Commentaries on Viewpoint: Can muscle size fully account for strength differences between children and adults?

ViewpointCommentaries 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 area could explain of the reported the is of on the of results obtained with various of muscle size, we that methodological factors can be for physiological (2). In a the Fspe using ACSA or anthropometric measurement of muscle volume increased from to no difference when used to (2). discrepancies can be related to the that muscle architecture and Ref. but we have to the lack of a simple of PCSA the related to ACSA and the scaling denominator for Fspe calculation should be measured with by and the relative in children ± compared with adults ± other factors cannot be we to that a reliable of is to strength during 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. A , Ratel S , Le Y , , of maturation on the relationship between muscle size and force Med Sci Sports Exerc | PubMed | ISI | Google Scholar3. , , , Muscle architecture of the human lower Clin | 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. A , Ratel S , Le Y , , of maturation on the relationship between muscle size and force Med Sci Sports Exerc | PubMed | ISI | Google Scholar3. , , , Muscle architecture of the human lower Clin | ISI | Google ScholarMUSCLE AND Lecturer and University and the editor: Morse et al. (3) data on numerous methodological factors when examining the relationship between adults and prepubertal children. Bouchant et al. (1) the potential for compared with true physiological the methodological factors we (e.g., scaling agonist activation, and tendon may the for the reported in the specific force data between Morse et al. (3) and O'Brien et al. of the and muscles are factors as as far as we are a of the of maturation on the is not As by Bouchant et al. (1), and reported a to muscle in children. However, a more tendon in children to a in the tension to muscle lengths because the tendon may greater The of this has been by Reeves et al. (5) that of the tendon in the elderly account for a of the the relationship with the of greater tendon in or the in has to be 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. V , R. The relationship between torque and joint during in boys and men. J Sports Sci 19: 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. of muscle with strength training in elderly humans. Muscle 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. V , R. The relationship between torque and joint during in boys and men. J Sports Sci 19: 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. of muscle with strength training in elderly humans. Muscle 2005.Crossref | PubMed | ISI | Google OF IN A AND in of Health and University of David A. and the editor: Bouchant et al. (1) the the greater strength of adults compared with whether any differences in muscle specific tension may a rightly the of maximal muscle force and muscle size cross-sectional and the that to so has in previous must be measured at length, than or an joint and account for agonist antagonist and moment for and for PCSA should be measured during contraction at optimal to these and that the specific tension of the quadriceps muscle is similar in adults and children However, these are more than from in muscle 2). is that this difference is by physiological it the of assumptions in in vivo in the calculation of including the joint and between these limitations, it must be that there muscles in which and PCSA cannot be because optimal contractile cannot be in vivo (e.g., 3). the calculation of specific tension in vivo is is to and for muscles it is 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. of skeletal Physiol Rev | ISI | Google Scholar3. Maganaris CN. of the in vivo human Clin | 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. of skeletal Physiol Rev | ISI | Google Scholar3. Maganaris CN. of the in vivo human Clin | 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 and et de de the editor: of muscle strength in children and adults is a in and The regarding this Viewpoint is that children adult muscle to an of all involved to In to torque and agonist activity, activation as well as and muscle architecture are parameters when comparing children adults (2). As in this Viewpoint, is not to but with since ACSA muscle area, to to further magnetic resonance differences in and in children adults during contraction and of muscle Furthermore, force is more at force than at force a hypothesis (2). However, as confounding physiological is by normalization of muscle For muscle is different between children and adults, children higher contribution to production at is (4). Furthermore, on muscle length, muscle and muscle In it that optimal and normalization should account for differences in muscle strength between children and adults, but physiological normalization is , , F , S. of muscle architecture in children and adults using magnetic resonance and J Biomech | ISI | Google Scholar2. , , D , activation of the in prepubertal children. J | ISI | Google Scholar3. DA , A , to J Biomech 38: 2005.Crossref | PubMed | ISI | Google Scholar4. A , Ratel S , Le Y , , , Muscle changes a J Appl Physiol | ISI | Google Scholar5. , , of force during of J Physiol | PubMed | ISI | Google ScholarREFERENCES1. , , F , S. of muscle architecture in children and adults using magnetic resonance and J Biomech | ISI | Google Scholar2. , , D , activation of the in prepubertal children. J | ISI | Google Scholar3. DA , A , to J Biomech 38: 2005.Crossref | PubMed | ISI | Google Scholar4. 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