Effect of age and sex on absolute strength
in human muscle
Tetsuo Fukunaga and Akifumi Matsuo
Departrnent of Sports Sciences, College of Arts and Sciences, University of Tokyo

Abstr.ct
Maximum voluntary strength per unit muscle area (absolute strength) rclated to age was investigated in normal l3l males and 127 female$, 7 to l8 years of age. A Cybex machine was us€d tomeasure the isometric muscle stlength in flexion and extension at elbow alrd knee joints, respectively.
The cross.sectional muscle area of extensor and flexor at right upper arm and thigh were determinedby using ultrasonic apparatus. The muscle area increased with age from 7 to 17 years in males and to
12 yeals in females. The absolute strength tended to increase with age from 7 to 12 years in males

and 7 to 9 years in females. Observing from the view point of relative gowth the absolute skength
increased with the increment of body height up to 150-160 cm in males and 140-150 cm ir females.

Above about these heights the absolute strength was independent of the height in both s€xes. There
were no differences in the absolute strength beh[een both sexes at a given ag€ or body height. These
result indicate that under l2 years (155 cm of height) fot boys and 9 years ( 145 cm) for girls the incrq'
metlt in muscle area with age is not enough accompanied with the development of muscle function.

Key wordt : muscle area, absolute ttrength, oge and rex.
Introduction
The maximum voluntary strength is considered to be affected by some factors of muscular andnervous system such as muscle cross-sectiotral a! ea(l I ' 13 ' 16), muscle fiber type(15'18), and level of ex

citation of centml nervous system and number of motor units recruitments in muscle contraction(6).
It is considered that these factots ate developed not altogether with age. The nervous system developed mostly in babyhood up to about l0 years old, while muscular system developed rapidly insecondary sex character period.

There are several repo s for the age trends of musclc strength. Maximum voluntary strength inhuman elbow flexor d€veloped above 12 yea$ old was caused by the increment of cross-section ofmuscle, because of no changes in strcngth per unit musclc arca with a8c and sex(6). However, in theatrimal experiments (mice) the tension per unit muscle area increased with ag€,

The purpose of the present study is to observe the effect of age on strength pet unit area ofmuscle (absolute strength) in the aSes of 7 to l8 yea$ old.

32

MethodSubject were l3l of males and 127 of fcmales, aEed'7 to l8 years old. The cross-sectional area of

flexor and extenso! muscle of upper arm and thigh were meagured by means of ultlasonic appiuatus(ALOKA SSD-120 connected to cfuculat compound system). The sites of meazurements of crosssection of limbs were as follows:

upper arm; 6070 distal poirt of humcrus length,

thigh ; 50% of femur length.
The qoss-sectional area were measured at the body position of full extension of both knee and elbow

joints in right side limbs.
The maximum isometric voluntary sttength of extension and flexion of elbow and knee joints
werc measured by Cybex I I at the sitting position on specially designed apparatus. The joint angle formcasu ng the strength were I l0 degees for flexion and 130 degees for the extension of elbow joint,
and that of 140 degrees for flexion and I l0 degrees for extension of knee joint, rcspectively.
Results

Figure I shows changes in crosgsectional area of flexor and extensor muscle at upper arm andthigh. ln males both flexor and extensor musclc area increascd with age. Above about 12 yeals
otd the hther increment of muscle area were observed. On the other hand, females indicated lower
increment of muscle arca than that of males abovc 13 yea$ old. It was observed that the differencesof muscle area between males and females increased above 13 years for arm muscle and 14 yeats for2a24

Elbow FIexor Muscle

20

t6
12
︵・日 ｅ ｃＰ ¨聖ｏｏ●
︐

8

4
100
90
80

Knee Flexor Muscle

70

60
50

40
30
20

t0
0

78 910 ll12 13 14 15 16 17 l8

7 8 9lOll12 13 14 15 16

Age (yrs)
Fig.

I Chartses in crosesectional a(ea of muscle with age

Elbow Flexor
200
０ ０
︒
０
０
８
１
︵Ｚ︶ 鶴 ●ｏ● ∽ 聖 ３ ●

100

0

800

︒
︒
０
︒
４
６
ｏ■一０日 ｏ留Knee Extensor

07

8 9 10 11 12 131415 161718

7

8

9

1011 12 131

16 17 18Age(yIS)町 .2 Changesln cro針

"ctlonal area of mutte with age

O Male O Female

a Male O Female

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５
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タ

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,ts#.if Jot# "t
00 120 140 160 20

Body Height (cm) BOdy Weight (k9)
勁B3The ab801ute strength oF elbow nexor and
eXtCn30r FeLtedtO body heut and welght

30

40

50

60 70

3ody Height(cm)3ody Weight(ko)Flg.4 The abS01ute strem嘔 lh of knec eXtenЮ r andnexOrreLtcd lo body hclght and weut

34thigh muscle. Figule 2 iqdicates changes in muscl€ strength with age. The strength for males increased mpidly above about 12 years old with age.. On the othe! hand,females indicated continuous
litrear sliSht incrcasing of the strength with inclease of the ages, ,esulting clear sex differences of thestlength above about l3 years old.

The absolute strength is shown in Table l. The absolute strength indicated significantry lower
values in 7-12 yea$ in boys and 7-9 years in gills than the other ages, except for elbow cxtensor
muscle.

The absolut€ stre[gth of elbow flexo! and extensor are observed as the changes with the bodyheight and weight in Fig. 3. Plots express as means and standald errors at each age. The absolutestlength in elbow flexor increased with the height and weight under about 150-160 cm and about 50
kg, respectively. However in elbow extelsor muscle the absolute strength indicated almost constantvalues, regardless of body height alld weight. In gererally, there were no significant diffcrenccs ofabsolute strength between both sexes. Figure 4 shows the charges in absolute strenSth of knee extensor and flexor with the height and weiSht. Knee extensor muscle indicatcd thc ilcrcment of absolute strength with height and weight under about 150-l60cm of height and about 50 kg of weight,

respectively. However, the absolute strength of knee flexor werc independelt of height and weightard indicated about 4-6 N/cm2. Between male and female no stnificant differences wcre observcd

in absolute strength of knee extensor and flexor at a given hcight and weight. The absolute strength
related to cross-sectional area of muscle and bone are observed in Figures 5 and 6. The absolute

O Malc O Fcmalc

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4

8

12

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16

20

Muscle area(cm2)1234
Bone area(,m2)

ol elboF flexor lrlal
extensot related to closs-s€ctiooal area ofFig, 5 The absolute fiength
muscle alrd bone.

Elbow

Age
(yiS)

11

Flexoi

Flexo,

Exl.ntor

kg′ Cn')
〈

Cn')
に′

(k8,/cm')

M

10,11■ 1 20

1153,224

4,3■ 0'5437=040F

10675■ 142

1307,3'2

496,092441■ 070

M

101031■ 2061167■ 164458■ 071

435■ 051F

10

945全 170

8'1,176405■ 069

419■071M

10,95,128

1049,236

434,0634531070F

101085■ 146

11 13■ 144306■ 042

4011074M 101013,140

1349,294

461■ 071

510,065

570,142F101459■ 2 14

14,6,230

521■ 201M

101159■ 1581083■ 232

426■ 085

458,064F:01125,121

117,■ 224

4,3■ 070

521,101M

iO

11 39■ 20̀

1099■ 334

SSO,109523,053F

101169■ 260

126,■ 282

421,107

5511068M 121486,228

1550,242

538■ 0'0586,120
580,1151211951148

1235,114

440,094M 121247■ 208

1227,318

S Sl,119583■ 147

F

1027,1 '6

lo ll■ 144

175■ 064

5'0■ 075

711,159758■ 134

F

12

M ll

1251■ 162

1345,178

543,l ll,r

131235,190

115'1196

5031122M

121524,190

11 81■ 238

60,■ 132

747■ 145

10

1433,168

113,■ 248

459,l l11

5 74,086

M 121540,2101329■ 266

564=555

781,032F

1012,7■ 240

1099■ 278

504tll,3'OS■ 127M 12

1526■ 220

119,■ 274

4,2■ 0,6

721,1● 2●

101311,■ 142

1149,180

5116■

101

721,113M

20

1590■ 208

1245,152

550■ 0F

20

1780■ 298

1059■ 212

551■ 071

Ｍ Ｆ

Male

F

762■ 09,693■ 162

m.3r l sD

Femalestlength of elbow flexor and knee extensoi in male subjects incrcased with thc musclc and bonc areas
in elementary school ages (under about 12-16 cm2 in elbow flexot muscle and about 40-50 cm2 of
ktrec extensor muscle, and under about 2-3 cmz of bonc area of humerus and about 4-5 cm2 of

femur). Howeyer, in elbow extensor and knec flexor the absolutc strength wele independent ofmuscle and bone area in both males and femalcs.

O Male O

Female︵ 日ｏヽぃ００■ ∽
Ｚ︶ｃｏ﹄ｏ２ｏ∽ 日 ■ ● ︼ｏＯ●一
・
︐

t
■
請芦

t.:♯

岬lφ ‐

:.:・・

20

50

30

40

Muscle arca(cm2)

蟷
ギ
ザ
3456
Bone area(cm2)

Fig. 6 The absolute sttenSlh of knee flexot and exten3or related to cross-sectional area of muscle and bone.

Discussion

In the present study changing in the stlength per unit area (absolute strength) with age indicatedto have different growth pattems due to vadous muscle groups. Elbow flexion and kltee extension
indicated clearty low strength per unit area under 12 years compared with other age goups. These
represent to have different growth pattern between cross-section and function of muscle tissues.

Interesting point in the present study was that the absolute strength increased with age in childhood under about l2 yea$ old. In animal experiments it was repo ed that the strength per unit area inmouse muscle increased with age from I to 5 weeks. These data are ageed with the present study.

It is considered that the absolute stlength is affected by the muscle fiber types(I2). Fast twitch

fibers exerts highe! tension and power of contraction compared to slow twitch fibers. There
werevadous repo s for the effect of fiber types on the strength per unit muscle area
in human and also
animal muscles. close(4) found that no significant differences of strength per unit area wasobserved
bet\r'een fast and slow twitch fibers. woitiez et ar.(2o) reported, however, highe!
strength per unit areaof fast fibers than that of slow fibers.
Accolding to the studics for the effect of age on the fiber types the ratios of number of FT fibcis
in vastus lateraris were reported to be almost the same in 6 years boys as in adults. On the othercaliber of muscle fiber indicated same values between type I fiber and type II fiber in humanhand,baby ofI year old(s), and the fiber area increased more in II fiber with age thar that of I fiber, resulting laBer
cross-sectional area of II fiber than that of I fiber in adults(Io). These may
indicate that FT fiber

increase its cross-section with growth than that of sr fiber. However, inthe present study above
about I 2 years in males and 9 years in females there were no significant differences of strength per
unit

37

crosssectional area of muscle, indicating no effect of fiber typcs on strenEth per unit musclc arca inlower ages.
Muscle fiber is mainly consisted of myofibril and sarcoplasm. It is considered that the latio of
myofibril to sarcoplasm affect on the relatiofl bctween strength and muscle area. In mouse expcriments the number of myofibri.l increased up to about 10-15 times with age. The pcrcent ratio of
myofibril increased mpidly in 30 days after birth. Assumirg for these tendency to apply to the humanmuscle, changes in strength per unit area with age in the present study may be caused by the changes

in number of myofibril in chitdhood.

Th€ factor for neryous system was reported to affect on the strcngth per unit muscle area.
Maximum voluntary Etrength was due to the number of motor ulits in contraction which was causcd
by the level of excitation of cerebral cortex. The nervous system developed rapidly in lowe! ages,
and reaches to about the same level as adults at the ages of l2-15 y€ars old.

It was observed that two types of muscle came into existence during human gowth. One type ofthat is the muscle groups such as elbow extensor and knee extensor which the absolute strength increased with age (or body height ard weight) in eleme'ltary school period. These diffcrcnces ofbetween both muscle groups may be considered to be induced by dai.ly physical activities; anti gravi-

tational muscl€ such as elbow flexor and knee cxtensor are activated more in physical moyement thanthe other muscles.
Refe!en@8(1) Be[, R.D., MacDouSall, J.D., Billeter, R. and Howald, H. (1980): Muscle fiber types ard morphometdc
analysis of skeletal muscle in six-yea! old children. Med. Sci. Sports Ex.t.,12,28 31.

(2) Burke, RE. and Edjerton, V.R. (1975): Motor unit prope ie3 and selective involvement in movement. In:
Exercire and sport sciences reviews, vot. 3, (ed) Wilrnore, J. H. and Keogh, ,.F., Acadenic press, New York,

p3l-81.

(3) Close, R.t. (1954) : Dyrumic propqties of fast and slow skeletal muscles of the Iat durirg development.
J. Physiol., 173, 74-95.

(4) Clo3e, R. I. (1972): Dynamic propelties of mamalian skeletal mu3cles. Physiol. Rev.,52,129-191 .
(5) Colin&Saltin, A.S. ( ): Enzyme histochemistry on skeletal muscle of the human fetus J. Neurol. Sci., 39,
l6 9- 185.

(6) Fukuna8a, T. (1976) : Die abrolute Muskelkaft und Muskelkrafttaining. Sportazt und Sportmedirin, ll,
225-265.

(?) Goldspink, G. (1970) : The proliferation of myofibrils during muscle fiber grofih. J. Cetl. sci., 6, 593-603.
(8) Cutman, E., Melichna, J. and Syrovy, I. (1973): Developmental changes in contraction time and m8cle frber
pattem of fast and slow muscle. Experimentla,2g ,435-436.

(9) Ikai, M. and Steinhaus, A. (1961): Some factors modyfying the expression of human strength. J. Appl.
Physiol. 16, 157 163.

(10) larsson, L., and Karlesson (19?8): Isometric and dynamic endurance as a function of age and skeletal muscle
chalacteristics. Acta Physiol. Scand.,104, 129 135.

(11) Maughan, R.J., Watlon, J.S. and Weir, J. (1983) : The influencr of variations in muscle liber composition on
muscle stienSlh and fioss{ectiotul area in untrained males. J. Physiol., 351, 299-311.

(12) Miya$ita, M. and Kanehisa, H. (19?9): Dyn mic pe3k torque related to age, sex, and performance. Res.
Quatt.,50, 249-255.

(13) NySaard, E., Houston, M., suzuki, Y., Yorgensen, K. and Salti4 B. (19!3): Morphologv of the brachialbiceps muscle and elbo\f, flexion in man. Acta Physiol. Scand., ll7,287 292.
(14) Rowh, E.S. (1951): Strenglh and enduEnce in the walking and hypnotic states. J. Appl. Physiol., 3,404-410.

(15) Saltin, B., Henriksrol, J., Nygaard, E. and Andersen, S. (197?): Fiber typ€s and metabolic potentiak of38skeletal muscles in sedentaty nran and enduratrce lunners. Ann. New York Acad. Sci., 301 , 3-29.

(16) Shant., P., Fox, E.R., Hutchison, W., Tyden, A. and Astrand, P.O. (1983): Muscle fiber type distribution,muscle cross-sectional area and maximal voluntary strength in humarB. Acta Physiol. Scand. ,111 ,219-226.

(17) Tesch, P. and J. Karlsson, (1978): Isometdc stenSth performance and muscle fiber type distribution in man.
Acta Physiol. Scand., 103,4?-51.

(18) Thorsterson, A., Grimby, G. and Karlssor, J. ( l9?6): Force-velocity relations and irber composition ir humanknee extenror muscle. J. Appl. Physiol.40, 12-16.

(19) Van Linge, B. (1962): The response of muscle to strenuous exersise. J. Bone and Joinr Sutg.,44,7ll-721.
(20) Woittiez, R.D., Huijing, P.A., Robbelt, M.F., Rozcndal, R.H. and Rijinsburger (1985): The power and force ofslow and fast muscle during concentdc and ecceltlic contiactions. In: loth InternatioDal Congress of Biomechanichs, UmeS,P296.