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MAEO SUMIAKI, BALSHAW THOMASG, MÄRZ BENJAMIN, ZHOU ZHAOXIA, HAUG BILL, MARTIN NEILRW, MAFFULLI NICOLA, FOLLAND JONATHANP. Long-Term Resistance Trained Human Muscles Have More Fibers, More Myofibrils, and Tighter Myofilament Packing Than Untrained. Med Sci Sports Exerc 2024; 56:1906-1915. [PMID: 38875487 PMCID: PMC11419278 DOI: 10.1249/mss.0000000000003495] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/16/2024]
Abstract
INTRODUCTION Increases in skeletal muscle size occur in response to prolonged exposure to resistance training that is typically ascribed to increased muscle fiber size. Whether muscle fiber number also changes remains controversial, and a paucity of data exists about myofibrillar structure. This cross-sectional study compared muscle fiber and myofibril characteristics in long-term resistance-trained (LRT) versus untrained (UNT) individuals. METHODS The maximal anatomical cross-sectional area (ACSAmax) of the biceps brachii muscle was measured by magnetic resonance imaging in 16 LRT (5.9 ± 3.5 yr' experience) and 13 UNT males. A muscle biopsy was taken from the biceps brachii to measure muscle fiber area, myofibril area, and myosin spacing. Muscle fiber number, and myofibril number in total and per fiber were estimated by dividing ACSAmax by muscle fiber area or myofibril area, and muscle fiber area by myofibril area, respectively. RESULTS Compared with UNT, LRT individuals had greater ACSAmax (+70%, P < 0.001), fiber area (+29%, P = 0.028), fiber number (+34%, P = 0.013), and myofibril number per fiber (+49%, P = 0.034) and in total (+105%, P < 0.001). LRT individuals also had smaller myosin spacing (-7%, P = 0.004; i.e., greater packing density) and a tendency toward smaller myofibril area (-16%, P = 0.074). ACSAmax was positively correlated with fiber area ( r = 0.526), fiber number ( r = 0.445), and myofibril number (in total r = 0.873 and per fiber r = 0.566), and negatively correlated with myofibril area ( r = -0.456) and myosin spacing ( r = -0.382) (all P < 0.05). CONCLUSIONS The larger muscles of LRT individuals exhibited more fibers in cross-section and larger muscle fibers, which contained substantially more total myofibrils and more packed myofilaments than UNT participants, suggesting plasticity of muscle ultrastructure.
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Affiliation(s)
- SUMIAKI MAEO
- Faculty of Sport and Health Science, Ritsumeikan University, Kusatsu, JAPAN
- School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM
| | - THOMAS G. BALSHAW
- School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM
- Versus Arthritis Centre for Sport, Exercise and Osteoarthritis Research, Loughborough University, Loughborough, UNITED KINGDOM
| | - BENJAMIN MÄRZ
- Loughborough Materials Characterization Centre, Department of Materials, Loughborough University, Loughborough, UNITED KINGDOM
- Shared Instrumentation Facility, Louisiana State University, Baton Rouge, LA
| | - ZHAOXIA ZHOU
- Loughborough Materials Characterization Centre, Department of Materials, Loughborough University, Loughborough, UNITED KINGDOM
| | - BILL HAUG
- School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM
| | - NEIL R. W. MARTIN
- School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM
| | - NICOLA MAFFULLI
- Department of Trauma and Orthopaedic Surgery, School Medicine, Surgery and Dentistry, University of Salerno, Salerno, ITALY
- School of Pharmacy and Bioengineering, Keele University School of Medicine, Stoke on Trent, UNITED KINGDOM
- Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, UNITED KINGDOM
| | - JONATHAN P. FOLLAND
- School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, UNITED KINGDOM
- Versus Arthritis Centre for Sport, Exercise and Osteoarthritis Research, Loughborough University, Loughborough, UNITED KINGDOM
- National Institute for Health and Care Research (NIHR) Leicester Biomedical Research Centre, UNITED KINGDOM
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Smith IC, Herzog W. Assumptions about the cross-sectional shape of skinned muscle fibers can distort the relationship between muscle force and cross-sectional area. J Appl Physiol (1985) 2023; 135:1036-1040. [PMID: 37732377 DOI: 10.1152/japplphysiol.00383.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2023] [Revised: 08/28/2023] [Accepted: 09/14/2023] [Indexed: 09/22/2023] Open
Abstract
Comparisons of muscle force output are often performed after normalization to muscle physiological cross-sectional area (CSA). Differences in force per CSA (i.e., specific force) suggest the presence of physiological differences in contractile function. Permeabilized mammalian skeletal muscle fibers frequently exhibit substantial declines in specific force with increasing CSA, suggesting that smaller fibers are intrinsically stronger than larger fibers of the same group. However, the potential for CSA assessment error to account for CSA-dependent differences in specific force has not received adequate attention. Assessment of fiber CSA typically involves measurement of fiber width and perhaps also height, and CSA is calculated by assuming the cross sections are either circular or elliptical with major and minor axes aligned with the optical measurement system. Differences between the assumed and real cross-sectional shapes would cause variability in the ratio of assessed CSA (aCSA) to real CSA (rCSA). This variability can insidiously bias aCSA such that large aCSAs typically overstate rCSAs of the fibers they represent, and small aCSAs typically understate the rCSAs of the fibers they represent. As aCSA is the denominator for the specific force calculation, scatterplots of specific force versus aCSA would be expected to show declines in specific force as aCSA increases without a corresponding effect in a scatterplot of specific force versus rCSA. When comparing active and passive muscle forces between data subsets defined by aCSA, the impact of CSA assessment error should be considered before exploring other physiological mechanisms.
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Affiliation(s)
- Ian C Smith
- NeuroMuscular Centre, Ottawa Hospital Research Institute, Ottawa, Ontario, Canada
| | - Walter Herzog
- Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, Alberta, Canada
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Monte A, Franchi MV. Regional muscle features and their association with knee extensors force production at a single joint angle. Eur J Appl Physiol 2023; 123:2239-2248. [PMID: 37256295 PMCID: PMC10492669 DOI: 10.1007/s00421-023-05237-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 05/19/2023] [Indexed: 06/01/2023]
Abstract
This study aimed (i) to investigate the role of regional characteristics of the knee extensors muscles (vastus lateralis: VL, vastus intermedius: VI and rectus femoris: RF) in determining maximum-voluntary force (MVF); and (ii) to understand which regional parameter of muscle structure would best predict MVF. Muscle architecture (e.g., pennation angle and fascicle length), muscle volume (Vol), anatomical (ACSA) and physiological cross-sectional-area (PCSA) were measured in the proximal (0-33% of the muscle length), middle (33-66% of the muscle length) and distal (66-100% of the muscle length) portions of each muscle in fifteen healthy males using ultrasound and Magnetic Resonance Imaging (MRI). Knee extensors force was calculated in isometric condition at a single knee joint angle of 90 degrees. Regional ACSA, Vol and PCSA were correlated with MVF production. Regional muscle geometry showed no significant correlations with MVF. Among regions, the middle portion of each muscle was largely correlated with MVF compared to all the other regions (distal and proximal). To understand which regional structural parameter best predicted MVF, a stepwise multiple linear regression was performed. This model showed a significant explanatory power (P < 0.001, R2 = 0.76, adjusted R2 = 0.71), including muscle Vol collected in the mid portions of VL and RF. Even if no significant differences were reported between Vol, PCSA and ACSA in determining MVF, our results showed that the RF and VL volume collected in the middle portion of the muscle length are strong determinants of MVF produced by the knee extensors at 90 degrees joint angle.
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Affiliation(s)
- Andrea Monte
- Department of Neurosciences, Biomedicine and Movement Sciences, University of Verona, Verona, Italy
| | - Martino V Franchi
- Department of Biomedical Sciences, University of Padua, Via Marzolo 3, 35131, Padua, Italy.
- CIR-MYO Myology Centre, University of Padua, Padua, Italy.
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Kirschner KM. Open research data - Expectations and limitations. Acta Physiol (Oxf) 2022; 236:e13900. [PMID: 36269606 DOI: 10.1111/apha.13900] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2022] [Accepted: 10/17/2022] [Indexed: 01/29/2023]
Affiliation(s)
- Karin M Kirschner
- Charité - Universitätsmedizin Berlin, corporate member of Freie Universität Berlin, Humboldt-Universität zu Berlin, and Berlin Institute of Health, Institute of Translational Physiology, Berlin, Germany
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Hubbard EF, Hinks A, Mashouri P, Power GA. Influence of 4 weeks of downhill running on calcium sensitivity of rat single muscle fibers. Physiol Rep 2022; 10:e15450. [PMID: 36222183 PMCID: PMC9554763 DOI: 10.14814/phy2.15450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2022] [Accepted: 08/14/2022] [Indexed: 06/16/2023] Open
Abstract
Improved Ca2+ sensitivity has been suggested as a mechanism behind enhancements in muscle mechanical function following eccentric training. However, little is known regarding the effects of eccentric training on single muscle fiber Ca2+ sensitivity. Adult male Sprague-Dawley rats (sacrificial age ~18 weeks; mass = 400.1 ± 34.8 g) were assigned to an eccentric training (n = 5) or sedentary control group (n = 6). Eccentric training consisted of 4 weeks of weighted downhill running 3×/week at a 15° decline and 16 m/min for 35 min per day in 5-min bouts. After sacrifice, vastus intermedius single muscle fibers were dissected, chemically permeabilized, and stored until testing. Fibers (n = 63) were isolated, and standard Ca2+ sensitivity, force, rate of force redevelopment (ktr ), and active instantaneous stiffness tests were performed using [Ca2+ ] ranging from 7.0 to 4.5. Following all mechanical testing, fiber type was determined using SDS-PAGE. There was no difference in pCa50 (i.e., [Ca2+ ] needed to elicit half of maximal force) between groups or between fiber types. However, when comparing normalized force across pCa values, fibers from the control group produced greater forces than fibers from the trained group at lower Ca2+ concentrations (p < 0.05), and this was most evident for Type I fibers (p = 0.002). Type II fibers produced faster (p < 0.001) ktr than Type I fibers, but there were no differences in absolute force, normalized force, or other measures of mechanical function between fibers from the trained and control groups. These findings indicate that eccentric training does not appear to improve single muscle fiber Ca2+ sensitivity.
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Affiliation(s)
- Emma F. Hubbard
- Department of Human Health and Nutritional Sciences, College of Biological SciencesUniversity of GuelphGuelphOntarioCanada
| | - Avery Hinks
- Department of Human Health and Nutritional Sciences, College of Biological SciencesUniversity of GuelphGuelphOntarioCanada
| | - Parastoo Mashouri
- Department of Human Health and Nutritional Sciences, College of Biological SciencesUniversity of GuelphGuelphOntarioCanada
| | - Geoffrey A. Power
- Department of Human Health and Nutritional Sciences, College of Biological SciencesUniversity of GuelphGuelphOntarioCanada
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Groeneveld K. Skeletal muscles do more than the loco-motion. Acta Physiol (Oxf) 2022; 234:e13791. [PMID: 35094479 DOI: 10.1111/apha.13791] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 01/21/2022] [Accepted: 01/24/2022] [Indexed: 11/30/2022]
Affiliation(s)
- Kathrin Groeneveld
- ThIMEDOP, Thüringer Innovationszentrum für Medizintechnik Lösungen Universitätsklinikum Jena Jena Germany
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Fox CD, Mesquita PHC, Godwin JS, Angleri V, Damas F, Ruple BA, Sexton CL, Brown MD, Kavazis AN, Young KC, Ugrinowitsch C, Libardi CA, Roberts MD. Frequent Manipulation of Resistance Training Variables Promotes Myofibrillar Spacing Changes in Resistance-Trained Individuals. Front Physiol 2021; 12:773995. [PMID: 34975527 PMCID: PMC8715010 DOI: 10.3389/fphys.2021.773995] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2021] [Accepted: 11/17/2021] [Indexed: 11/21/2022] Open
Abstract
We sought to determine if manipulating resistance training (RT) variables differentially altered the expression of select sarcoplasmic and myofibril proteins as well as myofibrillar spacing in myofibers. Resistance-trained men (n = 20; 26 ± 3 years old) trained for 8 weeks where a randomized leg performed either a standard (CON) or variable RT protocol (VAR: manipulation of load, volume, muscle action, and rest intervals at each RT session). A pre-training (PRE) vastus lateralis biopsy was obtained from a randomized single leg, and biopsies were obtained from both legs 96 h following the last training bout. The sarcoplasmic protein pool was assayed for proteins involved in energy metabolism, and the myofibril protein pool was assayed for relative myosin heavy chain (MHC) and actin protein abundances. Sections were also histologically analyzed to obtain myofibril spacing characteristics. VAR resulted in ~12% greater volume load (VL) compared to CON (p < 0.001). The mean fiber cross-sectional area increased following both RT protocols [CON: 14.6% (775.5 μm2), p = 0.006; VAR: 13.9% (743.2 μm2), p = 0.01 vs. PRE for both], but without significant differences between protocols (p = 0.79). Neither RT protocol affected a majority of assayed proteins related to energy metabolism, but both training protocols increased hexokinase 2 protein levels and decreased a mitochondrial beta-oxidation marker (VLCAD protein; p < 0.05). Citrate synthase activity levels increased with CON RT (p < 0.05), but not VAR RT. The relative abundance of MHC (summed isoforms) decreased with both training protocols (p < 0.05). However, the relative abundance of actin protein (summed isoforms) decreased with VAR only (13.5 and 9.0%, respectively; p < 0.05). A decrease in percent area occupied by myofibrils was observed from PRE to VAR (−4.87%; p = 0.048), but not for the CON (4.53%; p = 0.979). In contrast, there was an increase in percent area occupied by non-contractile space from PRE to VAR (10.14%; p = 0.048), but not PRE to CON (0.72%; p = 0.979). In conclusion, while both RT protocols increased muscle fiber hypertrophy, a higher volume-load where RT variables were frequently manipulated increased non-contractile spacing in resistance-trained individuals.
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Affiliation(s)
- Carlton D. Fox
- School of Kinesiology, Auburn University, Auburn, AL, United States
| | | | - Joshua S. Godwin
- School of Kinesiology, Auburn University, Auburn, AL, United States
| | - Vitor Angleri
- MUSCULAB, Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education, Federal University of São Carlos, São Carlos, Brazil
| | - Felipe Damas
- MUSCULAB, Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education, Federal University of São Carlos, São Carlos, Brazil
| | - Bradley A. Ruple
- School of Kinesiology, Auburn University, Auburn, AL, United States
| | - Casey L. Sexton
- School of Kinesiology, Auburn University, Auburn, AL, United States
| | - Michael D. Brown
- School of Kinesiology, Auburn University, Auburn, AL, United States
| | | | - Kaelin C. Young
- School of Kinesiology, Auburn University, Auburn, AL, United States
- Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine – Auburn Campus, Auburn, AL, United States
| | - Carlos Ugrinowitsch
- School of Physical Education and Sport, University of São Paulo, São Paulo, Brazil
| | - Cleiton A. Libardi
- MUSCULAB, Laboratory of Neuromuscular Adaptations to Resistance Training, Department of Physical Education, Federal University of São Carlos, São Carlos, Brazil
- *Correspondence: Cleiton A. Libardi, ; Michael D. Roberts,
| | - Michael D. Roberts
- School of Kinesiology, Auburn University, Auburn, AL, United States
- Department of Cell Biology and Physiology, Edward Via College of Osteopathic Medicine – Auburn Campus, Auburn, AL, United States
- *Correspondence: Cleiton A. Libardi, ; Michael D. Roberts,
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Affiliation(s)
- Tomas L Bothe
- Charité – Universitätsmedizin Berlincorporate member of Freie Universität Berlin and Humboldt‐Universität zu BerlinInstitute of Vegetative Physiology Berlin Germany
| | - Andreas Patzak
- Charité – Universitätsmedizin Berlincorporate member of Freie Universität Berlin and Humboldt‐Universität zu BerlinInstitute of Vegetative Physiology Berlin Germany
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Sarto F, Spörri J, Fitze DP, Quinlan JI, Narici MV, Franchi MV. Implementing Ultrasound Imaging for the Assessment of Muscle and Tendon Properties in Elite Sports: Practical Aspects, Methodological Considerations and Future Directions. Sports Med 2021; 51:1151-1170. [PMID: 33683628 PMCID: PMC8124062 DOI: 10.1007/s40279-021-01436-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/06/2021] [Indexed: 12/16/2022]
Abstract
Ultrasound (US) imaging has been widely used in both research and clinical settings to evaluate the morphological and mechanical properties of muscle and tendon. In elite sports scenarios, a regular assessment of such properties has great potential, namely for testing the response to training, detecting athletes at higher risks of injury, screening athletes for structural abnormalities related to current or future musculoskeletal complaints, and monitoring their return to sport after a musculoskeletal injury. However, several practical and methodological aspects of US techniques should be considered when applying this technology in the elite sports context. Therefore, this narrative review aims to (1) present the principal US measures and field of applications in the context of elite sports; (2) to discuss, from a methodological perspective, the strengths and shortcomings of US imaging for the assessment of muscle and tendon properties; and (3) to provide future directions for research and application.
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Affiliation(s)
- Fabio Sarto
- Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Jörg Spörri
- Sports Medical Research Group, Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
- Department of Orthopaedics, University Centre for Prevention and Sports Medicine, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Daniel P Fitze
- Sports Medical Research Group, Department of Orthopaedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland
| | - Jonathan I Quinlan
- School of Sport, Exercise and Rehabilitation Sciences, University of Birmingham, Birmingham, UK
- National Institute for Health Research, Birmingham Biomedical Research Centre at University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
| | - Marco V Narici
- Department of Biomedical Sciences, University of Padova, Padova, Italy
- CIR-MYO Myology Centre, University of Padova, Padova, Italy
| | - Martino V Franchi
- Department of Biomedical Sciences, University of Padova, Padova, Italy.
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Abstract
Skeletal muscle hypertrophy can be induced by hormones and growth factors acting directly as positive regulators of muscle growth or indirectly by neutralizing negative regulators, and by mechanical signals mediating the effect of resistance exercise. Muscle growth during hypertrophy is controlled at the translational level, through the stimulation of protein synthesis, and at the transcriptional level, through the activation of ribosomal RNAs and muscle-specific genes. mTORC1 has a central role in the regulation of both protein synthesis and ribosomal biogenesis. Several transcription factors and co-activators, including MEF2, SRF, PGC-1α4, and YAP promote the growth of the myofibers. Satellite cell proliferation and fusion is involved in some but not all muscle hypertrophy models.
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Affiliation(s)
| | - Carlo Reggiani
- Department of Biomedical Sciences, University of Padova, Italy
- Science and Research Centre Koper, Institute for Kinesiology Research, Koper, Slovenia
| | | | - Bert Blaauw
- Venetian Institute of Molecular Medicine, Padova, Italy
- Department of Biomedical Sciences, University of Padova, Italy
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Emphasizing Task-Specific Hypertrophy to Enhance Sequential Strength and Power Performance. J Funct Morphol Kinesiol 2020; 5:jfmk5040076. [PMID: 33467291 PMCID: PMC7739346 DOI: 10.3390/jfmk5040076] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 10/04/2020] [Accepted: 10/21/2020] [Indexed: 12/15/2022] Open
Abstract
While strength is indeed a skill, most discussions have primarily considered structural adaptations rather than ultrastructural augmentation to improve performance. Altering the structural component of the muscle is often the aim of hypertrophic training, yet not all hypertrophy is equal; such alterations are dependent upon how the muscle adapts to the training stimuli and overall training stress. When comparing bodybuilders to strength and power athletes such as powerlifters, weightlifters, and throwers, while muscle size may be similar, the ability to produce force and power is often inequivalent. Thus, performance differences go beyond structural changes and may be due to the muscle's ultrastructural constituents and training induced adaptations. Relative to potentiating strength and power performances, eliciting specific ultrastructural changes should be a variable of interest during hypertrophic training phases. By focusing on task-specific hypertrophy, it may be possible to achieve an optimal amount of hypertrophy while deemphasizing metabolic and aerobic components that are often associated with high-volume training. Therefore, the purpose of this article is to briefly address different types of hypertrophy and provide directions for practitioners who are aiming to achieve optimal rather than maximal hypertrophy, as it relates to altering ultrastructural muscular components, to potentiate strength and power performance.
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