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Kazem Malmir, Gholam Reza Olyaei, Saeed Talebian, Ali Ashraf Jamshidi and Majid Ashraf Ganguie

both for preventing injury and successfully performing an action. Time to stabilization (TTS) and dynamic postural stability index (DPSI) have been suggested as the measures of dynamic stability. 4 , 5 These measures can indicate the ability of a person to maintain his or her stability during

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Cathleen Brown, Scott Ross, Rick Mynark and Kevin Guskiewicz

Context:

Functional ankle instability (FAI) is difficult to identify and quantify.

Objective:

To compare joint position sense (JPS), time to stabilization (TTS), and electromy-ography (EMG) of ankle musculature in recreational athletes with and without FAI.

Design:

Case-control compared with t tests and ANOVAs.

Setting:

Sports medicine research laboratory.

Participants:

20 recreational athletes.

Main Outcome Measures:

Passive angle reproduction, TTS, and mean EMG amplitude of the tibialis anterior, peroneals, lateral gastrocnemius, and soleus muscles during single-leg-jump landing.

Results:

No differences in JPS or medial-lateral TTS measures between groups. Significantly longer anterior-posterior TTS (P < .05) in the unstable ankle group. The stable ankle group had significantly higher mean EMG soleus amplitude after landing (P < .05). No other significant differences were found for mean EMG amplitudes before or after landing.

Conclusions:

Subjects with FAI demonstrated deficits in landing stability and soleus muscle activity during landing that may represent chronic adaptive changes following injury.

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Doris Bolt, René Giger, Stefan Wirth and Jaap Swanenburg

Time-to-stabilization (TTS) is an example of an objective postural control measure. 3 An increased TTS after a jump has been found in athletes with chronic ankle instability (CAI) compared to uninjured controls. 2 In 27% of all ankle sprains, however, the underlying mechanism of injury is a fall

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Scott E. Ross and Kevin M. Guskiewicz

Column-editor : Thomas W. Kaminski

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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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Susan Miniello, Geoffrey Dover, Michael Powers, Mark Tillman and Erik Wikstrom

Context:

Previous studies have suggested that cryotherapy affects neuromuscu-lar function and therefore might impair dynamic stability. If cryotherapy affects dynamic stability, clinicians might alter their decisions regarding returning athletes to play immediately after treatment.

Objective:

To assess the effects of lower leg cold immersion on muscle activity and dynamic stability of the lower extremity.

Design:

Within-subject time-series design with 1 pretest and 2 posttests.

Setting:

A climate-controlled biomechanics laboratory.

Participants:

17 healthy women.

Interventions:

20-minute cold-water immersion.

Main Outcome Measures:

Preparatory and reactive electromyographic activity of the tibialis anterior and peroneus longus and time to stabilization after a jump landing.

Results:

Preparatory activity of the tibialis anterior increased after treatment, whereas preparatory and reactive peroneus longus activity decreased. Both returned to baseline after a 5-minute recovery. Time to stabilization did not change.

Conclusions:

Lower leg cold-immersion therapy does not impair dynamic stability in healthy women during a jump-landing task. Return to participation after a cryotherapy treatment is not contraindicated for healthy athletes.

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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

Purpose:

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

Methods:

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.

Results:

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.

Conclusions:

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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Abbis H. Jaffri, Thomas M. Newman, Brent I. Smith, Giampietro L. Vairo, Craig R. Denegar, William E. Buckley and Sayers J. Miller

static assessment tasks, where the maintenance of static alignment of the body segments is the goal. 14 Differences in dynamic balance between CAI and uninjured populations have been demonstrated with this testing method. 14 Subjects with CAI took more time to stabilize than healthy subjects. 14

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Dana M. Otzel, Chris J. Hass, Erik A. Wikstrom, Mark D. Bishop, Paul A. Borsa and Mark D. Tillman

found neither changes in dynamic postural control nor changes in muscle activity during preparatory or loading phases of the time-to-stabilization after a jump following a 6-minute session of WBV in individuals with CAI. A study by McBride et al 22 revealed increased triceps surae muscle force but no