DO GROUND REACTION FORCES REFLECT TIBIOFEMORAL JOINT LOADING IN ANTERIOR CRUCIATE LIGAMENT DEFICIENT SUBJECTS?

INTRODUCTION: Physiological loading imposed on the knee is composed of joint forces that the knee must transmit to support, accelerate and decelerate body mass, and muscle forces acting to control knee motion and provide stability. Although not representing quantification of muscle forces, ground reaction forces (GRF) are often used to estimate knee loading, particularly in studies examining injury mechanisms such as anterior cruciate ligament (ACL) rupture. The purpose of this study was to examine the relationship between GRF and tibiofemoral forces generated by control and ACL deficient (ACLD) patients during a task known to stress the knee, namely abrupt deceleration. METHODS: Eleven functional chronic unilateral ACLD patients and 11 uninjured matched controls landed in single-limb stance on a Kistler force platform after catching a chest level pass and then decelerating abruptly. Sagittal plane kinematics of each subject’s landing action were digitized (200 Hz) and GRF data were sampled (1000 Hz) for 3 trials per lower extremity. Joint reaction forces and sagittal planar net moments of force for the knee were calculated using Newtonian equations of motion and inverse dynamics. Tibiofemoral joint shear (FS) and compressive forces (FC) were derived using the method of Kuster et al. (1994). Pearson product moment correlations were calculated between temporal (ms) and magnitude (BW) aspects of the GRF and tibiofemoral force data to determine the relationship between these parameters for the two subject groups, analysed both individually and when the results were combined. RESULTS: Although the relationship between the magnitude of the anteriorposterior (Fx) and vertical (Fy) GRF components and the magnitude of FS and FC was high for controls, it was low for ACLDs (Table 1). However, the time from initial foot-ground contact (IC) to peak Fx was highly related to the time from IC to peak FS in both subject groups. CONCLUSIONS: It was concluded that the magnitude of GRF data should not be used to estimate loading imposed on the tibiofemoral joint in ACLD patients. However, timing of Fx may provide insight into timing of shear forces at the knee during dynamic tasks. Kuster, M., Wood, G. A., Sakurai, S., Blatter, G. (1994). Downhill Walking: A Stressful Task for the Anterior Cruciate Ligament? A Biomechanical Study with Clinical Implications. Knee Surgery, Sports Traumatology, Arthroscopy, 2, 2-7

Knee function of chronic ACLD patients during static knee laxity assessment and dynamic deceleration

Treatment of anterior cruciate ligament deficient (ACLD) patients is complicated by difficulty in accurately predicting those patients who will be functionally impaired by ACL rupture and those who will have minimum symptoms. Although the effects of ACL rupture on knee function during locomotor tasks have been studied, no research was located which examined whether the use of compensatory adaptations by ACL D subjects to perform dynamic tasks could be associated with knee function during knee laxity assessment. Therefore, the purpose of the thesis was to establish the relationship between knee function during arthrometric knee laxity assessment and knee function during a dynamic movement known to stress the ACL, namely abrupt deceleration. To achieve this three studies were conducted to establish a standardised arthrometric knee laxity assessment protocol using the Dynamic Cruciate Tester (DCT) and to verify reliability of the protocol (Experimental Section A). In Study 1 active and passive knee laxity was assessed for 10 uninjured subjects before and after the subjects cycled for 10 minutes and then performed hamstring stretches. As there were no significant differences between anterior tibial translation (ATT), knee extension force, or hamstring activity pre- compared to post-warm up it was concluded that a warm up suitable for use with ACLD patients was not required before arthrometric knee laxity assessment. In Study 2 active and passive knee laxity of 12 controls and 12 ACL D subjects was assessed with the subjects in three torso positions: vertical, reclined, and supine; while electromyographic (EMG) data were collected for the hamstring and quadriceps muscles. Although there was no significant difference in mean ATT as a function of torso position, subjects displayed significantly greater hamstring activity when seated vertically or reclined compared to when supine. As torso position also significantly affected knee extension force, it was recommended patients be supine during arthrometric knee laxity assessment to minimise muscle guarding. In Study 3 reproducibility of ATT and knee extension force data were examined for 13 ACLD subjects and 16 controls. The ATT and knee extension force results were found to be highly reproducible between and within test days. However, as a significant main effect of trial was found on ATT, a pretrial was recommended before knee laxity assessment to enhance reproducibility of the results. It was concluded that, following the standardised protocol, the DC T was a reliable tool to characterise ATT and isometric knee extension deficits and to monitor hamstring guarding by chronic ACL D subjects during active and passive arthrometric knee laxity assessment. Once the arthrometric assessment protocol was established, a kinematic, kinetic, and neuromuscular analysis was conducted of 11 chronic functional ACL D subjects and 11 matched controls performing a deceleration task (landing in single-limb stance after catching a ball) after each subject\u27s lower extremity strength and knee laxity were assessed (Experimental Section B). Compared to the controls, the ACLD subjects displayed: lower Lysholm knee scores; significantly lower peak knee extension torques assessed isokinetically (60°-s1); no evidence of knee flexion strength deficits and no significant reduction in thigh circumference; a significantly greater mean passive gap but a negligible limb-to-limb difference in active ATT; greater hamstring cocontraction during anterior tibial drawer to restrict excessive ATT; and took longer during active assessment to deactivate rectus femoris and vastus lateralis after reaching their maximal knee extension effort. During the deceleration task no significant alterations were evident in the kinematic parameters analysed at either Initial Contact (IC) or Peak Resultant Ground Reaction Force (PRGRF) or in the ground reaction forces generated by the ACL D subjects. However, compared to the controls, the ACL D subjects displayed: significantly less knee flexion motion from IC to PRGRF; a higher tibiofemoral compressive force (Fc) at IC caused by higher knee flexion moments; a delay in hamstring activation so that peak hamstring activity was more synchronous with IC and with the high tibiofemoral shear forces (F,) which occurred post IC; but no evidence of quadriceps-avoidance nor any increase in hamstring cocontraction intensity. These between-subject group differences were thought to be functional adaptations employed by the ACL D subjects to stabilise their involved knee against a giving-way episode via increased joint compression and posterior tibial drawer in preparation to withstand, rather than reduce or avoid, the high anterior F, generated during deceleration. Landing technique adaptations displayed by ACL D subjects were evident only at IC with the hamstring and quadriceps muscles activated before IC. These findings supported the notion that subjects preprogrammed their deceleration strategy before landing in anticipation of the joint loads. Although increased hamstring guarding during arthrometric knee laxity assessment and restricted knee flexion motion during deceleration were displayed bilaterally, alterations in Fc, knee flexion moments, and hamstring sequencing during deceleration were not transferred to the contralateral limb. It was postulated that task novelty or upper extremity motion involved in catching the ball may have interfered with the ACL D subjects\u27 motor programs developed to control lower extremity muscle function during deceleration. Thirty five correlations between variables characterising knee laxity and deceleration were significant across the pooled subject group results. However, the correlations were low (r = 0.299 - 0.483) such that most of the variance within the variables characterising knee function during deceleration could not be explained by their relationship to the variables characterising knee function during arthrometric knee laxity assessment. Therefore, although providing information pertaining to functional status during a closed isometric knee extension effort or during passive anterior tibial loading, it was concluded that the DC T could not be used to predict knee function of ACL D subjects during an open dynamic deceleration task

THE BIOMECHANICS OF BETTER BRAS: IMPROVING SUPPORT AND COMFORT DURING EXERCISE

The purpose of this paper is to provide an overview of a selected sample of key studies arising from research programs investigating the biomechanics of breast health and sports bra design. Examples have been provided to highlight how relevant research questions pertaining to sports bra design have been developed based on surveys of target cohorts and then how biomechanics principles have been applied to systematically investigate these research questions. Further examples have then been described to show how the scientific results of these applied biomechanics studies have been translated into practice and educational resources to improve bra fit and bra design so that women, irrespective of age, breast size, or disease status, can exercise in comfort and enjoy the health benefits associated with an active lifestyle

EFFECT OF MATCH PLAY ON THE KINEMATICS OF ONE-HANDED STATIONARY NETBALL SHOOTING

Anecdotal evidence has suggested that at the completion of a competitive netball match, shooters may experience match tiredness or fatigue that may negatively influence their shooting technique and accuracy. Although several studies have examined the effect of fatigue on the performance of sport skills such as running, no studies were found which examined the influence of match play on the mechanics of netball goal shooting. The purpose of the present study was therefore to identify the effect of match play on the kinematics of one-handed stationary netball shooting performed by 10 highly skilled shooters (mean age = 23 * 3.4 years). Subjects were filmed performing one-handed stationary shots for goal 3.0 m from the post, before and immediately after (within 5 minutes of match completion) participating in one of their scheduled New South Wales Netball Association State League Competition (Division 1) matches. The shooting action was filmed using a 16 mm LOCAM Model 5001 high speed camera (100 Hz; lateral view) and a Panasonic M7 VHS video camera (25 Hz; anterior view). Two successful representative shots, one before and one after the competition match, were selected for analysis for each subject The two trials per subject were digitised and smoothed using a second order Butterworth filter (cutoff = 10 Hz). Linear velocities, joint and segmental angles, and amplitudes of segmental movement were derived from the smoothed displacement data for each shot. The subjects' shooting accuracy was also quantified during match play via game analysis procedures. T-tests for dependent means showed there was no significant difference (p < 0 05) in the kinematics of one-handed shooting performed by the subjects when standing 3.0 from the goal post before and immediately after a competition netball match Observations of individual subject results reflected this high consistency in shooting technique, despite the limited number of shots analysed per subject. It was concluded the spatial and temporal aspects of the shooting technique of this sample of highly skilled netball shooters were sufficiently automated to prevent changes in technique as a consequence of the physical demands of participating in a competition match

Obese older adults suffer foot pain and foot-related functional limitation

There is evidence to suggest being overweight or obese places adults at greater risk of developing foot complications such as osteoarthritis, tendonitis and plantar fasciitis. However, no research has comprehensively examined the effects of overweight or obesity on the feet of individuals older than 60 years of age. Therefore we investigated whether foot pain, foot structure, and/or foot function is affected by obesity in older adults. Three hundred and twelve Australian men and women, aged over 60 years, completed validated questionnaires to establish the presence of foot pain and health related quality of life. Foot structure (anthropometrics and soft tissue thickness) and foot function (ankle dorsiflexion strength and flexibility, toe flexor strength, plantar pressures and spatiotemporal gait parameters) were also measured. Obese participants (BMI \u3e30) were compared to those who were overweight (BMI = 25-30) and not overweight (BMI \u3c25). Obese participants were found to have a significantly higher prevalence of foot pain and scored significantly lower on the SF-36. Obesity was also associated with foot-related functional limitation whereby ankle dorsiflexion strength, hallux and lesser toe strength, stride/step length and walking speed were significantly reduced in obese participants compared to their leaner counterparts. Therefore, disabling foot pain and altered foot structure and foot function are consequences of obesity for older adults, and impact upon their quality of life. Interventions designed to reduce excess fat mass may relieve loading of the foot structures and, in turn, improve foot pain and quality of life for older obese individuals

Bra strap orientations and designs to minimise bra strap discomfort and pressure during sport and exercise in women with large breasts

Background Bra straps are a primary source of discomfort during sport and exercise, particularly for women with large breasts. This study aimed to investigate the effects of altering bra strap orientation and design on bra strap comfort, pressure and breast support in women with large breasts. This is a descriptive laboratory study. Methods Bra strap discomfort (visual analogue scale, 0 to 10), pressure (custom-designed 10 mm2 calibrated pressure sensor, 0.5 to 24 kPa range, 50 Hz, S2011, Novel GmbH, Munich, Germany, placed under the right bra strap at the crest of each participant\u27s shoulder), preference ranking and vertical breast displacement (VBD; Optotrak Certus® motion capture system, 200 Hz, Northern Digital, Ontario, Canada) data during dynamic treadmill running and static upright standing (pressure only) were collected for 23 active women with large breasts (D+ cup size) while they wore an encapsulation sports bra with six different bra strap conditions (two bra strap orientations: vertical and cross-back; three bra strap designs: standard width, wide and gel). Results Bra strap discomfort was significantly less (p ≤ 0.001) in the vertical compared to the cross-back strap orientation, which was the most preferred orientation despite no significant difference in strap pressure. The wide strap design had the lowest discomfort scores, significantly lower strap pressure compared to the standard width and gel strap designs (p \u3c 0.001), and was equally the most preferred design with the gel straps. There was no significant difference in VBD among the six strap conditions. Conclusions Bra straps that are vertically orientated and wide (approximately 4.5 cm in width) are preferable for women with large breasts during sport and exercise to minimise bra strap pressure and discomfort. The addition of gel pads under bra straps may also decrease discomfort and prevent straps slipping off the shoulders, although this notion warrants further investigation

SPLIT-STEP VS SIDE-STEP EVASIVE RUNNING MANOEUVRES: WHICH IS MORE PROTECTIVE OF THE ACL?

Side-step movements are typically performed by athletes involved in sports that require the player to evade their opponents. However, the combination of internal rotation, valgus and flexion at the knee during side-stepping places high demands on the ACL such that these movements have been associated with a high incidence of ACL injury (Ebstrup & Bojsen-Moller, 2000). An alternative technique to the side-step is the split-step. Traditionally used in court sports, the split-step is characterised by a more symmetrical approach to the cut movement relative to the side-step and, due to the more even distribution of the ground reaction forces across two lower limbs, may provide greater protection to the ACL. However, as there has been no systematic comparison of the side-step versus the split-step technique, this study aimed to characterise differences in lower limb biomechanics during unplanned side-step and split-step movements, with implications for ACL injury prevention

LANDING TECHNIQUE IS RELATED TO PATELLAR TENDON LOADING DURING A VOLLEYBALL BLOCK JUMP MOVEMENT

Patellar tendinopathy is the most common overuse injury incurred in volleyball. Although high patellar tendon loading is thought to be a causative factor of patellar tendinopathy, it remains unknown how landing technique is related to high patellar tendon loading. Landing kinematics and patellar tendon loading were quantified for 49 volleyball players who performed a lateral stop-jump block movement. Correlations identified that volleyball players who displayed high ankle dorsiflexion velocity, high ankle dorsiflexion acceleration, and high knee flexion acceleration also generated greater peak patellar tendon force and faster patellar tendon force development. These results suggest that athletes who demonstrate rapid ankle and knee flexion when landing may be predisposed to developing patellar tendinopathy

CHARACTERISING SUCCESSFUL AND UNSUCCESSFUL AERIAL MANOEUVRES IN PROFESSIONAL SURFING COMPETITIONS

Although aerials are an effective way for a competitive surfer to increase their score during surfing competitions, less than half of aerial attempts are landed successfully during competition. This study aimed to identify which characteristics of performing an aerial during competition were associated with either a successful or unsuccessful landing. Video images of 121 aerials performed during the finals series of the 201 5 World Championship Tour season were qualitatively analysed. The Frontside Air Reverse was found to be the most commonly performed aerial, with critical features of landing, particularly features that improved a surfer's balanced landing position, significantly associated with successful aerials. These results provide evidence upon which coaches can modify a surfer's technique to encourage higher successful aerial completion rates

Fat flat frail feet: how does obesity affect the older foot

The prevalence of obesity is rising throughout the world at an alarming rate, and the elderly are no exception with 15% of men and 28% of women aged over 60 years considered to be obese [1]. Overweight and obesity have been shown to negatively affect foot structure and function in both children [2] and adults [3]. These structural changes appear to be associated with increased foot discomfort whereby overweight children have been found to report foot pain significantly more often than their leaner counterparts [4]. As feet are our base of support during most weight-bearing activities, it is postulated that increased foot pain could act as a deterrent for obese individuals to participate in physical activity and, in turn, perpetuate the cycle of obesity. For this reason compromised foot structure and foot pain associated with obesity is deemed a major health issue for children. However, whether these negative effects associated with childhood obesity persist in the elderly foot has not been comprehensively investigated. Therefore, the purpose of this study was to determine the effects of obesity on foot structure and function, and the foot pain experienced by older adults