Effectiveness of hard inserts in sports mouthguards: a systematic review.

Objectives To improve the protective capacity of conventional ethylene-vinyl acetate mouthguards, some authors have suggested reinforcement with a hard material to distribute impact energy more widely. The research question for this systematic review was: 'does the inclusion of a hard insert in mouthguards improve the protection of anterior teeth from a direct blow?'Data sources Three bibliographic databases (PubMed/Medline, Ovid/Embase and the Cochrane CENTRAL databases) were searched up to 20 February 2021. Additional searches included hand searching of key articles and journals.Data selection A systematic search of the literature included studies where the intervention was the incorporation of hard material into sports mouthguards and where the comparator was conventional mouthguard material. Eligibility required the use of anatomical specimens or anatomical analogues which included or represented anterior maxillary teeth. Twelve eligible publications were identified.Data extraction Data extraction was first carried out independently by two reviewers. Discrepancies were resolved by discussion.Data synthesis Results of individual studies were conflicting and methodological diversity created difficulty in making a synthesis of results. All studies employed low-energy impacts that did not represent the potentially high-energy impacts encountered in sport.Conclusion The efficacy of hard inserts in sports mouthguards has not been demonstrated.

Maturity-Associated Differences in Match Running Performance in Elite Male Youth Soccer Players.

PURPOSE: To investigate the influence of maturation on match running performance in elite male youth soccer players. METHODS: A total of 37 elite male youth soccer participants from an English professional soccer academy from the U14s, U15s, and U16s age groups were assessed over the course of 1 competitive playing season (2018-2019). Relative biological maturity was assessed using percentage of predicted adult height. A global positioning system device was used between 2 and 30 (mean = 8 [5]) times on each outfield player. The position of each player in each game was defined as defender, midfielder, or attacker and spine or lateral. A total of 5 match-running metrics were collected total distance covered, high-speed running distance, very high-speed running distance, maximum speed attained, and number of accelerations. RESULTS: Relative biological maturity was positively associated with all global positioning system running metrics for U14s. The U15/16s showed variation in the associations among the global positioning system running metrics against maturity status. A multilevel model which allowed slopes to vary was the best model for all parameters for both age groups. In the U14 age group, advanced maturation was associated with greater high-speed running distance. However, maturation did not contribute toward variance in any of the indices of running performance in the U15/16s. In the U15/16 age group, significance was observed in the spine/lateral playing positions when undertaking actions that required covering distance at high speeds. CONCLUSIONS: Maturation appeared to have an impact on match-running metrics within the U14s cohort. However, within the U15/16s, the influence of maturation on match-running metrics appeared to have less of an impact.

Greater maintenance of bone mineral content in male than female athletes and in sprinting and jumping than endurance athletes: a longitudinal study of bone strength in elite masters athletes.

We investigated longitudinal changes in tibia bone strength in master power (jumping and sprinting) and endurance (distance) athletes of both sexes. Bone mass but not cross-sectional moment of inertia was better maintained in power than endurance athletes over time, particularly in men and independent of changes in performance. OBJECTIVE: Assessment of effects of sex and athletic discipline (lower limb power events, e.g. sprint running and jumping versus endurance running events) on longitudinal changes in bone strength in masters athletes. METHODS: We examined tibia and fibula bone properties at distal (4% distal-proximal tibia length) and proximal (66% length) sites using peripheral quantitative computed tomography (pQCT) in seventy-one track and field masters athletes (30 male, 41 female, age at baseline 57.0 ± 12.2 years) in a longitudinal cohort study that included at least two testing sessions over a mean period of 4.2 ± 3.1 years. Effects of time, as well as time × sex and time × discipline interactions on bone parameters and calf muscle cross-sectional area (CSA), were examined. RESULTS: Effects of time were sex and discipline-dependent, even following adjustment for enrolment age, sex and changes in muscle CSA and athletic performance. Male sex and participation in power events was associated with better maintenance of tibia bone mineral content (BMC, an indicator of bone compressive strength) at 4% and 66% sites. In contrast, there was no strong evidence of sex or discipline effects on cross-sectional moment of inertia (CSMI, an indicator of bone bending and torsional strength-P > 0.3 for interactions). Similar sex and discipline-specific changes were also observed in the fibula. CONCLUSIONS: Results suggest that male athletes and those participating in lower limb power-based rather than endurance-based disciplines have better maintenance of bone compressive but not bending and torsional strength.

Predicting the timing of the peak of the pubertal growth spurt in elite male youth soccer players: evaluation of methods.

BACKGROUND: Three commonly used non-invasive protocols are implemented to estimate the timing at which PHV most likely occurs. Accurate estimation of circumpubertal years can aid in managing training load of adolescent athletes. AIM: Three protocols were compared against observed age at PHV: an estimate of 13.8 ± 1.0 years - generic age at PHV (from longitudinal measures); an estimate based on the maturity offset equation, predicted age at PHV ±1.0 year; a window of PHV based on 85-96% of predicted adult height at time of observation. SUBJECTS AND METHODS: A final sample of 23 (from 28) adolescent male participants were selected from the academy of an English Premier League club. Anthropometric measures were collected across five playing seasons; age at PHV was estimated with Super-Imposition by Translation and Rotation (SITAR). The three protocols were compared based on measures at 13.0 years. Results and Conclusions: An age window based on predicted maturity offset did not improve estimation of PHV compared to generic age method; however, the percentage of predicted adult height window showed improvement in performance shown by the following results. Predicted age at PHV correctly assigned 15 participants (65%) as experiencing PHV, while the percentage height correctly assigned 17 participants (74%). Generic age and predicted age at PHV correctly predicted observed age at PHV for 14 participants (61%), percentage of adult height window correctly predicted 22 participants (96%).

Elongation differences between the sub-tendons of gastrocnemius medialis and lateralis during plantarflexion in different frontal plane position of the foot.

BACKGROUND: Gastrocnemius medialis (GM) and lateralis (GL) act at the ankle complex in the sagittal and frontal planes and there is evidence that their actions can be somewhat uncoupled from each other. Some independence of GM and GL from each other could be advantageous, e.g. to stabilise the ankle complex in unstable walking conditions. Given the compartmentalised structure of the Achilles tendon, the sub-tendons of GM and GL may exhibit different elongation during plantarflexion contractions, particularly with the foot in different frontal plane positions. RESEARCH QUESTIONS: METHODS: Sub-tendon elongation was determined from 18 participants during ramped isometric plantarflexion contractions to 70% of their maximum voluntary contraction (MVC) level with the foot in neutral, inversion and eversion. One-dimensional statistical parametric mapping was applied to determine elongation differences. RESULTS: Elongation within a sub-tendon did not differ in the three foot positions. Elongation was similar between both sub-tendons at very low contraction levels, but GM sub-tendon elongation exceeded GL sub-tendon displacement significantly from 30% MVC. The elongation differences between the sub-tendons were not affected by foot position. SIGNIFICANCE: Greater GM sub-tendon elongation is likely caused by the greater force production capability of GM but may also indicate that the sub-tendons of GM and GL have different mechanical properties, which is currently unknown. Elongation differences were contraction level dependent suggesting that contributions of GM and GL to plantarflexion torque may also be contraction level dependent.

Circulating Tumor Necrosis Factor Alpha May Modulate the Short-Term Detraining Induced Muscle Mass Loss Following Prolonged Resistance Training.

INTRODUCTION: Tumor necrosis factor alpha (TNFα) is a pro-inflammatory cytokine that has been shown to modulate muscle mass, and is responsive to exercise training. The effects of resistance training (RT) followed by a short period of detraining on muscle size, architecture and function in combination with circulating TNFα levels have not been previously investigated in a young, healthy population. METHODS: Sixteen participants (8 males and 8 females) were randomly assigned to a training group (TRA; age 20 ± 3 years, mass 76 ± 7 kg), whilst fourteen participants (7 males and 7 females) age 22 ± 2 years, mass 77 ± 6 kg were assigned to a control group (CON). Measures of vastus lateralis (VL) muscle size (normalized physiological cross-sectional area allometrically scaled to body mass; npCSA), architecture (fascicle length; LF, pennation angle Pθ), strength (knee extensor maximal voluntary contraction; KE MVC), specific force, subcutaneous fat (SF) and circulating TNFα were assessed at baseline (BL), post 8 weeks RT (PT), and at two (DT1) and four (DT2) weeks of detraining. RESULTS: Pooled BL TNFα was 0.87 ± 0.28 pg/mL with no differences between groups. BL TNFα tended to be correlated with npCSA (p = 0.055) and KEMVC (p = 0.085) but not specific force (p = 0.671) or SF (p = 0.995). There were significant (p < 0.05) increases in npCSA compared to BL and CON in TRA at PT, DT1, and DT2, despite significant (p < 0.05) decreases in npCSA compared to PT at DT1 and DT2. There were significant (p < 0.05) increases in LF, Pθ and KE MVC at PT but only LF and torque at DT1. There were no significant (p > 0.05) changes in SF, specific force or TNFα at any time points. There was a significant correlation (p = 0.022, r = 0.57) between the relative changes in TNFα and npCSA at DT2 compared to PT. DISCUSSION: Neither RT nor a period of short term detraining altered the quality of muscle (i.e., specific force) despite changes in morphology and function. TNFα does not appear to have any impact on RT-induced gains in muscle size or function, however, TNFα may play a role in inflammatory-status mediated muscle mass loss during subsequent detraining in healthy adults.

Effect of mouthguard design on retention and potential issues arising with usability in sport.

BACKGROUND/AIMS: Mouthguard retention could potentially increase an athlete's motivation to wear the device, due to potential improvements in physical comfort. The aim of this study was to examine the retentive properties of selected customised mouthguard designs, during normal conditions (dry) and within the presence of artificial saliva (wet). Additionally, the correlation between thickness and retention was investigated. MATERIAL AND METHODS: Six different custom mouthguard designs (MG1-MG6) reported in previous studies, were pressure-formed with 2 and 4 mm blanks accordingly. Thickness was measured 10 times at seven anatomical points and the mean (±SD) was recorded. A novel rig was fabricated to connect the mouthguards to a Hounsfield H10KS Tensometer, which was used to fully displace each device from the model at a constant rate of 50 mm/min. The test was repeated under both dry and wet conditions. RESULTS: Retention forces recorded at the anterior region demonstrated higher measurements under wet conditions than dry (P < 0.001). The total retention of the mouthguards was influenced by alterations in their design. Trend analysis indicated that 64% of MG retention could be explained by their thickness under dry conditions and 55% when wet. CONCLUSIONS: Design and thickness of mouthguards are key factors in retention. Mouthguard fabrication techniques should be considered in order to minimize dislodgment of the devices as well as potentially increasing the wearability of mouthguards during sport.

Gender associated muscle-tendon adaptations to resistance training.

PURPOSE: To compare the relative changes in muscle-tendon complex (MTC) properties following high load resistance training (RT) in young males and females, and determine any link with circulating TGFß-1 and IGF-I levels. METHODS: Twenty-eight participants were assigned to a training group and subdivided by sex (T males [TM] aged 20±1 year, n = 8, T females [TF] aged 19±3 year, n = 8), whilst age-matched 6 males and 6 females were assigned to control groups (ConM/F). The training groups completed 8 weeks of resistance training (RT). MTC properties (Vastus Lateralis, VL) physiological cross-sectional area (pCSA), quadriceps torque, patella tendon stiffness [K], Young's modulus, volume, cross-sectional area, and length, circulating levels of TGFß-1 and IGF-I were assessed at baseline and post RT. RESULTS: Post RT, there was a significant increase in the mechanical and morphological properties of the MTC in both training groups, compared to ConM/F (p<0.001). However, there were no significant sex-specific changes in most MTC variables. There were however significant sex differences in changes in K, with females exhibiting greater changes than males at lower MVC (Maximal Voluntary Contraction) force levels (10% p = 0.030 & 20% MVC p = 0.032) and the opposite effect seen at higher force levels (90% p = 0.040 & 100% MVC p = 0.044). There were significant increases (p<0.05) in IGF-I in both TF and TM following training, with no change in TGFß-1. There were no gender differences (p>0.05) in IGF-I or TGFß-1. Interestingly, pooled population data showed that TGFß-1 correlated with K at baseline, with no correlations identified between IGF-I and MTC properties. CONCLUSIONS: Greater resting TGFß-1 levels are associated with superior tendon mechanical properties. RT can impact opposite ends of the patella tendon force-elongation relationship in each sex. Thus, different loading patterns may be needed to maximize resistance training adaptations in each sex.

Achilles tendon moment arm in humans is not affected by inversion/eversion of the foot: a short report.

The triceps surae primarily acts as plantarflexor of the ankle joint. However, the group also causes inversion and eversion at the subtalar joint. Despite this, the Achilles tendon moment arm is generally measured without considering the potential influence of inversion/eversion of the foot during plantarflexion. This study investigated the effect of foot inversion and eversion on the plantarflexion Achilles tendon moment arm. Achilles tendon moment arms were determined using the centre-of-rotation method in magnetic resonance images of the left ankle of 11 participants. The foot was positioned at 15° dorsiflexion, 0° or 15° plantarflexion using a Styrofoam wedge. In each of these positions, the foot was either 10° inverted, neutral or 10° everted using an additional Styrofoam wedge. Achilles tendon moment arm in neutral foot position was 47.93 ± 4.54 mm and did not differ significantly when the foot was positioned in 10° inversion and 10° eversion. Hence, inversion/eversion position of the foot may not considerably affect the length of the Achilles tendon moment arm. This information could be useful in musculoskeletal models of the human lower leg and foot and when estimating Achilles tendon forces during plantarflexion with the foot positioned in inversion or eversion.

Muscle-Tendon Unit Properties during Eccentric Exercise Correlate with the Creatine Kinase Response.

Aim: The aim of this paper was to determine whether; (1) patella tendon stiffness, (2) the magnitude of vastus lateralis fascicle lengthening, and (3) eccentric torque correlate with markers of exercise induced muscle damage. Method: Combining dynamometry and ultrasonography, patella tendon properties and vastus lateralis architectural properties were measured pre and during the first of six sets of 12 maximal voluntary eccentric knee extensions. Maximal isometric torque loss and creatine kinase activity were measured pre-damage (-48 h), 48, 96, and 168 h post-damage as markers of exercise-induced muscle damage. Results: A significant increase in creatine kinase (883 ± 667 UL) and a significant reduction in maximal isometric torque loss (21%) was reported post-eccentric contractions. Change in creatine kinase from pre to peak significantly correlated with the relative change in vastus lateralis fascicle length during eccentric contractions (r = 0.53, p = 0.02) and with eccentric torque (r = 0.50, p = 0.02). Additionally, creatine kinase tended to correlate with estimated patella tendon lengthening during eccentric contractions (p < 0.10). However, creatine kinase did not correlate with resting measures of patella tendon properties or vastus lateralis properties. Similarly, torque loss did not correlate with any patella tendon or vastus lateralis properties at rest or during eccentric contractions. Conclusion: The current study demonstrates that the extent of fascicle strain during eccentric contractions correlates with the magnitude of the creatine kinase response. Although at rest, there is no relationship between patella tendon properties and markers of muscle damage; during eccentric contractions however, the patella tendon may play a role in the creatine kinase response following EIMD.

The effect of model inclination during fabrication on mouthguard calliper-measured and CT scan-assessed thickness.

AIM: Excessive material thinning has been observed in the production of custom-made mouthguards in a number of studies, due to production anomalies that may lead to such thinning. This study investigated thinning material patterns of custom-made mouthguards when the anterior angulation of dental model was increased during the thermoforming process. MATERIALS AND METHODS: A total of 60 samples of mouthguard blanks were thermoformed on identical maxillary models under four anterior inclination conditions (n = 4 × 15): control 0, 15, 30 and 45°. Each mouthguard sample was measured, using an electronic calliper gauge at three anatomical points (anterior labial sulcus, posterior occlusion and posterior lingual). Mouthguards were then CT scanned to give a visual representation of the surface thickness. RESULTS: Data showed a significant difference (P < 0.005) in the anterior mouthguard thickness between the four levels of anterior inclination, with the 45° inclination producing the thickest mouthguards, increasing the mean anterior thickness by 75% (2.8 mm, SD: 0.16) from the model on a flat plane (1.6 mm, SD: 0.34). Anterior model inclination of 30 and 45° inclinations increased consistencies between the thickest and thinnest mouthguards in the anterior region of these sample groups. CONCLUSION: This study highlights the importance of standardizing the thermoforming process, as this has a significant effect on the quality and material distribution of the resultant product. In particular, greater model inclination is advised as this optimizes the thickness of the anterior sulcus of the mouthguard which may be more prominently at risk from sport-related impact.

An investigation into the relationship between thickness variations and manufacturing techniques of mouthguards.

BACKGROUND: The aim of this study was to measure the finished thickness of a single identical 4-mm EVA mouthguard model from a large fabricated sample group and to evaluate the degree of material thinning and variations during the fabrication process. MATERIALS AND METHODS: Twenty boxes were distributed to dental technician participants, each containing five duplicated dental models (n = 100), alongside 5 × 4 mm mouthguard blanks and a questionnaire. The mouthguards were measured using electronic callipers (resolution: ±0.01 mm) at three specific points. The five thickest and thinnest mouthguards were examined using a CT scanner to describe the surface typography unique to each mouthguard, highlighting dimensional thinning patterns during the fabrication process. RESULTS: Of the three measurement points, the anterior sulcus point of the mouthguard showed a significant degree of variation (up to 34% coefficient of variation), in finished mouthguard thickness between individuals. The mean thickness of the mouthguards in the anterior region was 1.62 ± 0.38 mm with a range of 0.77-2.80 mm. This variation was also evident in the occlusion and posterior lingual regions but to a lesser extent (up to 12.2% and 9.8% variations, respectively). CONCLUSION: This study highlights variability in the finished thickness of the mouthguards especially in the anterior sulcus region measurement point, both within and between individuals. At the anterior region measurement point of the mouthguard, the mean thickness was 1.62 mm, equating to an overall material thinning of 59.5% when using a single 4-mm EVA blank. This degree of thinning is comparative to previous single operator research studies.

Obesity decreases both whole muscle and fascicle strength in young females but only exacerbates the aging-related whole muscle level asthenia.

Obesity has previously been associated with greater muscle strength. Aging, on the other hand, reduces muscle specific force (the force per unit physiological cross-sectional area [PCSA] of muscle). However, neither the effect of obesity on skeletal muscle specific force nor the combined effects of aging and obesity on this parameter are known. This study aimed to describe the interplay between body mass index (BMI)/adiposity, aging, and skeletal muscle specific force. Ninety-four untrained healthy women categorized by age into young (Y; mean ± SD: 25.5 ± 9.0 years) versus old (O; 64.8 ± 7.2 years) were assessed for body composition, gastrocnemius medialis (GM) muscle volume (V), net maximum voluntary contraction (nMVC), and specific force (SF). The young obese, while demonstrating 71% and 29% (P < 0.001) higher V and nMVC compared to normal BMI individuals, were in fact 26% (P = 0.007) weaker than these, where V was used to scale nMVC (i.e., nMVC/V). The weakness associated with obesity was further exemplified in the 34% (P < 0.001) lower SF relative to normal BMI individuals. Similarly, ≥40% body fat was associated with 60% and 27% (P < 0.001) higher V and nMVC, but 11% and 25% (P < 0.01) lower nMVC/V and SF than <40% body fat. The aging-related rates of decline in V (-2 cm(3)/year P < 0.05) and nMVC (-1.2 cm(3)/year P < 0.05) were highest in obesity defined by BMI. This effect was also seen when segregating by >40% adiposity. Interestingly, however, obesity appeared advantageous to the aging-related changes in nMVC/V (P < 0.001) and SF (P < 0.001). Unlike previous reports of greater strength in the obese compared with leaner age-matched counterparts, we in fact demonstrate that the young sedentary obese, are substantially weaker, where the volume of skeletal muscle is used to scale the maximal torque output, or forces are quantified at the fascicular level. The seemingly positive impact of obesity on rate of aging, however, is complex and warrants further investigations.

Muscular adaptations and insulin-like growth factor-1 responses to resistance training are stretch-mediated.

INTRODUCTION: Modulation of muscle characteristics was attempted through altering muscle stretch during resistance training. We hypothesized that stretch would enhance muscle responses. METHODS: Participants trained for 8 weeks, loading the quadriceps in a shortened (SL, 0-50° knee flexion; n=10) or lengthened (LL, 40-90°; n=11) position, followed by 4 weeks of detraining. Controls (CON; n=10) were untrained. Quadriceps strength, vastus lateralis architecture, anatomical cross-sectional area (aCSA), and serum insulin-like growth factor-1 (IGF-1) were measured at weeks 0, 8, 10, and 12. RESULTS: Increases in fascicle length (29±4% vs. 14±4%), distal aCSA (53±12% vs. 18±8%), strength (26±6% vs. 7±3%), and IGF-1 (31±6% vs. 7±6%) were greater in LL compared with SL muscles (P<0.05). No changes occurred in CON. Detraining decrements in strength and aCSA were greater in SL than LL muscles (P<0.05). CONCLUSIONS: Enhanced muscle in vivo (and somewhat IGF-1) adaptations to resistance training are concurrent with muscle stretch, which warrants its inclusion within training.

Impact of range of motion during ecologically valid resistance training protocols on muscle size, subcutaneous fat, and strength.

The impact of using different resistance training (RT) kinematics, which therefore alters RT mechanics, and their subsequent effect on adaptations remain largely unreported. The aim of this study was to identify the differences to training at a longer (LR) compared with a shorter (SR) range of motion (ROM) and the time course of any changes during detraining. Recreationally active participants in LR (aged 19 ± 2.6 years; n = 8) and SR (aged 19 ± 3.4 years; n = 8) groups undertook 8 weeks of RT and 4 weeks of detraining. Muscle size, architecture, subcutaneous fat, and strength were measured at weeks 0, 8, 10, and 12 (repeated measures). A control group (aged 23 ± 2.4 years; n = 10) was also monitored during this period. Significant (p > 0.05) posttraining differences existed in strength (on average 4 ± 2 vs. 18 ± 2%), distal anatomical cross-sectional area (59 ± 15 vs. 16 ± 10%), fascicle length (23 ± 5 vs. 10 ± 2%), and subcutaneous fat (22 ± 8 vs. 5 ± 2%), with LR exhibiting greater adaptations than SR. Detraining resulted in significant (p > 0.05) deteriorations in all muscle parameters measured in both groups, with the SR group experiencing a more rapid relative loss of postexercise increases in strength than that experienced by the LR group (p > 0.05). Greater morphological and architectural RT adaptations in the LR (owing to higher mechanical stress) result in a more significant increase in strength compared with that of the SR. The practical implications for this body of work follow that LR should be observed in RT where increased muscle strength and size are the objective, because we demonstrate here that ROM should not be compromised for greater external loading.

The manipulation of strain, when stress is controlled, modulates in vivo tendon mechanical properties but not systemic TGF-ß1 levels.

Modulators of loading-induced in vivo adaptations in muscle-tendon complex (MTC) mechanical properties remain unclear. Similarly contentious, is whether changes in MTC characteristics are associated with growth factor levels. Four groups were subjected to varying magnitudes of stress/strain: Group 1 trained with the MTC at a shortened position (MTCS; n = 10); Group 2 at a lengthened position (MTCL; n = 11; stress levels matched to MTCS); Group 3 over a wide range of motion (MTCX; n = 11); and Group 4 (n = 10) was the control population (no training). Patella tendon Stiffness (P < 0.001), Young's modulus, and quadriceps torque (P < 0.05) increments (only seen in the training groups), showed MTCL and MTCX groups responses to be superior to those of MTCS (P < 0.05). In addition, MTCL and MTCX better maintained adaptations compared to MTCS (P < 0.05) following detraining, with a pattern of slower loss of improvements at the early phase of detraining in all training groups. There were no significant changes (P > 0.05) in antagonist cocontraction, patella tendon dimensions or circulating transforming growth factor beta (TGF-ß1) levels following training or detraining in any of the groups. We conclude that chronically loading the MTC in a relatively lengthened position (which involves greater strains) enhances its mechanical properties, more so than loading in a shortened position. This is true even after normalizing for internal stress. The underlying endocrine mechanisms do not appear to be mediated via TGF-ß1, at least not at the systemic level. Our findings have implications with regard to the effectiveness of eccentric loading on improved tendon structural and mechanical properties.

A review of facial protective equipment use in sport and the impact on injury incidence.

Sporting activities have an inherent risk of facial injury from traumatic impacts from fellow competitors, projectiles, and collisions with posts or the ground. This retrospective review systematically describes the interplay between the type of sport (including the level at which specific sports are played), the sex of the players and their musculoskeletal characteristics, the technology behind the materials used, the protective devices commonly used, the anatomical site, and the regularity of incidence of fractures. We describe how variations in sporting activities induce different orofacial fracture patterns, and critically consider the methods used to test protective headgear against more contemporary techniques. Facial injuries can have a profound psychological effect on those injured, can take a long time to heal, and have been known to end promising careers. Use of properly fitted protective head or facial equipment could reduce the number of facial fractures commonly seen in sports. We recommend that individual sports should have full risk assessments, and that mandatory standards should be agreed about protective devices that would be appropriate.

Simulation of creep in non-homogenous samples of human cortical bone.

Characterising the mechanisms causing viscoelastic mechanical properties of human cortical bone, as well as understanding sources of variation, is important in predicting response of the bone to creep and fatigue loads. Any better understanding, when incorporated into simulations including finite element analysis, would assist bioengineers, clinicians and biomedical scientists. In this study, we used an empirically verified model of creep strain accumulation, in a simulation of 10 non-homogeneous samples, which were created from micro-CT scans of human cortical bone of the femur midshaft obtained from a 74-year-old female cadaver. These non-homogeneous samples incorporate the presence of Haversian canals and resorption cavities. The influence of inhomogeneity on the response and variation in the samples in both creep and stress relaxation tests are examined. The relationship between steady-state creep rate, applied loads (stress relaxation and creep tests) and microstructure, that is bone apparent porosity, is obtained. These relations may provide insight into damage accumulation of whole human bones and be relevant to studies on osteoporosis.

Effects of smoking on tibial and radial bone mass and strength may diminish with age.

PURPOSE: The purpose of the study was to assess the effect of cigarette smoking on indicators of bone strength across a wide age range, controlling for physical activity and neuromuscular performance. METHODS: We conducted a cross-sectional study with 41 smokers (mean age +/- SD, 41.0 +/- 16.1 yr) and 53 nonsmokers (47.5 +/- 18.2 yr) of both sexes. Bone strength indicators (BSI) were assessed in the lower leg and forearm by peripheral quantitative computed tomography along with physical activity, muscle cross-sectional area, and maximal voluntary muscle force. RESULTS: Physical activity level and muscle cross-sectional area of the leg and arm were similar in smokers and nonsmokers. Although trabecular volumetric bone mineral density and epiphyseal bone mineral content, both indicators of BSI, decreased with age in the nonsmokers' tibia (P < 0.001), this was not observed in the smokers (interaction age x smoking: P = 0.014 and P = 0.032 for density and content, respectively). Regression coefficients were nonsignificant in nonsmokers, whereas coefficients in smokers were -1.24 mg/cm x yr [95% confidence interval (CI) = -2.16-0.33; P = 0.01] for content and -1.20 mg/cm(3) x yr (95% CI = -1.76-0.62; P < 0.001) for trabecular density. The BSI values in the smokers were independent of their smoking history (r(2) = 0.000-0.021), and no effects of sex were observed in the smoking-related differences in BSI. CONCLUSIONS: Smoking compromises bone strength by diaphyseal marrow cavity expansion and epiphyseal trabecular bone content reductions. These effects seem to wane with age. The causes of the attenuated effect of smoking on bone at old age remain enigmatic but might be linked to an interaction between the smoke-related factors and senescence processes affecting bone.

A comparison of the physiologic effects of acute whole-body vibration exercise in young and older people.

OBJECTIVE: To examine the acute physiologic effects of acute whole-body vibration (WBV) exercise in young and older people. DESIGN: Every participant performed 9 conditions in a static squat position, consisting of no vibration and WBV at 30Hz and 3 loads corresponding to (1) no load (0% body mass), (2) load of 20% body mass, and (3) load of 40% body mass. A Jendrassik voluntary contraction was also performed with no vibration and WBV at 30Hz with no load and 20% body mass. SETTING: Laboratory facilities at a university in the United Kingdom. PARTICIPANTS: Healthy young people (n=12; 6 men, 6 women; mean age, 21.5y) and 12 healthy older people (6 men, 6 women; mean age, 69.2y) from the local community. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: The Physical Activity Questionnaire, anthropometric measures, counter-movement jump, and isometric maximal voluntary contraction with the Jendrassik maneuver were assessed in both groups. Oxygen uptake (Vo2), blood pressure, heart rate, and rating of perceived exertion (RPE) were recorded during WBV and load conditions as the outcome of the study. RESULTS: Both vibration and load were associated with an increase (P<.001) in Vo2 for older and young groups. WBV elicited the equivalent of a .35 metabolic equivalent (MET) increase in Vo2, with additional loads of 20% and 40% body mass increasing Vo2 by 0.8 and 1.2 METs, respectively. Additionally, there was an interaction effect of vibration and group in which the WBV-related Vo2 increase was less in the old compared with the young. Both vibration and load caused an increase in heart rate, blood pressure, and RPE (all P<.001); however, there were no significant group differences between young and older groups. The Jendrassik maneuver elicited an increase in Vo2 by 27.6% for the old and 33% for the young group (P<.001); however, there was no significant difference between groups. CONCLUSIONS: Vo2 significantly increased in both the older and young people with vibration and additional load and when the Jendrassik maneuver was superimposed with vibration and load. However, the elicited increase in Vo2 (1.2mL x kg(-1).min(-1)) from WBV may be an insufficient stimulus to improve cardiovascular fitness.