An in vivo preparation for investigating neural responses to controlled loading of a lumbar vertebra in the anesthetized cat.

This paper describes a method for applying controlled loads to a lumbar vertebra while recording in vivo from primary afferents innervating the lumbar paraspinal tissues. Unlike the appendicular skeleton, the vertebral column poses a unique challenge for neurophysiological investigations. Distances between paraspinal tissues and the spinal cord are short. In addition, substantial removal of the paraspinal tissues to access the spinal roots or spinal cord appears necessary. The preparation described in this report takes advantage of the anatomical fact that the L6 dorsal root enters the spinal cord 2-2.5 vertebral segments rostral to its passage through the intervertebral foramina. This effectively lengthens the distance between the lumbar paraspinal tissues and central recording sites. The preparation has five unique features: (1) the L6 and L7 vertebrae remain intact; (2) lumbar paraspinal tissues and their attachments to the L6 and L7 vertebrae remain intact on one side of the vertebral column; (3) the intact L6 vertebra can be loaded at its spinous process; (4) the magnitude of the load applied at the L6 spinous process can be controlled with a feedback motor; (5) the direction of load relative to the long axis of the spine can be controlled. Using this preparation, single unit recordings were obtained from the L6 dorsal root during controlled loading of the L6 lumbar vertebra at its spinous process. The responses of two paraspinal muscle proprioceptors to vertebral loading are characterized in this report. With existing electrophysiological techniques this preparation can be used to study central processing of paraspinal inputs. By combining mechanical loading of the lumbar spine in the presence of inflammatory mediators this preparation can contribute to the understanding of the mechanisms by which interactions between mechanical and chemical stimuli likely produce low back pain.     

Neuromuscular dysfunction elicited by cyclic lumbar flexion

An attempt was made to develop an in vivo model that could explain the neurophysiological and biomechanical processes active in the development of the idiopathic low back disorder common in workers who perform repetitive lifting tasks in industry. Passive cyclic flexion of the feline lumbar spine at 0.1 HZ for 20 min resulted in creep of the supraspinous ligament and other lumbar viscoelastic tissues as well as spasms superimposed on a decreasing electromyogram (EMG) elicited reflexly from the multifidus muscles. Rest for 7 h did not allow full recovery of the viscoelastic creep; the multifidus EMG gradually increased with initial and delayed hyperexcitability. Increasing the peak load of the cyclic flexion resulted in larger creep in the passive tissues and required a longer time for recovery of reflex EMG activity and longer delayed hyperexcitability, but development of spasms and hyperexcitability was unaffected. It is conceivable that damage to the viscoelastic tissues elicits an inflammatory process that in turn triggers a transient neuromuscular disorder. The present findings provide a biomechanical and neurophysiological explanation for a common idiopathic low back disorder as well as for the development of a cumulative trauma disorder often seen in workers engaged in repetitive lumbar flexion.     

Severe forward flexion of the trunk in Parkinson's disease: focal myopathy of the paraspinal muscles mimicking camptocormia.

Pronounced forward flexion of the trunk, often termed camptocormia, is a typical symptom of patients with Parkinson's disease. In 4 parkinsonian patients with camptocormia, paraspinal muscles were studied by electromyography (EMG) and axial computerized tomography (CT) or magnetic resonance imaging (MRI) scans and muscle biopsy. EMG of the lumbar and thoracic paravertebral muscles showed abundant fibrillations, positive sharp waves, and bizarre high-frequency discharges. Spinal CT and MRI scans revealed variable degrees of atrophy and fatty replacement of the thoracolumbar paraspinal muscles on both sides. No other signs of neuromuscular disease were found. Biopsy of the paraspinal muscles revealed end-stage myopathy with autophagic vacuoles, chronic inflammatory myopathy, unspecific myopathic changes, or mitochondrial myopathy. In parkinsonian patients with pronounced forward flexion of the trunk, myopathy confined to the erector spinae muscles must be considered.     

Mitochondrial DNA deletions and depletion within paraspinal muscles

G. R. Campbell, A. Reeve, I. Ziabreva, T. M. Polvikoski, R. W. Taylor, R. Reynolds, D. M. Turnbull and D. J. Mahad (2013) Neuropathology and Applied Neurobiology 39, 377–389 Mitochondrial DNA deletions and depletion within paraspinal muscles Aims: Although mitochondrial abnormalities have been reported within paraspinal muscles in patients with axial weakness and neuromuscular disease as well as with ageing, the basis of respiratory deficiency in paraspinal muscles is not known. This study aimed to determine the extent and basis of respiratory deficiency in paraspinal muscles from cases undergoing surgery for degenerative spinal disease and post mortem cases without a history of spinal disease, where age‐related histopathological changes were previously reported. Methods: Cervical and lumbar paraspinal muscles were obtained peri‐operatively from 13 patients and from six post mortem control cases (age range 18–82 years) without a neurological disease. Sequential COX/SDH (mitochondrial respiratory chain complex IV/complex II) histochemistry was performed to identify respiratory‐deficient muscle fibres (lacking complex IV with intact complex II activity). Real‐time polymerase chain reaction, long‐range polymerase chain reaction and sequencing were used to identify and characterize mitochondrial DNA (mtDNA) deletions and determine mtDNA copy number status. Mitochondrial respiratory chain complex subunits were detected by immunohistochemistry. Results: The density of respiratory‐deficient fibres increased with age. On average, 3.96% of fibres in paraspinal muscles were respiratory‐deficient (range 0–10.26). Respiratory deficiency in 36.8% of paraspinal muscle fibres was due to clonally expanded mtDNA deletions. MtDNA depletion accounted for further 13.5% of respiratory deficiency. The profile of immunohistochemically detected subunits of complexes was similar in respiratory‐deficient fibres with and without mtDNA deletions or mtDNA depletion. Conclusions: Paraspinal muscles appeared to be particularly susceptible to age‐related mitochondrial respiratory chain defects. Clonally expanded mtDNA deletions and focal mtDNA depletion may contribute towards the development of age‐related postural abnormalities.     

Trunk muscle activation pattern in parkinsonian camptocormia as revealed with surface electromyography

IntroductionCamptocormia is frequently seen in Parkinson's disease (PD) and multiple system atrophy. It is characterized by a pathological forward bending of the trunk during standing, often combined with a lateral trunk deviation. The etiology of camptocormia in PD is still unknown. Muscle MRI studies show abnormalities mainly of the erector spinae confirmed by muscle biopsies. Quantitative electromyographic examination of trunk muscle activity is missing.MethodsVentral (rectus and obliquus externus abdominis) and dorsal (iliocostalis lumborum, longissimus, multifidus) trunk muscles and the rectus femoris were recorded bilaterally with surface electromyography in standing PD patients with camptocormia (n = 10) and matched healthy controls (n = 10) who mimicked the patients' posture. EMG amplitudes were compared quantitatively. In controls, the relation between varying degrees of trunk flexion and EMG was established systematically.ResultsIncreasing forward trunk flexion was associated with increasing back muscle activity in controls, while abdominal muscle activity was negligible. During anterolateral trunk flexion, back muscle activity increased particularly on the contralateral side. The patients showed a similar pattern. However, normalized EMG activity of their trunk extensors was significantly higher than in controls, often reaching half-maximal amplitudes. Their rectus femoris and oblique abdominal muscles were overactive, but to a lesser extent.ConclusionsPD patients with camptocormia must use the functional reserve of their lumbar trunk muscles to counteract gravity. We interpret this as a weakness of the paravertebral muscles. Compared to the other examined muscles the paravertebral muscles are most affected. The increased EMG activity of the rectus femoris warrants further research.     

慢性下腰痛患者腰部肌肉放电的均衡性

目的：观察慢性下腰痛患者腰部肌肉放电的均衡性。 方法：实验于2007-05在沈阳体育学院重点实验室完成。以14名健康受试者和14名慢性下腰痛患者为观察对象,让其在静力性收缩的条件下观察腰部肌肉放电的情况。使用表面肌电技术测量受试者腰部3个节段(L1,L2,L5)两侧最长肌、髂腰肋肌、多裂肌的放电情况,令受试者躯干分别在40%最大随意收缩和80%最大随意收缩的情况做等长收缩30 s,观察受试者腰部脊柱两侧肌肉的疲劳时的失衡情况。 结果：慢性下腰痛患者腰部肌肉的最大随意收缩仅仅是对照组最大随意收缩的55%,与对照组相比慢性下腰痛患者腰部肌肉疲劳程度较低, 可能与他们并没有产生真正的最大随意收缩有关;慢性下腰痛患者腰部两侧肌肉失衡程度较大。 结论：下腰痛患者出现疼痛时,其腰部两侧的肌肉活动重新分布;同时表面肌电可能成为一种无创伤地检测肌肉失衡的有效工具。     

Electromyographic activity of voluntarily activated trunk flexor and extensor muscles in post-stroke hemiparetic subjects.

OBJECTIVE: To study the EMG activity of selected trunk muscles during self-initiated voluntary flexion and extension of the trunk in post-stroke hemiparetic subjects, and to compare measurement results to corresponding findings in control subjects. METHODS: Using a sample of 50 patients and 30 control subjects, bilateral EMG activity of the rectus abdominis (RA) and external oblique (EO) muscles was studied during direct trunk flexion, and activity of the lumbar erector spinae (ES) and latissimus dorsi (LD) was studied during straight trunk extension. Variables of timing, magnitude, and temporal synchronization between muscle activity on the paretic and non-paretic sides of the body in the patient group were compared with the same measurements taken from the left and right sides of the body in the control group. RESULTS: Activity of the RA and LD muscles on the affected side of the body was reduced and delayed relative to the unaffected side in the patients and relative to the control subjects. Some deterioration was also observed in the function of the EO muscle, whereas the lumbar ES displayed normal activity on both sides of the body. Trunk velocity during both flexion and extension was slower in the patients than in the controls. CONCLUSIONS: Despite the existence of ipsilateral as well as contralateral higher inputs to axial and to a lesser extent also to more lateral trunk muscles, the function of the superficial abdominal muscles and of the LD muscle is adversely affected by a contralateral stroke. Conversely, the lumbar ES, which can be categorized as local trunk extensors, seem to normally fulfill their anti-gravitational task on both sides of the body.     

Prophylactic stretching does not reduce cramp susceptibility

Introduction: Some clinicians advocate stretching to prevent muscle cramps. It is unknown whether static or proprioceptive neuromuscular facilitation (PNF) stretching increases cramp threshold frequency (TF_c), a quantitative measure of cramp susceptibility. Methods: Fifteen individuals completed this randomized, counterbalanced, cross‐over study. We measured passive hallux range of motion (ROM) and then performed 3 minutes of either static stretching, PNF stretching (hold–relax—with agonist contraction), or no stretching. ROM was reassessed and TF_c was measured. Results: PNF stretching increased hallux extension (pre‐PNF 81 ± 11°, post‐PNF 90 ± 10°; P < 0.05) but not hallux flexion (pre‐PNF 40 ± 7°, post‐PNF 40 ± 7°; P > 0.05). Static stretching increased hallux extension (pre‐static 80 ± 11°, post‐static 88 ± 9°; P < 0.05) but not hallux flexion (pre‐static 38 ± 9°, post‐static 39 ± 8°; P > 0.05). No ROM changes occurred with no stretching (P > 0.05). TF_c was unaffected by stretching (no stretching 18 ± 7 Hz , PNF 16 ± 4 Hz , static 16 ± 5 Hz ; P = 0.37). Discussion: Static and PNF stretching increased hallux extension, but neither increased TF_c. Acute stretching may not prevent muscle cramping. Muscle Nerve 57 : 473–477, 2018     

High-repetition cyclic loading is a risk factor for a lumbar disorder

Epidemiological data suggest that prolonged exposure to cyclic lumbar flexion elicits a chronic neuromuscular disorder and disability in workers. This study provides a physiological and biomechanical assessment of various repetitions of cyclic lumbar flexion sessions as a risk factor for development of an acute neuromuscular disorder. An in vivo feline model was subjected to 10 minutes of cyclic (0.25-HZ) loading, followed by a 10-minute rest period, repeated three times in one experimental group, six times in a second group, and nine times in the third group, followed by rest for 7 hours. Displacement of the lumbar viscoelastic tissue and reflex electromyographic (EMG) activity from the lumbar multifidus muscle were monitored. Creep developed and accumulated during each load/rest period and partially recovered during the subsequent rest. Loading periods were characterized by a decrease in reflex EMG activity with superimposed spasms. In the 7-hour recovery period, initial hyperexcitability was present in all groups, whereas only the six- and nine-repetition groups displayed significant delayed hyperexcitability, indicating the presence of acute inflammation. The mathematical model developed fit the data reasonably well, as the R2 values were generally near 0.90. It was concluded that the resulting delayed muscular hyperexcitability constitutes an acute neuromuscular disorder associated with exposure to many repetitions of cyclic lumbar flexion. The acute disorder can become chronic if not allowed sufficient rest to resolve itself. Workers engaged in cyclic lumbar flexion (e.g., loading/unloading, assembly workers) should avoid long-term exposure in order to prevent the development of a chronic neuromuscular condition known as cumulative trauma disorder.     

Response of the dropped head/bent spine syndrome to treatment with intravenous immunoglobulin

Weakness of neck extension causing a dropped head may result from many neuromuscular disorders. One etiology is isolated neck extensor myopathy. A similar focal myopathy of the lower axial muscles may cause the bent spine syndrome, which manifests as flexion of the trunk and inability to stand upright. Combination of both dropped head and bent spine myopathies is uncommon. Inflammation is usually not pronounced in these conditions and response to immunosuppressive treatment is rare. We present an 81-year-old man who developed progressive weakness of neck and trunk extension over several months, with a prominent inflammatory process in the thoracic paraspinal muscles, which responded dramatically to treatment with intravenous immunoglobulin (IVIg). This case, together with other rare reports, suggests that the presence of inflammation in the biopsy of an affected muscle may predict treatment response.     

Neuromuscular control of lumbar instability following static work of various loads

Neuromuscular control of lumbar stability following exposure to prolonged static work, under low and high loads, was assessed in the in vivo feline model. Six sessions of 10 min work at 20N with 10 min between rest was compared to a group subjected to the same protocol but carrying high loads of 60N. Displacement and tension developed in the spine at the instant the multifidus muscles applied stabilizing contractions, and their amplitudes were obtained from their electromyogram (EMG). Significant (P < 0.001) laxity developed in the various viscoelastic tissues of the lumbar spine that did not recover during and up to 7 h of rest postwork. Simultaneously, there was a significant (P < 0.001) decrease in muscular activity in the 3–4 h immediately postwork under low load but only during the first hour in the high load group. After that period the musculature compensated for the laxity of the viscoelastic tissues by a significant (P < 0.001) increase in activity in the high‐load group and a nonsignificant increase in the low group. It was concluded that during 1–3 h immediately poststatic work a significant decrease in the stabilizing function of viscoelastic tissues together with a significant decrease in muscular activity is present, and they render the spine unstable and exposed to high risk of injury. Performance of prolonged static work under low loads, while not harmful during the work, cannot be designated as a “no‐risk” condition, as it may result in injury postwork. Muscle Nerve 39: 71–82, 2009     

Trunk muscle strength,but not trunk rigidity,is independently associated with bone mineral density of the lumbar spine in patients with Parkinson's disease

Previous literature suggested that muscle forces applied to the skeleton may be an important factor in increasing bone mineral density (BMD). This purpose of this study was to determine whether trunk rigidity and trunk muscle strength were associated with lumbar spine BMD in patients with Parkinson's disease (PD). Forty‐three PD patients and 29 controls participated in this study. Dual‐energy X‐ray absorptiometry was used to measure lumbar spine BMD of PD patients. Additionally, an isokinetic dynamometer was used to evaluate trunk rigidity and trunk muscle strength of all subjects. The results showed that PD patients had significantly lower trunk muscle strength, but more trunk rigidity than controls by 46.6 and 162.8%, respectively (P < 0.001). In bivariate correlation analysis, lumbar spine BMD was significantly related to trunk muscle strength (r = 0.475, P = 0.001), but not trunk rigidity (r = 0.271, P = 0.079). In multiple regression analysis, after adjusting for relevant factors, only trunk muscle strength remained independently associated with lumbar spine BMD, accounting for 10.0% of the variance (R² = 0.342, F_5,37 = 3.838, P = 0.007). Trunk muscle strength, but not trunk rigidity, is independently associated with lumbar spine BMD in patients with PD. Further randomized controlled studies are required to determine whether trunk muscle strengthening exercise is effective in enhancing lumbar spine BMD. © 2009 Movement Disorder Society     

The risk of hematoma following extensive electromyography of the lumbar paraspinal muscles

Introduction: The purpose of this study is to provide a controlled trial looking at the risk of paraspinal hematoma formation following extensive paraspinal muscle electromyography. Methods: 54 subjects ages 55–80 underwent MRI of the lumbar spine before or shortly after electromyography using the paraspinal mapping technique. A neuroradiologist, blinded to the temporal relationship between the EMG and MRI, reviewed the MRIs to look for hematomas in or around the paraspinal muscles. Results: Two MRIs demonstrated definite paraspinal hematomas, while 10 were found to have possible hematomas. All hematomas were < 15 mm, and none were close to any neural structures. There was no relationship between MRI evidence of hematoma and either the timing of the EMG or the use of aspirin or other nonsteroidal anti‐inflammatory drugs. Conclusions: Paraspinal electromyography can be considered safe in the general population and those taking nonsteroidal anti‐inflammatory drugs. Muscle Nerve 46:26–30, 2012     

Static load magnitude is a risk factor in the development of cumulative low back disorder

Occupations requiring frequent periods of static lumbar flexion are known epidemiologically to be risk factors for the development of cumulative low back disorder. The impact of the load magnitude sustained during a series of short static lumbar flexions followed by an equally long rest period on the development of a cumulative low back disorder was addressed in an in vivo feline model. Static loads of 20, 40, and 60 N were applied over 10 min of flexion followed by 10-min rest sessions that were repeated six times (for a total of 2 h) while monitoring lumbar viscoelastic creep (laxity) and reflex electromyographic (EMG) activity from the multifidus muscles. Creep and EMG were also monitored over 7 h of rest following the six flexion-rest sessions. It was found that the creep developed in the 10-min flexion periods did not recover completely during the following 10 min of rest, giving rise to a large cumulative creep at the end of the work-rest session. Muscle activity demonstrated spasms during the static flexion periods as well as initial and delayed hyperexcitability during the 7-h rest period. Loads of 20 and 40 N did not result in delayed hyperexcitability, whereas loads of 60 N resulted in delayed hyperexcitability. Statistical analysis demonstrated that increased load significantly intensified the magnitude of the hyperexcitabilities (P < 0.05). Thus, repeated periods of static lumbar flexion were found to result in a transient neuromuscular disorder with an intensity directly related to the load magnitude, which should be considered a compounding risk factor.     

Insufficiency of trunk extension and impaired control of muscle force in Parkinson’s disease with camptocormia

ObjectiveTo examine the aetiology of parkinsonian camptocormia, a non-fixed pathological forward bending of the trunk, by measuring trunk muscle activation and force regulation in Parkinson patients with (PD + CC) and without (PD) camptocormia matched for disease severity, and in age- and sex-matched healthy controls (HC).MethodsThe isometric forces of trunk extension and flexion were measured in PD + CC, PD and HC. Neuromuscular efficiency (increase of extension force per increase of paravertebral muscle surface electromyography signal) and the ability to maintain a constant submaximal trunk extension force were examined.ResultsPeak trunk extension force was significantly lower in PD + CC and PD than in HC, with PD + CC non-significantly weaker than PD. Compared with HC and with PD, the neuromuscular efficiency of trunk extension was significantly reduced in PD + CC. The variability of the force output (coefficient of variation) was significantly larger for PD + CC than for HC or PD.ConclusionThe reduced neuromuscular efficiency of trunk extension separates PD + CC from PD. Moreover, control of the trunk extensor force is impaired in PD + CC.SignificanceThere is weakness and a force control deficit in parkinsonian camptocormia suggesting a disturbed sensory-motor integration, which may contribute to myopathic changes in the trunk extensor muscles.     

Isolated gluteal and paravertebral muscle weakness due to anti‐3‐hydroxy‐3‐methylglutaryl‐coenzyme a reductase antibody–associated necrotizing autoimmune myopathy

Introduction: A 56‐year‐old man with a distant history of statin use presented with progressive isolated very proximal lower limb and truncal weakness. Electromyogram (EMG) showed isolated gluteal and lumbar paraspinal muscle involvement. Methods: Gluteus medius muscle biopsy was performed under general anesthesia. Results: The biopsy showed a pauci‐inflammatory necrotizing myopathy. Serum antibodies to 3‐hydroxy‐3‐methylglutaryl‐coenzyme A reductase (HMGCR) were positive. He has since partially responded to corticosteroids and methotrexate. Conclusions: Anti‐HMGCR–associated necrotizing autoimmune myopathy (NAM) can present in a restricted form after cessation of a statin. Biopsy of a symptomatic but uncommonly studied muscle is worthwhile. Muscle Nerve 54 : 150–152, 2016     

Test–retest reliability of wide‐pulse high‐frequency neuromuscular electrical stimulation evoked force

Introduction: We compare forces evoked by wide‐pulse high‐frequency (WPHF) neuromuscular electrical stimulation (NMES) delivered to a nerve trunk versus muscle belly and assess their test–retest intraindividual and interindividual reliability. Methods: Forces evoked during 2 sessions with WPHF NMES delivered over the tibial nerve trunk and 2 sessions over the triceps surae muscle belly were compared. Ten individuals participated in 4 sessions involving ten 20‐s WPHF NMES contractions interspaced by 40‐s recovery. Mean evoked force and force time integral of each contraction were quantified. Results: For both nerve trunk and muscle belly stimulation, intraindividual test–retest reliability was good (intraclass correlation coefficient > 0.9), and interindividual variability was large (coefficient of variation between 140% and 180%). Nerve trunk and muscle belly stimulation resulted in similar evoked forces. Discussion: WPHF NMES locations might be chosen by individual preference because intraindividual reliability was relatively good for both locations. Muscle Nerve 57 : E70–E77, 2018.     

Strength and fatigue of lumbar extensor muscles in older adults

Introduction: Loss of lumbar extensor muscle strength and fatigue resistance may contribute to functional disability. Methods: Two groups of subjects were recruited: young (n = 26, 20–35 years of age) and old (n = 26, ≥65 years of age) adults. Lumbar extensor muscle strength was measured with a load cell, and electromyographic activities were recorded to study muscle fatigue at 60% of maximum voluntary contraction. Results: We found that the muscle moments generated by the extensor muscles decreased with age (P < 0.05). Aging was associated with a significant increase in the power of the lower frequency band (101–200 Hz) of the electromyographic signals (P < 0.05), but the spectral characteristics did not appear to change with sustained contraction (P > 0.05). Conclusions: The changes in strength and spectral properties of the electromyographic signals of lumbar extensor muscles may be related to age‐related alterations in muscle fiber composition and recruitment. These changes should be considered in clinical functional task evaluation. Muscle Nerve 44: 74–79, 2011     

Camptocormia as presenting manifestation of a spectrum of myopathic disorders

Introduction: Camptocormia is the involuntary flexion of the thoracolumbar spine leading to an abnormal posture. Methods: We retrospectively identified patients with myopathy who manifested with camptocormia and were seen in our neuromuscular clinic. The diagnosis of myopathy was based on myopathic electromyographic changes, often accompanied by 1 or more of the following: elevated creatine kinase (CK); myopathic histopathological findings; and genetic confirmation. Results: Fifty‐two patients were identified; 35 had symptoms limited to camptocormia, but were found to have additional weakness of facial (8 patients), neck (11 patients), and limb muscles (17 patients). CK values were normal or mildly to moderately elevated. MRI/CT of the spine showed paraspinal muscle atrophy and fat replacement. Facioscapulohumeral muscular dystrophy and sporadic inclusion body myositis were the most commonly identified myopathies in this cohort. Conclusions: Despite the difficulty in characterizing the myopathy in patients with camptocormia, a definitive diagnosis was possible in 54% of cases. The pattern of associated extra‐axial weakness may provide clues to the diagnosis. Muscle Nerve 52 : 1008–1012, 2015     

Later stages of diabetic neuropathy affect the complexity of the neuromuscular system at the knee during low‐level isometric contractions

Introduction: This study evaluates the complexity of force and surface electromyography (sEMG) during knee extension and flexion at low‐level isometric contractions in individuals with different degrees of diabetic peripheral neuropathy (DPN). Methods: Ten control and 38 diabetic participants performed isometric contractions at 10%, 20%, and 30% of maximal voluntary contraction. Knee force and multichannel sEMG from vastus lateralis (VL) and biceps femoris were acquired. The SD of force and sample entropy (SaEn) of both force and sEMG were computed. Results: Participants with moderate DPN demonstrated high force‐SD and low force‐SaEn. Severely affected participants showed low SaEn in VL at all force levels. Discussion: DPN affects the complexity of the neuromuscular system at the knee for the extension task during low‐level isometric contractions, with participants in the later stages of the disease (moderate and severe) demonstrating most of the changes. Muscle Nerve 57 : 112–121, 2018