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Cross education and immobilisation: Mechanisms and implications for injury rehabilitation
Abstract
Unilateral strength training produces an increase in strength of the contralateral homologous muscle group. This process of strength transfer, known as cross education, is generally attributed to neural adaptations. It has been suggested that unilateral strength training of the free limb may assist in maintaining the functional capacity of an immobilised limb via cross education of strength, potentially enhancing recovery outcomes following injury. Therefore, the purpose of this review is to examine the impact of immobilisation, the mechanisms that may contribute to cross education, and possible implications for the application of unilateral training to maintain strength during immobilisation.
Critical review of literature.
Search of online databases.
Immobilisation is well known for its detrimental effects on muscular function. Early reductions in strength outweigh atrophy, suggesting a neural contribution to strength loss, however direct evidence for the role of the central nervous system in this process is limited. Similarly, the precise neural mechanisms responsible for cross education strength transfer remain somewhat unknown. Two recent studies demonstrated that unilateral training of the free limb successfully maintained strength in the contralateral immobilised limb, although the role of the nervous system in this process was not quantified.
Cross education provides a unique opportunity for enhancing rehabilitation following injury. By gaining an understanding of the neural adaptations occurring during immobilisation and cross education, future research can utilise the application of unilateral training in clinical musculoskeletal injury rehabilitation.
... 1,3 There are currently 2 hypotheses explaining the mechanisms underlying CE. In the "cross-activation" hypothesis, a bilateral increase in cortical motor activity during unilateral training reduces intracortical and interhemispheric inhibition, 4 with Lee and Carrol 5 postulating that this leads to adaptations in both the "trained" and "untrained" motor pathways. Conversely, the "bilateral-access hypothesis" suggests that neural adaptations in the trained hemisphere following unilateral strength training can be accessed by the untrained hemisphere. ...
... 8,11 CE may help to preserve plantar flexor function and reduce time taken to rehabilitate from such injuries as lab-based studies have shown that contralateral limb resistance training attenuates functional losses and prevents loss of muscle cross-sectional area in an injured, immobilized limb. 2,4,12 Laboratory-based unilateral plantar flexor strength training protocols have significantly increased contralateral limb strength by between 1.5% and 30.1%. [12][13][14][15][16][17][18] Although at-home rehabilitation programs are more convenient and cost-effective, and are less travel and resource intensive, there are currently no published home-based CE interventions in the plantar flexors. ...
... Thus, our study indicates that unilateral home-based strength training results in a significant and sizeable bilateral increase in plantar flexor power. It is also important to note that Tøien et al 18 conducted their study in an older male cohort (73 [4] y), had a smaller intervention group (n = 11), and utilized a supervised lab-based training protocol, which can maximize compliance and technique but is less applicable for wide use in rehabilitation. ...
Context:
Cross-education (CE) refers to neuromuscular gains in the untrained limb upon contralateral limb training. To date, only laboratory-based exercise programs have demonstrated CE. Home-based exercise prescription eliciting CE could have greater clinical applicability.
Objective:
To determine the effect of an 8-week, home-based unilateral strength training intervention on isokinetic muscle strength, muscular excitation, and power in trained and untrained plantar flexors.
Design:
Randomized controlled trial.
Methods:
Thirty-four healthy participants were randomized to intervention (n = 20) or control (n = 14). The intervention group completed 3 sets of 12 repetitions of progressively loaded unilateral calf raises 3 days per week. Concentric and eccentric peak torque were measured using isokinetic dynamometry at 30°/s and 120°/s. Maximal electromyogram amplitude was simultaneously measured. Power was measured using a jump mat. All variables were measured at preintervention, midintervention, and postintervention.
Results:
Strength significantly increased bilaterally pre-post at both velocities concentrically and eccentrically in intervention group participants. Maximal electromyogram amplitude significantly increased pre-post bilaterally at both velocities in the medial gastrocnemii of the intervention group. Power significantly increased bilaterally pre-post in the intervention group, with a dose-response effect demonstrated in the untrained plantar flexors. The CE effects of strength, power, and electromyogram activation were 23.4%, 14.6%, and 25.3%, respectively. All control group values were unchanged pre-post.
Conclusion:
This study shows that a simple at-home unilateral plantar flexor exercise protocol induces significant increases in contralateral strength, muscular excitation, and power. These results suggest the applicability of CE in home rehabilitation programs aiming to restore or maintain neuromuscular function in inactive individuals or immobilized ankles.
... In this study, WBV training significantly enhanced muscle strength (9.4%) in the trained extremity and (4.4%) in the untrained extremity, indicating that WBV can effectively induce cross-education in the contralateral limb. In previous studies it has been shown that the cross-education effect after unilateral strength training averages about 50% of that observed for the trained side (Hendy et al. 2012;Farthing and Zehr 2014). A similar finding was observed in our study. ...
... A similar finding was observed in our study. The magnitude of cross-education reported in the literature varies greatly between 3% and 77% for the untrained side, depending on the characteristics of the training protocol (Hendy et al. 2012;Farthing and Zehr 2014). A recent metaanalysis pooled existing data from a wide variety of training protocols to determine that the average increase in strength of the untrained limb was 11.9% (Manca et al. 2017). ...
... The sites of modulation that may have been involved in cross-education can be broadly categorized into muscular, spinal, or cortical. As strength transfer commonly occurs in the absence of any changes in muscle hypertrophy, it is widely believed that cross-education occurs as a result of neural adaptations at the spinal and supraspinal level; however, the exact mechanisms underlying the cross-transfer of strength are not clear (Hendy et al. 2012). There is a limited number of studies on the effects of WBV on the cross-transfer of strength. ...
Purpose: To determine whether unilateral leg whole-body vibration (WBV) strength training induces strength gain in the untrained contralateral leg muscle. The secondary aim was to determine the potential role of spinal neurological mechanisms regarding the effect of WBV exercise on contralateral strength training.
Materials and Methods: Forty-two young adult healthy volunteers were randomized into two groups: WBV exercise and Sham control. An isometric semi-squat exercise during WBV was applied regularly through 20 sessions. WBV training was applied to the right leg in the WBV group and the left leg was isolated from vibration. Sham WBV was applied to the right leg of participants in the Control group. Pre- and post-training isokinetic torque and reflex latency of both quadricepses were evaluated.
Results: The increase in the strength of right (vibrated) knee extensors was 9.4 ± 10.7% in the WBV group (p = .001) and was 1.2 ± 6.6% in the Control group (p = .724). The left (non-vibrated) extensorsvibrated) knee extensors w4 ± 8.4% in the WBV group (p = .038), whereas it decreased by 1.4 ± 7.0% in the Control (p = .294). The strength gains were significant between the two groups. WBV induced the reflex response of the quadriceps muscle in the vibrated ipsilateral leg and also in the non-vibrated contralateral leg, though with a definite delay. The WBV-induced muscle reflex (WBV-IMR) latency was 22.5 ± 7.7 ms for the vibrated leg and 39.3 ± 14.6 ms for the non-vibrated leg.
Conclusions: Chronic WBV training has an effect of the cross-transfer of strength to contralateral homologous muscles. The WBV-induced muscular reflex may have a role in the mechanism of cross-transfer strength.
... Apesar da relevância clínica e científica do cross-education, é importante que haja uma melhor compreensão do seu papel para a adaptação neural, a fim de maximizar seus benefícios terapêuticos da reabilitação clínica. Por conseguinte, torna-se importante o entendimento sobre as alterações neuromusculares e de seus mecanismos durante a fase inicial de treinamento-de força para a prescrição de exercícios, visto que é nesta fase que ocorrem as adaptações neurais por meio da ativação voluntária máxima dos músculos treinados [13][14][15][16][17][18][19][20][21][22][23][24][25] . Sendo assim, o presente artigo tem como objetivo fornecer informações sobre o fenômeno cross-education, apresentando suas evidências, mecanismos, implicações para a reabilitação e aplicações práticas. ...
... De acordo com estes estudos, o sucesso na manutenção da força muscular e da espessura muscular em indivíduos imobilizados fornece perspectivas promissoras para a recuperação mais efetiva, reduzindo assim o impacto da imobilização 8,24 .Para os atletas, a perda de força associada com a imobilização muitas vezes reduz o desempenho e exige ao indivíduo se submeter a um período de reabilitação 13 .Em outros casos, como o de pacientes idosos que necessitam de imobilização, muitas vezes apresentam maiores dificuldades de recuperar a função muscular, prejudicando assim sua independência e qualidade de vida 31 . Em qualquer caso, a manutenção da função muscular durante a imobilização irá fornecer resultados positivos para os pacientes.Neste sentido, os resultados de estudos sobre os efeitos relacionados ao crosseducation sugerem que a transferência de força pode desempenhar um papel vital para a recuperação de determinados pacientes14 . Neste caso, uma pesquisa descobriu que o treinamento de força no membro não imobilizado proporcionou uma manutenção da força no membro imobilizado após três semanas de imobilização 9 .Portanto, em todos os casos citados acima, o tema cross-education possui Enfoque Interdisciplinar na Educação Física e ...
... I Idoso 133,135,137,141,142,145,146,157,158,159,160,167,239,241,244 Inclusão Social 8,136 Interdisciplinaridade 112,114,118 Intervenção 1, 3,5,52,64,132,133,135,138,140,141,142,144,209,250,251,252,253,254,255,257,259,260 M Metodologia 16,18,20,22,26,32,37,41,75,78,79,106,111,119,123,164,176,204,222,227,233,235,245 R Reabilitação 185, 226, 257 S Saúde 2, 32,65,66,81,89,92,94,95,96,97,100,101,102,113,130,132,133,135,140,142,143,144,146,149,152,159,160,176,191,194,196,197,198,202,203,207,226,227,228,230,247,248,249,250,253,254,258,259,260,261 T Treinamento 174,187,188,189,196,226,228,229,231,233,234,236,237,241,244,247 U Universidade 1,2,5,6,14,21,38,40,50,51,52,66,67,68,79,81,84,91,97,103,112,114,115,119,120,124,127,133,151,161,164,165,173,180,181,194,203,204,217,228,237,261 ...
... Apesar da relevância clínica e científica do cross-education, é importante que haja uma melhor compreensão do seu papel para a adaptação neural, a fim de maximizar seus benefícios terapêuticos da reabilitação clínica. Por conseguinte, torna-se importante o entendimento sobre as alterações neuromusculares e de seus mecanismos durante a fase inicial de treinamento-de força para a prescrição de exercícios, visto que é nesta fase que ocorrem as adaptações neurais por meio da ativação voluntária máxima dos músculos treinados [13][14][15][16][17][18][19][20][21][22][23][24][25] . Sendo assim, o presente artigo tem como objetivo fornecer informações sobre o fenômeno cross-education, apresentando suas evidências, mecanismos, implicações para a reabilitação e aplicações práticas. ...
... De acordo com estes estudos, o sucesso na manutenção da força muscular e da espessura muscular em indivíduos imobilizados fornece perspectivas promissoras para a recuperação mais efetiva, reduzindo assim o impacto da imobilização 8,24 .Para os atletas, a perda de força associada com a imobilização muitas vezes reduz o desempenho e exige ao indivíduo se submeter a um período de reabilitação 13 .Em outros casos, como o de pacientes idosos que necessitam de imobilização, muitas vezes apresentam maiores dificuldades de recuperar a função muscular, prejudicando assim sua independência e qualidade de vida 31 . Em qualquer caso, a manutenção da função muscular durante a imobilização irá fornecer resultados positivos para os pacientes.Neste sentido, os resultados de estudos sobre os efeitos relacionados ao crosseducation sugerem que a transferência de força pode desempenhar um papel vital para a recuperação de determinados pacientes14 . Neste caso, uma pesquisa descobriu que o treinamento de força no membro não imobilizado proporcionou uma manutenção da força no membro imobilizado após três semanas de imobilização 9 .Portanto, em todos os casos citados acima, o tema cross-education possui Enfoque Interdisciplinar na Educação Física e ...
... I Idoso 133,135,137,141,142,145,146,157,158,159,160,167,239,241,244 Inclusão Social 8,136 Interdisciplinaridade 112,114,118 Intervenção 1, 3,5,52,64,132,133,135,138,140,141,142,144,209,250,251,252,253,254,255,257,259,260 M Metodologia 16,18,20,22,26,32,37,41,75,78,79,106,111,119,123,164,176,204,222,227,233,235,245 R Reabilitação 185, 226, 257 S Saúde 2, 32,65,66,81,89,92,94,95,96,97,100,101,102,113,130,132,133,135,140,142,143,144,146,149,152,159,160,176,191,194,196,197,198,202,203,207,226,227,228,230,247,248,249,250,253,254,258,259,260,261 T Treinamento 174,187,188,189,196,226,228,229,231,233,234,236,237,241,244,247 U Universidade 1,2,5,6,14,21,38,40,50,51,52,66,67,68,79,81,84,91,97,103,112,114,115,119,120,124,127,133,151,161,164,165,173,180,181,194,203,204,217,228,237,261 ...
... Apesar da relevância clínica e científica do cross-education, é importante que haja uma melhor compreensão do seu papel para a adaptação neural, a fim de maximizar seus benefícios terapêuticos da reabilitação clínica. Por conseguinte, torna-se importante o entendimento sobre as alterações neuromusculares e de seus mecanismos durante a fase inicial de treinamento-de força para a prescrição de exercícios, visto que é nesta fase que ocorrem as adaptações neurais por meio da ativação voluntária máxima dos músculos treinados [13][14][15][16][17][18][19][20][21][22][23][24][25] . Sendo assim, o presente artigo tem como objetivo fornecer informações sobre o fenômeno cross-education, apresentando suas evidências, mecanismos, implicações para a reabilitação e aplicações práticas. ...
... De acordo com estes estudos, o sucesso na manutenção da força muscular e da espessura muscular em indivíduos imobilizados fornece perspectivas promissoras para a recuperação mais efetiva, reduzindo assim o impacto da imobilização 8,24 .Para os atletas, a perda de força associada com a imobilização muitas vezes reduz o desempenho e exige ao indivíduo se submeter a um período de reabilitação 13 .Em outros casos, como o de pacientes idosos que necessitam de imobilização, muitas vezes apresentam maiores dificuldades de recuperar a função muscular, prejudicando assim sua independência e qualidade de vida 31 . Em qualquer caso, a manutenção da função muscular durante a imobilização irá fornecer resultados positivos para os pacientes.Neste sentido, os resultados de estudos sobre os efeitos relacionados ao crosseducation sugerem que a transferência de força pode desempenhar um papel vital para a recuperação de determinados pacientes14 . Neste caso, uma pesquisa descobriu que o treinamento de força no membro não imobilizado proporcionou uma manutenção da força no membro imobilizado após três semanas de imobilização 9 .Portanto, em todos os casos citados acima, o tema cross-education possui Enfoque Interdisciplinar na Educação Física e ...
... I Idoso 133,135,137,141,142,145,146,157,158,159,160,167,239,241,244 Inclusão Social 8,136 Interdisciplinaridade 112,114,118 Intervenção 1, 3,5,52,64,132,133,135,138,140,141,142,144,209,250,251,252,253,254,255,257,259,260 M Metodologia 16,18,20,22,26,32,37,41,75,78,79,106,111,119,123,164,176,204,222,227,233,235,245 R Reabilitação 185, 226, 257 S Saúde 2, 32,65,66,81,89,92,94,95,96,97,100,101,102,113,130,132,133,135,140,142,143,144,146,149,152,159,160,176,191,194,196,197,198,202,203,207,226,227,228,230,247,248,249,250,253,254,258,259,260,261 T Treinamento 174,187,188,189,196,226,228,229,231,233,234,236,237,241,244,247 U Universidade 1,2,5,6,14,21,38,40,50,51,52,66,67,68,79,81,84,91,97,103,112,114,115,119,120,124,127,133,151,161,164,165,173,180,181,194,203,204,217,228,237,261 ...
... [18][19][20][21] Instead, heeding the interconnected nature of the neuromuscular and fascial systems may be the key to producing meaningful injury prevention and performance enhancement strategies. Researchers have established that alterations in one region of the body affect not only local outcomes, such as positional changes in joints, tension dynamic changes across soft tissues, and alterations in stability, [22][23][24] mobility, [25][26][27] and motor control, 28,29 but invariably produce adjustments in other, interdependent, body regions. 26,27,[30][31][32] The term regional interdependence (RI) is used to describe this phenomenon. ...
... Total Motion Release ® (TMR ® ), a movement based orthopedic intervention, utilizes RI, potentially via cross education, [22][23][24][25] neural coupling, 28 and the common core hypothesis, 29 as well as the fascial interconnectedness of the trunk and upper limbs, [33][34][35] to produce changes in ROM, pain, and dysfunction, through targeted pain-free movement. 30 The TMR® system is based on the theory that pain alters motor control, movement patterns adapt to dysfunction created by pain, and that the body seeks symmetry and will correct dysfunctional movement patterns in the absence of pain. ...
... As the trunk stabilizes the spine, a more rigid platform is created throughout the lumbopelvic and thoracolumbar regions, potentially resolving stability and motor control dysfunctions at the core, glenohumeral joint, and scapulothoracic articulation. [18][19][20][21] When considering RI interventions like TMR ® as neurophysiological processes, RI may be a combined function of three interrelated neuromotor principles: cross education, [22][23][24][25] neural coupling, 28 and the common core hypothesis. 29 Currently, it is understood that neuromuscular control and strength production relies on stimuli received and communicated throughout the whole body for optimal function during complex integrated movements. ...
Healthy athletes commonly engage in pre-participation warm-up strategies designed to physiologically and mechanically prepare the body for training and competition. Alterations in rotational range of motion (ROM) of the dominant shoulder in overhead athletes, resulting in total rotation ROM loss, correlate with performance deficit, injury risk, and lost training time. Researchers have suggested that interventions using Total Motion Release® (TMR®) increase shoulder ROM more effectively than traditional warm-up methods. A randomized pre-test post-test trial was used to explore the effects of a regionally interdependent application of TMR® via a forward flexed trunk twist (FFTT) and seated straight leg raise (SLR) compared to a traditionally designed athletic warm-up on active shoulder internal rotation (IR) and external rotation (ER) in healthy overhead athletes measured with the Clinometer© smartphone application. Participants included twenty-two NCAA Division I, III, Club, and Secondary School senior student-athletes (9 javelin, 7 volleyball, 6 baseball; 13-females, 9-males; age= 19.3±1.1 years; height= 178±11.4 cm; weight= 76.4±11.2 kg), randomly assigned to TMR® (TMRG; n=11) and traditional warm-up (TWG; n=11) groups. The TMRG performed 3 sets of FFTT and SLR, each held for 20 seconds to the side of ease. The TWG completed a traditionally designed athletic warm-up including running, athletic drills, and dynamic and static stretching. The TMRG experienced significantly greater increases in dominant shoulder IR, non-dominant shoulder IR, and non-dominant shoulder ER (mean change =+9.5°, +7.5o, +4.7o), than the TWG (+1.7°, -6.7°, -4°) respectively. Intervention time to completion was also different between groups (TMRG = 7mins TWG = 25mins). This study indicates that an indirect TMR® application produces efficient meaningful changes in rotational active range of motion (AROM) of the shoulder in overhead athletes.
... A contralateral effect has been described, whereby exercising one limb prevents the atrophy of an immobilized contralateral limb [67,68]. Such studies have generally shown that eccentric exercise of the dominant arm [69], or leg [70], protects against the loss of size and function of the contralateral limb. ...
... It has been demonstrated that unilateral immobilization of a limb results in systemic metabolic disruption characterized by mitochondrial dysfunction in the immobilized limb [71], aligning with the results of the present study. Indeed, the clinical potential and implications of contralateral rehabilitation have not gone unnoticed [68]. ...
Background
Metabolic disruption commonly follows Anterior Cruciate Ligament Reconstruction (ACLR) surgery. Brief exposure to low amplitude and frequency pulsed electromagnetic fields (PEMFs) has been shown to promote in vitro and in vivo murine myogeneses via the activation of a calcium–mitochondrial axis conferring systemic metabolic adaptations. This randomized-controlled pilot trial sought to detect local changes in muscle structure and function using MRI, and systemic changes in metabolism using plasma biomarker analyses resulting from ACLR, with or without accompanying PEMF therapy.
Methods
20 patients requiring ACLR were randomized into two groups either undergoing PEMF or sham exposure for 16 weeks following surgery. The operated thighs of 10 patients were exposed weekly to PEMFs (1 mT for 10 min) for 4 months following surgery. Another 10 patients were subjected to sham exposure and served as controls to allow assessment of the metabolic repercussions of ACLR and PEMF therapy. Blood samples were collected prior to surgery and at 16 weeks for plasma analyses. Magnetic resonance data were acquired at 1 and 16 weeks post-surgery using a Siemens 3T Tim Trio system. Phosphorus (³¹P) Magnetic Resonance Spectroscopy (MRS) was utilized to monitor changes in high-energy phosphate metabolism (inorganic phosphate (Pi), adenosine triphosphate (ATP) and phosphocreatine (PCr)) as well as markers of membrane synthesis and breakdown (phosphomonoesters (PME) and phosphodiester (PDE)). Quantitative Magnetization Transfer (qMT) imaging was used to elucidate changes in the underlying tissue structure, with T1-weighted and 2-point Dixon imaging used to calculate muscle volumes and muscle fat content.
Results
Improvements in markers of high-energy phosphate metabolism including reductions in ΔPi/ATP, Pi/PCr and (Pi + PCr)/ATP, and membrane kinetics, including reductions in PDE/ATP were detected in the PEMF-treated cohort relative to the control cohort at study termination. These were associated with reductions in the plasma levels of certain ceramides and lysophosphatidylcholine species. The plasma levels of biomarkers predictive of muscle regeneration and degeneration, including osteopontin and TNNT1, respectively, were improved, whilst changes in follistatin failed to achieve statistical significance. Liquid chromatography with tandem mass spectrometry revealed reductions in small molecule biomarkers of metabolic disruption, including cysteine, homocysteine, and methionine in the PEMF-treated cohort relative to the control cohort at study termination. Differences in measurements of force, muscle and fat volumes did not achieve statistical significance between the cohorts after 16 weeks post-ACLR.
Conclusion
The detected changes suggest improvements in systemic metabolism in the post-surgical PEMF-treated cohort that accords with previous preclinical murine studies. PEMF-based therapies may potentially serve as a manner to ameliorate post-surgery metabolic disruptions and warrant future examination in more adequately powered clinical trials.
The Translational Potential of this Article
Some degree of physical immobilisation must inevitably follow orthopaedic surgical intervention. The clinical paradox of such a scenario is that the regenerative potential of the muscle mitochondrial pool is silenced. The unmet need was hence a manner to maintain mitochondrial activation when movement is restricted and without producing potentially damaging mechanical stress. PEMF-based therapies may satisfy the requirement of non-invasively activating the requisite mitochondrial respiration when mobility is restricted for improved metabolic and regenerative recovery.
... Questions for the third theme were informed by both seminal works [29][30][31][32] and the most recent syntheses of the available evidence [12,15,20]. Questions on the practical aspects and on the clinical outreach (themes 4 and 5) were developed iteratively by the members of the research team (AM, FD, TH) and based on the few clinically oriented reviews that are available [10,13,14,33]. mirror feedback training) [21]. The transfer effect is generally considered muscle-specific, mainly involving the contralateral homologous muscles, even though a small spatially distributed effect to at least synergists can occur [22]. ...
... The clinical relevance of cross-education, which has been the topic of a number of clinically oriented reviews [10,11,13,14,33], was one of the five themes of the present Delphi process, and was assessed by 5 questions (22,23,(25)(26)(27). In round 1, > 90% of respondents agreed on the potential clinical utility of the transfer, both for strength and motor skills. ...
Background
Cross-education refers to increased motor output (i.e., force generation, skill) of the opposite, untrained limb following a period of unilateral exercise training. Despite extensive research, several aspects of the transfer phenomenon remain controversial.
Methods
A modified two-round Delphi online survey was conducted among international experts to reach consensus on terminology, methodology, mechanisms of action, and translational potential of cross-education, and to provide a framework for future research.
Results
Through purposive sampling of the literature, we identified 56 noted experts in the field, of whom 32 completed the survey, and reached consensus (75% threshold) on 17 out of 27 items.
Conclusion
Our consensus-based recommendations for future studies are that (1) the term ‘cross-education’ should be adopted to refer to the transfer phenomenon, also specifying if transfer of strength or skill is meant; (2) functional magnetic resonance imaging, short-interval intracortical inhibition and interhemispheric inhibition appear to be promising tools to study the mechanisms of transfer; (3) strategies which maximize cross-education, such as high-intensity training, eccentric contractions, and mirror illusion, seem worth being included in the intervention plan; (4) study protocols should be designed to include at least 13–18 sessions or 4–6 weeks to produce functionally meaningful transfer of strength, and (5) cross-education could be considered as an adjuvant treatment particularly for unilateral orthopedic conditions and sports injuries. Additionally, a clear gap in views emerged between the research field and the purely clinical field.
The present consensus statement clarifies relevant aspects of cross-education including neurophysiological, neuroanatomical, and methodological characteristics of the transfer phenomenon, and provides guidance on how to improve the quality and usability of future cross-education studies.
... Another concept that sometimes is investigated when examining CT is the so-called "asymmetrical transfer" (AT), term that implies that the magnitude of transfer is not even for the two directions (i.e. it differs from dominant to non-dominant and from non-dominant to dominant limb or from right to left limb and vice versa) [1]. When referring to CT of strength or skills of the upper limbs, in some researches it has been argued that adaptations to the non-trained limb are greater when the dominant limb (i.e. the most proficient) receives the training [1,5,6] or that can be totally absent after left-arm training [5] revealing, in this way the existence of AT, while in others that CT of strength is bi-directional (symmetrical) between dominant and non-dominant sides after unilateral training of either the dominant or non-dominant limb in right-handed individuals [7]. Concerning CT of skills in the lower limbs, a study concluded that there was AT of a learned skill (moving a cursor towards targets using ankle movements) since CT occurred only from the non-dominant to the dominant side and not vice versa [8] while in a different study it was found that they didn't exist side-specific differences in the amount of CT from the right to the left side or vice versa in a novel ankle isometric force control skill [9]. ...
... As for studies that investigated leg dominance in relation to CT of locomotor 80 Investigation of the Effects of Leg Dominance on Cross-Transfer of Flexibility after a Unilateral Treatment with Foam Roller -A Pilot Study skills, differences in the amount of CT from the right to the left side or vice versa weren't found neither in a newly acquired locomotor skill (stepping over an obstacle on a treadmill) [10] nor during walking with a new motor learning task for one limb [11]. The investigation of CT is a promising step in the field of rehabilitation, since it could provide an alternative solution for the partial maintenance of some parameters of the physical condition during the period of immobilization of an injured limb through the training of its opposite limb [1,6,12]. Concerning AT, it also consists an important parameter that should be investigated in order to verify if differences should be expected depending on which limb receives the training (the dominant or the non-dominant). ...
... Despite its long known existence, cross-education has only recently been employed to augment the rehabilitation of asymmetrical limb disorders (Andrushko et al. 2018a, b;Hendy et al. 2012;Magnus et al. 2013). Cross-education has broad clinical utility as it has been shown to attenuate strength loss and muscle atrophy for the contralateral, immobilized limb , Magnus et al. 2013Andrushko et al. 2018b) and improve strength and functional outcomes for the affected limb of hemiplegic stroke patients (Dragert and Zehr 2013;Kim et al. 2015;Sun et al. 2018). ...
... Despite thorough reviews (Andrushko et al. 2018a;Hendy et al. 2012;Manca et al. 2018) outlining key aspects and candidate mechanisms for cross-education, discussion of the cross-limb transfer in rapid force is generally absent. The critical nature of rapid force for sport and daily living activities illustrates the value of examining this motor control property in an untrained homologous muscle. ...
PurposeThis study examined the time course of contralateral adaptations in maximal isometric strength (MVC), rate of force development (RFD), and rate of electromyographic (EMG) rise (RER) during 4 weeks of unilateral isometric strength training with the non-dominant elbow flexors.Methods
Twenty participants were allocated to strength training (n = 10, three female, two left hand dominant) or control (n = 10, three female, two left hand dominant) groups. Both groups completed testing at baseline and following each week of training to evaluate MVC strength, EMG amplitude, RFD and RER at early (RFD50, RER50) and late (RFD200, RER200) contraction phases for the dominant ‘untrained’ elbow flexors. The training group completed 11 unilateral isometric training sessions across 4 weeks.ResultsThe contralateral improvements for MVC strength (P < 0.01) and RFD200 (P = 0.017) were evidenced after 2 weeks, whereas RFD50 (P < 0.01) and RER50 (P = 0.02) showed significant improvements after 3 weeks. Each of the dependent variables was significantly (P < 0.05) greater than baseline values at the end of the training intervention for the trained arm. No changes in any of the variables were observed for the control group (P > 0.10).Conclusions
Unilateral isometric strength training for 2–3 weeks can produce substantial increases in isometric muscle strength and RFD for both the trained and untrained arms. These data have implications for rehabilitative exercise design and prescription.
... At the segmental level, the amplitude of contralateral Hoffman reflex has been demonstrated to be reduced in the lower limb [66] and in the upper limb [15,19]. Additionally, interhemispheric regulation through transcallosal pathways and therefore increase in corticospinal excitability of the contralateral side might occur [54,67] and thus yield a bilateral corticospinal activity [15,68,69]. Moreover, as about 10 to 15% of the ventral corticospinal fibers do not decussate at the medulla, the role of the ipsilateral fibers to the non-exercised limb could account for the cross-transfer of muscle activity we have observed [69,70]. ...
... Additionally, interhemispheric regulation through transcallosal pathways and therefore increase in corticospinal excitability of the contralateral side might occur [54,67] and thus yield a bilateral corticospinal activity [15,68,69]. Moreover, as about 10 to 15% of the ventral corticospinal fibers do not decussate at the medulla, the role of the ipsilateral fibers to the non-exercised limb could account for the cross-transfer of muscle activity we have observed [69,70]. Therefore, the motor irradiation observed during the 30-s exercise seemed to be independent of the sex of the participants. ...
Abstract Background While performing a unilateral muscle contraction, electrical muscle activity also arises in the contralateral homologous muscle, muscle group, or limb. When the muscle contraction induces muscle fatigue, females show not only a greater resistance than males but also a reduced contralateral muscle activation. The study aimed at investigating whether, during a high-intensity 30-s unilateral maximal effort isometric leg extension exercise, the contralateral non-exercising limb (NEL) knee extensor muscle activation would differ between females and males. Methods Twenty participants, 11 females (23.80 ± 2.15 years old) and 9 males (26.50 ± 2.45 years old), performed a unilateral 30-s exercise while surface electromyography (sEMG) was measured from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) on both limbs. The maximal voluntary contraction (MVC) was measured for both the exercising limb (EL) and the NEL before (MVC PRE) and after (MVC POST) the 30-s exercise to assess muscle fatigue. Results While both females and males exhibited muscle fatigue in the EL (p = 0.015), females exhibited a lower MVC reduction than males (p = 0.042), suggesting that females were less fatigued than males. Although no muscle fatigue, i.e., no MVC force reduction was found in the NEL for either group before and after the 30-s exercise, the muscle activity of the VL was found to be of greater magnitude during the MVC POST only for females (p = 0.047) while it remained unchanged for males. During the 30-s exercise, the force output of the EL decreased only for males (p = 0.029) while females showed a preservation of the force output (p > 0.05). The sEMG activity of the NEL during the 30-s unilateral exercise increased for both groups in all measured muscles (all p-values
... For example, effortful upper limb tasks such as lifting typically require co-activation of homologous muscle groups, whereas movements in the lower limbs often involve muscle pairs working in a reciprocal manner (such as gait). Further investigation of the properties of crossactivation specific to the lower limb is warranted, particularly when considering the potential for cross-activation and crosseducation to be utilized in unilateral lower limb rehabilitation settings such as anterior cruciate ligament (ACL) reconstruction and knee replacement (Hendy et al., 2012;Chiou et al., 2013a). ...
... The increase in background EMG of the resting limb during demanding single limb tasks has been frequently observed in the upper limb, and has been termed ''motor irradiation'' (Cernacek, 1961;Hendy et al., 2012). We asked participants to minimize these effects in order to remain consistent with previous literature, and also to provide a more simple interpretation of the neurophysiological response to single limb contractions. ...
Transcranial magnetic stimulation (TMS) studies have demonstrated that unilateral muscle contractions in the upper limb produce motor cortical activity in both the contralateral and ipsilateral motor cortices. The increase in excitability of the corticomotor pathway activating the resting limb has been termed “cross-activation”, and is of importance due to its involvement in cross-education and rehabilitation. To date, very few studies have investigated cross-activation in the lower limb. Sixteen healthy participants (mean age 29 ± 9 years) took part in this study. To determine the effect of varying contraction intensities in the lower limb, we investigated corticomotor excitability and intracortical inhibition of the right rectus femoris (RF) while the left leg performed isometric extension at 0%, 25%, 50%, 75% and 100% of maximum force output. Contraction intensities of 50% maximal force output and greater produced significant cross-activation of the corticomotor pathway. A reduction in silent period duration was observed during 75% and 100% contractions, while the release of short-interval intracortical inhibition (SICI) was only observed during maximal (100%) contractions. We conclude that increasing isometric contraction intensities produce a monotonic increase in cross-activation, which was greatest during 100% force output. Unilateral training programs designed to induce cross-education of strength in the lower limb should therefore be prescribed at the maximal intensity tolerable.
... A Educação Cruzada corresponde à adaptação neural em que ocorre a melhoria de desempenho do membro não treinado após um período de prática unilateral do membro contralateral homólogo 6 . Sendo assim, há uma transferência de força por meio de mecanismos do córtex motor, em que estruturas como o corpo caloso auxiliam na atividade cortico-espinhal e na interação hemisférica durante o movimento unilateral 7 . ...
A educação cruzada corresponde a uma adaptação neural em que ocorre a melhoria de desempenho do membro não treinado após um período de prática unilateral do membro contralateral homólogo. Sendo assim, há uma transferência de força por meio de mecanismos do córtex motor durante o movimento unilateral. O objetivo do estudo foi investigar os efeitos de diferentes protocolos de pré-ativação antagonista contralateral sobre o desempenho de repetições múltiplas. Quinze mulheres treinadas realizaram quatro protocolos usando cargas máximas de dez repetições em um total de três séries nos exercícios cadeira extensora (CE) e cadeira flexora (CF): protocolo preferido flexor-extensor (PPFE) CF membro não preferido + CE membros preferido; protocolo preferido extensor-flexor (PPEF) CE membro não preferido + CF membro preferido; protocolo não preferido extensor-flexor (PNPEF) CE membro preferido + CF membro não preferido; protocolo não preferido flexor-extensor (PNPFE) CF membro preferido + CE membro não preferido; Foi adotado um intervalo de dois minutos entre as séries e exercícios. Verificou-se um volume total de treinamento significativamente maior no protocolo flexor-extensor para a CE e no protocolo extensor-flexor para a CF. Na CE verificou um aumento significativo no tempo sob tensão (TST) no membro não preferido versus preferido no protocolo flexor-extensor. Enquanto na CF o tempo sob tensão foi significativamente maior no protocolo extensor-flexor para ambos os membros. Não houve diferença significativa entre os protocolos e exercícios para percepção subjetiva de esforço. A pré-ativação antagonista contralateral permitiu um aumento no volume total de treinamento e um aumento no tempo sob tensão em ambos os protocolos durante a CE e CF sendo uma possível alternativa para tal objetivo.
... Besides, a present meta-analysis revealed that the effect of mirror training performed with the functional tasks on motor performance is weak in healthy individuals 15 . The studies about cross-education revealed that the level of contraction force affects cross-activation 36,37 . ...
Aim: Unilateral exercise training is an effective and useful technique, especially in immobilization and neurological conditions, but the effect of unilateral muscle exercise training on muscle strength is modest. Therefore, the aim of this study is to detect the acute concomitant effect of mirror therapy and unilateral exercise training on muscle strength and joint position sense in healthy adults.Method: Thirty-one participants were randomly enrolled in two groups the mirror (n=16) and control groups (n=15). Hand grip (HG), pinch grip (PG) strengths, and joint position sense (JPS) of the wrist were assessed in both hands before and after a single exercise session which include 300 repetitive ball squeezing exercises by right (exercised) hand for all groups. The participants in the mirror group were asked to watch the mirror to see the reflection of their exercised hands, the control group only watched their exercised and unexercised hands without any visual feedback support during the exercise session. Repeated Measure ANOVA and Mixed ANOVA tests were performed to analyze in- and between-group differences.Results: The statistically significant differences were determined in unexercised hand HG and PG strength in the mirror group (F=10,105; p=0,006, ηp2=0,403; F=5,341; p=0,035; ηp2=0,263, respectively). However, any group×time interaction was found in JPS, HG, or PG tests (p<0;05). Additionally, no difference was shown in JPS in-group comparisons (p<0;05).Conclusion: The result of the study suggested that unilateral exercise training should apply concomitant with visual feedback. Further studies are needed to compare the effect of different sensory feedbacks on unilateral exercise training.
... First described by Scripture and colleagues in 1894 (Scripture et al., 1894), cross-education has since been reported in numerous studies (for reviews, see Carroll et al., 2006;Ruddy & Carson, 2013). Indeed, unilateral strength training of the contralateral limb has been postulated to benefit recovery after unilateral limb injuries (Andrushko et al., 2018;Hendy et al., 2012;Pearce et al., 2013) or in neurological rehabilitation settings such as stroke where impairments to one limb are evident (Ehrensberger et al., 2016). Importantly, the type of muscle contractions (i.e. ...
Cross-education is the phenomenon where training of one limb can cause neuromuscular adaptations in the opposite untrained limb. This effect has been reported to be greater after eccentric (ECC) than concentric (CON) strength training; however, the underpinning neurophysiological mechanisms remain unclear. Thus, we compared responses to transcranial magnetic stimulation (TMS) in both motor cortices following single sessions of unilateral CON and ECC exercise of the elbow flexors. Fourteen healthy adults performed 3 sets of 10 CON or ECC right elbow flexor contractions at 75% of respective maximum on separate days. Elbow flexor maximal voluntary isometric contraction (MVIC) torques were measured before and after exercise, and responses to single- and paired-pulse TMS were recorded from the non-exercised left and exercised right biceps brachii. Pre-exercise and post-exercise responses for ECC and CON were compared by repeated measures analyses of variance (ANOVAs). MVIC torque of the exercised arm decreased (P<0.01) after CON (-30±14%) and ECC (-39±13%) similarly. For the non-exercised left biceps brachii, resting motor threshold (RMT) decreased after CON only (-4.2±3.9% of maximum stimulator output [MSO], p<0.01) and intracortical facilitation (ICF) decreased (-15.2±20.0%, P=0.038) after ECC only. For the exercised right biceps, RMT increased after ECC (8.6±6.2% MSO, P=0.014) but not after CON (6.4±8.1% MSO, P=0.066). Thus, unilateral ECC and CON elbow flexor exercise modulated excitability differently for the non-exercised hemisphere. These findings suggest that responses after a single bout of exercise may not reflect longer term adaptations.
... Researchers and health practitioners have had a continued interest in the cross-education because it not only raises questions about the mechanisms of neural plasticity in response to unilateral exercise, but also has clinical implications, such as in rehabilitation for paresis post stroke, or after a single limb injury or surgical operation [4][5][6][7][8][9]. In respect to physiological mechanisms, the general consensus is that cross-education is mainly manifested by adaptations in the central nervous system (CNS). ...
It is known that resistance exercise using one limb can affect motor function of both the exercised limb and the unexercised contralateral limb, a phenomenon termed cross-education. It has been suggested that cross-education has clinical implications, e.g. in rehabilitation for orthopaedic conditions or post-stroke paresis. Much of the research on the contralateral effect of unilateral intervention on motor output is based on voluntary exercise. This scoping review aimed to map the characteristics of current literature on the cross-education caused by three most frequently utilised peripheral neuromuscular stimulation modalities in this context: electrical stimulation, mechanical vibration and percutaneous needling, that may direct future research and translate to clinical practice. A systematic search of relevant databases (Ebsco, ProQuest, PubMed, Scopus, Web of Science) through to the end of 2020 was conducted following the PRISMA Extension for Scoping Review. Empirical studies on human participants that applied a unilateral peripheral neuromuscular stimulation and assessed neuromuscular function of the stimulated and/or the unstimulated side were selected. By reading the full text, the demographic characteristics, context, design, methods and major findings of the studies were synthesised. The results found that 83 studies were eligible for the review, with the majority (53) utilised electrical stimulation whilst those applied vibration (18) or needling (12) were emerging. Although the contralateral effects appeared to be robust, only 31 studies claimed to be in the context of cross-education, and 25 investigated on clinical patients. The underlying mechanism for the contralateral effects induced by unilateral peripheral stimulation remains unclear. The findings suggest a need to enhance the awareness of cross-education caused by peripheral stimulation, to help improve the translation of theoretical concepts to clinical practice, and aid in developing well-designed clinical trials to determine the efficacy of cross-education therapies.
... This adaptive phenomenon, which is commonly attributed to neurally mediated mechanisms and is usually referred to as cross-education [1][2][3], has been observed for a variety of muscles (knee extensors, ankle plantar/dorsiflexors, elbow flexors) and resistance training modalities (concentric, eccentric, isometric) including neuromuscular electrical stimulation (NMES) [1,2,4,5]. The value of cross-education for restoring muscle (and physical) function in patients with unilateral impairments induced by injury, surgery, or neurological damage has only recently been considered [6,7], and thus evidence for effectiveness is still limited, and clinical utility remains elusive. ...
We compared the effectiveness of a home-based neuromuscular electrical stimulation (NMES) program applied to the quadriceps of the nonoperative side against sham-NMES as a complement to standard rehabilitation on knee extensor neuromuscular function in patients following anterior cruciate ligament (ACL) reconstruction. Twenty-four patients completed the 6 week NMES (n = 12) and sham-NMES (n = 12) post-operative interventions and were tested at different time points for neuromuscular function and self-reported knee function. Isometric, concentric, and eccentric strength deficits (muscle weakness) increased significantly from pre-surgery to 24 weeks post-surgery in the sham-NMES group (p < 0.05), while no significant changes were observed in the NMES group. On the stimulated (nonoperative) side, quadriceps voluntary activation and muscle thickness were respectively maintained (p > 0.05) and increased (p < 0.001) as a result of the NMES intervention, contrary to sham-NMES. Self-reported knee function improved progressively during the post-operative phase (p < 0.05), with no difference between the two groups. Compared to a sham-NMES intervention, a 6 week home-based NMES program applied to the quadriceps of the nonoperative side early after ACL reconstruction prevented the occurrence of knee extensor muscle weakness 6 months after surgery. We conclude that nonoperative-side NMES may help counteract muscle weakness after ACL reconstruction.
... Ai giorni nostri gli esperti sono d'accordo sul fatto che gli adattamenti neurali siano al centro del fenomeno e che i meccanismi corticali, spinali e periferici siano anch'essi coinvolti (Hendy et Al, 2012). ...
Lo scopo del presente studio è stato quello di mettere a confronto due metodologie di stretching: quella tradizionale di allungamento-mantenimento e quella di facilitazione neuromuscolare propriocettiva (PNF).
Queste sono state applicate all'esercizio di allungamento per la capsula articolare posteriore della spalla, chiamato sleeper stretch.
I soggetti che hanno preso parte allo studio sono sportivi praticanti discipline overhead: giavellottisti, giocatori di baseball e pallavolisti. La ripetizione continua delle azioni sport specifiche genera in questi atleti adattamenti anatomici e biomeccanici all'articolazione della spalla. In particolare lo studio si è focalizzato su uno di questi, il GIRD (Gleno-humeral Internal Rotation Deficit), ossia un parametro che indica una ridotta mobilità della rotazione interna della spalla dell'arto dominante.
Dopo 4 settimane di trattamento, che ha previsto l'esecuzione di uno specifico protocollo di stretching scelto casualmente tra tradizionale e PNF, tutti gli atleti avevano incrementato in maniera significativa la rotazione interna dell'arto dominante. Inoltre è stato visto che anche la rotazione interna dell'arto non dominante, al quale non era stato applicato alcun trattamento, era incrementata significativamente ed è stato ipotizzato un possibile effetto cross-over. Il confronto delle due metodologie di stretching non ha evidenziato delle differenze significative in termini di efficacia. Questo probabilmente a causa della complessità e difficoltà di esecuzione del protocollo PNF che può aver compromesso le sue potenzialità. Sicuramente un periodo di familiarizzazione con questa metodologia di allungamento avrebbe massimizzato gli effetti del trattamento.
... 1,30 However, the precise locations of those adaptations remain unclear. 3 Although cross-education effect is likely to be attributed to increases in corticospinal excitability in both contralateral and ipsilateral primary motor cortexes, 3 decreased inhibition in the ipsilateral cortex not directly involved in the motor task, 35,36 and the development of new motor engrams due to new motor learning. 37,38 With specific respect to eccentric exercise, it has been postulated that eccentric training uniquely modulates corticospinal excitability and inhibition of the untrained limb to a greater extent than concentric training, which may induce a shift in motor unit recruitment 39 and an enhancement in αmotoneuron excitability 40 in the contralateral limb muscles. ...
Purpose
We investigated the effects of three different unilateral isoinertial resistance training protocols with eccentric-overload on changes in lean mass and muscle function of trained (TL) and contralateral non-trained (NTL) legs.
Methods
Physically-active university students were randomly assigned to one of three training groups or a control group (n=10/group). Participants in the training groups performed dominant-leg isoinertial squat training twice a week for 6 weeks (4 sets of 7 repetitions) using either an electric-motor device with an eccentric phase velocity of 100% (EM100) or 150% (EM150) of concentric phase velocity or a conventional flywheel device (FW) with the same relative inertial load. Changes in thigh lean mass, unilateral leg-press one-repetition maximum (1-RM), muscle power at 40-80% 1-RM, and unilateral vertical jump height before and after training were compared between the groups and between TL and NTL.
Results
No changes in any variable were found for the control group. In TL, all training groups showed similar increases (P<0.05) in 1-RM strength (22.4-30.2%), lean tissue mass (2.5-5.8%), muscle power (8.8-21.7%) and vertical jump height (9.1-32.9%). In NTL, 1-RM strength increased 22.0-27.8% without significant differences between groups, however increases in lean mass (P<0.001) were observed for EM150 (3.5%) and FW (3.8%) only. Unilateral vertical jump height (6.0-32.9%) and muscle power (6.8-17.5%) also increased in NTL without significant differences between training groups.
Conclusion
The three eccentric-overload resistance training modalities produced similar neuromuscular changes in both the trained and non-trained legs, suggesting that strong cross-education effects were induced by the eccentric-overload training.
... Importantly, by using a within-person unilateral design, inter-individual differences in potential for hypertrophy and strength gains are minimized. However, the control arm (i.e., without added leg training) could be subject to cross-education, i.e., an enhanced performance due to neural factors, potentially blunting effects of elevated hormonal levels (16,18,20,26,28). Therefore, bilateral training and multiple-group designs examining the effect of lower-body resistance training on upper-body strength performances are of interest. ...
Resistance exercise has been shown to induce an acute hormonal response. The purpose of this study was to examine upper-body adaptations and the endocrine response to strength training in men and women when subjected to two different types of lower-body resistance training protocols. Nine males and eight females were assigned to either a Heavy Load (HL) (N = 10) or Mixed Load (ML) (N = 7) training routine three times per week for ten weeks. The HL-group executed low-volume, high-load resistance exercise for both lower and upper-body (4-6 reps at 80-90% of one repetition maximum (1-RM), three-minute inter-set rest). The ML-group performed the HL-protocol for the upper-body, but a high-volume, moderate-load protocol for the lower body (10-15 reps at 60-70% of 1-RM, one-minute inter-set rest). Volume load, 1-RM strength and hormonal measurements were analyzed by repeated-measures linear mixed models. Both groups increased their 1-RM in all assessments (p < 0.01) with no significant difference between groups at any time. Growth hormone (GH), testosterone and bioavailable testosterone (T/SHBG) increased in both groups during a standardized exercise session (p < 0.01) with ML having a greater increase in GH. The notion that acute elevations in anabolic hormones is important for muscle strength adaptation cannot be supported by the present study.
... Patients with TKA usually develop interlimb asymmetries (decrements in muscle size, strength, and voluntary activation) as a consequence of decreased mobilization before surgery and especially in the early post-operative phase (1,13). A review discussing the application of cross education during immobilization reported preservative short-term effects of unilateral training on muscle function of the immobilized, untrained leg (14) indicating cross education as a potential therapeutic approach for restoring limb symmetry and in turn improving recovery of function after TKA (15). However, the literature on how to benefit from cross education effects in orthopedic population is limited (16)(17)(18)(19)(20). ...
Background: Continuous passive motion (CPM) is frequently used during rehabilitation following total knee arthroplasty (TKA). Low-load resistance training (LLRT) using continuous active motion (CAM) devices is a promising alternative. We compared the effectiveness of CPM with LLRT using the affected leg (CAMuni) and both legs (CAMbi) in the early postoperative rehabilitation. Hypotheses: (I) LLRT (CAMuni and CAMbi) is superior to CPM, (II) additional training of the unaffected leg (CAMbi) is more effective than unilateral training (CAMuni).
Materials and Methods: Eighty-five TKA patients were randomly assigned to three groups, respectively: (i) unilateral CPM of the operated leg; (ii) unilateral CAM of the operated leg (CAMuni); (iii) bilateral alternating CAM (CAMbi). Patients were assessed one day before TKA (pre-test), one day before discharge (post-test), and three months postoperatively (follow-up). Primary outcome: active knee flexion range of motion (ROMFlex). Secondary outcomes: active knee extension ROM (ROMExt), swelling, pain, C-reactive protein, quality of life (Qol), physical activity, timed-up-and-go performance, stair-climbing performance, quadriceps muscle strength. Analyses of covariances were performed (intention-to-treat and per-protocol).
Results:
Hypothesis I:
Primary outcome: CAMbi resulted in a higher ROMFlex of 9.0° (95%CI -18.03 to 0.04°, d=0.76) and 6.3° (95%CI -14.31 to 0.99°, d=0.61) compared to CPM at post-test and follow-up, respectively.
Secondary outcomes: At post-test, C-reactive protein was lower in both CAM groups compared with CPM. Knee pain was lower in CAMuni compared to CPM. Improved ROMExt, reduced swelling, better stair-climbing and timed-up-and-go performance were observed for CAMbi compared to CPM. At follow-up, both CAM groups reported higher Qol and CAMbi showed a better timed-up-and-go performance.
Hypothesis II:
Primary outcome: CAMbi resulted in a higher knee ROMFlex of 6.5° (95% CI -2.16 to 15.21°, d=0.56) compared to CAMuni at post-test.
Secondary outcomes: At post-test, improved ROMExt, reduced swelling, and better timed-up-and-go performance were observed in CAMbi compared to CAMuni.
Conclusions: Additional LLRT of the unaffected leg (CAMbi) proved to be more effective for recovery of function than training of the affected leg only (CAMuni), which may be mediated by positive transfer effects from the unaffected to the affected limb (cross education) and/or preserved neuromuscular function of the trained, unaffected leg.
... High neural stimulus and muscular adaptations resulting in strength increases of the contralateral limb after performing high load unilateral exercises are well documented in the literature (Cirer-Sastre et al., 2017;Fisher, 2018). This concept of "cross education" was utilized during weeks one to six of the rehabilitation to increase strength and prevent atrophy, particularly within the calf musculature during the period of immobilization (Farthing & Zeir, 2014;Hendy et al., 2012;Lepley & Palmieri-Smith, 2014). ...
Lisfranc injuries, often accompanied with tarsometatarsal joint (TMTJ) disruption, are not well documented in football despite becoming increasingly more prevalent within other athletic populations. Currently there is a paucity of evidence documenting prognosis , rehabilitation strategy and outcome. The presented case summarizes the conservative rehabilitation and return to play of a 26-year-old elite professional footballer who presented with a Lisfranc injury alongside a 3 rd TMTJ coalition stress response. Injury was sustained when landing awkwardly from a jump causing the midfoot to be forced into a hyper-plantarflexed position. Palpation identified tenderness over the 2 nd and 3 rd MT, with a positive piano key test. Magnetic resonance imaging (MRI), computed tomography (CT), stork view x-ray and review from a leading foot and ankle specialist confirmed diagnosis, post-contradictory MRI results. Presented is a summary of the assessment process, conservative management of the injury and the resultant rehabilitation process followed, which led to the successful return to play of the athlete. ARTICLE HISTORY
... Since the left hemisphere is mainly responsible for muscle dynamics, 104 the cross-education effect of unilateral strength training might be higher in right-handed individuals. 111,112 The more significant improvements in grip strength in both EGs compared with CG are in contrast to the results of Dilek et al, 63 who examined the effects of a graded MI program after DRF. In their study, the MI group performed better on all functional outcome measures except grip strength. ...
Study Design: A randomized, single-blinded controlled trial.
Introduction: Therapy results after distal radius fractures (DRF) especially with older patients are often suboptimal. One possible approach for counteracting the problems are motor-cognitive training in- terventions such as Mental Practice (MP) or Mirror Therapy (MT), which may be applied in early reha- bilitation without stressing the injured wrist.
Purpose of the Study: The aim of the study is to investigate the effects of MP and MT on wrist function after DRF. The pilot study should furthermore provide information about the feasibility of these methods. Methods: Thirty-one women were assigned either to one of the two experimental groups (MP, MT) or to a control group (relaxation intervention). The participants completed a training for six weeks, adminis- tered at their homes. Measurements were taken at four times (weeks 0, 3, 6 and 12) to document the progression in subjective function (PRWE, QuickDASH) and objective constraints of the wrist (ROM, grip strength) as well as in health-related quality of life (EQ-5D).
Results: The results indicated that both experimental groups showed higher improvements across the intervention period compared to the control group; e.g. PRWE: MT 74.0%, MP 66.2%, CG 56.9%. While improvements in grip strength were higher for the MP group, the MT group performed better in all other measures. However, time by group interactions approached significance at best; e.g. ROM: p = .076; h2p = .141.
Conclusion: The superiority of MP as well as MT supports the simulation theory. Motor-cognitive inter- vention programs are feasible and promising therapy supplements, which may be applied in early rehabilitation to counteract the consequences of immobilization without stressing the injured wrist.
... 8,11 Although the neurophysiological adaptations to contralateral training are still debated, experimental findings on chronic unilateral training seem to assign a putative role for a combination of increased excitability and decreased inhibition in the ipsilateral hemisphere that may act as relevant neurophysiological correlates of contralateral training. 12,13 The transfer of performance has been demonstrated in healthy individuals, 8,9 orthopedic conditions, 14 stroke survivors 15,16 and, more recently, in multiple sclerosis (MS). 9,17 However, from a rehabilitative perspective, it has been pointed out that this indirect approach should not be recommended straightaway if the training goal is to improve not only strength but also functional outcomes. ...
Objective:
Direct strength training (DST) is effective in managing unilateral weakness in people with multiple sclerosis (MS). Its feasibility, however, is considerably reduced if one limb is too compromised to train. In this case, contralateral strength training (CST) of the unaffected side to induce a strength transfer to the untrained homologous muscles can help to establish a strength baseline in the weaker limb, eventually allowing direct training. Limited effects for CST, however, have been reported on patient's functioning. We tested the effects on dynamometric, electromyographic and functional outcomes of a sequential combination of CST and DST of the ankle dorsiflexors in a case of MS-related foot-drop.
Methods (case description):
A 56-year-old man diagnosed with relapsing-remitting MS, who exhibited severe weakness of the right dorsiflexors impairing functional dorsiflexion. The intervention consisted of a 6-week CST of the unaffected dorsiflexors followed by two consecutive 6-week DST cycles targeting the weaker dorsiflexors.
Results:
At baseline, the participant could not dorsiflex his right ankle but could do so after CST. Maximal strength of the affected dorsiflexors increased by 80% following CST, by 31.1% following DST-1 and by further 44.6% after DST-2. Neuromuscular recruitment was found progressively increased, with the largest changes occurring after DST-1. Improvements in mobility and walking speed were also detected, although plantarflexors' spasticity on the Modified Ashworth Scale increased from 1+ to 2.
Conclusion:
In this case the sequential combination of CST and DST proved a feasible approach to manage severe unilateral weakness in a patient who was not able, at least initially, to dorsiflex his weaker ankle. In this perspective, CST may prime a minimum gain in strength necessary to allow subsequent direct training.
... During immobilization of a limb, following bone fracture for example, there is significant loss of muscle mass. Physical training of the contralateral (free) limb has been shown to prevent, or slow down this process, resulting in reduced loss of muscle volume in the immobilized arm [33,34]. Training based on CE was shown also to improve grip precision learning and force in the hemiparetic UL [35][36][37][38]. ...
Aims
Modalities for rehabilitation of the neurologically affected upper-limb (UL) are generally of limited benefit. The majority of patients seriously affected by UL paresis remain with severe motor disability, despite all rehabilitation efforts. Consequently, extensive clinical research is dedicated to develop novel strategies aimed to improve the functional outcome of the affected UL. We have developed a novel virtual-reality training tool that exploits the voluntary control of one hand and provides real-time movement-based manipulated sensory feedback as if the other hand is the one that moves. The aim of this study was to expand our previous results, obtained in healthy subjects, to examine the utility of this training setup in the context of neuro-rehabilitation.
Methods
We tested the training setup in patient LA, a young man with significant unilateral UL dysfunction stemming from hemi-parkinsonism. LA underwent daily intervention in which he intensively trained the non-affected upper limb, while receiving online sensory feedback that created an illusory perception of control over the affected limb. Neural changes were assessed using functional magnetic resonance imaging (fMRI) scans before and after training.
Results
Training-induced behavioral gains were accompanied by enhanced activation in the pre-frontal cortex and a widespread increase in resting-state functional connectivity.
Discussion
Our combination of cutting edge technologies, insights gained from basic motor neuroscience in healthy subjects and well-known clinical treatments, hold promise for the pursuit of finding novel and more efficient rehabilitation schemes for patients suffering from hemiplegia.
•
Implications for rehabilitation
• Assistive devices used in hospitals to support patients with hemiparesis require expensive equipment and trained personnel – constraining the amount of training that a given patient can receive.
• The setup we describe is simple and can be easily used at home with the assistance of an untrained caregiver/family member.
• Once installed at the patient's home, the setup is lightweight, mobile, and can be used with minimal maintenance .
• Building on advances in machine learning, our software can be adapted to personal use at homes.
• Our findings can be translated into practice with relatively few adjustments, and our experimental design may be used as an important adjuvant to standard clinical care for upper limb hemiparesis.
... Unilateral training for bilateral strength gains has recently been highlighted for its possible use as a rehabilitation strategy during recovery from asymmetrical injuries (Barss, Pearcey, & Zehr, 2016;Farthing & Zehr, 2014;Hendy, Spittle, & Kidgell, 2012). 'Cross-education', 'inter-limb strength transfer', or the 'cross-transfer' effect is a neural adaptation defined as the increase in strength or functional performance of the untrained contralateral limb after unilateral training (Farthing & Chilibeck, 2003;Lee & Carroll, 2007;Ruddy & Carson, 2013;Scripture, Smith, & Brown, 1894). ...
The relative contribution of cutaneous sensory feedback to interlimb strength transfer remains unexplored. Therefore, this study aimed to determine the relative contribution of cutaneous afferent pathways as a substrate for cross‐education by directly assessing how “enhanced” cutaneous stimulation alters ipsilateral and contralateral strength gains in the forearm. Twenty‐seven right‐handed participants were randomly assigned to 1‐of‐3 training groups and completed 6 sets of 8 repetitions 3x/week for 5 weeks. Voluntary training (TRAIN) included unilateral maximal voluntary contractions (MVCs) of the wrist extensors. Cutaneous stimulation (STIM), a sham training condition, included cutaneous stimulation (2x radiating threshold; 3sec; 50Hz) of the superficial radial (SR) nerve at the wrist. TRAIN + STIM training included MVCs of the wrist extensors with simultaneous SR stimulation. Two pre‐ and one posttraining session assessed the relative increase in force output during MVCs of isometric wrist extension, wrist flexion, and handgrip. Maximal voluntary muscle activation was simultaneously recorded from the flexor and extensor carpi radialis. Cutaneous reflex pathways were evaluated through stimulation of the SR nerve during graded ipsilateral contractions. Results indicate TRAIN increased force output compared with STIM in both trained (85.0 ± 6.2 Nm vs. 59.8 ± 6.1 Nm) and untrained wrist extensors (73.9 ± 3.5 Nm vs. 58.8 Nm). Providing ‘enhanced’ sensory input during training (TRAIN + STIM) also led to increases in strength in the trained limb compared with STIM (79.3 ± 6.3 Nm vs. 59.8 ± 6.1 Nm). However, in the untrained limb no difference occurred between TRAIN + STIM and STIM (63.0 ± 3.7 Nm vs. 58.8 Nm). This suggests when ‘enhanced’ input was provided independent of timing with active muscle contraction, interlimb strength transfer to the untrained wrist extensors was blocked. This indicates that the sensory volley may have interfered with the integration of appropriate sensorimotor cues required to facilitate an interlimb transfer, highlighting the importance of appropriately timed cutaneous feedback. No study has directly assessed the relative contribution of somatosensory feedback to interlimb strength transfer. Providing ‘enhanced’ cutaneous input during unilateral wrist extension training blocked the interlimb strength transfer to the untrained limb that was seen when participants trained with voluntary contractions only. This study highlights the importance of appropriate cutaneous sensory feedback to the interlimb transfer of strength following unilateral training.
... During immobilization of a limb, following bone fracture for example, there is significant loss of muscle mass. Physical training of the contralateral (free) limb has been shown to prevent, or slow down this process, resulting in reduced loss of muscle volume in the immobilized arm [33,34]. Training based on CE was shown also to improve grip precision learning and force in the hemiparetic UL [35][36][37][38]. ...
... It is possible that a cross-education O n l i n e F i r s t O n l i n e F i r s t effect occurs after ACL injury, resulting in neuromuscular alterations, including submaximal force-control deficits, in both the involved and uninvolved limbs. 42 The deficits in force control may have implications for knee-joint loading and the development of early-onset knee osteoarthritis after ACL injury. Specifically, an inability to accurately control forces through the knee joint during everyday activities, particularly during activities requiring control of changing intensities of force, could alter joint-contact forces and load areas of the cartilage that are not adapted to regular loading. ...
Context:
Poor quadriceps force control has been observed after anterior cruciate ligament (ACL) reconstruction but has not been examined after ACL injury. Whether adaptations within the central nervous system are contributing to these impairments is unknown.
Objective:
To examine quadriceps force control in individuals who had sustained a recent ACL injury and determine the associations between cortical excitability and quadriceps force control in these individuals.
Design:
Cross-sectional study.
Setting:
Research laboratory.
Patients or other participants:
Eighteen individuals with a recent unilateral ACL injury (6 women, 12 men; age = 29.6 ± 8.4 years, height = 1.74 ± 0.07 m, mass = 76.0 ± 10.4 kg, time postinjury = 69.5 ± 42.5 days) and 18 uninjured individuals (6 women, 12 men; age = 29.2 ± 6.8 years, height = 1.79 ± 0.07 m, mass = 79.0 ± 8.4 kg) serving as controls participated.
Main outcome measure(s):
Quadriceps force control was quantified as the root mean square error between the quadriceps force and target force during a cyclical force-matching task. Cortical excitability was measured as the active motor threshold and cortical silent period. Outcome measures were determined bilaterally in a single testing session. Group and limb differences in quadriceps force control were assessed using mixed analyses of variance (2 × 2). Pearson product moment correlations were performed between quadriceps force control and cortical excitability in individuals with an ACL injury.
Results:
Individuals with an ACL injury exhibited greater total force-matching error with their involved (standardized mean difference [SMD] = 0.8) and uninvolved (SMD = 0.9) limbs than did controls (F1,27 = 11.347, P = .03). During the period of descending force, individuals with an ACL injury demonstrated greater error using their involved (SMD = 0.8) and uninvolved (SMD = 0.8) limbs than uninjured individuals (F1,27 = 4.941, P = .04). Greater force-matching error was not associated with any cortical excitability measures (P > .05).
Conclusions:
Quadriceps force control was impaired bilaterally after recent ACL injury but was not associated with selected measures of cortical excitability. The findings highlight a need to incorporate submaximal-force control tasks into rehabilitation and "prehabilitation," as the deficits were present before surgery.
... This makes it difficult to generate a clear conclusion or to speculate about Amp amplitude, EMG electromyography, Hmax Hoffman reflex, MEP motor-evoked potential, n number possible underlying mechanisms. However, in line with the present analysis, recent evidence of neuromuscular plasticity during immobilisation [16] and of cross-education during retraining after immobilisation [67] point to decreased corticospinal drive as a primary mechanism in the reduction in muscular function and performance. Mechanisms implicated in the degenerative effects of short-term immobilisation include increased excitability of corticospinal networks (MEP and H-reflex amplitudes), intracortical inhibition (prolonged silent period) as well as interhemispheric interactions (motor irradiation). ...
Background
Muscle strength loss following immobilisation has been predominantly attributed to rapid muscle atrophy. However, this cannot fully explain the magnitude of muscle strength loss, so changes in neuromuscular function (NMF) may be involved.
Objectives
We systematically reviewed literature that quantified changes in muscle strength, size and NMF following periods of limb immobilisation in vivo in humans.
Methods
Studies were identified following systematic searches, assessed for inclusion, data extracted and quality appraised by two reviewers. Data were tabulated and reported narratively.
Results
Forty eligible studies were included, 22 immobilised lower and 18 immobilised upper limbs. Limb immobilisation ranged from 12 h to 56 days. Isometric muscle strength and muscle size declined following immobilisation; however, change magnitude was greater for strength than size. Evoked resting twitch force decreased for lower but increased for upper limbs. Rate of force development either remained unchanged or slowed for lower and typically slowed for upper limbs. Twitch relaxation rate slowed for both lower and upper limbs. Central motor drive typically decreased for both locations, while electromyography amplitude during maximum voluntary contractions decreased for the lower and presented mixed findings for the upper limbs. Trends imply faster rates of NMF loss relative to size earlier in immobilisation periods for all outcomes.
Conclusions
Limb immobilisation results in non-uniform loss of isometric muscle strength, size and NMF over time. Different outcomes between upper and lower limbs could be attributed to higher degrees of central neural control of upper limb musculature. Future research should focus on muscle function losses and mechanisms following acute immobilisation.
Registration
PROSPERO reference: CRD42016033692.
... During immobilization of a limb, following bone fracture for example, there is significant loss of muscle mass. Physical training of the contralateral (free) limb has been shown to prevent, or slow down this process, resulting in reduced loss of muscle volume in the immobilized arm [33,34]. Training based on CE was shown also to improve grip precision learning and force in the hemiparetic UL [35][36][37][38]. ...
Cross education is a phenomenon in which motor training of one hand induces motor learning in the other hand. We have recently shown in healthy subjects that the effect of cross-education is significantly augmented by provision of real-time manipulated bi-modal (visual and kinesthetic) sensory feedback, creating an illusory sensation of voluntary training with the other hand. Here we tested whether this training method may be applicable also in pathological conditions affecting one side of the body. We present here data showing behavioral gain accompanied by functional magnetic resonance imaging dynamics following training with this setup in the case of patient LA, a young man with significant unilateral upper-limb dysfunction stemming from hemi-Parkinson’s disease. Following two weeks of daily sessions in which he intensively trained the non-affected upper limb, he showed improvement in motor capacity of the affected limb, accompanied by enhanced activation in the pre-frontal cortex and a widespread increase in functional coupling in the brain. Results from the current case study suggest that combining cross-education with manipulated sensory input may also have beneficial effects in clinical conditions.
... Previous meta-analyses and systematic reviews have determined that the average contralateral strength gain from cross education is approximately 8-12% [4][5][6][7]. This amount corresponds to approximately 35-60% of the strength increase that is found in the ipsilateral (trained) limb [4,6,8]. ...
Background: Cross education is the contralateral strength gain following unilateral training of the ipsilateral limb. This phenomenon provides an ideal rehabilitation model for acute or chronic rehabilitation; however, previous cross education meta-analyses have been limited to a handful of studies.
Objectives: The present meta-analysis aimed to (1) be as inclusive as possible, (2) compare cross education in young able-bodied, older able-bodied, and patient populations, (3) compare cross education between training modalities, and (4) detail the impact of methodological controls on the quantification of cross education.
Methodology: A review of English literature identified studies that employed unilateral resistance training and reported contralateral strength results. Studies were separated to examine the effect of population, training modality, limb, sex, and familiarization on the magnitude of cross education. The percent strength gain and effect size were calculated for ipsilateral and contralateral limbs.
Results: A total of 96 studies fit the predetermined inclusion criteria and were included in the analysis. The included studies were further divided into 141 units employing separate unilateral training paradigms. These were separated into young, able-bodied (n = 126), older, able-bodied (n = 9), and neuromuscular patients (n = 6). Cross education was an average of 18% (standardized mean difference (SMD) = 0.71) in young, able-bodied participants, 17% (SMD = 0.58) in healthy able-bodied participants, and 29% (SMD = 0.76) in neuromuscular patients.
Conclusion: Cross education was present in young, older, and patient populations and similar between upper and lower limbs and between males and females. Electromyostimulation training was superior to voluntary training paradigms.
... A transfer effect between the lower and upper body may be also related to neural mechanisms. Cross-education has been extensively studied in relation to injured limb and immobilization (17). Reduction in strength during limb immobilization, when the healthy limb was trained, has been attributed to complex mechanisms such as motor irradiation (4) and hemispheric interaction (20) that emanate from the spinal cord and cortical brain areas. ...
... "Cross-education," "interlimb strength transfer," or the "cross-transfer" effect as it has more recently been described is a neural adaptation defined as the increase in strength or functional performance of the untrained contralateral limb after unilateral training (21,46,58). Implementing cross-education has received consideration as a possible rehabilitation strategy during recovery from unilateral injuries (6,23,31). For unilateral resistance training to be effectively integrated within a rehabilitation setting, several fundamental issues must be addressed within the scientific literature. ...
'Cross-education' is the increase in strength or functional performance of an untrained limb after unilateral training. A major limitation for clinical translation from unilateral injury includes knowledge on the minimum time for the emergence of crossed effects. Therefore, the primary purpose was to characterize the time-course of bilateral strength changes during both 'traditional' (n=11) and 'daily' (n=8) unilateral handgrip training in neurologically intact participants. 'Traditional' training included 5 sets of 5 maximal voluntary handgrip contractions 3x/week for 6-weeks whereas 'daily' training included the same number of sessions and contractions but over 18 consecutive days. Three pre- and one post-test session evaluated strength, muscle activation, and reflex excitability bilaterally. Time course information was assessed by recording handgrip force for every contraction in the trained limb and from a single contraction on every third training session in the untrained limb. 6 weeks of 'traditional' training increased handgrip strength in the trained limb after the 9th session while the untrained limb was stronger after the 12th session. This was accompanied by increased peak muscle activation and bilateral alterations in Hoffmann (H-) reflex excitability. 'Daily' training revealed a similar number of sessions (15) were required to induce significant strength gains in the untrained limb (7.8% compared to 12.5%) in approximately half the duration of 'traditional' training. Therefore, minimizing rest days may improve the efficiency of unilateral training when the trained limb is not the focus. Establishing a 'dose' for the time-course of adaptation to strength training is paramount for effective translation to rehabilitative interventions.
... The basic exercises (i.e. the first three exercises) were compiled after this pattern. In a first exercise sequence, the respective movement was tested two to three times motorically using the non-operated extremity and with eyes open [51]. Afterwards, the movement was carried out with eyes closed twice to sensitize on its kinaesthetic aspects. ...
Background and objectives: Many research groups recommend mental practice as an (cost-) effective additional means in orthopaedic and neurological rehabilitation. Mental practice is supposed to stimulate neurological representations of movements (understood as the theory of functional equivalence of motor imagery and motor execution) and thus support rehabilitation. Accordingly, a mental training program supplemented by mirror visual feedback (action observation in a sagittal positioned mirror) added to the traditional rehabilitation program of the clinic was developed for patients with implanted total knee endoprosthesis. The effectiveness of this program was investigated within a randomized-controlled intervention study. The primary aim was to improve the range of motion in the patients’ knee flexion.
Methods: The therapeutic process of 40 patients (M = 62.54 years, SD = 9.64) was monitored over half a year. After the surgery, the experimental group (EG) conducted physiotherapeutic exercises mentally and with the mirror. The control group (CG) completed the same exercises physically. In the investigation, which was carried out with a five-fold repetition of measuring, the criteria surveyed were, among others, exion, gait parameters, physical function/symptoms, and the degree of coping with the disease.
Results: With regard to the main criterion of flexion, the EG attained values that were significantly higher than those of the CG. All secondary outcomes did not differ signficantly between the groups.
Conclusion: The study supports the hypothesis that patients who exercise mentally and with the mirror perform better with regard to the criterion of flexion. Mental training supplemented by mirror therapy can be regarded as a promising therapy component in orthopaedic rehabilitation.
... Taken together, these findings suggest that dramatic declines in protein synthesis rates are apparent in the early phase of immobilization, at least in the lower limbs. The early, and potent, declines in protein synthesis rates seem to coincide with many previous reports of rapid declines in strength and muscle activation during immobilization (Deschenes et al. 2002;Facchini et al. 2002), which suggests early strength declines that precede atrophy during disuse should not be ascribed only to neural mechanisms (Hortobágyi et al. 2000;Hendy et al. 2012). ...
The contralateral effects of unilateral strength training, known as cross-education of strength, date back well over a century. In the last decade, a limited number of studies have emerged demonstrating the preservation or "sparing" effects of cross-education during immobilization. Recently published evidence reveals that the sparing effects of cross-education show muscle site specificity and involve preservation of muscle cross-sectional area. The new research also demonstrates utility of training with eccentric contractions as a potent stimulus to preserve immobilized limb strength across multiple modes of contraction. The cumulative data in nonclinical settings suggest that cross-education can completely abolish expected declines in strength and muscle size in the range of ∼13% and ∼4%, respectively, after 3-4 weeks of immobilization of a healthy arm. The evidence hints towards the possibility that unique mechanisms may be involved in preservation effects of cross-education, as compared with those that lead to functional improvements under normal conditions. Cross-education effects after strength training appear to be larger in clinical settings, but there is still only 1 randomized clinical trial demonstrating the potential utility of cross-education in addition to standard treatment. More work is necessary in both controlled and clinical settings to understand the potential interaction of neural and muscle adaptations involved in the observed sparing effects, but there is growing evidence to advocate for the clinical utility of cross-education.
... It is clear that the values in the affected and unaffected knee (experimental group) is almost similar whereas the control knee shows significant difference in the values. This shows that there is a cross limb transfer phenomenon, which alters the proprioception in the contralateral knee [26][27][28][29][30][31][32]. ...
... In the context of cross-education and bilateral transfer, several acute studies that have used TMS have shown increased CSE (Muellbacher et al. 2000;Hortobágyi et al. 2003;Perez and Cohen 2008;Howatson et al. 2011;Frazer et al. 2017), decreased SICI (Perez and Cohen 2008;Leung et al. 2015), and decreased interhemispheric inhibition (IHI) (Perez and Cohen 2008;Howatson et al. 2011) in the iM1. While some structural changes occur within several motor areas (Ruddy et al. 2017;Pruitt et al. 2016), experimental findings from chronic cross-education studies support a mixture of increased CSE (Hendy et al. 2015;Kidgell et al. 2011Kidgell et al. , 2015 and a decrease in cortical inhibition (SICI, IHI and silent period duration) Hendy et al. 2012;Kidgell et al. 2015;Coombs et al. 2016;Mason et al. 2017) in the neural structures innervating the untrained limb. ...
This study aimed to identify the ipsilateral corticospinal responses of the contralateral limb following different types of unilateral motor-training. Three groups performing unilateral slow-paced strength training (SPST), non-paced strength training (NPST) or visuomotor skill training (VT) were compared to a control group. It was hypothesised that 4 weeks of unilateral SPST and VT, but not NPST, would increase ipsilateral corticospinal excitability (CSE) and reduce short-interval cortical inhibition (SICI), resulting in greater performance gains of the untrained limb. Tracking error of the untrained limb reduced by 29 and 41% following 2 and 4 weeks of VT. Strength of the untrained limb increased by 8 and 16% following 2 and 4 weeks of SPST and by 6 and 13% following NPST. There was no difference in cross-education of strength or tracking error. For the trained limb, SPST and NPST increased strength (28 and 26%), and VT improved by 47 and 58%. SPST and VT increased ipsilateral CSE by 89 and 71% at 2 weeks. Ipsilateral CSE increased 105 and 81% at 4 weeks following SPST and VT. The NPST group and control group showed no changes at 2 and 4 weeks. SPST and VT reduced ipsilateral SICI by 45 and 47% at 2 weeks; at 4 weeks, SPST and VT reduced SICI by 48 and 38%. The ipsilateral corticospinal responses are determined by the type of motor-training. There were no differences in motor performance between SPST, NPST and VT. The data suggests that the corticospinal responses to cross-education are different and determined by the type of motor-training.
... That is, the functional capacity of an impaired or immobile limb might benefit through transfer from physical practice performed by the uninjured limb. This phenomenon is also of theoretical importance because it can help revealing the basic neural processes involved in movement control and learning (Lee & Carroll, 2007;Hendy et al., 2012). Therefore, determining the conditions in which cross-limb transfer may occur is of theoretical and applied interest. ...
Skills learned through practice with one limb can often be transferred to the untrained limb. In the present report, we sought to determine whether movement direction biases, acquired through repeated movement with one limb, transfer to the untrained limb. In order to do so, we asked participants to perform synchronised bilateral contractions of muscles in both wrists, followed by the unilateral contraction of muscles in one wrist. In four experiments, we manipulated the position of the unilateral target to create use-dependent directional biases; changed the direction of the cursor in relation to the wrist movement to control for attentional biases; and sought to induce directional biases with both right and left unilateral movements. The results showed clear movement related biases for the wrist that performed unilateral contractions, but no evidence that movement-related bias transferred to the opposite limb during bilateral action. Thus motor preparation and execution of unilateral contractions does not affect the direction of movement made by the opposite limb during subsequent bilateral contractions.
... In more recent times, the investigation of the characteristics and mechanisms underpinning cross-education have received substantial interest from the scientific community. This is particularly due to the potential for the application of cross-education in rehabilitation following unilateral injury or immobilization (Farthing et al., 2009;Hendy et al., 2012;Magnus et al., 2014). ...
Objectives: Unilateral resistance training produces strength gains in the untrained homologous muscle group, an effect termed “cross-education.” The observed strength transfer has traditionally been considered a phenomenon of the nervous system, with few studies examining the contribution of factors beyond the brain and spinal cord. In this hypothesis and theory article, we aim to discuss further evidence for structural and functional adaptations occurring within the nervous, muscle, and endocrine systems in response to unilateral resistance training. The limitations of existing cross-education studies will be explored, and novel potential stakeholders that may contribute to the cross-education effect will be identified.
Design: Critical review of the literature.
Method: Search of online databases.
Results: Studies have provided evidence that functional reorganization of the motor cortex facilitates, at least in part, the effects of cross-education. Cross-activation of the “untrained” motor cortex, ipsilateral to the trained limb, plays an important role. While many studies report little or no gains in muscle mass in the untrained limb, most experimental designs have not allowed for sensitive or comprehensive investigation of structural changes in the muscle.
Conclusions: Increased neural drive originating from the “untrained” motor cortex contributes to the cross-education effect. Adaptive changes within the muscle fiber, as well as systemic and hormonal factors require further investigation. An increased understanding of the physiological mechanisms contributing to cross-education will enable to more effectively explore its effects and potential applications in rehabilitation of unilateral movement disorders or injury.
Introduction:
In climbing, research is needed to guide clinical and training advice regarding strength differences between hands. The objectives of this study were to establish test-retest reliability of a field-based apparatus measuring sport-specific unilateral isometric hand strength and to investigate whether these measures detect between-hand differences in climbers with and without a history of unilateral hand injury.
Methods:
A reliability and case-control injury study was carried out. Seventeen intermediate-advanced climbers without and 15 intermediate-advanced climbers with previous unilateral hand injury participated. Unilateral isometric fingertip flexor strength was assessed during maximal voluntary contraction (MVC) and peak rate of force development (RFD) tests in full-crimp overhead position. The magnitude of within-group between-hand differences was calculated using a generalized estimating equation to evaluate if prior injury was associated with lower MVC and RFD outcomes and whether hand dominance influenced the magnitude of these effects. The control group was assessed 1 wk later to determine intraclass correlation coefficients (ICCs) for all measures.
Results:
The MVC (ICC 0.91-0.93) and the RFD (ICC 0.92-0.83) tests demonstrated moderate-to-high reliability. When accounting for handedness, those with prior injury showed 7% (P=0.004) reduced MVC and 13% (P=0.008) reduced RFD in the injured hand. The nondominant hand was also significantly weaker in MVC (11%, P<0.001) and RFD (12%, P=0.02) outcomes. For uninjured climbers, MVC and RFD were not significantly higher in the dominant hand (differing by 4% and 5%, respectively).
Conclusions:
Previous climbing injury was associated with persistent weakness in the injured limb and exacerbated handedness effects. Therefore, recommendations for rehabilitation should be considered.
CALVERT, G.H.M., and CARSON, R.G. Neural mechanisms mediating cross education: with additional considerations for the ageing brain. NEUROSCI BIOBEHAV REV 21(1) XXX-XXX, 2021. - Cross education (CE) is the process whereby a regimen of unilateral limb training engenders bilateral improvements in motor function. The contralateral gains thus derived may impart therapeutic benefits for patients with unilateral deficits arising from orthopaedic injury or stroke. Despite this prospective therapeutic utility, there is little consensus concerning its mechanistic basis. The precise means through which the neuroanatomical structures and cellular processes that mediate CE may be influenced by age-related neurodegeneration are also almost entirely unknown. Notwithstanding the increased incidence of unilateral impairment in later life, age-related variations in the expression of CE have been examined only infrequently. In this narrative review, we consider several mechanisms which may mediate the expression of CE with specific reference to the ageing CNS. We focus on the adaptive potential of cellular processes that are subserved by a specific set of neuroanatomical pathways including: the corticospinal tract, corticoreticulospinal projections, transcallosal fibres, and thalamocortical radiations. This analysis may inform the development of interventions that exploit the therapeutic utility of CE training in older persons.
With an array of critical and engaging pedagogical features, the fifth edition of Motor Learning and Control for Practitioners offers the best practical introduction to motor learning available. This reader-friendly text approaches motor learning in accessible and simple terms and lays a theoretical foundation for assessing performance; providing effective instruction; and designing practice, rehabilitation, and training experiences that promote skill acquisition. Features such as Exploration Activities and Cerebral Challenges involve students at every stage, while a broad range of examples helps readers put theory into practice. The book also provides access to a fully updated companion website, which includes laboratory exercises, an instructors’ manual, a test bank, and lecture slides. As a complete resource for teaching an evidence-based approach to practical motor learning, this is an essential text for undergrad and post-grad students, researchers, and practitioners alike who plan to work in the areas of motor learning, motor control, physical education, kinesiology, exercise science, coaching, physical therapy, or dance.
Introduction
This study aimed to evaluate the effectiveness of proprioceptive neuromuscular facilitation (PNF) in promoting muscle irradiation to the lower limbs and to relate these findings with muscle activation during the sit-to-stand task.
Methods
Twenty-four healthy women were recruited via convenience sampling and submitted to four PNF patterns: upper limb pattern with flexion-abduction-external rotation (UL), lower limb pattern with flexion-adduction-external rotation with knee flexion (lower limb pattern 1 [LL1]), lower limb pattern with flexion-abduction-internal rotation with knee flexion (lower limb pattern 2 [LL2]), and lifting to the right. Electromyography was recorded from the gluteus maximus, gluteus medius, vastus medialis, vastus lateralis, and soleus during the PNF patterns and during the sit-to-stand task.
Results
The most recruited muscles during the sit-to-stand task were the vastus lateralis, vastus medialis, and soleus (p < 0.05). Lifting to the right induced the greatest activation of the gluteus maximus (p < 0.001). Lifting to the right and LL2 were better than UL at recruiting the gluteus medius (p < 0.05). Lifting to the right and LL1 were better than UL at recruiting the vastus medialis and lateralis (p < 0.05; p < 0.05). and Lower limb pattern 1 and 2 were better than UL at recruiting the soleus muscle (p < 0.05).
Conclusion
PNF can be used to induce muscle irradiation to maintain or improve muscle activity to the muscles recruited during the sit-to-stand task. The best PNF pattern for inducing muscle irradiation to muscles recruited during the sit-to-stand task are lifting to the right, LL2, and LL1.
The basic facilitation principles and proceduresBasic facilitation principles and procedures, when used correctly, provide tools for the therapist to use in helping the patient to gain efficient motor function and increased motor control.
Es gibt im PNF-Konzept zahlreiche Möglichkeiten die muskuläre Aktivität zu beeinflussen. Die jeweiligen Stimuli, Grundprinzipien und Prozeduren werden eingeteilt in: Exterozeptive Stimuli, propriozeptive Stimuli und Grundprinzipien. In diesem Kapitel wird jeweils erklärt, wann, wie, wo und weshalb die verschiedenen Stimuli eingesetzt werden.
Whole Body Vibrations: Physical and Biological Effects on the Human Body allows an understanding about the qualities and disadvantages of vibration exposure on the human body with a biomechanical and medical perspective. It offers a comprehensive range of principles, methods, techniques and tools to provide the reader with a clear knowledge of the impact of vibration on human tissues and physiological processes. The text considers physical, mechanical and biomechanical aspects and it is illustrated by key application domains such as sports and medicine. Consisting of 11 chapters in total, the first three chapters provide useful tools for measuring, generating, simulating and processing vibration signals. The following seven chapters are applications in different fields of expertise, from performance to health, with localized or global effects. Since unfortunately there are undesirable effects from the exposure to mechanical vibrations, a final chapter is dedicated to this issue. Engineers, researchers and students from biomedical engineering and health sciences, as well as industrial professionals can profit from this compendium of knowledge about mechanical vibration applied to the human body.
We reviewed the evidence from randomized controlled trials (RCTs) focusing on the neurophysiological adaptations in the untrained side associated with cross-education of strength (CE) and pooled data into definite effect estimates for neurophysiological variables assessed in chronic CE studies. Furthermore, scoping directions for future research were provided to enhance the homogeneity and comparability of studies investigating the neural responses to CE. The magnitude of CE was 21.1{plus minus}18.2% (p<0.0001) in 22 RCTs (467 subjects) that measured at least one neurophysiological variable in the untrained side, including: EMG (14 studies), MEP (8 studies), SICI, RC and M-wave (6 studies), cSP (5), IHI, ICF and H-reflex (2), V-wave, SICF, SAI and LAI (1). Only EMG, MEP, ICF, cSP and SICI could be included the meta-analysis (18 studies, n=387). EMG (p=0.26, n=235) and MEP amplitude (p=0.11, n=145) did not change in the untrained limb after CE. cSP duration (p=0.02, n=114) and SICI (p=0.001, n=95) decreased in the untrained hemisphere according to body region, type and intensity of training. The magnitude of CE did not correlate with changes in these TMS measures. The design of this meta-analytical study and the lack of correlations prevented the ability to link mechanistically the observed neurophysiological changes to CE. Notwithstanding the limited amount of data available for pooling, the use of TMS to assess the ipsilateral neurophysiological responses to unilateral training still confirms the central neural origin hypothesis of chronic CE induced by strength training. However, how these neural adaptations contribute to CE remains unclear.
Chronic unimanual motor practice increases the motor output not only in the trained but also in the nonexercised homologous muscle in the opposite limb. We examined the hypothesis that adaptations in motor cortical excitability of the nontrained primary motor cortex (iM1) and in interhemispheric inhibition from the trained to the nontrained M1 mediate this interlimb cross education.
Healthy, young volunteers (n=12) performed 1000 submaximal voluntary contractions (MVC) of the right first dorsal interosseus (FDI) at 80% MVC during 20 sessions.
Trained FDI's MVC increased 49.9%, and the untrained FDI's MVC increased 28.1%. Although corticospinal excitability in iM1, measured with transcranial magnetic stimulation (TMS) before and after every fifth session, increased 6% at rest, these changes, as those in intracortical inhibition and facilitation, did not correlate with cross education. When weak and strong TMS of iM1 were delivered on a background of a weak and strong muscle contraction, respectively, of the right FDI, excitability of iM1 increased dramatically after 20 sessions. Interhemispheric inhibition decreased 8.9% acutely within sessions and 30.9% chronically during 20 sessions and these chronic reductions progressively became more strongly associated with cross education. There were no changes in force or TMS measures in the trained group's left abductor minimi digiti and there were no changes in the nonexercising control group (n=8).
The findings provide the first evidence for plasticity of interhemispheric connections to mediate cross education produced by a simple motor task.
The purpose of this study was to investigate the effects of 4-week (16 sessions) unilateral, maximal isometric strength training on contralateral neural adaptations. Subjects were randomised to a strength training group (TG, n = 15) or to a control group (CG, n = 11). Both legs of both groups were tested for plantar flexion maximum voluntary isometric contractions (MVCs), surface electromyogram (EMG), H-reflexes and V-waves in the soleus (SOL) and gastrocnemius medialis (GM) superimposed during MVC and normalised by the M-wave (EMG/M(SUP), H(SUP)/M(SUP), V/M(SUP), respectively), before and after the training period. For the untrained leg, the TG increased compared to the CG for MVC torque (33%, P < 0.01), SOL EMG/M(SUP) (32%, P < 0.05) and SOL V/M(SUP) (24%, P < 0.05). For the trained leg, the TG increased compared to the CG for MVC torque (40%, P < 0.01), EMG/M(SUP) (SOL: 38%, P < 0.05; GM: 60%, P < 0.05) and SOL V/M(SUP) (72%, P < 0.01). H(SUP)/M(SUP) remained unchanged for both limbs. No changes occurred in the CG. These results reinforce the concept that enhanced neural drive to the contralateral agonist muscles contributes to cross-education of strength.
1. This study addressed potential neural mechanisms of the strength increase that occur before muscle hypertrophy. In particular we examined whether such strength increases may result from training-induced changes in voluntary motor programs. We compared the maximal voluntary force production after a training program of repetitive maximal isometric muscle contractions with force output after a training program that did not involve repetitive activation of muscle; that is, after mental training. 2. Subjects trained their left hypothenar muscles for 4 wk, five sessions per week. One group produced repeated maximal isometric contractions of the abductor muscles of the fifth digit's metacarpophalangeal joint. A second group imagined producing these same, effortful isometric contractions. A third group did not train their fifth digit. Maximal abduction force, flexion/extension force and electrically evoked twitch force (abduction) of the fifth digit were measured along with maximal integrated electromyograms (EMG) of the hypothenar muscles from both hands before and after training. 3. Average abduction force of the left fifth digit increased 22% for the Imagining group and 30% for the Contraction group. The mean increase for the Control group was 3.7%. 4. The maximal abduction force of the right (untrained) fifth digit increased significantly in both the Imagining and Contraction groups after training (10 and 14%, respectively), but not in the Control group (2.3%). These results are consistent with previous studies of training effects on contralateral limbs. 5. The abduction twitch force evoked by supramaximal electrical stimulations of the ulnar nerve was unchanged in all three groups after training, consistent with an absence of muscle hypertrophy. The maximal force of the left great toe extensors for individual subjects remained unchanged after training, which argues against strength increases due to general increases in effort level. 6. Increases in abduction and flexion forces of the fifth digit were poorly correlated in subjects of both training groups. The fifth finger abduction force and the hypothenar integrated EMG increases were not well correlated in these subjects either. Together these results indicate that training-induced changes of synergist and antagonist muscle activation patterns may have contributed to force increases in some of the subjects. 7. Strength increases can be achieved without repeated muscle activation. These force gains appear to result from practice effects on central motor programming/planning. The results of these experiments add to existing evidence for the neural origin of strength increases that occur before muscle hypertrophy.
Because short-term limb immobilization produces selective adaptations in the neuromuscular system that probably interact with the task-dependent expression of muscle fatigue, the purpose of this study was to determine the effects of limb immobilization on the ability of human subjects to sustain isometric contractions at low and moderate submaximal forces. Four weeks of elbow joint immobilization caused a substantial decrease in the daily activity of biceps brachii during immobilization, a significant reduction in the cross-sectional area and volume of the elbow flexor muscles as measured by magnetic resonance imaging, and a decline in the maximum voluntary contraction (MVC) activation and force of the elbow flexor muscles. Immobilization had a task-dependent effect on muscle fatigue with a substantially increased endurance time (reduced fatigability) at a low force (20% MVC) and no statistical effect at a moderate force (65% MVC). Despite atrophy of the elbow flexor muscles due to the immobilization, the twitch force elicited in biceps brachii by electrical stimulation was greater after immobilization. The selective improvement of fatigue resistance for the low-force contraction and the absence of a change in the time course of the twitch suggests that the immobilization-induced adaptations included an improved efficacy of some excitation-contraction processes and underscored the major role of these mechanisms in determining the endurance time for low-force, long-duration contractions.
We made estimates of absolute morbidity and mortality due to occupational factors for the world using all available published data as of 1994, and, where no data were available, applying the most appropriate (in terms of similar economy, race, and environment) age-/sex-/diagnosis-specific incidence and mortality rates to known working population distributions. We report results according to economic groupings determined by the World Bank (World Development Report, 1993) and disease and injury groupings according to The Global Burden of Disease project (1997). This was part of a larger study that estimated the total global disease burden. We present aggregate results and analyses by region and disease. We estimate that approximately 100,000,000 occupational injuries (100,000 deaths) and 11,000,000 occupational diseases (700,000 deaths) occur in the world each year. We regard these as very conservative estimates which, although unavoidably crude, can nevertheless provide a basis for health priority planning at global level.
1. Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. 2. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. 3. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. 4. Total RNA/wet muscle weight and ty I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72-fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9-fold and 1.2-fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r = 0.66, r = 0.07 and r = -0.71, respectively). 5. The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.
Using transcranial magnetic stimulation (TMS) over the contralateral motor cortex, motor evoked potentials (MEPs) were recorded from resting abductor pollicis brevis (APB) and first dorsal interosseous (FDI) muscles of eight subjects while they either rested or produced one of six levels of force with the APB ipsilateral to the TMS. F-waves were recorded from each APB at rest in response to median nerve stimulation while subjects either rested or produced one of two levels of force with their contralateral APB. Contraction of the APB ipsilateral to TMS produced facilitation of the MEPs recorded from resting APB and FDI muscles contralateral to TMS but did not modulate F-wave amplitude. Negligible asymmetries in MEP facilitation were observed between dominant and subdominant hands. These results suggest that facilitation arising from isometric contraction of ipsilateral hand muscles occurs primarily at supraspinal levels, and this occurs symmetrically between dominant and subdominant hemispheres.
The purpose of this study was to determine whether cross-education, defined as the increase in strength of an untrained limb after training of the contralateral homologous limb, is specific to low and high velocity eccentric training. Twenty-six subjects were randomized into two groups ( n=13 each) that performed unilateral eccentric training of the elbow flexors on an isokinetic dynamometer at velocities of either 30 degrees s(-1) (0.52 rad s(-1)) or 180 degrees s(-1) (3.14 rad s(-1 )). Subjects trained three times per week for 8 weeks. Ten subjects served as controls and did not train. Subjects were tested before and after training for peak torque of the elbow flexors during eccentric and concentric contractions at 30 degrees s(-1) and 180 degrees s(-1). Eccentric peak torque at the velocity of 180 degrees s(-1) in the untrained arm increased only for the group that trained at that velocity (P<0.05). There were no other changes in untrained arms for any of the groups at velocities of 30 degrees s(-1) or 180 degrees s(-1). For the trained arm, the increase in eccentric torque (pooled over velocities) was greatest for the group training at 180 degrees s(-1), whereas the increase in concentric torque was similar for the groups training at 30 degrees s(-1) and 180 degrees s(-1). For the trained arm, there was no specificity for velocity or contraction type. We conclude that cross-education was specific to contraction type and velocity when fast (but not slow) eccentric contractions were used during training; whereas there was no specificity of training in the trained arm.
It is often claimed that strength training of one limb increases the strength of the contralateral limb, but this has not been demonstrated consistently, particularly in well-controlled studies. The aim was to quantitatively combine the results of other studies on the effects of unilateral training on contralateral strength in humans to provide an answer to this physiological question. We analyzed all randomized controlled studies of voluntary unilateral resistance training that used training intensities of at least 50% of maximal voluntary strength for a minimum of 2 wk. Studies were identified by computerized and hand searches of the literature. Data on changes in strength of contralateral and control limbs were extracted and statistically pooled in a meta-analysis. This approach allows conclusions to be based on a statistically meaningful sample size, which might be difficult to achieve in other ways. Seventeen studies met the inclusion criteria, and 13 provided enough data for statistical pooling. The contralateral effects of strength training reported in individual studies varied from -2.7 to 21.6% of initial strength. The pooled estimate of the effect of unilateral resistance training on the maximal voluntary strength of the contralateral limb was 7.8% (95% confidence interval: 4.1-11.6%). This was 35.1% (95% confidence interval: 20.9-49.3%) of the effect on the trained limb. Pooling of all available data shows that unilateral strength training produces modest increases in contralateral strength.
The purpose of this study was to determine the effects of short-term (14-day) unilateral leg immobilization using a simple knee brace (60 degree flexion)- or crutch-mediated model on muscle function and morphology in men (M, n = 13) and women (W, n = 14). Isometric and isokinetic (concentric-slow, 0.52 rad/s and fast, 5.24 rad/s) knee extensor peak torque was determined at three time points (Pre, Day-2, and Day-14). At the same time points, magnetic resonance imaging was used to measure the cross-sectional area of the quadriceps femoris and dual-energy X-ray absorptiometry scanning was used to calculate leg lean mass. Muscle biopsies were taken from vastus lateralis at Pre and Day-14 for myosin ATPase and myosin heavy chain analysis. Women showed greater decreases (Pre vs. Day-14) compared with men in specific strength (N/cm2) for isometric [M = 3.1 +/- 13.3, W = 17.1 +/- 15.9%; P = 0.055 (mean +/- SD)] and concentric-slow (M = 4.7 +/- 11.3, W = 16.6 +/- 18.4%; P < 0.05) contractions. There were no immobilization-induced sex-specific differences in the decrease in quadriceps femoris cross-sectional area (M = 5.7 +/- 5.0, W = 5.9 +/- 5.2%) or leg lean mass (M = 3.7 +/- 4.2, W = 2.7 +/- 2.8%). There were no fiber-type transformations, and the decreases in type I (M = 4.8 +/- 5.0, W = 5.9 +/- 3.4%), IIa (M = 7.9 +/- 9.9, W = 8.8 +/- 8.0%), and IIx (M = 10.7 +/- 10.8, W = 10.8 +/- 12.1%) fiber areas were similar between sexes. These findings indicate that immobilization-induced loss of knee extensor muscle strength is greater in women compared with men despite a similar extent of atrophy at the myofiber and whole muscle levels after 14 days of unilateral leg immobilization. Furthermore, we have described an effective and safe knee immobilization method that results in reductions in quadriceps muscle strength and size.
Recognizing that electrically stimulating the motor cortex could relieve chronic pain sparked development of non-invasive technologies. In transcranial magnetic stimulation (TMS), electromagnetic coils held against the scalp influence underlying cortical firing. Multi-day repetitive TMS (rTMS) can induce long-lasting, potentially therapeutic, brain plasticity. Nearby ferromagnetic or electronic implants are contraindications, and adverse effects are minimal, primarily headaches. Single provoked seizures are very rare. TMS devices are marketed for depression and migraine in the U.S. and for multiple indications elsewhere. Although multiple studies report that high-frequency rTMS of motor cortex reduces neuropathic pain, their quality has been insufficient to support FDA application. Harvard's Radcliffe Institute therefore sponsored a workshop to solicit advice from experts in TMS, pain research, and clinical trials. They recommended that researchers standardize and document all TMS parameters, and improve strategies for sham and double-blinding. Subjects should have common, well-characterized pain conditions amenable to motor-cortex rTMS and samples should be adequately powered. They recommended standardized assessment tools (e.g., NIH's PROMIS) plus validated condition-specific instruments and consensus-recommended metrics (e.g. IMMPACT). Outcomes should include pain intensity and qualities, patient and clinician impression of change, and proportions achieving 30% and 50% pain relief. Secondary outcomes could include function, mood, sleep, and/or quality of life. Minimum required elements include sample sources, sizes, and demographics, recruitment methods, inclusion/exclusion criteria, baseline and post-treatment means and standard deviations, adverse effects, safety concerns, discontinuations, and medication-usage records. Outcomes should be monitored for at least 3 months post-initiation with pre-specified statistical analyses. Multi-group collaborations or registry studies may be needed for pivotal trials.
Lt has been proved repeatedly that the activity of a part of the cerebral cortex influences the homologous part of the cortex on the opposite side. Bykov1 in 1925 reported that the conditioned salivary reflex to tactile stimuli of a certain point of the skin in the dog may be obtained also from the symmetrical point of the opposite side of the body. In the visual sphere Myers and Sperry,2-5 by ingenious experiments in the cat, recently demonstrated that the ability for pattern discrimination acquired by the visual cortex of one hemisphere is also present in the visual cortex of the opposite hemisphere. The experiments of Burešová and Bureš6 gave similar results with other methods. Stamm and Sperry7 report analogous observations in the somesthetic sphere. Dawson,8,9 stimulating sensory nerves, registered cortical evoked potentials both in the homologous and in the opposite senory region of the
High-resistance strength training (HRST) is one of the most widely practiced forms of physical activity, which is used to enhance athletic performance, augment musculo-skeletal health and alter body aesthetics. Chronic exposure to this type of activity produces marked increases in muscular strength, which are attributed to a range of neurological and morphological adaptations. This review assesses the evidence for these adaptations, their interplay and contribution to enhanced strength and the methodologies employed.
The primary morphological adaptations involve an increase in the cross-sectional area of the whole muscle and individual muscle fibres, which is due to an increase in myofibrillar size and number. Satellite cells are activated in the very early stages of training; their proliferation and later fusion with existing fibres appears to be intimately involved in the hypertrophy response. Other possible morphological adaptations include hyperplasia, changes in fibre type, muscle architecture, myofilament density and the structure of connective tissue and tendons.
Indirect evidence for neurological adaptations, which encompasses learning and coordination, comes from the specificity of the training adaptation, transfer of unilateral training to the contralateral limb and imagined contractions. The apparent rise in whole-muscle specific tension has been primarily used as evidence for neurological adaptations; however, morphological factors (e.g. preferential hypertrophy of type 2 fibres, increased angle of fibre pennation, increase in radiological density) are also likely to contribute to this phenomenon. Changes in inter-muscular coordination appear critical. Adaptations in agonist muscle activation, as assessed by electromyography, tetanic stimulation and the twitch interpolation technique, suggest small, but significant increases. Enhanced firing frequency and spinal reflexes most likely explain this improvement, although there is contrary evidence suggesting no change in cortical or corticospinal excitability.
The gains in strength with HRST are undoubtedly due to a wide combination of neurological and morphological factors. Whilst the neurological factors may make their greatest contribution during the early stages of a training programme, hypertrophic processes also commence at the onset of training.
The size of compound motor evoked potentials (cMEPs) to transcranial magnetic stimulation of the motor cortex was measured in the relaxed first dorsal interosseous muscle of the nondominant hand (ndFDI) during different levels of voluntary contraction in the homonymous muscle of the dominant hand (dFDI). cMEP responses in the ndFDI became larger when the dFDI was contracted to forces ranging 10–70% of maximum voluntary contraction. Variability in the amplitude of the cMEP responses in ndFDI decreased when dFDI was contracted. Comparison with cMEPs to spinal cord stimulation suggested a large component of the facilitation was occurring at a cortical level. The amplitude of cMEP responses in ndFDI also increased when the tibialis anterior muscle of the leg on the contralateral side was contracted. The observed facilitation of motoneurons during contraction of contralateral muscles might involve a transcallosal pathway modulating the excitability of one cortex when the other is activated. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:1033–1039, 1998
We mapped the cortical representations of the abductor pollicis brevis, flexor carpi radialis, biceps and deltoid muscles in six subjects with unilateral wrist fractures, immediately after the removal of the splint. This was repeated 1 month later in three out of the six subjects. Duration of immobilization was 1 month. Muscle maps were obtained by delivering four focal magnetic pulses for each scalp position (1 cm apart with reference to Cz) over the contralateral hemisphere. Motor evoked potentials (MEPs) were averaged off-line and expressed as a percentage of the motor action potential evoked by supramaximal peripheral nerve stimulation. Volume, area and threshold of the motor maps showed no significant hemispheric differences within each muscle in 10 control subjects. In the first recording session the volume of each immobilized muscle was distinctly higher when compared to that of controls in terms of absolute value and side-to-side ratio. This finding disappeared 1 month later. Moreover, MEP amplitude difference recorded from hand muscle could be reversed during a small tonic voluntary contraction. Immobilization had no significant effect on the threshold for activation of the target muscles and on the area of the motor map. The increase in MEP amplitudes occurred without changes in spinal excitability as tested by the F wave. These findings suggest that immobilization of the upper limb induces a reversible enhancement of the excitability of structures along the corticomotoneuronal pathway. Sustained restriction of volitional movements and reduction in somatic sensory inputs might promote this functional modulation of the motor system.
H-reflex and motor evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) in soleus muscle of five normal subjects were investigated before and after 20 days 6° head-down bed rest (BR). Soleus H-reflex during standing following bed rest decreased in all five subjects. The size of the maximum H-reflex (Hmax), expressed as a percentage of the maximum M-response (Mmax), decreased from 63.3±23.3% before BR to 26.7±12.5% after BR. However, there were no significant differences between MEPs before and after bed rest. Moreover, MEP/Hmax after bed rest was larger than before bed rest in all subjects. These results indicate a strong inhibition of H-reflex and no adaptation of MEP in soleus muscle during standing following bed rest.
Prolonged reductions in muscle activity results in alterations in neuromuscular properties; however, the time course of adaptations is not fully understood, and many of the specific adaptations have not been identified. This study evaluated the temporal evolution of adaptations in neuromuscular properties during and following 3 wk of immobilization. We utilized a combination of techniques involving nerve stimulation and transcranial magnetic stimulation to assess changes in central activation of muscle, along with spinal (H reflex) and corticospinal excitability [i.e., motor-evoked potential (MEP) amplitude, silent period (SP)] and contractile properties in 10 healthy humans undergoing 3 wk of forearm immobilization and 9 control subjects. Immobilization induced deficits in central activation (85 +/- 3 to 67 +/- 7% ) that returned to baseline levels 1 wk after cast removal. The flexor carpii radialis MEP amplitude increased greater than twofold after the first week of immobilization and remained elevated throughout immobilization and 1 wk after cast removal. Additionally, we observed a prolongation of the SP 1 wk after cast removal compared with baseline (78.5 +/- 7.1 to 98.2 +/- 8.7 ms). The contractile properties were also altered, since the rate of evoked force relaxation was slower following immobilization (-14.5 +/- 1.4 to -11.3 +/- 1.0% peak force/ms), and remained depressed 1 wk after cast removal (-10.5 +/- 0.8% peak force/ms). These observations detail the time course of adaptations in corticospinal and contractile properties associated with disuse and illustrate the profound effect of immobilization on the human neuromuscular system as evidenced by the alterations in corticospinal excitability persisting 1 wk following cast removal.
It has long been believed that training for increased strength not only affects muscle tissue, but also results in adaptive changes in the central nervous system. However, only in the last 10 years has the use of methods to study the neurophysiological details of putative neural adaptations to training become widespread. There are now many published reports that have used single motor unit recordings, electrical stimulation of peripheral nerves, and non-invasive stimulation of the human brain [i.e. transcranial magnetic stimulation (TMS)] to study neural responses to strength training. In this review, we aim to summarize what has been learned from single motor unit, reflex and TMS studies, and identify the most promising avenues to advance our conceptual understanding with these methods. We also consider the few strength training studies that have employed alternative neurophysiological techniques such as functional magnetic resonance imaging and electroencephalography. The nature of the information that these techniques can provide, as well as their major technical and conceptual pitfalls, are briefly described. The overall conclusion of the review is that the current evidence regarding neural adaptations to strength training is inconsistent and incomplete. In order to move forward in our understanding, it will be necessary to design studies that are based on a rigorous consideration of the limitations of the available techniques, and that are specifically targeted to address important conceptual questions.
Training a muscle group in one limb yields strength gains bilaterally-the so-called cross-education effect. However, to date there has been little study of the targeted application of this phenomenon in a manner relevant to clinical rehabilitation. For example, it may be applicable post-stroke, where hemiparesis leads to ankle flexor weakness. The purpose of this study was to examine the effects of high-intensity unilateral dorsiflexion resistance training on agonist (tibialis anterior, TA) and antagonist (plantarflexor soleus, SOL) muscular strength and H-reflex excitability in the trained and untrained limbs. Ankle flexor and extensor torque, as well as SOL and TA H-reflexes evoked during low-level contraction, were measured before and after 5 weeks of dorsiflexion training (n = 19). As a result of the intervention, dorsiflexor maximal voluntary isometric contraction force (MVIC) significantly increased (P < 0.05) in both the trained and untrained limbs by 14.7 and 8.4%, respectively. No changes in plantarflexor MVIC force were observed in either limb. Significant changes in H-reflex excitability threshold were also detected: H(@thresh) significantly increased in the trained TA and SOL; and H(@max) decreased in both SOL muscles. These findings reveal that muscular crossed effects can be obtained in the ankle dorsiflexor muscles and provide novel information on agonist and antagonist spinal adaptations that accompany unilateral training. It is possible that the ability to strengthen the ankle dorsiflexors bilaterally could be applied in post-stroke rehabilitation, where ankle flexor weakness could be counteracted via dorsiflexor training in the less-affected limb.
The purpose of this study was to apply cross-education during 4 wk of unilateral limb immobilization using a shoulder sling and swathe to investigate the effects on muscle strength, muscle size, and muscle activation. Twenty-five right-handed participants were assigned to one of three groups as follows: the Immob + Train group wore a sling and swathe and strength trained (n = 8), the Immob group wore a sling and swathe and did not strength train (n = 8), and the Control group received no treatment (n = 9). Immobilization was applied to the nondominant (left) arm. Strength training consisted of maximal isometric elbow flexion and extension of the dominant (right) arm 3 days/wk. Torque (dynamometer), muscle thickness (ultrasound), maximal voluntary activation (interpolated twitch), and electromyography (EMG) were measured. The change in right biceps and triceps brachii muscle thickness [7.0 ± 1.9 and 7.1 ± 2.2% (SE), respectively] was greater for Immob + Train than Immob (0.4 ± 1.2 and -1.9 ± 1.7%) and Control (0.8 ± 0.5 and 0.0 ± 1.1%, P < 0.05). Left biceps and triceps brachii muscle thickness for Immob + Train (2.2 ± 0.7 and 3.4 ± 2.1%, respectively) was significantly different from Immob (-2.8 ± 1.1 and -5.2 ± 2.7%, respectively, P < 0.05). Right elbow flexion strength for Immob + Train (18.9 ± 5.5%) was significantly different from Immob (-1.6 ± 4.0%, P < 0.05). Right and left elbow extension strength for Immob + Train (68.1 ± 25.9 and 32.2 ± 9.0%, respectively) was significantly different from the respective limb of Immob (1.3 ± 7.7 and -6.1 ± 7.8%) and Control (4.7 ± 4.7 and -0.2 ± 4.5%, P < 0.05). Immobilization in a sling and swathe decreased strength and muscle size but had no effect on maximal voluntary activation or EMG. The cross-education effect on the immobilized limb was greater after elbow extension training. This study suggests that strength training the nonimmobilized limb benefits the immobilized limb for muscle size and strength.
Cross-education of strength is much greater when the dominant arm is trained in right-handed individuals. This asymmetry of strength transfer in the upper limbs is similar to what has been shown for skill transfer between limbs. The discussion focuses on the connection between transfer of strength and skills and the potential for cross-education to be used during recovery from unilateral injury.
Although it has long been known that practicing a motor task with one limb can improve performance with the limb opposite, the mechanisms remain poorly understood. Here we tested the hypothesis that improved performance with the untrained limb on a fastest possible (i.e. ballistic) movement task depends partly on cortical circuits located ipsilateral to the trained limb. The idea that crossed effects, which are important for the learning process, might occur in the 'untrained' hemisphere following ballistic training is based on the observation that tasks requiring strong descending drive generate extensive bilateral cortical activity. Twenty-one volunteers practiced a ballistic index finger abduction task with their right hand, and corticospinal excitability was assessed in two hand muscles (first dorsal interosseus, FDI; adductor digiti minimi, ADM). Eight control subjects did not train. After training, repetitive transcranial magnetic stimulation (rTMS; 15 min at 1 Hz) was applied to the left (trained) or right (untrained) motor cortex to induce a 'virtual lesion'. A third training group received sham rTMS, and control subjects received rTMS to the right motor cortex. Performance and corticospinal excitability (for FDI) increased in both hands for training but not control subjects. rTMS of the left, trained motor cortex specifically reduced training-induced gains in motor performance for the right, trained hand, and rTMS of the right, untrained motor cortex specifically reduced performance gains for the left, untrained hand. Thus, cortical processes within the untrained hemisphere, ipsilateral to the trained hand, contribute to early retention of ballistic performance gains for the untrained limb.
Inactivity is a recognized compounding factor in sarcopenia and muscle weakness in old age. However, while the negative effects of unloading on skeletal muscle in young individuals are well elucidated, only little is known about the consequence of immobilization and the regenerative capacity in elderly individuals. Thus the aim of this study was to examine the effect of aging on changes in muscle contractile properties, specific force, and muscle mass characteristics in 9 old (61-74 yr) and 11 young men (21-27 yr) after 2 wk of immobilization and 4 wk of retraining. Both young and old experienced decreases in maximal muscle strength, resting twitch peak torque and twitch rate of force development, quadriceps muscle volume, pennation angle, and specific force after 2 wk of immobilization (P < 0.05). The decline in quadriceps volume and pennation angle was smaller in old compared with young (P < 0.05). In contrast, only old men experienced a decrease in quadriceps activation. After retraining, both young and old regained their initial muscle strength, but old had smaller gains in quadriceps volume compared with young, and pennation angle increased in young only (P < 0.05). The present study is the first to demonstrate that aging alters the neuromuscular response to short-term disuse and recovery in humans. Notably, immobilization had a greater impact on neuronal motor function in old individuals, while young individuals were more affected at the muscle level. In addition, old individuals showed an attenuated response to retraining after immobilization compared with young individuals.