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Does Unilateral High‐Load Resistance Training Influence Strength Change in the Contralateral Arm Also Undergoing High‐Load Training?

Authors:
Jun Seob Song at Texas A&M University – San Antonio
Jun Seob Song
Yujiro Yamada at University of Mississippi
Yujiro Yamada
Ryo Kataoka at University of Mississippi
Ryo Kataoka
William B. Hammert
William B. Hammert
William B. Hammert
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Training one limb with a high‐load has been shown to augment strength changes in the opposite limb training with a low‐load (via cross‐education of strength), indicating that within‐subject models can be problematic when investigating strength changes. This study examined if the cross‐education of strength from unilateral high‐load training could augment the strength changes in the opposite arm undergoing the same unilateral high‐load training. 160 participants were randomized to one of four groups: (1) training on the dominant arm followed by the non‐dominant arm (D + ND), (2) training on the dominant arm only (D‐Only), (3) training on the non‐dominant arm only (ND‐Only), and (4) a non‐exercise control. All exercise groups performed 18 sessions of unilateral high‐load elbow flexion exercise over 6 weeks. Participants were compared for changes in 1RM strength and muscle thickness. Changes in strength of the non‐dominant arm were greater in D + ND (2.7 kg) and ND‐Only (2.6 kg) compared to D‐Only (1.5 kg) and control (−0.2 kg), while the changes were greater in D‐Only compared to control. The same finding was observed in the dominant arm. Only the arms being directly trained observed increases in muscle thickness. Unilateral high‐load resistance training increased strength in the opposite untrained arm, without changes in muscle thickness. This cross‐education of strength did not augment the strength changes in the contralateral arm undergoing the same unilateral high‐load training. However, it does not necessarily indicate that within‐subject models are methodologically sound to investigate strength change if both limbs are trained with a high‐load.
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Scandinavian Journal of Medicine & Science in Sports, 2024; 34:e14772
https://doi.org/10.1111/sms.14772
Scandinavian Journal of Medicine & Science in Sports
ORIGINAL ARTICLE
Does Unilateral High- Load Resistance Training Influence
Strength Change in the Contralateral Arm Also Undergoing
High- Load Training?
JunSeobSong1 | YujiroYamada2 | RyoKataoka2 | WilliamB.Hammert2 | AnnaKang2 | RobertW.Spitz3 |
VickieWong4 | AldoSeffrin5 | WitaloKassiano2 | JeremyP.Loenneke2
1Department of Counseling, Health, and Kinesiolog y, Texas A&M University- San Antonio, San Antonio, Texas, USA | 2Department of Health, Exercise
Science, and Recreation Management. Kevser Ermin Applied Physiology Laboratory, The University of Mississippi, Mississippi, USA | 3Department of
Physiology and Biophysics, University of Mississippi Medical Center, Jackson, Mississippi, USA | 4Department of Sport and Health, Solent University,
Southampton, Hampshire, UK | 5Postgraduate Program in Translation Medicine, Federal University of São Paulo, São Paulo, Brazil
Correspondence: Jeremy P. Loenneke (jploenne@olemiss.edu)
Received: 19 July 2024 | Revised: 5 November 2024 | Accepted: 12 November 2024
Funding: The authors received no specific funding for this work.
Keywords: bilateral transfer| cross education| interlimb transfer| w ithin subject
ABSTRACT
Training one limb with a high- load has been shown to augment strength changes in the opposite limb training with a low- load
(via cross- education of strength), indicating that within- subject models can be problematic when investigating strength changes.
This study examined if the cross- education of strength from unilateral high- load training could augment the strength changes
in the opposite arm undergoing the same unilateral high- load training. 160 participants were randomized to one of four groups:
(1) training on the dominant arm followed by the non- dominant arm (D + ND), (2) training on the dominant arm only (D- Only),
(3) training on the non- dominant arm only (ND- Only), and (4) a non- exercise control. All exercise groups performed 18 sessions
of unilateral high- load elbow f lexion exercise over 6 weeks. Participants were compared for changes in 1RM strength and muscle
thickness. Changes in strength of the non- dominant arm were greater in D + ND (2.7 kg) and ND- Only (2.6 kg) compared to
D- Only (1.5 kg) and control (−0.2 kg), while the changes were greater in D- Only compared to control. The same finding was ob-
served in the dominant arm. Only the arms being directly trained observed increases in muscle thickness. Unilateral high- load
resistance training increased strength in the opposite untrained arm, without changes in muscle thickness. This cross- education
of strength did not augment the strength changes in the contralateral arm undergoing the same unilateral high- load training.
However, it does not necessarily indicate that within- subject models are methodologically sound to investigate strength change
if both limbs are trained with a high- load.
1 | Introduction
Performing unilateral resistance training has been shown to in-
crease muscle strength not only in the trained limb but also in
the contralateral untrained limb [1–3]. This transfer of strength
to the opposite untrained limb is commonly referred to as the
cross- education of strength [1, 2]. Cross- education of strength
was first reported as early as the late nineteenth century, [4] and
since then, numerous studies have shown this effect in different
muscle groups [e.g., upper [5, 6] and lower [7, 8] limbs] and fol-
lowing various training modalities such as isotonic [9, 10], iso-
metric [6, 11], and isokinetic [12, 13] resistance train ing. There is
general consensus that the cross- education of strength is likely
driven by neural adaptations since changes at the muscle level
© 2024 J ohn Wiley & Sons A/S . Published by John W iley & Sons Ltd.
... Further investigations are warranted exploring these aspects as well as the neuroplasticity of the strength adaptation (Škarabot et al. 2021). Of additional note, any potential cross-education interference effect on maximum strength (i.e., improvements in the contralateral, traditionally nontrained, and arm) appears negligible in this context, as it is unlikely to occur when both limbs are trained, particularly with similar loads (Song et al. 2024). ...
Comparison Between Shoulder Flexed and Extended Positions in Elbow Flexion Resistance Training on Regional Hypertrophy and Maximum Strength: Preacher versus Bayesian Cable Curls
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Introduction The application of blood flow restriction (BFR) to low-intensity exercise may be able to increase strength not only in the trained limb but also in the homologous untrained limb. Whether this effect is repeatable and how that change compares to that observed with higher intensity exercise is unknown. Purpose Examine whether low-intensity training with BFR enhances the cross-education of strength compared to exercise without BFR and maximal efforts. Methods A total of 179 participants completed the 6-week study, with 135 individuals performing isometric handgrip training over 18 sessions. Participants were randomly assigned to one of four groups: 1) low-intensity (4 × 2 min of 30% MVC; LI, n = 47), 2) low-intensity with blood flow restriction (LI + 50% arterial occlusion pressure; LI-BFR, n = 41), 3) maximal effort (4 × 5 s of 100% MVC; MAX, n = 47), and 4) non-exercise control (CON, n = 44). Results LI-BFR was the only group that observed a cross-education in strength (CON: 0.64 SD 2.9 kg, LI: 0.95 SD 3.6 kg, BFR-LI: 2.7 SD 3.3 kg, MAX: 0.80 SD 3.1 kg). In the trained hand, MAX observed the greatest change in strength (4.8 SD 3.3 kg) followed by LI-BFR (2.8 SD 4.0 kg). LI was not different from CON. Muscle thickness did not change in the untrained arm, but ulna muscle thickness was increased within the trained arm of the LI-BFR group (0.06 SD 0.11 cm). Conclusion Incorporating BFR into low-intensity isometric training led to a cross-education effect on strength that was greater than all other groups (including high-intensity training).
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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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Unilateral high-load resistance training influences strength changes in the contralateral arm undergoing low-load training
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  • Jun 2023
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Objectives: Within-subject training models have become common within the exercise literature. However, it is currently unknown if training one arm with a high load would impact muscle size and strength of the opposing arm training with a low load. Design: Parallel group. Methods: 116 participants were randomized to one of three groups that completed 6-weeks (18 sessions) of elbow flexion exercise. Group 1 trained their dominant arm only, beginning with a one-repetition maximum test (≤5 attempts), followed by four sets of exercise using a weight equivalent to 8-12 repetition maximum. Group 2 completed the same training as Group 1 in their dominant arm, while the non-dominant arm completed four sets of low-load exercise (30-40 repetition maximum). Group 3 trained their non-dominant arm only, performing the same low-load exercise as Group 2. Participants were compared for changes in muscle thickness and elbow flexion one-repetition maximum. Results: The greatest changes in non-dominant strength were present in Groups 1 (Δ 1.5 kg; untrained arm) and 2 (Δ1.1 kg; low-load arm with high load on opposite arm), compared to Group 3 (Δ 0.3 kg; low-load only). Only the arms being directly trained observed changes in muscle thickness (≈Δ 0.25 cm depending on site). Conclusions: Within-subject training models are potentially problematic when investigating changes in strength (though not muscle growth). This is based on the finding that the untrained limb of Group 1 saw similar changes in strength as the non-dominant limb of Group 2 which were both greater than the low-load training limb of Group 3.
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The contraction history of the muscle and strength change: lessons learned from unilateral training models
Article
  • Oct 2019
Participation in resistance exercise is encouraged throughout the lifetime, offering such benefits as improved strength and muscle mass accretion. Considerable research has been completed on this topic within the past several decades, with the current narrative dictating that increased muscle size yields further increases in muscle strength. However, there remain unanswered questions relating to the observation that certain training interventions yield only one specific adaptation (strength or size). Studies investigating resistance training often include either bilateral or unilateral exercise programs. Unilateral exercise programs are often used as they allow for comparison between two separate training interventions within the same individual. This is viewed as an advantage, relating to statistical power, but a limitation insofar as one intervention could be confounded by the intervention within the opposing limb. For example, when only one limb is trained both limbs often get stronger (albeit to differing magnitudes), termed the cross-education effect. However, we propose that when both limbs are trained that the cross-education effect may not occur and that the adaptations produced are reflective of the contraction history of the muscle. Herein, we discuss ways to test the idea that strength change may be dictated by the contraction history of the muscle. If each limb responds only to the contraction history within each limb (as opposed to the opposite limb), then this would have immediate ramifications for research design. Furthermore, this would certainly be of importance among injured populations undergoing rehabilitation, seeking to find the most efficacious exercise regimens.
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