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Contralateral strength training attenuates muscle performance loss following anterior cruciate ligament (ACL) reconstruction: a randomised-controlled trial

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PurposeTo investigate the effects of cross-education (CE) exercise on strength and performance at 10 and 24 weeks post anterior cruciate ligament (ACL) surgery.Methods Design: randomised controlled trial. N = 44 ACL-reconstruction patients, randomly-allocated into: CE: strength training of the non-operative limb, or CON: sham exercise of upper limb stretching. Each patient underwent standardised ACL rehabilitation, plus 8 weeks of thrice weekly CE or CON, commencing at 2 weeks post surgery. The primary outcome was quadriceps peak force (QPF) of the ACL-reconstructed limb at 10 weeks post surgery. Secondary measures were hamstrings peak force (HPF), rate of force development (RFD) and International Knee Documentation Committee score (IKDC) at 10 and 24 weeks; QPF and hop for distance (HOP) at 24 weeks post surgery.ResultsCE significantly attenuated the decline in QPF of the ACL-reconstructed limb at 10 weeks compared to CON (16.6% decrease vs. 32.0%, respectively); that advantage was not retained at 24 weeks. A training effect was observed in the trained limb for HPF and QPF, which was retained at 24 weeks. No significant differences were observed for IKDC, HOP, RFD, or HPF of the reconstructed limb. Inter-limb symmetry (ILS) ranged from 0.78 to 0.89 and was not significantly different between groups.Conclusion High-intensity CE strength training attenuated the post-operative decline in QPF and should be considered in early-phase ACL rehabilitation. ILS data showed good symmetry, but it masked significantly inferior performance between groups and should be used with caution.Trial registration numberNCT02722876.
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European Journal of Applied Physiology (2021) 121:3551–3559
https://doi.org/10.1007/s00421-021-04812-3
ORIGINAL ARTICLE
Contralateral strength training attenuates muscle performance
loss followinganterior cruciate ligament (ACL) reconstruction:
arandomised‑controlled trial
ClaireMinshull1,2 · PeterGallacher1· SimonRoberts1· AndrewBarnett1· JanHermanKuiper1,3· AndreaBailey1
Received: 26 April 2021 / Accepted: 11 September 2021 / Published online: 20 September 2021
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021
Abstract
Purpose To investigate the effects of cross-education (CE) exercise on strength and performance at 10 and 24weeks post
anterior cruciate ligament (ACL) surgery.
Methods Design: randomised controlled trial. N = 44 ACL-reconstruction patients, randomly-allocated into: CE: strength
training of the non-operative limb, or CON: sham exercise of upper limb stretching. Each patient underwent standardised
ACL rehabilitation, plus 8weeks of thrice weekly CE or CON, commencing at 2weeks post surgery. The primary outcome
was quadriceps peak force (QPF) of the ACL-reconstructed limb at 10weeks post surgery. Secondary measures were ham-
strings peak force (HPF), rate of force development (RFD) and International Knee Documentation Committee score (IKDC)
at 10 and 24weeks; QPF and hop for distance (HOP) at 24weeks post surgery.
Results CE significantly attenuated the decline in QPF of the ACL-reconstructed limb at 10weeks compared to CON (16.6%
decrease vs. 32.0%, respectively); that advantage was not retained at 24weeks. A training effect was observed in the trained
limb for HPF and QPF, which was retained at 24weeks. No significant differences were observed for IKDC, HOP, RFD,
or HPF of the reconstructed limb. Inter-limb symmetry (ILS) ranged from 0.78 to 0.89 and was not significantly different
between groups.
Conclusion High-intensity CE strength training attenuated the post-operative decline in QPF and should be considered in
early-phase ACL rehabilitation. ILS data showed good symmetry, but it masked significantly inferior performance between
groups and should be used with caution.
Trial registration number NCT02722876.
Keywords Cross-education· Cross-transfer· Rehabilitation· Strength training
Abbreviations
ACL Anterior cruciate ligament
CE Cross-education
CON Control
QPF Quadriceps peak force
HPF Hamstrings peak force
RFD Rate of force development
ILS Inter-limb symmetry
IKDC International knee documentation
Introduction
Anterior cruciate ligament (ACL) injury is a common and
debilitating injury (Ardern etal. 2011; Sanders etal. 2016)
and without intervention often prevents return to play. Surgi-
cal reconstruction to restore mechanical rotational instability
(Krause etal. 2018) is the preferred treatment option, where
patients have ongoing symptoms of instability despite con-
servative treatment (Schmitt etal. 2012).
ACL reconstruction (ACLR) often results in significant
and prolonged functional impairments, in particular asym-
metry of quadriceps strength (Gokeler etal. 2014; Kuenze
Communicated by Toshio Moritani.
* Claire Minshull
minshullc@hotmail.com
1 Research Department, RJAH Orthopaedic Hospital NHS
Foundation Trust, OswestrySY107AG, UK
2 Get Back To Sport Ltd, Nottingham, UK
3 School ofPharmacy andBioengineering, Keele University,
Keele, StaffordshireST55BG, UK
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... For example, considerable deficits in knee extensor muscle strength (i.e., muscle weakness) persist for years following anterior cruciate ligament (ACL) reconstruction, with inevitable functional consequences [8,9]. Because the impossibility to adequately exercise the knee extensor muscles on the operative side early after ACL reconstruction surgery seems to be one of the main contributors to the resulting muscle weakness, contralateral (i.e., nonoperative-side) resistance training has been proposed as a potential countermeasure against muscle weakness [10][11][12][13]. Even if this type of training is not considered in ACL rehabilitation guidelines [14], in the last 10 years, four randomized controlled trials have investigated the effectiveness of different contralateral training protocols on knee extensor muscle strength early following ACL reconstruction [10][11][12][13]. ...
... Because the impossibility to adequately exercise the knee extensor muscles on the operative side early after ACL reconstruction surgery seems to be one of the main contributors to the resulting muscle weakness, contralateral (i.e., nonoperative-side) resistance training has been proposed as a potential countermeasure against muscle weakness [10][11][12][13]. Even if this type of training is not considered in ACL rehabilitation guidelines [14], in the last 10 years, four randomized controlled trials have investigated the effectiveness of different contralateral training protocols on knee extensor muscle strength early following ACL reconstruction [10][11][12][13]. In all these studies, resistance exercise consisted of concentric and/or eccentric voluntary contractions of the knee extensors of the nonoperative side performed on variable-resistance weight-lifting (leg extension and leg press) or isokinetic apparatuses, always as a complement to standard rehabilitation. ...
... The observed cross-education effect had positive short-term and/or longterm effects on operative-side knee extensor strength in all the studies, except in the one entailing the lowest contraction intensities [13]. Interestingly, higher-intensity contractions involving high-threshold fast motor unit recruitment have recently been suggested to play a role in explaining cross-education occurrence and magnitude [11]. In this perspective, it would be extremely relevant to explore the cross-education effect induced by NMES, which has the unique ability to recruit fast (in addition to slow) motor units even at relatively low contraction intensities [15]. ...
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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.
... Finally, 7 randomized clinical trials met the eligibility criteria and were included in this systematic review. [26][27][28][29][30][31][32] The kappa agreement between reviewers in the selection process was 1.0. ...
... 29 In the randomization process, 85.7% of the clinical trials were rated as having a low risk of bias. [26][27][28][30][31][32] For the missing outcome data, 100% of the clinical trials were rated as having a low risk of bias. [26][27][28][29][30][31][32] Finally, for the selection of the reported result, 57.1% of the clinical trials were rated as having a high risk for bias. ...
... [26][27][28][30][31][32] For the missing outcome data, 100% of the clinical trials were rated as having a low risk of bias. [26][27][28][29][30][31][32] Finally, for the selection of the reported result, 57.1% of the clinical trials were rated as having a high risk for bias. [26][27][28][29] ...
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Context: Unilateral training of the uninjured limb could be a useful therapeutic tool to induce cross-education in periods of immobilization, however, the effectiveness of this training in patients with anterior cruciate ligament (ACL) reconstruction is unknown. Objective: To determine the effectiveness of unilateral training of the uninjured limb on muscle strength and knee function in patients with ACL reconstruction. Design: Systematic review and meta-analysis. Evidence acquisition: An electronic search was performed in the MEDLINE, LILACS, CENTRAL, Embase, Scopus, Web of Science, CINAHL, SPORTDiscus, and PEDro databases from inception until March 2021. The authors included randomized clinical trials that evaluated the effectiveness of unilateral training of the uninjured limb on muscle strength and knee function in patients after ACL reconstruction. Evidence synthesis: Seven clinical trials met the eligibility criteria, and for the quantitative synthesis, 5 studies were included. The standardized mean difference for isometric quadriceps strength was 0.60 at 8 to 12 weeks (95% confidence interval, 0.29 to 0.92; P = .01; I2 = 6%). There was a high quality of evidence according to the Grading of Recommendation, Assessment, Development and Evaluation rating. Four studies assessed knee function through different self-administered questionnaires at 8, 24, and 26 weeks. Only one study reported significant differences in knee function at 8 weeks, favoring the unilateral training group. Conclusions: There was a moderate to high quality of evidence, with statistical significance that the addition of unilateral training to standard rehabilitation improved the cross-education of quadriceps strength after ACL reconstruction. More research is needed to assess the consistency of these results. International Prospective Register of Systematic Reviews registration number: CRD42020199950.
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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.
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Purpose: Cross-education (CE) of strength is a well-known phenomenon whereby exercise of one limb can induce strength gains in the contralateral untrained limb. The only available meta-analyses on CE, which date back to a decade ago, estimated a modest 7.8% increase in contralateral strength following unilateral training. However, in recent years new evidences have outlined larger contralateral gains, which deserve to be systematically evaluated. Therefore, the aim of this meta-analysis was to appraise current data on CE and determine its overall magnitude of effect. Methods: Five databases were searched from inception to December 2016. All randomized controlled trials focusing on unilateral resistance training were carefully checked by two reviewers who also assessed the eligibility of the identified trials and extracted data independently. The risk of bias was assessed using the Cochrane Risk-of-Bias tool. Results: Thirty-one studies entered the meta-analysis. Data from 785 subjects were pooled and subgroup analyses by body region (upper/lower limb) and type of training (isometric/concentric/eccentric/isotonic-dynamic) were performed. The pooled estimate of CE was a significant 11.9% contralateral increase (95% CI 9.1-14.8; p < 0.00001; upper limb: + 9.4%, p < 0.00001; lower limb: + 16.4%, p < 0.00001). Significant CE effects were induced by isometric (8.2%; p = 0.0003), concentric (11.3%; p < 0.00001), eccentric (17.7%; p = 0.003) and isotonic-dynamic training (15.9%; p < 0.00001), although a high risk of bias was detected across the studies. Conclusions: Unilateral resistance training induces significant contraction type-dependent gains in the contralateral untrained limb. Methodological issues in the included studies are outlined to provide guidance for a reliable quantification of CE in future studies.
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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.
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Background: Individuals who experience a subsequent ipsilateral anterior cruci (cruciate)ate ligament (ACL) reinjury may use hazardous muscle activation strategies after primary ACL reconstruction (ACLR). The purpose of this study was to compare electromyograms (EMGs) of the quadriceps, hamstrings, and gastrocnemius muscles during a dynamic hopping task among individuals with a single ACL injury (ACLx1), individuals who went on to have secondary ipsilateral ACL injury (ACLx2), and individuals who have never sustained an ACL injury (ACLx0). Hypothesis: We expected that individuals who went on to experience a secondary ACL injury would use less quadriceps muscle activity as compared with individuals who experienced a single ACL injury. Study design: Cross-sectional study. Level of evidence: Level 3. Methods: Fourteen individuals that were returned to play post-ACLR and 7 non-ACL-injured individuals participated. Individuals who had undergone an ACLR were placed into groups depending on whether they had experienced a secondary ipsilateral ACL reinjury postprimary ACLR. EMG data of the vastus lateralis, biceps femoris, and lateral gastrocnemius were measured during 2 phases of a single-leg dynamic hopping task: preactivity (100 ms prior to ground contact) and reactivity (250 ms post-ground contact). Processed EMG data were compared across groups using 1-way analyses of variance, with post hoc independent t tests where appropriate (P ≤ 0.05). Results: At preactivity, ACLx1 (0.48% ± 0.2%max) was found to use significantly more hamstring activity than ACLx2 (0.20% ± 0.1%max, P = 0.018), but not than ACLx0 (0.38% ± 0.1%max, P > 0.05). At reactivity, both ACL groups were found to use less quadriceps activity than ACLx0 (ACLx1: 0.38% ± 0.1%max, P = 0.016; ACLx2: 0.40% ± 0.1%max, P = 0.033; ACLx0: 0.58% ± 0.1%max), but not than each other (P > 0.05). Conclusion: Quadriceps muscle activity during landing was diminished in all ACL participants as compared with participants who had never sustained an ACL injury. Individuals who did not experience a secondary ipsilateral ACL reinjury (ACLx1) used greater levels of hamstring activity prior to landing. Clinical relevance: The higher hamstring activity in patients who did not experience a secondary injury may be interpreted as a protective mechanism that is used to dynamically stabilize the reconstructed limb.