Sara Blocquiaux1, Tatiane Gorski2, Evelien Van Roie3, Monique Ramaekers4, Ruud Van Thienen5, Henri Nielens6, Christophe Delecluse7, Katrien De Bock8, Martine Thomis9. 1. Physical Activity, Sport & Health Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. Electronic address: sara.blocquiaux@kuleuven.be. 2. Laboratory of Exercise and Health, Department of Health Sciences and Technology, ETH Zürich - Swiss Federal Institute of Technology in Zürich, Schorenstrasse 16, 8603 Schwerzenbach, Switzerland. Electronic address: tatiane-gorski@ethz.ch. 3. Physical Activity, Sport & Health Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. Electronic address: evelien.vanroie@kuleuven.be. 4. Exercise Physiology Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. Electronic address: monique.ramaekers@kuleuven.be. 5. Exercise Physiology Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. 6. Research Group for Neurorehabilitation, Department of Rehabilitation Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1501, 3001 Leuven, Belgium; Saint-Luc University Hospital and Institute of NeuroScience, System and Cognition Division, UCLouvain - University of Louvain, Avenue Mounier 53, box B1.53.02, 1200 Woluwe-Saint-Lambert, Belgium. Electronic address: henri.nielens@uclouvain.be. 7. Physical Activity, Sport & Health Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. Electronic address: christophe.delecluse@kuleuven.be. 8. Laboratory of Exercise and Health, Department of Health Sciences and Technology, ETH Zürich - Swiss Federal Institute of Technology in Zürich, Schorenstrasse 16, 8603 Schwerzenbach, Switzerland. Electronic address: katrien-debock@ethz.ch. 9. Physical Activity, Sport & Health Research Group, Department of Movement Sciences, KU Leuven - University of Leuven, Tervuursevest 101, Box 1500, 3001 Leuven, Belgium. Electronic address: martine.thomis@kuleuven.be.
Abstract
INTRODUCTION: Ageing is associated with an attenuated hypertrophic response to resistance training and periods of training interruptions. Hence, elderly would benefit from the 'muscle memory' effects of resistance training on muscle strength and mass during detraining and retraining. As the underlying mechanisms are not yet clear, this study investigated the role of myonuclei during training, detraining and retraining by using PCM1 labelling in muscle cross-sections of six older men. METHODS: Knee extension strength and power were measured in 30 older men and 10 controls before and after 12 weeks resistance training and after detraining and retraining of similar length. In a subset, muscle biopsies from the vastus lateralis were taken for analysis of fibre size, fibre type distribution, Pax7+ satellite cell number and myonuclear domain size. RESULTS: Resistance training increased knee extension strength and power parameters (+10 to +36%, p < .001) and decreased the frequency of type IIax fibres by half (from 20 to 10%, p = .034). Detraining resulted in a modest loss of strength and power (-5 to -15%, p ≤ .004) and a trend towards a fibre-type specific decrease in type II fibre cross-sectional area (-17%, p = .087), type II satellite cell number (-30%, p = .054) and type II myonuclear number (-12%, p = .084). Less than eight weeks of retraining were needed to reach the post-training level of one-repetition maximum strength. Twelve weeks of retraining were associated with type II fibre hypertrophy (+29%, p = .050), which also promoted an increase in the number of satellite cells (+72%, p = .036) and myonuclei (+13%, p = .048) in type II fibres. Changes in the type II fibre cross-sectional area were positively correlated with changes in the myonuclear number (Pearson's r between 0.40 and 0.73), resulting in a stable myonuclear domain. CONCLUSION: Gained strength and power and fibre type changes were partially preserved following 12 weeks of detraining, allowing for a fast recovery of the 1RM performance following retraining. Myonuclear number tended to follow individual changes in type II fibre size, which is in support of the myonuclear domain theory.
INTRODUCTION: Ageing is associated with an attenuated hypertrophic response to resistance training and periods of training interruptions. Hence, elderly would benefit from the 'muscle memory' effects of resistance training on muscle strength and mass during detraining and retraining. As the underlying mechanisms are not yet clear, this study investigated the role of myonuclei during training, detraining and retraining by using PCM1 labelling in muscle cross-sections of six older men. METHODS: Knee extension strength and power were measured in 30 older men and 10 controls before and after 12 weeks resistance training and after detraining and retraining of similar length. In a subset, muscle biopsies from the vastus lateralis were taken for analysis of fibre size, fibre type distribution, Pax7+ satellite cell number and myonuclear domain size. RESULTS: Resistance training increased knee extension strength and power parameters (+10 to +36%, p < .001) and decreased the frequency of type IIax fibres by half (from 20 to 10%, p = .034). Detraining resulted in a modest loss of strength and power (-5 to -15%, p ≤ .004) and a trend towards a fibre-type specific decrease in type II fibre cross-sectional area (-17%, p = .087), type II satellite cell number (-30%, p = .054) and type II myonuclear number (-12%, p = .084). Less than eight weeks of retraining were needed to reach the post-training level of one-repetition maximum strength. Twelve weeks of retraining were associated with type II fibre hypertrophy (+29%, p = .050), which also promoted an increase in the number of satellite cells (+72%, p = .036) and myonuclei (+13%, p = .048) in type II fibres. Changes in the type II fibre cross-sectional area were positively correlated with changes in the myonuclear number (Pearson's r between 0.40 and 0.73), resulting in a stable myonuclear domain. CONCLUSION: Gained strength and power and fibre type changes were partially preserved following 12 weeks of detraining, allowing for a fast recovery of the 1RM performance following retraining. Myonuclear number tended to follow individual changes in type II fibre size, which is in support of the myonuclear domain theory.
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