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.

Effects of Kilohertz Frequency, Burst Duty Cycle, and Burst Duration on Evoked Torque, Perceived Discomfort and Muscle Fatigue: A Systematic Review.

ABSTRACT: Kilohertz-frequency alternating current is used to minimize muscle atrophy and muscle weakness and improve muscle performance. However, no systematic reviews have evaluated the best Kilohertz-frequency alternating current parameters for this purpose. We investigated the effects of the carrier frequency, burst duty cycles, and burst durations on evoked torque, perceived discomfort, and muscle fatigue. A search of eight data sources by two independent reviewers resulted in 13 peer-reviewed studies being selected, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, and rated using the PEDro scale to evaluate the methodological quality of the studies. Most studies showed that carrier frequencies up to 1 kHz evoked higher torque, while carrier frequencies between 2.5 and 5 kHz resulted in lower perceived discomfort. In addition, most studies showed that shorter burst duty cycles (10%-50%) induced higher evoked torque and lower perceived discomfort. Methodological quality scores ranged from 5 to 8 on the PEDro scale. We conclude that Kilohertz-frequency alternating current develops greater evoked torque for carrier frequencies between 1 and 2.5 kHz and burst duty cycles less than 50%. Lower perceived discomfort was generated using Kilohertz-frequency alternating currents between 2.5 and 5 kHz and burst duty cycles less than 50%.

Are dose-response relationships of resistance training reliable to improve functional performance in frail and pre-frail older adults? A systematic review with meta-analysis and meta-regression of randomized controlled trials.

This systematic review with meta-analyses investigates the impact of resistance training (RT), using meta-regressions, on functional performance in frail and pre-frail adults aged ≥ 65 years to determine the key variables of RT. Ten randomized controlled trials involving 1303 participants were analyzed. Five studies assessed habitual walking speed (HWS), three studies evaluated performance in the timed-up-and-go test (TUG), three studies evaluated performance in the Short Physical Performance Battery (SPPB), and three studies assessed performance in the sit-to-stand test (STS). RT alone improved STS time and SPPB scores in frail and pre-frail older adults. RT improved STS performance (Effect Size (ES):- 0.536; 95% CI - 0.874 to - 0.199; p = .002) and led to a 2.261-point increase in SPPB performance (ES:1.682; 95% CI 0.579-2.786; p = .003). At least two weekly training sessions are required to increase SPPB scores, and three sessions seem to optimize the improvements. Higher training volume per exercise and volume per session reduce the gains in SPPB performance. We did not observe any association between different doses of RT and STS time improvements. RT alone positively influenced TUG performance only in community-dwelling older frail and pre-frail adults but not in institutionalized older individuals. RT alone did not improve the HWS compared to the non-active control group.

Different Cryotherapy Modalities Demonstrate Similar Effects on Muscle Performance, Soreness, and Damage in Healthy Individuals and Athletes: A Systematic Review with Metanalysis.

BACKGROUND: There are extensive studies focusing on non-invasive modalities to recover physiological systems after exercise-induced muscle damage (EIMD). Whole-body cryotherapy (WBC) and Partial-body cryotherapy (PBC) have been recommended for recovery after EIMD. However, to date, no systematic reviews have been performed to compare their effects on muscle performance and muscle recovery markers. METHODS: This systematic review with metanalysis compared the effects of WBC and PBC on muscle performance, muscle soreness (DOMS), and markers of muscular damage following EIMD. We used Pubmed, Embase, PEDro, and Cochrane Central Register of Controlled Trials as data sources. Two independent reviewers verified the methodological quality of the studies. The studies were selected if they used WBC and PBC modalities as treatment and included muscle performance and muscle soreness (DOMS) as the primary outcomes. Secondary outcomes were creatine kinase and heart rate variability. RESULTS: Six studies with a pooled sample of 120 patients were included. The methodological quality of the studies was moderate, with an average of 4.3 on a 0-10 scale (PEDro). RESULTS: Both cryotherapy modalities induce similar effects without difference between them. CONCLUSION: WBC and PBC modalities have similar global responses on muscle performance, soreness, and markers of muscle damage.

Contraction fatigue, strength adaptations, and discomfort during conventional versus wide-pulse, high-frequency, neuromuscular electrical stimulation: a systematic review.

Neuromuscular electrical stimulation (NMES) can be delivered in a conventional form (CONVNMES) and using relatively wide-pulses and high-frequencies (WPHFNMES). WPHFNMES is proposed to reduce contraction fatigability and generate larger contractions with less discomfort than CONVNMES; however, there are no systematic reviews to guide the selection of NMES types. This systematic review compared the effects of CONVNMES versus WPHFNMES on contraction fatigability, strength adaptations, and perceived discomfort in clinical and non-clinical populations. Eight studies were included. When averaged across all non-clinical participants in individual short- and long-term studies, there was either no difference between CONVNMES and WPHFNMES for all outcomes or WPHFNMES produced more fatigability. In a subset of non-clinical participants ("responders"), however, WPHFNMES reduced contraction fatigability during a single session. Long-term studies found no differences between protocols for strength adaptations in non-clinical participants and those with multiple sclerosis. We concluded that WPHFNMES reduces contraction fatigability only in the short-term studies and in non-clinical responder participants and may exacerbate fatigability in non-responders. This review was registered in the prospective international registry of systematic reviews/PROSPERO (Registration Number: CRD42020153907). Novelty: WPHF NMES may reduce fatigue in some participants and exacerbate fatigue in others. There were no differences in long-term studies between WPHF and CONV NMES on strength adaptations. Future high-quality research is needed to optimize outcomes of NMES-based programs.

The effects of neuromuscular electrical stimulation on strength, pain, and function in individuals with knee osteoarthritis: a systematic review with meta-analysis / Efeitos da estimulação elétrica neuromuscular na força, dor e função em indivíduos com osteoartrite de joelho: uma revisão sistemática com meta-análise / Efectos de la electroestimulación neuromuscular sobre la fuerza, el dolor y la función en personas con osteoartritis de la rodilla: una revisión sistemática con metaanálisis

ABSTRACT We aimed to investigate the effects of neuromuscular electrical stimulation on muscle strength, pain relief, and improvement in function in patients with knee osteoarthritis. Databases were searched from December 2017 to July 2020 and included PubMed, Embase, LILACS, and the Cochrane Central Register of Controlled Trials. A manual search was also performed by checking the reference lists of eligible articles. The PRISMA guidelines were followed. The studies selected compared NMES with an exercise program on isometric muscle strength as a primary outcome. The secondary outcomes were pain and function. The quality of the studies was assessed using the Risk of Bias assessment and PEDro scale, and the overall quality of the evidence was assessed using the GRADE approach. Eight studies were included in this systematic review. A total of 571 patients were analyzed. Neuromuscular electrical stimulation associated with exercise promoted an increase in isometric strength of the quadriceps muscle compared to the active control group, demonstrating heterogeneity and statistical difference (95% CI=1.16 to 5.10, I2=97%, p=0.002; very low-certainty evidence). NMES associated with exercise did not improve physical function (95% CI=−0.37 to 0.59, I2=0%, p=0.67; low-certainty evidence) and showed controversial results for pain compared to an active control group (qualitative assessment). In conclusion, NMES induces an increase in muscle strength in patients with osteoarthritis compared to an active control group. No differences were found for physical function and pain outcomes. Further research is needed due to the uncertain level of evidence.

RESUMO O objetivo deste estudo foi investigar os efeitos da estimulação elétrica neuromuscular (EENM) na força muscular, alívio da dor e melhora da função em pacientes com osteoartrite de joelho. Realizou-se uma pesquisa em diferentes bases de dados, como PubMed, Embase, LILACS e o Cochrane Central Register of Controlled Trials, no período de dezembro de 2017 até julho de 2020. Procedeu-se a uma busca manual com o intuito de verificar as listas de referências dos artigos elegíveis. As diretrizes PRISMA foram seguidas. Os estudos selecionados comparavam a estimulação elétrica neuromuscular com um programa de exercícios de força muscular isométrica como desfecho primário. Os resultados secundários foram dor e função. A qualidade dos estudos foi avaliada usando avaliação de risco de viés e a escala PEDro e a qualidade geral das evidências foi avaliada usando a abordagem GRADE. Oito estudos foram incluídos nesta revisão sistemática com um total de 571 pacientes analisados. A EENM associada ao exercício promoveu o aumento da força isométrica do músculo quadríceps em relação ao grupo controle ativo, demonstrando heterogeneidade e diferença estatística (IC 95%=1,16 a 5,10, I2=97%, p=0,002; evidência de muito baixa certeza), mas não melhorou a função física (IC 95%=−0,37 a 0,59, I2=0%, p=0,67; evidência de baixa certeza) e mostrou resultados controversos para dor em comparação ao grupo de controle ativo (avaliação qualitativa). Conclui-se que a EENM induz o aumento da força muscular em pacientes com osteoartrite, porém não foram encontradas diferenças nos resultados de funcionalidade e dor em comparação com o grupo de controle ativo. Devido à incerteza das evidências, são necessárias mais pesquisas sobre o assunto.

RESUMEN El objetivo de este estudio fue analizar los efectos de la electroestimulación neuromuscular (NMES) sobre la fuerza muscular, el alivio del dolor y la mejora de la función en pacientes con osteoartritis de la rodilla. Se realizó una búsqueda en las bases de datos PubMed, Embase, LILACS y Cochrane Central Register of Controlled Trials, en el periodo de diciembre de 2017 y julio de 2020. Se llevó a cabo una búsqueda manual para verificar las listas de referencias de los artículos elegibles. Se aplicó las pautas PRISMA. Los estudios seleccionados compararon la electroestimulación neuromuscular con un programa de ejercicio de fuerza muscular isométrica como resultado primario. Los resultados secundarios fueron el dolor y la función. La calidad de los estudios se evaluó mediante la evaluación del riesgo de sesgo y la escala PEDro, y la calidad general de la evidencia se estimó con el uso del sistema GRADE. Ocho estudios con un total de 571 pacientes compusieron esta revisión sistemática. La EENM asociada con el ejercicio aumentó la fuerza isométrica del músculo cuádriceps en comparación con el grupo control activo, demostrando una heterogeneidad y diferencia estadística (IC 95%=1,16 a 5,10, I2=97%, p=0,002; evidencia con muy baja seguridad), pero no mejoró la función física (IC 95%=−0,37 a 0,59, I2=0%, p=0,67; evidencia con baja seguridad) y mostró resultados controvertidos para el dolor en comparación con el grupo control activo (evaluación cualitativa). Se concluyó que la EENM indujo un aumento de la fuerza muscular en pacientes con osteoartritis, pero no se encontraron diferencias en los resultados de función y dolor en comparación con el grupo control activo. Debido a la incertidumbre de la evidencia, se necesitan más estudios sobre el tema.