The financial cost of hamstring strain injuries in the Australian Football League

The Hamstrings: Anatomic and Physiologic Variations and Their Potential Relationships With Injury Risk

The incidence and recurrence of hamstrings injuries are very high in sports, posing elevated performance and financial-related costs. Attempts to identify the risk factors involved in predicting vulnerability to hamstrings injury is important for designing exercise-based programs that aim to mitigate the rate and severity of hamstrings injuries and improve rehabilitation strategies. However, research has shown that non-modifiable risk factors may play a greater role than modifiable risk factors. Recognizing non-modifiable risk factors and understanding their implications will afford the prescription of better suited exercise programs, i.e., that are more respectful of the individual characteristics. In a nutshell, non-modifiable risk factors can still be acted upon, even if indirectly. In this context, an underexplored topic is how intra and inter- individual anatomic and physiologic variations in hamstrings (e.g., muscle bellies, fiber types, tendon length, aponeurosis width, attachment sites, sex- and age-related differences) concur to alter hamstrings injuries risk. Some anatomic and physiologic variations may be modifiable through exercise interventions (e.g., cross-sectional area), while others may not (e.g., supernumerary muscle bellies). This apparent dichotomy may hide a greater complexity, i.e., there may be risk factors that are partially modifiable. Therefore, we explored the available information on the anatomic variations of the hamstrings, providing a deeper insight into the individual risk factors for hamstrings injuries and contributing with better knowledge and potential applications toward a more individualized exercise prescription.

Specificity of eccentric hamstring training and the lack of consistency between strength assessments using conventional test devices

Hamstring injuries are endemic, but influences of test-specific training and the application of different test methods on decision making remain elusive. Sport-students were randomised to isokinetic (IG) or Nordic hamstring (NG) exercise or a control group (CG) for six weeks. Training and testing procedures were matched to biomechanical parameters. Hamstring strength (EPT), work, muscle soreness (visual analogue scale (VAS)), biceps femoris (BF_lh) muscle size and architecture were assessed. Anthropometrics and strength parameters did not differ at baseline. Yet, body mass normalised EPT, and work revealed a significant group × time × device effect, with a significant main effect for devices. Experimental conditions triggered meaningful increases in EPT compared to the control group, but the effects were higher when recorded on the training device. Despite significant group × time interactions, normalised average work on the NHD was only higher in the NG compared to CG of the left leg (+ 35%). No effects were found for BF_lh parameters. Hamstrings showed a high training specificity, but adaptations likely remain undetected owing to the low sensitivity of conventional test devices. Moreover, strength increase of ~ 15% does not necessarily have to be reflected in BF_lh parameters.

Return to Play After a Hamstring Strain Injury: It is Time to Consider Natural Healing

Return to play (RTP) criteria after hamstring strain injuries (HSIs) help clinicians in deciding whether an athlete is ready to safely resume previous sport activities. Today, functional and sport-specific training tests are the gold standard in the decision-making process. These criteria lead to an average RTP time between 11 and 25 days after a grade 1 or 2 HSI. However, the high re-injury rates indicate a possible inadequacy of the current RTP criteria. A possible explanation for this could be the neglect of biological healing time. The present review shows that studies indicating time as a possible factor within the RTP-decision are very scarce. However, studies on biological muscle healing showed immature scar tissue and incomplete muscle healing at the average moment of RTP. Twenty-five percent of the re-injuries occur in the first week after RTP and at the exact same location as the index injury. This review supports the statement that functional recovery precedes the biological healing of the muscle. Based on basic science studies on biological muscle healing, we recommend a minimum period of 4 weeks before RTP after a grade 1 or 2 HSI. In conclusion, we advise a comprehensive RTP functional test battery with respect for the natural healing process. Before deciding RTP readiness, clinicians should reflect whether or not it is biologically possible for the injured tissue to have regained enough strength to withstand the sport-specific forces. In an attempt to reduce the detrimental injury-reinjury cycle, it is time to start considering (biological healing) time.

A prospective study of risk factors for hamstring injury in Australian football league players

This study aimed to explore the association between hamstring strength, age and lower limb soft tissue injury history and subsequent hamstring injury among Australian Football League (AFL) players. This prospective cohort study recruited 125 players from three professional AFL teams. Eccentric knee flexor strength was assessed while performing the Nordic hamstring exercise in pre-season, and injury data were collected retrospectively (hamstring, groin, calf, quadriceps and knee), and prospectively (hamstring injuries) for one AFL playing season. Fourteen players (11%) sustained a hamstring injury in the subsequent playing season. Nordic strength was not significantly associated with future hamstring injury (Odds Ratio (OR) 1.9, p = 0.36), whereas player age greater than 25 years (OR = 2.9, p < 0.05), report of a hamstring injury within the previous year (OR = 3.7, p = 0.01), or greater than 1-year (OR = 3.6, p = 0.01), a previous groin (OR = 8.6, p < 0.01) or calf injury (OR = 4.6, p = 0.01) were factors significantly associated with subsequent hamstring injury. Based on these findings, increasing age and previous hamstring, groin and calf injury are all associated with an elevated risk of subsequent hamstring injury in AFL players.

Sprinting, Strength, and Architectural Adaptations Following Hamstring Training in Australian Footballers

The aim of this study was to determine the sprinting, strength, and architectural adaptations following a hip-dominant flywheel (FLY) or Nordic hamstring exercise (NHE) intervention in Australian footballers. Twenty-seven male athletes were randomized to FLY (n = 13) or NHE (n = 14) training across a 39-week period (inclusive of pre-season and in-season). Biceps femoris long head (BFlh) architecture was assessed throughout. Eccentric hamstring strength and 40 m sprint times (with force-velocity profiling) were assessed at baseline, end of pre-season, and following the intervention. After the intervention, BFlh fascicle length was longer in both groups compared to baseline (FLY: 1.16 cm, 95%CI: 0.66 to 1.66 cm, d = 1.99, p < 0.001; NHE: 1.08 cm, 95%CI: 95%CI 0.54 to 1.61 cm, d = 1.73, p < 0.001). Both groups also increased their eccentric strength (FLY: mean change 82 N, 95%CI 12 to 152 N, d = 1.34, p = 0.026; NHE: mean change 97 N, 95%CI 47 to 146 N, d = 1.77, p = 0.001). After pre-season, the NHE group improved their 5 m sprint time by 3.5% (±1.2%) and were 3.7% (±1.4%) and 2.0% (±0.5%) faster than the FLY group across 5 m and 10 m, respectively. At the end of pre-season, the FLY group improved maximal velocity by 3.4% (±1.4%) and improved horizontal force production by 9.7% in-season (±2.2%). Both a FLY and NHE intervention increase BFlh fascicle length and eccentric strength in Australian Footballers. An NHE intervention led to enhanced acceleration capacity. A FLY intervention was suggested to improve maximal sprint velocity and horizontal force production, without changes in sprint times. These findings have implications for hamstring injury prevention but also programs aimed at improving sprint performance.

Progressive Workload Periodization Maximizes Effects of Nordic Hamstring Exercise on Muscle Injury Risk Factors

ABSTRACT

Severo-Silveira, L, Dornelles, MP, Lima-e-Silva, FX, Marchiori, CL, Medeiros, TM, Pappas, E, and Baroni, BM. Progressive workload periodization maximizes effects of Nordic hamstring exercise on muscle injury risk factors. J Strength Cond Res 35(4): 1006-1013, 2021-This study aimed to investigate the effect of 2 different Nordic hamstring exercise (NHE) training programs (constant workload vs. progressive workload) on multiple risk factors for hamstring strain injury in high competitive level athletes. Twenty-one premier league rugby union players (∼26 years) were randomized into 1 of 2 experimental groups and completed an 8-week NHE training program: constant training group (CTG) or progressive training group (PTG). Knee flexor/extensor strength and biceps femoris long head (BFLH) muscle architecture were assessed through isokinetic dynamometry and ultrasonography, respectively, before and after the training programs. Increased hamstring concentric (Δ = 8%, p = 0.004, d = 0.42) and eccentric (Δ = 7%, p = 0.041, d = 0.39) peak torques, as well as H:Q conventional (Δ = 7%, p = 0.015, d = 0.54) and functional (Δ = 6%, p = 0.026, d = 0.62) ratios were observed in the follow-up compared with baseline for the PTG group only. Nordic hamstring exercise training significantly increased BFLH muscle thickness (CTG: Δ = 7%, p = 0.001, d = 0.60; PTG: Δ = 7%, p < 0.001, d = 0.54) and fascicle length (CTG: Δ = 8%, p < 0.001, d = 0.29; PTG: Δ = 10%, p < 0.001, d = 0.35) in both groups. Training adaptations on hamstring peak torque (concentric and eccentric) and H:Q ratio (conventional and functional) "likely favor" PTG, whereas changes in BFLH fascicle length "possibly favor" PTG. In conclusion, only PTG enhanced hamstring strength; both NHE training programs increased BFLH muscle thickness and fascicle length, but progressive training generated greater changes on fascicle length than constant training. Medical/coaching staff should be aware that NHE with adequate training periodization with workload progression to maximize its benefits.

Semitendinosus and biceps femoris long head active stiffness response until failure in professional footballers with vs. without previous hamstring injury

This study sought to examine the active stiffness of semitendinosus (ST) and biceps femoris long head (BFlh) during a knee flexor isometric contraction at 20% of maximal voluntary isometric contraction until failure in elite footballers (n=50, age: 22.3±5.3 years; height: 1.82±0.08 m; body mass: 74.7±9.0 kg). Active stiffness was assessed using ultrasound-based shear wave elastography by means of shear modulus quantification. Comparisons were performed between limbs with (n=11) vs. without (n=89) previous hamstring injury. Similar time until failure in the knee flexor fatigue task was observed between groups (p=0.401). At the start of the task, lower limbs with previous hamstring injury showed a lower BFlh active stiffness (31.0.1±10.4 kPa, p=0.023) and BFlh/ST active stiffness ratio (0.50±0.29), and no differences for ST (72.8±26.8 kPa, p=0.221) compared to lower limbs without previous hamstring injuries (BFlh: 38.0±9.6 kPa; ST: 64.0±18.4 kPa; BFlh/ST: 0.65±0.27). During the task, the ST active stiffness in both groups decreased from 80% of task time (p=0.032), in the absence of changes in BFlh active stiffness (p=0.534), resulting in an increase in BFlh/ST active stiffness from 80% of task time (p=0.029). No differences between limbs were observed during the fatigue task for all parameters (p>0.099). Future research is warranted to verify if the differences found represent an increased risk of hamstring injury.

Effect of Knee Joint Angle on Regional Hamstrings Activation During Isometric Knee-Flexion Exercise

CONTEXT

Each hamstring muscle is subdivided into several regions by multiple motor nerve branches, which implies each region has different muscle activation properties. However, little is known about the muscle activation of each region with a change in the knee joint angle. Understanding of regional activation of the hamstrings could be helpful for designing rehabilitation and training programs targeted at strengthening a specific region.

OBJECTIVE

To investigate the effect of knee joint angle on the activity level of several regions within the individual hamstring muscles during isometric knee-flexion exercise with maximal effort (MVCKF).

DESIGN

Within-subjects repeated measures.

SETTING

University laboratory.

PARTICIPANTS

Sixteen young males with previous participation in sports competition and resistance training experience.

INTERVENTION

The participants performed 2 MVCKF trials at each knee joint angle of 30°, 60°, and 90°.

OUTCOME MEASURES

Surface electromyography was used to measure muscle activity in the proximal, middle, and distal regions of the biceps femoris long head (BFlh), semitendinosus, and semimembranosus of hamstrings at 30°, 60°, and 90° of knee flexion during MVCKF.

RESULTS

Muscle activity levels in the proximal and middle regions of the BFlh were higher at 30° and 60° of knee flexion than at 90° during MVCKF (all: P < .05). Meanwhile, the activity levels in the distal region of the BFlh were not different among all of the evaluated knee joint angles. In semitendinosus and semimembranosus, the activity levels were higher at 30° and 60° than at 90°, regardless of region (all: P < .05).

CONCLUSION

These findings suggest that the effect of knee joint angle on muscle activity level differs between regions of the BFlh, whereas that is similar among regions of semitendinosus and semimembranosus during MVCKF.

Injury Profile in Women's Football: A Systematic Review and Meta-Analysis

BACKGROUND

Football is the most popular sport among women; however, little is known about the injury profile in this population. This information would help design tailored injury risk mitigation strategies that may make football safer for women.

OBJECTIVE

The aim of this study was to perform a systematic review and meta-analysis of epidemiological data of injuries in women´s football.

METHODS

A systematic review following PRISMA guidelines was performed up to January 2020 in PubMed, Web of Science, Sportdiscus and the Cochrane Library databases. Twenty-two studies reporting the incidence of injuries in women football were analysed. Two reviewers independently extracted data (intraclass correlation coefficient [ICC] for inter-reviewer reliability = 0.87) and assessed study quality using the STROBE statement, GRADE approach, Newcastle Ottawa Scale and Downs and Black assessment tools. Studies were combined in pooled analyses (injury incidence and injury proportion) using a Poisson random effects regression model.

RESULTS

The overall incidence of injuries in female football players was 6.1 injuries/1000 h of exposure. Match injury incidence (19.2 injuries/1000 h of exposure) was almost six times higher than training injury incidence rate (3.5 injuries/1000 h of exposure). Lower extremity injuries had the highest incidence rates (4.8 injuries/1000 h of exposure). The most common types of injuries were muscle/tendon (1.8 injuries/1000 h of exposure) and joint (non-bone) and ligament (1.5 injuries/1000 h of exposure), which were frequently associated with traumatic incidents. Slight/minimal injuries (1-3 days of time loss) were the most common. The incidence rate of injuries during matches in the top five world ranking leagues was higher than the rest of the leagues (19.3 vs 10.7 injuries/1000 h of exposure, respectively). The weighted injury proportion was 1.1 (95% confidence interval = 0.6-1.7) whereby on average players sustained more than one injury per season.

CONCLUSIONS

Female football players are exposed to a substantial risk of sustaining injuries, especially during matches that require the highest level of performance. To markedly reduce overall injury burden, efforts should focus on introducing and evaluating preventative measures that target match specific dynamics to make football players more capable of responding to the challenges that they have to deal with during match play.

REGISTRATION

This systematic review was registered in the PROSPERO international prospective register of systematic reviews (ID = CRD42019118152).

Sprinting and hamstring strain injury: Beliefs and practices of professional physical performance coaches in Australian football

OBJECTIVES

The purpose of this study was to establish beliefs and practices of physical performance coaches regarding sprinting and Hamstring Strain Injury (HSI) in Australian Rules football.

DESIGNS

Delphi-validated questionnaire.

SETTING

Online.

PARTICIPANTS

Eighteen high-performance managers of the Australian Football League.

MAIN OUTCOME MEASURES

Descriptive statistics were collected to establish experience; central themes were established for the analyses of the beliefs and practices.

RESULTS

Nine (50%) physical performance coaches responded to an invitation to complete the questionnaire. Participants held an undergraduate degree and had 9.2 ± 4.3 years of experience. Accelerations (n = 9), maximum speed sprints (n = 9) and running with hip flexion (n = 7) were the most common activities associated with HSI. Coaches believed sprinting, eccentric strength training and proper periodisation were effective strategies to reduce HSI risk. There's a disparity between beliefs and practices when using GPS to monitor sprinting, however, all coaches reported regular exposure to sprint training across both pre and in-season. Overstriding (n = 9) and pelvic instability (n = 6) were identified as key flaws in running mechanics.

CONCLUSIONS

This information can be used to improve training strategies, whilst these findings indicate further investigations into sprint training and running mechanics for HSI risk reduction.

Hamstring muscle injury in the athlete: state of the art

Hamstring injuries (HSI) are the source of significant impairment and disability for both professional and recreational athletes. The incidence and prevalence of HSIs has been well documented in the literature, as they are among the most common soft tissue injuries reported. The significant time loss due to injury and the inherent risk of reinjury pose a significant issue to the athlete, their career longevity and the success of their respective team. This review will deal predominantly with describing the prevalence and incidence of HSI in athletes, discuss risk factors and the mechanisms of injury for HSI, how to properly diagnose, image and prognosticate appropriate return to sport (RTS) for individuals who have sustained an HSI, prescribe treatment and prevention strategies and to discuss relevant options to decrease overall risk of primary and secondary recurrence of HSI.Current treatments of acute HSI necessitate a thorough understanding of the mechanism of injury, identifying muscle imbalances and/or weakness, inclusion of eccentric and concentric hamstring (HS) and hip extension (HE) exercises, evaluation of pathokinematic movement patterns and use non-surgical methods to promote healing and RTS. This methodology can be used prospectively to mitigate the overall risk of HSI. Injection therapies for HSI, including ultrasound-guided platelet-rich plasma and corticosteroids, may impart some short-term benefit, but the existing literature is largely inconclusive with respect to long-term functional outcomes. Future directions should prioritise injury prevention, early diagnosis and targeted interventions that combine both non-surgical and minimally invasive orthobiological approaches and identifying biomechanical risk factors prospectively to mitigate risk.

Potential prognostic factors for hamstring muscle injury in elite male soccer players: A prospective study

Hamstring injuries remain the most common injury type across many professional sports. Despite a variety of intervention strategies, its incidence in soccer players playing in the UEFA Champions League has increased by 4% per year over the last decade. Test batteries trying to identify potential risk factors have produced inconclusive results. The purpose of the current study was to prospectively record hamstring injuries, to investigate the incidence and characteristics of the injuries, and to identify possible risk factors in elite male soccer players, playing in the Kosovo national premier league. A total of 143 soccer players from 11 teams in Kosovo were recruited. To identify possible prevalent musculoskeletal or medical conditions a widespread health and fitness assessment was performed including isokinetic strength testing, Nordic hamstring strength test, functional tests, and a comprehensive anamnesis surveying previous hamstring injuries. On average 27.9% of the players sustained at least one hamstring injury with three players suffering bilateral strains with the re-injury rate being 23%. Injured players were significantly older and heavier and had a higher body mass index compared to non-injured ones (p < 0.05). There was a lower passing rate in the Nordic hamstring strength test and a higher injury incidence among the previously injured players compared to non-injured ones (p < 0.05). Except for hamstring/quadriceps ratio and relative torque at 60°/sec (p < 0.05) for dominant and non-dominant leg, there were no other significant differences in isokinetic strength regardless of the angular velocity. No differences were observed for functional tests between cohorts. Regression analysis revealed that age, Nordic hamstring strength test, previous injury history, and isokinetic concentric torque at 240°/sec could determine hamstring injuries by 25.9%, with no other significant predicting risk factors. The battery of laboratory and field-based tests performed during preseason to determine performance related skills showed limited diagnostic conclusiveness, making it difficult to detect players at risk for future hamstring injuries.

Differences in Lower Limb Strength and Structure After 12 Weeks of Resistance, Endurance, and Concurrent Training

PURPOSE

To investigate strength and structural adaptations after 12 weeks of resistance, endurance cycling, and concurrent training.

METHODS

Thirty-two healthy males undertook 12 weeks of resistance-only (RT; n = 10), endurance-only (END; n = 10), or concurrent resistance and endurance training (CONC; n = 12). Biceps femoris long head (BFlh) architecture, strength (3-lift 1-repetition maximum), and body composition were assessed.

RESULTS

Fascicle length of the BFlh reduced 15% (6%) (P < .001) and 9% (6%) (P < .001) in the END and CONC groups postintervention, with no change in the RT group (-4% [11%], P = .476). All groups increased BFlh pennation angle (CONC: 18% [9%], RT: 14% [8%], and END: 18% [10%]). Thickness of the BFlh increased postintervention by 7% (6%) (P = .002) and 7% (7%) (P = .003) in the CONC and RT groups, respectively, but not in the END group (0% [3%], P = .994). Both the CONC and RT groups significantly increased by 27% (11%) (P < .001) and 33% (12%) (P < .001) in 3-lift totals following the intervention, with no changes in the END cohort (6% [6%], P = .166). No significant differences were found for total body (CONC: 4% [2%], RT: 4% [2%], and END: 3% [2%]) and leg (CONC: 5% [3%], RT: 6% [3%], and END: 5% [3%]) fat-free mass.

CONCLUSIONS

Twelve weeks of RT, END, or CONC significantly modified BFlh architecture. This study suggests that conventional resistance training may dampen BFlh fascicle shortening from cycling training while increasing strength simultaneously in concurrent training. Furthermore, the inclusion of a cycle endurance training stimulus may result in alterations to hamstring architecture that increase the risk of future injury. Therefore, the incorporation of endurance cycling training within concurrent training paradigms should be reevaluated when trying to modulate injury risk.

The mechanism of hamstring injuries - a systematic review

Background

Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined.

Purpose

To investigate the hamstring injury mechanism by conducting a systematic review.

Study design

A systematic review following the PRISMA statement.

Methods

A systematic search was conducted using PubMed, EMBASE and the Cochrane Library. Studies 1) written in English and 2) deciding on the mechanism of hamstring injury were eligible for inclusion. Literature reviews, systematic reviews, meta-analyses, conference abstracts, book chapters and editorials were excluded, as well as studies where the full text could not be obtained.

Results

Twenty-six of 2372 screened original studies were included and stratified to the mechanism or methods used to determine hamstring injury: stretch-related injuries, kinematic analysis, electromyography-based kinematic analysis and strength-related injuries. All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle.

Conclusion

A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle.

Level of evidence

Level IV

Clinical utility of measuring the size of the lumbar multifidus and quadratus lumborum muscles in the Australian football league setting: A prospective cohort study

OBJECTIVES

Test the odds of factors previously associated with lower limb injury (decreased size of the multifidus (MF) and increased size of the quadratus lumborum (QL) muscle) in an independent sample of Australian Rules Football (ARF) players.

DESIGN

Prospective cohort study.

SETTING

Professional ARF.

PARTICIPANTS

Forty-three male ARF players.

MAIN OUTCOME MEASURES

Cross-sectional areas (CSAs) of MF and QL muscles measured from pre-season ultrasound images. Playing season injuries were recorded by club personnel. A multivariable logistic regression model was used to evaluate the usefulness of MF and QL muscle size for predicting playing season lower limb injuries.

RESULTS

Fifteen players (35%) sustained a playing season lower limb injury. The multivariable model indicated that the odds of sustaining a lower limb injury during the season was 2.38 (95% CI: 1.18, 5.00; P = 0.017) times less likely for a one cm² increase from the mean value in MF muscle CSA at the L5 vertebral level after adjusting for CSA of the QL, age and BMI. The main effect and interaction models positively predicted 75% of players that sustained a lower limb injury during the season (sensitivity 80%, specificity 85%).

CONCLUSION

Future studies could examine the efficacy, feasibility and adherence of 'at risk' players to a pre-season training program aimed at increasing MF muscle size and monitor playing season injuries.

Global Positioning System-Derived Workload Metrics and Injury Risk in Team-Based Field Sports: A Systematic Review

OBJECTIVE

To evaluate the current literature regarding the utility of global positioning system (GPS)-derived workload metrics in determining musculoskeletal injury risk in team-based field-sport athletes.

DATA SOURCES

PubMed entries from January 2009 through May 2019 were searched using terms related to GPS, player workload, injury risk, and team-based field sports.

STUDY SELECTION

Only studies that used GPS metrics and had injury as the main outcome variable were included.

DATA EXTRACTION

Total distance, high-speed running, and acute : chronic workload ratios were the most common GPS metrics analyzed, with the most frequent sports being soccer, rugby, and Australian rules football.

DATA SYNTHESIS

Many distinct workload metrics were associated with increased injury risk in individual studies performed in particular sport circumstances; however, the body of evidence was inconclusive as to whether any specific metrics could consistently predict injury risk across multiple team-based field sports.

CONCLUSIONS

Our results were inconclusive in determining if any GPS-derived workload metrics were associated with an increased injury risk. This conclusion is due to a myriad of factors, including differences in injury definitions, workload metrics, and statistical analyses across individual studies.

Training Load and Its Role in Injury Prevention, Part I: Back to the Future

The purpose of this 2-part commentary series is† to explain why we believe our ability to control injury risk by manipulating training load (TL) in its current state is an illusion and why the foundations of this illusion are weak and unreliable. In part 1, we introduce the training process framework and contextualize the role of TL monitoring in the injury-prevention paradigm. In part 2, we describe the conceptual and methodologic pitfalls of previous authors who associated TL and injury in ways that limited their suitability for the derivation of practical recommendations. The first important step in the training process is developing the training program: the practitioner develops a strategy based on available evidence, professional knowledge, and experience. For decades, exercise strategies have been based on the fundamental training principles of overload and progression. Training-load monitoring allows the practitioner to determine whether athletes have completed training as planned and how they have coped with the physical stress. Training load and its associated metrics cannot provide a quantitative indication of whether particular load progressions will increase or decrease the injury risk, given the nature of previous studies (descriptive and at best predictive) and their methodologic weaknesses. The overreliance on TL has moved the attention away from the multifactorial nature of injury and the roles of other important contextual factors. We argue that no evidence supports the quantitative use of TL data to manipulate future training with the purpose of preventing injury. Therefore, determining "how much is too much" and how to properly manipulate and progress TL are currently subjective decisions based on generic training principles and our experience of adjusting training according to an individual athlete's response. Our message to practitioners is to stop seeking overly simplistic solutions to complex problems and instead embrace the risks and uncertainty inherent in the training process and injury prevention.

Individual Region- and Muscle-specific Hamstring Activity at Different Running Speeds

INTRODUCTION

Hamstring strain injuries typically occur in the proximal biceps femoris long head (BFlh) at high running speeds. Strain magnitude seems to be the primary determinant of strain injury, and may be regulated by muscle activation. In running, BFlh strain is largest in the proximal region, especially at high speeds. However, region-specific activity has not been examined. This study examined the proximal-distal and intermuscular activity of BFlh and semitendinosus (ST) as a function of increasing running speed.

METHODS

Thirteen participants ran at steady speeds of 4.1 (slow), 5.4 (moderate), and 6.8 m·s (fast) on a treadmill. Region- and muscle-specific EMG activity were recorded at each speed using high-density EMG, and were normalized to maximal voluntary isometric activity. Muscle-tendon unit lengths were calculated from kinematic recordings. Speed effects, regional, and intermuscular differences were tested with Statistical Parametric Mapping.

RESULTS

With increasing running speed, EMG activity increased in all regions of both muscles to a similar extent in the clinically relevant late swing phase. Increases in muscle-tendon unit lengths in late swing as a function of running speed were comparatively small. In fast running, EMG activity was highest in late swing in all regions, and reached 115% ± 20% (proximal region, mean ± 95% confidence limit), 106% ± 11% (middle), and 124% ± 16% (distal) relative to maximal voluntary isometric activity in BFlh. Regional and intermuscular EMG patterns were highly individual, but each individual maintained similar proximal-distal and intermuscular EMG activity patterns across running speeds.

CONCLUSIONS

Running is associated with highly individual hamstring activity patterns, but these patterns are similar across speeds. It may thus be crucial to implement running at submaximal speeds early after hamstring injury for restoration of normal neuromuscular function.

Estimation of injury costs: financial damage of English Premier League teams' underachievement due to injuries

Background

In individual sports, the effect that injuries have on an athlete’s performance, success and financial profit is implicit. In contrast, the effect of a single player’s injury or one player’s absence in team sports is much more difficult to quantify, both from the performance perspective and the financial perspective.

Objectives

In this study, we attempted to estimate the effect of injuries on the performance of football teams from the English Premier League (EPL), and the financial implications derived from this effect.

Methods

Our analysis is based on data regarding game results, injuries and estimations of the players’ financial value for the 2012–2013 through the 2016–2017 seasons.

Results

We found a statistically significant relationship (r=−0.46, 95% CI −0.6 to −0.28, p=0.001) between the number of days out due to injuries suffered by team members during a season and the place difference between their actual and expected finish in the EPL table (according to overall player value). Moreover, we can interpolate that approximately 136 days out due to injury causes a team the loss of one league point, and that approximately 271 days out due to injury costs a team one place in the table. This interpolation formula is used as a heuristic model, and given the relationship specified above accounts for a significant portion of the variance in league placement (21%), the remaining variance is related to other factors. Calculating the costs of wage bills and prize money, we estimate that an EPL team loses an average of £45 million sterling due to injury-related decrement in performance per season.

Conclusion

Professional football clubs have a strong economic incentive to invest in injury prevention and rehabilitation programmes.

Hamstring strength and architectural adaptations following inertial flywheel resistance training

OBJECTIVES

To investigate the architectural and strength adaptations of the hamstrings following 6-weeks of inertial flywheel resistance training.

DESIGN

Randomised, stratified training intervention METHODS: Twenty healthy males undertook 6-weeks of a conventional (n=10) or eccentrically biased (n=10) flywheel leg-curl training intervention as well as a subsequent 4-week detraining period. Biceps femoris long head (BFlh) architecture was assessed weekly, whilst assessments of eccentric and isometric knee flexor strength and rate of force development (RFD) were conducted prior to and following the intervention and detraining periods.

RESULTS

The participants who undertook the eccentrically biased flywheel intervention showed a significant 14±5% (p<0.001, d=1.98) increase in BFlh fascicle length after 6-weeks of training. These improvements in fascicle length subsequently declined by 13±4% (p<0.001. d=-2.04) following the 4-week detraining period. The conventional flywheel leg-curl training group saw no changes in BFlh fascicle length after the intervention (-0.5%±0.8%, p=0.939, d=-0.04) or detraining (-1.1%±1%, p=0.984, d=-0.03) periods. Both groups saw no changes in any of the strength or RFD variables after the intervention or the detraining period.

CONCLUSIONS

Flywheel leg-curl training performed with an eccentric bias led to significant lengthening of BFlh fascicles without a change in RFD, eccentric or isometric strength. These increases in fascicle length were lost following a 4-week detraining period. Conventional flywheel leg-curl training resulted in no changes in fascicle length, strength and RFD. These findings suggest that additional eccentric bias is required during inertial flywheel resistance training to promote fascicle lengthening in the BFlh, however this may still be insufficient to cause alterations to strength and RFD.

Diagnosis, prevention and treatment of common lower extremity muscle injuries in sport - grading the evidence: a statement paper commissioned by the Danish Society of Sports Physical Therapy (DSSF)

This statement summarises and appraises the evidence on diagnosis, prevention and treatment of the most common lower extremity muscle injuries in sport. We systematically searched electronic databases, and included studies based on the highest available evidence. Subsequently, we evaluated the quality of evidence using the Grading of Recommendations Assessment, Development and Evaluation framework, grading the quality of evidence from high to very low. Most clinical tests showed very low to low diagnostic effectiveness. For hamstring injury prevention, programmes that included the Nordic hamstring exercise resulted in a hamstring injury risk reduction when compared with usual care (medium to large effect size; moderate to high quality of evidence). For prevention of groin injuries, both the FIFA 11+programme and the Copenhagen adductor strengthening programme resulted in a groin injury risk reduction compared with usual care (medium effect size; low to moderate quality of evidence). For the treatment of hamstring injuries, lengthening hamstring exercises showed the fastest return to play with a lower reinjury rate compared with conventional hamstring exercises (large effect size; very low to low quality of evidence). Platelet-rich plasma had no effect on time to return-to-play and reinjury risk (trivial effect size; moderate quality of evidence) after a hamstring injury compared with placebo or rehabilitation. At this point, most outcomes for diagnosis, prevention and treatment were graded as very low to moderate quality of evidence, indicating that further high-quality research is likely to have an important impact on the confidence in the effect estimates.

Recalibrating the risk of hamstring strain injury (HSI): A 2020 systematic review and meta-analysis of risk factors for index and recurrent hamstring strain injury in sport

OBJECTIVE

To systematically review risk factors for hamstring strain injury (HSI).

DESIGN

Systematic review update.

DATA SOURCES

Database searches: (1) inception to 2011 (original), and (2) 2011 to December 2018 (update). Citation tracking, manual reference and ahead of press searches.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies presenting prospective data evaluating factors associated with the risk of index and/or recurrent HSI.

METHOD

Search result screening and risk of bias assessment. A best evidence synthesis for each factor and meta-analysis, where possible, to determine the association with risk of HSI.

RESULTS

The 78 studies captured 8,319 total HSIs, including 967 recurrences, in 71,324 athletes. Older age (standardised mean difference=1.6, p=0.002), any history of HSI (risk ratio (RR)=2.7, p<0.001), a recent HSI (RR=4.8, p<0.001), previous anterior cruciate ligament (ACL) injury (RR=1.7, p=0.002) and previous calf strain injury (RR=1.5, p<0.001) were significant risk factors for HSI. From the best evidence synthesis, factors relating to sports performance and match play, running and hamstring strength were most consistently associated with HSI risk. The risk of recurrent HSI is best evaluated using clinical data and not the MRI characteristics of the index injury.

SUMMARY/CONCLUSION

Older age and a history of HSI are the strongest risk factors for HSI. Future research may be directed towards exploring the interaction of risk factors and how these relationships fluctuate over time given the occurrence of index and recurrent HSI in sport is multifactorial.

Eccentric hamstring strength in elite track and field athletes on the British Athletics world class performance program

OBJECTIVES

This novel study aims to provide unique data on eccentric hamstring strength in elite track and field athletes.

DESIGN

Clinical measurement, cross-sectional study.

SETTING

Across two British Athletics performance centres.

PARTICIPANTS

44 elite British track and field athletes.

MAIN OUTCOME MEASURES

Eccentric hamstring force and torque were evaluated using the Nordbord device. Injury history and demographic data was collected to assess whether differences between gender, event group, limb symmetry and previous injury history were present.

RESULTS

Average peak force for males and females was 418.38N and 318.54N. Relative to body weight there were no gender differences (Male 5.21N.kg^-1, Female 4.99N.kg^-1) (p = 0.62). The right limb was significantly stronger in long sprint (400m athletes) (p = 0.00018) (d = 0.56). No differences in relative force or torque were observed between previously injured and non-injured limbs.

CONCLUSIONS

This study provides unique data in elite track and field athletes. Relative force per kilogram should be used when comparing male and female athletes. Unlike other studies, we found no difference in eccentric strength between previously injured and non-injured limbs. The novel finding of increased eccentric strength demonstrated in the right limb in 400m sprinters may be due to the asymmetric demands of bend running and may be considered normal.

Does a recent hamstring muscle injury affect the timing of muscle activation during high speed overground running in professional Australian Football players?

OBJECTIVES

To investigate if the temporal characteristics of hamstring and gluteal muscle activation are altered during high speed overground running in professional Australian Football players following hamstring muscle injury.

DESIGN

Cohort study.

SETTING

Field-based testing.

PARTICIPANTS

Elite professional Australian Football players who had sustained a hamstring muscle injury in the six months prior to testing (n = 7) and a group of players from the same club who had no history of hamstring muscle injury (n = 8).

MAIN OUTCOME MEASURES

Muscle onset timing, muscle offset timing and muscle onset duration of the medial hamstrings, biceps femoris and gluteus maximus muscles during high-speed running using electromyographic data.

RESULTS

No significant differences in any of the temporal aspects of muscle activation were found between groups for any of the muscles tested (p > 0.05).

CONCLUSIONS

Persistent alterations to the timing of muscle activation following hamstring muscle injury that have been reported in recreational athletes were not observed during high speed running in professional athletes who have completed comprehensive rehabilitation programs.

Relationships Among PlayerLoad, High-Intensity Intermittent Running Ability, and Injury Risk in Professional Rugby League Players

PURPOSE

To examine relationships among physical performance, workload, and injury risk in professional rugby league players.

METHODS

Maximal-effort (n = 112) and submaximal (n = 1084) running performances of 45 players were recorded from 1 club over 2 consecutive seasons. Poorer and better submaximal running performance was determined by higher and lower exercise heart rates, respectively. Exponentially weighted moving averages and daily rolling averages were used to assess microtechnology-derived acute and chronic field-based workloads. The associations among within-individual submaximal running performance, workload, and noncontact lower-limb injury were then investigated.

RESULTS

The injury risk associated with poorer submaximal performance was "likely" greater than stable (relative risk = 1.8; 90% confidence interval, 0.9-3.7) and better submaximal performance (relative risk = 2.0; 90% confidence interval, 0.9-4.4). Compared with greater submaximal performance, poorer performance was associated with lower chronic workloads (effect size [d] = 0.82 [0.13], large) and higher acute:chronic workload ratios (d = 0.49 [0.14], small). Chronic workload demonstrated a "nearly perfect" positive relationship with maximal-effort running performance (exponentially weighted moving average, R2 = .91 [.15]; rolling average, R2 = .91 [.14]). At acute:chronic workload ratios >1.9, no differences in injury risk were found between rolling average and exponentially weighted moving average methods (relative risk = 1.1; 90% confidence interval, 0.3-3.8; unclear).

CONCLUSIONS

Reductions in submaximal running performance are related with low chronic workloads, high acute:chronic workload ratios, and increased injury risk. These findings demonstrate that a submaximal running assessment can be used to provide information on physical performance and injury risk in professional rugby league players.

Pain-Free Versus Pain-Threshold Rehabilitation Following Acute Hamstring Strain Injury: A Randomized Controlled Trial

OBJECTIVE

The primary aim was to compare time from acute hamstring strain injury (HSI) to return-to-play (RTP) clearance following a standardized rehabilitation protocol performed within either pain-free or pain-threshold limits. Secondary aims were to compare isometric knee flexor strength, biceps femoris long head (BFLH) fascicle length, fear of movement, and reinjury occurrence at the 6-month follow-up between pain-free and pain-threshold groups.

DESIGN

Randomized controlled trial.

METHODS

Forty-three men with acute HSIs were randomly allocated to a pain-free (n = 22) or pain-threshold (n = 21) rehabilitation group. Days from HSI to RTP clearance, isometric knee flexor strength, BFLH fascicle length, fear of movement, and reinjury occurrence at the 6-month follow-up were reported.

RESULTS

Median time from HSI to RTP clearance was 15 days (95% confidence interval [CI]: 13, 17) in the pain-free group and 17 days (95% CI: 11, 24) in the pain-threshold group, which was not significantly different (P = .37). Isometric knee flexor strength recovery at 90° of hip and 90° of knee flexion was greater in the pain-threshold group at RTP clearance by 15% (95% CI: 1%, 28%) and by 15% (95% CI: 1%, 29%) at 2-month follow-up, respectively. Improvement in BFLH fascicle length from baseline was 0.91 cm (95% CI: 0.34, 1.48) greater at 2-month follow-up in the pain-threshold group. Two reinjuries occurred in both the pain-free and pain-threshold groups between RTP clearance and the 6-month follow-up.

CONCLUSION

Pain-threshold rehabilitation did not accelerate RTP clearance, but resulted in greater recovery of isometric knee flexor strength and better maintenance of BFLH fascicle length, compared to pain-free rehabilitation. J Orthop Sports Phys Ther 2020;50(2):91-103. Epub 28 Jun 2019. doi:10.2519/jospt.2020.8895.

Device and method matter: A critical evaluation of eccentric hamstring muscle strength assessments

Equivocal findings exist on isokinetic and Nordic hamstring exercise testing of eccentric hamstring strength capacity. Here, we propose a critical comparison of the mechanical output of hamstring muscles as assessed with either a dynamometer (IKD) or a Nordic hamstring device (NHD). Twenty-five volunteers (26 ± 3 years) took part in a counterbalanced repeated-measures protocol on both devices. Eccentric peak torque, work, angle of peak torque, bilateral strength ratios, and electromyography activity of the biceps femoris long head, semitendinosus and gastrocnemius muscles were assessed. There was a very poor correlation in eccentric peak torque between the devices (r < 0.58), with a systematic and proportional bias toward lower torque values on the IKD (~28%) and a high typical error (~19%) in IKD and NHD measurements comparison. Furthermore, participants performed a higher total eccentric work on IKD, reached peak torques at greater knee extension angles, and showed a greater side-to-side strength difference compared to the Nordic hamstring exercise. Gastrocnemius muscle activity was lower during the Nordic hamstring exercise. Reliability was low for work on NHD and for angle of peak torque and bilateral strength ratios on either device. We conclude that the evaluation of eccentric knee flexor strength depends on the testing conditions and even under standardized procedures, the IKD and NHD measure a different trait. Both tests have limitations in terms of assessing strength differences within an individual, and measurements of the angle of peak torque or side-to-side differences in eccentric knee flexor strength revealed low reliability and should be considered with caution.

The effects of sprint training and the Nordic hamstring exercise on eccentric hamstring strength and sprint performance in adolescent athletes

BACKGROUND

Hamstring strain injuries (HSI) are among the most common injuries in field-based team sports with a high-speed running component. The implementation of the Nordic hamstring exercise (NHE) is a well-documented method of improving eccentric hamstring strength to mitigate the risk of HSI occurrence. Sprint training is specific to the injury mechanism and is thought to activate the hamstrings through maximal eccentric contractions. The purpose of this study was to compare the effects of sprint training and the NHE on eccentric hamstring strength and sprint performance.

METHODS

Twenty-eight participants (mean±SD age=16.21±1.34 years; height=1.75m±0.10m; body mass=68.5kg±12.1kg) completed an eccentric hamstring strength assessment and 40m sprint to assess acceleration and maximum speed. Participants were randomly allocated to either a NHE training or sprint training group. Two sessions per week for four-weeks of training was performed with baseline testing procedures repeated in the week following the intervention. Perceptions of soreness were recorded following the warm-up in each training session.

RESULTS

Both the NHE (effect size=0.39, P<0.05) and sprint training (effect size=0.29, P<0.05) groups displayed significant gains in eccentric hamstring strength. The NHE group reported trivial improvements in sprint performance, whilst the sprint training group experienced a moderate improvement, specifically in maximum speed (ES=0.83 Moderate). Sprint training also produced greater perceptions of soreness than the NHE following a four-week training intervention, specifically before the start of the last session (P<0.05).

CONCLUSIONS

These findings indicate that sprint training had a beneficial effect for both eccentric hamstring strength and sprint performance, whilst also producing greater soreness than the NHE following the final training session. It was concluded that a four-week block of maximum speed training may have both an injury prevention and performance enhancement benefit.

Early return to sport post maxillofacial fracture injury in the professional athlete: A systematic review

INTRODUCTION

To summarize the current literature on return to sport times post-maxillofacial fracture injury in the professional athlete.

MATERIALS AND METHODS

A literature search on six databases for articles relating to maxillofacial fractures, professional athletes, and return to sport times. Study design, clinical data, and author recommendations were analysed.

RESULTS

17 studies were retrieved. One prospective study returned 17 athletes to competitive rugby union and soccer at 3 weeks post injury without complication. Two large retrospective studies (n = 278) returned patients to sport at approximately 7 weeks without complication. 64% (n = 7) of patients from case based studies returned to sport at 3-14 days, 4 of which utilized protective facemasks. Athletes generally returned to competition earlier for lower grade (3-10 days) compared to higher grade contact sport (21 days at least). 2 articles recommended a 3 months recovery period for combat sports. 8 articles supported the utility of protective facemasks.

CONCLUSION

Early return to sport (<6 weeks) in the professional athlete post maxillofacial fracture injury is achievable. The optimal clinical approach may be to grade the sport according to its impact forces, discuss an early return with reference to the available literature, the potential utility of facemasks, risks of refracture and its operative implications.

Impact of Hip Flexion Angle on Unilateral and Bilateral Nordic Hamstring Exercise Torque and High-Density Electromyography Activity

BACKGROUND

In the bilateral Nordic hamstring exercise (NHE), hamstrings operate at relatively short lengths, which may limit the efficacy of the NHE in hamstring injury prevention.

OBJECTIVES

To examine knee flexion torque and biceps femoris long head (BFLH) and semitendinosus (ST) high-density electromyography (EMG) activity during the unilateral and bilateral NHE, performed with either neutral (NHE0) or 90°-flexed (NHE90) hips.

METHODS

In this laboratory study, exercises were performed on a novel device at the eccentric 1-repetition maximum load defined for 90° to 15° of knee range of motion. Torque and EMG signals normalized to maximal voluntary isometric activity were compared in different phases of the exercises with statistical parametric mapping.

RESULTS

The EMG levels were lower in NHE90 than in NHE0, mainly in the second half of the movement. Knee flexor eccentric torque was higher in NHE90 than in NHE0 from the beginning to 87% of the bilateral movement, and over the entire unilateral movement. In NHE0, ST activity compared to BFLH activity was higher during the initial movement phase and lower when the movement was close to knee extension. Torque and EMG activity were generally similar in the bilateral and unilateral modes.

CONCLUSION

If performed with neutral hips, the NHE selectively activates the BFLH near full knee extension. Performing the NHE with hips flexed to 90° is preferable when higher passive torque and ST selectivity are targeted at a longer muscle length. Performing these exercises unilaterally could help train each limb separately, with similar torque and EMG output to those of the bilateral conditions. J Orthop Sports Phys Ther 2019;49(8):584-592. Epub 26 Mar 2019. doi:10.2519/jospt.2019.8801.

Modeling the Risk of Team Sport Injuries: A Narrative Review of Different Statistical Approaches

Injuries are a common occurrence in team sports and can have significant financial, physical and psychological consequences for athletes and their sporting organizations. As such, an abundance of research has attempted to identify factors associated with the risk of injury, which is important when developing injury prevention and risk mitigation strategies. There are a number of methods that can be used to identify injury risk factors. However, difficulty in understanding the nuances between different statistical approaches can lead to incorrect inferences and decisions being made from data. Accordingly, this narrative review aims to (1) outline commonly implemented methods for determining injury risk, (2) highlight the differences between association and prediction as it relates to injury and (3) describe advances in statistical modeling and the current evidence relating to predicting injuries in sport. Based on the points that are discussed throughout this narrative review, both researchers and practitioners alike need to carefully consider the different types of variables that are examined in relation to injury risk and how the analyses pertaining to these different variables are interpreted. There are a number of other important considerations when modeling the risk of injury, such as the method of data transformation, model validation and performance assessment. With these technical considerations in mind, researchers and practitioners should consider shifting their perspective of injury etiology from one of reductionism to one of complexity. Concurrently, research implementing reductionist approaches should be used to inform and implement complex approaches to identifying injury risk. However, the ability to capture large injury numbers is a current limitation of sports injury research and there has been a call to make data available to researchers, so that analyses and results can be replicated and verified. Collaborative efforts such as this will help prevent incorrect inferences being made from spurious data and will assist in developing interventions that are underpinned by sound scientific rationale. Such efforts will be a step in the right direction of improving the ability to identify injury risk, which in turn will help improve risk mitigation and ultimately the prevention of injuries.

Pain-Free Versus Pain-Threshold Rehabilitation Following Acute Hamstring Strain Injury: A Randomized Controlled Trial

STUDY DESIGN

Randomized controlled trial.

BACKGROUND

Conventional guidelines recommend hamstring strain injury (HSI) rehabilitation should only be performed and progressed in complete absence of pain, despite lack of comparison to alternative approaches.

OBJECTIVES

The primary aim of this study was to compare the number of days from acute HSI to return to play (RTP) clearance following a standardised rehabilitation protocol performed within either pain-free or pain-threshold limits. The secondary aims were to compare isometric knee flexor strength, biceps femoris long head (BFlh) fascicle length, fear of movement and re-injury during a six-month follow-up between pain-free and pain-threshold groups.

METHODS

Forty-three men with acute HSIs were randomly allocated to either a pain-free (n=22) or pain-threshold (n=21) rehabilitation group. Days from HSI to RTP clearance, isometric knee flexor strength, BFlh fascicle length, fear of movement and re-injuries within six-month follow-up were reported.

RESULTS

The median time from HSI to RTP clearance was 15 days (95% CI = 13 to 17) in the pain-free group and 17 days (95% CI = 11 to 24) in the pain-threshold group, which was not significantly different (p = 0.37). Recovery of isometric knee flexor strength at 90/90 degrees of hip/knee flexion was greater in the pain-threshold group at RTP clearance by 15% (95% CI = 1 to 28) and by 15% (95% CI = 1 to 29) at two-month follow-up. BFlh fascicles were 0.91cm (95% CI = 0.34 to 1.48) longer at two-month follow-up in the pain-threshold group. Two re-injuries occurred in both the pain-free and pain-threshold group during six-month follow-up.

CONCLUSION

Pain-threshold rehabilitation did not accelerate RTP clearance but did result in greater recovery of isometric knee flexor strength and better maintenance of BFlh fascicle length improvements compared to pain-free rehabilitation. J Orthop Sports Phys Ther, Epub 28 Jun 2019. doi:10.2519/jospt.2019.8895.

Session Availability as a Result of Prior Injury Impacts the Risk of Subsequent Non-contact Lower Limb Injury in Elite Male Australian Footballers

Prior injury is a commonly identified risk factor for subsequent injury. However, a binary approach to classifying prior injury (i.e., yes/no) is commonly implemented and may constrain scientific findings, as it is possible that variations in the amount of time lost due to an injury will impact subsequent injury risk to differing degrees. Accordingly, this study investigated whether session availability, a surrogate marker of prior injury, influenced the risk of subsequent non-contact lower limb injury in Australian footballers. Data were collected from 62 male elite Australian footballers throughout the 2015, 2016, and 2017 Australian Football League seasons. Each athlete's participation status (i.e., full or missed/modified) and any injuries that occurred during training sessions/matches were recorded. As the focus of the current study was prior injury, any training sessions/matches that were missed due to reasons other than an injury (e.g., load management, illness and personal reasons) were removed from the data prior to all analyses. For every Monday during the in-season periods, session availability (%) in the prior 7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, and 84 days was determined as the number of training sessions/matches fully completed (injury free) relative to the number of training sessions/matches possible in each window. Each variable was modeled using logistic regression to determine its impact on subsequent injury risk. Throughout the study period, 173 non-contact lower limb injuries that resulted in at least one missed/modified training session or match during the in-season periods occurred. Greater availability in the prior 7 days increased injury probabilities by up to 4.4%. The impact of session availability on subsequent injury risk diminished with expanding windows (i.e., availability in the prior 14 days through to the prior 84 days). Lesser availability in the prior 84 days increased injury probabilities by up to 14.1%, only when coupled with greater availability in the prior 7 days. Session availability may provide an informative marker of the impact of prior injury on subsequent injury risk and can be used by coaches and clinicians to guide the progression of training, particularly for athletes that are returning from long periods of injury.

Predictive Modeling of Hamstring Strain Injuries in Elite Australian Footballers

PURPOSE

Three of the most commonly identified hamstring strain injury (HSI) risk factors are age, previous HSI, and low levels of eccentric hamstring strength. However, no study has investigated the ability of these risk factors to predict the incidence of HSI in elite Australian footballers. Accordingly, the purpose of this prospective cohort study was to investigate the predictive ability of HSI risk factors using machine learning techniques.

METHODS

Eccentric hamstring strength, demographic and injury history data were collected at the start of preseason for 186 and 176 elite Australian footballers in 2013 and 2015, respectively. Any prospectively occurring HSI were reported to the research team. Using various machine learning techniques, predictive models were built for 2013 and 2015 within-year HSI prediction and between-year HSI prediction (2013 to 2015). The calculated probabilities of HSI were compared with the injury outcomes and area under the curve (AUC) was determined and used to assess the predictive performance of each model.

RESULTS

The minimum, maximum, and median AUC values for the 2013 models were 0.26, 0.91, and 0.58, respectively. For the 2015 models, the minimum, maximum and median AUC values were, correspondingly, 0.24, 0.92, and 0.57. For the between-year predictive models the minimum, maximum, and median AUC values were 0.37, 0.73, and 0.52, respectively.

CONCLUSIONS

Although some iterations of the models achieved near perfect prediction, the large ranges in AUC highlight the fragility of the data. The 2013 models performed slightly better than the 2015 models. The predictive performance of between-year HSI models was poor however. In conclusion, risk factor data cannot be used to identify athletes at an increased risk of HSI with any consistency.

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 NHE_bodyweight (n = 10), NHE_weighted (n = 10), or RHC_weighted 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 NHE_weighted 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 NHE_weighted group (-0.96 cm, P = 0.021, d = -0.90). Comparatively, BFlh fascicle length and NHE strength responses were moderate in the NHE_bodyweight group and negligible in the RHC_weighted group. The greatest RHC strength changes (+82N, P = 0.038, d = 1.15) were seen in the RHC_weighted group.

CONCLUSIONS

NHE_weighted interventions induce large BFlh fascicle lengthening responses and these adaptations decay after just 1 week of detraining. NHE_bodyweight training has a moderate impact on BFlh architecture while the RHC_weighted 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.

Validation study of the Functional Assessment Scale for Acute Hamstring injuries in Spanish professional soccer players

Objective:

To cross-culturally adapt and validate the Functional Assessment Scale for acute hamstring injury for professional Spanish-speaking soccer players.

Design:

Clinical measurement study. Cross-cultural adaptation was conducted following international recommendations. Indicators of validity, reliability and responsiveness are provided.

Subjects:

The Spanish version of the Functional Assessment Scale for acute hamstring injury scale was administered to 165 participants: 45 professional soccer players with acute hamstring muscle injury diagnosis, 40 healthy subjects, 40 individuals at-risk for a hamstring muscle injury and 40 patients with injuries of the lower limb other than hamstring muscle injury.

Main measures:

The Functional Assessment Scale for acute hamstring injury.

Reference measures:

Spanish version of the Quality of Life Short-Form 36 questionnaire (SF-36) and the Lower Limb Functional Index (LLFI).

Results:

Cronbach’s alpha (internal consistency) for the Spanish version of the Functional Assessment Scale for acute hamstring injury scale was >0.8. The intraclass correlation coefficient using the two-way random model (ICC2,1) (test–retest) was 0.993 (95% confidence interval (CI): 0.991–0.995; P < 0.05). In the exploratory factor analysis, a one-factor solution explained 85% of the variance. Subjects with hamstring muscle injury scored significantly lower than the other groups in the Spanish version of the Functional Assessment Scale for acute hamstring injury scale ( P < 0.001). The Spanish version of the Functional Assessment Scale for acute hamstring injury scale score within the hamstring muscle injury group showed moderate and significant correlations with SF-36 physical components (Spearman’s rs > 0.6; P < 0.001), and LLFI score at baseline ( rs = 0.42; P < 0.01). The standard error of measurement (SEM) and minimum detectable change threshold (MDC95%) were 2.6 and 7.2 points, respectively. The responsiveness indicators have an effect size of 3.62, and the standardized response mean is 3.24.

Conclusion:

The Spanish version of the Functional Assessment Scale for acute hamstring injury scale showed satisfactory psychometric properties. It can be considered a reliable and valid instrument to assess the functional impact of acute hamstring muscle injury in professional Spanish-speaking football players.

The design, development, implementation and evaluation of IRISweb; A rugby-specific web-based injury surveillance system

OBJECTIVES

To describe the development, implementation and evaluation of a comprehensive injury surveillance system.

DESIGN

The four phases; i) A survey of 58 medical professionals working in amateur rugby. ii) The design of a web-based injury surveillance system (IRISweb). iii) Recruitment of 21 of the top 58 amateur clubs to use IRISweb. iv) An evaluation survey of the 21 participating clubs.

SETTING

Irish amateur rugby clubs.

PARTICIPANTS

Medical professionals working in amateur rugby.

MAIN OUTCOME MEASURES

Phase one investigated the injury monitoring practices in operation prior to the IRIS project. Phase four investigated the effectiveness and usefulness of IRISweb.

RESULTS

Twenty-one clubs were recruited, however 2 clubs failed to provide a full season of data (10% dropout rate). Eighty-two percent of the remaining 19 clubs rated IRISweb as 'good' or 'very good'. Facilitators of injury surveillance were; increased player adherence (65%) and notifications to update the system (59%), however, poor player adherence (71%) and medical staff availability (24%) were the main barriers.

CONCLUSIONS

The IRIS project is the first prospective long-term injury surveillance system in Irish amateur rugby, effectively tracking injuries to guide future evidence-based injury prevention strategies. This study highlights facilitators and barriers to injury surveillance within amateur sport.

Acute adaptations and subsequent preservation of strength and speed measures following a Nordic hamstring curl intervention: a randomised controlled trial

This randomised controlled trial investigated changes in eccentric hamstring strength, 10m sprint speed, and change-of-direction (COD) performance immediately post Nordic hamstring curl (NHC) intervention and following a 3-week detraining period. Fourteen male team sports athletes were randomised to a do-as-usual control group (CG; n = 7) or to a NHC intervention group (NHC; n = 7). Isokinetic dynamometry at 180°/s evaluated eccentric hamstring strength immediately post-intervention as the primary outcome measure. Secondary outcomes included 10 m sprint time and COD. Each outcome was measured, pre, immediately post-intervention and following a 3-week detraining period. Immediately post-intervention significant group differences were observed in the NHC group for eccentric hamstring strength (31.81 Nm^-1 vs. 6.44 Nm^-1, P = 0.001), COD (-0.12 s vs. 0.20 s; P = 0.003) and sprint (- 0.06 s vs. 0.05 s; P = 0.024) performance. Performance improvements were maintained following a detraining period for COD (-0.11 s vs. 0.20 s; P = 0.014) and sprint (-0.05 s vs. 0.03 s, P = 0.031) but not eccentric hamstring strength (15.67 Nm^-1 vs. 6.44 Nm^-1, P = 0.145) These findings have important implications for training programmes designed to reduce hamstring injury incidence, whilst enhancing physical qualities critical to sport.

Is neuromuscular inhibition detectable in elite footballers during the Nordic hamstring exercise?

BACKGROUND

The presence of neuromuscular inhibition following injury may explain the high incidence of biceps femoris injury recurrence in elite (soccer) footballers. This phenomenon may be detectable in elite players during the Nordic hamstring exercise. Thus, the first purpose of this study was to assess biceps femoris muscle activation during this exercise in players with hamstring injury history. Additionally, following injury, observed increases in synergistic muscle activation may represent a protective mechanism to the presence of neuromuscular inhibition. Thus, the second purpose was to identify if the relative contributions of biceps femoris, and its synergists reflected a post-injury pattern of activation suggestive of these potentially compensatory neural mechanisms.

METHODS

Ten elite players with a history of hamstring injury and ten elite players without a history of hamstring injury, completed six repetitions of the Nordic hamstring exercise. During each trial, biceps femoris, semitendinosus and gluteus maximus muscle activations were collected at 90-30° and 30-0° of knee flexion.

FINDINGS

Biceps femoris activation was significantly higher at 90-30° of knee flexion compared to 30-0° (P < 0.001) but did not differ between the groups. In players with a history of injury, muscle activation ratios for the biceps femoris/semitendinosus (P = 0.001) and biceps femoris/gluteus maximus (P = 0.023) were significantly greater at 30-0° of knee flexion than in the control group.

INTERPRETATION

Neuromuscular inhibition of the biceps femoris was not detected during the exercise within elite footballers, yet the relative contributions of biceps femoris and its synergists appear to change following injury.

The First Decade of Web-Based Sports Injury Surveillance: Descriptive Epidemiology of Injuries in US High School Girls' Soccer (2005-2006 Through 2013-2014) and National Collegiate Athletic Association Women's Soccer (2004-2005 Through 2013-2014)

CONTEXT:

The advent of Web-based sports injury surveillance via programs such as the High School Reporting Information Online system and the National Collegiate Athletic Association Injury Surveillance Program has aided the acquisition of girls' and women's soccer injury data.

OBJECTIVE:

To describe the epidemiology of injuries sustained in high school girls' soccer in the 2005-2006 through 2013-2014 academic years and collegiate women's soccer in the 2004-2005 through 2013-2014 academic years using Web-based sports injury surveillance.

DESIGN:

Descriptive epidemiology study.

SETTING:

Online injury surveillance from soccer teams in high school girls (annual average = 100) and collegiate women (annual average = 52).

PATIENTS OR OTHER PARTICIPANTS:

Female high school and collegiate soccer players who participated in practices or competitions during the 2004-2005 through 2013-2014 academic years.

MAIN OUTCOME MEASURE(S):

Athletic trainers collected time-loss (≥24 hours) injury and exposure data. Injury rates per 1000 athlete-exposures (AEs), injury rate ratios (IRRs) with 95% confidence intervals (CIs), injury proportions by body site, and diagnoses were calculated.

RESULTS:

The High School Reporting Information Online system documented 3242 time-loss injuries during 1 393 753 AEs; the National Collegiate Athletic Association Injury Surveillance Program documented 5092 time-loss injuries during 772 048 AEs. Injury rates were higher in college than in high school (6.60 versus 2.33/1000 AEs; IRR = 2.84; 95% CI = 2.71, 2.96), and during competitions than during practices in high school (IRR = 4.88; 95% CI = 4.54, 5.26) and college (IRR = 2.93; 95% CI = 2.77, 3.10). Most injuries at both levels affected the lower extremity and were ligament sprains or muscle/tendon strains. Concussions accounted for 24.5% of competition injuries in high school but 14.6% of competition injuries in college. More than one-third of competition injuries to high school goalkeepers were concussions.

CONCLUSIONS:

Injury rates were higher in college versus high school and during competitions versus practices. These differences may be attributable to differences in reporting, activity intensity, and game-play skill level. The high incidence of lower extremity injuries and concussions in girls' and women's soccer, particularly concussions in high school goalkeepers, merits further exploration and identification of prevention strategies.

The effect of Nordic hamstring exercise training volume on biceps femoris long head architectural adaptation

The aim of this study was to determine the time course of architectural adaptations in the biceps femoris long head (BF_LH ) following high or low volume eccentric training. Twenty recreationally active males completed a two week standardized period of eccentric Nordic hamstring exercise (NHE) training, followed by four weeks of high (n = 10) or low volume (n = 10) training. Eccentric strength was assessed pre- and post intervention and following detraining. Architecture was assessed weekly during training and after two and four weeks of detraining. After six weeks of training, BF_LH fascicles increased significantly in the high (23% ± 7%, P < .001, d = 2.87) and low volume (24% ± 4%, P < .001, d = 3.46) groups, but reversed following two weeks of detraining (high volume: -17% ± 5%, P < .001, d = -2.04; low volume: -15% ± 3%, P < .001, d = -2.56) after completing the intervention. Both groups increased eccentric strength after six weeks of training (high volume: 28% ± 20%, P = .009, d = 1.55; low volume: 34% ± 14%, P < .001, d = 2.09) and saw no change in strength following a four week period of detraining (high volume: -7% ± 7%, P = .97, d = -0.31; low volume: -2% ± 5%, P = .99, d = -0.20). Both low and high volume NHE training stimulate increases in BF_LH fascicle length and eccentric knee flexor strength. Architectural adaptations reverted to baseline levels within two weeks after ceasing training, but eccentric strength was maintained for at least four weeks. These observations provide novel insight into the effects of training volume and detraining on BF_LH architecture and may provide guidance for the implementation of NHE programs.

Knee flexion not hip extension strength is persistently reduced following hamstring strain injury in Australian Football athletes: Implications for Periodic Health Examinations

OBJECTIVES

Determine whether clinically feasible tests of isometric lower limb strength and range of motion (ROM) in Australian Football (AF) athletes are useful in Periodic Health Examinations to identify persistent deficits following hamstring strain injury (HSI).

DESIGN

Case-control.

METHODS

Thirty-seven male, semi-professional AF athletes (mean±SD; age, 20.2±2.9years; height, 1.7±0.5m; mass, 81±9.2kg) participated, ten athletes (37%) reported HSI within the previous three seasons of competition. Comparisons of pre-season isometric knee flexion and hip extension strength variables (peak force, torque and torque normalised to body mass) and hip, knee and ankle ROM measures were made between athletes with and without past-history of HSI using linear mixed-effect models. A logistic regression evaluated whether any of the outcome measures could differentiate athletes with a past-history of HSI.

RESULTS

Knee flexion peak force, torque and torque normalised to body mass were significantly reduced in athletes with a past-history of HSI (coefficient, 95% CI) (-44.8N, -86.3 to -3.3), (-22.2Nm, -40.5 to -3.7) and (-0.2Nmkg^-1, -0.4 to 0.0) respectively. Knee flexion peak torque normalised to body mass (Nmkg^-1) approached significance as a test was able to differentiate athletes with history of HSI (p=0.068). There were no differences between groups for any hip extension strength or lower limb ROM outcome measures.

CONCLUSIONS

Deficits in isometric peak knee flexion strength persist for up to three seasons following HSI in AF athletes. Isometric knee flexion strength testing may be a clinically feasible option for Periodic Health Examinations and inform tertiary injury prevention strategies.

The associations between training load and baseline characteristics on musculoskeletal injury and pain in endurance sport populations: A systematic review

OBJECTIVES

To determine the associations between training load, baseline characteristics (e.g. age or previous injury) and rate of musculoskeletal injury and/or pain specifically within an Endurance Sporting Population (ESP).

DESIGN

Prospectively registered systematic review.

METHODS

Eight electronic databases were searched by two independent reviewers. Studies were required to prospectively monitor both (i) training loads and (ii) musculoskeletal injury and/or pain for >3 months. Methodological quality and risk of bias were determined utilising the Critical Skills Appraisal Program (CASP). Reported effect sizes were categorised as small, medium or large.

RESULTS

Twelve endurance sport studies were eligible (running, triathlon, rowing). Increased injury and/or pain risk was associated with: (i) high total training distances per week/month (medium effect size) (ii) training frequency <2 sessions/week (medium effect size) and (iii) both low weekly (<2hours/week) and high monthly (large effect size) training durations. None of the studies reported internal training load data or acute:chronic workload ratios. Baseline characteristics found to increase the rate of injury and/or pain included: (i) a history of previous injury (medium effect size), (ii) age >45 years (small effect size), (iii) non-musculoskeletal comorbidities (large effect size), (iv) using older running shoes (small effect size) and (v) non-competitive behaviour.

CONCLUSIONS

This review identifies a range of external training load factors and baseline characteristics associated with an increased rate of injury and/or pain within ESPs. There is an absence of research relating to internal training loads and acute:chronic workload ratios in relation to rate of injury and/or pain within ESPs.

A Novel Apparatus to Measure Knee Flexor Strength During Various Hamstring Exercises: A Reliability and Retrospective Injury Study

Study Design Reliability and case-control injury study. Background Knee flexor strength is a key variable when dealing with hamstring strain injury (HSI), and methodologies of objective measurement of strength are often limited to single exercises. Objectives To establish test-retest reliability of a novel apparatus to measure knee flexor strength during various hamstring exercises, and to investigate whether the measure can detect between-leg differences in male participants with and without history of unilateral HSI. Methods Twenty male participants without and 10 male participants with previous unilateral HSI participated. Isometric knee flexor strength and peak rate of force development (RFD) at 0°/0°, 45°/45°, and 90°/90° of hip/knee flexion were measured, as well as force impulse during bilateral and unilateral variations of an eccentric slider and hamstring bridge, using a novel apparatus. Intraclass correlation coefficient (ICC), typical error, and typical error as a coefficient of variation were calculated for all measures. The magnitudes of between-leg differences within each group were calculated using estimates of effect sizes, reported as Cohen's d and 90% confidence interval (CI). Results Moderate to high test-retest reliability was observed for isometric knee flexor strength (ICC = 0.87-0.92) and peak RFD (ICC = 0.88-0.95) across 3 positions and for mean force impulse during the eccentric slider (ICC = 0.83-0.90). In those with prior HSI, large deficits were observed in the previously injured leg compared to the contralateral uninjured leg for mean force impulse during the unilateral eccentric slider (d = -1.09; 90% CI: -0.20, -1.97), isometric strength at 0°/0° (d = -1.06; 90% CI: -0.18, -1.93) and 45°/45° (d = -0.88; 90% CI: -0.02, -1.74), and peak RFD at 45°/45° (d = -0.88; 90% CI: -0.02, -1.74). Conclusion The novel apparatus provides a reliable measure of isometric knee flexor strength, peak RFD, and force impulse during an eccentric slider, with deficits seen in previously injured hamstrings for these measures. J Orthop Sports Phys Ther 2018;48(2):72-80. Epub 26 Oct 2017. doi:10.2519/jospt.2018.7634.