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Oren Tirosh and W.A. Sparrow

Analysis of human gait requires accurate measurement of foot-ground contact, often determined using either foot-ground reaction force thresholds or kinematic data. This study examined the differences in calculating event times across five vertical force thresholds and validated a vertical acceleration-based algorithm as a measure of heel contact and toe-off. The experiment also revealed the accuracy in determining heel contact and toe-off when raw displacement/time data were smoothed using a range of digital filter cutoff frequencies. Four healthy young participants completed 10 walking trials: 5 at normal speed (1.2 m/s) and 5 at fast speed (1.8 m/s). A 3D optoelectric system was synchronized with a forceplate to measure the times when vertical force exceeded (heel contact) or fell below (toe-off) 10, 20, 30, 40, and 50 N. These were then compared and subsequently used to validate an acceleration-based method for calculating heel contact and toe-off with the displacement/time data filtered across a range of four cutoff frequencies. Linear regression analyses showed that during both normal and fast walking, any force threshold within 0 to 50 N could be used to predict heel-contact time. For estimating toe-off low force thresholds, 10 N or less should be used. When raw data were filtered with the optimal cutoff frequency, the absolute value (AbsDt) of the difference between the forceplate event times obtained using a 10-N threshold and the event times of heel contact and toe-off using the acceleration-based algorithms revealed average AbsDt of 10.0 and 16.5 ms for normal walking, and 7.4 and 13.5 ms for fast walking. Data smoothing with the non-optimal cutoff frequencies influenced the event times computed by the algorithms and produced greater AbsDt values. Optimal data filtering procedures are, therefore, essential for ensuring accurate measures of heel contact and toe-off when using the acceleration-based algorithms.

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Nili Steinberg, Gordon Waddington, Roger Adams, Janet Karin and Oren Tirosh

Background: Postural balance (PB) is an important component skill for professional dancers. However, the effects of different types of postures and different underfoot surfaces on PB have not adequately been addressed. Purpose: The main aim of this study was to investigate the effect of different conditions of footwear, surfaces, and standing positions on static and dynamic PB ability of young ballet dancers. Methods: A total of 36 male and female young professional ballet dancers (aged 14–19 years) completed static and dynamic balance testing, measured by head and lumbar accelerometers, while standing on one leg in the turnout position, under six different conditions: (1) “relaxed” posture; (2) “ballet” posture; (3) barefoot; (4) ballet shoes with textured insoles; (5) barefoot on a textured mat; and (6) barefoot on a spiky mat. Results: A condition effect was found for static and dynamic PB. Static PB was reduced when dancers stood in the ballet posture compared with standing in the relaxed posture and when standing on a textured mat and on a spiky mat (p < .05), and static PB in the relaxed posture was significantly better than PB in all the other five conditions tested. Dynamic PB was significantly better while standing in ballet shoes with textured insoles and when standing on a spiky mat compared with all other conditions (p < .05). Conclusions: The practical implications derived from this study are that both male and female dancers should try to be relaxed in their postural muscles when practicing a ballet aligned position, including dance practice on different types of floors and on different types of textured/spiky materials may result in skill transfer to practice on normal floor surfaces, and both static and dynamic PB exercises should be assessed and generalized into practical dance routines.

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Oren Tirosh, Guy Orland, Alon Eliakim, Dan Nemet and Nili Steinberg

This study aimed to identify differences in ground impact shock attenuation between overweight and healthy-weight children during running. Twenty overweight children aged 8.4 (1.1) years and 12 healthy-weight children aged 10.7 (1.3) years ran on a treadmill (120% of baseline speed) while wearing 2 inertial sensors located on their distal tibia and lower back (L3). Peak acceleration attenuation coefficient at foot contact and transfer function of the acceleration were calculated. Peak positive acceleration values were not significantly different between the overweight children and healthy-weight children (3.98 [1.17] g and 3.71 [0.84] g, respectively, P = .49). Children with healthy weight demonstrated significant greater attenuation as evident by greater peak acceleration attenuation coefficient (35.4 [19.3] and 11.9 [27.3], respectively, P < .05) and lower transfer function of the acceleration values (−3.8 [1.9] and −1.2 [1.5], respectively, P < .05). Despite the nonsignificant differences between groups in tibia acceleration at foot–ground impact that was found in the current study, the shock absorption of overweight children was reduced compared with their healthy-weight counterparts.

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Nili Steinberg, Roger Adams, Oren Tirosh, Janet Karin and Gordon Waddington

Context: Ankle sprains are common among adolescent ballet dancers and may be attributed to inadequate ankle proprioception. Thus, a short period of training utilizing proprioceptive activities requires evaluation. Objective: To assess training conducted for 3 or 6 weeks on a textured-surface balance board using ankle proprioception scores for ballet dancers with and without chronic ankle instability, and with and without previous ankle sprain (PAS). Design: Intervention study. Setting: The Australian Ballet School. Participants: Forty-two ballet dancers, aged 14–18 years. Interventions: Dancers randomized into 2 groups: group 1 undertook 1 minute of balance board training daily for 3 weeks; group 2 undertook the same training for 6 weeks. Main Outcome Measures: Preintervention, Cumberland Ankle Instability Tool questionnaire data were collected, and PAS during the last 2 years was reported. Active ankle inversion movement discrimination ability was tested immediately pre and post intervention and at 3 and 4 weeks. Results: Ankle discrimination acuity scores improved over time for both groups, with a performance decline associated with the early cessation of training for group 1 (P = .04). While dancers with PAS had significantly worse scores at the first test, before balance board training began (P < .01), no significant differences in scores at any test occasion were found between dancers with and without chronic ankle instability. A significantly faster rate of improvement in ankle discrimination ability score over the 4 test occasions was found for dancers with PAS (P = .002). Conclusions: Three weeks of textured balance board training improved the ankle discrimination ability of ballet dancers regardless of their reported level of chronic ankle instability and at a faster rate for dancers with PAS. Previous ankle sprain was associated with a lower level of ankle discrimination ability; however, following 3 weeks of balance board training, previously injured dancers had significantly improved their ankle discrimination acuity scores.

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Rob van der Straaten, Oren Tirosh, William A. (Tony) Sparrow and Rezaul Begg

Minimum toe clearance (MTC ∼10–30 mm) is a hazardous mid-swing gait event, characterized by high-foot velocity (∼4.60 m·s−1) and single-foot support. This experiment tested treadmill-based gait training effects on MTC. Participants were 10 young (4 males and 6 females) and 10 older (6 males and 4 females) healthy ambulant individuals. The mean age, stature, and body mass for the younger group was 23 (2) years, 1.72 (0.10) m, and 67.5 (8.3) kg, and for older adults was 77 (9) years, 1.64 (0.10) m, and 71.1 (12.2) kg. Ten minutes of preferred speed treadmill walking (baseline) was followed by 20 minutes with MTC information (feedback) and 10 minutes without feedback (retention). There were no aging effects on MTC in baseline or feedback. The MTC in baseline for older adults was 14.2 (3.5) mm and feedback 27.5 (8.7) mm, and for the younger group, baseline was 12.7 (2.6) mm and feedback 28.8 (5.1) mm, respectively. Retention MTC was significantly higher for both groups, indicating a positive effect of augmented information: younger 40.8 (7.3) mm and older 27.7 (13.6) mm. Retention joint angles relative to baseline indicated that the young modulated joint angles control MTC differently using increased ankle dorsiflexion at toe off and modulating knee and hip angles later in swing closer to MTC.