Predicting Hamstring Strain Injury in Elite Athletes

Do athletes with hamstring strain injury have shorter muscle fascicles in the injured limb?

INTRODUCTION

Previous studies have suggested that a reduced length of the biceps femoris long head (BFlh) fascicles may increase the risk of hamstring strain injury (HSI). However, it remains unclear whether the BFlh fascicles of the injured limb are shorter than those of the contralateral limb in athletes with an acute HSI.

OBJECTIVE

To investigate the between-limb asymmetry of BFlh fascicle length in amateur athletes with an acute HSI.

METHODS

Male amateur athletes were evaluated using ultrasound scans within five days following an HSI. The BFlh fascicle length was estimated using a validated equation.

RESULTS

Eighteen injured athletes participated in this study. There was no significant difference (p = 0.27) in the length of BFlh fascicles between the injured limb (9.53 ± 2.55 cm; 95%CI 8.26 to 10.80 cm) and the uninjured limb (10.54 ± 2.87 cm; 95%CI 9.11 to 11.97 cm). Individual analysis revealed high heterogeneity, with between-limb asymmetries (percentage difference of the injured limb compared to the uninjured limb) ranging from -42% to 25%. Nine out of the 18 athletes had a fascicle length that was more than 10% shorter in the injured limb compared to the uninjured limb, five athletes had a difference of less than 10%, and four athletes had a fascicle length that was more than 10% longer in the injured limb compared to the uninjured limb.

CONCLUSION

The architecture characteristics of injured and uninjured muscles is not consistent among athletes with HSI. Therefore, rehabilitation programs focused on fascicle lengthening should be evaluated on a case-by-case basis.

A retrospective comparison of the biceps femoris long head muscle structure in athletes with and without hamstring strain injury history

INTRODUCTION

Hamstring strain injuries (HSI) and re-injuries are endemic in high-speed running sports. The biceps femoris long head (BFlh) is the most frequently injured muscle among the hamstrings. Structural parameters of the hamstring muscle are stated to be susceptible to strain injuries at this location. This retrospective study targeted comparing the BFlh's structural parameters between previously injured and uninjured athletes.

METHODS

Nineteen male athletes with previous BFlh strain injury history and nineteen athletes without former lower extremity injury history were included in this study. Fascicle length, mid-muscle belly and distal musculotendinous (MTJ) passive stiffnesses of the biceps femoris long head (BFlh) were examined via b-mode panoramic ultrasound scanning and ultrasound-based shear-wave elastography. Parameter comparisons of both legs within and between athletes with and without injury history were performed.

RESULTS

Comparison of the BFlh fascicle length between the injured leg of the injured group and the legs of the controls revealed a trend to shorter fascicle lengths in the injured leg (p = 0.067, d = -0.62). However, the mid-muscle belly passive stiffness of the BFlh was significantly higher in the injured legs (p = 0.009, d = 0.7) compared with the controls. Additionally, the distal MTJ stiffness was much higher in the previously injured legs compared with controls (p < 0.001, d = 1.6).

CONCLUSIONS

Outcomes support the importance of BFlh properties related to stiffness, and fascicle length for injury susceptibility in athletes. Future prospective studies should determine whether the higher stiffness in the injured athletes is a cause or consequence of the HSI. Physical therapy and rehabilitation programmes after HSI should focus on BFlh muscle properties i.e., elasticity and fascicle length for reducing re-injury and increasing sports performance.

Effects of Eccentric-Oriented Strength Training on Return to Sport Criteria in Late-Stage Anterior Cruciate Ligament (ACL)-Reconstructed Professional Team Sport Players

Background and Objectives: An effective post-injury training program is essential to regain performance and fulfill criteria for return to sport for team sport athletes following anterior cruciate ligament (ACL) reconstruction. The aim of this study was to compare the effects of 6 weeks of eccentric-oriented strength training vs. traditional strength training during the late-stage ACL-rehab phase on leg strength and vertical and horizontal jumping performance in professional team sport athletes. Materials and Methods: Twenty-two subjects (14 males, 8 females, age 19.9 ± 4.4 years, mass 77.4 ± 15.6 kg, height 182.4 ± 11.7 cm) (mean ± SD) with a unilateral reconstructed ACL (BTB graft) were included in the study. All participants enrolled in the same rehabilitation protocol prior to the training study. Players were randomly assigned to an experimental (ECC: n = 11, age 21.8 ± 4.6 years, mass 82.7 ± 16.6 kg, height 185.4 ± 12.2 cm), and a control group (CON: n = 11, age 19.1 ± 2.1 years, mass 76.6 ± 16.5 kg, height 182.5 ± 10.2 cm). Both groups underwent an equivolumed rehabilitation program, with the only difference being in strength training, which consisted of flywheel training vs. traditional strength training for the experimental and control groups, respectively. Testing was organized before and after the 6-week training programs and included isometric semi-squat tests (ISOSI-injured and ISOSU-uninjured legs), vertical jump tests (CMJ), single-leg vertical jump tests (SLJI-injured and SLJU-uninjured legs), single-leg hop tests (SLHI-injured and SLHU-uninjured legs), and triple hop tests (TLHI-injured and TLHU-uninjured legs). In addition, limb symmetry indexes were calculated for the isometric semi-squat (ISOSLSI) test, the single-leg vertical jump (SLJLSI), and the hop (SLHLSI) tests, as well as the triple-leg hop (THLLSI) test. Results: Main effects of time across training were observed for all dependent variables (posttest > pretest, p < 0.05). Significant group-by-time interactions were found for ISOSU (p < 0.05, ES = 2.51, very large), ISOSI (p < 0.05, ES = 1.78, large), CMJ (p < 0.05, ES = 2.23, very large), SLJI (p < 0.05, ES = 1.48, large), SLHI (p < 0.05, ES = 1.83, large), and TLHI (p < 0.05, ES = 1.83, large). Conclusions: This study suggests that eccentric-oriented strength training in late-stage ACL recovery, undertaken twice or three times weekly for 6 weeks, results in better outcomes than traditional strength training in leg strength, vertical jump ability, and single and triple hop tests with injured legs in professional team sport athletes. It seems that flywheel strength training can be recommended in late-stage ACL recovery for professional team sport athletes in order to regain recommended performance outcome levels faster.

Isokinetic Assessment of Knee Flexor and Extensor Strength and Lower Extremity Flexibility Assessment of an NCAA Division III Men's Soccer Team

Background

Strength imbalances and flexibility deficits of the hamstrings and hip flexors have been identified as potential risk factors for hamstring injuries, but research on athletes at the Division III level are limited, potentially due to a lack of resources and technology.

Purpose

The purpose of this study was to conduct isokinetic and flexibility assessments to screen male soccer athletes at risk of sustaining a hamstring injury.

Study Design

Observational cohort.

Methods

Standardized isokinetic testing of concentric muscle performance, measured by peak torque of the quadriceps and hamstrings and hamstring-to-quadriceps ratios, was conducted using a Biodex isokinetic dynamometer at speeds of 60 and 180°/sec. Additionally, the Active Knee Extension (AKE) test and the Thomas test were performed bilaterally to objectively measure flexibility. Paired sample t-tests were used to compare left and right lower extremities for all outcomes, with the level of significance set at p<0.05. Participants were ranked for risk and given a set of exercises sourced from the FIFA 11 Injury Prevention Program.

Results

At 60°/sec, the mean PT/BW bilateral deficit was 14.1% for extension and 12.9% for flexion. At 180°/sec, the mean deficit was 9.9% for extension and 11.4% for flexion. The team's average for left and right H:Q ratios for each speed were 54.4 and 51.4 at 60°/sec and 61.6 and 63.1 at 180°/sec, respectively. The team's average AKE range of motion was 158° for the left leg and 160° for the right leg. The mean Thomas test measurements were 3.6° away from the neutral position on the right and 1.6° on the left, with nine positive tests. There were no statistically significant differences between left and right knee extension or flexion PT/BW or H:Q ratios at either speed. There was no significant difference between left and right AKE measurements (p=0.182).

Conclusion

The results of this screening suggest that isokinetic testing and flexibility testing may be useful to identify non-optimal strength ratios and flexibility deficits in male collegiate soccer players. The benefits of this research have direct implications, as participants received both their screening data and a set of exercises aimed to help decrease their injury risk, in addition to the offering data that is useful for determining what normative values for flexibility and strength profiles might look like for Division III male soccer players.

Level of Evidence

Level 3.

Effects of Myofascial Release Using Finding-Oriented Manual Therapy Combined with Foam Roller on Physical Performance in University Athletes. A Randomized Controlled Study

Sport is a science of constant reinvention that is always searching for strategies to improve performance. Objective: This study seeks to compare the effects of myofascial release with Findings-Oriented Orthopedic Manual Therapy (OMT) combined with Foam Roller (FR), versus FR by itself, on the physical performance of university athletes. A randomized controlled study was conducted with a total of twenty-nine university athletes, measuring Range of Motion (ROM), jump height and flight time, strength and dynamic flexibility using Goniometer pro, CMJ protocol in OptoGait, 1 Repetition Maximum (1RM) and Mean Propulsive Velocity (MPV) and the Sit and Reach (V) test, correspondingly. This study was registered at clinicaltrials.gov prior to the initial measurement of the participants under the code NCT05347303. Through a univariate analysis, together with an analysis of independent groups with ANOVA and an analysis of covariance, it was evidenced that OMT combined with FR generated more and better effects in all the evaluated ROM, jump height and flight time, RM and VMP tests. Finally, it was found that OMT combined with FR is better when it is desired to improve ROM, muscle power, strength and flexibility, while FR alone only improves dynamic flexibility.

Neuromuscular characteristics of agonists and antagonists during maximal eccentric knee flexion in soccer players with a history of hamstring muscle injuries

BACKGROUND

Muscle strain injuries (MSIs) in the hamstrings are among the most prevalent injuries in elite soccer. We aimed to examine the relation between biomechanical maladaptation in eccentric strength and neuromuscular factors separated by their time and frequency domains.

METHODS

20 elite soccer players with a previous history of unilateral MSI in the M. biceps femoris (BF) long head and 20 without MSI participated. Knee flexion torques, rate of torque development (RTD) and electromyographic signals (EMG) of the BF, the M. semitendinosus (SMT) and knee extensors were obtained during unilateral maximal eccentric knee flexions performed at slow (30°/s) and fast (120°/s) angular speeds. Root mean squares and mean power frequency (MF) was calculated.

RESULTS

In the group with a history of MSI, reduced maximal eccentric flexion torque (slow eccentrics -8±11, p<0.05; fast eccentrics -18±13 N*m, p<0.05) and RTD (-33±28 N*m/s, p<0.05; -95±47 N*m/s, p<0.05) concomitantly occurred with diminished agonistic myoelectrical activities (-4±5% of MVC, p<0.05; -10±7% of MVC, p<0.05) and MFs (-24±13 Hz, p<0.05; -24±18 Hz, p<0.05) in the BF. Simultaneously, antagonistic myoelectric activity was elevated (+4±3% of MVC, p<0.05; +3±3% of MVC, p<0.05) in MSI affected legs as compared to unaffected legs for both eccentric contractions. Deficits in myoelectrical activity (r2 = 0.715, p<0.05; r2 = 0.601, p<0.05) and MF (r2 = 0.484, p<0.05; r2 = 0.622, p<0.05) correlated with deficits in maximal torque in the affected leg in the MSI group. Analysis of SMT demonstrated no significant differences.

CONCLUSION

Positive relationships between neuromuscular deficits and the reduced eccentric strength profile underpin neuronal inhibition after MSI. This persistent involvement of dysfunctional synergist and antagonist neural hamstring function in strength weakness is of clinical relevance in sports medicine for prevention and rehabilitation.

Associations of time to return to performance following acute posterior thigh injuries with running biomechanics, hamstring function, and structure in collegiate sprinters: A prospective cohort design

BACKGROUND

The time to return to sport from acute hamstring strain injuries is associated with several functional and structural impairments. However, not all previous studies assessed the preinjury level before acute hamstring strain injuries directly. The purpose of this study was to examine the associations of the time to return to performance following acute hamstring strain injuries with deficits in running biomechanics, hamstring function and structure in collegiate sprinters by a prospective study.

METHODS

Using a prospective cohort design, 72 participants were recruited from a collegiate track and field team. At the preinjury assessment, a 60-m running-specific test, passive straight leg raise test and isometric knee flexion strength test were assessed at the beginning of the competitive season for three consecutive years (2017-2019). Afterwards, postinjury examinations were performed only in sprinters with acute hamstring strain injuries.

FINDINGS

Twelve sprinters strained their hamstring muscle (incidence rate of hamstring strain injuries: 16.7%); the majority (n = 10) were classified as grades 0-2. The running speed deficit of the running-specific test was associated with the time to return to performance as well as the passive straight leg raise test deficit. In the running-specific test, lower-limb kinetic deficits were more strongly associated with the time to return to performance compared to lower-limb kinematic deficits.

INTERPRETATION

A running-specific test may be considered one of the most convenient and valid tests for assessing rehabilitation progress after acute hamstring strain injuries.

Application of Shear-Wave Elastography in the Evaluation of Hamstring Stiffness in Young Basketball Athletes

Background

Previous literature has postulated a relationship between greater hamstring stiffness and a higher risk of sustaining injury. Shear wave elastography (SWE) presents a relatively new means for non-invasive evaluation of soft tissue elasticity pre- and post- injury or intervention.

Purpose

1. To establish baseline hamstring stiffness measures for young competitive athletes and (2) determine effect of targeted neuromuscular training (TNMT) on shear wave stiffness of the hamstring.

Study Design

Un-blinded, prospective, non-randomized, cohort study.

Methods

Six-hundred forty-two lower extremities from 321 high school and collegiate basketball athletes (177 F: 139 M) were examined for hamstring stiffness prior to the start of their competitive basketball season. Teams were cluster assigned to either the control or intervention (TNMT) group. Subjects in the control group underwent regular season activities as directed, with no influence from the research team. For the TNMT group, the research team introduced a hamstring targeted dynamic warm-up program as an intervention focused on activating the hamstring musculature.

Results

Collegiate status was significant to hamstring stiffness for both sexes (p ≤ 0.02), but hamstring stiffness did not correlate to age or sex (r2 ≤ 0.08). Intervention was a significant factor to hamstring stiffness when the hip was positioned in extension (p ≤ 0.01), but not in deeper flexion (p = 0.12). This effect was sex-specific as TNMT influenced hamstring stiffness in females (p = 0.03), but not in males (p ≥ 0.13). Control athletes suffered three HAM injuries; TNMT athletes suffered 0 hamstring injuries.

Conclusion

Higher SWE measurements correlated with increased risk of injury, male sex, and collegiate athletics. TNMT intervention can lessen muscle stiffness which may reduce relate to injury incidence. Intervention effectiveness may be sex specific.

Level of Evidence

II.

Hamstring muscle architecture assessed sonographically using wide field of view: A reliability study

Purpose

To assess the intra-rater reliability of static wide field of view ultrasound to quantify the architectural characteristics of the hamstring muscles.

Methods

Twenty amateur male athletes were recruited. Their left hamstring muscles were assessed using static wide field of view ultrasound on two separate occasions. Static ultrasound images were acquired by a single sonographer using a 92mm linear transducer. The architectural characteristics (muscle length, fascicle length, pennation angle and muscle thickness) from two distinct locations of the bicep femoris long head and semimembranosus were evaluated. Muscle length and thickness of the bicep femoris short head and semitendinosus muscle were also evaluated. Intraclass correlation coefficient analyses were performed to determine the intra-rater reliability of the performed measurements.

Results

Both muscle (intraclass correlation coefficient = 0.99; standard error of measurement = 4.3 to 6.6mm) and fascicle (intraclass correlation coefficient = 0.92 to 0.98; standard error measurement = 1.1 to 2.4mm) length were measured with excellent intra-rater reliability. Muscle thickness was measured with excellent reliability (intraclass correlation coefficient = 0.9 to 0.96; standard error of measurement = 0.91mm to 1.4mm) for all hamstring muscles except for the proximal segments of the bicep femoris short head (intraclass correlation coefficient = 0.85; standard error of measurement = 0.84mm) and semitendinosus (intraclass correlation coefficient = 0.88; standard error of measurement = 0.82mm), which were measured with good reliability. Pennation angle was measured with good reliability (intraclass correlation coefficient = 0.77 to 0.87; standard error of measurement = 1 to 1.6°).

Conclusion

The architectural characteristics of the hamstring muscles of male amateur athletes can be reliably quantified using static wide field of view ultrasound.

The chronic effects of eccentric exercise interventions in different populations: an umbrella review

The effectiveness of eccentric exercise interventions (EEI) has been extensively explored in different populations. The aim of our umbrella review was to combine all systematic reviews about the chronic efficiency of EEI and to summarize the literature on the chronic effects of different types of eccentric exercise protocols, with or without extra loads and devices (e.g., Flywheel device), compared to other therapeutic interventions, exercise interventions, or no intervention. We screened four major electronic scientific databases (PubMed, Scopus, Web of Science, and PEDro), using one combined string for all included databases (eccentric exercise OR flywheel OR isoinertial exercise OR eccentric training). Included reviews needed to be based on any human population, that executed EEI in comparison with any other type of intervention. The methodological quality of the included reviews was assessed using AMSTAR 2 tool. Considering the inclusion criteria, we included 35 reviews. EEI were found suitable for chronic or long-term pain reduction in patient populations. EEI largely improved muscle performance (muscle strength, and muscle power), muscle architecture (e.g., pennation angle, fascicle length, cross-sectional area, muscle thickness, and muscle mass), decreased risk of injury, incidence, and severity of the injury, and increased range of motion of the joints There is less evidence about the effects of EEI in older adult populations, compared to athletes and younger populations, however, eccentric exercise seems promising for these populations as well.

Hamstrings force-length relationships and their implications for angle-specific joint torques: a narrative review

Temporal biomechanical and physiological responses to physical activity vary between individual hamstrings components as well as between exercises, suggesting that hamstring muscles operate differently, and over different lengths, between tasks. Nevertheless, the force-length properties of these muscles have not been thoroughly investigated. The present review examines the factors influencing the hamstrings’ force-length properties and relates them to in vivo function. A search in four databases was performed for studies that examined relations between muscle length and force, torque, activation, or moment arm of hamstring muscles. Evidence was collated in relation to force-length relationships at a sarcomere/fiber level and then moment arm-length, activation-length, and torque-joint angle relations. Five forward simulation models were also used to predict force-length and torque-length relations of hamstring muscles. The results show that, due to architectural differences alone, semitendinosus (ST) produces less peak force and has a flatter active (contractile) fiber force-length relation than both biceps femoris long head (BFlh) and semimembranosus (SM), however BFlh and SM contribute greater forces through much of the hip and knee joint ranges of motion. The hamstrings’ maximum moment arms are greater at the hip than knee, so the muscles tend to act more as force producers at the hip but generate greater joint rotation and angular velocity at the knee for a given muscle shortening length and speed. However, SM moment arm is longer than SM and BFlh, partially alleviating its reduced force capacity but also reducing its otherwise substantial excursion potential. The current evidence, bound by the limitations of electromyography techniques, suggests that joint angle-dependent activation variations have minimal impact on force-length or torque-angle relations. During daily activities such as walking or sitting down, the hamstrings appear to operate on the ascending limbs of their force-length relations while knee flexion exercises performed with hip angles 45–90° promote more optimal force generation. Exercises requiring hip flexion at 45–120° and knee extension 45–0° (e.g. sprint running) may therefore evoke greater muscle forces and, speculatively, provide a more optimum adaptive stimulus. Finally, increases in resistance to stretch during hip flexion beyond 45° result mainly from SM and BFlh muscles.

Angle-specific analysis of knee strength deficits after ACL reconstruction with patellar and hamstring tendon autografts

After anterior cruciate ligament reconstruction (ACLR) there are differences in the neuromuscular deficits observed in patients with bone-patellar tendon-bone (BPTB) and with hamstring tendon (HT) autografts. Differences in knee extensor and flexor strength are commonly reported, but analyses have largely focused on peak torque metrics despite the requirement to generate torque through range when returning to sport. The aim of this study was to investigate the angle-specific strength and strength asymmetry differences between BPTB and HT around the time of return to play after ACLR. A total of 357 male field sport athletes with either a BPTB (n=297) or an HT (n=60) autograft underwent concentric knee flexor and extensor isokinetic strength testing nine months post-ACLR. Angle-specific torques were compared between grafts and limbs using 1D Statistical Parametric Mapping and discrete-point variables. Inter-limb extensor torque asymmetry was greater in BTPB than HT at knee angles of >30° (p=0.001, peak d=5.53), with flexor torque asymmetry lower in BPTB than HT at flexion angles of >25° (p=0.001, peak d=2.68). Angle of maximum asymmetry and angle of operated limb peak torque differed in knee extension for BPTB (p<0.001, d=0.32) but not HT, whereas knee flexion angle of maximum asymmetry and operated limb peak torque differed in both BTPB (p<0.001, d=0.75) and HT (p<0.001, d=0.43). Graft type affected extensor torque at knee angles of 67-85° and flexor torque at knee angles of 27-85°. Angle-specific strength analysis may inform the rehabilitation process and improve rehabilitation and return-to-play decision making strategies in comparison to the use of peak torque values alone.

Shoulder rotation strength and overhead shooting speed associated with prior shoulder injury in water polo players

This study aimed to differentiate peak ball speed during shooting and shoulder rotation strength of the dominant arm between previously injured (PI) and uninjured (UI) water polo players. Nine PI and nine UI players performed 10 shots at 6 m from the goal mouth and three sets of three repetitions of isokinetic shoulder strength tests at 180 degrees/s on a dynamometer. Peak ball speed and shoulder concentric internal rotation (CIR) and eccentric external rotation (EER) peak torque (PT) and total work (TW) normalised to body mass were measured. EER:CIR PT and TW ratios were calculated. All PI versus UI comparisons were made using an Independent Samples T-Test. PI players shot 6% faster, produced 18% more CIR PT, and had lower EER:CIR PT (22%) and TW (34%) ratios compared with UI players. Shoulder TW compared with PT ratios could be more sensitive in differentiating PI versus UI players as TW takes into account the muscles' capacity throughout full active ROM. Practitioners could expand their foci to monitor shoulder EER:CIR TW ratios, in addition to PT ratios, to identify muscle imbalances in water polo athletes who might be at risk of injury/reinjury, and thereafter design interventions to reduce these imbalances.

Effects of Various Numbers of Runs on the Success of Hamstring Injury Prevention Program in Sprinters

Studies have not adequately addressed the influence of fatigue, which is considered a major risk factor for hamstring injuries. Therefore, this study aimed to clarify how a muscle fatigue condition affects the success of hamstring injury prevention programs in sprinters. The study subjects were 613 collegiate male sprinters. They employed submaximal/maximal running for a large number of runs and supramaximal running for a small number of runs in daily training. The hamstring injury prevention program had become the most effective strategy in the past 24 seasons of track and field for preventing hamstring injuries. The number of sprinters who experienced hamstring injuries in three periods over the 24 seasons was recorded. The incidents of hamstring injuries during supramaximal running per athlete-seasons were 137.9, 60.6, and 6.7 for Periods I, II, and III, respectively, showing a significant decline (p < 0.01). Furthermore, the incidents of hamstring injuries during submaximal and maximal running per season showed no significant change. The results of this study indicate that by inducing muscle fatigue, a small number of runs makes hamstring injury prevention programs effective.

Immediate effects of diacutaneous fibrolysis in athletes with hamstring shortening. A randomized within-participant clinical trial

Background

Diacutaneous fibrolysis is a non-invasive instrumental physiotherapeutic technique, used to treat mechanical or inflammatory pain and normalize function in the musculoskeletal system. Different studies have reported positive effects on range of motion, strength or function in musculoskeletal disorders, mainly in the upper extremity. The incidence and recurrence rates of hamstring injuries are high in many sports. However, there are no studies assessing these parameters in the hamstring and gluteus maximus in athletes. Objective. To evaluate the immediate and 30 minutes post-treatment effects of a single diacutaneous fibrolysis session on hamstring length, flexibility, muscle strength, myoelectrical activity and lower limb performance in athletes with hamstring shortening.

Methods

A randomized within-participant clinical trial. Sixty-six athletes with hamstring shortening were recruited. A single session of diacutaneous fibrolysis was applied following the cetripetal protocol to the gluteus maximus, biceps femoris and semitendinosus of for the experimental lower limb, whereas the control limb was not treated. Hamstring length (Passive knee extension test), hamstring and low back flexibility (Modified back saver sit and reach test), hamstring and gluteus maximus strength and electrical activity (dynamometry and surface electromyography, respectively) and lower limb performance (Countermovement Jump) were tested before treatment (T0), after treatment (T1), and 30 minutes post-treatment (T2).

Results

We only found a statistically significant difference between T0-T2 for the hamstring length favouring the experimental limbs (p<0.001). There were no statistically significant changes for hamstring and lower back flexibility, strength and electrical activity outcomes between groups. In the countermovement jump, we found a decrease of 0.58 cm in the high jump and a decrease of 9.19 N in the power jump at T1. These values recovered and improved at T2. However, these changes were not statistically significant (p>0.05).

Conclusions

A single session of diacutaneous fibrolysis in athletes with hamstring shortening, following the centripetal protocol for the posterior part of the thigh, produces improvements in hamstring length 30 minutes after, and in gluteus maximus strength immediately and 30 minutes after the treatment. It seems to have no effects on the overall hamstring and lower back flexibility or myoelectric activity. Importantly, the lower limb performance was not impaired after the treatment.

Screening Hamstring Injury Risk Factors Multiple Times in a Season Does Not Improve the Identification of Future Injury Risk

PURPOSE

To determine if eccentric knee flexor strength and biceps femoris long head (BFlh) fascicle length were associated with prospective hamstring strain injury (HSI) in professional Australian Football players, and if more frequent assessments of these variables altered the association with injury risk.

METHODS

Across two competitive seasons, 311 Australian Football players (455 player seasons) had their eccentric knee flexor strength during the Nordic hamstring exercise and BFlh architecture assessed at the start and end of preseason and in the middle of the competitive season. Player age and injury history were also collected in preseason. Prospective HSIs were recorded by team medical staff.

RESULTS

Seventy-four player seasons (16%) sustained an index HSI. Shorter BFlh fascicles (<10.42 cm) increased HSI risk when assessed at multiple time points only (relative risk [RR], 1.9; 95% confidence interval [CI], 1.2-3.0). Neither absolute (N) nor relative (N·kg-1) eccentric knee flexor strength was associated with HSI risk, regardless of measurement frequency (RR range, 1.0-1.1); however, between-limb imbalance (>9%), when measured at multiple time points, was (RR, 1.8; 95% CI, 1.1-3.1). Prior HSI had the strongest univariable association with prospective HSI (RR, 2.9; 95% CI, 1.9-4.3). Multivariable logistic regression models identified a combination of prior HSI, BFlh architectural variables and between-limb imbalance in eccentric knee flexor strength as optimal input variables; however, their predictive performance did not improve with increased measurement frequency (area under the curve, 0.681-0.726).

CONCLUSIONS

More frequent measures of eccentric knee flexor strength and BFlh architecture across a season did not improve the ability to identify which players would sustain an HSI.

Is Muscle Architecture Different in Athletes with a Previous Hamstring Strain? A Systematic Review and Meta-Analysis

Hamstring strains are a frequent injury in sports and are characterized by a high recurrence rate. The aim of this review was to examine the muscle and tendon architecture in individuals with hamstring injury. A systematic literature search in four databases yielded eleven studies on architecture following injury. Differences in the fascicle length (FL), pennation angle (PA) and muscle size measures (volume, thickness and physiological cross-sectional area) at rest were not significantly different between the previously injured limb and the contralateral limb (p > 0.05). There was moderate evidence that biceps femoris long head (BFlh) FL shortening was greater during contraction in the injured compared to the contralateral limb. The BFlh FL was smaller in athletes with a previous injury compared to uninjured individuals (p = 0.0015) but no differences in the FL and PA of other muscles as well as in the aponeurosis/tendon size were observed (p > 0.05). An examination of the FL of both leg muscles in individuals with a previous hamstring strain may be necessary before and after return to sport. Exercises that promote fascicle lengthening of both injured and uninjured leg muscles may be beneficial for athletes who recover from a hamstring injury.

The Efficacy of Flywheel Inertia Training to Enhance Hamstring Strength

The purpose of this narrative review is to examine the efficacy of flywheel inertia training to increase hamstring strength. Hamstring strain injury is common in many sports, and baseline strength deficits have been associated with a higher risk of hamstring strain injury. As a result, strength and conditioning professionals actively seek additional techniques to improve hamstring strength with the aim of minimising the incidence of hamstring strain injury. One method of strength training gaining popularity in hamstring strength development is flywheel inertia training. In this review, we provide a brief overview of flywheel inertia training and its supposed adaptions. Next, we discuss important determinants of flywheel inertia training such as familiarisation, volume prescription, inertia load, technique and specific exercise used. Thereafter, we investigate its effects on hamstring strength, fascicle length and hamstring strain injury reduction. This article proposes that hamstring specific flywheel inertia training can be utilised for strength development, but due to the low number of studies and contrary evidence, more research is needed before a definite conclusion can be made. In addition, as with any training modality, careful consideration should be given to flywheel inertia training determinants. This review provides general recommendations of flywheel inertia training determinants that have value when integrating flywheel inertia training into a hamstring strengthening program.

The Inclusion of a Complementary Running Progression Program in the Rehabilitation of Acute Hamstring Injuries: A Critically Appraised Topic

Introduction/Clinical Scenario: As many hamstring injuries occur when the hamstrings are in a lengthened state during the deceleration phase of running when the muscle is eccentrically contracting to slow the body down this functional aspect needs to be addressed. Thus, a rehabilitation program with a focus on progressive targeted eccentric hamstring exercises by gradually placing and exposing the muscle to eccentric force in a lengthened state supplemented with progressive running drills should be evaluated. Focused Clinical Question: Does the inclusion of a complementary running progression program for the rehabilitation of an acute hamstring injury reduce the time to safe return to sport with less hamstring reinjury occurrence for an athletic population? Summary of Key Findings: Three studies assessed the inclusion of a progressive running program with several types of running progression parameters addressed. Progressive running drills will load the hamstring in a functional manner, with a gradual increase in velocity of movement and lengthening of the muscle. Clinical Bottom Line: It appears that a complementary progressive running program within an acute hamstring rehabilitation program should be included as it caused no further harm and does not tend to increase hamstring reinjury occurrence. Strength of Recommendation: There is grade B evidence to include a complementary running progression program within an acute hamstring rehabilitation program.

The Intelligent Phenotypic Plasticity Platform (IP3) for Precision Medicine-Based Injury Prevention in Sport

The best predictor of future injury is previous injury and this has not changed in a quarter century despite the introduction of evidence-based medicine and associated revisions to post-injury treatment and care. Nearly nine million sports-related injuries occur annually, and the majority of these require medical intervention prior to clearance for the athlete to return to play (RTP). Regardless of formal care, these athletes remain two to four times more likely to suffer a second injury for several years after RTP. In the case of children and young adults, this sets them up for a lifetime of negative health outcomes. Thus, the initial injury is the tipping point for a post-injury cascade of negative sequelae exposing athletes to more physical and psychological pain, higher medical costs, and greater risk of severe long-term negative health throughout their life. This chapter details the technologies and method that make up the automated Intelligent Phenotypic Plasticity Platform (IP3)-a revolutionary new approach to the current standard of post-injury care that identifies and targets deficits that underly second injury risk in sport. IP3 capitalizes on the biological concept of phenotypic plasticity (PP) to quantify an athlete's functional adaptability across different performance environments, and it is implemented in two distinct steps: (1) phenomic profiling and (2) precision treatment. Phenomic profiling indexes the fitness and subsequent phenotypic plasticity of an individual athlete, which drives the personalization of the precision treatment step. IP3 leverages mixed-reality technologies to present true-to-life environments that test the athlete's ability to adapt to dynamic stressors. The athlete's phenotypic plasticity profile is then used to drive a precision treatment that systematically stresses the athlete, via a combination of behavioral-based and genetic fuzzy system models, to optimally enhance the athlete's functional adaptability. IP3 is computationally light-weight and, through the integration with mixed-reality technologies, promotes real-time prediction, responsiveness, and adaptation. It is also the first ever phenotypic plasticity-based precision medicine platform, and the first precision sports medicine platform of any kind.

Artificial Intelligence and Machine Learning in Sport Research: An Introduction for Non-data Scientists

In the last two decades, artificial intelligence (AI) has transformed the way in which we consume and analyse sports. The role of AI in improving decision-making and forecasting in sports, amongst many other advantages, is rapidly expanding and gaining more attention in both the academic sector and the industry. Nonetheless, for many sports audiences, professionals and policy makers, who are not particularly au courant or experts in AI, the connexion between artificial intelligence and sports remains fuzzy. Likewise, for many, the motivations for adopting a machine learning (ML) paradigm in sports analytics are still either faint or unclear. In this perspective paper, we present a high-level, non-technical, overview of the machine learning paradigm that motivates its potential for enhancing sports (performance and business) analytics. We provide a summary of some relevant research literature on the areas in which artificial intelligence and machine learning have been applied to the sports industry and in sport research. Finally, we present some hypothetical scenarios of how AI and ML could shape the future of sports.

Hamstring and ACL injuries impacts on hamstring-to-quadriceps ratio of the elite soccer players: A retrospective study

This study aimed to compare the angle-specific (AS) and non-angle-specific (NAS) hamstring to quadriceps conventional and functional ratios between healthy, hamstring- and ACL-injured elite soccer players. One hundred and eleven players (27.42 ± 8.01 years, 182.11 ± 6.79 cm, 75.93 ± 7.25 kg) completed a series of concentric knee flexor and extensor strength in addition to eccentric knee flexor strength was measured at an angular velocity of 60°.s^-1. Normalized and raw peak torque values, and the torque-angle profiles were extracted for analysis. Conventional and functional NAS (peak values) and AS (waveform ratios) hamstring to quadriceps ratios were calculated and compared between the groups. Healthy players produced greater functional and conventional ratios compared to players with either ACL or hamstring injury. Players with hamstring injury produced a lower AS functional ratios between 46° and 54° of knee flexion. Players suffering from ACL injury depicted a lower value for the AS functional ratio between 33° and 56° of knee flexion. Although NAS can identify soccer players with previous hamstring or ACL injury, the range where there is a strength deficiency is eluded. With the use of AS the range where the deficiency is present can be identified, and clinicians can benefit from this analysis to design robust rehabilitation protocols.

The deficits of isometric knee flexor strength in lengthened hamstring position after hamstring strain injury

OBJECTIVE

To investigate the effects of knee flexion angle on peak torque, rate of torque development (RTD) during isometric contraction and hamstring flexibility after hamstring strain injury (HSI).

DESIGN

Cross-sectional.

SETTING

Controlled laboratory research.

PARTICIPANTS

Fourteen male athletes with a history of HSI and 14 athletes without HSI (controls).

MAIN OUTCOME MEASURES

Hamstring flexibility was evaluated using active knee extension test. Isometric knee flexion peak torque and RTD were determined at 30°, 60°, and 90° of knee flexion measured by an isokinetic dynamometer.

RESULTS

Individuals with a history of HSI had statistically significant, moderate deficits in isometric peak torque at 30° of knee flexion (P = 0.037; effect size = 0.55) in the HSI limb than in the uninjured limb, but not at 60° and 90° of knee flexion. In the control group, no significant differences in isometric peak torque at any angle were found between limbs. No differences in peak RTD and flexibility were found between limbs in both groups.

CONCLUSIONS

Isometric peak torque at 30° of knee flexion was lower in the injured limb than in the uninjured limb. Isometric strength deficits after HSI tended to be affected by lengthened hamstring angles.

Shoulder Range of Motion, Rotator Strength, and Upper-Extremity Functional Performance in Junior Tennis Players

PURPOSE

Repetitive and asymmetric movements in tennis can result in biomechanical adaptation in shoulder joint. The aim of this study was to investigate the differences in shoulder range of motion (ROM), strength, and functional performance tests between the dominant and nondominant shoulders, as well as to identify gender differences in junior tennis players.

METHODS

Forty-two junior tennis players (age mean: 11.3 [1.2] y, body mass index 18.3 [2.4] kg/m2) were included in the study. Shoulder internal rotation (IR), external rotation (ER) ROM, and total ROM, IR and ER isokinetic strength and closed kinetic chain upper-extremity stability, seated medicine ball throw used, grip hold tests were applied bilaterally. Paired sample t test and Student t test were used to compare the differences.

RESULTS

ER ROM was greater, while IR ROM and total ROM were lower on the dominant shoulder (all P values < .05). Nineteen players had glenohumeral IR deficit (IR ROM difference >13°). The players had a greater ER strength on the dominant side and similar IR strength between shoulders. There was significant difference in seated medicine ball throw results between the dominant and nondominant sides (P < .001). The mean distance for bilateral seated medicine ball throw was 377.02 (85.70) m, and closed kinetic chain upper-extremity stability results were calculated as a mean of 15.85 (1.72) touches. Differences between the genders: total ROM of the dominant shoulder was higher in female players (P = .045), the IR PT/BW at 60°/s angular speed was higher in male players' dominant shoulder (P = .030), and closed kinetic chain upper-extremity stability performance was higher in male players (P = .019).

CONCLUSIONS

Adolescent tennis players demonstrated differences in strength, ROM, and functional performance results between the dominant and nondominant shoulders. Gender differences were also seen in the aforementioned parameters in junior tennis players. Determining these differences may improve our understanding of sport-specific shoulder joint adaptations in tennis.

Short and Long-Term Effects of a Simple-Strength-Training Program on Injuries Among Elite U-19 Soccer Players

Purpose: The aim of this study was to examine the short and long-term effects of a simple strength training program on muscle injury prevention in soccer players. Methods: Twenty-seven U-19 elite male soccer players participated in the study. The investigation was conducted over two consecutive and similar seasons (e.g., the same staff, players, weekly training schedule), the first being the control and the second the experimental season. The strength program was carried out 2 times per week, for 10 weeks, during part of the preseason and in-season. Injury incidence and absence days were compared between both seasons, according to the injury rate ratio (IRR), with 95% CI and the Z test. Results: A lower number of total and hamstring injuries were recorded during the experimental (9 and 2, respectively) compared to the control (15 and 7, respectively) period. During the 10 weeks intervention period, the injury rate ratio (IRR) was lower in the experimental season than in the control season (IRR = 8.12; 95% CI: 1.00-66.03; effect size (ES) = 3.30, large). In addition, there was a decline in absence days per injury and in the number of absence days/1000 h (IRR = 2.44; 95% CI: 1.90-3.14; ES = 1.12) during the experimental season. Conclusion: The results of this study suggest that this simple strength-training program could reduce the muscle injury incidence during its application period in young soccer players.

Can the history of injury influence shoulder isokinetic torque parameters in volleyball players?

The aim of the present study was to compare shoulder internal rotator and external rotator isokinetic parameters in concentric and eccentric contractions between volleyball players with and without a history of shoulder injury. Thirty male volleyball players participated of this study, divided into two groups: with a history of injury (WHI) in the dominant shoulder (11 athletes; age: 19.4 ± 3.6 years) and no history of injury (NHI) (19 athletes; age: 18.3 ± 2.9 years). The peak torque (PT) and concentric (Con) and eccentric (Ecc) PT angles in internal (IR) and external rotation (ER) at velocities of 60 and 180°/s were measured. The conventional (Con_ER:Con_IR), functional spiking (Ecc_ER:Con_IR), and cocking ratios (Ecc_IR:Con_ER) were calculated. No significant differences were found between groups for PT and PT angle, or for conventional, functional spiking, and cocking ratios. However, the spiking ratio was considered low (0.87) in the WHI group. Moreover, for the spiking ratio in the WHI group, PT at 60°/s occurred at different angles. We conclude that previous injury in shoulder did not affect the peak torque, as well as conventional, spiking or cocking ratio. However, the PT angles at 60°/s used to calculate the spiking ratio shifted due the prior injury.

Hamstring Injury Prevention Program and Recommendation for Stride Frequency during Tow-Training Optimization

(1) Background: Although innovations and improvements in towing systems have been available, tow-training method has not been considered favored in the training context. Tow-training may enable high stride frequency if hamstring injuries do not occur. The purpose of this study was to prevent hamstring injuries during supramaximal running and to optimize tow-training. (2) Methods: We investigated the relationship between the number of hamstring injuries that occurred during supramaximal running and the contents of the prevention programs that have been implemented, i.e., 4 years of the baseline programs and 12 years of the intervention. (3) Results: The incidence of hamstring injuries per 1000 sprinters was 57.5 for baseline and 6.7 for intervention. A significant difference was observed in the incidence of hamstring injury between the different combinations of prevention programs (p < 0.01). (4) Conclusions: Tow-training was optimized by (1) preventing hamstring injuries by combination of strength, agility, and flexibility training programs and (2) advising the sprinters to press the leg onto the ground as fast as possible to increase stride frequency and to prevent stride lengthening.

Chronic Effects of a Static Stretching Program on Hamstring Strength

ABSTRACT

Nakao, S, Ikezoe, T, Nakamura, M, Umegaki, H, Fujita, K, Umehara, J, Kobayashi, T, Ibuki, S, and Ichihashi, N. Chronic effects of a static stretching program on hamstring strength. J Strength Cond Res 35(7): 1924-1929, 2021-This study investigated the effects of a 4-week static stretching (SS) program on isokinetic and isometric knee flexor peak torque and angle of peak torque. Thirty healthy men (age, 22.7 ± 2.2 years) were randomized to receive either of the following: (a) a 4-week stretch intervention for the hamstrings (SS intervention group; n = 15) or (b) no intervention (control group; n = 15). The maximum pain-free knee angle, passive stiffness, which was determined by a slope of torque-angle curve, isometric and isokinetic (at 60°·s-1 and 180°·s-1) peak torque, and angle of peak torque for knee flexors were measured before and after 4 weeks. After 4 weeks, passive stiffness decreased significantly in the intervention group. There were no significant changes in isometric and isokinetic (neither at 60°·s-1 nor at 180°·s-1) peak torque, or angle of peak torque at 180°·s-1. A significantly increased peak extension angle at 60°·s-1 was observed in the intervention group. These results suggest that SS intervention is effective for decreasing musculotendinous unit stiffness of the hamstrings and that an SS program influences the angle of peak torque, whereas no significant changes occur in peak torque. Because a previous study suggests that angle of peak torque is associated with hamstring strain injuries, the results of this study would be helpful when considering the training program for preventing or treating hamstring strain injuries.

The Influence of Active Hamstring Stiffness on Markers of Isotonic Muscle Performance

Background: Previous research demonstrates hamstring muscle-tendon stiffness (HMTS) influences isometric strength, landing biomechanics and architectural tissue properties. However, the influence on kinetics & kinematics during other modes of strength testing (isotonic dynamometry) has yet to be established. Purpose: Investigate how HMTS influences kinetics and kinematics during a novel isotonic muscle performance test which has never been done for the hamstrings. Previous work using dynamometry has been limited to isometric or isokinetic contractions, so the novelty arises from our custom isotonic protocol which allows quantitative assessment of the stretch-shortening cycle. Methods: Twenty-six recreationally active individuals (15 males, 11 females, 23.8 ± 2.5 years) completed baseline testing for anthropometry and maximum isometric hamstring strength (MVIC). At least 48 h later, subjects completed a measure of HMTS (damped oscillation technique) followed by an isotonic knee flexion test (eccentric velocity 180°/s; concentric torque 25% of MVIC). Separate linear regression models with examination of residuals were conducted between HMTS and each muscle performance variable. Standardized coefficients determined the magnitude of the relationships. Results: Significance was found for all outcome variables tested. HMTS and rate of torque development demonstrated the strongest relationship followed by isotonic concentric peak torque. The weakest relationship observed was with isometric peak torque. Conclusions: These findings build off previous work quantifying HMTS by showing HMTS more strongly relates to dynamic versus static muscle testing and identifies the potential clinical utility of isotonic dynamometry.

Prevalence of Hamstring Strain Injury Risk Factors in Professional and Under-20 Male Football (Soccer) Players

CONTEXT

Hamstring strain injury (HSI) is the most prevalent injury in football (soccer), and a few intrinsic factors have been associated with higher injury rates.

OBJECTIVE

To describe the prevalence of the main intrinsic risk factors for HSI in professional and under-20 football players.

DESIGN

Cross-sectional study.

SETTING

Physiotherapy laboratory, Federal University of Health Sciences of Porto Alegre (Brazil).

PARTICIPANTS

A total of 101 football players (52 professional and 49 under-20 players).

INTERVENTION

An evidence-based testing protocol for screening HSI risk factors.

MAIN OUTCOME MEASURES

Anamnesis, ultrasonography of the hamstrings, passive straight-leg raise test, Functional Movement Screen, and isokinetic dynamometry were performed. Eleven HSI risk factors for each leg were assessed, besides the player's age as a systemic risk factor. Reports were delivered to the coaching staff.

RESULTS

Professionals had greater prevalence of HSI history compared with under-20 players (40% vs 18%). No between-group differences were found for the other screening tests. Altogether, 30% of players had already sustained at least one HSI; 58% had a history of injuries in adjacent regions; 49% had short biceps femoris fascicles; 66% and 21% had poor passive and active flexibility, respectively; 42% and 29% had deficits in functional movements and core stability, respectively; 7% and 26% presented bilateral imbalance for hamstring concentric and eccentric strength, respectively; 87% and 94% obtained low values for hamstring-to-quadriceps conventional and functional ratios, respectively. Two-thirds of players had 3 to 5 risk factors per leg. None of the players was fully free of HSI risk factors.

CONCLUSION

Most football players present multiple risk factors for sustaining an HSI. Hamstring weakness is the most prevalent risk factor, but the teams should also be aware of deficits in flexibility, core stability, functional movements, and hamstring fascicle length.

Greater Hamstrings Muscle Hypertrophy but Similar Damage Protection after Training at Long versus Short Muscle Lengths

PURPOSE

We investigated the effects of seated versus prone leg curl training on hamstrings muscle hypertrophy and susceptibility to eccentric exercise-induced muscle damage.

METHODS

Part 1: Twenty healthy adults conducted seated leg curl training with one leg (Seated-Leg) and prone with the other (Prone-Leg), at 70% one-repetition maximum (1RM), 10 repetitions per set, 5 sets per session, 2 sessions per week for 12 wk. Magnetic resonance imaging (MRI)-measured muscle volume of the individual and whole hamstrings was assessed pre- and posttraining. Part 2: Nineteen participants from part 1 and another 12 untrained controls (Control-Leg) performed eccentric phase-only leg curl exercise at 90% 1RM, 10 repetitions per set, 3 sets for each of the seated/prone conditions with each leg. MRI-measured transverse relaxation time (T2) and 1RM of seated/prone leg curl were assessed before, 24, 48, and 72 h after exercise.

RESULTS

Part 1: Training-induced increases in muscle volume were greater in Seated-Leg versus Prone-Leg for the whole hamstrings (+14% vs +9%) and each biarticular (+8%-24% vs +4%-19%), but not monoarticular (+10% vs +9%), hamstring muscle. Part 2: After eccentric exercise, Control-Leg had greater increases in T2 in each hamstring muscle (e.g., semitendinosus at 72 h: +52%) than Seated-Leg (+4%) and Prone-Leg (+6%). Decreases in 1RM were also greater in Control-Leg (e.g., seated/prone 1RM at 24 h: -12%/-24%) than Seated-Leg (0%/-3%) and Prone-Leg (+2%/-5%). None of the changes significantly differed between Seated-Leg and Prone-Leg at any time points.

CONCLUSION

Hamstrings muscle size can be more effectively increased by seated than prone leg curl training, suggesting that training at long muscle lengths promotes muscle hypertrophy, but both are similarly effective in reducing susceptibility to muscle damage.

Development of a Novel Nordic Hamstring Exercise Device to Measure and Modify the Knee Flexors' Torque-Length Relationship

The Nordic hamstring exercise (NHE) has been shown to reduce hamstring injury risk when employed in training programs. This study investigates a novel device to modify the NHE torque-length relationship of the knee flexors, as targeting the hamstrings at a more extended length may have benefits for hamstring strain injury prevention and rehabilitation. Eighteen recreational male participants completed three bilateral NHE repetitions at a conventional 0° flat position, a 10° incline, and a 10° decline slope on a novel device (HALHAM°). Measures of peak torque and break-torque angle explored the effect of inclination on the knee flexors' length-tension relationship. Relative thigh-to-trunk angle and angular velocity of the knee joint were used to assess influence of inclination on technique and exercise quality. Break-torque angle increased when performed at an incline (134.1 ± 8.6°) compared to both the decline (112.1 ± 8.3°, p <0.0001, g = 2.599) and standard flat NHE positions (126.0 ± 9.8°, p = 0.0002, g = 0.885). Despite this, altering inclination did not affect eccentric knee flexor peak torque (decline = 132.0 ± 63.1 Nm, flat = 149.7 ± 70.1 Nm, incline = 148.9 ± 64.9 Nm, F = 0.952, p = 0.389), angular velocity of the knee joint at break-torque angle (decline = 23.8 ± 14.4°, flat = 29.2 ± 22.6°, incline = 24.5 ± 22.6°, F = 0.880, p = 0.418) or relative thigh-to-trunk angle at break-torque angle (decline = 20.4 ± 10.4°, flat = 16.7 ± 10.8°, incline = 20.2 ± 11.2°, F = 1.597, p = 0.207). The report recommends the use of arbitrary metrics such as break-torque angle that can be replicated practically in the field by practitioners to assess proxy muscle length changes i.e., the angular range over which the torque can be produced. Inclination of the Nordic hamstring exercise leads to hamstring muscle failure at longer muscle lengths without reductions in the maximal force exuded by the muscle. Therefore, the NHE performed on an incline may be a more effective training intervention, specific to the proposed mechanism of hamstring strain injury during sprinting that occurs whilst the muscle is rapidly lengthening. Using a graded training intervention through the inclinations could aid gradual return-to-play rehabilitation.

HAMSTRING MUSCLE ARCHITECTURE AND VISCOELASTIC PROPERTIES: RELIABILITY AND RETROSPECTIVE COMPARISON BETWEEN PREVIOUSLY INJURED AND UNINJURED ATHLETES

The architecture of the biceps femoris (BF) and stiffness of the hamstrings have been found to be associated with injury risk. However, less is known about the architecture of the equally voluminous semitendinosus (ST) and viscoelastic properties of both muscles in individuals with a prior injury. Methods: BF and ST of 15 athletes (previously injured, [Formula: see text]; control, [Formula: see text]) were assessed using ultrasonography and myotonometry. Mean architecture (muscle thickness (MT), pennation angle (PA) and fascicle length (FL)) and viscoelastic measures (stiffness, oscillation frequency and decrement) were compared between the previously injured and contralateral uninjured limb, and between the previously injured and control limbs (mean of both limbs of the control group). Control group participants returned for a duplicate measurement. Findings: Both muscles exhibited high reliability between sessions (intraclass correlation coefficient [Formula: see text]) for architecture. BF PA was larger in the previously injured than both uninjured [Formula: see text] and control [Formula: see text]. BF fascicles were shorter in the previously injured limb compared to the uninjured [Formula: see text] and control [Formula: see text]. BF was stiffer in the previously injured compared to uninjured [Formula: see text]. ST architecture and viscoelasticity were similar across limbs. Conclusion: A prior hamstring strain injury is associated with a stiffer BF characterized by larger PAs and shorter fascicles.

A Field-Based Approach to Determine Soft Tissue Injury Risk in Elite Futsal Using Novel Machine Learning Techniques

Lower extremity non-contact soft tissue (LE-ST) injuries are prevalent in elite futsal. The purpose of this study was to develop robust screening models based on pre-season measures obtained from questionnaires and field-based tests to prospectively predict LE-ST injuries after having applied a range of supervised Machine Learning techniques. One hundred and thirty-nine elite futsal players underwent a pre-season screening evaluation that included individual characteristics; measures related to sleep quality, athlete burnout, psychological characteristics related to sport performance and self-reported perception of chronic ankle instability. A number of neuromuscular performance measures obtained through three field-based tests [isometric hip strength, dynamic postural control (Y-Balance) and lower extremity joints range of motion (ROM-Sport battery)] were also recorded. Injury incidence was monitored over one competitive season. There were 25 LE-ST injuries. Only those groups of measures from two of the field-based tests (ROM-Sport battery and Y-Balance), as independent data sets, were able to build robust models [area under the receiver operating characteristic curve (AUC) score ≥0.7] to identify elite futsal players at risk of sustaining a LE-ST injury. Unlike the measures obtained from the five questionnaires selected, the neuromuscular performance measures did build robust prediction models (AUC score ≥0.7). The inclusion in the same data set of the measures recorded from all the questionnaires and field-based tests did not result in models with significantly higher performance scores. The model generated by the UnderBagging technique with a cost-sensitive SMO as the base classifier and using only four ROM measures reported the best prediction performance scores (AUC = 0.767, true positive rate = 65.9% and true negative rate = 62%). The models developed might help coaches, physical trainers and medical practitioners in the decision-making process for injury prevention in futsal.

Returning a Division I Hurdler to Sport After Multiple Knee Ligament Injuries

An 18-year-old male hurdler reported to preparticipation physicals, with a history of anterior cruciate ligament, lateral collateral ligament, and posterior cruciate ligament sprain; medial meniscocapsular sprain; and biceps femoris tendon avulsion. The patient received full clearance from his surgeon, despite functional deficits. Rehabilitation and return-to-play decision making included analysis of patient-reported outcome scores and tests of symmetry and neuromuscular control. After graduated intervention and multiple batteries of assessments, the patient was allowed to return to full participation. The nature of this sport and the time between surgery and the intervention made thorough evaluation of function and graduated progression a necessity.

Recommendations for Hamstring Function Recovery After ACL Reconstruction

It is important to optimise the functional recovery process to enhance patient outcomes after major injury such as anterior cruciate ligament reconstruction (ACLR). This requires in part more high-quality original research, but also an approach to translate existing research into practice to overcome the research to implementation barriers. This includes research on ACLR athletes, but also research on other pathologies, which with some modification can be valuable to the ACLR patient. One important consideration after ACLR is the recovery of hamstring muscle function, particularly when using ipsilateral hamstring autograft. Deficits in knee flexor function after ACLR are associated with increased risk of knee osteoarthritis, altered gait and sport-type movement quality, and elevated risk of re-injury upon return to sport. After ACLR and the early post-operative period, there are often considerable deficits in hamstring function which need to be overcome as part of the functional recovery process. To achieve this requires consideration of many factors including the types of strength to recover (e.g., maximal and explosive, multiplanar not just uniplanar), specific programming principles (e.g., periodised resistance programme) and exercise selection. There is a need to know how to train the hamstrings, but also apply this to the ACLR athlete. In this paper, the authors discuss the deficits in hamstring function after ACLR, the considerations on how to restore these deficits and align this information to the ACLR functional recovery process, providing recommendation on how to recover hamstring function after ACLR.

Modulation of physiological cross-sectional area and fascicle length of vastus lateralis muscle in response to eccentric exercise

In the current study, we investigated the effect of lengthening velocity during eccentric exercise on the modulation of the physiological cross-sectional area (PCSA) and fascicle length of the vastus lateralis (VL) muscle. We hypothesized a greater increase in muscle PCSA after training with lower lengthening velocities and a greater increase in fascicle length after higher lengthening velocities. Forty-seven young men were randomly assigned to either a control (n = 14) or an intervention group (n = 33). The participants of the intervention group were randomly allocated to one of four isokinetic eccentric training protocols of the knee extensors, with four different knee angular velocities (45°/s, 120°/s, 210°/s and 300°/s), yet similar range of motion (25-100° knee joint angle), load magnitude (100% of isometric maximum) and load volume (i.e. similar time under tension for one training set). Before and after an 11-week training period with 3 times per week exercise, muscle volume, pennation angle, fascicle length and PCSA of the VL muscle were measured using magnetic resonance imaging and ultrasonography. After the training, the VL muscle volume and fascicle length increased similarly and approximately 5% in all investigated protocols. The PCSA and pennation angles of the VL did not change after any exercise protocol, indicating negligible radial muscle adaptation after the training. The reason for the found hypertrophy of VL muscle after eccentric training in a wide range of lengthening velocities was mainly a longitudinal muscle growth. Further, the longitudinal muscle growth was independent of the lengthening velocity.

Can musculoskeletal screening test findings guide interventions for injury prevention and return from injury in field hockey?

OBJECTIVES

The aim of this study is to identify if intrinsic factors tested in the preseason screening (PSS) can identify an elevated risk of injury. This aim has two aspects; to assess whether previous injury is associated with ongoing deficits in performance, and to assess if the PSS can identify differences in intrinsic factors that profile risk of future injury.

DESIGN

A cohort of state level field hockey players were tested on a screening test battery including proprioception, postural stability, muscular strength and range of motion, to establish if these intrinsic factors were useful in identifying elevated risk of injury. Retrospective injury data was collated to determine association with previous injury and prospective injury data was collated to determine association with future injury.

PARTICIPANTS

A total of 130 field hockey players were included in this study, from state level squads (age ± SD = 20.96 (3.75); height = 176.09 cm). Groups for prescreening and post screening injury status (injured/not injured) were established for comparison to screening test results.

RESULTS

Right Active Movement Extent Discrimination Assessment (AMEDA), left AMEDA and right Y-balance test (YBT) anterior direction (Ant) were significantly associated (p < 0.05) with injury prior to screening. Right YBTAnt and right and left hip internal rotation (IR) were significantly associated (p < 0.05) with injury post screening. The YBTAnt and YBT posteromedial (PMed) reach directions and Hip IR are associated with previous hamstring injury and show a difference between post screening injured and non-injured groups.

CONCLUSIONS

AMEDA, R YBTAnt, Hip IR tests should be a focus for recovery after previous injury and during season preparation. Full recovery may improve readiness to return to play and reduce risk of primary injury or re-injury. YBTAnt and YBTPmed and Hip IR show a performance deficit link between previous injury and subsequent re-injury of hamstrings. Since these are the most common re-injury types in this cohort, these tests are clinically useful in informing return to play decisions for hockey players.

The Effect of Nordic Hamstring Exercise Intervention Volume on Eccentric Strength and Muscle Architecture Adaptations: A Systematic Review and Meta-analyses

Background

Although performance of the Nordic hamstring exercise (NHE) has been shown to elicit adaptations that may reduce hamstring strain injury (HSI) risk and occurrence, compliance in NHE interventions in professional soccer teams is low despite a high occurrence of HSI in soccer. A possible reason for low compliance is the high dosages prescribed within the recommended interventions. The aim of this review was to investigate the effect of NHE-training volume on eccentric hamstring strength and biceps femoris fascicle length adaptations.

Methods

A literature search was conducted using the SPORTDiscus, Ovid, and PubMed databases. A total of 293 studies were identified prior to application of the following inclusion criteria: (1) a minimum of 4 weeks of NHE training was completed; (2) mean ± standard deviation (SD) pre- and post-intervention were provided for the measured variables to allow for secondary analysis; and (3) biceps femoris muscle architecture was measured, which resulted in 13 studies identified for further analysis. The TESTEX criteria were used to assess the quality of studies with risk of bias assessment assessed using a fail-safe N (Rosenthal method). Consistency of studies was analysed using I² as a test of heterogeneity and secondary analysis of studies included Hedges’ g effect sizes for strength and muscle architecture variables to provide comparison within studies, between-study differences were estimated using a random-effects model.

Results

A range of scores (3–11 out of 15) from the TESTEX criteria were reported, showing variation in study quality. A ‘low risk of bias’ was observed in the randomized controlled trials included, with no study bias shown for both strength or architecture (N = 250 and 663, respectively; p < 0.001). Study consistency was moderate to high for strength (I² = 62.49%) and muscle architecture (I² = 88.03%). Within-study differences showed that following interventions of ≥ 6 weeks, very large positive effect sizes were seen in eccentric strength following both high volume (g = 2.12) and low volume (g = 2.28) NHE interventions. Similar results were reported for changes in fascicle length (g ≥ 2.58) and a large-to-very large positive reduction in pennation angle (g ≥ 1.31). Between-study differences were estimated to be at a magnitude of 0.374 (p = 0.009) for strength and 0.793 (p < 0.001) for architecture.

Conclusions

Reducing NHE volume prescription does not negatively affect adaptations in eccentric strength and muscle architecture when compared with high dose interventions. These findings suggest that lower volumes of NHE may be more appropriate for athletes, with an aim to increase intervention compliance, potentially reducing the risk of HSI.

Strength and Power Training in Rehabilitation: Underpinning Principles and Practical Strategies to Return Athletes to High Performance

Injuries have a detrimental impact on team and individual athletic performance. Deficits in maximal strength, rate of force development (RFD), and reactive strength are commonly reported following several musculoskeletal injuries. This article first examines the available literature to identify common deficits in fundamental physical qualities following injury, specifically strength, rate of force development and reactive strength. Secondly, evidence-based strategies to target a resolution of these residual deficits will be discussed to reduce the risk of future injury. Examples to enhance practical application and training programmes have also been provided to show how these can be addressed.

The cumulative and residual changes in eccentric knee flexor strength indices following soccer-specific treadmill running: Novel considerations of angle specific torque

With potential implications for recovery and conditioning practices, the aim of this study was to assess the cumulative and residual response of angle specific eccentric knee flexor (eccKF) strength indices following soccer-specific activity. Thirteen semi-professional soccer players were therefore required to complete a 90-minute soccer-specific treadmill running. with eccKF isokinetic strength assessments completed pre-trial, immediately post-trial, and 48 hours post-trial. The strength assessments comprised the completion of 5 repetitions at angular velocities of 60 and 300 deg·s^-1. Isokinetic data was analysed for measures of peak torque (PT), angle of peak torque (APT), functional range (FR), and angle specific torque (AST). Significant post-trial impairments were observed for measures of slow velocity PT₆₀ (6.6%) and AST₃₀₀ (12.5%). Further significant differences were observed 48 hours post-trial for PT₃₀₀ (10.7%) and PT₆₀ (12.8%) PT, APT₆₀ (~15°), and AST₃₀₀ (>13.6%). These data have implications for post exercise recovery monitoring and the prescription of recovery modalities and conditioning practices in the 2 days following match-play. The AST and APT responses highlight the importance of analysis of the entire strength-angle curve and at a range of angular velocities.

Hamstring Injuries Prevention in Soccer: A Narrative Review of Current Literature

Hamstring injuries and reinjuries are one of the most important sport lesions in several sport activities including soccer, Australian football, track and field, rugby, and in general in all sport activities requiring sprinting and acceleration. However, it is important to distinguish between the lesions of the biceps femoris and semitendinosus and semimembranosus. Indeed, three muscles representing the hamstring complex have a very different injury etiology and consequently require different prevention strategies. This fact may explain, at least in part, the high incidence of reinjuries. In soccer, hamstring injuries cause an important rate of time loss (i.e., in average 15–21 matches missed per club per season). The hamstring injury risk factors may be subdivided in three categories: “primary injury risk factors” (i.e., the risk factors mainly causing a first lesion), “recurrent injury risk factors” (i.e., the risk that can cause a reinjury), and bivalent injury risk factors” (i.e., the risk factors that can cause both primary injuries and reinjuries). The high incidence of hamstring lesions caused consequently an important increase in hamstring injury research. However, although the prevention has increased paradoxically, epidemiological data do not show a loss in injuries and/or reinjuries but, on the contrary, they show an increase in hamstring injuries. This apparent paradox highlights the importance both of the improvement in the prevention programs quality and the criteria for return to play after hamstring injury.

A conceptual model and detailed framework for stress-related, strain-related, and overuse athletic injury

A multitude of athletic injuries occur when the various tissues that make up the human body experience stresses and strains that exceed their material strength. The precise amount of stress and strain that any given tissue can withstand is determined by the mechanical properties and resultant strength of that particular tissue. These mechanical properties are directly determined by an individual's physiology and acute regulation of these properties. A number of theoretical frameworks for athletic injury occurrence have been proposed, however, a detailed conceptual framework for injury aetiology that considers the interplay between the physiological and mechanical factors and outlines the causal pathways to tissue damage and injury is needed. This will guide injury research towards a more thorough investigation of causal mechanisms and understanding of risk factors. Further, it is important to take into account the considerable differences in loading patterns which can result in varying injury outcomes such as acute stress-related, strain-related, or overuse injury. Within this article a simplified conceptual model of athletic injury is proposed along with a detailed, evidence-informed, conceptual framework for athletic injury aetiology that focuses on stress-related, strain-related, and overuse injury.

Effects of flexibility and strength interventions on optimal lengths of hamstring muscle-tendon units

OBJECTIVES

The aim of the present study was to determine the effects of altering both hamstring flexibility and strength on hamstring optimal lengths.

DESIGN

Controlled laboratory study.

METHODS

A total of 20 male and 20 female college students (aged 18-24 years) participated in this study and were randomly assigned to either a flexibility intervention group or a strength intervention group. Passive straight leg raise and isokinetic strength test were performed before and after interventions. Paired T-tests were performed to determine hamstring flexibility or strength intervention effects on hamstring optimal lengths.

RESULTS

Male participants in the flexibility intervention group significantly increased range of hip joint flexion (P=0.001) and optimal lengths of semimembranosus and biceps long head (P≤0.026). Male participants in the strength intervention group significantly increased hamstring strength (P=0.001), the range of hip joint flexion (P=0.037), and optimal lengths of all three bi-articulated hamstring muscles (P≤0.041). However, female participants did not significantly increase their hamstring optimal lengths in either intervention groups (P≥0.097) although both groups significantly increased the range of hip joint flexion and strength (P≤0.009).

CONCLUSION

Hamstring optimal lengths can be modified through flexibility intervention as well as strength intervention for male participants, but not for female participants in this study. Hamstring optimal lengths should be considered as hamstring flexibility measures in future prospective studies to identify potentially modifiable risk factors for hamstring injury.