Previous hamstring muscle strain injury alters passive tissue stiffness and vibration sense

BackgroundHamstring strain is one of the most common among sports injuries. A previous history of this injury is considered a strong predictor of recurrent hamstring strain injury. It has been suggested that fascial tissue alters after muscle strain injury. However, the association between previous hamstring strain injury and tissue stiffness and vibration sense detection has not been investigated.ObjectivesWe aimed to determine whether a previous history of hamstring strain injury affects tissue stiffness and vibration sense in professional soccer players.MethodThe stiffness (MyotonPRO®) and vibration disappearance threshold (tuning fork) were measured in eight professional soccer players with previous history of hamstring strain and eight uninjured players. The differences between two groups’ means were analyzed. Side-to-side differences between injured and uninjured legs were also analyzed. Results: The tissue stiffness was higher, and the vibration disappearance threshold was lower, in previously injured players when compared to uninjured players. Similar differences were found between injured and uninjured legs. No significant relationship was detected between the age or body mass index (BMI) for both tissue stiffness and vibration disappearance threshold (all P < 0.05).ConclusionsSoccer players with a previous history of hamstring strain injury exhibited higher tissue stiffness and lower vibration sensitivity in the injured leg, regardless of the age and BMI. The results that players who have a previous hamstring strain injury with altered tissue stiffness and vibration sense will be useful and feasible evaluation for chronic muscle strain condition.     

Neuromuscular changes in football players with previous hamstring injury

BackgroundImpact of prior injury on myoelectrical activity of the hamstrings during isokinetic eccentric contractions has received increased literature attention. This cross-sectional study aimed to assess neuromuscular adaptations, namely proprioception, core stability, muscle strength, extensibility and activity, in football players with history of hamstring strain injury.MethodsSeventeen players, 10 with history of hamstring injury and 7 without prior injury underwent isokinetic strength testing, eccentric knee extension at 30 and 120°/s. Myoelectrical activity of bicep femoris and medial hamstrings was calculated at 30, 50 and 100 ms after onset of contraction. Functional tests included core stability, muscle strength, and knee proprioception tests.FindingDifferences were observed between Hamstring Group injured and uninjured and Control Group dominant limbs in the bicep femoris activity at almost all times in both velocities (p < 0.05). Joint position sense error was higher in the injured side compared to uninjured and control dominant limb; additionally there were also differences between injured and uninjured limb in the triple-hop test.InterpretationPreviously injured side showed deficits in bicep femoris myoelectrical activity after onset of contraction during eccentric testing, proprioceptive deficits, and functional asymmetry.     

Effects of prior hamstring strain injury on strength,flexibility, and running mechanics

Background

Previous studies have shown evidence of residual scar tissue at the musculotendon junction following a hamstring strain injury, which could influence re-injury risk. The purpose of this study was to investigate whether bilateral differences in strength, neuromuscular patterns, and musculotendon kinematics during sprinting are present in individuals with a history of unilateral hamstring injury, and whether such differences are linked to the presence of scar tissue.

Methods

Eighteen subjects with a previous hamstring injury (> 5 months prior) participated in a magnetic resonance (MR) imaging exam, isokinetic strength testing, and a biomechanical assessment of treadmill sprinting. Bilateral comparisons were made for peak knee flexion torque, angle of peak torque, and the hamstrings:quadriceps strength ratio, as well as muscle activations and peak hamstring stretch during sprinting. MR images were used to measure the volumes of the proximal tendon/aponeurois of the biceps femoris, with asymmetries considered indicative of scar tissue.

Findings

A significantly enlarged proximal biceps femoris tendon volume was measured on the side of prior injury. However, no significant differences between the previously injured and uninjured limbs were found in strength measures, peak hamstring stretch, or muscle activation patterns. Further, the degree of asymmetry in tendon volume was not correlated to any of the functional measures.

Interpretation

Injury-induced changes in morphology do not seem discernable from strength measures, running kinematics, or muscle activation patterns. Further research is warranted to ascertain whether residual scarring alters localized musculotendon mechanics in a way that may contribute to the high rates of muscle re-injury that are observed clinically.     

SPRINT PERFORMANCE IN FOOTBALL (SOCCER) PLAYERS WITH AND WITHOUT A PREVIOUS HAMSTRING STRAIN INJURY: AN EXPLORATIVE CROSS-SECTIONAL STUDY

Background:Hamstring strain injuries are common in many sports. Following a hamstring injury, deficits in peak and explosive strength may persist after return to sport potentially affecting sprint performance. Assessment of repeated-sprint ability is recognized as an important part of the return to sport evaluation after a hamstring injury.Purpose: This purpose of this exploratory cross-sectional study was to compare sprinting performance obtained during a repeated-sprint test between football players with and without a previous hamstring strain injury.Methods:Forty-four fully active sub-elite football players, 11 with a previous hamstring strain injury during the preceding 12 months (cases; mean age, SD: 25.6 ± 4.4) and 33 demographically similar controls (mean age, SD: 23.2 ± 3.7), were included from six clubs. All players underwent a repeated-sprint test, consisting of six 30-meter maximal sprints with 90 seconds of recovery between sprints. Sprint performance was captured using high-speed video-recording and subsequently assessed by a blinded tester to calculate maximal sprint velocity, maximal horizontal force, maximal horizontal power, and mechanical effectiveness.Results:A significant between-group difference was seen in favor of players having a previous hamstring injury over 6 sprints for maximal velocity (mean difference: 0.457 m/s, 95% CI: 0.059-0.849, p = 0.025) and mechanical effectiveness (mean difference: 0.009, 95% CI: 0.001-0.016, p = 0.020)Conclusion:Repeated-sprint performance was not impaired in football players with a previous hamstring strain injury; in fact, higher mean maximal sprinting velocity and better mechanical effectiveness were found in players with compared to without a previous hamstring injury. The higher sprinting velocity, which likely increases biomechanical load on the hamstring muscles, in previously injured players may increase the risk of recurrent injuries.Level of evidence:3b     

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

BackgroundThe 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.MethodsTen 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.FindingsBiceps 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.InterpretationNeuromuscular 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.     

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

BackgroundPrevious 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.Purpose1. 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 DesignUn-blinded, prospective, non-randomized, cohort study.MethodsSix-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.ResultsCollegiate 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.ConclusionHigher 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 EvidenceII     

Conséquences et prédiction des lésions musculaires des ischiojambiers à partir des paramètres isocinétiques concentriques et excentriques du joueur de football professionnelConsequences and prediction of hamstring muscle injury with concentric and eccentric isokinetic parameters in elite soccer players

OBJECTIVE: To know if isokinetic parameters identify previous hamstring (H) injury and predict a new muscle injury in high-level soccer player. METHOD: Concentric (con) and eccentric (ecc) isokinetic torque was measured at the angular speed of 60 degrees /s in 28 elite soccer players (23 years +/- 3.3; 74 kg +/- 7.5; 178 cm +/- 6.5). First, 11 players, victims of 15 moderate or major hamstring injuries in the preceding 2 years, were compared with 17 players without previous hamstring injury. Comparisons were carried out from isokinetic knee flexors-extensors ratios [Hcon/Qcon and Hecc/Qcon] and bilateral knee flexors ratios [Hcon/Hcon and Hecc/Hecc]. Secondly, all the population was followed during 12 months and the isokinetic muscular profile of players who presented a recurrence or a new hamstring muscle injury was analysed. RESULTS: A concentric ratio hamstring-to-quadriceps lower than 0.6 and a hamstring asymmetry of more than 10% do not allow to identify previous hamstring injury. On the other hand, the mixed ratio eccentric hamstring-to-concentric quadriceps lower than 0.6 represents the best indicator (probability: 77.5%). The rate of recurrence is 30% (three cases of 10) and the rate of new hamstring muscle injury is 31% (five cases of 16) (P > 0.05). One of the five injured soccer players presented a concentric ratio hamstring-to-quadriceps lower than 0.6 and no player presented a mixed ratio lower than 0.6. However, four of the five injured players presented a concentric and an eccentric asymmetry. But, it is the strongest side, which presented a new hamstring muscle injury. CONCLUSION:The mixed ratio eccentric hamstring-to-concentric quadriceps lower than 0.6 identify a previous hamstring injury despite the resumption of competitive soccer. However, this ratio and the others isokinetic studied parameters do not predict a recurrence or a new hamstring muscle injury.     

Coronal plane hip muscle activation in football code athletes with chronic adductor groin strain injury during standing hip flexion

BackgroundGroin pain arising from adductor muscle injury is common amongst football code athletes and can result in significant time lost from sporting participation. The associated motor control deficits are not well understood.AimsThe aim of this study was to better understand the coronal plane muscle activation patterns associated with chronic adductor injury.MethodologyMeasures of muscle activation at various stages of the standing hip flexion manoeuvre were made with surface electromyography and motion capture in 9 male football code subjects with chronic adductor injury, and 9 matched controls.ResultsThe gluteus medius to adductor longus activation ratio was significantly reduced in subjects with groin pain when the injured leg was either moving (F = 64.3, p < 0.001) or in stance phase (F = 32.4, p < 0.001) when compared to activity-matched uninjured subjects, equating to a difference varying between 20 and 40% depending on phase of movement. These differences were particularly due to decreased abductor muscle activation. No significant differences between the uninjured and injured side of patients was found.ConclusionFootball code athletes with groin pain exhibit significantly altered coronal plane muscle activation with comparison to uninjured subjects. These findings need to be taken into account when planning rehabilitation for these athletes.     

Sex comparison of hamstring structural and material properties

Background

Musculotendinous stiffness provides an estimate of resistance to joint perturbation, thus contributing to joint stability. Females demonstrate lesser hamstring stiffness than males, potentially contributing to the sex discrepancy in anterior cruciate ligament injury risk. However, it is unclear if the sex difference in hamstring stiffness is due to differences in muscle size or to inherent/material properties of the musculotendinous unit. It was hypothesized that hamstring stiffness, stress, strain, and elastic modulus would be greater in males than in females, and that hamstring stiffness would be positively correlated with muscle size.

Methods

Stiffness was assessed in 20 males and 20 females from the damping effect imposed by the hamstrings on oscillatory knee flexion/extension following joint perturbation. Hamstring length and change in length were estimated via motion capture, and hamstring cross-sectional area was estimated using ultrasound imaging. These characteristics were used to calculate hamstring material properties (i.e., stress, strain, and elastic modulus).

Findings

Stiffness was significantly greater in males than in females (P < 0.001). However, stress, strain, and elastic modulus did not differ across sex (P > 0.05). Stiffness was significantly correlated with cross-sectional area (r = 0.395, P = 0.039) and the linear combination of cross-sectional area and resting length (R² = 0.156, P = 0.043).

Interpretation

Male’s hamstrings possess a greater capacity for resisting changes in length imposed via joint perturbation from a structural perspective, but this property is similar across sex from a material perspective. Females demonstrate lesser hamstring stiffness compared to males in response to standardized loading conditions, indicating a compromised ability to resist changes in length associated with joint perturbation, and potentially contributing to the higher female ACL injury risk. However, the difference in hamstring stiffness is attributable in large part to differences in muscle size.     

Effect of increased relative stiffness of the lumbar spine on hamstring muscle stretching in individuals with a history of low back pain suspected to have a clinical lumbar instability: A randomized crossover design

BackgroundTheoretically, lumbopelvic stabilization techniques during hamstring muscle stretching could increase lumbar stiffness relative to hamstring muscle in individuals with a history of low back pain and suspected clinical lumbar instability. However, evidence to support this theory is limited. This study aimed to 1) determine changes in lumbopelvic, lumbar, and hip motions, and hamstring muscle length after stretching exercises with lumbopelvic stiffening or relaxing techniques, and 2) compare those changes between techniques.MethodsThis study used a randomized crossover design. Thirty-two participants with a history of low back pain and bilateral hamstring muscle tightness were recruited. The order of the first technique was randomly assigned. After a 2-day washout, participants were crossed over to the second technique. Motion data during active forward trunk bending and bilateral hamstring muscle length during passive knee extension were collected pre- and post-intervention.FindingsSignificant increases (P < 0.05) were found in bilateral hamstring muscle length for both techniques. However, stiffening technique demonstrated a significant decrease in lumbar motion (P < 0.05) and increase in hip motion (P < 0.05), while relaxing technique demonstrated trends showing increases in lumbar and hip motions (P = 0.134 and 0.115, respectively). The findings showed significantly greater improvement (P < 0.05) in lumbar and hip motions with stiffening technique.InterpretationThe findings suggest increased relative stiffness of the lumbar spine during hamstring muscle stretching can specifically lengthen bilateral hamstring muscle and decrease excessive lumbar motion. This stiffening technique may prevent excessive movement of the lumbar spine, thereby reducing the risk of recurrent low back pain.     

实验性肌肉拉伤的生物学和生物力学研究

目的探讨骨骼肌牵拉伤的生物学与生物力学特性。方法采用生物力学方法,建立肌肉拉伤的实验模型,70只兔的左胫前肌为实验肌,右胫前肌作为对照,分别在拉伤后0,1,2,3d和7d,进行组织学、酶组织化学与生物力学研究,生物力学指标包括最大肌力、断裂载荷、断裂时伸长、能量吸收与肌肉硬度。结果以相当于128%动物体重的载荷牵拉兔胫前肌,可建立肌肉拉伤的实验模型;部分肌纤维断裂和肌肉完全断裂均发生于靠近肌肉—肌腱连接处;最大肌力在拉伤后0d下降,1d时最低,7d时恢复正常;极限断裂载荷在拉伤后0d下降,2d时最低,7d时仍没有恢复正常。结论肌肉的被动强度比肌力恢复缓慢,提示拉伤肌肉易于再伤;损伤部位肌内膜纤维化和瘢痕组织形成,是肌肉拉伤后频繁复发的重要原因。     

Reliability and discriminative validity of real-time ultrasound elastography in the assessment of tissue stiffness after calf muscle injury

ObjectiveTo investigate the reliability and discriminative validity of real-time ultrasound elastography (RTE) measures of soft-tissue elasticity after calf muscle tear.DesignCross-sectional, intra/inter-examiner reliability and comparative validity study.SettingDepartment of Physical Therapy.ParticipantsTwenty-one recreational athletes were included and examined 6 weeks after sustaining a grade I-II calf musculature tear.Main outcome measuresSoft-tissue elasticity was measured by two experienced assessors using RTE assessments in both the longitudinal and transverse planes of the athletes’ injured and uninjured calf muscles. Elasticity was estimated by using the strain ratio (SR), which was calculated by dividing the strain (displacement) value taken at the medial gastrocnemius-soleus myotendinous junction (reference) by the strain value taken at the centre of the injury (index) as visualized on B-mode sonogram. Intra- and inter-observer reliability was estimated calculating intra-class correlation coefficients (ICCs) and standard error of measurement (SEM). Differences in elasticity between injured and healthy legs were assessed using t-tests or Wilcoxon tests for repeated measures.ResultsAll RTE assessments in both planes showed ICC values ranging from 0.77 to 0.95 and SEM values ranging from 0.72 to 0.99. Additionally, RTE enabled both assessors to determine differences in elastic properties between injured and control legs (p < 0.001).ConclusionRTE measures of calf muscles demonstrated good reliability and were able to differentiate injured from non-injured muscle tissue. RTE may provide a fast and objective measure in sports medicine to improve the detection of risk factors for muscle injury related to alterations of the mechanical behaviour of soft tissues during healing process.     

Hip Adduction and Abduction Strength Profiles Among Bantam,High School,Juniors, and Collegiate American Ice Hockey Players

BackgroundAdductor strains are the most common non-contact musculoskeletal injury sustained in ice hockey. Systematic reviews have determined higher level of play and lower hip adduction to abduction strength ratios to be associated with an increased risk of adductor strain across multiple sports. Limited research exists regarding hip adduction and abduction strength profiles across various levels of ice hockey players.PurposeTo compare isometric hip adduction and abduction strength profiles among bantam, high school, tier one juniors, and NCAA Division I collegiate ice hockey players. A secondary purpose was to identify whether differences in strength profiles between dominant and non-dominant limbs exist.Study DesignCross-sectional cohort study.MethodsA questionnaire of demographic data, hockey, and injury specific information was completed by all subjects. The mean of three reps of maximal hip isometric adduction and abduction strengths were quantified using a handheld dynamometer with external belt-fixation. Ratios of hip adduction-to-abduction strength were calculated and normalized for body weight.ResultsA total of 87 uninjured skaters were included in this study with a mean age of 17 years. Mean hip adductor-to-abductor ratios for Bantam hockey players were 121% followed by collegiate (115%), Juniors (111%), and high school (109%) hockey players. No statistically significant differences were found between peak hip adduction and abduction isometric strength and playing level. In addition, there was no difference between unilateral hip strength ratios and shooting hand or leg dominance. While 34.5% of subjects reported a history of adductor injury, no significant differences existed regarding strength ratios during bilateral comparison or when compared to their team norms. Three subjects were found to have unilateral ratios of less than 80%, while two subjects demonstrated bilateral ratios of less than 80%.ConclusionsSymmetry is illustrated between dominant and non-dominant legs in ice hockey players with and without a history of adductor injury. Results align well with previously established cross-sectional data from Australian football, with ratios of 103% in high school players, 107% in semi-professional players, and 113% in collegiate players.Level of EvidenceLevel 3     

Unilateral lower limb injury: its long-term effects on quadriceps, hamstring, and plantarflexor muscle strength.

OBJECTIVE: To ascertain if long-term deficits in quadriceps, hamstring, and plantarflexor muscle strength remain after unilateral lower-limb musculoskeletal injury and to quantify whether improvements in performance continue once a subject concludes rehabilitation and returns to everyday activities. The relation between the size of decrement and limb dominance, type of injury, and time since injury was also considered. DESIGN: Isometric and/or dynamic muscle strength of both legs was measured (using the KinCom 500H isokinetic dynamometer) in 48 subjects. SETTING: A physiological laboratory at Brunel University. PATIENTS: Patients were recruited locally via a district general hospital, sports injury clinic, and university. MAIN OUTCOME MEASURES: Muscle strength in the injured limb, reported as a percentage of muscle strength in the uninjured limb. It was assumed that the preinjury state of the injured limb was similar to that of the uninjured limb. RESULTS: Decrements were seen in mean isometric and peak isometric, concentric, and eccentric quadriceps activity (p < .0001) and isometric plantarflexor activity (p < .05) in the injured limb, with the type of injury influencing the size of the decrement. Minimal difference was found in the hamstring muscles. CONCLUSIONS: The decrements in performance in the quadriceps muscle imply that full recovery (as defined by the preinjury state) is frequently not achieved and stress the need for accurate, objective assessment of muscle strength and further investigation into the nature and duration of rehabilitation after musculoskeletal injury.     

Influences of hamstring stiffness and strength on anterior knee joint stability

Background

Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively.

Methods

Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests.

Findings

Anterior tibial translation was correlated with hamstring stiffness (r = −0.538; P = 0.002), but not with hamstring strength (r = −0.088; P = 0.644). Hamstring stiffness and strength were not correlated (r = 0.054; P = 0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t₂₈ = 2.186; P < 0.037; ES = 0.36), but hamstring strength did not differ between these groups (t₂₈ = 1.057; P < 0.300; ES = 0.17).

Interpretation

Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings’ ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs.     

Musculoskeletal profile of male collegiate soccer players

Twenty-five collegiate soccer players were evaluated for lower extremity flexibility and muscle strength at the end of preseason training and before the onset of the collegiate soccer season on two successive seasons. The purpose of the evaluation was to determine whether symmetry was present in their legs and whether deficits in flexibility or strength would affect the susceptibility to hamstring or groin muscle strain injuries. The mean (+/- SE) flexibility of the dominant leg for hip abduction was 41 degrees +/- 1.2 degree; for hip flexion, 76 degrees +/- 1.9 degree; for hip extension, 174 degrees +/- 0.7 degree; and for ankle dorsiflexion, 33 degrees +/- 1.3 degree. The mean (+/- SE) isokinetic torque of the dominant leg (tested at 30 degrees per second) for knee extension was 214 +/- 8 newton meters and for flexion was 128 +/- 4 newton meters, while isometric strength for hip flexion was 315 +/- 8 newtons and for ankle plantar flexion was 1721 +/- 58 newtons. No significant differences were found between the dominant and nondominant legs in flexibility or strength. During this study no hamstring or groin strain injuries occurred. The lack of leg muscle strain injuries appeared to be directly related to the initiation of a controlled warmup and stretching program and underlines the importance of this in injury prevention. Interestingly, more than 50% (13 of 25) of the players were found to have significant deficits in one or more specific muscle groups. Two athletes sustained low back strain injuries and one athlete had a knee sprain injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

Normative parameters and anthropometric variability of lumbar muscle stiffness using ultrasound shear-wave elastography

BackgroundQuantifying stiffness of the lumbar spine musculature using shear-wave elastography (SWE) maybe beneficial in the diagnosis and treatment of non-specific low back pain (LBP). The primary purpose of this study was to establish normative parameter and variance estimates of lumbar spine muscle stiffness at rest and during submaximal contraction levels using SWE in healthy individuals. A second aim was to determine the relationship between lumbar spine muscle stiffness and a variety of demographic, anthropometric, and medical history variables.MethodsThis cross-sectional study included stiffness measurements of the lumbar musculature in 120 asymptomatic individuals using ultrasound SWE. The lumbar erector spinae muscle was measured during rest only and lumbar multifidus muscle was measured during rest and during submaximal contraction using a prone contralateral arm lift. Statistical comparisons of shear modulus were made between sex (male vs. female) and muscle condition (erector spinae rest, lumbar multifidus rest, lumbar multifidus contracted) using 2 × 3 repeated measures analysis of variance (ANOVA). Univariate associations between shear modulus and age, sex, BMI, activity level, and history of back pain were assessed using correlation analysis.FindingsShear modulus at rest was approximately 4 kPa for the erector spinae muscles and approximately 6 kPa for the lumbar multifidus muscles. Shear modulus substantially increased during contraction, and varied by sex, BMI, and self-reported activity level, with men and more active individuals generally having stiffer muscles.InterpretationVariability in shear modulus of the lumbar musculature may be mediated through a combination of muscle size and contractile state, which is consistent with our findings of higher stiffness in the more postural lumbar multifidi muscles, during contraction, and in larger and more active individuals. These findings should inform and be accounted for in future comparative clinical studies.     

Personal Characteristics and Back Injury Among Hospital Nursing Personnel

Since back injury is the largest workman's compensation claim in most industries, the relationship between selected personal characteristics and back injury in hospital nursing personnel were studied. The sample included 64 female nursing personnel, half back injured and half not. Demographic: Workers were more likely to be back injured if they were older, worked longer on nursing units requiring frequent lifting, had family members with back problems, and had family members whose back problems began at an early age. Physical: The back injured had less muscle flexibility, less keen proprioception, and greater unequal leg length. Life style: Back injured were more vulnerable to frustration and stress overload (overstimulation), smoked more cigarettes, spent fewer hours exercising, and rated their physical condition lower. The variables with the greatest discriminatory power to predict back injury were a sense of overload, muscle flexibility, proprioception, family history of back problems, difference in leg length, years of risk in nursing practice, and smoking.     

Predisposing factors to hamstring neuromuscular deficits—implications for prevention and rehabilitation of hamstring strain injuries: a narrative review

Background: Scientific knowledge on hamstring strain injuries (HSI) constantly accumulates for the last 100 years. However HSI still exhibit high injury/re-injury rates and new areas of research must be thoroughly explored. Deficiencies that impact the close relationship between the nervous system and muscle functioning constitute a promising research direction, according to existing literature.

Objectives: To outline the often-overlooked factors that pre-dispose to hamstring neuromuscular deficits, with a special emphasis on hamstring strain injury and re-injury.

Major Findings: Sensory input impairment, neural tension, fatigue, competitive anxiety and lumbar-pelvic motor control deficit can all induce dysregulations of the hamstring neuromuscular functioning that may be detrimental during high-speed running. They constitute therefore serious risk factors for hamstring strain injury and re-injury.

Conclusions: We devised an intervention algorithm including both evaluation procedures and hamstring management plan, by compiling and adjusting the most promising doctrines of the literature reviewed. Further research, such as randomized controlled trials, is required to provide evidence of the effectiveness and feasibility of this algorithm for patients in post-HSI recovery or as a preventive approach in the event of high suspicion of re-injury.