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Eur J Appl Physiol (2008) 103:481–484

DOI 10.1007/s00421-008-0737-3

 123

SHORT COMMUNICATION

Quadriceps muscle function characteristics in severely

obese and nonobese adolescents

Nicola A. MaYuletti · Marc Jubeau · Fiorenza Agosti ·

Alessandra De Col · Alessandro Sartorio

Accepted: 24 March 2008 / Published online: 4 April 2008

© Springer-Verlag 2008

Abstract The purpose of this cross-sectional study was to

compare quadriceps muscle strength and fatigue between

severely obese (body mass index 34 kg/m2) and nonobese

adolescents. Maximal isokinetic torque and angle of peak 

torque as well as isometric torque at short (40° of knee Xex-

ion) and long (80° of knee Xexion) muscle length were

measured using an isokinetic dynamometer. Muscle fatigue

was quantiWed as the percent torque loss during an isoki-

netic voluntary protocol and an electrical stimulation iso-

metric protocol. Obese adolescents produced greater

absolute isokinetic (+16%; P < 0.05) and isometric torque

at short (+25%; P < 0.01) but not at long muscle length

(P > 0.05) compared to their lean counterparts. The angle

of peak torque was signiWcantly lower in obese than in non-

obese subjects (¡11%; P < 0.05), i.e., obese produced their

maximal strength at shorter muscle length. Isokinetic and

isometric torque normalized to the fat-free mass were not

signiWcantly diV erent between the two groups. No signiW-

cant diV erence in voluntary and stimulated torque loss was

observed between groups. Muscle strength per unit of fat-

free mass and muscle fatigue were similar in the obese and

nonobese adolescents tested in this study, therefore

suggesting that obesity has little or no eV ect on quadriceps

muscle function characteristics. On the other hand, it

remains to be conWrmed whether the observed quadriceps

muscle length speciWcity contributes to the reduced func-

tional capacity of obese adolescents during complex motor

tasks involving deep knee Xexion (squatting, kneeling).

Keywords Peak torque · Fatigue · Muscle length ·

Isometric · Isokinetic

Introduction

Although it is generally admitted that young obese sub-

 jects—who are ridiculed because of body size and form and

who are more likely to voluntarily reduce habitual physical

activity (Parizkova and Hills 2001)—would exhibit inade-

quacies in the performance of motor tasks (Beunen et al.

1983; Korsten-Reck et al. 2007), very few studies have

attempted to compare motor performance between obese

and nonobese adolescents. SpeciWcally, the function of the

quadriceps femoris muscle—which is responsible for knee

extensor torque production and therefore plays a key role

during ambulatory, functional and sport activities—has

been investigated only in one instance. Blimkie et al.

(1990) measured maximal voluntary isometric and isoki-

netic strength of the quadriceps muscle in obese (mean

body mass index 31 kg/m2) and nonobese male adolescents

(mean age 16.6 years). They reported no signiWcant diV er-

ences between groups for absolute strength, fat-free body

mass, lean thigh area, and contractile properties, therefore

suggesting that muscular factors do not contribute to the

poorer motor performance of the young obese. It would be

interesting to know if the quadriceps muscle of severely

obese adolescents, who present greater fat-free mass (in

addition to fat mass) than their lean pairs (Lazzer et al.

N. A. MaYuletti (&)Neuromuscular Research Laboratory, Schulthess Klinik,

Lengghalde 2, 8008 Zurich, Switzerland

e-mail: Nicola.MaYuletti@kws.ch

M. Jubeau

Laboratoire INSERM U887, Faculté des Sciences du Sport,

Université de Bourgogne, Dijon, France

F. Agosti · A. De Col · A. Sartorio

Laboratorio Sperimentale di Ricerche Endocrinologiche,

Istituto Auxologico Italiano, IRCCS,

Piancavallo (VB) e, Milan, Italy

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482 Eur J Appl Physiol (2008) 103:481–484

 123

2007), would produce greater absolute strength, similar to

adults who are severely obese (MaYuletti et al. 2007).

To our knowledge, the eV ect of obesity on muscle

fatigue, which—besides muscle strength—represents an

important link to normal daily-living tasks, has never been

addressed in adolescents. This information is essential since

several daily (e.g., stair climbing, walking) as well as sport

activities (e.g., cycling, running) involve repetitive contrac-tions of the quadriceps muscles, where possible greater

fatigue in the obese (MaYuletti et al. 2007) could be seen

as a limiting factor for motor performance.

The main objective of this study was to compare quadri-

ceps muscle strength and fatigue characteristics between

severely obese and nonobese adolescents, in an attempt to

determine if factors other than fatness may account for poor

motor performance capacity in obesity.

Methods

Subjects

Ten severely obese (body mass index >97th percentile)

male adolescents (age ¸13 and ·17 years) volunteered to

participate in this study (mean age § SD 15.6 § 1.2 years;

height 171 § 6 cm; body mass index 34 § 3 kg/m2). Ten

age- and height-matched (age 14.9 § 1.1 years; height

170 § 9 cm; body mass index 19§ 1 kg/m2) nonobese

male adolescents recruited from the hospital staV  families

were also tested. Maturity level (estimated according to

Tanner staging) was comparable between groups (15% of 

Tanner stage III, 50% of stage IV and 35% of stage V).

Physical activity level was also similar between groups; all

the adolescents performed recreational physical activity for

¸2 h/week within the past month and none of them was

involved in very vigorous physical activity. None of the

adolescents had orthopedic or cardiovascular problems

interfering with the execution of the tests. Signed informed

parental permission and signed informed assent of each

individual were obtained. The study protocol was approved

by the Ethics Committee of the Italian Institute for Auxol-

ogy. All the procedures were conducted according to

Helsinki Declaration.

Fat-free mass estimation

Bioelectric impedance analysis was performed in the early

morning after an overnight fast, according to a conventional

standard technique (Lukaski et al. 1986). Subjects were

asked not to drink within 4 h of the test, to empty their uri-

nary bladder at least 30 min before the analysis, and to

remain in the supine position for 5 min before the acquisi-

tion. The electrodes were placed on the right wrist and ankle

of the subjects while lying comfortably supine in a bed with

the limbs abducted from the body. Whole-body resistance to

an applied current (at 1, 5, 10, 50 and 100 kHz, 0.8 mA) was

measured with a tetrapolar device (Human IM, Dietosystem,

Milan, Italy). Fat-free mass was calculated with the speciWc

equations derived by Gray et al. (1989).

Isokinetic and isometric muscle function

Details of the testing procedures have been reported previ-

ously (MaYuletti et al. 2007). In brief, assessments con-

sisted of isokinetic and isometric quadriceps muscle

strength and fatigue over two testing sessions (session 1:

isokinetic; session 2: isometric; interval: 24 h). The right

quadriceps muscle was tested by using an isokinetic dyna-

mometer (Cybex, Lumex, Ronkonkoma, NY, USA). Sub-

 jects were comfortably seated (90° at the hip) on the

dynamometer chair. The dynamometer lever arm was

attached 2–3 cm above the lateral malleoulus by using a

strap. Straps were also applied across the chest, pelvis and

mid-thigh. Torque data were corrected for gravity using

Cybex software. Visual feedback and verbal encourage-

ment from the investigator were consistently provided.

Warm-up consisted of several submaximal contractions of 

the quadriceps muscle at diV erent angular velocities and

knee joint positions.

Muscle strength

Isokinetic measurements involved 3–4 consecutive (maxi-

mal) knee extensions performed at an angular velocity of 

180°/s. Range of motion was 90°, from 90° of Xexion to 0°

(knee fully extended). All knee angles were provided by the

isokinetic device. We consistently assumed that knee joint

angle was linearly related to quadriceps muscle length (0° of 

Xexion: shortest quadriceps length; 90° of Xexion: longest

quadriceps length). Isometric measurements consisted of 

two maximal knee extensions realized at two diV erent joint

positions (randomly presented): 40° of knee Xexion (short

quadriceps muscle length) and 80° of knee Xexion (long

quadriceps muscle length). Rest periods of »2 min were

allowed between series of contractions. For isokinetic trials,

peak torque and angle of peak torque were measured. For

isometric trials, the maximal torque at the two knee joint

positions was retained. In each case, only the best perfor-

mance was included in the analyses. Both isokinetic and iso-

metric torque data were recorded as absolute values (Nm)

and subsequently normalized to fat-free mass (Nm/kg).

Muscle fatigue

The voluntary isokinetic fatigue test consisted of 50 con-

secutive knee extensions completed at an angular velocity

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Eur J Appl Physiol (2008) 103:481–484 483

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of 180°/s. The average peak torque of the Wrst three con-

tractions was considered as the reference value (100%).

Voluntary fatigue was then expressed as the percent torque

loss with respect to the reference after 10, 20, 30, 40 and 50

contractions (average of 3–5 peak torque values).

The stimulated fatigue test was completed under isomet-

ric conditions (60° at the knee) and consisted of 60 trains of 

stimuli (1.5 s on ¡3.5 s oV ; frequency 40 Hz; pulse dura-tion 600 s) delivered over a 5-min period. A commercially

available stimulator was used (Compex Sport-P, Medicom-

pex SA, Ecublens, Switzerland). Stimulating electrodes

were placed over the vastus lateralis and vastus medialis

motor points (25 cm2 each), and proximal to the femoral tri-

angle (50 cm2). Current amplitude was progressively

increased to attain 10% of the maximal voluntary isometric

torque. The average torque of the Wrst three contractions

was considered as the reference value (100%). Stimulated

fatigue was then expressed as the percent torque loss with

respect to the reference after 1, 2, 3, 4 and 5 min (average

of 3–5 peak torque values).

Statistical analyses

Statistical methods including means and their SD or SE

were calculated for each parameter. Statistical diV erences

between obese and nonobese adolescents were assessed

using unpaired (one-tailed) t  tests. The level of signiWcance

was established at P < 0.05.

Results

Muscle strength

Absolute isokinetic torque was signiWcantly higher in obese

than in nonobese adolescents (+16.3%; P < 0.05), while

isokinetic torque normalized to the fat-free mass was almost

identical between the two groups (Table 1). The angle of 

peak torque was signiWcantly smaller in obese than in non-

obese subjects (»6°; P < 0.05), that is to say obese adoles-

cents produced their maximal strength at shorter quadriceps

muscle length compared to their lean counterparts.

Absolute isometric torque was signiWcantly higher in the

obese group at short (+24.6%; P < 0.01) but not at long quad-

riceps muscle length (+16.4%; P > 0.05). Isometric torque

normalized to the fat-free mass did not diV er signiWcantly

between the two groups whatever the position of the knee.

Muscle fatigue

No signiWcant diV erence in voluntary torque loss was

observed between obese and lean adolescents throughout

and at the end (obese ¡52.6%; lean ¡52.2%) of the

isokinetic fatigue test (Fig. 1a). In the same way, stimulated

torque decreased similarly in the two groups during the

5-min isometric fatigue test (Fig. 1b).

Discussion

The main Wndings of the present study were that muscle

fatigue, both voluntary and stimulated, and muscle strength

per unit of fat-free mass, both isokinetic and isometric, did

not diV er signiWcantly between severely obese and nonob-

ese adolescents, therefore suggesting that obesity has little

or no eV ect on quadriceps muscle function characteristics.

We also demonstrated that maximal quadriceps strength

was produced at diV erent knee joint angles in nonobese and

obese adolescents, the latter privileging more extended

positions (shorter muscle lengths).

Muscle fatigue is deWned as an exercise-induced reduc-

tion in the ability of a muscle to generate force (Gandevia

2001) and may develop at various levels of the neuromus-

cular system. In the present study, we used two diV erent

fatigue protocols (voluntary and stimulated) to gain insight

into central and peripheral factors underlying muscle

fatigue. Since voluntary and stimulated torque decreased

similarly both throughout and at the end of the fatigue

Table 1 Fat-free mass and

muscle strength in obese and

lean adolescents

Obese Lean Obese versus

lean (%)

P

FFM (kg) 62.2 § 7.4 52.9 § 8.5 +15.0 0.009Isokinetic strength

Torque (Nm) 135.4 § 25.1 116.5 § 23.9 +16.3 0.032

Torque/FFM (Nm/kg) 2.20 § 0.38 2.20 § 0.38 ¡0.3 NS

Angle of peak torque (°) 48.1 § 6.2 53.9 § 3.4 ¡10.7 0.018

Isometric strength

40°-torque (Nm) 193.8 § 26.0 155.5 § 31.4 +24.6 0.004

40°-torque/FFM (Nm/kg) 3.15 § 0.49 2.94 § 0.32 +7.3 NS

80°-torque (Nm) 232.0 § 44.9 199.3 § 49.5 +16.4 NS

80°-torque/FFM (Nm/kg) 3.73 § 0.63 3.77 § 0.67 ¡1.0 NS

Values are mean § SD

FFM  fat-free mass,

 NS non signiWcant

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484 Eur J Appl Physiol (2008) 103:481–484

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protocols in the two subject groups, there is no reason to

believe that central and/or peripheral mechanisms of mus-

cle fatigue could diV er between obese and nonobese adoles-

cents—contrary to what we have recently reported for male

adults (MaYuletti et al. 2007). Obese adults demonstrated

indeed signiWcantly greater fatigue during voluntary but not

during stimulated knee extensions compared to their lean

counterparts (MaYuletti et al. 2007). Interestingly, volun-

tary fatigue—in addition to stimulated fatigue—was com-

parable between these nonobese adults and the adolescents

tested in this study (both obese and nonobese).

Quadriceps force-generating capacity depends upon

many neural and muscular factors, such as the extent of 

motor unit activation and muscle cross-sectional area. The

severely obese adolescents tested in this study produced

signiWcantly higher absolute muscle torque (both isokinetic

and isometric) than their lean counterparts, except at long

muscle length. This was mainly the result of greater fat-free

mass (and probably of greater quadriceps cross-sectional

area) in obese than in lean adolescents. The fact that muscle

strength adjusted to fat-free mass was comparable between

obese and nonobese subjects, allows one to speculate that

severe obesity in male adolescents would not aV ect intrinsic

muscle contractile properties as well as muscle activation

during maximal eV orts. Using the twitch interpolation tech-

nique, Blimkie et al. (1990) demonstrated lower quadriceps

activation in obese (body mass index 31 kg/m2; age

16.6 years) than in nonobese adolescents, however their

obese and nonobese subjects had similar absolute strength

and fat-free body mass, contrary to the adolescents evalu-

ated in our study.

Interestingly, we observed signiWcant quadriceps muscle

strength diV erences between obese and lean adolescents

related to knee joint position (as provided by the isokinetic

device), for both isokinetic and isometric tests. Althoughpossible diV erences in actual (not device) knee angle

between the two groups cannot be excluded (see Tsaopou-

los et al. 2007), we speculate that obese subjects would

present an advantage at short rather than at long muscle

length. Adolescents who are obese would probably limit

deliberately their range of motion during daily and sport

activities involving deep knee Xexion, because of excessive

stress acting on articular joint surfaces. This speciWc train-

ing stimulus would inevitably result in favorable adapta-

tions at short muscle length—which could explain the

present Wndings—but this would also engender a disadvan-

tage at long muscle length, which remains to be ascertained

in future studies.

Acknowledgments This study was partially supported by “Progetto

di Ricerca Corrente”, Istituto Auxologico Italiano, IRCCS, Milan, Ita-

ly. The authors are extremely grateful to the Auxology Division staV 

(Istituto Auxologico Italiano, Piancavallo, Italy).

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Fig. 1 Mean (§SE) torque decrease during the 50 voluntary isokinet-

ic contractions (a) and during the 5-min electrical stimulation protocol

(b) in obese and nonobese adolescents

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