A systematic review opens the black box of "usual care" in stroke rehabilitation control groups and finds a black hole.

INTRODUCTION: In experimental trials, new methods are tested against the "best" or "usual" care. To appraise control group (CG) interventions provided as "usual care," we focused on stroke as a leading cause of disability demanding rehabilitation as a complex intervention. EVIDENCE ACQUISITION: For this methodological appraisal, we conducted a systematic review of RCTs without timespan limitation. The PICO included stroke survivors, rehabilitation, control group intervention, lower limb function. To assess the risk of bias, we used the Cochrane risk of bias tool (RoB). We identified the terminology describing the CG Program (CGP), performed a knowledge synthesis and conducted a frequency analysis of provided interventions. EVIDENCE SYNTHESIS: We included 155 publications. 13.6% of the articles did not describe the CG, and 11.6% indicated only the professionals involved. In the remaining 116 studies, three studies provided an intervention according to specific guidelines, 106 different "usual care" CGPs were detected, with nine proposed twice and two between four and five times. The most adopted terminology to state "usual care" was "conventional physiotherapy." CONCLUSIONS: This study shows that usual care in CG does not actually exist, as both specific terminology and consistency within CGP contents are missing. Reporting guidelines should give better assistance on this issue. These results should be verified in other fields.

Management of whiplash-associated disorder in the Italian emergency department: the feasibility of an evidence-based continuous professional development course provided by physiotherapists.

PURPOSE: The management of whiplash and associated disorders (WAD) in the Italian Health System is still empirical and influenced by a single professional's expertise. Therefore, the purpose of our study is to describe a structured management changes in an Italian emergency department (ED) after an evidence based continuous professional development (CPD) course. METHODS: A CPD course was organized by Orthopedic Manipulative Physical Therapists (OMPT) for personnel of ED in the hospital Girolamo Fracastoro (San Bonifacio, Verona, Italy), based on latest scientific evidence. Data regarding the number of X-Rays, computed tomography (CT) scan, orthopaedic referrals, neck collars and WAD IV (i.e., severe diagnosis) before and after the course were compared. RESULTS: 3066 cases of WAD have been analyzed in 2016 and 2185 in 2017/2018. The number of X-Rays dropped down from 15.1% to 13.5%; the CT scans increased from 1.3% to 1.9%; the WAD IV diagnosis increased from 0.7% to 1.6%; the orthopaedic referrals dropped from 1.5% to 1.1%; the collars prescription dropped from 8.8% to 2.5%. CONCLUSION: An updated framework increased the efficiency of ED's maintaining the same level of safety (i.e., WAD IV diagnosis). Given that, it can also be argued that, in line with other countries, the implementation of an OMPT role within the ED multidisciplinary team is advised also in Italy.Implications for rehabilitationPhysiotherapists were commissioned to organize a management change of patients in an Italian Emergency Department clinical setting for the management of whiplash;Guidelines and other appropriate clinical rules facilitate the delivery of an evidence-based and more appropriate management and care plan;An inter-disciplinary continuous professional development course has the potential to positively influence patients' journey and to optimize the use of departmental resources;The involvement of other health professionals (e.g., Physiotherapists) within the Italian Emergency Department organizational chart might lead to further improvement of service provided.

Functional and Structural Neuroplastic Changes Related to Sensitization Proxies in Patients with Osteoarthritis: A Systematic Review.

OBJECTIVE: Several reports in literature have identified sensitization as a possible basis for the enhanced pain reactions associated with osteoarthritis (OA). The aim of this current systematic review is to summarize functional and structural brain changes associated with surrogate sensitization parameters assessed in patients with OA-related pain. DESIGN: Systematic review. SUBJECTS: Patients with OA related pain. METHODS: A literature search was conducted systematically in MEDLINE, CINAHL, EMBASE databases for human studies up to December 2019. Articles were included if they assessed brain imaging and sensitization parameters (quantitative sensory testing and questionnaires) in adults with OA-related pain. Methodological quality was assessed using the Methodological Index for Non-Randomized Studies (MINORS) score. RESULTS: Five studies reporting on 138 patients were included in this review. The MINORS scale yielded mean scores of 8.5/16 and 12.3/24, for the cohort and case-control studies respectively. Four low-quality studies suggest a greater pain matrix activation associated with clinical measures of sensitization in patients with OA, while another study underlined the presence of structural changes (reduced gray matter volume) in the cortical areas involved in the nociceptive processing possible also related to sensitization. CONCLUSIONS: This review shows conflicting evidence for structural and functional neuroplastic brain changes related to sensitization proxies in patients with OA.

Perspective-dependent activation of frontoparietal circuits during the observation of a static body effector.

The perspective from which body-related stimuli are observed plays a fundamental role in modulating cerebral activity during the processing of others' bodies and actions. Previous research has shown perspective-dependent cerebral responses during the observation of both ongoing actions and static images of an acting body with implied motion information, with an advantage for the egocentric viewpoint. The present high-density EEG study assessed event-related potentials triggered by the presentation of a forearm at rest before reach-to-grasp actions, shown from four different viewpoints. Through a spatiotemporal analysis of the scalp electric field and the localization of cortical generators, our study revealed overall different processing for the third-person perspective relative to other viewpoints, mainly due to a later activation of motor-premotor regions. Since observing a static body effector often precedes action observation, our results integrate previous evidence of perspective-dependent encoding, with cascade implications on the design of neurorehabilitative or motor learning interventions based on action observation.

A reappraisal of the strength-duration test to assess neuromuscular impairment of critically ill patients.

INTRODUCTION: Neuromuscular impairment (NMI) affects almost half of critically ill patients. The purpose was to investigate the role of neuromuscular electrical stimulation (NMES) to gain more insight into the nature of the NMI associated with ICU admission. To this aim, we analyzed the strength-duration (S-D) curves of the rectus femoris muscles of ICU patients compared to healthy volunteers. METHODS: S-D curves were recorded from 44 healthy volunteers and 29 ICU patients. Three electrophysiological parameters were used to classify the neuromuscular function, from grade 0 (normal function), to grade 3 (no evocable muscle contraction). ICU patients underwent electroneurographic peroneal nerve testing (PENT) to analyze NMI by electroneurography (ENG). RESULTS: Three patients were classified as Grade 0; nine as mild NMI (Grade 1), 13 as Grade 2, and four showed unexcitable muscles (Grade 3). Mean CMAP amplitudes were 6.1, 3.4, 2.9 and 0.81 mV from Grade 0 to Grade 3, respectively. CMAP was inversely correlated to NMI grade (-1.7 mV, R2 = 0.946, p < 0.05). CONCLUSIONS: The normative parameters of the S-D curves obtained by NMES in healthy volunteers allowed identification of NMI in ICU patients. NMES was an affordable tool to evaluate NMI in ICU patients, providing additional information to that obtained by ENG.

Short-Term Morphological Changes in Asymptomatic Perimandibular Muscles after Dry Needling Assessed with Rehabilitative Ultrasound Imaging: A Proof-of-Concept Study.

Facial anatomical structures are not easily accessible to manual palpation. The aim of our study is to objectively assess temporomandibular joint and perimandibular muscles dimensions by means of sonographic measurements before and after dry needling (DN) in asymptomatic subjects. Seventeen subjects participated in this before-after study with a within-subject control. After random allocation, one side of the face was used for the intervention and the contralateral as control. DN was performed on the temporal, masseter, and sternocleidomastoid muscles. Each subject was examined bilaterally before, immediately after, and one month after the intervention through Rehabilitative Ultrasound Imaging (RUSI) of the temporomandibular articular disc and the three target muscles. Maximum mouth opening was measured at baseline and at one month. After a single DN session, articular disc thickness significantly decreased; muscles' thicknesses (except for temporal thickness) significantly decreased immediately and at follow-up on the treated side; no significant changes resulted for the control side. The maximum mouth opening increased from 4.77 mm to 4.86 mm. RUSI may be useful to assess the dimensions and thickness of the temporomandibular disc and muscles before and after an intervention. DN influences muscle morphology, and it has a positive influence on mouth opening in the short term.

"Does isometric exercise improve leg stiffness and hop pain in subjects with Achilles tendinopathy? A feasibility study".

BACKGROUND: In Achilles tendinopathy (AT) the ability to store and recycle elastic energy during ground contact phase is often altered. A measure of this function is represented by leg stiffness (LS). Immediate responses in LS following therapeutic intervention have not been examined. OBJECTIVE: The aim of this paper was to examine the feasibility of the protocol in participants with AT. DESIGN: Single cohort feasibility study. PARTICIPANTS: Adults with persistent AT pain, symptoms on palpation and less than 80 points on the Visa-A questionnaire. INTERVENTION: heavy isometric exercise sequence in plantarflexion. OUTCOME MEASURES: Feasibility was assessed by evaluating: the willingness of participants to enroll into the study, the number of eligible participants, the recruitment rate, adherence to the intervention, the drop-out rate, the tolerability of the protocol. LS, reactive strength index, pain and rate of perceived effort were secondary outcomes. RESULTS: 22 AT were eligible for data collection and 19 entered the statistical analysis. The intervention was well tolerated, no withdrawals. Pain scores were low during both the intervention and the assessment. Immediate improvements in LS and pain were recorded. CONCLUSIONS: The isometric exercise protocol was feasible. Future research should investigate its effectiveness.

Exercise Combined with Electrotherapy Enhances Motor Function in an Adolescent with Spinal Muscular Atrophy Type III.

BACKGROUND: Electrotherapy is widely used in physical therapy to increase muscle mass, improve motor function, and assist physical activity in several neurologic conditions. However, concerning Spinal Muscular Atrophy (SMA), limited evidence exists on the role of electrotherapy as an adjunct for improving muscle strength and function. CASE REPORT: An adolescent (13 y.o.) with SMA type III underwent an 18-week strengthening program divided into two stages. During Phase I (weeks: 1-8), a home-based program for quadriceps strengthening through neuromuscular electrical stimulation (NMES) was provided. In Phase II (weeks: 9-18), at-home NMES was combined with functional electrical stimulation (FES) assisting volitional cycling for a broader, systemic conditioning. The treatment improved patient's structural and functional motor outcomes (quadriceps circumference and strength, Tinetti scale, and Hammersmith scale) as well as independence in stair climbing. CLINICAL REHABILITATION IMPACT: The purpose of this report is to raise awareness of the potential role of electrotherapy to help improving motor performance in SMA patients and, secondly, to foster further research aimed at assessing the actual contribution this intervention may have as an add-on therapy to existing care.

Perspective-dependent reactivity of sensorimotor mu rhythm in alpha and beta ranges during action observation: an EEG study.

During action observation, several visual features of observed actions can modulate the level of sensorimotor reactivity in the onlooker. Among possibly relevant parameters, one of the less investigated in humans is the visual perspective from which actions are observed. In the present EEG study, we assessed the reactivity of alpha and beta mu rhythm subcomponents to four different visual perspectives, defined by the position of the observer relative to the moving agent (identifying first-person, third-person and lateral viewpoints) and by the anatomical compatibility of observed effectors with self- or other individual's body (identifying ego- and allo-centric viewpoints, respectively). Overall, the strongest sensorimotor responsiveness emerged for first-person perspective. Furthermore, we found different patterns of perspective-dependent reactivity in rolandic alpha and beta ranges, with the former tuned to visuospatial details of observed actions and the latter tuned to action-related parameters (such as the direction of actions relative to the observer), suggesting a higher recruitment of beta motor rhythm in face-to-face interactions. The impact of these findings on the selection of most effective action stimuli for "Action Observation Treatment" neurorehabilitative protocols is discussed.

The degree of arm elevation impacts the endurance and cardiopulmonary adaptations of COPD patients performing upper-limb exercise: a cross-over study.

BACKGROUND: In Chronic Obstructive Pulmonary Disease (COPD), upper limb exercise is widely recommended. However, how the degree of shoulder flexion may influence the exercise response is unknown. AIM: We compared metabolic, ventilatory and symptomatic responses during constant-load supported and unsupported exercise performed at 80° and 120° arm elevation. DESIGN: Randomized cross-over study. SETTING: Pulmonary Pathophysiology Service in an Italian Respiratory Rehabilitative Division, in-patients were enrolled. METHODS: Twelve patients with moderate-to-severe COPD (FEV1 51%, BMI 26.7 ± 6.3 Kg/m2) performed 4 symptom-limited constant-load tests at 70% of their individual maximal workload: 2 supported and 2 unsupported, respectively at 80° and 120° of glenohumeral joint flexion, executed in a random order. RESULTS: Time to exhaustion (Tlim), evaluated by Kaplan-Maier curve, was shorter at 120° than 80° arm elevation in both supported (360 vs.. 486 seconds, p=0.031) and unsupported exercise (210 vs.. 375 seconds, p=0.005). No difference in dynamic hyperinflation was found between 80° and 120° elevation, even at the peak of exercise and at iso-ventilation. When normalized to Tlim, 120° arm elevation had a significantly higher metabolic cost, heart rate, minute ventilation and dyspnea/fatigue symptoms compared to 80° elevation, both in unsupported and supported conditions. CONCLUSIONS: A larger shoulder flexion shortens per se exercise endurance due to the increased metabolic, ventilatory and cardiac response, without worsening dynamic hyperinflation. CLINICAL REHABILITATION IMPACT: Arm position should be considered when prescribing individual exercise training and may be adjusted to modulate the workload.

Hand Passive Mobilization Performed with Robotic Assistance: Acute Effects on Upper Limb Perfusion and Spasticity in Stroke Survivors.

This single arm pre-post study aimed at evaluating the acute effects induced by a single session of robot-assisted passive hand mobilization on local perfusion and upper limb (UL) function in poststroke hemiparetic participants. Twenty-three patients with subacute or chronic stroke received 20 min passive mobilization of the paretic hand with robotic assistance. Near-infrared spectroscopy (NIRS) was used to detect changes in forearm tissue perfusion. Muscle tone of the paretic UL was assessed by the Modified Ashworth Scale (MAS). Symptoms concerning UL heaviness, joint stiffness, and pain were evaluated as secondary outcomes by self-reporting. Significant (p = 0.014) improvements were found in forearm perfusion when all fingers were mobilized simultaneously. After the intervention, MAS scores decreased globally, being the changes statistically significant for the wrist (from 1.6 ± 1.0 to 1.1 ± 1.0; p = 0.001) and fingers (from 1.2 ± 1.1 to 0.7 ± 0.9; p = 0.004). Subjects reported decreased UL heaviness and stiffness after treatment, especially for the hand, as well as diminished pain when present. This study supports novel evidence that hand robotic assistance promotes local UL circulation changes, may help in the management of spasticity, and acutely alleviates reported symptoms of heaviness, stiffness, and pain in subjects with poststroke hemiparesis. This opens new scenarios for the implications in everyday clinical practice. Clinical Trial Registration Number is NCT03243123.

Does Heel Height Cause Imbalance during Sit-to-Stand Task: Surface EMG Perspective.

The purpose of this study was to determine whether electromyography (EMG) muscle activities around the knee differ during sit-to-stand (STS) and returning task for females wearing shoes with different heel heights. Sixteen healthy young women (age = 25.2 ± 3.9 years, body mass index = 20.8 ± 2.7 kg/m2) participated in this study. Electromyography signals were recorded from the two muscles, vastus medialis (VM) and vastus lateralis (VL) that involve in the extension of knee. The participants wore shoes with five different heights, including 4, 6, 8, 10, and 12 cm. Surface electromyography (sEMG) data were acquired during STS and stand-to-sit-returning (STSR) tasks. The data was filtered using a fourth order Butterworth (band pass) filter of 20-450 Hz frequency range. For each heel height, we extracted median frequency (MDF) and root mean square (RMS) features to measure sEMG activities between VM and VL muscles. The experimental results (based on MDF and RMS-values) indicated that there is imbalance between vasti muscles for more elevated heels. The results are also quantified with statistical measures. The study findings suggest that there would be an increased likelihood of knee imbalance and fatigue with regular usage of high heel shoes (HHS) in women.

The age related slow and fast contributions to the overall changes in tibialis anterior contractile features disclosed by maximal single twitch scan.

UNLABELLED: This work aimed to verify if maximal electrically evoked single twitch (STmax) scan discloses the relative functional weight of fast and slow small bundles of fibres (SBF) in determining the contractile features of tibialis anterior (TA) with ageing. SBFs were recruited by TA main motor point stimulation through 60 increasing levels of stimulation (LS): 20 stimuli at 2Hz for each LS. The lowest and highest LS provided the least ST and STmax, respectively. The scanned STmax was decomposed into individual SBF STs. They were identified when twitches from adjacent LS were significantly different and then subtracted from each other. Nine young (Y) and eleven old (O) subjects were investigated. Contraction time (CT) and STarea/STpeak (A/PT) were calculated per each SBF ST. 143 and 155 SBF STs were obtained in Y and O, respectively. Y: CT and A/PT range: 45-105ms and 67-183mNs/mN, respectively. Literature data set TA fast fibres at 34% so, from the arrays of CT and A/PT, 65ms and 100mNs/mN were identified as the upper limit for SBF fast ST classification. O: no SBF ST could be classified as fast. CONCLUSIONS: STmax scan reveals age-related changes in the relative contribution of fast and slow SBFs to the overall muscle mechanics.

Validity and everyday clinical applicability of lumbar muscle fatigue assessment methods in patients with chronic non-specific low back pain: a systematic review.

PURPOSE: This systematic literature review aimed at examining the validity and applicability in everyday clinical rehabilitation practise of methods for the assessment of back muscle fatiguability in patients with chronic non-specific low back pain (CNSLBP). METHODS: Extensive research was performed in MEDLINE, Cumulative Index of Nursing and Allied Health Literature (CINAHL), Embase, Physiotherapy Evidence Database (PEDro) and Cochrane Central Register of Controlled Trials (CENTRAL) databases from their inception to September 2014. Potentially relevant articles were also manually looked for in the reference lists of the identified publications. Studies examining lumbar muscle fatigue in people with CNSLBP were selected. Two reviewers independently selected the articles, carried out the study quality assessment and extracted the results. A modified Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) scale was used to evaluate the scientific rigour of the selected works. RESULTS: Twenty-four studies fulfilled the selection criteria and were included in the systematic review. We found conflicting data regarding the validity of methods used to examine back muscle fatigue. The Biering-Sorensen test, performed in conjunction with surface electromyography spectral analysis, turned out to be the most widely used and comparatively, the most optimal modality currently available to assess objective back muscle fatigue in daily clinical practise, even though critical limitations are discussed. CONCLUSIONS: Future research should address the identification of an advanced method for lower back fatigue assessment in patients with CNSLBP which, eventually, might provide physical therapists with an objective and reliable test usable in everyday clinical practise. Implications for Rehabilitation Despite its limitations, the Biering-Sorensen test is currently the most used, convenient and easily available fatiguing test for lumbar muscles. To increase validity and reliability of the Biering-Sorensen test, concomitant activation of synergistic muscles should be taken into account. Pooled mean frequency and half-width of the spectrum are currently the most valid electromyographic parameters to assess fatigue in chronic non-specific low back pain. Body mass index, grading of pain and level of disability of the study population should be reported to enhance research quality.

Motor unit activation strategy during a sustained isometric contraction of finger flexor muscles in elite climbers.

The aim of the study was to evaluate, by an electromyographic (EMG) and mechanomyographic (MMG) combined approach, whether years of specific climbing activity induced neuromuscular changes towards performances related to a functional prevalence of fast resistant or fast fatigable motor units. For this purpose, after the maximum voluntary contraction (MVC) assessment, 11 elite climbers and 10 controls performed an exhaustive handgrip isometric effort at 80% MVC. Force, EMG and MMG signals were recorded from the finger flexor muscles during contraction. Time and frequency domain analysis of EMG and MMG signals was performed. In climbers: (i) MVC was higher (762 ± 34 vs 512 ± 57 N; effect size: 1.64; confidence interval: 0.65-2.63; P < 0.05); (ii) endurance time at 80% MVC was 43% longer (34.2 ± 3.7 vs 22.3 ± 1.5 s; effect size: 1.21; confidence interval: 0.28-2.14; P < 0.05); (iii) force accuracy and stability were greater during contraction (P < 0.05); (iv) EMG and MMG parameters were higher throughout the entire isometric effort (P < 0.05). Collectively, force, EMG and MMG combined analysis revealed that several years of specific climbing activity addressed the motor control system to adopt muscle activation strategies based on the functional prevalence of fast resistant motor units.

Association Between Sagittal Balance and Scoliosis in Patients with Parkinson Disease: A Cross-sectional Study.

OBJECTIVE: The aim of this study was to describe the association between scoliosis and sagittal balance parameters in Parkinson disease patients. DESIGN: This is a cross-sectional study. RESULTS: Fifty percent of the cohort presented a scoliosis larger than 11 degrees; 84% of the patients with scoliosis presented a thoracolumbar curve, 10% presented a thoracic one, and 6% presented a lumbar one. The group with scoliosis curves presented a lower spinosacral angle (111.6 [21.9] degrees vs. 121.7 [9.8] degrees, P < 0.05), whereas thoracic kyphosis, lumbar lordosis, and spinopelvic angle were similar. Pelvic incidence, pelvic tilt, and sacral slope were not statistically different. In the scoliosis group, the authors found negative correlations for lumbar lordosis/spinopelvic angle, sacral slope/spinosacral angle, and lumbar lordosis/pelvic tilt. Moreover, the sacral slope/pelvic tilt correlation was positive in patients without scoliosis and negative in others. The two groups did not present differences regarding age, years of disease, Hoehn-Yahr score, and Unified Parkinson Disease Rating Scale-motor section. CONCLUSIONS: Pelvic parameters were similar in the two groups, whereas spinosacral angle was lower in patients with scoliosis. The prevalence of scoliosis in Parkinson disease was higher than what was previously described and the thoracolumbar spine was the mostly affected.

Spinopelvic balance and body image perception in Parkinson's disease: analysis of correlation.

PURPOSE: The purpose of this study was to describe the association between body image perception and sagittal balance (SB) parameters in Parkinson's Disease (PD) patients. METHODS: 77 consecutive PD patients were included: 44 males, 33 females; 68.9 ± 6.8 years; 5.3 ± 3.8 years from diagnosis (YFD); Hoehn Yahr (HY) 2.0 ± 0.8, Unified Parkinson's Disease rating Score-Motor section (UPDRS-M) 11.8 ± 9.3. Spinopelvic angles and SB were radiographically assessed. Body image perception was assessed through Trunk appearance scale (TAPS) and Stunkard Figure rating scale for BMI. Beck Depression Inventory (BDI) was used to evaluate depressive mood. RESULTS: We detected 32 (41.5 % of cohort) Parkinson Disease patients with scoliosis ≥15° Cobb. The mean calculated BMI was 27.1 ± 3.9 kg/m(2). According to the Figure Rating Scale, the perceived BMI averaged 27.2 ± 4.5 kg/m(2), while the mean desired BMI was 24.4 ± 2.7 kg/m(2), TAPS scored 3.4 ± 0.9 points, while BDI 12.3 ± 7.9 points. TAPS had a weak negative correlation with the duration of disease (r = -0.25, p < 0.05) and a correlation with H&Y score (r = 0.28, p < 0.05). Sacral Slope was weakly correlated to the calculated BMI (r = -0.24, p < 0.05). SSA and SPA had a negative correlation with the TAPS mean score (respectively, r = -0.36 and -0.24, p < 0.05). BDI presented a weak correlation with TAPS (r = 0.27, p < 0.05) but not with self esteemed BMI values (p > 0.05). CONCLUSIONS: Spinopelvic parameters and depression had a specific and concurrent influence on trunk deformity perception but not on BMI self-esteem.

Methods for the assessment of neuromotor capacity in non-specific low back pain: Validity and applicability in everyday clinical practice.

BACKGROUND: Physiotherapists and clinicians require methods that can be used in everyday practice for measuring proprioception of the trunk in individuals with non-specific low back pain (NSLBP). OBJECTIVE: Our objective was to conduct a systematic literature review of methods used for assessment of proprioception of the trunk in individuals with non-specific low back pain. METHOD: Data were obtained from MEDLINE, CINAHL, Embase, PEDro and CENTRAL databases from their inception to December 2011. Reference lists of the selected reviews were hand searched for other potentially relevant studies. Randomized and nonrandomized controlled studies proprioception of the trunk in individuals with low back pain were selected. Thirty-six studies satisfied the selection criteria and were included in this review. RESULTS: Two reviewers independently selected the studies, conducted the quality assessment, and extracted data from each study. The Strobe scale was used to evaluate the scientific rigor of each selected study. CONCLUSIONS: This systematic review covered all the relevant literature, but none of the included studies offered a valid, reliable and feasible method to assess neuromotor capacity in everyday physiotherapy clinical practice.

A novel method to attain sinusoidal mechanical responses from single motor units.

INTRODUCTION: The relationship between output force and motor command depends on the intrinsic dynamic responses of motor units (MUs), which can be characterized by evoking accurate sinusoidal force responses at different frequencies. In this study we sought to determine whether sinusoidal modulation of the stimulation rate of single MUs results in reliable sinusoidal force changes. METHODS: Single axons of rat ventral roots were stimulated electrically by changing the pulse rate sinusoidally at different frequency modulation (0.4-1.0-2.0-4.0 Hz for slow, 1.0-2.0-4.0-7.0 Hz for fast MUs). The twitching sinusoidal force signal was interpolated. We calculated harmonic distortion (HD) and the correlation coefficient (r) between theoretical sines and interpolated signals. RESULTS: HD was always <5%, and r was always >0.97. CONCLUSIONS: The HD and r-values obtained indicate highly reliable sinusoidal responses, which supports the potential use of this method to further characterize the dynamic behavior of single MUs.