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- Changes in strain patterns after implantation of a short stem with metaphyseal anchorage compared to a standard stem: an experimental study in synthetic bone. [Journal Article]
- Orthop Rev (Pavia) 2014 Jan 20; 6(1):5211.
Short stem hip arthroplasties with predominantly metaphyseal fixation, such as the METHA® stem (Aesculap, Tuttlingen, Germany), are recommended because they are presumed to allow a more physiologic load transfer and thus a reduction of stress-shielding. However, the hypothesized metaphyseal anchorage associated with the aforementioned benefits still needs to be verified. Therefore, the METHA short stem and the Bicontact® standard stem (Aesculap, Tuttlingen, Germany) were tested biomechanically in synthetic femora while strain gauges monitored their corresponding strain patterns. For the METHA stem, the strains in all tested locations including the region of the calcar (87% of the non-implanted femur) were similar to conditions of synthetic bone without implanted stem. The Bicontact stem showed approximately the level of strain of the non-implanted femur on the lateral and medial aspect in the proximal diaphysis of the femur. On the anterior and posterior aspect of the proximal metaphysis the strains reached averages of 78% and 87% of the non-implanted femur, respectively. This study revealed primary metaphyseal anchorage of the METHA short stem, as opposed to a metaphyseal-diaphyseal anchorage of the Bicontact stem.
- Mechanical analysis of the roundhouse kick according to height and distance in taekwondo. [Journal Article]
- Biol Sport 2013 Dec; 30(4):275-9.
Competition regulation in taekwondo has experienced several changes during the last few years, for example, kicks to the head score more points than kicks to the chest. In addition, some external factors such as the height of target and execution distance seem to affect the kick performance. The aim of this study was to analyse selected biomechanical parameters (impact force, reaction time, and execution time) according to the height and execution distance in two different male groups (experts (n = 12) and novices (n = 21)). Athletes kicked twice from every execution distance (short, normal and long) and towards two different heights of target (chest and head) in a random order. Novices kicked to the head with a longer reaction time than to the chest (p < 0.05) but experts were able to kick with similar performance for both heights. From short and normal distances experts kicked with similar performance; whereas from the normal distance novices had longer reaction and execution time than from the short distance (p < 0.05). In conclusion, in counterattacking situations, experts should perform the roundhouse kick to the head instead of to the chest, because it produces better scores with similar performance; whereas novice athletes should avoid kicking to the head because they are not able to kick with similar performance. Moreover, it is recommended that during counterattacks higher-level taekwondo athletes should intend to kick from normal distances.
- Biomechanics of head injury in olympic taekwondo and boxing. [Journal Article]
- Biol Sport 2013 Dec; 30(4):263-8.
The purpose was to examine differences between taekwondo kicks and boxing punches in resultant linear head acceleration (RLA), head injury criterion (HIC15), peak head velocity, and peak foot and fist velocities. Data from two existing publications on boxing punches and taekwondo kicks were compared.For taekwondo head impacts a Hybrid II Crash Dummy (Hybrid II) head was instrumented with a tri-axial accelerometer mounted inside the Hybrid II head. The Hybrid II was fixed to a height-adjustable frame and fitted with a protective taekwondo helmet. For boxing testing, a Hybrid III Crash Dummy head was instrumented with an array of tri-axial accelerometers mounted at the head centre of gravity.Differences in RLA between the roundhouse kick (130.11±51.67 g) and hook punch (71.23±32.19 g, d = 1.39) and in HIC15 (clench axe kick: 162.63±104.10; uppercut: 24.10±12.54, d = 2.29) were observed.Taekwondo kicks demonstrated significantly larger magnitudes than boxing punches for both RLA and HIC.
- Kinematics that differentiate the beach flags start between elite and non-elite sprinters. [Journal Article]
- Biol Sport 2013 Dec; 30(4):255-61.
This study differentiated the kinematics of the beach flags sprint start between five elite (three males, two females; age = 21.2 ± 2.6 years; height = 1.71 ± 0.04 m; mass = 66.2 ± 5.9 kg) and five non-elite (three males, two females; age = 20.4 ± 1.7 years; height = 1.69 ± 0.08 meters [m]; mass = 61.6 ± 5.7 kilograms) sprinters. A high-speed camera filmed the start. Timing gates recorded the 0-2, 0-5, and 0-20 m intervals. Data included body position during the start and at take-off; start time; first step length; and sprint times. A Mann-Whitney U-test determined significant (p < 0.05) between-group differences; effect sizes (ES) were also calculated. Elite sprinters had a greater take-off trajectory angle (p = 0.01; ES = 2.57), and were faster over the 0-2 (p = 0.02; ES = 1.77), 0-5 (p = 0.05; ES = 1.20), and 0-20 m (p = 0.02; ES = 1.83) intervals. Large effects were found for: greater take-off swing leg hip flexion (ES = 1.13) and trunk lean (ES = 1.37); longer duration start time (ES = 1.33); and longer first step length (ES = 1.23) in elite sprinters. A longer start time assists with force generation, which in conjunction with increased hip flexion, could translate to a longer first step. Increased trunk lean shifts the take-off trajectory angle towards the horizontal. A greater trajectory angle at start take-off, which could be advantageous for force production during sprint performance, is likely necessary for beach flags.
- Differences in ground contact time explain the less efficient running economy in north african runners. [Journal Article]
- Biol Sport 2013 Sep; 30(3):181-7.
The purpose of this study was to investigate the relationship between biomechanical variables and running economy in North African and European runners. Eight North African and 13 European male runners of the same athletic level ran 4-minute stages on a treadmill at varying set velocities. During the test, biomechanical variables such as ground contact time, swing time, stride length, stride frequency, stride angle and the different sub-phases of ground contact were recorded using an optical measurement system. Additionally, oxygen uptake was measured to calculate running economy. The European runners were more economical than the North African runners at 19.5 km · h(-1), presented lower ground contact time at 18 km · h(-1) and 19.5 km · h(-1) and experienced later propulsion sub-phase at 10.5 km · h(-1),12 km · h(-1), 15 km · h(-1), 16.5 km · h(-1) and 19.5 km · h(-1) than the European runners (P < 0.05). Running economy at 19.5 km · h(-1) was negatively correlated with swing time (r = -0.53) and stride angle (r = -0.52), whereas it was positively correlated with ground contact time (r = 0.53). Within the constraints of extrapolating these findings, the less efficient running economy in North African runners may imply that their outstanding performance at international athletic events appears not to be linked to running efficiency. Further, the differences in metabolic demand seem to be associated with differing biomechanical characteristics during ground contact, including longer contact times.
- Landing quality in artistic gymnastics is related to landing symmetry. [Journal Article]
- Biol Sport 2013 Mar; 30(1):29-33.
In gymnastics every exercise finishes with a landing. The quality of landing depends on subjective (e.g. biomechanical) and objective (e.g. mechanical characteristics of landing area) factors. The aim of our research was to determine which biomechanical (temporal, kinematic and dynamic) characteristics of landing best predict the quality of landing. Twelve male gymnasts performed a stretched forward and backward salto; also with 1/2, 1/1 and 3/2 turns. Stepwise multiple regression extracted five predictors which explained 51.5% of landing quality variance. All predictors were defining asymmetries between legs (velocities, angles). To avoid asymmetric landings, gymnasts need to develop enough height; they need higher angular momentum around the transverse and longitudinal axis and they need to better control angular velocity in the longitudinal axis.
- Are There Differences Between the Upper and Lower Parts of the Superficial Musculoaponeurotic System? A Preliminary Biomechanical Study. [JOURNAL ARTICLE]
- Aesthet Surg J 2014 Apr 17.
Background:The superficial musculoaponeurotic system (SMAS) becomes thinner and gradually disappears from the midface. In rhytidectomy, manipulation of the SMAS occurs in the lateral area, and previous research has focused primarily on the SMAS region as a whole.Objectives:In this preliminary study, the authors compared the viscoelasticity of the upper and lower regions of the SMAS using biomechanical techniques.Methods:Two adjacent projection regions of the SMAS were designated: region 1 and region 2, representing the upper and lower parts, respectively. The SMAS tissues from 8 fresh-frozen cadaver heads were cut into 64 samples before biomechanical testing, and the following variables were recorded for subsequent analysis: stress-strain curve, elastic modulus, ultimate strength, and elongation at break.Results:The stiffness of region 1 was markedly greater than that of region 2. Energy dissipation was greater in region 2. Elastic modulus and ultimate strength were significantly higher for region 1, and elongation at break was longer in region 2. The fit curve of the 2 regions deviated markedly.Conclusions:The biomechanical properties of the upper and lower regions of the lateral SMAS are functionally different. Such knowledge will help refine the planning and design of facial surgery and improve outcomes for patients who undergo rhytidectomy.
- Biocompatibility of MG-63 cells on collagen, poly-L-lactic acid, hydroxyapatite scaffolds with different parameters. [JOURNAL ARTICLE]
- J Appl Biomater Funct Mater 2014 Apr 11.:0.
Purpose: In this study, osteoblast-like MG-63 cells were cultured on 3 different scaffold types composed of (a) collagen + poly-L-lactic acid (PLLA), (b) collagen + hydroxyapatite (HA; 30ºC) or (c) collagen + hydroxyapatite (HA; 37ºC) and produced with different porosities. Methods: Biomechanical properties of the scaffolds were characterized by tensile strength measurements. Properties of the cell-seeded scaffolds were evaluated with scanning electron microscopy (SEM). Cell adhesion and proliferation capacities were evaluated. Alkaline phosphatase (ALP) levels in media were measured. Transmission electron microscopy (TEM) and histological analyses were used to assess morphological characteristics.ResultsOur results showed that collagen-based PLLA and HA scaffolds have good cell biocompatibility. MTT test showed that the scaffolds exhibited no cytotoxicity. According to the force and displacement data, collagen + HA at 37ºC showed the highest mechanical strength and displacement. Conclusion: The results suggest that collagen-based PLLA and HA scaffolds might improve osteoblastic growth in vitro and have biomaterial integration potential in possible therapeutic approaches for future clinical studies.
- Iris concavity, corneal biomechanics and their correlations to ocular biometry in a cohort of 10-12 year old UK school boys: baseline data. [JOURNAL ARTICLE]
- Invest Ophthalmol Vis Sci 2014 Apr 17.
Purpose: Pigment dispersion syndrome is associated with iris concavity. This study investigated the prevalence of iris concavity, defined as a measurement of≤ -0.1mm, in a cohort of 10-12 year old boys and explored the relationship between iris curvature and anterior segment biometry. Associations with corneal biomechanical parameters were also explored. Methods:A cohort of school boys (n=96) was recruited from a local school. Anterior segment optical coherence tomography (AS-OCT) (VisanteTM, Carl Zeiss Meditec, Inc., Dublin, CA) was performed under accommodative and non-accommodative conditions and iris curvature quantified. Corneal hysteresis (CH) and corneal resistance factor (CRF) were measured with the Ocular Response Analyzer (ORA). Non-contact axial biometry was performed using laser interferometry. Results:The prevalence of iris concavity was 24% on distance fixation increasing to 65% on accommodation. Variables significantly associated with non-accommodating iris curvature were lens vault (P = 0.02) and mean keratometry (P = 0.02). For both variables acting jointly, R(2) = 0.30. Variables significantly associated with accommodating iris curvature were anterior chamber depth (P = 0.009), lens vault (P = 0.049) and mean scleral spur angle (P < 0.0001). For these 3 variables acting jointly, R(2) = 0.33. Significant association was found between CH and spur-to-spur distance (R(2) = 0.07, P = 0.025). Conclusions:Iris concavity was a common finding in this cohort and related to anterior segment biometric parameters. Further work is required to clarify whether anatomical differences exist between iris concavity seen in the adolescent eye and that found in adults with pigment dispersion syndrome.
- Mental Representation and Mental Practice: Experimental Investigation on the Functional Links between Motor Memory and Motor Imagery. [Journal Article]
- PLoS One 2014; 9(4):e95175.
Recent research on mental representation of complex action has revealed distinct differences in the structure of representational frameworks between experts and novices. More recently, research on the development of mental representation structure has elicited functional changes in novices' representations as a result of practice. However, research investigating if and how mental practice adds to this adaptation process is lacking. In the present study, we examined the influence of mental practice (i.e., motor imagery rehearsal) on both putting performance and the development of one's representation of the golf putt during early skill acquisition. Novice golfers (N = 52) practiced the task of golf putting under one of four different practice conditions: mental, physical, mental-physical combined, and no practice. Participants were tested prior to and after a practice phase, as well as after a three day retention interval. Mental representation structures of the putt were measured, using the structural dimensional analysis of mental representation. This method provides psychometric data on the distances and groupings of basic action concepts in long-term memory. Additionally, putting accuracy and putting consistency were measured using two-dimensional error scores of each putt. Findings revealed significant performance improvements over the course of practice together with functional adaptations in mental representation structure. Interestingly, after three days of practice, the mental representations of participants who incorporated mental practice into their practice regime displayed representation structures that were more similar to a functional structure than did participants who did not incorporate mental practice. The findings of the present study suggest that mental practice promotes the cognitive adaptation process during motor learning, leading to more elaborate representations than physical practice only.