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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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Scott Ross, Kevin Guskiewicz, William Prentice, Robert Schneider and Bing Yu

Objective:

T o determine differences between contralateral limbs’ strength, proprio-ception, and kinetic and knee-kinematic variables during single-limb landing.

Setting:

Laboratory.

Subjects:

30.

Measurements:

Hip, knee, and foot isokinetic peak torques; anterior/posterior (AP) and medial/lateral (ML) sway displacements during a balance task; and stabilization times, vertical ground-reaction force (VGRF), time to peak VGRF, and knee-flexion range of motion (ROM) from initial foot contact to peak VGRF during single-limb landing.

Results:

The kicking limb had significantly greater values for knee-extension (P = .008) and -flexion (P = .047) peak torques, AP sway displacement (P = .010), knee-flexion ROM from initial foot contact to peak VGRF (P < .001), and time to peak VGRF (P = .004). No other dependent measures were significantly different between limbs (P > .05).

Conclusion:

The kicking limb had superior thigh strength, better proprioception, and greater knee-flexion ROM than the stance limb.

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Stephen M. Glass, Brian L. Cone, Christopher K. Rhea, Donna M. Duffy and Scott E. Ross

Context: Previous work suggests that balance behavior is a sex-dependent, complex process that can be characterized by linear and nonlinear metrics. Although a certain degree of center of pressure variability may be expected based on sexual dimorphism, there is evidence to suggest that these effects are obscured by potential interactions between sex and anthropometric factors. To date, no study has accounted for such interactive effects using both linear and nonlinear measures. Objective: This investigation sought to analyze interactive models featuring sex, height, and weight as predictors of linear and nonlinear aspects of postural control. Design: Cross-sectional study. Setting: Controlled laboratory. Participants: A total of 26 males (23.80 [3.44] y, 177.87 [6.44] cm, 81.70 [10.80] kg) and 28 females (21.14 [2.03] y, 169.57 [8.80] cm, 64.48 [8.86] kg) were sampled from a healthy university population. MainOutcomeMeasures: Linear (range [RNG], velocity [VEL], and SD) and nonlinear (detrended fluctuation analysis scaling exponent, multivariate multiscale sample entropy [MMSECI]) summary metrics of center of pressure time series. Procedure: Participants stood on a force plate for 20 seconds in 3 conditions: double (D), single (S), and tandem (T) stance. Data for each stance condition were analyzed using regression models with interaction terms for sex × height and sex × weight. In D, weight had a positive, significant main effect on VELy, MMSECId, and MMSECIv. In men, height was observed to have a positive effect on SDy (S), RNGy (S), and RNGx (T) and a negative effect on MMSECIv (T). In women, weight was observed to have a positive effect on SDy and VELx (both T). Conclusions: Our findings suggest that men and women differ with respect to certain linear and nonlinear aspects of balance behavior, and that these differences may reflect sex-specific behavioral patterns in addition to effects related to sexual dimorphism.

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Stephen M. Glass, Christopher K. Rhea, Matthew W. Wittstein, Scott E. Ross, John P. Florian and F.J. Haran

Transitioning between different sensory environments is known to affect sensorimotor function and postural control. Water immersion presents a novel environmental stimulus common to many professional and recreational pursuits, but is not well-studied with regard to its sensorimotor effects upon transitioning back to land. The authors investigated the effects of long-duration water immersion on terrestrial postural control outcomes in veteran divers. Eleven healthy men completed a 6-hour thermoneutral pool dive (4.57 m) breathing diver air. Center of pressure was observed before and 15 minutes after the dive under 4 conditions: (1) eyes open/stable surface (Open-Stable); (2) eyes open/foam surface (Open-Foam); (3) eyes closed/stable surface (Closed-Stable); and (4) eyes closed/foam surface (Closed-Foam). Postdive decreases in postural sway were observed in all testing conditions except for Open-Stable. The specific pattern of center of pressure changes in the postdive window is consistent with (1) a stiffening/overregulation of the ankle strategy during Open-Foam, Closed-Stable, and Closed-Foam or (2) acute upweighting of vestibular input along with downweighting of somatosensory, proprioceptive, and visual inputs. Thus, our findings suggest that postimmersion decreases in postural sway may have been driven by changes in weighting of sensory inputs and associated changes in balance strategy following adaptation to the aquatic environment.

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Scott E. Ross and Kevin M. Guskiewicz

Column-editor : Thomas W. Kaminski

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Chanel T. LoJacono, Ryan P. MacPherson, Nikita A. Kuznetsov, Louisa D. Raisbeck, Scott E. Ross and Christopher K. Rhea

Obstacle crossing, such as stepping over a curb, becomes more challenging with natural aging and could lead to obstacle-related trips and falls. To reduce fall-risk, obstacle training programs using physical obstacles have been developed, but come with space and human resource constraints. These barriers could be removed by using a virtual obstacle crossing training program, but only if the learned gait characteristics transfer to a real environment. We examined whether virtual environment obstacle crossing behavior is transferred to crossing real environment obstacles. Forty participants (n = 20 younger adults and n = 20 older adults) completed two sessions of virtual environment obstacle crossing, which was preceded and followed by one session of real environment obstacle crossing. Participants learned to cross the virtual obstacle more safely and that change in behavior was transferred to the real environment via increased foot clearance and alterations in foot placement before and after the real environment obstacle. Further, while both age groups showed transfer to the real environment task, they differed on the limb in which their transfer effects applied. This suggests it is plausible to use virtual reality training to enhance gait characteristics in the context of obstacle avoidance, potentially leading to a novel way to reduce fall-risk.