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Joseph Myers, John Jolly, Takashi Nagai, and Scott Lephart

Context:

In vivo scapular kinematics during humeral movements are commonly assessed with electromagnetic tracking devices despite few published data related to reliability and precision of these measurements.

Objective:

To determine the intrasession reliability and precision of assessing scapular kinematics using an electromagnetic tracking device.

Design:

Scapular position and orientation were measured with an electromagnetic tracking device during humeral elevation/depression in several planes. Intrasession reliability and precision were established by comparing 2 trials performed in succession.

Setting:

A human-movement research laboratory.

Participants:

15 healthy individuals.

Main Outcome Measures:

Intrasession intraclass correlation coefficients and standard error of measurement of all scapular variables were established.

Results:

The mean intrasession reliability for all variables was ICC = .97 ± .03. The mean intrasession precision was .99° ± .36°.

Conclusions:

In vivo scapular kinematics can be measured with high reliability and precision during intrasession research designs.

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Yoshiyuki Ohno, Rie Aoki, Akiko Tamakoshi, Takashi Kawamura, Kenji Wakai, Shuji Hashimoto, Norito Kawakami, and Masaki Nagai

To explore successful aging and high social activity in old age, data from a self-administered survey of 5,239 participants aged 65 years or more were analyzed. The questionnaire inquired about physical conditions and lifestyles of Japanese seniors during middle age and their present social activities in 4 regions of Japan in 1993. The authors first defined social activities and then developed a social-activity measure. Next, they examined the association between present social activity and physical conditions and lifestyles during middle age. Data analysis revealed that the most socially active seniors rated themselves as healthy and physically active during middle age. Socially active seniors differed from less active seniors: They had participated in more hobbies during middle age, had higher levels of education, and had had a more varied diet between the ages of 30 and 50. The data suggest that maintaining general health habits and lifestyles from middle age on is important for successful aging and high social activity in old age.

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Anne Z. Beethe, Elizabeth F. Nagle, Mita Lovalekar, Takashi Nagai, Bradley C. Nindl, and Christopher Connaboy

Purpose: To examine strength, range of motion, anthropometric, and physiological contributions to novice surface-combat-swimming (sCS) performance and establish differences from freestyle-swimming (FS) performance to further understand the transition of FS to sCS performance. Methods: A total of 13 competitive swimmers (7 male and 6 female; 27.7 [2.3] y; 176.2 [2.6] cm; 75.4 [3.9] kg) completed 8 testing sessions consisting of the following: physiological land-based measurements for maximal anaerobic and aerobic capacity and upper- and lower-extremity strength and range of motion, an sCS anaerobic capacity swim test measuring peak and mean force and fatigue index, 2 aerobic capacity tests measuring maximal aerobic capacity for both FS and sCS, and four 500-m performance swims for time, 1 FS, and 3 sCS. Separate multiple linear-regression analysis was used to analyze predictors of both sCS and FS performance models. Results: FS performance was predicted by the final FS maximal oxygen uptake with an R 2 of 42.03% (F 1,10 = 7.25; P = .0226), whereas sCS performance was predicted by isometric hip-extension peak strength with an R 2 of 41.46% (F 1,11 = 7.79; P = .0176). Conclusions: Results demonstrate that different physiological characteristics predict performance, suggesting that an altered strategy is used for novice sCS than FS. It is suggested that this may be due to the added constraints as mandated by mission requirements including boots, weighted gear, and clandestine requirements with hips lowered beneath the surface. Further research should examine the kinematics of the sCS flutter kick to improve performance by developing training strategies specific for the task.

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Timothy C. Sell, Mita T. Lovalekar, Takashi Nagai, Michael D. Wirt, John P. Abt, and Scott M. Lephart

Context: Postural stability is essential for injury prevention and performance. Differences between genders may affect training focus. Objective: To examine static and dynamic postural stability in male and female soldiers. Design: Descriptive laboratory study. Setting: Biomechanics laboratory. Participants: 25 healthy female soldiers (26.4 ± 5.3 y) and 25 healthy male soldiers (26.4 ± 4.9 y) matched on physical demand rating and years of service from the Army’s 101st Airborne Division (Air Assault). Interventions: Each person underwent static and dynamic postural stability testing. Main Outcome Measures: Standard deviation of the ground reaction forces during static postural stability and the dynamic stability index for dynamic postural stability. Results: Female soldiers had significantly better static postural stability than males but no differences were observed in dynamic postural stability. Conclusions: Postural stability is important for injury prevention, performance optimization, and tactical training. The differences observed in the current study may indicate the need for gender-specific training emphasis on postural stability.

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Valerie J. Williams, Takashi Nagai, Timothy C. Sell, John P. Abt, Russell S. Rowe, Mark A. McGrail, and Scott M. Lephart

Context:

Dynamic postural stability is important for injury prevention, but little is known about how lower-extremity musculoskeletal characteristics (range of motion [ROM] and strength) contribute to dynamic postural stability. Knowing which modifiable physical characteristics predict dynamic postural stability can help direct rehabilitation and injury-prevention programs.

Objective:

To determine if trunk, hip, knee, and ankle flexibility and strength variables are significant predictors of dynamic postural stability during single-leg jump landings.

Design:

Cross-sectional study.

Setting:

Laboratory.

Participants:

94 male soldiers (age 28.2 ± 6.2 y, height 176.5 ± 2.6 cm, weight 83.7 ± 26.0 kg).

Intervention:

None.

Main Outcome Measures:

Ankle-dorsiflexion and plantar-flexion ROM were assessed with a goniometer. Trunk, hip, knee, and ankle strength were assessed with an isokinetic dynamometer or handheld dynamometer. The Dynamic Postural Stability Index (DPSI) was used to quantify postural stability. Simple linear and backward stepwise-regression analyses were used to identify which physical characteristic variables were significant predictors of DPSI.

Results:

Simple linear-regression analysis revealed that individually, no variables were significant predictors of the DPSI. Stepwise backward-regression analysis revealed that ankle-dorsiflexion flexibility, ankle-inversion and -eversion strength, and knee-flexion and -extension strength were significant predictors of the DPSI (R 2 = .19, P = .0016, adjusted R 2 = .15).

Conclusion:

Ankle-dorsiflexion ROM, ankle-inversion and -eversion strength, and knee-flexion and -extension strength were identified as significant predictors of dynamic postural stability, explaining a small amount of the variance in the DPSI.

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Alice D. LaGoy, Caleb Johnson, Katelyn F. Allison, Shawn D. Flanagan, Mita T. Lovalekar, Takashi Nagai, and Chris Connaboy

Warfighter performance may be compromised through the impact of load carriage on dynamic postural stability. Men and women may experience this impact to differing extents due to postural stability differences. Therefore, the authors investigated the effect of load magnitude on dynamic postural stability in men and women during a landing and stabilization task. Dynamic postural stability of 32 subjects (16 women) was assessed during the unilateral landing of submaximal jumps under 3 load conditions: +0%, +20%, and +30% body weight. Dynamic postural stability was measured using the dynamic postural stability index, which is calculated from ground reaction force data sampled at 1200 Hz. Two-way mixed-measures analysis of variance compared dynamic postural stability index scores between sexes and loads. Dynamic postural stability index scores were significantly affected by load (P = .001) but not by sex or by the sex by load interaction (P > .05). Dynamic postural stability index scores increased between the 0% (0.359 ± 0.041), 20% (0.396 ± 0.034), and 30% (0.420 ± 0.028) body weight conditions. Increased load negatively affects dynamic postural stability with similar performance decrements displayed by men and women. Men and women warfighters may experience similar performance decrements under load carriage conditions of similar relative magnitudes.

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Takashi Nagai, Nicholas C. Clark, John P. Abt, Timothy C. Sell, Nicholas R. Heebner, Brian W. Smalley, Michael D. Wirt, and Scott M. Lephart

Context:

The cervical spine can be divided into upper and lower units, each making a different contribution to the magnitude of rotation and proprioception. However, few studies have examined the effect of the cervical-rotation positions on proprioception.

Objective:

To compare cervical-spine rotation active joint-position sense (AJPS) near midrange of motion (mid-ROM; 30°) and near end-ROM (60°).

Design:

Cross-sectional study.

Setting:

Human performance research laboratory.

Participants:

53 military helicopter pilots (age 28.4 ± 6.2 y, height 175.3 ± 9.3 cm, weight 80.1 ± 11.8 kg).

Main Outcome Measures:

A motion-analysis system was used to record cervical-rotation kinematics. Subjects sat in a chair wearing a headband and blindfold. First, they actively rotated the head right or left to a target position (30°/60°), with real-time verbal cues provided by the tester. Subjects held the target position for 5 s and then returned to the start position. After this, they replicated the target position as closely as possible. Five trials were performed in both directions to both target positions (R30/R60/L30/L60). Order of direction/position was randomized. The difference between target and replicated positions was calculated and defined as absolute error (AE), and the mean of 5 trials was used for analyses. Wilcoxon signed-ranks tests were used to compare AJPS at the different target positions (P < .0125 with Bonferroni adjustments).

Results:

End-ROM AEs were significantly more accurate than mid-ROM AEs (P = .001).

Conclusion:

Cervical-spine-rotation AJPS is more accurate near end-ROM than mid-ROM. Both target positions should be used to examine cervical-spine-rotation AJPS of both the upper and lower units.