Effect of muscle length on maximum evoked torque, discomfort, contraction fatigue, and strength adaptations during electrical stimulation in adult populations: A systematic review.

Neuromuscular electrical stimulation (NMES) can improve physical function in different populations. NMES-related outcomes may be influenced by muscle length (i.e., joint angle), a modulator of the force generation capacity of muscle fibers. Nevertheless, to date, there is no comprehensive synthesis of the available scientific evidence regarding the optimal joint angle for maximizing the effectiveness of NMES. We performed a systematic review to investigate the effect of muscle length on NMES-induced torque, discomfort, contraction fatigue, and strength training adaptations in healthy and clinical adult populations (PROSPERO: CRD42022332965). We conducted searches across seven electronic databases: PUBMED, Web of Science, EMBASE, PEDro, BIREME, SCIELO, and Cochrane, over the period from June 2022 to October 2023, without restricting the publication year. We included cross-sectional and longitudinal studies that used NMES as an intervention or assessment tool for comparing muscle lengths in adult populations. We excluded studies on vocalization, respiratory, or pelvic floor muscles. Data extraction was performed via a standardized form to gather information on participants, interventions, and outcomes. Risk of bias was assessed using the Revised Cochrane risk-of-bias tool for cross-over trials and the Physiotherapy Evidence Database scale. Out of the 1185 articles retrieved through our search strategy, we included 36 studies in our analysis, that included 448 healthy young participants (age: 19-40 years) in order to investigate maximum evoked torque (n = 268), contraction fatigability (n = 87), discomfort (n = 82), and muscle strengthening (n = 22), as well as six participants with spinal cord injuries, and 15 healthy older participants. Meta-analyses were possible for comparing maximal evoked torque according to quadriceps muscle length through knee joint angle. At optimal muscle length 50° - 70° of knee flexion, where 0° is full extension), there was greater evoked torque during nerve stimulation compared to very short (0 - 30°) (p<0.001, CI 95%: -2.03, -1.15 for muscle belly stimulation, and -3.54, -1.16 for femoral nerve stimulation), short (31° - 49°) (p = 0.007, CI 95%: -1.58, -0.25), and long (71° - 90°) (p<0.001, CI 95%: 0.29, 1.02) muscle lengths. At long muscle lengths, NMES evoked greater torque than very short (p<0.001, CI 95%: -2.50, -0.67) and short (p = 0.04, CI 95%: -2.22, -0.06) lengths. The shortest quadriceps length generated the highest perceived discomfort for a given current amplitude. The amount of contraction fatigability was greater when muscle length allowed greater torque generation in the pre-fatigue condition. Strength gains were greater for a protocol at the optimal muscle length than for short muscle length. The quality of evidence was very high for most comparisons for evoked torque. However, further studies are necessary to achieve certainty for the other outcomes. Optimal muscle length should be considered the primary choice during NMES interventions, as it promotes higher levels of force production and may facilitate the preservation/gain in muscle force and mass, with reduced discomfort. However, a longer than optimal muscle length may also be used, due to possible muscle lengthening at high evoked tension. Thorough understanding of these physiological principles is imperative for the appropriate prescription of NMES for healthy and clinical populations.

Involvement of Matrix Metalloproteinases in COVID-19: Molecular Targets, Mechanisms, and Insights for Therapeutic Interventions.

MMPs are enzymes involved in SARS-CoV-2 pathogenesis. Notably, the proteolytic activation of MMPs can occur through angiotensin II, immune cells, cytokines, and pro-oxidant agents. However, comprehensive information regarding the impact of MMPs in the different physiological systems with disease progression is not fully understood. In the current study, we review the recent biological advances in understanding the function of MMPs and examine time-course changes in MMPs during COVID-19. In addition, we explore the interplay between pre-existing comorbidities, disease severity, and MMPs. The reviewed studies showed increases in different MMP classes in the cerebrospinal fluid, lung, myocardium, peripheral blood cells, serum, and plasma in patients with COVID-19 compared to non-infected individuals. Individuals with arthritis, obesity, diabetes, hypertension, autoimmune diseases, and cancer had higher MMP levels when infected. Furthermore, this up-regulation may be associated with disease severity and the hospitalization period. Clarifying the molecular pathways and specific mechanisms that mediate MMP activity is important in developing optimized interventions to improve health and clinical outcomes during COVID-19. Furthermore, better knowledge of MMPs will likely provide possible pharmacological and non-pharmacological interventions. This relevant topic might add new concepts and implications for public health in the near future.

Intra- and inter-rater reliability and agreement of stimulus electrodiagnostic tests in post-COVID-19 patients.

Background. COVID-19 patients may present sequelae, such as neuromuscular electrophysiological disorders (NED), that can be assessed using the stimulus electrodiagnostic test (SET). However, little is known about the reliability and agreement of the SET in post-COVID-19 patients.Objective. We aimed to verify the intra-inter-rater reliability and agreement of SET measurements in the rectus femoris, vastus medialis, vastus lateralis, tibialis anterior, and gastrocnemius lateralis (GL) in post-COVID-19 participants.Methods. We designed an observational prospective study to evaluate 20 (10 males and 10 females) post-COVID-19 patients, age: 44.95 ± 11.07 years, weight: 87.99 ± 19.08 kg, height: 1.69 ± 0.09 m. Two independent raters took two evaluations using the SET on selected muscles. The intra-class correlation coefficient (ICC) and 95% limits of the agreement defined the quality and magnitude of the measures.Results. For intra-rater reliability, all measurements presented correlations classified as high or very high (ICC: 0.71-1.0). For inter-rater reliability, the rheobase, chronaxie, accommodation, and accommodation index presented high or very high correlations, except for the accommodation index of the GL (ICC = 0.65), which was moderate.Conclusion. The reliability of the SET obtained by independent raters was very high, except for the GL accommodation, which presented moderate ICC. Therefore, the SET is a reliable tool for evaluating NED in post-COVID-19 patients.

The Influence of Hip and Knee Joint Angles on Quadriceps Muscle-Tendon Unit Properties during Maximal Voluntary Isometric Contraction.

Determining how the quadriceps femoris musculotendinous unit functions, according to hip and knee joint angles, may help with clinical decisions when prescribing knee extension exercises. We aimed to determine the effect of hip and knee joint angles on structure and neuromuscular functioning of all constituents of the quadriceps femoris and patellar tendon properties. Twenty young males were evaluated in four positions: seated and supine in both 20° and 60° of knee flexion (SIT20, SIT60, SUP20, and SUP60). Peak knee extension torque was determined during maximal voluntary isometric contraction (MVIC). Ultrasound imaging was used at rest and during MVIC to characterize quadriceps femoris muscle and tendon aponeurosis complex stiffness. We found that peak torque and neuromuscular efficiency were higher for SUP60 and SIT60 compared to SUP20 and SIT20 position. We found higher fascicle length and lower pennation angle in positions with the knee flexed at 60°. The tendon aponeurosis complex stiffness, tendon force, stiffness, stress, and Young's modulus seemed greater in more elongated positions (60°) than in shortened positions (20°). In conclusion, clinicians should consider positioning at 60° of knee flexion rather than 20°, regardless if seated or supine, during rehabilitation to load the musculotendinous unit enough to stimulate a cellular response.

Neuromuscular disorders in women and men with spinal cord injury are associated with changes in muscle and tendon architecture.

OBJECTIVE: The present study aimed to determine the association between neuromuscular function, motor function impairment, and muscle and tendon structures in individuals with spinal cord injury (SCI) compared to a control (non-disabled) population. DESIGN: A cross-sectional study with a control group. SETTING: Center of Adapted Sports Training and Special Physical Education. PARTICIPANTS: Fifteen individuals with SCI and motor function impairments participated in the study. A paired non-disabled group was recruited for comparison. INTERVENTIONS: Not applicable. OUTCOME MEASURES: Muscle (biceps brachii, rectus femoris, vastus lateralis, vastus medialis, and tibialis anterior) and tendon (quadriceps and patellar tendons) structures were assessed by ultrasound imaging (thickness, pennation angle, fascicle length, and echogenicity). Neuromuscular electrophysiological disorders were also assessed using electrodiagnosis techniques (stimulus non-responsivity and chronaxie) in the same muscles. RESULTS: Except for the biceps brachii muscle, muscle thickness, pennation angle, and fascicle length were lower (p < 0.01) while echogenicity and chronaxie were greater (p < 0.01) in SCI participants. The SCI participants had a higher prevalence of neuromuscular electrophysiological disorders for all muscles, except the biceps brachii. CONCLUSION: Neuromuscular disorders occur in association with muscle and tendon maladaptation in individuals with chronic SCI. A higher prevalence of electrophysiological disorders suggests an acquired polyneuromyopathy for muscles with motor function impairment even though the muscle was innerved, in addition to widespread muscle atrophy.

Intra- and Inter-Rater Reliability and Agreement of Ultrasound Imaging of Muscle Architecture and Patellar Tendon in Post-COVID-19 Patients Who Had Experienced Moderate or Severe COVID-19 Infection.

COVID-19 is associated with musculoskeletal disorders. Ultrasound is a tool to assess muscle architecture and tendon measurements, offering an idea of the proportion of the consequences of the disease, since significant changes directly reflect the reduction in the ability to produce force and, consequently, in the functionality of the patient; however, its application in post-COVID-19 infection needs to be determined. We aimed to assess the intra- and inter-rater reliability of ultrasound measures of the architecture of the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM), gastrocnemius lateralis (GL), gastrocnemius medialis (GM), soleus (SO), and tibialis anterior (TA) muscles, as well as the patellar tendon (PT) cross-sectional area (CSA) in post-COVID-19 patients. An observational, prospective study with repeated measures was designed to evaluate 20 post-COVID-19 patients, who were measured for the pennation angle (θp), fascicular length (Lf), thickness, echogenicity of muscles, CSA and echogenicity of the PT. The intra-class correlation coefficient (ICC) and 95% limits of agreement were used. The intra-rater reliability presented high or very high correlations (ICC = 0.71-1.0) for most measures, except the θp of the TA, which was classified as moderate (ICC = 0.69). Observing the inter-rater reliability, all the evaluations of the PT, thickness and echogenicity of the muscles presented high or very high correlations. For the Lf, only the RF showed as low (ICC = 0.43), for the θp, RF (ICC = 0.68), GL (ICC = 0.70) and TA (ICC = 0.71) moderate and the SO (ICC = 0.40) low. The ultrasound reliability was acceptable for the muscle architecture, muscle and tendon echogenicity, and PT CSA, despite the low reliability for the Lf and θp of the RF and SO, respectively.

Hip and Knee Joint Angles Determine Fatigue Onset during Quadriceps Neuromuscular Electrical Stimulation.

Neuromuscular electrical stimulation (NMES) has been used to increase muscle strength and physical function. However, NMES induces rapid fatigue, limiting its application. To date, the effect of quadriceps femoris (QF) muscle length by knee and hip joint manipulation on NMES-induced contraction fatigability is not clear. We aimed to quantify the effects of different muscle lengths on NMES-induced contraction fatigability, fatigue index, and electromyographic (EMG) activity for QF muscle. QF maximum evoked contraction (QMEC) was applied in a 26 min protocol (10 s on; 120 s off; 12 contractions) in 20 healthy participants (24.0 ± 4.6 years old), over 4 sessions on different days to test different conditions. The tested conditions were as follows: supine with knee flexion of 60° (SUP60), seated with knee flexion of 60° (SIT60), supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). Contraction fatigability (torque decline assessed by maximal voluntary contraction [MVC] and during NMES), fatigue index (percentage reduction in MVC), and EMG activity (root mean square [RMS] and median frequency) of the superficial QF' constituents were assessed. After NMES, all positions except SUP20 had an absolute reduction in MVC (p < .001). Fatigue index was greater in SIT20 than in SIT60 (p < .001) and SUP20 (p = .01). There was significant torque reduction across the 12 QMEC in SUP60 and SIT60, up to 10.5% (p < .001-.005) and 9.49% (p < .001-.033), respectively. There was no torque reduction during NMES in SUP20 and SIT20. Fatigue was accompanied by an increase in RMS (p = .032) and a decrease in median frequency for SUP60 (p < .001). Median frequency increased only in the SUP20 condition (p = .021). We concluded that QF NMES-induced contraction fatigability is greater when the knee is flexed at 60° compared to 20°. In addition, a supine position promotes earlier fatigue for a 60° knee flexion, but it delays fatigue onset for a 20° knee flexion compared to the seated position. These results provide a rationale for lower limb positioning during NMES, which depends on training objectives, e.g., strengthening or task-specific functionality training.

The Effect of Quadriceps Muscle Length on Maximum Neuromuscular Electrical Stimulation Evoked Contraction, Muscle Architecture, and Tendon-Aponeurosis Stiffness.

Muscle-tendon unit length plays a crucial role in quadriceps femoris muscle (QF) physiological adaptation, but the influence of hip and knee angles during QF neuromuscular electrical stimulation (NMES) is poorly investigated. We investigated the effect of muscle length on maximum electrically induced contraction (MEIC) and current efficiency. We secondarily assessed the architecture of all QF constituents and their tendon-aponeurosis complex (TAC) displacement to calculate a stiffness index. This study was a randomized, repeated measure, blinded design with a sample of twenty healthy men aged 24.0 ± 4.6. The MEIC was assessed in four different positions: supine with knee flexion of 60° (SUP60); seated with knee flexion of 60° (SIT60); supine with knee flexion of 20° (SUP20), and seated with knee flexion of 20° (SIT20). The current efficiency (MEIC/maximum tolerated current amplitude) was calculated. Ultrasonography of the QF was performed at rest and during NMES to measure pennation angle (θ p ) and fascicle length (L f ), and the TAC stiffness index. MEIC and current efficiency were greater for SUP60 and SIT60 compared to SUP20 and SIT20. The vastus lateralis and medialis showed lower θ p and higher L f at SUP60 and SIT60, while for the rectus femoris, in SUP60 there were lower θ p and higher L f than in all positions. The vastus intermedius had a similar pattern to the other vastii, except for lack of difference in θ p between SIT60 compared to SUP20 and SIT20. The TAC stiffness index was greater for SUP60. We concluded that NMES generate greater torque and current efficiency at 60° of knee flexion, compared to 20°. For these knee angles, lengthening the QF at the hip did not promote significant change. Each QF constituent demonstrated muscle physiology patterns according to hip and/or knee angles, even though a greater L f and lower θ p were predominant in SUP60 and SIT60. QF TAC index stiffened in more elongated positions, which probably contributed to enhanced force transmission and slightly higher torque in SUP60. Our findings may help exercise physiologist better understand the impact of hip and knee angles on designing more rational NMES stimulation strategies. CLINICAL TRIAL REGISTRATION: www.ClinicalTrials.gov, identifier NCT03822221.

Effects of different electrical stimulation currents and phase durations on submaximal and maximum torque, efficiency, and discomfort: a randomized crossover trial.

BACKGROUND: Neuromuscular electrical stimulation (NMES) is an important therapeutic tool for rehabilitation. However, best stimulation parameters remain to be determined. OBJECTIVE: To determine the influence of different electrical stimulation currents and phase durations on torque, efficiency, and discomfort. METHODS: Using a cross-over design, kHz frequency alternating currents (KFAC) and pulsed currents (PC) with narrow (200 µs) or wide (500 µs) phase durations were randomly applied on knee extensor muscles of healthy participants with a minimum of seven days between sessions. The NMES-evoked torque, NMES-efficiency, and discomfort (visual 0-10 cm analogue scale) were measured for each stimulation intensity increments (10 mA). Statistics were conducted using a three-way analysis of variances (phase duration x current x intensity), followed by Tukey post-hoc. RESULTS: Twenty-four males (age 22.3 ±â€¯3.5years) were included. No effect of NMES current was observed for torque, efficiency, and discomfort. For wide phase durations (500 µs), torque significantly increased for all stimulation intensities. For narrow phase durations (200 µs) evoked torque significantly increased only after 40% of maximal stimulation intensity. Phase durations of 500 µs produced greater torque than 200 µs. Discomfort was greater with 500 µs when compared to 200 µs. Submaximal relative torque, for example 40% of maximum voluntary contraction (MVC), was obtained with ∼ 60% and ∼ 80% of the maximal current intensity for 500 µs and 200 µs, respectively. CONCLUSION: KFAC and PC current applied with the same phase duration induced similar relative submaximal and maximum evoked-torque, efficiency, and perceived discomfort. However, currents with 500 µs induced higher evoked-torque, current efficiency, and perceived discomfort.

Intra and inter-raters reliability and agreement of stimulus electrodiagnostic tests with two different electrodes in sedated critically-ill patients.

Objective: The aim of the present study was to verify the intra- and inter-rater reliability and agreement of the stimulus electrodiagnostic test (SET) measurements obtained by pen and square electrodes in the vastus lateralis and tibialis anterior muscles. Design: An intra- and inter-rater reliability and agreement study was performed for the SET by two independent raters. Two different sizes of cathode electrodes (1 cm2 and 25 cm2) and two muscles were assessed (tibialis anterior and vastus lateralis). Results: Chronaxie did not change according to the different electrodes. A high intra-rater reliability (0.72 ≤ r ≤ 0.88) was detected independently of the electrode and muscle assessed. Moreover, moderate and almost perfect agreements (0.51 ≤ Kappa ≤ 1.00) were detected on intra-rater assessment. Similar correlations (0.74 ≤ r ≤ 0.79) were found for intra-rater reliability. However, dissimilar inter-rater agreement was detected: Kappa ≤ 0.40 for tibialis anterior and Kappa = 1.00 for vastus lateralis. Conclusion: The SET presented high reliability and moderate agreement in intra-rater evaluations. A fair agreement was found in the inter-rater assessment of the tibialis anterior. Evaluations performed with different electrode sizes did not influence the results. Therefore, the SET should be performed by a unique rater in test retest situations.

Intra- and inter-rater reproducibility of ultrasound imaging of patellar and quadriceps tendons in critically ill patients.

Since the outset of body image reconstruction for diagnosis purposes, ultrasound has been used to investigate structural changes located in tendons. Ultrasound has clinical applications in the intensive care unit, but its utility for tendon imaging remains unknown. Thus, we aimed to determine intra- and inter-rater reproducibility of measures obtained by images generated through morphological tendon sonographic analysis recorded from critically ill patients. We designed a cross-sectional study to assess thickness, cross-sectional area, and echogenicity of patellar and quadriceps tendons in a convenience sample formed with 20 critically ill patients. Two independent raters (experienced and novice) recorded repeated measures, checking for agreement (Kappa statistics) and reliability (Intraclass coefficient Correlation-ICC and Bland-Altman). The quality of images acquired by the two independent raters substantially agreed (k = 0.571-1.000), regardless of the region on the patellar tendon or the studied tendon (patellar or quadriceps). Regardless of how much experience the rater had, their repeated records (intra-rater reliability) always demonstrated almost complete correlation, ICC ranging from 0.89 to 0.98 for both tendons in all outcomes. At the same way, the statistically significant inter-rater ICC ranging from 0.87 to 0.97. Both repeated measures by the raters (intra-rater) and the repeated single and double measures between the raters (inter-rater) presented a minimum measurement error constituting a predominant pattern of random variability. We conclude that ultrasound imaging acquisition performed by independent raters for tendon thickness, CSA, and echogenicity monitoring of critically ill patients are acceptable and are not influenced by rater experience.

Multiple Cold-Water Immersions Attenuate Muscle Damage but not Alter Systemic Inflammation and Muscle Function Recovery: A Parallel Randomized Controlled Trial.

The aim of this study was to investigate the effects of multiple cold-water immersions (CWIs) on muscle function, markers of muscle damage, systemic inflammation and ECM degradation following exercise-induced muscle damage (EIMD). Thirty physically active males were randomly assigned to either a control (n = 15) or cold-water immersion (CWI) group (n = 15). The CWI group performed one immersion (10 °C for 20 min) at post-exercise and every 24 h for the following 72 h, while the control group remained in a seated position during these corresponding periods. Muscle strength, vertical jump height, muscle thickness, delayed-onset muscle soreness (DOMS), systemic creatine kinase (CK), C-reactive protein (CRP), inflammatory cytokines and matrix metalloproteinase-2 (MMP-2) activity were assessed at Pre, Post, 24, 48, 72, 96 and 168 h following EIMD. No significant time × group interaction was obtained for muscle strength, vertical jump height recovery and MMP-2 activity (p > 0.05). At 24 h, muscle thickness from the CWI group returned to baseline and was lower than the control (p = 0.04). DOMS returned to baseline at 168 h for the CWI group (p = 0.109) but not for the control (p = 0.008). At 168 h, CK showed a time-group difference with a greater peak for the control group (p = 0.016). In conclusion, multiple CWIs attenuated muscle damage, but not altered systemic inflammation and muscle function recovery.

Training Effects of Alternated and Pulsed Currents on the Quadriceps Muscles of Athletes.

The aim of the study was to evaluate the effects of 6 weeks training with different neuromuscular electrical stimulation (NMES) currents (medium alternated and low-frequency pulsed current) on muscle architecture and neuromuscular performance of competitive athletes. A double-blind controlled and randomized experimental study was carried out with 33 athletes (22.2±2.6 yrs, 74.7±9.8 kg, 176.8±6.0 cm), divided into 3 groups: mid-frequency current (MF, n=12), pulsed current (PC, n=11) and the control group (CG, n=10). Quadriceps maximal voluntary peak torque (PT) and corresponding vastus lateralis electromyographic activity, evoked torque (PT-NMES), vastus lateralis muscle thickness, fascicle length, pennation angle, and level of discomfort were assessed before and after the interventions. NMES training was performed 3 times per week and consisted of 18 sessions, 15 min/session, 6 s duration in each contraction interspersed with 18 s rest. After the training period, muscle thickness increased in the MF and PC groups (p<0.05). PT-NMES increased only in the PC group (p<0.05). All currents produced similar levels of discomfort (p>0.05). Quadriceps NMES training applied through alternated or pulsed currents produced similar effects in architecture and neuromuscular performance in competitive athletes.

Neuromuscular fatigue after low- and medium-frequency electrical stimulation in healthy adults.

INTRODUCTION: In this study we investigated fatigue origins induced by low-frequency pulsed current (PC) and medium-frequency current (MF) neuromuscular electrical stimulation (NMES) after a clinical-like session. METHODS: Eleven healthy men randomly underwent 2 NMES sessions, PC and MF, on quadriceps muscle (15-minute duration, 6 seconds on and 18 seconds off). Maximal voluntary contraction (MVC), central activation ratio (CAR), vastus lateralis electromyographic activity (EMG), and evoked contractile properties were determined before and after the sessions. Evoked torque and discomfort during the sessions were also measured. RESULTS: Both currents produced decreases in MVC, EMG, and evoked contractile properties after the sessions. No difference was found between currents for all variables (P > 0.05). Evoked torque during sessions decreased (P < 0.05). No difference was observed in mean evoked torque and discomfort (P > 0.05). DISCUSSION: Both currents induced similar neuromuscular fatigue. Clinicians can choose either PC or MF and expect similar treatment effects when the goal is to generate gains in muscle strength. Muscle Nerve 58: 293-299, 2018.