Variants in the Late Cornified Envelope Gene Locus Are Associated With Elevated T-helper 17 Responses in Patients With Postinfectious Lyme Arthritis.

BACKGROUND: Postinfectious Lyme arthritis (LA) is associated with dysregulated immunity and autoreactive T- and B-cell responses in joints. Here we explored the role of host genetic variation in this outcome. METHODS: The frequency of 253 702 single-nucleotide polymorphisms (SNPs) was determined in 147 patients with LA (87 with postinfectious LA and 60 with antibiotic-responsive LA), and for comparison in 90 patients with erythema migrans or the general population (n = 2504). Functional outcome of candidate SNPs was assessed by evaluating their impact on clinical outcome and on immune responses in blood and synovial fluid in patients with LA. RESULTS: Six SNPs associated with late cornified envelope (LCE3) genes were present at greater frequency in patients with postinfectious LA compared to those with antibiotic-responsive LA (70% vs 30%; odds ratio, 2; P < .01). These SNPs were associated with heightened levels of inflammatory Th17 cytokines in serum but lower levels of interleukin 27, a regulatory cytokine, implying that they may contribute to dysregulated Th17 immunity in blood. Moreover, in patients with postinfectious LA, the levels of these Th17 mediators correlated directly with autoantibody responses in synovial fluid, providing a possible link between LCE3 SNPs, maladaptive systemic Th17 immunity, and autoreactive responses in joints. CONCLUSIONS: Variation in the LCE3 locus, a known genetic risk factor in psoriasis and psoriatic arthritis, is associated with dysregulated systemic Th17 immunity and heightened autoantibody responses in joints. These findings underscore the importance of host genetic predisposition and systemic Th17 immunity in the pathogenesis of postinfectious (antibiotic-refractory) Lyme arthritis.

Neuraminidase-induced externalization of phosphatidylserine activates ADAM17 and impairs insulin signaling in endothelial cells.

Endothelial insulin resistance represents a causal factor in the pathogenesis of type 2 diabetes (T2D) and vascular disease, thus the need to identify molecular mechanisms underlying defects in endothelial insulin signaling. We previously have shown that a disintegrin and metalloproteinase-17 (ADAM17) is increased while insulin receptor α-subunit (IRα) is decreased in the vasculature of patients with T2D, leading to impaired insulin-induced vasodilation. We have also demonstrated that ADAM17 sheddase activity targets IRα; however, the mechanisms driving endothelial ADAM17 activity in T2D are largely unknown. Herein, we report that externalization of phosphatidylserine (PS) to the outer leaflet of the plasma membrane causes ADAM17-mediated shedding of IRα and blunting of insulin signaling in endothelial cells. Furthermore, we demonstrate that endothelial PS externalization is mediated by the phospholipid scramblase anoctamin-6 (ANO6) and that this process can be stimulated by neuraminidase, a soluble enzyme that cleaves sialic acid residues. Of note, we demonstrate that men and women with T2D display increased levels of neuraminidase activity in plasma, relative to age-matched healthy individuals, and this occurs in conjunction with increased ADAM17 activity and impaired leg blood flow responses to endogenous insulin. Collectively, this work reveals the neuraminidase-ANO6-ADAM17 axis as a novel potential target for restoring endothelial insulin sensitivity in T2D.NEW & NOTEWORTHY This work provides the first evidence that neuraminidase, an enzyme increased in the circulation of men and women with type 2 diabetes (T2D), promotes anoctamin-6 (ANO6)-dependent externalization of phosphatidylserine in endothelial cells, which in turn leads to activation of a disintegrin and metalloproteinase-17 (ADAM17) and consequent shedding of the insulin receptor-α from the cell surface. Hence, this work supports that consideration should be given to the neuraminidase-ANO6-ADAM17 axis as a novel potential target for restoring endothelial insulin sensitivity in T2D.

Tracing fluid infiltration into oceanic crust up to ultra-high-pressure conditions.

Fluid-rock interaction within the altered oceanic crust and across the slab-mantle boundary during subduction facilitates element transfer, but the dynamics of fluid transport and fluid-rock exchange during upward fluid migration are still unclear. A study of metamorphic fluid-rock interaction within a section of subducted oceanic crust was carried out on eclogites and metasediments of the ultra-high-pressure Lago di Cignana Unit (NW Italian Alps). The P-T modeling of a quartzschist shows that garnet grew during the prograde and sporadically during the retrograde path and that phengite mainly records the peak to retrograde conditions. Microscale geochemical analysis of garnets has revealed a systematic evolution of oxygen isotopic composition with garnet major element zonation, with extreme within-sample core-rim variations in δ18O between 18 and 4‰ providing evidence for external fluid influx. Garnet in eclogites and calcschists, as well as garnet cores in quartz-rich lithologies, shows normal compositional zoning, as expected for prograde garnet growth, and a relatively constant oxygen isotopic composition. The outer garnet growth zones within a few metasediments show reverse or discontinuous zoning and progressively lower δ18O. Despite major element zoning, the isotopic composition of mica is homogeneous across chemical zoning in one eclogite and one quartzschist, but shows 6‰ variability in another quartzschist. In the underlying Zermatt-Saas serpentinites, antigorite from nine serpentinite samples shows some variation in δ18O, with average δ18O values for individual samples ranging from 1 to 6‰. These results provide evidence for two main stages of external fluid infiltration: (i) fluids from the dehydration of mafic lithologies entered the sequence at peak conditions around 3 GPa, as indicated by the oxygen composition of intermediate zones of mica and garnet, and (ii) low δ18O fluids from serpentinites infiltrated parts of the sedimentary package during exhumation prior to 1.5 GPa, as recorded by the 4‰ garnet outer rims. Samples recording external fluid infiltration are concentrated in the lower part of the sequence, indicating channelized fluid flow, suggesting focused fluid infiltration due to permeability contrasts between metasedimentary and eclogitic lithologies. Channelized fluid flow in the ultra-high-pressure metasediments of Lago di Cignana has not resulted in systematic decarbonation of the metasediments. Supplementary Information: The online version contains supplementary material available at 10.1007/s00410-023-02060-6.

Explosive hamstrings strength asymmetry persists despite maximal hamstring strength recovery following anterior cruciate ligament reconstruction using hamstring tendon autografts.

PURPOSE: To investigate the differences in maximal (isometric and concentric peak torque) and explosive (rate of torque development (RTD)) hamstring and quadriceps strength symmetry between males and females during early- and late-phase rehabilitation after anterior cruciate ligament reconstruction (ACLR) using hamstring tendon (HT) autografts and to determine the interaction of time and sex on maximal and explosive strength symmetry. METHODS: A total of 38 female and 51 male participants were assessed during early (3-6 months post-operative) and late (7-12 months post-operative) phases of rehabilitation following ACLR. Maximal (concentric and isometric peak torque) and explosive (isometric RTD) hamstring and quadriceps strength were assessed and presented as limb symmetry index (LSI). RESULTS: Maximal concentric hamstrings asymmetry (Early: 86 ± 14; Late 92 ± 13; p = 0.005) as well as maximal concentric (Early, 73 ± 15; Late 91 ± 12; p < 0.001) and explosive (Early: 82 ± 30; Late: 92 ± 25; p = 0.03) quadriceps asymmetry decreased from early to late rehabilitation. However, there were no significant changes in maximal isometric quadriceps strength and explosive isometric hamstring strength in the same time period. Females had a larger asymmetry in maximal concentric (Females: 75 ± 17; Males: 81 ± 15; p = 0.001) and explosive (Females: 81 ± 32; Males: 89 ± 25; p = 0.01) quadriceps strength than males throughout rehabilitation. There were no sex differences in maximal and explosive hamstring strength. There were no sex by time interactions for any variables. CONCLUSION: Explosive hamstring strength asymmetry did not improve despite recovery of maximal hamstring strength during rehabilitation following ACLR with HT autografts. While sex did not influence strength recovery, females had larger maximal and explosive quadriceps strength asymmetry compared to males throughout rehabilitation following ACLR. LEVEL OF EVIDENCE: Level III.

Establishing the Role of Inflammatory Markers in the Diagnosis and Treatment of Acute Hand Infections in the Pediatric Population.

INTRODUCTION: Distinguishing the severity of the diagnosis and an appropriate treatment plan in pediatric hand infections can be complex due to the variable amount of information available at the presentation. Inflammatory blood markers, including white blood cell count, erythrocyte sedimentation rate, and C-reactive protein are reported to aid in determining the severity of infection and response to treatment in adult hand infections. The purpose of this study was to identify the relevance of inflammatory marker levels in pediatric patients with hand and wrist infections and to determine their utility in diagnosis and treatment. METHODS: This multicenter, retrospective, cohort study included patients aged 0 to 18 who received treatment for an acute hand or wrist infection between 2009 and 2020. Data collected included demographics, time to presentation, diagnosis, inflammatory markers, culture results, antibiotic treatment, and surgical treatment. Infections were categorized as deep (osteomyelitis, tenosynovitis, abscess) and superficial (paronychia, felon, cellulitis). Exclusion criteria included: patients above 18 years of age, chronic infection, open fractures, and absence of any documented inflammatory markers. Statistically, t tests were used to compare mean differences in inflammatory markers between patients who did and did not receive pretreatment antibiotics and between patients who had superficial versus deep hand infections. RESULTS: A total of 123 patients met the inclusion criteria. Pretreatment with antibiotics before definitive management was not significantly associated with differences in laboratory markers compared with patients not pretreated with antibiotics. Deep hand infections had inflammatory markers similar to superficial infections. Patients with deep hand infections required a bedside or operative procedure 78.9% of the time compared with superficial infections (21.2%) ( P <0.001). Patients with an isolated methicillin-resistant Staphylococcus aureus infection had inflammatory marker values that were not significantly different from patients infected with all other microbes. CONCLUSIONS: Inflammatory markers were not significantly different between patients who received pretreatment with antibiotics and those who did not. While deep infections were often treated with bedside or surgical procedures, the inflammatory marker values were similar to those of superficial infections. The same held true for patients infected with culture-positive, isolated methicillin-resistant Staphylococcus aureus bacteria. Consequently, inflammatory markers may be useful to identify the presence of infection and monitor the response to treatment, they did not aid in determining the specific type of infection or selection of a treatment plan. LEVEL OF EVIDENCE: Level III-retrospective comparative study.

Assessing isometric kicking force and post-match responses using the Kicker test.

This study examined the inter-session reliability of force output from a novel isometric strength assessment protocol (the Kicker); and its suitability to monitor soccer player's combined hip flexion and knee extension force capacity over 72-h post-competitive matches. Reliability (Part-A) testing was completed over three sessions on 20 individuals participating in various sports at a recreational level or higher. Post-match strength response (Part-B) data were collected for 72-h after a game (24-h (+24), 48-h (+48) and 72-h (+72) post-match) in 17 male academy soccer players. After familiarisation, Kicker force for each limb showed high inter-session reliability (ICC >0.95; typical error <14 N, CV <6%); minimum detectable change at a 95% confidence interval <40 N). Across the 72-h post-match period, Kicker force for each limb was suppressed compared to baseline (force loss range = -5.8% to -12.5%; effect sizes range = -0.26 to -0.43) at all time points. The Kicker assessment protocol measures combined isometric hip flexor and knee extensor force capacity with high inter-session reliability. The proof of concept that the protocol can be used as a monitoring tool was evidenced by sustained suppression of baseline force capacity in both kicking limbs for 72-h post soccer matches.

Field based lower limb strength tests provide insight into sprint and change of direction ability in academy footballers.

Conducting field-based strength assessments is embedded within football academy development processes. Yet, there is a limited understanding of how hip and groin strength assessments relate to vital game-based tasks such as sprinting and change of direction (COD) performance. Our aim was to explore field-based strength assessments and their relationships with both sprint and COD performance in male academy footballers. Participants (n = 146; age 14.2 ± 2.2 years; stature 166.3 ± 15.4 cm; body mass 55.6 ± 15.6 kg) performed maximal countermovement jump (CMJ), Nordic hamstring strength (NHS), isometric hip adductor (ADD)/abductor (ABD), 5 m, 10 m, 20 m sprints, and modified 505 agility test. All strength measures were allometrically scaled to account for body weight. Between-limb differences were reported as imbalance scores. Principal component analysis reduced sprint and COD variables to a single "running ability" component score. Scaled strength and imbalance, when controlled for age, were associated with "running ability" (adjusted R2  = 0.78, p < 0.001). Significant effects on "running ability" included the following: age, CMJ impulse, NHS, and hip-ADD. When the sprint and COD variables were explored independently, age and CMJ-impulse were featured in all sprint and COD models. For 10 m and 20 m sprint distances, hip-ADD emerged as a significant effect. Mean 505 performance was explained by age, CMJ-impulse, hip-ADD, but also with the addition of NHS. Our findings suggest that insight into the underpinning strength qualities of "running ability" of academy footballers can be obtained from a suite of field-based tests.

Strength development and non-contact lower limb injury in academy footballers across age groups.

Non-contact lower limb injuries are common in academy football. Yet, the impact these injuries have on strength development in academy footballers remains unclear. This study aimed to investigate the impact of non-contact lower limb injury on hip, groin, and knee flexor strength development in male academy youth footballers. Furthermore, this study: reports normative strength data of emerging field-based tests that can be easily deployed in football academies; explores the effect of age on injury occurrence; and highlights the number of days lost from injury in male youth footballers. Assessments of hip adductor, abductor, and eccentric knee flexor strength were obtained from 195 academy football players during pre-season and at the end of season. In-season injuries were recorded by medical staff. Those footballers who sustained non-contact lower limb injury were compared with those who did not sustain a non-contact lower limb injury. No between-group differences were observed for any strength assessments when controlled for pre-season measures. Stronger footballers at pre-season experienced strength loses, while those weaker players gained strength across the season. Hip strength development was impaired in older age group footballers. Sustaining a non-contact lower limb injury had minimal impact on strength development. In the absence of in-season lower limb strength monitoring, development in academy youth footballers may not progress as expected, and in particular, stronger and older youth athletes may benefit from individualized strength training.

Hamstring and gluteal activation during high-speed overground running: Impact of prior strain injury.

This study examined the spatial patterns of hamstring and gluteal muscle activation during high-speed overground running in limbs with and without aprior hamstring strain injury. Ten active males with arecent (<18 month) unilateral biceps femoris long head (BFLH) strain injury underwent functional magnetic resonance imaging before and immediately after arepeat-sprint running protocol. Transverse relaxation (T2) time, an index of muscle activation, of the BFLH and short head (BFSH), semitendinosus (ST), semimembranosus (SM), gluteus maximus (GMAX) and medius (GMED) was assessed pre-post exercise. No significant between-limb differences in running-induced mean T2 changes were observed (p = 0.949), however, decision tree induction revealed that previously injured limbs were characterised by highly variable intramuscular activation of the ST (SD5.3). T2 times increased more for GMAX than all other muscles (all p< 0.001, d= 0.5-2.5). Further, T2 changes were greater for ST than BFSH, SM, GMED, and BFLH (all p≤ 0.001, d= 0.5-2.9); and were greater for BFLH than BFSH, SM, and GMED (all p< 0.001, d= 1.2-1.6). Athletes display heterogenous patterns of posterior thigh activation when sprinting (GMAX>ST>BFLH>GMED>SM>BFSH) and may exhibit altered intramuscular hamstring activation after returning to sport from BFLH strain injury.

Hamstring muscle activation and morphology are significantly altered 1-6 years after anterior cruciate ligament reconstruction with semitendinosus graft.

PURPOSE: Harvest of the semitendinosus (ST) tendon for anterior cruciate ligament reconstruction (ACLR) causes persistent hypotrophy of this muscle even after a return to sport, although it is unclear if hamstring activation patterns are altered during eccentric exercise. It was hypothesised that in comparison with contralateral control limbs, limbs with previous ACLR involving ST grafts would display (i) deficits in ST activation during maximal eccentric exercise; (ii) smaller ST muscle volumes and anatomical cross-sectional areas (ACSAs); and (iii) lower eccentric knee flexor strength. METHODS: Fourteen athletes who had successfully returned to sport after unilateral ACLR involving ST tendon graft were recruited. Median time since surgery was 49 months (range 12-78 months). Participants underwent functional magnetic resonance imaging (MRI) of their thighs before and after the Nordic hamstring exercise (NHE) and percentage change in transverse (T2) relaxation time was used as an index of hamstring activation. Muscle volumes and ACSAs were determined from MRI and distal ST tendons were evaluated via ultrasound. Eccentric knee flexor strength was determined during the NHE. RESULTS: Exercise-induced T2 change was lower for ST muscles in surgical than control limbs (95% CI - 3.8 to - 16.0%). Both ST muscle volume (95% CI - 57.1 to - 104.7 cm3) and ACSA (95% CI - 1.9 to - 5.0 cm2) were markedly lower in surgical limbs. Semimembranosus (95% CI 5.5-14.0 cm3) and biceps femoris short head (95% CI 0.6-11.0 cm3) volumes were slightly higher in surgical limbs. No between-limb difference in eccentric knee flexor strength was observed (95% CI 33 N to - 74 N). CONCLUSION: ST activation is significantly lower in surgical than control limbs during eccentric knee flexor exercise 1-6 years after ACLR with ST graft. Lower levels of ST activation may partially explain this muscle's persistent hypotrophy post ACLR and have implications for the design of more effective rehabilitation programs. LEVEL OF EVIDENCE: IV.

Razor hamstring curl and Nordic hamstring exercise architectural adaptations: Impact of exercise selection and intensity.

OBJECTIVES: To investigate knee flexor strength and biceps femoris long head (BFlh) architectural adaptations following two different Nordic hamstring exercise (NHE) interventions and one razor hamstring curl (RHC) intervention. METHODS: Thirty recreationally active males performed a total of 128 reps of NHEbodyweight (n = 10), NHEweighted (n = 10), or RHCweighted training (n = 10) across 6 weeks. Following the intervention, participants avoided any eccentric training for 4 weeks (detraining period). Strength results during the NHE and RHC were recorded pre- and post-intervention, as well as following detraining. Architectural characteristics of the BFlh were assessed weekly throughout the intervention and detraining periods. RESULTS: For the NHEweighted group, NHE strength increased (+81N, P = 0.044, d = 0.90) and BFlh fascicles lengthened (+1.57 cm, P < 0.001, d = 1.41) after 6 weeks of training. After 1 week of detraining, BFlh fascicle lengths shortened, with the largest reductions seen in the NHEweighted group (-0.96 cm, P = 0.021, d = -0.90). Comparatively, BFlh fascicle length and NHE strength responses were moderate in the NHEbodyweight group and negligible in the RHCweighted group. The greatest RHC strength changes (+82N, P = 0.038, d = 1.15) were seen in the RHCweighted group. CONCLUSIONS: NHEweighted interventions induce large BFlh fascicle lengthening responses and these adaptations decay after just 1 week of detraining. NHEbodyweight training has a moderate impact on BFlh architecture while the RHCweighted group has the least. Weighted NHE and RHC training promoted exercise-specific increases in strength. These findings suggest that exercise selection and intensity should be considered when prescribing exercises aiming to increase eccentric strength and BFlh fascicle length.

Running exposure is associated with the risk of hamstring strain injury in elite Australian footballers.

BACKGROUND: To investigate the association between running exposure and the risk of hamstring strain injury (HSI) in elite Australian footballers. METHODS: Elite Australian footballers (n=220) from 5 different teams participated. Global positioning system (GPS) data were provided for every athlete for each training session and match for the entire 2015 season. The occurrences of HSIs throughout the study period were reported. Receiver operator characteristic curve analyses were performed and the relative risk (RR) of subsequent HSI was calculated for absolute and relative running exposure variables related to distance covered above 10 and 24 km/hour in the preceding week/s. RESULTS: 30 prospective HSIs occurred. For the absolute running exposure variables, weekly distance covered above 24 km/hour (>653 m, RR=3.4, 95% CI 1.6 to 7.2, sensitivity=0.52, specificity=0.76, area under the curve (AUC)=0.63) had the largest influence on the risk of HSI in the following week. For the relative running exposure variables, distance covered above 24 km/hour as a percentage of distance covered above 10 km/hour (>2.5%, RR=6.3, 95% CI 1.5 to 26.7, sensitivity=0.93, specificity=0.34, AUC=0.63) had the largest influence on the risk of HSI in the following week. Despite significant increases in the RR of HSI, the predictive capacity of these variables was limited. CONCLUSIONS: An association exists between absolute and relative running exposure variables and elite Australian footballers' risk of subsequent HSI, with the association strongest when examining data within 7-14 days. Despite this, the use of running exposure variables displayed limited clinical utility to predict HSI at the individual level.

A functional MRI Exploration of Hamstring Activation During the Supine Bridge Exercise.

The single leg supine bridge (SLB) is a commonly employed strengthening exercise and is used as a clinical test for hamstring function in sports, however, little is known about the patterns of muscle activation in this task. To explore these activation patterns, nine healthy, recreationally active males underwent functional magnetic resonance imaging (fMRI) of their thighs at rest and immediately after 5 sets of 10 repetitions of the SLB exercise. Exercise-induced increases in the transverse (T2) relaxation time of the biceps femoris long and short heads, semitendinosus and semimembranosus, were determined via signal intensity changes in pre- and post-exercise images and used as an index of muscle activation. The Bonferroni adjusted alpha was set at p<0.008. The semitendinosus exhibited a greater T2 increase than the biceps femoris short head (p<0.001, d=2.0) and semimembranosus (p=0.001, d=1.2), but not biceps femoris long head (p=0.029, d=0.9). Furthermore, the percentage change in T2 for biceps femoris long head was greater than its short head (p=0.003, d=1.4). During the SLB exercise, the semitendinosus is most selectively targeted and the biceps femoris long head is preferentially activated over its short head. These findings may have implications for the use of the SLB in hamstring injury prevention and rehabilitation programs.

Impact of exercise selection on hamstring muscle activation.

OBJECTIVE: To determine which strength training exercises selectively activate the biceps femoris long head (BFLongHead) muscle. METHODS: We recruited 24 recreationally active men for this two-part observational study. Part 1: We explored the amplitudes and the ratios of lateral (BF) to medial hamstring (MH) normalised electromyography (nEMG) during the concentric and eccentric phases of 10 common strength training exercises. Part 2: We used functional MRI (fMRI) to determine the spatial patterns of hamstring activation during two exercises which (1) most selectively and (2) least selectively activated the BF in part 1. RESULTS: Eccentrically, the largest BF/MH nEMG ratio occurred in the 45° hip-extension exercise; the lowest was in the Nordic hamstring (Nordic) and bent-knee bridge exercises. Concentrically, the highest BF/MH nEMG ratio occurred during the lunge and 45° hip extension; the lowest was during the leg curl and bent-knee bridge. fMRI revealed a greater BF(LongHead) to semitendinosus activation ratio in the 45° hip extension than the Nordic (p<0.001). The T2 increase after hip extension for BFLongHead, semitendinosus and semimembranosus muscles was greater than that for BFShortHead (p<0.001). During the Nordic, the T2 increase was greater for the semitendinosus than for the other hamstring muscles (p≤0.002). SUMMARY: We highlight the heterogeneity of hamstring activation patterns in different tasks. Hip-extension exercise selectively activates the long hamstrings, and the Nordic exercise preferentially recruits the semitendinosus. These findings have implications for strategies to prevent hamstring injury as well as potentially for clinicians targeting specific hamstring components for treatment (mechanotherapy).

Impact of the Nordic hamstring and hip extension exercises on hamstring architecture and morphology: implications for injury prevention.

BACKGROUND: The architectural and morphological adaptations of the hamstrings in response to training with different exercises have not been explored. PURPOSE: To evaluate changes in biceps femoris long head (BFLH) fascicle length and hamstring muscle size following 10-weeks of Nordic hamstring exercise (NHE) or hip extension (HE) training. METHODS: 30 recreationally active male athletes (age, 22.0±3.6 years; height, 180.4±7 cm; weight, 80.8±11.1 kg) were allocated to 1 of 3 groups: (1) HE training (n=10), NHE training (n=10), or no training (control, CON) (n=10). BFLH fascicle length was assessed before, during (Week 5) and after the intervention with a two-dimensional ultrasound. Hamstring muscle size was determined before and after training via MRI. RESULTS: Compared with baseline, BFLH fascicles were lengthened in the NHE and HE groups at mid-training (d=1.12-1.39, p<0.001) and post-training (d=1.77-2.17, p<0.001) and these changes did not differ significantly between exercises (d=0.49-0.80, p=0.279-0.976). BFLH volume increased more for the HE than the NHE (d=1.03, p=0.037) and CON (d=2.24, p<0.001) groups. Compared with the CON group, both exercises induced significant increases in semitendinosus volume (d=2.16-2.50, ≤0.002) and these increases were not significantly different (d=0.69, p=0.239). CONCLUSION: NHE and HE training both stimulate significant increases in BFLH fascicle length; however, HE training may be more effective for promoting hypertrophy in the BFLH.

Architectural adaptations of muscle to training and injury: a narrative review outlining the contributions by fascicle length, pennation angle and muscle thickness.

BACKGROUND: The architectural characteristics of muscle (fascicle length, pennation angle muscle thickness) respond to varying forms of stimuli (eg, training, immobilisation and injury). Architectural changes following injury are thought to occur in response to the restricted range of motion experienced during rehabilitation and the associated neuromuscular inhibition. However, it is unknown if these differences exist prior to injury, and had a role in injury occuring (prospectively), or if they occur in response to the incident itself (retrospectively). Considering that the structure of a muscle will influence how it functions, it is of interest to understand how these architectural variations may alter how a muscle acts with reference to the force-length and force-velocity relationships. OBJECTIVES: Our narrative review provides an overview of muscle architectural adaptations to training and injury. Specifically, we (1) describe the methods used to measure muscle architecture; (2) detail the impact that architectural alterations following training interventions, immobilisation and injury have on force production and (3) present a hypothesis on how neuromuscular inhibition could cause maladaptations to muscle architecture following injury.

Hamstring strength and flexibility after hamstring strain injury: a systematic review and meta-analysis.

OBJECTIVE: To systematically review the evidence base related to hamstring strength and flexibility in previously injured hamstrings. DESIGN: Systematic review and meta-analysis. DATA SOURCES: A systematic literature search was conducted of PubMed, CINAHL, SPORTDiscus, Cochrane Library, Web of Science and EMBASE from inception to August 2015. INCLUSION CRITERIA: Full-text English articles which included studies which assessed at least one measure of hamstring strength or flexibility in men and women with prior hamstring strain injury within 24 months of the testing date. RESULTS: Twenty-eight studies were included in the review. Previously injured legs demonstrated deficits across several variables. Lower isometric strength was found <7 days postinjury (d=-1.72), but this did not persist beyond 7 days after injury. The passive straight leg raise was restricted at multiple time points after injury (<10 days, d=-1.12; 10-20 days, d=-0.74; 20-30 days, d=-0.40), but not after 40-50 days postinjury. Deficits remained after return to play in isokinetically measured concentric (60°/s, d=-0.33) and Nordic eccentric knee flexor strength (d=-0.39). The conventional hamstring to quadricep strength ratios were also reduced well after return to play (60:60°/s, d=-0.32; 240:240°/s, d=-0.43) and functional (30:240°/s, d=-0.88), but these effects were inconsistent across measurement methods. CONCLUSIONS: After hamstring strain, acute isometric and passive straight leg raise deficits resolve within 20-50 days. Deficits in eccentric and concentric strength and strength ratios persist after return to play, but this effect was inconsistent across measurement methods. Flexibility and isometric strength should be monitored throughout rehabilitation, but dynamic strength should be assessed at and following return to play.

Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study.

BACKGROUND/AIM: To investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI). METHODS: Elite soccer players (n=152) from eight different teams participated. Eccentric knee flexor strength during the Nordic hamstring exercise and BFlh fascicle length were assessed at the beginning of preseason. The occurrences of HSIs following this were recorded by the team medical staff. Relative risk (RR) was determined for univariate data, and logistic regression was employed for multivariate data. RESULTS: Twenty seven new HSIs were reported. Eccentric knee flexor strength below 337 N (RR=4.4; 95% CI 1.1 to 17.5) and possessing BFlh fascicles shorter than 10.56 cm (RR=4.1; 95% CI 1.9 to 8.7) significantly increased the risk of a HSI. Multivariate logistic regression revealed significant effects when combinations of age, history of HSI, eccentric knee flexor strength and BFlh fascicle length were explored. From these analyses the likelihood of a future HSI in older athletes or those with a HSI history was reduced if high levels of eccentric knee flexor strength and longer BFlh fascicles were present. CONCLUSIONS: The presence of short BFlh fascicles and low levels of eccentric knee flexor strength in elite soccer players increases the risk of future HSI. The greater risk of a future HSI in older players or those with a previous HSI is reduced when they have longer BFlh fascicles and high levels of eccentric strength.

Effect of high-speed running on hamstring strain injury risk.

BACKGROUND: Hamstring strain injuries (HSIs) are common within the Australian Football League (AFL) with most occurring during high-speed running (HSR). Therefore, this study investigated possible relationships between mean session running distances, session ratings of perceived exertion (s-RPE) and HSIs within AFL footballers. METHODS: Global positioning system (GPS)-derived running distances and s-RPE for all matches and training sessions over two AFL seasons were obtained from one AFL team. All HSIs were documented and each player's running distances and s-RPE were standardised to their 2-yearly session average, then compared between injured and uninjured players in the 4 weeks (weeks -1, -2, -3 and -4) preceding each injury. RESULTS: Higher than 'typical' (ie, z=0) HSR session means were associated with a greater likelihood of HSI (week -1: OR=6.44, 95% CI=2.99 to 14.41, p<0.001; summed weeks -1 and -2: OR=3.06, 95% CI=2.03 to 4.75, p<0.001; summed weeks -1, -2 and -3: OR=2.22, 95% CI=1.66 to 3.04, p<0.001; and summed weeks -1, -2, -3 and -4: OR=1.96, 95% CI=1.54 to 2.51, p<0.001). However, trivial differences were observed between injured and uninjured groups for standardised s-RPE, total distance travelled and distances covered whilst accelerating and decelerating. Increasing AFL experience was associated with a decreased HSI risk (OR=0.77, 95% CI 0.57 to 0.97, p=0.02). Furthermore, HSR data modelling indicated that reducing mean distances in week -1 may decrease the probability of HSI. CONCLUSIONS: Exposing players to large and rapid increases in HSR distances above their 2-yearly session average increased the odds of HSI. However, reducing HSR in week -1 may offset HSI risk.

Characteristics impacting on session rating of perceived exertion training load in Australian footballers.

The relationship between external training load and session rating of perceived exertion (s-RPE) training load and the impact that playing experience, playing position and 2-km time-trial performance had on s-RPE training load were explored. From 39 Australian Football players, 6.9 ± 4.6 training sessions were analysed, resulting in 270 samples. Microtechnology devices provided external training load (distance, average speed, high-speed running distance, player load (PL) and player loadslow (PLslow)). The external training load measures had moderate to very large associations (r, 95% CI) with s-RPE training load, average speed (0.45, 0.35-0.54), high-speed running distance (0.51, 0.42-0.59), PLslow (0.80, 0.75-0.84), PL (0.86, 0.83-0.89) and distance (0.88, 0.85-0.90). Differences were described using effect sizes (d ±95% CL). When controlling for external training load, the 4- to 5-year players had higher s-RPE training load than the 0- to 1- (0.44 ± 0.33) and 2- to 3-year players (0.51 ± 0.30), ruckmen had moderately higher s-RPE training load than midfielders (0.82 ± 0.58), and there was a 0.2% increase in s-RPE training load per 1 s increase in time-trial (95% CI: 0.07-0.34). Experience, position and time-trial performance impacted the relationship between external training load and s-RPE training load. This suggests that a given external training load may result in different internal responses between athletes, potentially leaving individuals at risk of overtraining or failing to elicit positive adaptation. It is therefore vital that coaches and trainers give consideration to these mediators of s-RPE training load.