Commentaries on Viewpoint: Can muscle size fully account for strength differences between children and adults?
2011; American Physiological Society; Volume: 110; Issue: 6 Linguagem: Inglês
10.1152/japplphysiol.00371.2011
ISSN8750-7587
AutoresWalter Herzog, Alessandro Sartório, Claudio L. Lafortuna, Hiroaki Kanehisa, Tetsuo Fukunaga, Raffy Dotan, Bareket Falk, Louise Wood, Anne Tonson, Yann Le Fur, Patrick J. Cozzone, David Bendahan, Keith Tolfrey, Christopher I. Morse, Thomas D. O’Brien, Neil D. Reeves, Vasilios Baltzopoulos, David A. Jones, Constantinos N. Maganaris, Daniel Lambertz, J. Grosset, Chantal Pérot,
Tópico(s)Children's Physical and Motor Development
ResumoViewpointCommentaries on Viewpoint: Can muscle size fully account for strength differences between children and adults?Published Online:01 Jun 2011https://doi.org/10.1152/japplphysiol.00371.2011MoreSectionsPDF (55 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations Walter Herzog.Author AffiliationsProfessor University of Calgary.to the editor: As comprehensively explained in their Viewpoint article (1), the answer to the question posed in the title has received conflicting answers. Since the contractile machinery in children is the same as that in adults, there is no reason to believe that specific force should differ as a function of developmental stage. However, this question can only be answered unequivocally in studies using preparations where muscle force can be measured directly, activation is controlled, and the physiological cross-sectional area can be measured accurately.In human studies, muscle forces are estimated based on resultant joint moments obtained from the interaction of agonistic and antagonistic muscles, a mathematically indeterminate problem that has not been solved to date (e.g., Ref. 2). Furthermore, perfect alignment of the joint axis with the strength dynamometer and no movement of this axis during contraction is required: an impossible task. Finally, comparison across maximal voluntary contractions (MVCs) is not made easily, as MVCs cannot be defined uniquely because muscles have a greater force potential than the forces that can be produced voluntarily (3). The twitch interpolation technique does not help either to resolve this problem, as it is associated with large uncertainties (4).Differences in specific muscle strengths between adult and children are likely small, if they exist at all. Therefore, accurate force measurements and perfectly controlled nerve activation in conjunction with PCSA measurements that account for noncontractile components are required to determine specific strength differences in skeletal muscles across the developmental stages.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Erdemir A , McLean S , Herzog W , van den Bogert AJ. Model-based estimation of muscle forces exerted during movements. Clin Biomech 22: 131–154, 2007.Crossref | PubMed | ISI | Google Scholar3. Kent-Braun JA , LeBlanc R. Quantification of central activation failure during maximal voluntary contractions in humans. Muscle Nerve 19: 861–869, 1996.Crossref | PubMed | ISI | Google Scholar4. Suter E , Herzog W , Huber A. Extent of motor unit activation in the quadriceps muscles of healthy subjects. Muscle Nerve 19: 1046–1048, 1996.Crossref | PubMed | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Erdemir A , McLean S , Herzog W , van den Bogert AJ. Model-based estimation of muscle forces exerted during movements. Clin Biomech 22: 131–154, 2007.Crossref | PubMed | ISI | Google Scholar3. Kent-Braun JA , LeBlanc R. Quantification of central activation failure during maximal voluntary contractions in humans. Muscle Nerve 19: 861–869, 1996.Crossref | PubMed | ISI | Google Scholar4. Suter E , Herzog W , Huber A. Extent of motor unit activation in the quadriceps muscles of healthy subjects. Muscle Nerve 19: 1046–1048, 1996.Crossref | PubMed | ISI | Google ScholarMUSCLE QUANTITY AND QUALITY IN OBESE CHILDREN AND ADULTS—AN OPEN COMPELLING ISSUEAlessandro SartorioDirector and Claudio L. LafortunaIstituto Auxologico Italiano Experimental Laboratory for Auxo-Endocrinological Research Milan, Italy.to the editor: The Viewpoint by Bouchant et al. (1) truly enlightens the entangling issue of coping with confounding factors in the assessment and comparison of strength generation in different groups of subjects, as adults and children. As pointed out by the authors (1), besides the biomechanical allowance for the different moment arm, a major problem in comparing the capability of strength production between individuals of different body size is the parameter normalization by unit mass of involved contractile elements. This point is particularly relevant in obesity, a condition growing exponentially also among children/adolescents and impacting on both muscle quantity and quality with considerable effects on muscle function by acting as a chronic training load (4) and by altering muscle composition with fat infiltration, in concert with age (2). By comparing average lower limb power output per unit fat-free mass (FFM) obtained during a Margaria stair test in prepubertal obese children [8.86 ± 1.38 (SD) W/kg, n = 33 (5)] and in obese adults [8.89 ± 1.96 (SD) W/kg, n = 364 (3)], we are not able to disclose any significant difference (P = 0.936, unpaired Student's t-test). Indeed FFM is a very crude estimate of muscle mass, and no conclusive evidence could be generalized from these results. A considerable help in tissue evaluation, for obese as well as lean individuals, could be gained from imaging techniques (as magnetic resonance imaging and computerized tomography) suitable for skeletal muscle quantity and quality analysis, along with geometrical reconstruction required for biomechanical modeling of implicated forces.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Goodpaster BH , Carlson CL , Visser M , Kelley DE , Scherzinger A , Harris TB , Stamm E , Newman AB. Attenuation of skeletal muscle and strength in the elderly: The Health ABC Study. J Appl Physiol 90: 2157–2165, 2001.Link | ISI | Google Scholar3. Lafortuna CL , Agosti F , Marinone PG , Marazzi N , Sartorio A. The relationship between body composition and muscle power output in men and women with obesity. J Endocrinol Invest 27: 854–861, 2004.Crossref | ISI | Google Scholar4. Lafortuna CL , Maffiuletti NA , Agosti F , Sartorio A. Gender variations of body composition, muscle strength and power output in morbid obesity. Int J Obes 29: 833–841, 2005.Crossref | PubMed | ISI | Google Scholar5. Sartorio A , Agosti F , De Col A , Lafortuna CL. Age- and gender-related variations of leg power output and body composition in severely obese children and adolescents. J Endocrinol Invest 29: 48–54, 2006.Crossref | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Goodpaster BH , Carlson CL , Visser M , Kelley DE , Scherzinger A , Harris TB , Stamm E , Newman AB. Attenuation of skeletal muscle and strength in the elderly: The Health ABC Study. J Appl Physiol 90: 2157–2165, 2001.Link | ISI | Google Scholar3. Lafortuna CL , Agosti F , Marinone PG , Marazzi N , Sartorio A. The relationship between body composition and muscle power output in men and women with obesity. J Endocrinol Invest 27: 854–861, 2004.Crossref | ISI | Google Scholar4. Lafortuna CL , Maffiuletti NA , Agosti F , Sartorio A. Gender variations of body composition, muscle strength and power output in morbid obesity. Int J Obes 29: 833–841, 2005.Crossref | PubMed | ISI | Google Scholar5. Sartorio A , Agosti F , De Col A , Lafortuna CL. Age- and gender-related variations of leg power output and body composition in severely obese children and adolescents. J Endocrinol Invest 29: 48–54, 2006.Crossref | ISI | Google ScholarHiroaki KanehisaProfessor and Tetsuo FukunagaNational Institute of Fitness and Sports in Kanoya.to the editor: Recently, a study provided evidence indicating that the specific tension of muscle is similar between children and adults (4). The procedures for determining the physiological cross-sectional area and muscle force used in that study will be criteria in future studies aiming to examine the specific tension of human muscles in vivo and to clarify growth- and/or muscle-related differences. However, it is true that there are technical difficulties in accurately determining the muscle architecture and moment arm during maximal voluntary contractions. This may be a source of new discrepancies among findings. On the other hand, the accuracy of joint torque and muscle volume measurements is relatively high. Assuming that the muscle strength is associated with the muscle size in children and adults, without age-related differences in the muscle strength per size, the y-intercept of the regression line for the relationship between the two variables in each of the two age groups must not differ from zero, without age-related differences between the two regression lines. This may be satisfied using the joint torque and muscle volume as variables representing the muscle strength and size, respectively (1, 3). Our comment on the Viewpoint (2), not on the age- and/or muscle-related differences in specific tension, is that tests of how joint torque is related to muscle volume in various muscle groups for children and adults will be a simple and optimal approach for examining whether muscle size accounts for strength differences between the two age groups.REFERENCES1. Akagi R , Takai Y , Ohta M , Kanehisa H , Kawakami Y , Fukunaga T. Muscle volume compared to cross-sectional area is more appreciated for evaluating muscle strength in young and elderly individuals. Age and Ageing 38: 564–569, 2009.Crossref | ISI | Google Scholar2. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar3. Fukunaga T , Miyatani M , Tachi M , Kouzaki M , Kawakami Y , Kanehisa H. Muscle volume is a major determinant of joint torque in humans. Acta Physiol Scand 172: 249–255, 2001.Crossref | PubMed | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google ScholarREFERENCES1. Akagi R , Takai Y , Ohta M , Kanehisa H , Kawakami Y , Fukunaga T. Muscle volume compared to cross-sectional area is more appreciated for evaluating muscle strength in young and elderly individuals. Age and Ageing 38: 564–569, 2009.Crossref | ISI | Google Scholar2. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar3. Fukunaga T , Miyatani M , Tachi M , Kouzaki M , Kawakami Y , Kanehisa H. Muscle volume is a major determinant of joint torque in humans. Acta Physiol Scand 172: 249–255, 2001.Crossref | PubMed | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google ScholarDIFFERENTIAL MOTOR-UNIT ACTIVATION PATTERN—THE “MISSING LINK” IN UNDERSTANDING CHILD-ADULT STRENGTH AND OTHER DIFFERENCESRaffy DotanFaculty of Applied Health Sciences and Bareket FalkBrock University St. Catharines, Ontario, Canada.to the editor: Bouchant et al. (1) raise the question of whether the increasing muscle strength during growth and maturation can be fully explained by the increasing muscle size. The authors justly point out that factors such as changes in tendon compliance, agonist-antagonist cocontraction, and volitional muscle activation, should be considered. To these, possible differences in muscle composition should also be added. No study has examined all these factors in conjunction with the numerous morphological changes taking place during growth. However, in a carefully conducted study, O'Brien et al. (4) recently showed that 75% of boys-men (50% of girls-women) differences in muscle strength are attributable to differences in muscle size (cross-sectional area, volume, moment arm) and that the remainder of the age-difference is mainly due to differences in volitional muscle activation.We suggest, more specifically, that this age-related difference in muscle activation is largely a difference in the utilization of type II motor units. Namely, that compared with adults, children are substantially less capable of recruiting, or fully employing, their higher-threshold, type II motor units. This hypothesis of differential motor-unit activation can explain not only size-normalized differences in muscle strength, but also other strength-related differences, such as, lower short-term power (2), slower force kinetics, faster recovery from exercise (2), and children's non-hypertrophic response to resistance training (3). Also explained are non-strength-related differences, such as greater muscle endurance, lower glycolytic enzyme activity, greater fat utilization, and lower carbohydrate utilization during exercise (5).No other single factor can account for all these observations.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Falk B , Dotan R. Child-adult differences in the recovery from high-intensity exercise. Exerc Sport Sci Rev 34: 107–112, 2006.Crossref | PubMed | ISI | Google Scholar3. Falk B , Eliakim A. Resistance training, skeletal muscle and growth. Pediatr Endocrinol Rev 1: 120–127, 2003.Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google Scholar5. Timmons BW , Bar-Or O , Riddell MC. Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men. J Appl Physiol 94: 278–284, 2003.Link | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Falk B , Dotan R. Child-adult differences in the recovery from high-intensity exercise. Exerc Sport Sci Rev 34: 107–112, 2006.Crossref | PubMed | ISI | Google Scholar3. Falk B , Eliakim A. Resistance training, skeletal muscle and growth. Pediatr Endocrinol Rev 1: 120–127, 2003.Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google Scholar5. Timmons BW , Bar-Or O , Riddell MC. Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men. J Appl Physiol 94: 278–284, 2003.Link | ISI | Google ScholarSCALING DENOMINATORS AND INTERPRETATION OF STRENGTH DIFFERENCESLouise E. Wood.Author AffiliationsSenior Lecturer University of Portsmouth.to the editor: The Viewpoint (1) demonstrates the challenges of ascribing changes in strength to differences in muscle size since this requires measurement of agonist and antagonist muscle activation and moment arm length(s)/mechanical advantage alongside the parameters required for the measurement of physiological cross-sectional area. Bouchant et al. (1) emphasize many methodological limitations, including the common use of anatomical cross-sectional area (ACSA) to normalize strength data in the pediatric literature. In addition, both ACSA and moment arm lengths are often approximated using assumed proportionality to anthropometric measures. This is despite the inaccuracies inherent in these approaches and a lack of research supporting scaling relationships between moment arms and anthropometric dimensions (4). As more assumptions are made to consider the adjustment of strength for differences in muscle size, moment arm length, and muscle activation; the potential for identifying the mechanism(s) of strength differences declines. By addressing many of the limitations of previous studies, Morse et al. (3) and O'Brien et al. (5) provide the most valid interpretation of the role of muscle size in strength development in prepubertal/early pubertal children. However further studies are required to support their findings. For example, it is unclear whether, during rapid phases of growth when musculoskeletal growth lags have been associated with both increased tissue preload and muscular overload (2), the relative contribution of neuromusculoskeletal parameters to strength differences alters. The age and maturation of children included in strength studies may therefore further add to the complexity of addressing whether muscle size can fully account for child-adult strength differences.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Hawkins D , Metheny J. Overuse injuries in youth sports: biomechanical considerations. Med Sci Sports Exerc 33: 1701–1707, 2001.Crossref | ISI | Google Scholar3. Morse CI , Tolfrey K , Thom JM , Vassilopoulos V , Maganaris CN , Narici MV. Gastrocnemius muscle specific force in boys and men. J Appl Physiol 104: 469–474, 2008.Link | ISI | Google Scholar4. Murray WM , Buchanan TS , Delp SL. Scaling of peak moment arms of elbow muscles with upper extremity bone dimensions. J Biomech 35: 19–26, 2002.Crossref | PubMed | ISI | Google Scholar5. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2009.Crossref | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Hawkins D , Metheny J. Overuse injuries in youth sports: biomechanical considerations. Med Sci Sports Exerc 33: 1701–1707, 2001.Crossref | ISI | Google Scholar3. Morse CI , Tolfrey K , Thom JM , Vassilopoulos V , Maganaris CN , Narici MV. Gastrocnemius muscle specific force in boys and men. J Appl Physiol 104: 469–474, 2008.Link | ISI | Google Scholar4. Murray WM , Buchanan TS , Delp SL. Scaling of peak moment arms of elbow muscles with upper extremity bone dimensions. J Biomech 35: 19–26, 2002.Crossref | PubMed | ISI | Google Scholar5. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2009.Crossref | ISI | Google ScholarAnne TonsonPostdoctoral Student, Yann Le Fur, Patrick J. Cozzone, and David BendahanCentre de Resonance Magnetique Biologique et Medicale (UMR CNRS 6612).to the editor: In their Viewpoint, Bouchant et al. (1), mentioned various physiological and methodological factors, which could account for discrepancies regarding specific force (Fspe) differences reported so far during development. As they rightly indicated, results are tightly related to the scaling denominator used for Fspe calculation and a carefully designed normalization procedure is a prerequisite for reliable comparisons. Although potential differences between anatomical (ACSA) and physiological cross sectional (PCSA) area could explain some of the reported discrepancies, the corresponding quantification method is of utmost importance. Indeed, on the basis of results obtained with various quantification methods of muscle size, we clearly demonstrated that methodological factors can be misleading for physiological interpretations (2). In a given population, the Fspe calculated using ACSA or anthropometric measurement of muscle volume (MV) significantly increased from childhood to adulthood, whereas no difference was found when MRI was used to quantify MV (2). These discrepancies can indeed be related to the fact that ASCA ignores muscle architecture (i.e., pennation angle and fiber length; Ref. 3) but we have to acknowledge the lack of a simple method of PCSA measurement. Considering the approximations related to ACSA and anthropometry, the appropriate scaling denominator for Fspe calculation should be MV measured with MRI. Indeed, MV was systematically overestimated by anthropometry and the relative overestimation was significantly larger in children (43.1 ± 15.2%) compared with adults (20.0 ± 10.5%). While other factors cannot be ruled out, we would like to underline that a reliable quantitative method of MV is mandatory to properly investigate strength ability during growth.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Tonson A , Ratel S , Le Fur Y , Cozzone P , Bendahan D. Effect of maturation on the relationship between muscle size and force production. Med Sci Sports Exerc 40: 918–925, 2008.Crossref | PubMed | ISI | Google Scholar3. Wickiewicz TL , Roy RR , Powell PL , Edgerton VR. Muscle architecture of the human lower limb. Clin Orthop Relat Res 179: 275–283, 1983.Crossref | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Tonson A , Ratel S , Le Fur Y , Cozzone P , Bendahan D. Effect of maturation on the relationship between muscle size and force production. Med Sci Sports Exerc 40: 918–925, 2008.Crossref | PubMed | ISI | Google Scholar3. Wickiewicz TL , Roy RR , Powell PL , Edgerton VR. Muscle architecture of the human lower limb. Clin Orthop Relat Res 179: 275–283, 1983.Crossref | ISI | Google ScholarMUSCLE SIZE AND STRENGTHKeith TolfreySenior Lecturer and Christopher I. MorseLoughborough University and Manchester Metropolitan University.to the editor: Morse et al. (3) presented novel data on numerous critical methodological factors requiring close scrutiny when examining the strength-size relationship between adults and prepubertal children. Bouchant et al. (1) reiterated the potential for experimental variability, compared with true maturity-dependent physiological variability. Indeed, the methodological factors we identified (e.g., mechanical advantage, scaling modality, agonist activation, and viscoelastic tendon properties) may form the basis for the inter-muscle discrepancy reported in the specific force data between Morse et al. (3) and O'Brien et al. (4).The working length of the gastrocnemius and vastus lateralis muscles are additional factors as discussed previously (3, 4). Indeed, as far as we are aware, a systematic examination of the influence of maturation on the length-tension relation is not available. As discussed by Bouchant et al. (1), Marginson and Eston (2) reported a shift to “longer muscle lengths” in children. However, a more compliant tendon in children would lead to a shift in the length tension relation to shorter muscle lengths because the tendon may experience greater strain under loading. The inverse of this has been proposed previously by Reeves et al. (5) who noted that stiffening of the tendon in the elderly would account for a longer working length of the vastus lateralis. When considering the size-strength relationship with maturation, the influence of greater tendon compliance in children, or indeed the fascicular length-tension relation in vivo, has yet to be elucidated.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Marginson V , Eston R. The relationship between torque and joint angle during knee extension in boys and men. J Sports Sci 19: 875–880, 2001.Crossref | ISI | Google Scholar3. Morse CI , Tolfrey K , Thom JM , Vassilopoulos V , Maganaris CN , Narici MV. Gastrocnemius muscle specific force in boys and men. J Appl Physiol 104: 469–474, 2008.Link | ISI | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google Scholar5. Reeves ND , Maganaris CN , Narici MV. Plasticity of dynamic muscle performance with strength training in elderly humans. Muscle Nerve, 31: 355–364, 2005.Crossref | PubMed | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Marginson V , Eston R. The relationship between torque and joint angle during knee extension in boys and men. J Sports Sci 19: 875–880, 2001.Crossref | ISI | Google Scholar3. Morse CI , Tolfrey K , Thom JM , Vassilopoulos V , Maganaris CN , Narici MV. Gastrocnemius muscle specific force in boys and men. J Appl Physiol 104: 469–474, 2008.Link | ISI | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google Scholar5. Reeves ND , Maganaris CN , Narici MV. Plasticity of dynamic muscle performance with strength training in elderly humans. Muscle Nerve, 31: 355–364, 2005.Crossref | PubMed | ISI | Google ScholarQUANTIFICATION OF HUMAN MUSCLE SPECIFIC TENSION IN VIVO: A METHODOLOGICALLY CHALLENGING AND SOME TIMES IMPOSSIBLE EXERCISEThomas D. O'BrienLecturer in Biomechanics Department of Sport, Health and Exercise Science University of Hull, Neil D. Reeves, Vasilios Baltzopoulos, David A. Jones, and Constantinos N. MaganarisIRM, Manchester Metropolitan University.to the editor: Bouchant et al. (1) highlight the widely contradicting literature surrounding the greater strength of adults compared with children, specifically questioning whether any differences in muscle specific tension may play a role. They rightly identify the importance of correctly quantifying maximal muscle force (Fmax) and muscle size (physiological cross-sectional area; PCSA) and the impact that failing to do so has had in previous studies; Fmax must be measured at optimum fiber length, rather than optimum or an arbitrary joint angle, and account for agonist inactivation, antagonist coactivation, and moment arms. Additionally, pennation for Fmax and fiber length for PCSA should be measured during contraction at optimal length.We attempted to systematically address these issues and concluded that the specific tension of the quadriceps muscle is similar in adults and children (55–60 N/cm−2; 4). However, these values are more than twice those from experiments in isolated animal muscle (22.5 N/cm−2; 2). It is unlikely that this difference is underpinned by some physiological mechanism. Rather, it probably highlights the impact of inevitable assumptions in current in vivo models, specifically in the calculation of Fmax, including simplifying the joint biomechanics and force-sharing between synergistic muscles. Notwithstanding these limitations, it must be stressed that there remain muscles in which Fmax and PCSA cannot be quantified because optimal contractile length cannot be reached in vivo (e.g., gastrocnemius; 3). Evidently, the calculation of specific tension in vivo is always complex requiring several assumptions/simplifications, is limited to whole muscle/muscle groups, and for some muscles it is actually impossible.REFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Close RI. Dynamic properties of mammalian skeletal muscle. Physiol Rev 52: 129–197, 1972.Link | ISI | Google Scholar3. Maganaris CN. Force-length characteristics of the in vivo human gastrocnemius muscle. Clin Anat 16: 215–223, 2003.Crossref | ISI | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google ScholarREFERENCES1. Bouchant A , Martin V , Maffiuletti NA , Ratel S. Viewpoint: Can muscle size fully account for strength differences between children and adults? J Appl Physiol; doi:10.1152/japplphysiol.01333.2010.ISI | Google Scholar2. Close RI. Dynamic properties of mammalian skeletal muscle. Physiol Rev 52: 129–197, 1972.Link | ISI | Google Scholar3. Maganaris CN. Force-length characteristics of the in vivo human gastrocnemius muscle. Clin Anat 16: 215–223, 2003.Crossref | ISI | Google Scholar4. O'Brien TD , Reeves ND , Baltzopoulos V , Jones DA , Maganaris CN. In vivo measurements of muscle specific tension in adults and children. Exp Physiol 95: 202–210, 2010.Crossref | ISI | Google ScholarDaniel Lambertz, Jean-Francois Grosset, and Chantal Perot.Author AffiliationsBiomécanique et Bioingénierie Université de Technologie de Compiègne, France.to the editor: Evaluation of muscle strength in children and adults is a challenging debate, useful in aspects concerning development, nutrition, immobilization, and training. The main observation regarding this Viewpoint is that children vs. adult muscle capacity need multidimensional investigations to get an overview of all involved mechanisms, to avoid erroneous conclusions. In addition to torque and agonist EMG activity, activation deficit (twitch interpolation) as well as coactivation and muscle architecture are indispensable parameters when comparing children vs. adults (2). As properly discussed in this Viewpoint, MVC is not exactly proportional to ACSA, but with PCSA, since ACSA underestimates muscle fiber area, leading to overestimate MVC/ACSA ratio. With regard to further architectural parameters, magnetic resonance elastography (MRE) indicate differences in phase images and fascicle angles in children vs. adults during low level contraction and thus architectural dependence of muscle stiffness (1). Furthermore, target force matching is more difficult at low force than at high force levels (5), a hypothesis already put forward (2). However, maturation, as confounding physiological factor, is disregarded by architectural normalization of muscle strength. For instance, muscle metabolic consumption is different between children and adults, children having higher aerobic contribution to ATP production at initial contractions, while PCr breakdown is reduced (4). Furthermore, sarcoplasmic reticulum [Ca2+] depends on muscle length, what influences muscle stiffness (3), and probably muscle length-strength characteristic relationships. In conclusion, it seems that optimal architectural and neuromechanical normalization should account partly for differences in muscle strength between children and adults, but physiological normalization is seldom taken into consideration.REFERENCES1. Debernard L , Robert L , Charleux F , Bensamoun S. Characterization of muscle architecture in children and adults using magnetic resonance elastography and ultrasound techniques. J Biomech 44: 397–401, 2011.Crossref | ISI | Google Scholar2. Grosset JF , Mora I , Lambertz D , Perot C. Voluntary activation of the triceps surae in prepubertal children. J Electromyogr Kinesiol 18: 455–465, 2008.Crossref | ISI | Google Scholar3. Kistemaker DA , Van Soest A , Bobbert MF. Length-dependent [Ca2+] sensitivity adds stiffness to muscle. J Biomech 38: 1816–1821, 2005.Crossref | PubMed | ISI | Google Scholar4. Tonson A , Ratel S , Le Fur Y , Vilmen C , Cozzone PJ , Bendahan D. Muscle energetics changes throughout maturation: a quantitative 31P-MRS analysis. J Appl Physiol 109: 1769–1778, 2010.Link | ISI | Google Scholar5. Walsh LD , Taylor JL , Gandevia SC. Overestimation of force during matching of externally generated forces. J Physiol 589: 547–557, 2011.Crossref | PubMed | ISI | Google ScholarREFERENCES1. Debernard L , Robert L , Charleux F , Bensamoun S. Characterization of muscle architecture in children and adults using magnetic resonance elastography and ultrasound techniques. J Biomech 44: 397–401, 2011.Crossref | ISI | Google Scholar2. Grosset JF , Mora I , Lambertz D , Perot C. Voluntary activation of the triceps surae in prepubertal children. J Electromyogr Kinesiol 18: 455–465, 2008.Crossref | ISI | Google Scholar3. Kistemaker DA , Van Soest A , Bobbert MF. Length-dependent [Ca2+] sensitivity adds stiffness to muscle. J Biomech 38: 1816–1821, 2005.Crossref | PubMed | ISI | Google Scholar4. Tonson A , Ratel S , Le Fur Y , Vilmen C , Cozzone PJ , Bendahan D. Muscle energetics changes throughout maturation: a quantitative 31P-MRS analysis. J Appl Physiol 109: 1769–1778, 2010.Link | ISI | Google Scholar5. Walsh LD , Taylor JL , Gandevia SC. Overestimation of force during matching of externally generated forces. J Physiol 589: 547–557, 2011.Crossref | PubMed | ISI | Google Scholar Download PDF Previous Back to Top Next FiguresReferencesRelatedInformation Cited ByNarrative Review of Sex Differences in Muscle Strength, Endurance, Activation, Size, Fiber Type, and Strength Training Participation Rates, Preferences, Motivations, Injuries, and Neuromuscular Adaptations15 November 2022 | Journal of Strength and Conditioning Research, Vol. 37, No. 2Maturity status effects on torque and muscle architecture of young soccer players21 March 2019 | Journal of Sports Sciences, Vol. 38, No. 11-12Muscle Thickness During Core Stability Exercises in Children and Adults31 January 2020 | Journal of Human Kinetics, Vol. 71, No. 1Age-related features in the formation of spinal inhibition of skeletal muscles in males5 December 2015 | Human Physiology, Vol. 41, No. 6Imaging of the Muscle-Bone Relationship6 August 2014 | Current Osteoporosis Reports, Vol. 12, No. 4 More from this issue > Volume 110Issue 6June 2011Pages 1750-1753 Copyright & PermissionsCopyright © 2011 the American Physiological Societyhttps://doi.org/10.1152/japplphysiol.00371.2011PubMed21666148History Published online 1 June 2011 Published in print 1 June 2011 Metrics
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