force endurance and change of the muscle type
following anterior cruciate ligament reconstruction
Running title: Stamina increase and fiber plasticity
Gian Nicola (1-5) , Combi Franco (2),
Forloni Fabio (3), Petrone Nilton
- Ph.D, Dipartimento
"Entraînement et Performance "
Facoltà di Scienze dello Sport, Università
di Lione (F).
- MD., Direttore
Dipartimento Medicina Fisica e Riabilitativa
Azienda Ospedaliera S.Gerardo, Monza (I).
- MD., Centro
Universitario Studi e Ricerche In Medicina
e Traumatologia dello Sport, Università
Estacio de Sa, Rio de Janeiro (BR).
- Scuola Universitaria
Interfacoltà in Scienze Motorie, Università
di Torino (I).
words: ACL, , stamina, fiber plasticity, rehabilitation.
this study we considered 13 subjects whose age,
weight and height were respectively 26 +2
years (mean + standard deviation), 72.3
+7.1 kg, 178.6 +4.7 cm; all the
subjects regularly performed a sport and had reported
an isolated or associated injury of the ACL, that
had been surgically treated by means of an arthroscopic
reconstruction. Each subject was asked to effect
a femoral quadriceps isometric contraction of
the two inferior limbs with intensity equal to
the 50% of the maximal isometric force, up to
the complete exhaustion of the muscle. The times
of maintenance of the contraction on the injured
limb and on the healthy limb were respectively
of 60.00 +14.14 seconds (range 82.55
41.99 seconds) and 46.63 +11.85 seconds
(range 74.0 43.0 seconds). The difference,
equal to the 21.84 +8.42%, resulted statistically
significant (p0.002). The increase in the
capacity of the muscular resistance of the pathological
limb is probably to be charged to a selective
atrophy of the fibres type II and to a conversion
of the typology of the fibres themselves from
type II o type I. Moreover the values deduced
from this study have been proposed as valuation
parameter in the protocols for physiotherapy work
after a surgical reconstruction of the ACL
of the peculiar characteristics of the injuries
of the ACL is constituted by the loss of maximal
force of the extensors of the leg on the thigh,
in a period immediately after the operation (post-operation)
and after a follow-up period (1, 2, 3, 4), whereas
the loss of force of the flexors seems more limited
(5). The loss of the capacity of the maximal force
after an operation of the ACL is found by means
of the mode of isometric contraction (2, 3) and
by means of an isokinetic contraction (6, 7,8).
This deficit of force in the injured limb is found
also in the case in which the ACL has not been
surgically treated (6). However, it is necessary
to consider that the deficit in force in the injured
limb many times is charged, at least in part,
to the algic sensation, reported by the patient
during a maximal muscular contraction that puts
the neo-ligament in tension. This eventuality
is particularly recurrent above all in the case
in which the dynamometric test is effected in
open kinetic chain (OKC), mode during which the
anterior translation of the tibia verifies, which
may cause an important tensioning of the neo-ligament
itself (9). Beside a deficit in contractile force,
after the reconstruction of the ACL the injured
limb normally shows a more or less marked atrophy
of the femoral quadriceps (5, 10) and above all
of the vastus medialis obliquus (11). Up
to certain levels the maximal force shows a strong
correlation with the cross sectional area of the
muscle but in the case of ACL reconstruction the
loss of muscular trophism shows itself scarcely
correlated to the contractile capacity of the
femoral quadriceps (6, 12). It is then possible
to hypotheses that at least a part of the contractile
deficit of the injured limb is due to a change
of the metabolic and/or mechanical typology of
the muscular fibre (8) and to an altered activation
pattern of the motor units caused by the damage
of the sensorial receptors of the injured ACL
(13, 14). Besides the decrease of the maximal
force, an other parameter always relative to the
muscular contractility, that may result altered
after a reconstruction operation of the ACL, is
the muscular stamina: that is the capacity of
a determined muscular group to resist to the fatigue
induced by a prolonged contraction (15). The few
studies found within this field report that the
muscular resistance, understood as capacity to
resist to a sub-maximum muscular contraction induced
by means of an electro-stimulation to the femoral
quadriceps, is major in the injured limb after
the reconstruction of the ACL than in the healthy
counter part (8). Moreover, other studies prove
that after a reconstruction of the ACL and the
consequent hypokinesia period that follows the
first, there is a conversion of the muscular fibres
from rapid (FT) to slow (ST) in the femoral quadriceps
(16, 17). As a high percentage of ST leads to
an increase of the stamina capacities (18, 19,
20), we could hypothesize that an increase of
the capacities of the musculature tested to resist
to a prolonged sub-maximal contraction may constitute
an indirect index of the grade of conversion of
the typology of the muscular fibres. The aim of
this study is exactly the verification and quantification
of the increase of the capacities of the stamina
of the femoral quadriceps of the traumatised limb,
in patients submitted to surgical reconstruction
of the ACL, by means of a voluntary sub-maximal
contraction prolonged up to the complete exhaustion
of the muscle. The individualisation of this medium
value may in fact constitute, in our opinion,
an important reference index in the rehabilitative
this study 13 subjects were taken into account
whose age, weight and height were respectively
26 +2 years (mean + standard deviation),
72.3 +7.1 kg and 178.6 +4.7 cm;
they all took part in some kind of sports activity
(table 1) and had suffered an isolated or associated
injury of the ACL, which had been surgically reconstructed
by means of arthroscopy (table 2).
the test period all subjects continued their normal
physiotherapy rehabilitation and none showed symptoms
of muscular or neuromuscular problems, apart from
that described above. When the test was carried
out, the subjects were in their 95° +7°
post- operative day and had completely recuperated
the articular mobility of the injured limb. Moreover,
all the subjects had been informed of the aim
of the study and of the possible risks involved.
previous warm up, each subject was asked to perform
an isometric contraction, with an articular angle
standardised at 90°, with the extensors of
the leg, whose intensity is equal to 50%
of the isometric maximal force preventively measured
at the same articular angle. The choice of MIF
50% was dictated by the fact that the maintenance
of this percentage of isometric force induced
to a total muscular fatiguing in times relatively
short of the order of approximately
50 (21, 22, 23). The production
of force was measured by means of a load cell
with a strain gauge (Mod. Ergometer, sample rate
100 Hz, non-linearity histeresis and repeatability
0.002 of RO, temperature compensated 0° to
50°, charge scale 0-300 kg). Each contraction
was maintained as long as the value of force expressed
did not result minor to the prefixed target for
a period superior to 3 second. During the execution
of the contraction the subject was supplied with
a biofeedback of vision that enabled him to remain
within the prefixed target of force production
(MIF 50% +5%). The data were read directly
on a dedicated software that automatically calculated
the time of maintenance of the contraction within
the demanded target. The same type of measurement
was effected in a randomised way both for the
pathological limb and the healthy counter part.
statistical indexes such as average, standard
deviation and variance were calculated for each
single variable and situation.
difference between the mean values of maximal
isometric force (MIF 100%) and of maintenance
of the MIF 50% (with a range of tolerance of +5%)
of the injured limb and of the healthy counter
part were tested by means of a non parametric
level of statistical significance was fixed at
values of MIF 100% of the healthy limb were equal
to 660.61 +162.78 N.
values of MIF 100% of the pathological limb were
equal to 433.66 +132.62 N.
difference, equal to 33.73 +14.61% was
statistically significant (p0.001).
values of maintenance of the MIF 50% in the healthy
limb were equal to 46.63 +11.85 seconds
(range 74.0-43.0 seconds).
values of maintenance of the MIF 50% in the pathological
limb were equal to 60.00 +14.14 seconds
(range 82.55-41.99 seconds).
difference, equal to 21.84 +8.42%, was
statistically significant (p0.002).
1: Subjects distribution in function of the practiced
Type of suffered
ACL isolated breakage
ACL breakage associated
to MCL second degree injury
ACL breakage associated
to a medial and lateral meniscus injury
ACL breakage associated
to a lateral meniscus injury
2: Subjects distribution in function to the suffered
muscular stamina found in this study, major in
the injured limb than in the healthy counter part
(21.84± 8.42%, p<0.002), can be compared,
although not perfectly superposable to the one
reported by Snyders-Mackler and coll. (8), who
report that the extensive musculature of the limb
that has undergone a surgical reconstruction of
the ACL is 11% (p0.001) more resistant than
the one of the healthy limb. The difference that
may be found between these data is undoubtedly
to be imputed to the different study protocols,
given that in the study mentioned above that required
the maintenance of the 20% of the maximal isometric
force by means of an electro-induced contraction.
There is one datum in particular that must be
underlined: independently on the type of contraction
considered, voluntary or electro-induced, the
extensor musculature of the pathological limb
in every case shows a major stamina capacity than
the healthy counter part. This difference in the
characteristics of muscular stamina may support
the hypothesis, already suggested by other Authors,
of a selective atrophy of the fibres type II,
after the artroscopic reconstruction of ACL (16,
17, 24) and the conversion of the fibres from
type II to type I, that is a consequence to the
chronic stimulation at low frequency (25, 26,
27, 28), typical during the rehabilitative period
after the operation. The conversion of the typologies
of the muscular fibres is physiologically justified
by the fact that also in adults the same fibres
show that they are able to change their molecular
composition, altering in such way their gene expression
(27). Above all the low frequencies of discharge,
typical of the training of muscular stamina and
therefore also of the rehabilitative programs,
can induce in animals and in men, if repeated
chronically and for periods relatively prolonged,
a conversion of the light chains (MLC) and of
the heavy chains (MHC) of the myosin, from fast
to the their slow iso-form (27, 29). The alteration
of the nervous activation pattern determines in
fact a change of the synthesis of the different
contractile proteins (25). In this type of mechanism
the main role is mainly played by the nervous
activation pattern, but it is also necessary to
remind the important role played by other two
factors, constituted by the neuromuscular activity
and by the mechanical load (28). The possible
typological conversion of fibres from type II
to type I, consequent to a post-operation event
as the ACL reconstruction, is more probable to
be imputed to the stimulus at low frequency that
the muscle receives during the rehabilitative
period, rather to the immobilisation period after
the operation. It is in fact known that the musculature
of the femoral quadriceps in paraplegic patients
shows a predominance of fibres of type II, as
a consequence of the loss of the muscular functions
this change of the fibers typology could explain
the fact that the quadriceps femoris loss of force,
in the case of ACL reconstruction, is slightly
correlated to the cross sectional area of the
quadriceps femoris itself (6, 12).
considering the major resistance to fatigue of
the fibres of type I compared to the fibres of
type II (15, 18, 30), the increase of the characteristics
of the stamina of the extensor musculature of
the injured limb, as found in this study, may
be the indirect witness of a selective atrophy
of the fibres of type II and of a conversion of
the typology of the fibres from type II to type
I. An excessive atrophy of the fibres type II
united to a massive conversion of the fibres from
type II to type I, may prove to be inauspicious
especially in sport activities as sprint and jumping
but also in team sports as football, where sudden
and frequent cutting actions require a rapid and
massive recruitment of fibres of type II (20,
32). The value of percentage increase in muscular
stamina found in this study (that can be easily
recorded by means of an isometric test) may be
an important reference parameter in the field
of physiotherapy in the rehabilitative protocols
of the ACL. As in fact the biological plasticity
typical of the muscle permits the reversibility
of the structural changes induced in the latter
(28, 33), the surmounting of such parameter can
suggest the introduction of specific exercises
in the work plan of the athletes ,especially of
some particular disciplines, in order to induce
a preferential recruitment of fibres of type II
and balance again the typological situation of
the muscles of the two limbs.
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