Lateral Hamstrings Research Articles

Muscular co-contraction is related to varus thrust in patients with knee osteoarthritis

BackgroundPatients with knee osteoarthritis often present with varus thrust and muscular co-contraction during gait. It is unclear if these adaptations are related. The objective was to examine the relationship between muscle co-contraction and varus thrust during gait in patients with knee osteoarthritis and to determine if these relationships are modulated by disease severity or history of knee ligament rupture. MethodsParticipants (n = 42, 23 women, mean age 58 years) with knee osteoarthritis completed gait trials at self-selected speeds. Varus thrust was measured with an eight camera motion capture system sampled at 100 Hz. Co-contraction ratios were measured with surface electromyography sampled at 2000 Hz over the quadriceps, hamstrings, and gastrocnemius. Disease severity was measured on radiographs and history of anterior cruciate ligament rupture was confirmed on magnetic resonance imaging. Linear regression analyses examined the relationship between varus thrust and co-contraction ratios after controlling for radiographic disease severity and history of anterior cruciate ligament rupture. FindingsHigher vastus lateralis–lateral hamstring (b = 0.081, P < 0.001; R2 = 0.353) and vastus medialis–medial hamstring (b = 0.063, P = 0.028; R2 = 0.168) co-contraction ratios were associated with greater varus thrust. Quadriceps-gastrocnemius co-contractions ratios were not related to varus thrust (P > 0.05). Radiographic disease severity or history of anterior cruciate ligament injury did not significantly contribute to regression models. InterpretationGreater quadriceps-hamstring co-contraction is associated with greater varus thrust in patients with knee osteoarthritis. Potential explanations include increased co-contraction may provide stability or there is a proprioceptive reflex that is independent of any stabilizing role. Research is needed to test these hypotheses.

Muscle Activity Pattern Dysfunction During Sit to Stand and Stand to Sit in the Movement System Impairment Subgroups of Low Back Pain

ObjectiveTo investigate impairment in the activity pattern of some muscles involved in sit to stand (STD) and stand to sit (STS) among 2 low back pain (LBP) subgroups of the Movement System Impairment (MSI) model. DesignCase-control study. SettingA university medical center. ParticipantsFifteen women without chronic LBP and 22 women with chronic LBP (N=37) in 2 subgroups (15 into the lumbar extension rotation (LER) and 7 into lumbar flexion rotation [LFR]) voluntarily participated in this study. InterventionsParticipants were asked to perform STD and STS at a preferred speed. Surface electromyography (EMG) were measured bilaterally from the internal oblique (IO), lumbar erector spine (ES), medial hamstring (MH), and lateral hamstring (LH) muscles. Main Outcome MeasuresChanges in mean and maximum amplitude, time to peak amplitude, duration of muscle activity, and bilateral asymmetry of these variables. ResultsDuring STD, bilateral asymmetry in mean amplitude of MH in the LER subgroup (P=.031) and bilateral asymmetry in duration of LH in the LFR subgroup (P=.026) were exhibited. Also, in this task reduced time to peak left MH activation were found in the LFR subgroup than 2 other groups (control; P=.028/LER; P=.004). During STS, increased left ES maximum amplitude were observed in the LFR subgroup than LER subgroup (P=.029). Also, reduced time to peak right ES (P=.035) and left LH (P=.038) activation in the LER subgroup than control subjects and reduced time to peak left LH activation in LFR subgroup than control subjects (P=.041) were observed during STS. ConclusionsThe differences between the 2 LBP subgroups may be a result of impairment in the activity pattern of some muscles during functional activity.

Empirical Based Modeling for the Assessment of Dynamic Knee Stability: Implications for Anterior Cruciate Ligament Injury Risk.

Anterior cruciate ligament (ACL) injuries are common sports injuries, costing the U.S. roughly $1 billion annually. To better understand the underlying injury mechanism, Nyquist and Bode stability criteria were applied to assess frontal plane dynamic knee stability among male Australian Football players during the weight-acceptance phase of single-leg jump landing. Out of 30 landings, 19 were classified as stable and 11 as unstable. Medial and lateral vasti, hamstring and gastrocnemii muscle activation waveforms were analyzed in parallel to determine if individuals with stable and unstable frontal plane joint biomechanics possessed different lower limb neuromuscular strategies. The total quadriceps muscle activation during the stable landings were significantly higher (p=0.02) than during the unstable landings. Additionally, the vasti exhibited a medial dominance during the stable landings compared to the unstable (p=0.06). These results suggest that individuals with unstable frontal plane knee landing mechanics may have reduced recruitment of the muscles crossing the knee; specifically, the medial muscles, which could limit their ability to compress and support the joint. The stability criteria were able to classify stable and unstable knee mechanics. And the differences in muscle activation during these stable and unstable landings provided new insights towards the ACL injury mechanism and possible injury prevention countermeasures.

O 023 - Crouch gait in children with Cerebral Palsy and the impact on trunk kinematics and lower lumbar spinal loading

Osteoarthritis (OA) of the knee joint is a common disease accompanied by pain and impaired mobility. Despite some recent concerns on the lack of correlation between the medial load and the knee adduction moment (KAM), KAM is routinely considered as a surrogate measure of medial load and hence a marker where its reduction is the main focus of preventive and treatment interventions.Determine the relative sensitivity of the tibiofemoral medial-lateral contact load partitioning to changes in the knee adduction angle (KAA) versus KAM.Using a lower extremity hybrid musculoskeletal (MS) model driven by gait kinematics and kinetics, we compute here in asymptomatic subjects the sensitivity of the knee joint biomechanical response (muscle and ligament forces) in general and medial/lateral load partitioning in particular to the relative changes in the reported KAA versus changes in reported KAM (both by one standard deviation).As KAA increased (at constant KAM), so did the passive moment resistance of the knee joint which as a result and at all stance periods substantially reduced forces in lateral hamstrings while increasing those in medial hamstrings. At 25% and 75% stance as two highly loaded periods of gait, the drop in KAA (from + SD to –SD while at constant KAM) drastically reduced the medial contact force by 44% and 30% and the medial over lateral contact load and area ratios by 92% and 79% as well as 64% and 51%, respectively. In contrast, the equivalent alterations in KAM (by ± SD at constant KAA) had lower and less consistent effects (<7%) showing much smaller sensitivity to changes in KAM alone. Ligament forces altered at various stance periods with inconsistent trends; peak values of 418 N in the anterior cruciate ligament (90% carried by the posterolateral bundle) and 1056 N in the patellar tendon were computed both at 25% stance and minimum KAA.These findings indicate a poor correlation between KAM and tibiofemoral load distribution suggesting instead that KAA and knee alignment should be in focus as the primary marker of knee joint load partitioning and associated prevention and treatment interventions.

Differences in Hip Joint Biomechanics and Muscle Activation in Individuals With Femoroacetabular Impingement Compared With Healthy, Asymptomatic Individuals: Is Level-Ground Gait Analysis Enough?

Background:Femoroacetabular impingement (FAI) is a recognized cause of hip and groin pain and a significant factor in hip joint function during sport. Objective tests for understanding hip function are lacking in this population.Purpose:To determine whether biomechanical and electromyographic features of hip function during level-ground walking differ between a group diagnosed with FAI and those with no symptoms of FAI.Study Design:Controlled laboratory study.Methods:A total of 20 asymptomatic individuals and 20 individuals with FAI walked on a dual-belt instrumented treadmill at self-selected walking velocities. Sagittal and frontal plane joint motions, moments, and muscle activation for the gluteus medius, gluteus maximus, rectus femoris, and medial and lateral hamstrings were analyzed. Discrete measures were extracted from each biomechanical waveform, and principal component analysis was used to determine hip joint muscle activation and hip adduction moment patterns. Statistical significance was determined by use of Student t tests with Bonferroni adjustments for multiple comparisons (α = .05).Results:Individuals with FAI walked more slowly (P = .015) and had lower self-reported function (P < .001). No differences in muscle strength were found between the symptomatic and contralateral legs in the FAI group (P > .017), but those with FAI had lower strength in the knee extensors and flexors and the hip extensors, flexors, and adductors compared with the asymptomatic group (P < .017). Individuals with unilateral symptomatic FAI walked with similar biomechanical and hip muscle electromyographic results bilaterally. The only differences found were a greater amplitude of gluteus maximus activation in the FAI symptomatic leg compared with the asymptomatic group and greater medial hamstring activation than lateral hamstring activation in the FAI group in both limbs compared with the asymptomatic group.Conclusion:Individuals with FAI were generally deconditioned and reported significantly more functional limitations. No biomechanical differences existed between groups during level walking, yet hamstring and gluteus maximus activation differed when the symptomatic group was compared with the asymptomatic group.Clinical Relevance:The field lacks objective testing of hip joint function to understand implications of FAI for dynamic movements, particularly with applications to biomechanics and electromyography. Level walking was of limited value for understanding FAI hip function, and the development of a more challenging gait assessment is warranted.

Long Ground Contact Time Enhances Running Economy at High-Intensity Running

Running economy (RE) determines the difference in distance running performance in highly-trained runners. Studies have highlighted RE importance during high-intensity running. Although RE is related to ground contact time (Tc), the relationship between RE at high-intensity running and Tc is not elucidated. It is also unclear whether the hamstrings muscle, which contribute to high-intensity running, affect RE and Tc. PURPOSE: We aimed to clarify the relationships among RE, Tc at intensity below and above the lactate threshold (LT) run, and hamstring muscle’s cross-sectional area in highly-trained long-distance runners. METHODS: We enrolled 11 highly trained male distance runners (IAAF score: 1038 ± 48). They underwent treadmill running test to assess the LT, and RE. RE was evaluated at 270 (RE270) and 360 m/min (RE360) as the intensity below and above the LT, respectively. Tc was also valuated at the same velocity (Tc270; Tc360). Both medial and lateral hamstring muscles’ cross-sectional areas (MHA and LHA, respectively) were calculated using MRI at 50% position of the right thigh. RESULTS: The subjects’ LT, RE270 and RE360 were 337 ± 17 m/min, 0.90 ± 0.08 kcal/ kg/km, and 1.00 ± 0.07 kcal/kg/km, respectively. The Tc270, Tc360, MHA and LHA values were 195 ± 17 ms, 164 ± 9 ms, 1.24 ± 0.18 cm2/kg0.67, and 0.99 ± 0.11 cm2/kg0.67, respectively. RE270 showed a significant relationship with Tc270, MHA, and LHA (r = -0.81, 0.75, and 0.60, respectively; P < 0.05), but no relationship was noted with IAAF score (r = -0.55; P = 0.08). Tc270 was related to MHA and LHA (r = -0.63 and -0.67; P < 0.05). Although RE360 showed a significant relationship with IAAF score, Tc360, and MHA (r = -0.73, -0.65, and 0.69, respectively; P < 0.05), no relationship was noted with LHA (r = 0.35; P = 0.30). Tc360 did not exhibit any significant relationship with MHA (r = -0.55; P = 0.08) and LHA (r = -0.52; P = 0.10). CONCLUSION: The findings of this study are as follows: (a) RE at high rather than low intensity is related to running performance; (b) longer Tc enhances RE; (c) superior RE and long Tc at low intensity are related to small hamstring muscles, but these associations disappear, except between RE and MHA, at high intensity. These results suggest that long Tc at high-intensity contributes to superior RE, but not to hamstring muscles, and leads to higher running performance.

Neuromuscular changes of the aged human hamstrings.

Despite the life-long importance for posture and locomotion, neuromuscular properties of the hamstrings muscle have not been explored with adult aging. The purpose of this study was to assess and compare age-related effects on contractile function, spinal motor neuron output expressed as motor unit (MU) discharge rates in the hamstrings of 11 young (26 ± 4 yr) and 10 old (80 ± 5 yr) men. Maximal voluntary isometric contractions (MVC), stimulated contractile properties, and surface and intramuscular electromyography (EMG) from submaximal to MVC were recorded in the biceps femoris (BF) and semimembranosus-semitendinosus (SS) muscles. MVC torque was ~50% less in the old with both age groups attaining ≥93% mean voluntary activation. Evoked twitches in the old were ~50% lower in amplitude and >150% longer in duration compared with those in the young. At successive voluntary contractions of 25, 50, and 100% MVC, MU discharge rates were up to 45% lower in old, with no differences in relative submaximal surface EMG between age groups. Furthermore, the old had significantly lower MU discharge rates in the SS at all contraction intensities compared with the BF muscle. Men in their 8th to 10th decades of life demonstrate substantially lower strength and MU discharge rates in this functionally important large lower limb muscle group, with greater age-related effect on discharge rates in the medial hamstrings. These findings, compared with those in other muscles studied, highlight that the neuromuscular properties of limb muscles, and indeed within functionally similar portions of a muscle group, are not all affected equally by the aging process. NEW & NOTEWORTHY In the hamstrings, we found that both contractile function and motor unit discharge rates across the range of voluntary intensities were lower in the old. The differences in discharge rates due to age were greater in the medial hamstrings muscle group compared with the lateral hamstrings. Compared with previous studies, these results highlight that not all muscles are affected equally by aging and there may be compartmental differences within functionally similar muscles.

Effect of Fatigue on Electromyographic Activity Patterns of the Knee Joint Muscles in Anterior Cruciate Ligament Reconstructed and Deficient Patients during Landing Task

Lower extremity fatigue causes a number of neuromuscular alterations that may increase the risk of knee (re)injury. It has therefore been suggested that fatigue-resistance training be incorporated into injury prevention and rehabilitation programs. The purpose of this study was to determine the effects of fatigue on knee-muscle activity patterns after anterior cruciate ligament injury (ACL). Twelve healthy, 12 ACL reconstructed (ACLR) and 12 ACL deficient (ACLD) recreationally active male volunteers participated in this case-control study. Fatigue was induced via repetitive sets of double-leg squats and drop landings. Muscle activity was assessed via surface electromyography during a single-leg drop landing task pre- and post-fatigue. After fatigue, medial hamstring, lateral hamstring and vastus lateralis muscles turned on significantly earlier in ACLR compared to the control group. Significantly greater vastus medialis muscle activity was observed in ACLD compared to ACLR and control participants post-fatigue. Finally, fatigue decreased lateral gastrocnemius muscle activity in ACLD and control participants. It seems ACLR patients rely on earlier muscle pre-activation to establish knee joint stability upon landing after fatigue. This feed-forward strategy should be emphasized during post-operative rehabilitation in ACLR patients. Furthermore, according to our results, quadriceps and gastrocnemius muscles play an important role in establishing knee joint stability post impact in ACLD patients.

Lower limb muscle activation patterns during foot rotation gait modification in people with knee osteoarthritis

Lower limb muscle activation patterns during foot rotation gait modification in people with knee osteoarthritis

The effect of knee joint effusion on gait mechanics and muscle activations in individuals with moderate knee osteoarthritis

Purpose: Knee osteoarthritis (OA) is the most common joint disease and is often characterized by pain, stiffness, swelling and limited tolerance to weight-bearing activities. It has been shown to be associated with biological inflammatory processes in the synovium, synovitis, and mechanical insults that lead to the deterioration of the joint structures. Synovitis is usually characterized by knee joint swelling and the mechanical knee joint environment during a loading stimulus can be studied in vivo using state-of-the-art gait analyses. The study objective is to compare knee mechanics and muscle activation patterns during gait in individuals with knee OA who have and do not have knee joint swelling. Methods: 45 patients diagnosed with moderate medial compartment knee OA were recruited. Knee swelling was measured at three locations (mid, medial, lateral) of the supra-patellar recess (SRD) using ultrasound imaging. A maximum depth, regardless of the location was determined. Effusion presence was defined as a SRD depth >4 mm. Knee joint motion was calculated from skin markers and net external moments calculated through inverse dynamics during walking on a dual-belt instrumented treadmill at self-selected speed. Electromyography (EMG) from vastus medialis (VM) and lateralis (VL), medial (MH) and lateral hamstrings (LH), medial (MG) and lateral gastrocnemius (LG) was recorded using standardized procedures. Two-sample unpaired t-tests were used to test for significant differences in sagittal plane knee joint angles, sagittal and frontal external moments, pain, Knee Osteoarthritis Outcome Scores, age, body mass index, stride characteristics, and knee extensor and flexor strength. Principal component analysis (PCA) was performed on the EMG waveforms to capture amplitude and temporal based features. Principal Pattern (PP)-scores were calculated from principal patterns that together explained >90% of the waveform variability. Two-way mixed-model Analysis of Variance models were performed on the PP-scores to identify muscle, group and interaction effects. Bonferroni corrected pairwise post-hoc comparisons were made. A P-value of 0.05 was used to determine statistical significance. Results: Of the 45 participants, 25 had effusion (SRD > 4mm). No significant differences were found between groups in subject demographic and anthropometrics, questionnaire outcomes, and knee strength (P > 0.05). Both groups had a similar radiographic grade distribution. No biomechanical differences existed between both groups, however the effusion group had greater overall amplitudes of VM and VL (PP1-scores) and greater early stance activation of the gastrocnemius muscles (PP2-scores). No other group differences or group by muscle interactions existed. Conclusions: These results, as shown in Figure 1, indicate that specific amplitude knee joint muscle activation patterns are altered in the presence of knee effusion during gait in individuals with knee OA. Greater stance phase amplitudes in the quadriceps and gastrocnemius muscles are consistent with responses aimed at providing neuromuscular knee joint support and increasing early stance active stiffness, respectively, in order to preserve knee function when effusion is present. These muscular adaptations have been previously reported with increased OA severity suggesting a possible link between gait mechanics and knee swelling as knee OA progresses. The 4 mm SRD threshold has previously been linked to a higher risk of knee OA progression, supporting findings of this study. Future studies can investigate different cut-off values for the detection of effusion sonographically to establish whether biomechanical subgroups may exist.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Influence of hamstring activity on knee moments during loading response of gait in individuals following ACL reconstruction

Purpose: Clinically, restoration of gait mechanics following anterior cruciate ligament reconstruction (ACLr) is expected by 3 months post-surgery. However, biomechanical studies at this time consistently report the presence of reduced knee extensor moments in the surgical limb during loading response (LR). This reduction in knee loading is quantified by net joint moments (NJM) estimated using inverse dynamics and represents the minimum moment required for the given kinematics. As a result, the NJM does not consider the contribution from individual muscle groups including quadriceps and hamstrings. Thus, alterations in quadriceps or hamstrings activity could confound our interpretation of the NJM and characterization of knee loading in the surgical limb. In the presence of increased knee flexor activity, the true contribution from the knee extensors may not be reduced at all. Moreover, increased hamstring and consequential quadriceps activity could result in increased tibiofemoral compressive forces and lead to the progression of knee osteoarthritis. Thus, the purpose of this study is to compare the influence of hamstring activity on knee moments during LR between limbs in individuals post-ACLr. Methods: 17 individuals (11F, 24 ± 11 yrs) 114 ±1 7 days post-ACLr walked at 1.4 m/s. 3D kinematics (250 Hz), ground reaction forces (GRF; 1000 Hz) and anthropometrics were used to quantify sagittal plane joint kinematics and kinetics (inverse dynamics). Medial and lateral hamstring surface electromyography (EMG; 1000 Hz) was collected. Maximum voluntary isometric contractions (MVIC) were performed bilaterally. Raw EMG signals were band-pass filtered (10–500 Hz) and rectified. A 6 Hz low-pass filter was used to create a linear envelope. All data were normalized to 101 points of stance. A standard musculoskeletal SIMM (Software for Interactive Musculoskeletal Modeling) model was used to estimate knee flexor moments. Sagittal plane hip, knee, and ankle kinematics and hamstring EMG (biceps femoris long head, BFLH, and short head, BFSH, semimembranosus, SM, and semitendinosus, ST) normalized to MVIC were used as inputs. SM and BFSH activation were assumed to be the same as ST and BFLH, respectively. To account for differences in hamstring strength, the knee flexor moment from SIMM was scaled using a ratio of the subject’s maximum knee flexor torque during MVIC divided by the maximum knee flexor torque of the SIMM model in the testing position. The sum of the scaled estimated knee flexor moment and net knee moment (Visual3D) were used to estimate knee extensor torque. Moment impulses were calculated as the area under the curve from initial contact to peak knee flexion. Four successful trials were collected for the surgical (ACLr) and non-surgical (NS) limbs. Paired sample t-tests were used to compare net knee and estimated flexor and extensor moment impulses between limbs (mean ± SE); α = 0.05. Results: Net knee (P = 0.02; ACLr: −0.028 ± 0.003; NS: −0.041 ± 0.004 Nm*s/kg) and estimated extensor (P = 0.02; ACLr: −0.035 ± 0.004; NS: −0.048 ± 0.005 Nm*s/kg) moment impulses during LR were reduced in ACLr compared to NS limb. However, estimated knee flexor moment impulse (P = 0.99; ACLr:0.008 ± 0.001; NS:0.008 ± 0.001 Nm*s/kg) was not different. Conclusions: These data are consistent with the literature reporting reduced net knee loading in the surgical limb post-ACLr. When accounting for the torque-producing capabilities of the knee flexors, the estimated knee extensor moment was greater than the net moment in both limbs. The estimated knee extensor moment remained reduced in the ACLr limb compared to the NS limb in the absence of between limbs differences in SIMM estimated knee flexor moment. These data indicate that individuals do not disproportionately increase hamstring contribution to the net knee moment in the surgical knee during gait and the reduced net knee moment reflects a pattern in which the contribution of knee extensors is reduced during LR of gait.

Surface EMG patterns for quantification of thigh muscle co-contraction in school-age children: Normative data during walking

Muscle co-contractions are particularly relevant in analyzing children pathologies. To interpret surface electromyography (sEMG) in pathological conditions, reliable normative data in non-pathological children are required for direct comparison. Aim of the study was the quantification of co-contraction activity between quadriceps femoris (QF) and hamstring muscles during walking in healthy children. To this aim, Statistical gait analysis was performed on sEMG signals from rectus femoris (RF), vastus medialis (VM), and lateral hamstrings (LH), in 16401 strides walked by 100 healthy school-age children. Co-contractions were assessed as overlapping period between activation intervals of considered muscles. Results showed full superimpositions of LH with both RF and VL activity from terminal swing, 80–100% of gait cycle, to successive loading response (0–15% of gait cycle), in around 90% of strides, as reported in adults. This indicates that children regularly use a cocontraction activity between QF and hamstring muscles in weight acceptance during walking, supporting the hypothesis of a regulatory role of co-contraction in providing knee joint stability. Concomitant activity of QF and hamstring muscles was detected also during push-off phase (30–50% of gait cycle), showing a large variability intra and inter subjects and a lower occurrence frequency (around 25% of strides). This could be intended for controlling rapid knee flexion and/or stabilizing pelvis during body progression. Present findings represent the first attempt to provide normative sEMG dataset on variability of QF and hamstring muscles co-contractions during child walking, useful for discriminating physiological and pathological behavior and for designing future studies on maturation of gait.

Force musculaire et fonction postopératoire après résection des muscles fléchisseurs du genou pour sarcomes des tissus mous aux membres inférieurs

Summary Introduction Oncological margins and prognosis are the most important factors for operative planning of soft tissue sarcomas, but prediction of postoperative function is also necessary. The purpose of this study was to predict the knee flexion strength and postoperative function after knee flexor muscle resection for soft tissue sarcoma of the lower limbs. Materials and methods Seventeen patients underwent knee flexor muscle resection for soft tissue sarcoma of the lower limbs between 1991 and 2015. The type of resected muscles was surveyed, knee flexion strength (ratio of affected to unaffected side) was evaluated using the Biodex System isokinetic dynamometer, and differences between the type of resected muscles were examined. The Musculoskeletal Tumor Society (MSTS) score, Toronto Extremity Salvage Score (TESS), European Quality of Life-5 Dimensions (EQ-5D), and Short Form 8 (SF-8) were used to assess postoperative function and examine correlations with flexion strength. The cutoff value for flexion strength to predict good postoperative results was calculated by a receiver operating characteristic (ROC) curve and Fisher's exact test. Results Median flexion strength decreased in the resection of sartorius (97.8%), gracilis (95.4%), gastrocnemius (85.2%; interquartile range [IQR], 85.0–86.2), medial hamstrings (semimembranosus and semitendinosus, 76.2%; IQR, 73.3–78.0), lateral hamstrings (long and short head of biceps femoris, 66.1%; IQR, 65.9–70.4), and bilateral hamstrings (27.3%; IQR, 26.6–31.5). A significant difference was observed between lateral and bilateral hamstrings resection (P = 0.049). Flexion strength was associated with lower functional scales (MSTS score, P = 0.021; TESS, P = 0.008; EQ-5D, P = 0.034). Satisfactory function was obtained at a flexion strength cut-off value of 65.7%, and strength remained above the cutoff value up to unilateral hamstrings resection. Discussion Greater knee flexor muscles resection can result in functional deficits that are associated with decreased flexion strength. If continuity of unilateral hamstrings is maintained, good postoperative results can be expected. Level of evidence IV, retrospective study.

Relationships of hamstring muscle volumes to lateral tibial slope

BackgroundGreater posterior–inferior directed slope of the lateral tibial plateau (LTS) has been demonstrated to be a prospective ACL injury risk factor. Trainable measures to overcome a greater LTS need to be identified for optimizing injury prevention protocols.It was hypothesized that Healthy individuals with greater LTS who have not sustained an ACL injury would have a larger lateral hamstring volume. MethodsEleven healthy females (mean +/- standard deviation) (1.63±0.07m, 62.0±8.9kg, 22.6±2.9years) & 10 healthy males (1.80±0.08m, 82.3±12.0kg, 23.2±3.4years) underwent magnetic resonance imaging of the left knee and thigh. LTS, semitendinosus muscle volume, and biceps femoris long head muscle volume were obtained from imaging data. ResultsAfter controlling for potential sex confounds (R2=.00; P=.862), lesser semitendinosus volume and greater biceps femoris-long head volume were indicative of greater LTS (R2∆=.30, P=.008). ConclusionsHealthy individuals with greater LTS have a muscular morphologic profile that includes a larger biceps femoris-long head volume. This may be indicative of a biomechanical strategy that relies more heavily on force generation of the lateral hamstring and is less reliant on force generation of the medial hamstring. Level of evidenceLevel IV.

Differences in hamstring activation characteristics between the acceleration and maximum-speed phases of sprinting

ABSTRACTThis study aimed to investigate activation characteristics of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles during the acceleration and maximum-speed phases of sprinting. Lower-extremity kinematics and electromyographic (EMG) activities of the BFlh and ST muscles were examined during the acceleration sprint and maximum-speed sprint in 13 male sprinters during an overground sprinting. Differences in hamstring activation during each divided phases and in the hip and knee joint angles and torques at each time point of the sprinting gait cycle were determined between two sprints. During the early stance of the acceleration sprint, the hip extension torque was significantly greater than during the maximum-speed sprint, and the relative EMG activation of the BFlh muscle was significantly higher than that of the ST muscle. During the late stance and terminal mid-swing of maximum-speed sprint, the knee was more extended and a higher knee flexion moment was observed compared to the acceleration sprint, and the ST muscle showed higher activation than that of the BFlh. These results indicate that the functional demands of the medial and lateral hamstring muscles differ between two different sprint performances.

Computational stability of human knee joint at early stance in Gait: Effects of muscle coactivity and anterior cruciate ligament deficiency.

As one of the most complex and vulnerable structures of body, the human knee joint should maintain dynamic equilibrium and stability in occupational and recreational activities. The evaluation of its stability and factors affecting it is vital in performance evaluation/enhancement, injury prevention and treatment managements. Knee stability often manifests itself by pain, hypermobility and giving-way sensations and is usually assessed by the passive joint laxity tests. Mechanical stability of both the human knee joint and the lower extremity at early stance periods of gait (0% and 5%) were quantified here for the first time using a hybrid musculoskeletal model of the lower extremity. The roles of muscle coactivity, simulated by setting minimum muscle activation at 0-10% levels and ACL deficiency, simulated by reducing ACL resistance by up to 85%, on the stability margin as well as joint biomechanics (contact/muscle/ligament forces) were investigated. Dynamic stability was analyzed using both linear buckling and perturbation approaches at the final deformed configurations in gait. The knee joint was much more stable at 0% stance than at 5% due to smaller ground reaction and contact forces. Muscle coactivity, when at lower intensities (<3% of its maximum active force), increased dynamic stability margin. Greater minimum activation levels, however, acted asan ineffective strategy to enhance stability. Coactivation also substantially increased muscle forces, joint loads and ACL force and hence the risk of further injury and degeneration. A deficiency in ACL decreases total ACL force (by 31% at 85% reduced stiffness) and the stability margin of the knee joint at the heel strike. It also markedly diminishes forces in lateral hamstrings (by up to 39%) and contact forces on the lateral plateau (by up to 17%). Current work emphasizes the need for quantification of the lower extremity stability margin in gait.

Prediction of muscle strength and postoperative function after knee flexor muscle resection for soft tissue sarcoma of the lower limbs

IntroductionOncological margins and prognosis are the most important factors for operative planning of soft tissue sarcomas, but prediction of postoperative function is also necessary. The purpose of this study was to predict the knee flexion strength and postoperative function after knee flexor muscle resection for soft tissue sarcoma of the lower limbs. Materials and methodsSeventeen patients underwent knee flexor muscle resection for soft tissue sarcoma of the lower limbs between 1991 and 2015. The type of resected muscles was surveyed, knee flexion strength (ratio of affected to unaffected side) was evaluated using the Biodex System isokinetic dynamometer, and differences between the type of resected muscles were examined. The Musculoskeletal Tumor Society (MSTS) score, Toronto Extremity Salvage Score (TESS), European Quality of Life-5 Dimensions (EQ-5D), and Short Form 8 (SF-8) were used to assess postoperative function and examine correlations with flexion strength. The cutoff value for flexion strength to predict good postoperative results was calculated by a receiver operating characteristic (ROC) curve and Fisher's exact test. ResultsMedian flexion strength decreased in the resection of sartorius (97.8%), gracilis (95.4%), gastrocnemius (85.2%; interquartile range (IQR): 85.0–86.2), medial hamstrings (semimembranosus and semitendinosus, 76.2%; IQR: 73.3–78.0), lateral hamstrings (long and short head of biceps femoris, 66.1%; IQR: 65.9–70.4), and bilateral hamstrings (27.3%; IQR: 26.6–31.5). A significant difference was observed between lateral and bilateral hamstrings resection (P=0.049). Flexion strength was associated with lower functional scales (MSTS score, P=0.021; TESS, P=0.008; EQ-5D, P=0.034). Satisfactory function was obtained at a flexion strength cutoff value of 65.7%, and strength remained above the cutoff value up to unilateral hamstrings resection. DiscussionGreater knee flexor muscles resection can result in functional deficits that are associated with decreased flexion strength. If continuity of unilateral hamstrings is maintained, good postoperative results can be expected. Level of evidenceIV, retrospective study.

Peak medial (but not lateral) hamstring activity is significantly lower during stance phase of running. An EMG investigation using a reduced gravity treadmill

The hamstrings are seen to work during late swing phase (presumably to decelerate the extending shank) then during stance phase (presumably stabilizing the knee and contributing to horizontal force production during propulsion) of running. A better understanding of this hamstring activation during running may contribute to injury prevention and performance enhancement (targeting the specific role via specific contraction mode). Twenty active adult males underwent surface EMG recordings of their medial and lateral hamstrings while running on a reduced gravity treadmill. Participants underwent 36 different conditions for combinations of 50%–100% altering bodyweight (10% increments) & 6–16km/h (2km/h increments, i.e.: 36 conditions) for a minimum of 6 strides of each leg (maximum 32). EMG was normalized to the peak value seen for each individual during any stride in any trial to describe relative activation levels during gait. Increasing running speed effected greater increases in EMG for all muscles than did altering bodyweight. Peak EMG for the lateral hamstrings during running trials was similar for both swing and stance phase whereas the medial hamstrings showed an approximate 20% reduction during stance compared to swing phase. It is suggested that the lateral hamstrings work equally hard during swing and stance phase however the medial hamstrings are loaded slightly less every stance phase. Likely this helps explain the higher incidence of lateral hamstring injury. Hamstring injury prevention and rehabilitation programs incorporating running should consider running speed as more potent stimulus for increasing hamstring muscle activation than impact loading.

Restriction in lateral bending range of motion, lumbar lordosis, and hamstring flexibility predicts the development of low back pain: a systematic review of prospective cohort studies

BackgroundLow back pain (LBP) is an increasingly common condition worldwide with significant costs associated with its management. Identification of musculoskeletal risk factors that can be treated clinically before the development of LBP could reduce costs and improve the quality of life of individuals. Therefore the aim was to systematically review prospective cohort studies investigating lower back and / or lower limb musculoskeletal risk factors in the development of LBP.MethodsMEDLINE, EMBASE, AMED, CINAHL, SPORTDiscus, and the Cochrane Library were searched from inception to February 2016. No age, gender or occupational restrictions of participants were applied. Articles had to be published in English and have a 12 month follow-up period. Musculoskeletal risk factors were defined as any osseous, ligamentous, or muscular structure that was quantifiably measured at baseline. Studies were excluded if participants were pregnant, diagnosed with cancer, or had previous low back surgery. Two authors independently reviewed and selected relevant articles. Methodological quality was evaluated independently by two reviewers using a generic tool for observational studies.ResultsTwelve articles which evaluated musculoskeletal risk factors for the development of low back pain in 5459 participants were included. Individual meta-analyses were conducted based on risk factors common between studies. Meta-analysis revealed that reduced lateral flexion range of motion (OR = 0.41, 95% CI 0.24-0.73, p = 0.002), limited lumbar lordosis (OR = 0.73, 95% CI 0.55-0.98, p = 0.034), and restricted hamstring range of motion (OR = 0.96, 95% CI 0.94-0.98, p = 0.001) were significantly associated with the development of low back pain. Meta-analyses on lumbar extension range of motion, quadriceps flexibility, fingertip to floor distance, lumbar flexion range of motion, back muscle strength, back muscle endurance, abdominal strength, erector spinae cross sectional area, and quadratus lumborum cross sectional area showed non-significant results.ConclusionIn summary, we found that a restriction in lateral flexion and hamstring range of motion as well as limited lumbar lordosis were associated with an increased risk of developing LBP. Future research should aim to measure additional lower limb musculoskeletal risk factors, have follow up periods of 6-12 months, adopt a standardised definition of LBP, and only include participants who have no history of LBP.

Increasing Body Weight Alters Lower Limb Muscle Balance And Foot Control

Obesity is a well established risk factor for developing osteoarthritis (OA). Population-based studies in particular have consistently shown a link between obesity and knee OA. Yet many factors for diseases and conditions associated with obesity could contribute to OA initiation and/or progression. The present study examined the effects systematically increasing subject weight and the effects on quadriceps femoris muscle function and foot balance stability during walking and squatting. METHODS: Twenty asymptomatic healthy young adults (Age = 22 ± 2; 19 kg/m(2) < BMI < 22 kg/m(2)) were studied. A three-dimensional gait analysis was conducted for all subjects. Plantar pressure distribution (the peak pressure of the eight plantar surface areas) and foot kinematics, surface electromyograms from the lateral and medial gastrocnemii, lateral and medial hamstrings, vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) were recorded during squatting and self-selected speed walking. Weight increase (10, 20 and 30% of subject body weight) was achieved by placing a belly bag on the subject’s body attached around the hip and to the shoulders. Principal component analysis was used to extract major features of amplitude and temporal pattern variability from the electromyograms of each muscle group (gastrocnemii, quadriceps, hamstrings separately). Analysis of variance models tested for weight load effects and interaction effects for these features (α = 0.05). RESULTS: Significant weight load effects were found for features that described more prolonged activation of the gastrocnemii and quadriceps muscles during the stance phase of gait (P < 0.05). Load increase selectively activated the VL compared to the VM during walking and the first 20 degrees of knee flexion during the squat. Load increase was also associated with increased mid-rear-foot pressure and delay in both the onset of the second wave of flexion at the knee joint and reduced range of motion of the ankle (P < 0.05). CONCLUSIONS: We confirm the effects of increasing body weight on lower extremity muscle activation and foot balance control, both of which may contribute to knee OA development and progression.