Current peri-operative imaging concepts surrounding shoulder arthroplasty.

Glenohumeral osteoarthritis is a prevalent degenerative disease that can lead to excruciating pain and debility. End-stage osteoarthritis can be treated by both conservative and surgical interventions. Along with a comprehensive history and physical exam, pre-operative imaging with plain radiographs, computerized tomography, and magnetic resonance imaging plays an essential role in the decision-making process guiding whether the patient undergoes a shoulder hemiarthroplasty, anatomic total shoulder arthroplasty, or a reverse total shoulder arthroplasty. The most important pre-operative imaging factors are the integrity of the rotator cuff and presence of significant glenoid erosion. Imaging is also critical postoperatively, as signs of prosthetic loosening, rotator cuff failure (especially involving the subscapularis), periprosthetic fracture, and stress fractures are important entities to recognize. This article will review pertinent imaging findings related to the pre- and post-operative management of patients with glenohumeral osteoarthritis.

Understanding successful and unsuccessful landings of aerial maneuver variations in professional surfing.

Although performing aerial maneuvers can increase wave score and winning potential in competitive surfing, the critical features underlying successful aerial performance have not been systematically investigated. This study aimed to analyze highly skilled aerial maneuver performance and to identify the critical features associated with successful or unsuccessful landing. Using video recordings of the World Surf League's Championship Tour, every aerial performed during the quarterfinal, semifinal, and final heats from the 11 events in the 2015 season was viewed. From this, 121 aerials were identified with the Frontside Air (n = 15) and Frontside Air Reverse (n = 67) being selected to be qualitatively assessed. Using chi-squared analyses, a series of key critical features, including landing over the center of the surfboard (FS Air χ2  = 14.00, FS Air Reverse χ2  = 26.61; P < .001) and landing with the lead ankle in dorsiflexion (FS Air χ2  = 3.90, FS Air Reverse χ2  = 13.64; P < .05), were found to be associated with successful landings. These critical features help surfers land in a stable position, while maintaining contact with the surfboard. The results of this study provide coaches with evidence to adjust the technique of their athletes to improve their winning potential.

Effect of aging on breast skin thickness and elasticity: implications for breast support.

BACKGROUND/PURPOSE: The skin overlying a woman's breast acts as an anatomical support structure to the breast. Although aging is known to affect the thickness and elasticity of human skin, limited research has examined age-related changes to skin covering the breast or related these changes to breast support requirements. The purpose of this study was to determine the effect of age on female breast skin thickness and elasticity. METHODS: The left breast of 339 women (18-84 years), classified into four age groups (18-24 years, 25-44 years, 45-64 years, and 65 + years), was divided into four quadrants. Skin thickness (dermal layer; 20 MHz ultrasound probe) and skin elasticity (Cutometer® MPA 580) were measured for each breast quadrant and then compared to determine whether there was any significant (P < 0.05) effect of aging on breast skin. RESULTS: Breast skin thickness significantly decreased from 45 years of age onwards. A significant decline in breast skin elasticity was evident from the mid 20's. CONCLUSION: Aging is associated with a significant decline in breast skin thickness and elasticity, which is likely to reduce anatomical breast support. Women might therefore benefit from increased external breast support (i.e. a more supportive bra) with increasing age.

Previously identified patellar tendinopathy risk factors differ between elite and sub-elite volleyball players.

Patellar tendinopathy is the most common knee injury incurred in volleyball, with its prevalence in elite athletes more than three times that of their sub-elite counterparts. The purpose of this study was to determine whether patellar tendinopathy risk factors differed between elite and sub-elite male volleyball players. Nine elite and nine sub-elite male volleyball players performed a lateral stop-jump block movement. Maximum vertical jump, training history, muscle extensibility and strength, three-dimensional landing kinematics (250 Hz), along with lower limb neuromuscular activation patterns (1500 Hz), and patellar tendon loading were collected during each trial. Multivariate analyses of variance (P < 0.05) assessed for between-group differences in risk factors or patellar tendon loading. Significant interaction effects were further evaluated using post-hoc univariate analysis of variance tests. Landing kinematics, neuromuscular activation patterns, patellar tendon loading, and most of the previously identified risk factors did not differ between the elite and sub-elite players. However, elite players participated in a higher training volume and had less quadriceps extensibility than sub-elite players. Therefore, high training volume is likely the primary contributor to the injury discrepancy between elite and sub-elite volleyball players. Interventions designed to reduce landing frequency and improve quadriceps extensibility are recommended to reduce patellar tendinopathy prevalence in volleyball players.

Variations in jump height explain the between-sex difference in patellar tendon loading during landing.

Patellar tendinopathy is the most common overuse knee injury in volleyball, with men reporting more than twice the injury prevalence than women. Although high patellar tendon loading is thought to be a causative factor of patellar tendinopathy, it is unknown whether between-sex variations in landing technique account for differences in patellar tendon loading. It was hypothesized that male volleyball players would display differences in landing technique and would generate higher patellar tendon loading than their female counterparts. The landing technique and patellar tendon loading of 20 male and 20 female volleyball players performing a lateral stop-jump block movement were collected. Independent t-tests were used to identify any between-sex differences in landing technique with the data grouped to account for differences in jump height and in anthropometry. Male volleyball players were taller and heavier, landed from a higher height, displayed differences in landing kinematics, generated a significantly greater knee extensor moment, and experienced higher patellar tendon loading than female players when all 40 participants were compared. However, when participants were matched on jump height, they generated similar patellar tendon loading, irrespective of their sex. These results imply that jump height is a more important determinant of patellar tendon loading than sex.

Passive dorsiflexion stiffness is poorly correlated with passive dorsiflexion range of motion.

OBJECTIVES: The purpose of this study was to determine the relationships among passive measures of weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness, thereby establishing whether they assess similar mechanical characteristics, as each measure has been implicated in injury risk during landings. DESIGN: Cross-sectional study. METHODS: Passive weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness were quantified for 42 males (22.8±5.0 years). The relationship between each data set was calculated using Pearson product-moment correlation coefficients. RESULTS: Although weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were significantly correlated, the strength of the relationship was poor (r(2)=0.18; p=0.004). Weight-bearing dorsiflexion range of motion (mean=43.0±5.0°) was significantly greater than non-weight-bearing dorsiflexion range of motion (29.8±5.9°; p<0.001) and weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were also poorly correlated with passive dorsiflexion stiffness (1.48±0.55Nm°(-1); r(2)=0.04 and r(2)=0.14, respectively), despite the latter relationship being significant (p=0.017). CONCLUSIONS: Passive dorsiflexion stiffness was not strongly associated with dorsiflexion range of motion, despite the significant correlation in the non-weight-bearing condition. It must be acknowledged that passive dorsiflexion stiffness was weakly associated with dorsiflexion range of motion, although the strength of the association suggests that it may not necessarily determine dorsiflexion range of motion. Furthermore, the functional dorsiflexion limits of the ankle during weight-bearing tasks may be underestimated or misrepresented by non-weight-bearing measures of dorsiflexion range of motion. Therefore, although ankle dorsiflexion range of motion and dorsiflexion stiffness have been implicated in injury risk during weight-bearing tasks such as landings, it may be due to different mechanisms.

Determining the osmolality of over-concentrated and supplemented infant formulas.

BACKGROUND: Hyperosmolar infant feeds can cause osmotic diarrhoea and may be a risk factor for necrotising enterocolitis; the osmolality of infant formula is therefore usually <400 mOsm kg(-1) . However, in fluid-restricted infants and those needing nutritional support, formulas may be over-concentrated or supplemented. The present study aimed to determine the effect of these practices on osmolality. METHODS: A clinical laboratory osmometer was used to measure the osmolality of infant formulas. The effect of over-concentration and supplementation on osmolality was then determined using three and seven different infant formulas, respectively. Osmolalities were measured in triplicate. RESULTS: The effect of over-concentration was shown to be linear using Pepti Junior (Cow & Gate, Trowbridge, UK) at concentrations of 12.8% (standard), 17% and 19%. This linear relationship was also demonstrated with Enfamil A.R. (Mead Johnson Nutritionals, Uxbridge, UK) (15%) and Neocate (SHS International Ltd, Liverpool, UK) (21%). The effect of individual additives on osmolality was found to be similar for the seven infant formulas. All preparations of SMA High Energy (SMA Nutrition, Maidenhead, UK) and five of the 12 preparations of Nutriprem 1 (Cow & Gate) exceeded an osmolality of 400 mOsm kg(-1) . CONCLUSIONS: The effect of over-concentrating infant formulas was shown to be linear, meaning that the osmolality at different concentrations can be predicted accurately. The over-concentrated infant formulas that were measured in the present study did not exceed 400 mOsm kg(-1) , with the exception of 21% Neocate, which would not be used in practice. When supplemented, some infant formulas exceeded an osmolality of 400 mOsm kg(-1) ; this may be relevant in cases of feed intolerance or in those at risk of necrotising enterocolitis.

Effects of passive ankle dorsiflexion stiffness on ankle mechanics during drop landings.

OBJECTIVES: Vertical landing tasks strain the Achilles tendon and plantar-flexors, increasing acute and overuse strain injury risk. This study aimed to determine how passive ankle dorsiflexion stiffness affected ankle mechanics during single limb drop landings at different vertical descent velocities. DESIGN: Cross-sectional study. METHODS: Passive ankle dorsiflexion stiffness and passive weight-bearing dorsiflexion range of motion (DROM) were quantified for 42 men. Participants were then grouped as having low (LPS: 0.94±0.15 Nm°â»¹; n=16) or high (HPS: 2.05±0.36 Nm°â»¹; n=16; p<0.001) passive ankle dorsiflexion stiffness. Three-dimensional ankle joint kinematics was quantified while participants performed drop landings onto a force platform at two vertical descent velocities (slow: 2.25±0.16 ms⁻¹; fast: 3.21±0.17 ms⁻¹). RESULTS: Although affected by landing velocity, there were no significant effects of passive ankle dorsiflexion stiffness, nor any significant ankle dorsiflexion stiffness×vertical descent velocity interactions on any outcome variables characterising ankle mechanics during drop landings. Furthermore, there was no significant difference between the groups for passive weight-bearing DROM (LPS: 43.9±4.1°; HPS: 42.5±5.7°), indicating that the results were not confounded by between-group differences in ankle range of motion. CONCLUSIONS: Neither high nor low passive ankle dorsiflexion stiffness was found to influence ankle biomechanics during drop landings at different descent velocities. Landing strategies were moderated more by the demands of the task than by passive ankle dorsiflexion stiffness, indicating that passive ankle dorsiflexion stiffness may not affect plantar-flexor strain during a drop landing.

Characterizing patellar tendon loading during the landing phases of a stop-jump task.

Excessive extensor mechanism loading from repeated landing has been associated with overuse knee injuries, especially patellar tendinopathy. In order to reduce these loads, it is important to establish which landing task places the highest load on the patellar tendon. It was hypothesized that the horizontal landing would create higher patellar tendon force (F(PT)) compared with the vertical landing. Sixteen male athletes with healthy patellar tendons performed five successful trials of a stop-jump task, which involved a symmetrical two-foot landing after a horizontal approach (horizontal landing) followed by another symmetrical two-foot landing after a vertical jump (vertical landing). For both lower limbs during each trial, the participants' ground reaction forces were recorded, three-dimensional kinematics measured and F(PT) calculated by dividing the net knee joint moment by the patellar tendon moment arm. Compared with the vertical landing, significantly higher F(PT), posterior ground reaction forces and F(PT) loading rates were generated during the horizontal landing, despite lower vertical ground reaction forces (F(V)), highlighting the notion that F(V) should not be used to reflect F(PT). Understanding that a horizontal landing task places the highest load on the patellar tendon, provides an appropriate framework for future research to investigate lower limb landing strategies in athletes with patellar tendinopathy.

Are the feet of obese children fat or flat? Revisiting the debate.

OBJECTIVE: There is debate as to the effects of obesity on the developing feet of children. We aimed to determine whether the flatter foot structure characteristic of obese primary school-aged children was due to increased medial midfoot plantar fat pad thickness (fat feet) or due to structural lowering of the longitudinal arch (flat feet). METHODS AND PROCEDURES: Participants were 75 obese children (8.3 ± 1.1 years, 26 boys, BMI 25.2 ± 3.6 kg m(-2)) and 75 age- and sex-matched non-obese children (8.3 ± 0.9 years, BMI 15.9 ± 1.4 kg m(-2)). Height, weight and foot dimensions were measured with standard instrumentation. Medial midfoot plantar fat pad thickness and internal arch height were quantified using ultrasonography. RESULTS: Obese children had significantly greater medial midfoot fat pad thickness relative to the leaner children during both non-weight bearing (5.4 and 4.6 mm, respectively; P<0.001) and weight bearing (4.7 and 4.3 mm, respectively; P < 0.001). The obese children also displayed a lowered medial longitudinal arch height when compared to their leaner counterparts (23.5 and 24.5 mm, respectively; P = 0.006). CONCLUSION: Obese children had significantly fatter and flatter feet compared to normal weight children. The functional and clinical relevance of the increased fatness and flatness values for the obese children remains unknown.

Does a drop landing represent a whole skill landing and is this moderated by fatigue?

This study aimed to determine whether the landing phase of a drop landing (DL) differed with respect to a complete jumping and landing task, a spike jump (SJ), and whether fatigue altered the landing of these movements. Fourteen male volleyball players performed five DL and SJ in a counterbalanced order under two experimental conditions: non-fatigued and fatigued. Fatigue, induced by repetitive jumping sets, was confirmed by decrements in vertical jump height >25% and increased blood lactate >6 mmol/L. Each landing task was characterized by the resultant ground reaction forces (GRF), sagittal plane kinematics and muscle recruitment patterns of six lower extremity muscles. Two-way repeated analysis of variance results indicated a main effect of movement on many of the GRF, kinematic and electromyographic variables characterizing landing, indicating that the two tasks required substantially different lower limb biomechanics during landing. Although fatigue did not alter the GRF in either task, there were significant movement x fatigue condition interactions. The significant between-task differences in the biomechanical variables characterizing landing and the differential effects of fatigue on each landing task, question the validity of using a DL as an experimental task to investigate lower limb landing mechanics of whole jumping and landing movements.

The impact of child and adolescent obesity treatment interventions on physical activity: a systematic review.

Efforts to treat obesity in childhood and adolescence would benefit from a greater understanding of evidence-based strategies to modify physical activity behaviour. A systematic review was conducted to examine the impact of child and adolescent obesity treatment interventions on physical activity. Studies included were randomized controlled trials or controlled trials, with overweight and obese youth (aged < 18 years), which reported statistical analysis of free-living physical activity at pretreatment and post-treatment. Two independent reviewers assessed each study for methodological quality. Seventeen child and three adolescent studies were retrieved, half of which were conducted in the USA. Studies were characterized by small samples of limited cultural and economic diversity. Fifteen studies reported an increase in at least one physical activity outcome at post-test or follow-up. Overall, study quality was rated as low (child median score = 3/10, range = 0-9; adolescent median score = 3/10, range = 2-5) with three child studies classified as high quality (>or=6/10). Research evaluating the effect of child and adolescent obesity treatment trials on physical activity is limited in both quantity and quality. Studies testing innovative, theoretically driven treatment approaches that use robust methodologies are required to better understand generalizable approaches for promoting physical activity participation among obese youth.

What are the breast support choices of Australian women during physical activity?

OBJECTIVES: This study aimed to quantify the breast support wearing and purchasing habits of young women and to assess factors that affect their sports bra usage during physical activity. DESIGN: Study results were obtained from a self-administered mail survey, which was posted to participants after gaining their verbal consent via random telephone recruitment. PARTICIPANTS: 413 women aged 20 to 35 years were recruited from New South Wales, Australia. RESULTS: From the returned (65%) surveys only 41% of respondents currently wore an encapsulating sports bra during physical activity, primarily due to a lack of awareness of the importance of good breast support during physical activity. Bra size was a predictor of sports bra usage, whereby participants with large breasts were more than twice as likely to wear a sports bra as their smaller-breasted counterparts. CONCLUSIONS: It was concluded that, although encapsulating sports bras have been shown to effectively reduce breast motion and associated exercise-induced breast discomfort, these bras were not the breast support option most commonly chosen by young women during physical activity. It is recommended that all women, irrespective of breast size, be educated on the importance of wearing a well-fitted and supportive bra during physical activity to decrease excessive strain on breast tissue structures and related breast discomfort.

How do respiratory state and measurement method affect bra size calculations?

OBJECTIVES: To investigate the effects of respiratory state and measurement method on bra size calculation. METHODS: The bra sizes of 16 large-breasted women were measured during two respiratory states, end voluntary inspiration and relaxed voluntary expiration, and using two sizing methods, which were compared against subject-reported bra sizes. RESULTS: Both respiratory state and measurement method significantly affected bra size estimations, whereby measuring chest circumference during inspiration increased both band and decreased cup size. However, whereas bra size calculated using the standard method differed significantly from subject-reported bra size, cup size calculated using the breast hemi-circumference method did not differ significantly from subject-reported cup size. CONCLUSIONS: As respiratory state significantly affects bra sizes, it should be standardised during bra size measurements. A more valid and reliable bra sizing method should be developed, possibly using the breast hemi-circumference method for cup size estimations and raw under-bust chest circumference values for band size.

Musculoskeletal disorders associated with obesity: a biomechanical perspective.

Despite the multifactorial nature of musculoskeletal disease, obesity consistently emerges as a key and potentially modifiable risk factor in the onset and progression of musculoskeletal conditions of the hip, knee, ankle, foot and shoulder. To date, the majority of research has focused on the impact of obesity on bone and joint disorders, such as the risk of fracture and osteoarthritis. However, emerging evidence indicates that obesity may also have a profound effect on soft-tissue structures, such as tendon, fascia and cartilage. Although the mechanism remains unclear, the functional and structural limitations imposed by the additional loading of the locomotor system in obesity have been almost universally accepted to produce aberrant mechanics during locomotor tasks, thereby unduly raising stress within connective-tissue structures and the potential for musculoskeletal injury. While such mechanical theories abound, there is surprisingly little scientific evidence directly linking musculoskeletal injury to altered biomechanics in the obese. For the most part, even the biomechanical effects of obesity on the locomotor system remain unknown. Given the global increase in obesity and the rapid rise in musculoskeletal disorders, there is a need to determine the physical consequences of continued repetitive loading of major structures of the locomotor system in the obese and to establish how obesity may interact with other factors to potentially increase the risk of musculoskeletal disease.

The impact of childhood obesity on musculoskeletal form.

Despite the greater prevalence of musculoskeletal disorders in obese adults, the consequences of childhood obesity on the development and function of the musculoskeletal system have received comparatively little attention within the literature. Of the limited number of studies performed to date, the majority have focused on the impact of childhood obesity on skeletal structure and alignment, and to a lesser extent its influence on clinical tests of motor performance including muscular strength, balance and locomotion. Although collectively these studies imply that the functional and structural limitations imposed by obesity may result in aberrant lower limb mechanics and the potential for musculoskeletal injury, empirical verification is currently lacking. The delineation of the effects of childhood obesity on musculoskeletal structure in terms of mass, adiposity, anthropometry, metabolic effects and physical inactivity, or their combination, has not been established. More specifically, there is a lack of research regarding the effect of childhood obesity on the properties of connective tissue structures, such as tendons and ligaments. Given the global increase in childhood obesity, there is a need to ascertain the consequences of persistent obesity on musculoskeletal structure and function. A better understanding of the implications of childhood obesity on the development and function of the musculoskeletal system would assist in the provision of more meaningful support in the prevention, treatment and management of the musculoskeletal consequences of the condition.

The biomechanics of restricted movement in adult obesity.

In spite of significant advances in the knowledge and understanding of the multi-factorial nature of obesity, many questions regarding the specific consequences of the disease remain unanswered. In particular, there is a relative dearth of information pertaining to the functional limitations imposed by overweight and obesity. The limited number of studies to date have mainly focused on the effect of obesity on the temporospatial characteristics of walking, plantar foot pressures, muscular strength and, to a lesser extent, postural balance. Collectively, these studies have implied that the functional limitations imposed by the additional loading of the locomotor system in obesity result in aberrant mechanics and the potential for musculoskeletal injury. Despite the greater prevalence of musculoskeletal disorders in the obese, there has been surprisingly little empirical investigation pertaining to the biomechanics of activities of daily living or into the mechanical and neuromuscular factors that may predispose the obese to injury. A better appreciation of the implications of increased levels of body adiposity on the movement capabilities of the obese would afford a greater opportunity to provide meaningful support in preventing, treating and managing the condition and its sequelae. Moreover, there is an urgent need to establish the physical consequences of continued repetitive loading of major structures of the body, particularly of the lower limbs in the obese, during the diverse range of activities of daily living.

What are the effects of obesity in children on plantar pressure distributions?

OBJECTIVE: This study examined the effects of obesity on static and dynamic plantar pressure distributions displayed by children. DESIGN: Field-based experimental data on body mass index (BMI) and plantar pressures were collected for 10 obese children and 10 nonobese controls. SUBJECTS: In all, 10 obese (age 8.8+/-2.0 y, BMI 25.8+/-3.8 kg m(-2)) children matched to 10 nonobese children (age 8.9+/-2.1 y, BMI 16.8+/-2.0 kg m(-2)), for gender, age and height. MEASUREMENTS: Height and weight were measured to calculate BMI. Right and left foot plantar pressures were obtained using an AT-4 emed pressure platform (Novel(gmbh), Munich) to calculate the peak force and pressure experienced under areas of each child's feet during static and dynamic conditions. RESULTS: While standing, the obese children generated significantly higher forces over a larger foot area and experienced significantly higher plantar pressures compared to their nonobese counterparts (41.8+/-17.7; 30.1+/-12.0 N cm(-2), respectively; P<0.022). Similarly, while walking, the obese children generated significantly higher forces over all areas of their feet, except the toes. Despite distributing these higher forces over a significantly larger foot area when walking, the obese children experienced significantly higher plantar pressures in the midfoot (P<0.003) and under the second to fifth metatarsal heads (P<0.006) compared to the nonobese children. CONCLUSIONS: It is postulated that obese children are at an increased risk of developing foot discomfort and/or foot pathologies due to increased plantar loads being borne by the small forefoot bones. Furthermore, continual bearing of excessive mass by children appears to flatten the medial midfoot region during walking. As the long-term consequences of these increased plantar loads are currently unknown, it is recommended that the effects of obesity on the structural and functional characteristics of obese children's feet be further investigated.

The force-velocity relationship of the human soleus muscle during submaximal voluntary lengthening actions.

In experiments on isolated animal muscle, the force produced during active lengthening contractions can be up to twice the isometric force, whereas in human experiments lengthening force shows only modest, if any, increase in force. The presence of synergist and antagonist muscle activation associated with human experiments in situ may partly account for the difference between animal and human studies. Therefore, this study aimed to quantify the force-velocity relationship of the human soleus muscle and assess the likelihood that co-activation of antagonist muscles was responsible for the inhibition of torque during submaximal voluntary plantar flexor efforts. Seven subjects performed submaximal voluntary lengthening, shortening(at angular, velocities of +5, -5, +15, -15 and +30, and -30 degrees s(-1)) and isometric plantar flexor efforts against an ankle torque motor. Angle-specific (90 degrees ) measures of plantar flexor torque plus surface and intramuscular electromyography from soleus, medial gastrocnemius and tibialis anterior were made. The level of activation (30% of maximal voluntary isometric effort) was maintained by providing direct visual feedback of the soleus electromyogram to the subject. In an attempt to isolate the contribution of soleus to the resultant plantar flexion torque, activation of the synergist and antagonist muscles were minimised by: (1) flexing the knee of the test limb, thereby minimising the activation of gastrocnemius, and (2) applying an anaesthetic block to the common peroneal nerve to eliminate activation of the primary antagonist muscle, tibialis anterior and the synergist muscles, peroneus longus and peroneus brevis. Plantar flexion torque decreased significantly ( P<0.05) after blocking the common peroneal nerve which was likely due to abolishing activation of the peroneal muscles which are synergists for plantar flexion. When normalised to the corresponding isometric value, the force-velocity relationship between pre- and post-block conditions was not different. In both conditions, plantar flexion torques during shortening actions were significantly less than the isometric torque and decreased at faster velocities. During lengthening actions, however, plantar flexion torques were not significantly different from isometric regardless of angular velocity. It was concluded that the apparent inhibition of lengthening torques during voluntary activation is not due to co-activation of antagonist muscles. Results are presented as mean (SEM).

Effect of verbal instructions on muscle activity and risk of injury to the anterior cruciate ligament during landing.

BACKGROUND: Minimising the likelihood of injury to the anterior cruciate ligament (ACL) during abrupt deceleration requires proper synchrony of the quadriceps and hamstring muscles. However, it is not known whether simple verbal instructions can alter landing muscle activity to protect the knee. OBJECTIVE: To assess the efficacy of verbal instructions to alter landing muscle activity. METHODS: Twenty four athletes landed abruptly in single limb stance. Sagittal plane motion was recorded with an optoelectric device, and ground reaction force and surface electromyographic data were recorded for the rectus femoris, vastus lateralis, biceps femoris, and semimembranosus muscles. Subjects performed 10 landings per condition: normal landing (N); repeat normal landing (R); landing after instruction to increase knee flexion (K); and landing after instruction to recruit hamstring muscles earlier (M). Muscle bursts immediately before landing were analysed relative to initial foot-ground contact (IC). RESULTS: The K condition resulted in significantly (p