ): 1677 – 1682 . PubMed ID: 18714215 doi:10.1519/JSC.0b013e318182034b 18714215 10.1519/JSC.0b013e318182034b 19. Markwick WJ , Bird SP , Tufano JJ , Seitz LB , Haff GG . The intraday