Full text of DOI:10.1007/BF03351039

J. Endocrinol. Invest. 24: 393-398, 2001
Changes in motor control and muscle performance after a
1
short-term body mass reduction program in obese subjects
A. Sartorio*,**, C.L. Lafortuna***, G. Conte**, G. Faglia****, and M.V. Narici*****
*Experimental Laboratory of Endocrinological Research, Istituto Auxologico Italiano, IRCCS, Milan;
**Division of Metabolic Diseases III, Istituto Auxologico Italiano, IRCCS, Piancavallo (VB); ***Institute of
Advanced Biomedical Technologies, CNR, Milan; ****Institute of Endocrine Sciences, University of
Milan, Ospedale Maggiore, Milan, Italy; *****Department of Exercise and Sport Science, Metropolitan
University of Manchester, Alsager, UK
ABSTRACT. Two hundred and thirty obese sub-
jects (age: 18-77 yr, BMI: 31.1-65.8 kg/m2) were
studied before and after a 3-week body mass re-
duction (BMR) program, coupling restricted en-
ergy diet (1200-1500 kcal/day) with low intensi-
ty exercise prescription. It involved 5 days per
week (consisting of one-hour dynamic aerobic
standing and floor exercise plus 30 min of cyclo-
ergometer exercise at 60 W or, alternatively, 4
km outdoor leisure walking on flat terrain) and
psychological counseling. One-leg standing bal-
ance test (OLSB) and stair climbing test (SCT)
were employed to assess motor control and max-
imal lower limb muscle power, respectively. The
BMR program induced a significant weight loss
(4.1%; p<0.001), a higher reduction of body
mass index (BMI) being observed in males than in
females (p<0.001). OLSB performance time in-
creased by 20.5% (p<0.001) after treatment, the
improvement being evident in both genders. A
20.8% reduction in SCT time (p<0.05) was also
observed and corresponded to a 13.2% increase
(p<0.001) in average absolute muscle power and
15.0% increase (p<0.001) in specific muscle pow-
er (i.e. the power output per kg of body mass),
with no differences between genders. In conclu-
sion, in spite of the moderate reduction of body
mass after restricted energy diet and low inten-
sity physical conditioning, significant improve-
ments in motor control and performance, likely
to ameliorate the execution of simple daily ac-
tivities, were observed in obese subjects.
(J. Endocrinol. Invest. 24: 393-398, 2001)
©2001, Editrice Kurtis
INTRODUCTION
fat loss, less is known about how this approach may
influence muscle function and the ability to perform
muscular work over a set period of time, that is the
ability to deliver muscular power.
One of the most plausible explanations for the lack
of data concerning the combined effect of diet plus
physical activity on muscle performance is proba-
bly the difficulty in finding easy, economic and re-
liable tests to be used in severe obese patients on
a large scale.
Although several studies have explored the impact
of physical conditioning of various intensities on the
reduction of weight and body fat (1-3), to date few-
er data are available on the influence of restricted
energy diet and physical activity on muscle func-
tion in obese patients (4). In fact, while it is well es-
tablished that diet plus physical activity affects body
composition and weight favourably, by provoking
Therefore, the aim of the present study was to in-
vestigate the effects of a short-term body mass
reduction (BMR) program (consisting of energy-
restricted diet, low intensity exercise prescription
and psychological counseling) on motor control
and muscle performance employing two simple
tests (one-leg standing balance, OLSB; stair
climbing test, SCT) for the evaluation of motor fit-
ness and lower limb muscle power on a large
group of obese patients of different age and gen-
der.
1This study was partially supported by Progetti di Ricerca Corrente (grant
no. 05C907), Istituto Auxologico Italiano, IRCCS, Milan, Italy.
Key words: Muscle performance, obesity, physical activity, weight loss.
Correspondence: Dr. Alessandro Sartorio, Laboratorio Sperimentale di
Ricerche Endocrinologiche (LSRE), Istituto Auxologico Italiano, IRCCS,
Via Ariosto 13, 20145 Milano, Italy.
E-mail: sartorio@auxologico.it
Accepted October 20, 2000.
393

Muscle performance in obesity
SUBJECTS AND METHODS
Subjects
ii) Stair climbing test (SCT). The subjects were invit-
ed to climb up ordinary stairs at the highest possible
speed, according to the subject’s capabilities. The
stairs consisted of 13 steps of 15.3 cm each, thus co-
vering a total vertical distance of 1.99 m. An operator
measured the time employed to cover the test with a
digital stopwatch. The test was considered to start at
the moment when the first foot was lifted and to ter-
minate with the contact of the same foot on the last
step. The operator also ranked the subject’s test per-
formance according to a three-level qualitative scale,
similarly to the previous test. If subjects were not able
to complete the stair climbing, that is they failed in
reaching the final step or did not complete the test
within 60 s, they were coded as abnormal (AB). If they
were able to complete the test without any difficulty
they were coded as normal (N), and if they complet-
ed the test but had some apparent difficulty as stop-
ping and restarting or searching for handrail support
they were coded as adaptive (AD). The vertical com-
ponent of the speed was calculated from the vertical
and horizontal dimensions of the steps. In these con-
ditions the specific mechanical power (i.e. the power
per unit body mass) is directly proportional to the ver-
tical component of the speed, since, whatever the
speed, the subject raises every unit of his body mass
by a height (in m) equivalent to his vertical speed (in
m·s-1).
Two hundred and thirty obese patients (43 male
and 187 female, age range: 18-77 yr, mean SE:
49.9 0.9 yr, BMI range: 31.1-65.8 kg/m2, mean SE:
41.4 0.4 kg/m2) were admitted to the study after
giving informed consent. No one dropped out dur-
ing the study.
Patients with liver, heart, lung or kidney failure or
diabetes were excluded. All subjects were in-pa-
tients of the 3rd Division of Metabolic Diseases
(Italian Institute for Auxology, Piancavallo, Italy) and
were evaluated before and after a 3-week BMR pro-
gram, consisting of restricted energy diet (1200-
1500 kcal/day), low intensity exercise prescription
and psychological counseling.
BMR program
The diet contained 21% protein, 53% carbohydrate
and 26% lipid. Estimated water content of food was
1000 ml water, 1560 mg Na, 3600 mg K and 900
mg Ca. Fluid intake of at least 2000 ml/day was en-
couraged. All subjects underwent low intensity ex-
ercise activity supervised by a physiotherapist, ac-
cording to a daily program performed throughout
5 days/week and consisting of: i) one-hour dynam-
ic aerobic standing and floor exercise performed
with arms and legs at moderate intensity under the
guide of a therapist, and ii) 30 min of cycloergo-
meter exercise at 60 W or, alternatively, according
to individual capabilities and clinical status, 4 km
outdoor leisure walking on flat terrain.
At the moment of the first execution of both tests
upon admittance, 2-3 practice trials were allowed
so that the subjects gained a good control of the
performing technique. No further repetition was
tried until the completion of the BMR program.
Functional tests
Statistical analysis
The following functional tests were performed in a
random order upon subject admittance and re-
peated at the completion of the BMR program (i.e.
after 21 days):
All the values are given as means SE. The mean val-
ues of the investigated variables before and after
BMR program were compared using Student’s
paired-sample t test, while differences between gen-
der and age groups in the response to BMR program
were tested with a two-factor analysis of variance
(ANOVA) for repeated measurements. p values less
than 0.05 were considered statistically significant.
i) One-leg standing balance (OLSB). The subjects
were invited to stand on one leg with the other flexed
for as long as possible, looking straight ahead. The
test was considered to terminate with the ground
contact of the flexed leg or with an overt loss of equi-
librium, although compensatory movements of arms
and lifted leg were allowed. An operator noted the
value in seconds with a digital stopwatch and ranked
the subject’s performance according to a three-level
qualitative scale, as described by Vellas et al. (5).
According to this ranking, subjects not able to stand
were coded as abnormal (AB); if they were able to
stand unsupported on one leg without any difficulty
they were coded as normal (N); and if they were able
to stand unsupported on one leg but had some ap-
parent difficulty in maintaining the balance they were
coded as adaptive (AD);
RESULTS
Weight loss
The 21-day BMR program induced a significant
weight loss in both gender (from 106.9 1.2 kg to
102.7 1.1 kg, p<0.001, corresponding to a – 4.1%
change), a significantly higher reduction of BMI be-
ing observed in males than in females (F=14.47,
p<0.001).
Figure 1 shows the effects of treatment on BMI val-
ues in the study group, subdivided for age ranges.
394

A. Sartorio, C.L. Lafortuna, G. Conte, et al.
45
44
43
42
41
40
39
38
37
36
35
Before BMR
After BMR
p<0.001). The improvement was evident in both
sexes (males: from 37.4 3.5 s to 43.5 3.4 s,
p<0.05; females: from 25.0 1.5 s to 30.5 1.6 s,
p<0.001), and there was no significant difference
between genders in the response to BMR program
(F=0.04, p>0.05).
The general picture of the results obtained in the
OLSB test in relation with age is shown in Figure
2. A significant decrease in OLSB time as a func-
tion of age can also be appreciated, either before
and after BMR (F=14.7 and 20.3, respectively,
p<0.001); a marked effect is apparent in all age
subgroups.
<30
30-39
40-49
50-59
>59
Age (yr)
Fig. 1 - Age class distribution of the body mass index (BMI) in
230 obese patients before and after a short-term body mass
reduction (BMR) program. Changes due to the treatment were
statistically significant in all classes of age, as assessed with
ANOVA (F=1290, p<0.001).
Upon admission, 177 patients were classified as N,
25 patients as AB and 28 patients as AD. After BMR
period, the ranks N, AB and AD included 193, 19
and 18 patients, respectively.
SCT
Before starting the BMR program, males performed
SCT better than females, the SCT time before the
treatment being significantly (p<0.01) lower in
males (4.5 0.4 s vs 7.8 0.6 s), in all age groups.
In all subjects, SCT time significantly decreased by
20.8% (from 7.2 0.5 s to 5.7 0.4 s, p<0.05) after
the BMR program. The decrease was evident in
both gender (males: from 4.5 0.4 s to 4.1 0.4 s,
p<0.05; females: from 7.8 0.6 s to 6.1 0.5 s,
p<0.005), the change in SCT time for effect of BMR
program being not influenced by gender (F=1.49,
p>0.05).
It is clearly evident that, in spite of different baseline
and final BMI values (higher in the middle ages),
the effects of BMR program were similar in all sub-
groups (delta BMI range: 1.54-1.85 kg/m2).
OLSB
Before starting the BMR program, the standing time
during the OLSB test was 37.4 3.5 s in males and
25.0 1.5 s in females (49.6% difference, p<0.001).
This tendency for a better OLSB performance in
male than in female patients was observed in all
age groups.
After the BMR program, OLSB performance time
increased significantly by an average of 20.5% in
all subjects (from 27.3 1.4 s to 32.9 0.5 s,
Figure 3 shows the results of SCT in relation with age.
It appears that SCT times significantly increased with
age either before and after BMR (F=8.35 and 4.09,
respectively; p<0.001 and p<0.01). After treatment,
60
50
40
30
20
10
0
Before BMR
After BMR
Before BMR
After BMR
14
12
10
8
6
4
2
<30
30-39
40-49
50-59
>59
0
<30
30-39
40-49
50-59
>59
Age (yr)
Age (yr)
Fig. 2 - Standing time during the one-leg standing balance test
(OLSB time) observed in 230 obese patients of different class-
es of age, before and after a short-term body mass reduction
(BMR) program. ANOVA showed significant effects of BMR pro-
gram in all classes of age (F= 31.1, p<0.001).
Fig. 3 - Time of execution of the stair climbing test (SCT time) in 230
obese patients of different classes of age, before and after a short-
term body mass reduction (BMR) program. The program signifi-
cantly affected the performance for age groups higher than 50 yr.
395

Muscle performance in obesity
DISCUSSION
Before BMR
After BMR
700
600
500
400
300
200
100
0
The present study reveals that a short-term period
of restricted energy diet associated with low inten-
sity exercise in obese patients, beside a moderate
but significant reduction in body weight and BMI,
entails an improvement in motor control and max-
imal lower limb power, as assessed by the func-
tional tests performed.
In this respect, OLSB is a simple and commonly em-
ployed test found to be a reliable indicator of health
related motor fitness in populations with different
levels of physical activity patterns and age (6-9).
This test correlates with leg muscular force, train-
ing degree (9, 10), as well as with the level of sen-
sory-motor co-ordination in health, disease, and ag-
ing (5, 11).
Moreover SCT, first introduced by the present study
as a modification of the Margaria test (12), is a sim-
ple but reliable method for the measurement of
lower limb mechanical power, often used in many
athletic activities as routine assessment for opti-
mizing performance (13).
This test is generally well accepted by the subjects,
being easy to perform and not exhaustive, eco-
nomical and well suitable for large population sur-
veys.
In spite of these advantages, these tests have nev-
er been employed, to our knowledge, for the study
of motor fitness and maximal power output in large
obese populations, before and after BMR.
Performances in the tests investigated in the pre-
sent study were gender-dependent. In fact obese
females, presumably due to a lower muscular mass,
maintain a shorter OLSB time and display a signif-
icantly lower average muscular power during the
execution of SCT than obese males. Similar differ-
ences between males and females were reported
in non-obese subjects with the standard balance
test (6, 14) and the original and modified Margaria
test (12, 15).
The present data also show a progressive age-de-
pendent decline in motor fitness and maximal low-
er limb power, which appears in line with the re-
sults obtained in non-obese subjects in both tests
(11, 12, 14, 16).
To our knowledge, the only comparable study eval-
uating SCT power in obese subjects is the report
by Kitagawa et al. (17), who however examined a
selected group of young, mildly obese patients.
These authors found significantly higher power out-
put in obese than in lean subjects of the same age,
the results being attributed to the training effect of
inert mass of fat.
<30
30-39
40-49
50-59
>59
Age (yr)
Fig. 4 - Average muscular power developed during the execu-
tion of the stair climbing test (SCT power) in 230 obese patients
of different age, before and after a short-term body mass re-
duction (BMR) program. Performance significantly declines with
age (F=6.42, p<0.001) and BMR program had statistically sig-
nificant effects in all age groups (F=60.6, p<0.001).
the most relevant improvement in SCT time was ob-
served in older patients (>50 yr).
Upon admission, 208 patients were classified as N,
15 as AB and 7 as AD. After the BMR period, SCT
rank was N, AB and AD in 219, 6 and 5 subjects,
respectively.
SCT power output
Male obese patients developed a significantly high-
er average absolute muscle power than females dur-
ing SCT, both before (571.5 29.6 W vs 345.5 10.8
W, p<0.001) and after BMR program (599.9 28.5 W
vs 402.1 12.2 W, p<0.001).
In all subjects, the treatment induced a 13.2% in-
crease in average absolute muscle power (from
387.7 11.9 W to 439.1 12.3 W, p<0.001), which
was evident in both gender.
Figure 4 shows how the average absolute muscle
power significantly declines with age (F=6.42,
p<0.001), both before and after BMR, the positive
effect of treatment being evident in young as well
as in older patients.
In terms of specific power (i.e. the power output per
kg of body mass), BMR program determined a 15.0%
increase in all subjects (from 3.48 1.45 W kg-1 to
4.09 1.50 W kg-1, p<0.001), without differences be-
tween the two sexes.
In order to investigate the impact of body weight
loss alone on the observed muscle functional im-
provements, a correlation analysis between
weight loss and the improvements in both OLSB
and SCT was carried out. No significant correla-
tion resulted (p>0.05, assessed with Fisher’s z
test)
Although in the present study we have not actual-
ly selected an age-matched control group of nor-
396

A. Sartorio, C.L. Lafortuna, G. Conte, et al.
mal weight subjects, preliminary data from our lab-
oratory seem to suggest that severe obese patients
have reduced SCT power, both in terms of abso-
lute (-19%) and specific values(-38%), in compari-
son with non-obese subjects.
The discrepancy between the two studies might be
explained both by the different age ranges (previ-
ous study: 18-22 yr vs present study: 18-77 yr) and,
particularly, by the different BMI (26 vs 41 kg/m2)
of the study groups.
A=obese patients before BMR
B=obese patients after BMR
Force
Power
A
B
C
As far as the effects of BMR program are concerned,
significant improvements in OLSB and SCT perfor-
mances were observed in these obese patients, with-
out significant differences between males and fe-
males. On the contrary, some differences were de-
tected in the effects of BMR on SCT between the dif-
ferent classes of age, being more marked over 50
years. Although body weight loss is one of the fac-
tors responsible for the functional improvements ob-
served in OLSB and SCT, it does not appear to be
alone a direct determinant of muscle functional im-
provement, at least within the statistical confidence
of this sample, as indicated by the correlation anal-
ysis performed between weight loss and both tests.
Yet, several mechanisms may be at the basis of the
observed performance improvement in the tests
proposed in the present investigation.
Physical conditioning per se might play a substantial
role by increasing the absolute active muscle mass
of obese patients, although we have actually no di-
rect measurements of this parameter. On the other
hand, the improvement of SCT power per unit body
mass might be attributed to the simple reduction of
body weight. However, since the 4% reduction of
body mass is associated with a 15% increase of spe-
cific power, it seems plausible that a combination
of these factors may have a role in determining the
results we observed after the BMR program.
Velocity of shortening
Fig. 5 - Schematic representation of the force-velocity (solid
line) and its derivative power-velocity (broken line) relationship
of skeletal muscle. The hypothetical position of operational set-
ting point along these functions is also shown for three different
conditions. Due to fat mass overload, muscles of obese patients
(A) perform at lower shortening velocity and higher force to at-
tain a given motor task, possibly operating in a suboptimal
range of power-velocity curve as compared with normal sub-
jects (C). BMR program (B), by decreasing body mass and per-
mitting higher velocity of contraction, may contribute to shift
setting point toward normality.
spective BMR, by decreasing the load, might shift
the operational condition of muscles toward the
optimal setting point (that is the optimum velocity
at which peak power is attained) of normal subjects.
In conclusion, a short-term BMR program (restrict-
ed energy diet associated with low intensity exer-
cise) produces significant improvements both in
motor control and muscle performance, likely to im-
prove the execution of simple daily activities of
obese patients.
The finding of favorable effects of BMR program in
older obese subjects is of relevant interest, since
these results are obtained throughout a simple,
well-tolerated and suitable protocol.
Moreover, a change in muscle operational condi-
tion (i.e. a shift along the force-velocity diagram)
for effect of the BMR program can not be ruled out.
In fact muscle power, that is the rate of performing
mechanical work, can be derived from the force-
velocity relationship of the muscle, as traditionally
described by Hill (18). Normal muscle power (Fig. 5)
is optimally developed under a well-determined
combination of muscle force and velocity of short-
ening (at approximately 1/3 of maximum shortening
velocity). As far as obese subjects are concerned,
it can be hypothesized that in order to perform the
same movement of a non-obese individual, the
muscles of these patients may have to use a high-
er force but a lower velocity (because of the added,
inert fat mass), thus operating in a sub-optimal re-
gion of the power-velocity curve. Under this per-
ACKNOWLEDGEMENTS
The authors wish to thank Ms. Franca Pera, head of
the nursing staff at the 3rd Division of Metabolic
Diseases for her appreciated professional contri-
bution in this study.
REFERENCES
1. Blix G.G., Blix A.G.
The role of exercise in weight loss.
Behav. Med. 1995, 21: 31-39.
2. Hunter G.R., Weinsier R.L., Bamman M.M., Larson D.E.
A role for high intensity exercise on energy balance
and weight control.
Int. J. Obes. Relat. Metab. Disord. 1998, 22: 489-493.
397

Muscle performance in obesity
3. Westerterp K.R.
10. Goldie P.A., Evans O.M., Bach T.M.
Obesity and physical activity.
Steadiness in one-legged stance: development of a
reliable force-platform testing procedure.
Int. J. Obes. Relat. Metab. Disord. 1999, 23: 59-64.
Arch. Phys. Med. Rehabil. 1992, 73: 348-354.
4. Kraemer W.J., Volek J.S., Clark K.L., Gordon S.E.,
Puhl S.M., Koziris L.P., McBride J.M., Triplett-
McBride N.T., Putukian M., Newton R.U., Hakkinen
K., Bush J.A., Sebastianelli W.J.
11. Cohen H., Blatchly C.A., Gombash L.L.
A study of the clinical test of sensory interaction and
balance.
Phys. Ther. 1993, 73: 351-354.
12. Margaria R., Aghemo P., Rovelli E.
Measurement of muscular power (anaerobic) in man.
J. Appl. Physiol. 1966, 21: 1662-1664.
13. Francis K.
Methods of anaerobic power assessment.
Phys. Ther. 1987, 67: 270-275.
14. Balogun J.A., Akindele K.A., Nihinlola J.O.,
Marzouk D.K.
Influence of exercise training on physiological and
performance changes with weight loss in men.
Med. Sci. Sports Exerc. 1999, 31: 1320-1329.
5. Vellas B.J., Rubenstein L.Z., Ousset P.J., Faisant C.,
Kostek V., Nourhashemi F., Allard M., Albarede J.L.
One-leg standing balance and functional status in a
population of 512 community-living elderly persons.
Aging 1997, 9: 95-98.
6. Ekdal C., Jarnlo G.B., Andersson S.I.
Standing balance in healthy subjects. Evaluation of a
quantitative test battery on a force platform.
Scand. J. Rehabil. Med. 1989, 21: 187-195.
Age-related changes in balance performance.
Disabil. Rehabil. 1994, 16: 58-62.
15. Huskey T., Mayhew J.L., Ball T.E., Arnold M.D.
Factors affecting anaerobic power output in the
Margaria-Kalamen test.
7. Suni J.H., Oja P., Laukkanen R.T., Miilunpalo S.I.,
Pasanen M.E., Vuori I.M., Vartiainen T.M., Bös K.
Health-related fitness test battery for adults: aspects
of reliability.
Ergonomics 1989, 32: 959-965.
16. Bohannon R.W., Larkin P.A., Cook A.C., Gear J., Singer J.
Decrease in time balance test scores with aging.
Phys. Ther. 1984, 64: 1067-1070.
Arch. Phys. Med. Rehabil.1996, 77: 399-405.
8. Suni J.H., Oja P., Miilunpalo S.I., Pasanen M.E., Vuori
I.M., Bös K.
17. Kitagawa K., Suzuki M., Miyashita M.
Health-related fitness test battery for middle-aged
adults: association with physical activity patterns.
Int. J. Sports Med. 1999, 20: 183-191.
Anaerobic power of young obese men: comparison
with non-obese men and the role of excess of fat.
Eur. J. Appl. Physiol. 1980, 43: 229-234.
9. Hahn T., Foldspang A., Vestergaard E., Ingemann-
Hansen T.
18. Hill A.V.
The heat of shortening and dynamic constants of
muscle.
One-leg standing balance and sport activity.
Scand. J. Med. Sci. Sports 1999, 9: 15-18.
Proc. Royal Soc. 1938, 126: 136-195.
398