Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training
IntroductionEarly increases in muscle strength following unilateral resistance training are typically accompanied by strength gains in the contralateral untrained muscles, a phenomenon known as cross-education. However, the specific motor unit adaptations responsible for this gain transfer remain po...
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Frontiers Media S.A.
2025-01-01
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| Series: | Frontiers in Physiology |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/fphys.2024.1512309/full |
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| author | Edoardo Lecce Alessandra Conti Alessandro Del Vecchio Francesco Felici Alessandro Scotto di Palumbo Massimo Sacchetti Ilenia Bazzucchi |
| author_facet | Edoardo Lecce Alessandra Conti Alessandro Del Vecchio Francesco Felici Alessandro Scotto di Palumbo Massimo Sacchetti Ilenia Bazzucchi |
| author_sort | Edoardo Lecce |
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| description | IntroductionEarly increases in muscle strength following unilateral resistance training are typically accompanied by strength gains in the contralateral untrained muscles, a phenomenon known as cross-education. However, the specific motor unit adaptations responsible for this gain transfer remain poorly understood. To address this gap, we recorded myoelectrical activity from the biceps brachii using high-density electromyography.MethodsNine participants performed 8-week unilateral resistance training and were compared to nine control individuals who did no intervention. Discharge characteristics of longitudinally tracked motor units were assessed during maximal voluntary contractions and isometric ramp contractions at 35% and 70% of the maximal voluntary force (MVF) at baseline (T0), 4 weeks (T1), and 8 weeks (T2) post-intervention.ResultsMVF increased by 7% in untrained muscles at T1 and 10% at T2 (p < 0.05). These gains were accompanied by significant decreases in motor unit recruitment thresholds (p < 0.01) and higher net discharge rate (i.e., gain in discharge rate from recruitment to peak) following intervention (p < 0.05). Trained muscles presented greater MVF (+11%, T1; +19%, T2) with similar motor unit adaptations, including a lower recruitment threshold (p < 0.01) and a higher net discharge rate (p < 0.01).DiscussionOur findings indicate that higher strength in untrained muscles is associated with a higher net discharge rate, implying a greater spinal motoneuron output to muscles. The present results underscore the role of motor unit adaptations in the transfer of strength gains to non-trained muscles, offering novel insights into the neural mechanisms underlying cross-education. |
| format | Article |
| id | doaj-art-8413412241ba4386aab395b9473cfdf9 |
| institution | Kabale University |
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| language | English |
| publishDate | 2025-01-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Physiology |
| spelling | doaj-art-8413412241ba4386aab395b9473cfdf92025-01-07T06:49:33ZengFrontiers Media S.A.Frontiers in Physiology1664-042X2025-01-011510.3389/fphys.2024.15123091512309Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance trainingEdoardo Lecce0Alessandra Conti1Alessandro Del Vecchio2Francesco Felici3Alessandro Scotto di Palumbo4Massimo Sacchetti5Ilenia Bazzucchi6Laboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyLaboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyDepartment Artificial Intelligence in Biomedical Engineering, Faculty of Engineering, Zentralinstitut für Medizintechnik (ZIMT), Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, GermanyLaboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyLaboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyLaboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyLaboratory of Exercise Physiology, Department of Movement, Human, and Health Sciences, University of “Foro Italico, Rome, ItalyIntroductionEarly increases in muscle strength following unilateral resistance training are typically accompanied by strength gains in the contralateral untrained muscles, a phenomenon known as cross-education. However, the specific motor unit adaptations responsible for this gain transfer remain poorly understood. To address this gap, we recorded myoelectrical activity from the biceps brachii using high-density electromyography.MethodsNine participants performed 8-week unilateral resistance training and were compared to nine control individuals who did no intervention. Discharge characteristics of longitudinally tracked motor units were assessed during maximal voluntary contractions and isometric ramp contractions at 35% and 70% of the maximal voluntary force (MVF) at baseline (T0), 4 weeks (T1), and 8 weeks (T2) post-intervention.ResultsMVF increased by 7% in untrained muscles at T1 and 10% at T2 (p < 0.05). These gains were accompanied by significant decreases in motor unit recruitment thresholds (p < 0.01) and higher net discharge rate (i.e., gain in discharge rate from recruitment to peak) following intervention (p < 0.05). Trained muscles presented greater MVF (+11%, T1; +19%, T2) with similar motor unit adaptations, including a lower recruitment threshold (p < 0.01) and a higher net discharge rate (p < 0.01).DiscussionOur findings indicate that higher strength in untrained muscles is associated with a higher net discharge rate, implying a greater spinal motoneuron output to muscles. The present results underscore the role of motor unit adaptations in the transfer of strength gains to non-trained muscles, offering novel insights into the neural mechanisms underlying cross-education.https://www.frontiersin.org/articles/10.3389/fphys.2024.1512309/fullcross-educationEMGmotor unitneuromuscular adaptationsresistance trainingstrength |
| spellingShingle | Edoardo Lecce Alessandra Conti Alessandro Del Vecchio Francesco Felici Alessandro Scotto di Palumbo Massimo Sacchetti Ilenia Bazzucchi Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training Frontiers in Physiology cross-education EMG motor unit neuromuscular adaptations resistance training strength |
| title | Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training |
| title_full | Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training |
| title_fullStr | Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training |
| title_full_unstemmed | Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training |
| title_short | Cross-education: motor unit adaptations mediate the strength increase in non-trained muscles following 8 weeks of unilateral resistance training |
| title_sort | cross education motor unit adaptations mediate the strength increase in non trained muscles following 8 weeks of unilateral resistance training |
| topic | cross-education EMG motor unit neuromuscular adaptations resistance training strength |
| url | https://www.frontiersin.org/articles/10.3389/fphys.2024.1512309/full |
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