Does high-intensity running to fatigue influence lower limb injury risk?

OBJECTIVES: The aim of this study was to quantify changes in peak bending moments at the distal tibia, peak patellofemoral joint contact forces and peak Achilles tendon forces during a high-intensity run to fatigue at middle-distance speed. DESIGN: Observational study. METHODS: 16 high-level runners (7 female) ran on a treadmill at the final speed achieved during a preceding maximum oxygen uptake test until failure (~3 min). Three-dimensional kinetics and kinematics were used to derive and compare tibial bending moments, patellofemoral joint contact forces and Achilles tendon forces at the start, 33 %, 67 % and the end of the run. RESULTS: Average running speed was 5.7 (0.4) m·s-1. There was a decrease in peak tibial bending moments (-6.8 %, p = 0.004) from the start to the end of the run, driven by a decrease in peak bending moments due to muscular forces (-6.5 %, p = 0.001), whilst there was no difference in peak bending moments due to joint reaction forces. There was an increase in peak patellofemoral joint forces (+8.9 %, p = 0.026) from the start to the end of the run, but a decrease in peak Achilles tendon forces (-9.1 %, p < 0.001). CONCLUSIONS: Running at a fixed, high-intensity speed to failure led to reduced tibial bending moments and Achilles tendon forces, and increased patellofemoral joint forces. Thus, the altered neuromechanics of high-intensity running to fatigue may increase patellofemoral joint injury risk, but may not be a mechanism for tibial or Achilles tendon overuse injury development.

Effects of a range of 6 prefabricated orthotic insole designs on plantar pressure in a healthy population: A randomized, open-label crossover investigation.

BACKGROUND: Prefabricated orthotic insoles are widely commercially available for self-selection to treat foot and lower-body musculoskeletal pain, without requiring advice from health care professionals. Although they are generally designed to mimic traditional design features of custom-made orthotics used in clinical practice, the effects of prefabricated insoles on plantar pressure distribution are poorly understood. OBJECTIVE: This investigation aimed to evaluate and directly compare the effects of a range of 6 different commercially available prefabricated orthotic insole designs on plantar pressure in healthy individuals. METHODS: This was a single-center, randomized, open-label, crossover investigation. In-shoe dynamic pressure (F-scan) was investigated in 24 healthy subjects with normal foot posture, wearing standard shoes alone and in combination with 6 different orthotic insoles, consecutively, measured on a single day. The biomechanical impact of each insole was determined by the statistical significance of changes from baseline measurements (standard shoe alone). RESULTS: Insoles with heel cups and medial arch geometries consistently increased contact area at medial arch and whole-foot regions and reduced both plantar peak pressure (PP) and pressure time integral at medial arch and heel regions. CONCLUSIONS: This investigation has aided in further understanding the mode of action of prefabricated insoles in a healthy population. The insoles in this study redistributed plantar pressure at key regions of the foot, based on design features common to prefabricated insoles. Prefabricated orthotic insoles represent an easily accessible means of reducing lower-body musculoskeletal stress for those who spend prolonged periods of time on their feet.

'Probably just sexism'- gendered experiences of resource access in rugby.

Research pertaining to the experiences of women in rugby is scarce, which, coupled with the limited visibility of the sport and difficulty accessing resources, suggest that women's rugby remains undervalued. Indeed, evidence of such gender inequalities remains largely anecdotal, with little rigorous research undertaken to understand the perspectives of women in rugby. This study aimed to explore the experiences of a diverse cohort of rugby players in relation to their participation in the sport and their ability to access resources. Twenty UK-based rugby players (10 men, 9 women and 1 non-binary person aged 29.1 ± 8.3 years) from school, university, club, military, and semi-professional environments, volunteered to participate in semi-structured interviews (36 ± 12 minutes) discussing their rugby experiences in relation to their gender and playing level. Interviews were transcribed verbatim, and a reflexive thematic analysis was undertaken. A widespread under-prioritisation of women in rugby was highlighted. Gender biases were apparent in access to changing rooms, pitches, quality coaches, and playing opportunities, and were reportedly propagated at the managerial level. Irrespective of gender, some amateur players reported difficulty accessing a suitable rugby environment. Insufficient player numbers precluded the formation of second teams, often resulting in inexperienced players competing beyond their ability. Women's rugby players experienced considerable gender bias. This exploratory study highlights a need to address such issues to protect player welfare. Interventions to change the culture in rugby clubs and increased representation of women in managerial positions in rugby are recommended to enact meaningful change.

Concussion response and recovery in men and women's rugby union: A reflexive thematic analysis of player interviews.

Numerous concussion-management protocols have been developed in rugby, though little is known about player's personal experiences of concussion. Specifically, research typically refers to clinical recovery, with social and psychological sequelae post-concussion gaining little attention. This study aimed to explore the experiences of rugby players in relation to being concussed and recovering from concussion. UK-based rugby players (10 men, 9 women and 1 non-binary person) from school, university, club, military and semi-professional teams took part in semi-structured interviews (36 ± 12 minutes). Interviews were transcribed verbatim, and a reflexive thematic analysis was conducted. Players considered pitch-side healthcare a necessity, though amateur players highlighted the difficulty in consistently accessing this resource. In the absence of medical staff, players were reliant on the goodwill of volunteers, but their response to concussion did not always align with current concussion guidance. Players highlighted that concussion recovery could be socially isolating and that current return-to-play programmes did little to restore lost confidence, resulting in retirement from the game in some instances. Participants expressed a desire for more in-person concussion education and for greater coverage of holistic methods to support their recovery. This study highlights a need for further investigation of the post-concussion social and psychological changes that players may experience during their recovery. Greater focus on information relating to concussion recovery and return-to-contact in education programmes would likely benefit player welfare.

Knee Offloading by Patients During Walking and Running After Meniscectomy.

Background: Changes in knee loading have been reported after meniscectomy. Knee loading has previously been assessed during jogging and treadmill running rather than overground running, which could give altered results. Purpose/Hypothesis: The purpose of this study was to evaluate knee function during overground running and walking after meniscectomy. It was hypothesized that the affected limb would demonstrate higher external knee adduction moment, lower knee flexion moment (KFM), and lower knee rotation moment (KRM) compared with the contralateral limb and with healthy individuals. Study Design: Controlled laboratory study. Methods: Kinematic and kinetic data were collected during running and walking in individuals after a meniscectomy and healthy individuals. Total knee joint moments (TKJM) were calculated from the sagittal, frontal, and transverse knee moments. Isometric quadriceps strength, perceived knee function, and kinesiophobia were also assessed. A mixed linear model compared differences between the affected leg, the contralateral leg, and the healthy leg. Results: Data were collected on 20 healthy individuals and 30 individuals after a meniscectomy (mean ± SD, 5.7 ± 2.9 months postsurgery), with 12, 16, and 2 individuals who had medial, lateral, and both medial and lateral meniscectomy, respectively. The affected limb demonstrated lower TKJM (P < .001), KFM (P = .004), and KRM (P < .001) during late stance of walking compared with the healthy group. Lower TKJM and KFM were observed during running in the affected limb compared with the contralateral limb and healthy group. No significant differences were observed between contralateral and healthy limbs except for KRM during late stance of walking. Lower quadriceps strength was observed in the affected (P < .001) and contralateral limbs (P = .001) compared with the healthy group. Individuals after a meniscectomy also reported greater kinesiophobia (P = .006) and lower perceived knee function (31.1%; P < .001) compared with the healthy group. Conclusion: After meniscectomy, individuals who sustained a traumatic meniscal injury showed lower TKJM in the affected limb compared with the contralateral limb and healthy individuals. This decrease in TKJM can be attributed to altered knee-loading strategies in the sagittal and transverse planes. Clinical Relevance: Improving movement strategies, quadriceps strength, and kinesiophobia through rehabilitation approaches will allow individuals to load their knee appropriately when returning to sport. Registration: NCT03379415 (ClinicalTrials.gov identifier).

No differences in knee joint loading between individuals who had a medial or lateral meniscectomy: An ancillary study.

BACKGROUND: Arthroscopic partial meniscectomy is a frequently undertaken procedure for traumatic meniscal injuries. The location of knee joint degeneration and long-term prognosis differs between knees who have had a medial or lateral meniscectomy. However, there is no evidence comparing knee loading following a medial or lateral meniscectomy during sporting tasks. This study compared knee loading during walking and running between individuals who either had a medial or lateral meniscectomy. METHODS: Knee kinematic and kinetic data were collected during walking and running in individuals three to twelve months post-surgery. Participants were grouped according to the location of surgery (medial, n = 12, and lateral, n = 16). An independent t-test compared knee biomechanics between the groups and Hedge's g effects sizes were also conducted. RESULTS: External knee adduction and knee flexion moments were similar between groups for walking and running with negligible to small effect sizes (effect size, 0.08-0.30). Kinematic (effect size, 0.03-0.22) and spatiotemporal (effect size, 0.02-0.59) outcomes were also similar between the groups. CONCLUSIONS: The lack of differences in surrogate knee loading variables between medial and lateral meniscectomy groups was unexpected. These findings suggest that combining groups in the short-term period following surgery is applicable. However, the data presented in this study cannot explain the differences in long-term prognosis between medial and lateral meniscectomies.

The effect of foot position during static calibration trials on knee kinematic and kinetics during walking.

BACKGROUND: Gait analysis has been used extensively for computing knee kinematics and kinetics, in particular, in healthy and impaired individuals. One variable assessed is the external knee adduction moment (EKAM). Variations in EKAM values between investigations may be caused by changes in static standing position, especially foot placement angles which may increase or reduce any differences seen. PURPOSE OF THE STUDY: The current study aimed to explore the influence of static trial foot position on knee kinematic and kinetic variables during walking. METHODS: Twelve healthy male participants completed three different static standing trials; 1) 20-degrees toe-in, 2) 0° and 3) 20-degrees toe-out before walking at their own pace during a lower limb kinematics and kinetics assessment. First and second peak EKAM was compared between static foot position trials, as well other knee kinematic and kinetic outcomes. Repeated measures ANOVA was used with post hoc pairwise comparison to determine the differences between static foot position trials. RESULTS: The first peak of EKAM was significantly smaller in the 20o toe-out angle, than the 20o toe-in angle (p = 0.04-8.16% reduction). Furthermore, significant changes were found in peak knee kinematics and kinetics variables (adduction angle, external rotation angle, knee flexion moment external rotation moment, abduction angle and internal rotation angle) in the different positions. CONCLUSION: Modification in static foot position between study visits may result in changes especially in the 1st peak EKAM and other kinematics and kinetics variables during walking. Therefore, standardisation of static foot position should be utilised in longitudinal studies to ensure changes in EKAM are not masked or accentuated between assessments.

Inter and intra-examiner reliability of musculoskeletal ultrasound scanning of Anterior Talofibular Ligament and ankle muscles.

PURPOSE: Although the function of subjects with chronic ankle instability (CAI) has been examined, structural analysis by ultrasound scanning of the structures surrounding the ankle is limited. Before such structural comparisons between injured and uninjured people can be made it is important to investigate a reliable measurement protocol of structures possibly related to CAI. The aim of this study was to investigate the inter-intra examiner reliability of ultrasonic characteristics of selected structures in healthy subjects. METHODS: Eleven healthy participants were assessed by an experienced sonographer and inexperienced certificated examiner. Ultrasound images were collected of the ATFL length and ankle muscles of gastrocnemius medialis (GM), tibialis anterior (TA) and peroneals. Thickness was measured for the muscles, whilst cross-sectional area (CSA) was measured for the peroneals. Inexperienced examiner repeated the measurements a week later. RESULTS: Inter-examiner reliability was excellent for all structures (ICC3,1 = 0.91-0.98). Intra-examiner reliability shows excellent agreement for all structures (ICC3,1 = 0.92-0.98) except GM (good agreement) (ICC3,1 = 0.82). LoA, relative to structure size, ranged from 1.38 to 6.88% for inter-reliability and from 0.07 to 5.79% for intra-reliability. CONCLUSION: This study shows a high level of inter-intra examiner reliability in measuring the structures possibly related to CAI. Future research has been planned to investigate the structural analysis in CAI by using applied MSUS protocol.

A new integrated behavioural intervention for knee osteoarthritis: development and pilot study.

BACKGROUND: Exercise-based approaches have been a cornerstone of physiotherapy management of knee osteoarthritis for many years. However, clinical effects are considered small to modest and the need for continued adherence identified as a barrier to clinical efficacy. While exercise-based approaches focus on muscle strengthening, biomechanical research has identified that people with knee osteoarthritis over activate their muscles during functional tasks. Therefore, we aimed to create a new behavioural intervention, which integrated psychologically informed practice with biofeedback training to reduce muscle overactivity, and which was suitable for delivery by a physiotherapist. METHODS: Through literature review, we created a framework linking theory from pain science with emerging biomechanical concepts related to overactivity of the knee muscles. Using recognised behaviour change theory, we then mapped a set of intervention components which were iteratively developed through ongoing testing and consultation with patients and physiotherapists. RESULTS: The underlying framework incorporated ideas related to central sensitisation, motor responses to pain and also focused on the idea that increased knee muscle overactivity could result from postural compensation. Building on these ideas, we created an intervention with five components: making sense of pain, general relaxation, postural deconstruction, responding differently to pain and functional muscle retraining. The intervention incorporated a range of animated instructional videos to communicate concepts related to pain and biomechanical theory and also used EMG biofeedback to facilitate visualization of muscle patterns. User feedback was positive with patients describing the intervention as enabling them to "create a new normal" and to be "in control of their own treatment." Furthermore, large reductions in pain were observed from 11 patients who received a prototype version of the intervention. CONCLUSION: We have created a new intervention for knee osteoarthritis, designed to empower individuals with capability and motivation to change muscle activation patterns and beliefs associated with pain. We refer to this intervention as Cognitive Muscular Therapy. Preliminary feedback and clinical indications are positive, motivating future large-scale trials to understand potential efficacy. It is possible that this new approach could bring about improvements in the pain associated with knee osteoarthritis without the need for continued adherence to muscle strengthening programmes. TRIAL REGISTRATION: ISRCTN51913166 (Registered 24-02-2020, Retrospectively registered).

The effect of speed on Achilles tendon forces and patellofemoral joint stresses in high-performing endurance runners.

Achilles tendinopathy and patellofemoral pain are common running injuries associated with increased Achilles tendon (AT) forces and patellofemoral joint (PFJ) stresses. This study examined AT forces and PFJ stresses at different running speeds in high-performing endurance runners. Twenty runners ran overground at four running speeds (3.3, 3.9, 4.8, and 5.6 m/s). AT forces and PFJ stresses were estimated from kinematic and kinetic data. Repeated measures ANOVA with partial eta squared effect sizes was conducted to assess differences between running speeds. Increased peak AT forces (19.5%; p < 0.001) and loading rates (57.3%; p < 0.001) from 3.3 m/s to 5.6 m/s were observed. Cumulative AT loading was greater in the faster speeds compared to the slower speeds. Faster running speeds resulted in increased peak plantar flexor moments, increased peak plantar flexion angles, and a more flexed knee and an anterior center of pressure position at touchdown. Peak PFJ stress was lower in the slowest speed (3.3 m/s) compared to the faster running speeds (3.9-5.6 m/s; p = 0.005). PFJ stress loading rate significantly increased (43.6%; p < 0.001). Greater AT loading observed could be associated with strategies such as increased plantar flexor moments and altered lower body position at touchdown which are commonly employed to generate greater ground contact forces. Greater AT and PFJ loading rates were likely due to shorter ground contact times and therefore less time available to reach the peak. Running at faster speeds could increase the risk of developing Achilles tendinopathy and patellofemoral pain or limit recovery from these injuries without sufficient recovery.

Are there common walking gait characteristics in patients diagnosed with late-onset Pompe disease?

Late-onset Pompe disease (LOPD) is a rare disease, defined as a progressive accumulation of lysosomal glycogen resulting in muscle weakness and respiratory problems. Anecdotally, individuals often have difficulties walking, yet, there is no three-dimensional data supporting these claims. We aimed to assess walking patterns in individuals with LOPD and compare with healthy individuals. Kinematic, kinetic and spatiotemporal data were compared during walking at a self-selected speed between individuals with LOPD (n = 12) and healthy controls (n = 12). Gait profile scores and movement analysis profiles were also determined to indicate gait quality. In comparison with healthy individuals, the LOPD group demonstrated greater thoracic sway (96%), hip adduction angles (56%) and pelvic range of motion (77%) and reduced hip extensor moments (36%). Greater group variance for the LOPD group were also observed. Individuals with LOPD had a slower (15%) walking speed and reduced cadence (7%). Gait profile scores were 37% greater in the LOPD group compared to the healthy group. Proximal muscular weakness associated with LOPD disease is likely to have resulted in a myopathic gait pattern, slower selected walking speeds and deviations in gait patterns. Although individuals with LOPD presented with some common characteristics, greater variability in gait patterns is likely to be a result of wide variability in phenotype spectrum observed with LOPD. This is the first study to examine walking in individuals with LOPD using instrumented gait analysis and provides an understanding of LOPD on walking function which can help orientate physiotherapy treatment for individuals with LOPD.

Conservative Treatment for Acute Ankle Sprain: A Systematic Review.

The aim was to identify conservative treatments available for acute ankle sprain and to evaluate their effectiveness with respect to pain relief and short-term recovery of functional capacity. A systematic review of the relevant literature was conducted via a data search of the PROSPERO, PubMed, Scopus, CINAHL, PyscINFO and SPORTDiscus databases, from inception until December 2019, focusing on randomised control trial studies. Two of the authors independently assessed the quality of each study located and extracted the relevant data. The quality of each paper was assessed using the Cochrane risk of bias tool included in RevMan 5. In all, 20 studies met the inclusion criteria. In terms of absence of bias, only nine papers were classed as "high quality". Studies (75%) were of low quality in terms of the blinding of participants and personnel and uncertainty in blinding of outcome assessment and all presented one or more other forms of bias. Despite the generally low quality of the studies considered, it can be concluded that conservative treatment for acute ankle sprain normally achieves pain relief and rapidly improved functionality. Research based on higher-quality study designs and procedures would enable more definitive conclusions to be drawn.

EMG gait data from indwelling electrodes is attenuated over time and changes independent of any experimental effect.

The effect of time on the validity of electromyography (EMG) signals from indwelling fine-wire electrodes has not been explored. This is important because experiments using intramuscular electrodes are often long and biochemical and mechanical factors, may impair measurement accuracy over time. Measures over extended periods might therefore be erroneous. Twelve healthy participants (age = 33 ± 8 years) walked for 50 min at a controlled speed. Fine-wire electrodes were inserted into tibialis anterior and a surface EMG sensor attached near the fine-wire insertion site. EMG signals progressively and significantly decreased with time with the fine-wire electrode, but not the surface electrode. For the fine-wire electrode, after 25 min mean amplitude had reduced by 11% (p < 0.001) and after 50 min by 16% (p < 0.001), and peak amplitude reduced 22% at 20 min (p = 0.006) and 37% at 50 min (p < 0.001). Reduced amplitude with indwelling EMG without concurrent changes in surface EMG signal suggests an important inconsistency in data from fine-wire EMG electrodes. Changes in EMG signal will occur over time independent of the experimental condition and this questions their use in experiments of more than 30 min. These results should impact on experimental study design. They also invite reinterpretation of prior literature and sensor innovation to improve measurement performance.

The value of tibial mounted inertial measurement units to quantify running kinetics in elite football (soccer) players. A reliability and agreement study using a research orientated and a clinically orientated system.

In elite football, measurement of running kinetics with inertial measurement units (IMUs) may be useful as a component of periodic health examination (PHE). This study determined the reliability of, and agreement between a research orientated IMU and clinically orientated IMU system for initial peak acceleration (IPA) and IPA symmetry index (SI) measurement during running in elite footballers. On consecutive days, 16 participants performed treadmill running at 14kmph and 18kmph. Both IMUs measured IPA and IPA SI concurrently. All measurements had good or excellent within-session reliability (intraclass correlation coefficient (ICC2,1) range = 0.79-0.96, IPA standard error of measurement (SEM) range = 0.19-0.62 g, IPA SI SEM range = 2.50-8.05%). Only the research orientated IMU demonstrated acceptable minimal detectable changes (MDCs) for IPA at 14kmph (range = 7.46-9.80%) and IPA SI at both speeds (range = 6.92-9.21%). Considering both systems, between-session IPA reliability ranged from fair to good (ICC2,1 range = 0.63-0.87, SEM range = 0.51-1.10 g) and poor to fair for IPA SI (ICC2,1 range = 0.32-0.65, SEM range = 8.07-11.18%). All MDCs were >10%. For IPA and SI, the 95% levels of agreement indicated poor between system agreement. Therefore, the use of IMUs to evaluate treadmill running kinetics cannot be recommended in this population as a PHE test to identify prognostic factors for injuries or for rehabilitation purposes.

Ultrasound Characteristics of Foot and Ankle Structures in Healthy, Coper, and Chronically Unstable Ankles.

OBJECTIVE: Ankle sprains constitute approximately 85% of all ankle injuries, and up to 70% of people experience residual symptoms. While the injury to ligaments is well understood, the potential role of other foot and ankle structures has not been explored. The objective was to characterize and compare selected ankle structures in participants with and without a history of lateral ankle sprain. METHODS: A total of 71 participants were divided into 31 healthy, 20 coper, and 20 chronic ankle instability groups. Ultrasound images of the anterior talofibular and calcaneofibular ligaments, fibularis tendons and muscles, tibialis posterior, and Achilles tendon were obtained. Thickness, length, and cross-sectional areas were measured and compared among groups. RESULTS: When under tension, the anterior talofibular ligament (ATFL) was longer in copers and chronic ankle instability groups compared to healthy participants (P < .001 and P = .001, respectively). The chronic ankle instability group had the thickest ATFL and calcaneofibular ligament among the 3 groups (p < 0.001). No significant differences (P > .05) in tendons and muscles were observed among the 3 groups. CONCLUSIONS: The ultrasound protocol proved reliable and was used to evaluate the length, thickness, and cross-sectional areas of selected ankle structures. The length of the ATFL and the thickness of the ATFL and calcaneofibular ligament were longer and thicker in injured groups compared to healthy.

Are tibial angles measured with inertial sensors useful surrogates for frontal plane projection angles measured using 2-dimensional video analysis during single leg squat tasks? A reliability and agreement study in elite football (soccer) players.

During single leg squats (SLS), tibial angle (TA) quantification using inertial measurement units (IMU) may offer a practical alternative to frontal plane projection angle (FPPA) measurement using 2-dimensional (2D) video analysis. This study determined: (i) the reliability of IMUs and 2D video analysis for TA measurement, and 2D video analysis for FPPA measurement; (ii) the agreement between IMU TA and both 2D video TA and FPPA measurements during single leg squats in elite footballers. 18 players were tested on consecutive days. Absolute TA (ATA) and relative TA (RTA) were measured with IMUs. ATA and FPPA were measured concurrently using 2D video analysis. Within-session reliability for all measurements varied across days (intraclass correlation coefficient (ICC) range = 0.27-0.83, standard error of measurement (SEM) range = 2.12-6.23°, minimal detectable change (MDC) range = 5.87-17.26°). Between-sessions, ATA reliability was good for both systems (ICCs = 0.70-0.74, SEMs = 1.64-7.53°, MDCs = 4.55-7.01°), while IMU RTA and 2D FPPA reliability ranged from poor to good (ICCs = 0.39-0.72, SEMs = 2.60-5.99°, MDCs = 7.20-16.61°). All limits of agreement exceeded a 5° acceptability threshold. Both systems were reliable for between-session ATA, although agreement was poor. IMU RTA and 2D video FPPA reliability was variable. For SLS assessment, IMU derived TAs are not useful surrogates for 2D video FPPA measures in this population.

Biomechanical responses to changes in friction on a clay court surface.

OBJECTIVES: To examine the influence of clay court frictional properties on tennis players' biomechanical response. DESIGN: Repeated measures. METHODS: Lower limb kinematic and force data were collected on sixteen university tennis players during 10×180° turns (running approach speed 3.9±0.20ms-1) on a synthetic clay surface of varying friction levels. To adjust friction levels the volume of sand infill above the force plate was altered (kg per m2 surface area; 12, 16 and 20kgm-2). Repeated measures ANOVA and Bonferroni's corrected alpha post-hoc analyses were conducted to identify significant differences in lower limb biomechanics between friction levels. RESULTS: Greater sliding distances (ηp2=0.355, p=0.008) were observed for the lowest friction condition (20kgm-2) compared to the 12 and 16kgm-2 conditions. No differences in ankle joint kinematics and knee flexion angles were observed. Later peak knee flexion occurred on the 20kgm-2 condition compared to the 12kgm-2 (ηp2=0.270, p=0.023). Lower vertical (ηp2=0.345, p=0.027) and shear (ηp2=0.396, p=0.016) loading rates occurred for the 20kgm2 condition compared to the 16kgm2. CONCLUSIONS: Lower loading rates and greater sliding distances when clay surface friction was reduced suggests load was more evenly distributed over time reducing players' injury risks. The greater sliding distances reported were accompanied with later occurrence of peak knee flexion, suggesting longer time spent braking and a greater requirement for muscular control increasing the likelihood of fatigue.

The influence of tennis court surfaces on player perceptions and biomechanical response.

This study aimed to examine player perceptions and biomechanical responses to tennis surfaces and to evaluate the influence of prior clay court experience. Two groups with different clay experiences (experience group, n = 5 and low-experience group, n = 5) performed a 180° turning movement. Three-dimensional ankle and knee movements (50 Hz), plantar pressure of the turning step (100 Hz) and perception data (visual analogue scale questionnaire) were collected for two tennis courts (acrylic and clay). Greater initial knee flexion (acrylic 20. 8 ± 11.2° and clay 32.5 ± 9.4°) and a more upright position were reported on the clay compared to the acrylic court (P < 0.05). This suggests adaptations to increase player stability on clay. Greater hallux pressures and lower midfoot pressures were observed on the clay court, allowing for sliding whilst providing grip at the forefoot. Players with prior clay court experience exhibited later peak knee flexion compared to those with low experience. All participants perceived the differences in surface properties between courts and thus responded appropriately to these differences. The level of previous clay court experience did not influence players' perceptions of the surfaces; however, those with greater clay court experience may reduce injury risk as a result of reduced loading through later peak knee flexion.

Exercise-induced muscle damage and the repeated bout effect: evidence for cross transfer.

We examined whether a prior bout of eccentric exercise in the elbow flexors provided protection against exercise-induced muscle damage in the contralateral arm. Fifteen males (age 22.7 ± 2.1 years; height 178.6 ± 6.8 cm, mass 75.8 ± 9.3 kg) were randomly assigned to two groups who performed two bouts of 60 eccentric contractions (30°/s) separated by 2 weeks: ipsilateral (n = 7, both bouts performed in the same arm), contralateral (n = 8, one bout performed in each arm). Strength, muscle soreness and resting arm angle (RAA) were measured at baseline and at 1, 24 and 48 h post exercise. Surface electromyography was recorded during both bouts of exercise. The degree of strength loss was attenuated (p < 0.05) in the ipsilateral group after the second bout of eccentric exercise (-22 cf. -3% for bout 1 and 2 at 24 h, respectively). Strength loss following eccentric exercise was also attenuated (p < 0.05) at 24 h in the contralateral group (-30 cf. 13% for bout 1 and 2, respectively). Muscle soreness (≈34 cf 19 mm) and change in RAA (≈5 cf. 3%) were also lower following the second bout of eccentric exercise (p < 0.05), although there was no difference in the overall change in these values between groups. Median frequency (MF) was decreased by 31% between bouts, with no difference between groups. Data support observations that the repeated bout effect transfers to the opposite (untrained) limb. The similar reduction in MF between bouts for the two groups provides evidence for a centrally mediated, neural adaptation.