Journal of Electromyography and Kinesiology 20 (2010) 298–304
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Journal of Electromyography and Kinesiology
journal homepage: www.elsevier.com/locate/jelekin
Which type of repetitive muscle contractions induces a greater acute impairment
of position sense?
Sylvie Fortier a, Fabien A. Basset a,*, François Billaut b, David Behm a, Normand Teasdale c
a
School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, NL, Canada A1C 5S7
The Department of Kinesiology and Physical Education, University of Lethbridge, Lethbridge, AB, Canada T1K 3M4
c
Groupe de Recherche en Analyse du Mouvement et Ergonomie, Division de Kinésiologie, Département de Médecine Sociale et Préventive, Faculté de Médecine,
Université Laval, Québec (Qc), Canada G1K 7P4
b
a r t i c l e
i n f o
Article history:
Received 4 August 2008
Received in revised form 1 April 2009
Accepted 1 April 2009
Keywords:
Elbow
Muscle contraction
Position sense
Force
Matching
a b s t r a c t
The objective of this study was to determine which type of repetitive muscle contractions induces a
greater acute impairment of elbow position sense. Eleven male subjects participating in the study underwent (i) an exercise task (ET) consisting of 9 sets of 10 voluntary isometric, concentric, or eccentric contractions randomly performed on three separate sessions, and (ii) a pre- and post-exercise maximal
voluntary isometric contraction (iMVC). Prior to and between sets of ET, a proprioception task (PT) consisting of matching the right arm to the left reference arm was performed at three different target angular
positions (70°, 110° and 150°). Each ET was immediately followed by 3 PT and 1 min rest. The statistical
analysis revealed that post-exercise iMVCs were significantly decreased compared to pre-exercise iMVC
in all conditions with a greater drop following the eccentric task. Despite this greater drop, position sense
was significantly affected by the concentric exercise task. In addition, the spectral EMG signals significantly shifted towards lower frequencies from the initial values, regardless of exercise task. The results
showed that concentric muscle contractions impaired position sense to a greater extent compared to isometric and eccentric contractions.
Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
1. Introduction
A complex combination of many different signal sources, such
as those from the tendon organs, muscle spindles, joint receptors,
and cutaneous receptors, results in very sensitive and unambiguous sensations about our movement and limb position in space
(McCloskey, 1978). In fact, in the absence of visual input, we have
an accurate sense of position implying that we know the position
of our limbs at any time during a movement. Attaining the aimed
final position of either a limb or a particular end-point of the locomotor apparatus is an important motor task of our everyday
behaviour; it can be crucial for success in various professional or
sporting activities. Indeed, it has been suggested that muscle
fatigue could predispose a joint to injury and thus an eventual
decrease in athletic performance (Skinner et al., 1986). Proprioception has also been a topic of interest in sport rehabilitation because
injuries have been found to have a detrimental effect on proprioception through the damage of mechanoreceptors in ligaments.
* Corresponding author. Tel.: +1 709 737 6132; fax: +1 709 737 3979.
E-mail addresses: [email protected] (S. Fortier), [email protected] (F.A. Basset),
[email protected] (F. Billaut), [email protected] (D. Behm), normand.teasdale@kin.
msp.ulaval.ca (N. Teasdale).
Fatigue studies have demonstrated that changes induced by
muscle fatigue may well be influenced by whether the contraction
is static (Bigland-Ritchie et al., 1983) or dynamic (Colliander et al.,
1988). Likewise, it is also well known that strenuous eccentric
exercise induces greater acute damage to muscle fibres than concentric and isometric exercises (Clarkson and Newham, 1995;
Faulkner et al., 1993; Komi and Rusko, 1974). The main difference
between the three muscle contractions is that in an isometric contraction the muscle length remains constant while the contracting
muscle is forcibly lengthened during an eccentric contraction and
shortens during a concentric contraction. Therefore, comparing
the three types of muscle contractions on a matching task becomes
appealing to find out whether the type of contraction could have
an effect on proprioception.
As a matter of fact, it has been recently shown that proprioception is weakened following repetitive muscle contractions. The size
of the matching errors was correlated with the drop in force (Saxton et al., 1995; Walsh et al., 2006). It was then concluded that the
fall in force led to an increase in the effort required to maintain position of the limb against the force of gravity and that this increase
in effort led to the matching errors (Walsh et al., 2004). Moreover,
the direction of the matching errors suggested that we make use of
signals of both peripheral and central origin in determining the position of our limbs in space by reliance, in part, on the amount of
1050-6411/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.jelekin.2009.04.002
S. Fortier et al. / Journal of Electromyography and Kinesiology 20 (2010) 298–304
299
effort required to maintain limb position against gravity (Walsh
et al., 2006).
Muscle fatigue and proprioception has been the focus of many
studies in which the majority of them have sought the effect of
either isometric, concentric, or eccentric exercise on position sense
(Allen and Proske, 2006; Forestier et al., 2002; Walsh et al., 2006;
Winter et al., 2005). Other authors studied the effect of concentric
and eccentric exercises on position sense (Allen et al., 2007; Brockett et al., 1997; Walsh et al., 2004). However, because different protocols were used for the concentric and eccentric experiments, a
direct comparison between them was not possible. Therefore, the
aim of this study was to directly compare the effect of the three
types of muscle contraction within the same study and consequently determine which one would express the greater acute
impairment of elbow position sense. Knowing that eccentric exercise exhibits a large acute drop in force in the exercised muscles,
the purpose of the present study was to test the hypothesis that
eccentric contractions would lead to the greater decrease of force
and would therefore impair proprioception to a greater degree
than concentric and isometric contractions.
2. Methods
2.1. Subjects
This study was conducted on 11 right handed male subjects
(mean age 28.9 ± 10.6 years; mean height 173.8 ± 6.2 cm; mean
weight 80.4 ± 11 kg), without any previous history of upper limb
musculoskeletal problems (see Table 1). They were all aerobically
active at least three times a week and 9 subjects also included
weight training in their fitness program. All subjects gave their
written inform consent in compliance with Memorial University
of Newfoundland Human Investigation Committee regulations,
were all instructed regarding the procedure of the experiment,
and filled in a Physical Activity Readiness Questionnaire (PAR-Q)
(Canadian Society of Exercise Physiology, 2003).
2.2. Apparatus
As displayed in Fig. 1, a supporting frame with two handles fully
adjustable in the horizontal and vertical planes was instrumented
with linear potentiometers (Model K/RV4, Precision Electronic
Components Ltd, Weston, Ont.) and a strain gauge (Omega Engineering Inc. LCCA-250, Laval, Qc). The signals from potentiometers
and strain gauge were amplified and sampled (Biopac Systems Inc.,
Santa Barbara, CA) at a rate of 1 kHz (12-bit A/D). In addition, the
EMG activity was sampled at 1 kHz, with a Blackman 61 dB
band-pass filter between 10 and 500 Hz, amplified (bi-polar differential amplifier, input impedance = 2 kX, common mode rejection
Table 1
Participants’ physical characteristics.
Subjects
Age (years)
Height (cm)
Body mass (kg)
1
2
3
4
5
6
7
8
9
10
11
23
49
43
43
24
25
23
21
22
20
25
172
175
163
163
173
171
185
175
175
180
180
80
99
71
67
67
86
82
76
84
74
98
Mean (±SD)
29 (±10)
174 (±7)
80.4 (±11.0)
Fig. 1. Position sense apparatus consisting of a supporting frame with two handles
fully adjustable in the horizontal and vertical planes instrumented with linear
potentiometers. The axis of rotation of the subject’s elbow was aligned with the axis
of rotation of the handle where the potentiometer lain. Shoulders and waist were
tightly strapped with safety belts.
ratio P 110 dB min (50/60 Hz), gain 2000, noise P 5 lV). A voltage pulse (0–5 V) was also triggered to synchronize kinetics, kinematics and EMG data. Accuracy of angular displacements and force
output were 60.05% (0–5 V) and 60.03% with a full scale ranged
from 0° to 314° and from 0 to 1000 N, respectively. The axis of rotation of the subject’s elbow (lateral epicondyle) was aligned with
the axis of rotation of the handle where the potentiometer was
positioned. Shoulders and waist were tightly strapped with safety
belts to limit trunk motion. The subjects’ arms were kept next to
the body with their hands holding the handles at different angles.
For the exercise tasks (ET), the resistance was attached to the right
handle by a strain gauge. Surface EMG recording electrodes (MediTrace, Tyco Healthcare Group, Mansfield, MA) were placed over
the belly of the biceps brachii and triceps brachii muscles in a bipolar fashion and approximately 3 cm apart. Electrodes were placed
along the estimated direction of the muscle fibres. The ground
electrode was placed on the clavical shaft. Skin preparation for
all electrodes included removal of body hair with a razor and
cleaning dead epithelial cells using an isopropyl alcohol swab.
2.3. Experimental procedure
Subjects first attended a familiarization session in which
anthropometric measurements were obtained to fit the subjects
to the manipulandum. In addition, maximal isometric force output
was determined by producing three maximal voluntary isometric
contractions (iMVC) with the dominant arm flexed at 90° and a
5 min rest interval. According to Schmidtbleicher (1985), maximal
isometric force output is approximately 20% higher and 20% lower
300
S. Fortier et al. / Journal of Electromyography and Kinesiology 20 (2010) 298–304
than maximal concentric and eccentric force outputs, respectively.
Based on this assertion, maximal isometric force output was used
to predict maximal concentric and eccentric force outputs. The
exercise workload was, then, calculated by multiplying maximal
force outputs for each muscle contraction by a factor of 0.75. For
instance, for an individual reaching an iMVC of 200 N, the exercise
workload for the exercise task would be set at 150 N, 120 N, and
180 N for isometric, concentric, and eccentric contractions, respectively. All subjects participated in three different sessions separated by a minimum interval of 7 days. For each session, testing
was conducted at the same time of day to nullify possible differences attributed to diurnal rhythms. The three experimental sessions (randomly presented) were differentiated by the nature of
the exercise tasks (ET) which consisted of isometric contractions,
concentric contractions–concentric phase only, or eccentric contractions–eccentric phase only. All experimental sessions started
by collecting the resting blood lactate level (AccutrendÒ Lactate
Analyzer, Mannheim, Germany) followed by four tasks: (i) preexercise (control) proprioception task at each target angular position (TAP), (ii) exercise task (isometric, concentric or eccentric),
(iii) proprioception task (PT) at each TAP, and (iv) iMVC (see Fig. 2).
The PT consisted of matching angular position of the right indicator arm to that of the left reference arm. Target angular positions
were set at 70°, 110° and 150° of elbow flexion. During the PT the
subjects voluntarily positioned their reference arm at the TAP
using visual feedback provided through the computer screen. They
were asked to maintain, unsupported, this reference position, to
close their eyes, and then, to match with their indicator arm. No
feedback was given about their performance. When the subject
indicated that both arms matched, a voltage pulse was triggered
by the experimenter to identify the matching (Fig. 3). Between
each TAP, subjects returned both arms to 90°. In each experimental
session, subjects performed 9 sets of the exercise task. Each set
consisted of 10 voluntary contractions of 4 s with a 2 s rest between muscle contractions. For the isometric condition, the elbow
was flexed at 90° and the force output was provided on the computer screen. For the concentric condition, subjects were asked to
extend their elbow starting from an elbow angle of 180° and to flex
the arm until the arm was fully flexed, keeping their shoulder stable. At this point, they were required to relax their indicator arm
while the experimenter returned the weight to its initial position.
Fig. 3. Typical set of kinematic data. The solid line represents the angular
displacement of the reference arm and the dash line represents angular displacement of the indicator arm. The starting position of both arms was always set at 90°
of elbow flexion and when both arms were matched, a voltage pulse was triggered
and corresponds to by the dotted vertical line in this figure.
Similar procedures were adopted for the eccentric condition; subjects were asked to do series of lifts from full flexion to full extension. Each set of 10 contractions was separated by approximately
2 min (about 1-min to complete the 3 PT at the same TAP and 1min of complete rest). This procedure was completed three times
for each TAP for a total of 9 sets per session. The TAP were semirandomized and differed from set to set. Once subjects could no
longer maintain the imposed rhythm of the exercise task for two
consecutive muscle contractions, the ongoing set was stopped. Finally, immediately after the last set, a post-exercise iMVC and
blood lactate concentration were collected for each experimental
session.
2.4. Data analysis
All kinetic and kinematic parameters were analysed using MATLAB software (MathWorks Inc., Natick, MA). From these parame-
3X
iMVC
3x iMVC
Pre-exercise PT
ET
3x
PT70
ET
3x
PT110
ET
3x
PT150
1 min
3x
PT150
Set 3
1 min
A) Familiarization
session
3x
PT110
1 min
5 min
5 min
3x
PT70
Set 2
Set 1
B) Experimental session
Blood lactate
sample
Blood lactate
sample
Fig. 2. (A) Subjects first attended a familiarization session where they produced 3 iMVCs. (B) All subjects then participated to 3 different experimental sessions (randomly
presented) differentiated by the nature of the exercise tasks (isometric, concentric, or eccentric contractions). Each session included three tasks: an exercise task (ET), a
proprioception task (PT), and an iMVC. All sessions started by collecting the resting blood lactate level followed by 3 pre-exercise PT at each target angular position (70°, 110°,
and 150°). Thereafter, subjects performed the first of nine sets of the exercise task. Each set consisted of 10 voluntary contractions and was immediately followed by 3 PT at
the same angular position. Each ET was separated by approximately 2 min (about 1-min to complete the 3 PT and 1-min of complete rest). This procedure was completed nine
times for a total of 3 sets of PT at each angular position. Finally, immediately after the ninth set, post-exercise iMVC and blood lactate level were collected.
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S. Fortier et al. / Journal of Electromyography and Kinesiology 20 (2010) 298–304
ters, the following variables were determined: (a) maximal voluntary isometric contraction (iMVC): the force curve was filtered
(second-order low-pass Butterworth filter with a 7 Hz cutoff frequency) and the iMVC was determined by the maximal force output of the curve; (b) position matching errors: the angular position
signal was filtered with a fourth-order Butterworth filter (10 Hz
lowpass cutoff frequency with dual pass to remove phase shift)
and position matching error was calculated as:
where 90° = horizontal forearm and 180° = vertical forearm. For
each trial, matching accuracy was determined using the constant
error (CE). Constant error is the mathematical operation difference
between the position of the arms. By convention, a negative value
refers to a more extended indicator arm whereas a positive value
refers to a more flexed indicator arm; (c) total matching time: defined as the time between the first movement of the right arm from
the starting position and the onset of the voltage pulse; (d) muscle
contraction time: defined as the time between the start and the end
of a muscle contraction performed during the exercise task; and (e)
integrated EMG (iEMG): the EMG signals from the biceps brachii
were full-wave rectified, integrated between onsets and offsets of
bursts, and normalized by time. The onset and offset of initial and
terminal bursts of first, fifth and last sets were determined from
EMG signal using a threshold value of 10% of peak value. The frequency spectrum of each epoch of EMG data was analysed by a fast
Fourier transformation algorithm. The frequency spectrum was restricted to frequencies in the range 5–500 Hz and was defined by
512 points in amplitude and phase. The median frequency (MF)
was then computed.
2.5. Statistical analysis
All variables are presented as mean (±SE) and 95% confidence
intervals unless otherwise mentioned. In all instances, Greenhouse-Geisser corrections were applied if violation of sphericity
was detected (Mauchly procedures). First, a one-way analysis of
variance [4 experimental conditions; 1 pre-exercise (control) and
3 exercise tasks (isometric, concentric, and eccentric)] with repeated measures was performed on the iMVC parameters to look
at the effect of types of contraction on post iMVC performance. Second, a two-way analysis of variance [2 data acquisition time (pre–
post) 3 exercise tasks (isometric, concentric, and eccentric)] with
repeated measures was computed on blood lactate. Third, a threeway analysis of variance [2 bursts (initial terminal bursts) 3
sets (first, fifth and last) 3 exercise tasks] was performed on
iEMG and MF values. Fourth, a one-way analysis of variance with
repeated measure (3 exercise tasks) was performed on muscle contraction time to determine any variation in EMG burst duration
among exercise tasks. Finally, a two-way analysis of variance [4
experimental conditions 3 PT (70°, 110°, and 150°)] with repeated measures was computed on CE. A post-hoc HDS Tukey test
was used for statistical comparisons of means. The level of significance was set at a p-value of 0.05. For all statistical tests, SPSS
14.0 for Windows was used (SPSS inc., Chicago, IL).
Table 2
Mean values (±SE) in Newtons for iMVC.
*
Isometric
Concentric
Eccentric
Mean
Post-exercise
Mean value
±SE
[95% CI]
Mean value
±SE
[95% CI]
1.8
1.8
1.8
1.8
±0.2
±0.1
±0.3
±0.1
[1.4–2.2]
[1.5–2.2]
[1.2–2.5]
[1.6–2.1]
3.6
3.7
3.6
3.6*
±0.3
±0.2
±0.5
±0.2
[2.8–4.2]
[3.2–4.3]
[2.5–4.8]
[3.1–4.1]
Significantly different from pre-exercise at p 6 0.05.
3. Results
The pre-and post-exercise mean value (±SE) for iMVCs, and
blood lactate concentration are presented in Tables 2 and 3, respectively. The statistical analysis revealed a significant effect of exercise tasks on iMVCs (p < 0.05); Post hoc analysis showed a
significant decrease in post-exercise iMVCs compared to pre-exercise with the greater drop in force seen with the eccentric contractions. Indeed, subjects achieved 92.6%, 84.0%, and 75.4% of their
initial iMVC values during post-exercise iMVC for isometric, concentric, and eccentric muscle contractions, respectively. In parallel
with force output decrement, there was a main significant effect of
exercise tasks on blood lactate concentrations (p < 0.05). Yet it is
worth noticing that blood lactate concentrations significantly increased regardless of exercise task.
The mean values (±SE) of iEMG and MF are presented in Table 4.
The three-way analysis of variance did not reveal a significant effect of the sets. The data were, then, pooled in order to further perform a two-way analysis of variance [2 data acquisition time
(initial terminal bursts) 3 exercise tasks] on same variables.
No significant difference in iEMG between initial and terminal values in all exercise tasks was observed (p > 0.05). On the other hand,
there was a main significant effect of data acquisition time on MF
(p < 0.05). Indeed, the spectral EMG signal significantly shifted towards lower frequencies from the initial values, regardless of exercise task.
Fig. 4 displays CE for all experimental conditions (pre-, isometric, concentric, and eccentric). Recall that negative CE values correspond to a more extended indicator arm position. The statistical
analysis revealed a main significant effect of experimental conditions on CE. In fact, CE decreased significantly after the concentric
exercise compared to pre-exercise (p < 0.05). The statistical analysis also revealed that CE tends to be larger at 110° than at 70° and
150° of elbow flexion (p < 0.09) as shown in Table 5.
The muscle contraction time was 3.65 s (±0.03) [95% CI = 3.59–
3.70] for isometric, 3.71 s (±0.03) [95% CI = 3.66–3.78] for concentric, and 4.00 s (±0.04) [95% CI = 3.93–4.07] for eccentric contractions. The analysis reveals a significant effect of exercise tasks on
muscle contraction. Further Post hoc analysis showed that the muscle contraction time was significantly higher for the eccentric contractions compared to the isometric and concentric contractions.
Despite the statistical significance, the 350 ms time difference in
muscle contraction between the eccentric and isometric contractions is not believed to have resulted in a greater eccentric muscle
fatigue, as confirmed by the blood lactate concentrations. Hence,
this parameter will not be further discussed.
4. Discussion
Mean value (N)
±SE
[95% CI]
244
226*
205*
184*
±10
±14
±14
±15
[221–268]
[195–258]
[172–238]
[150–218]
Significantly different from pre-exercise at p 6 0.05.
Pre-exercise
*
angle ðreference armÞ angle ðindicator armÞ;
Pre-exercise
Post-exercise isometric
Post-exercise concentric
Post-exercise eccentric
Table 3
Mean values (±SE) in mmol L1 for blood lactate concentration.
The objective of this study was to determine which type of muscle contractions would impair to the greater degree position sense.
The hypothesis was that eccentric exercise would lead to a larger
decrease in force and consequently to a greater impairment of position sense. Our results partly confirmed our hypothesis by reveal-
302
S. Fortier et al. / Journal of Electromyography and Kinesiology 20 (2010) 298–304
Table 4
Mean values (±SE) for iEMG (mV s1) and MF (Hz).
Initial burst
Terminal burst
Mean value
±SE
[95% CI]
Mean value
±SE
[95% CI]
iEMG
Isometric
Concentric
Eccentric
0.193
0.243
0.178
±0.027
±0.056
±0.025
[0.131–0.256]
[0.113–0.373]
[0.120–0.236]
0.177
0.178
0.169
±0.019
±0.037
±0.017
[0.133–0.220]
[0.092–0.263]
[0.130–0.208]
Mean
0.205
±0.027
[0.143–0.267]
0.174
±0.018
[0.133-0.216]
MF
Isometric
Concentric
Eccentric
129.8
128.9
125.0
±3.5
±2.9
±3.8
[121.7–137.8]
[122.2–135.6]
[116.3–133.8]
115.0
105.9
119.4
±4.7
±6.0
±3.5
[104.2–125.9]
[92.1–119.7]
[111.3–127.5]
Mean
127.9
±2.2
[122.8–132.9]
113.4*
±3.1
[106.4–120.5]
*
Significantly different from initial burst at p 6 0.05.
ing that eccentric exercise induced a greater force loss compared to
isometric and concentric exercises. However, data of the present
study do not confirm the second half of the research hypothesis.
In fact, proprioception was significantly affected with the concentric exercise indicated by matching errors resulting in a more extended indicator arm position.
The results of the present study showed that post-exercise
iMVCs were significantly reduced in all exercise tasks indicating
that fatigue occurred with all types of muscle contraction (Table
2). There was an 8%, 16%, and 25% decline in iMVC after the isometric, concentric, and eccentric exercise task, respectively. Indeed,
possible causes of the muscle performance decline may be different according to the type of contraction. It is known that when a
muscle lengthens (eccentric) during activation the energy requirement and mechanical response differ from those of shortening
Fig. 4. Subjects (n = 11) mean constant error (CE), that is the sign difference
between the reference arm and the indicator arm, for the pre-exercise matching
condition, the isometric condition, the concentric condition, and the eccentric
condition (*p < 0.05; Error bars + SE).
(concentric) contractions (Clarkson and Newham, 1995; Enoka,
1996). Eccentric contractions used in the present study could be
associated with a lower energy cost, but with a higher tension output that may damage the muscle–tendon system (Clarkson and
Newham, 1995; Friden and Lieber, 1992; Lieber et al., 1996) leading to a greater acute force loss with eccentric compared to isometric and concentric contractions. Along with the force output
decrement, the blood lactate increased from pre- to post-exercise
regardless of exercise task suggesting that the fatigue protocol
used in this study induced the same metabolic stress in all exercise
tasks. In parallel, spectral EMG signal values significantly compressed towards lower frequencies from the initial burst of the first
set to the terminal burst of the last set, corroborating blood lactate
outcomes. Spectral analysis also provides reliable information
about metabolic activity and membrane potential changes (Billaut
et al., 2006; Taylor et al., 1997). Our results agree with previous
studies conducted during isometric and dynamic contractions (Billaut et al., 2006; Hagg, 1992). Hence, in the present study, the significant iMVC and CE differences observed between the types of
contraction should not be related to difference in metabolic stress
induced by the exercise tasks.
It is generally accepted that fatigue negatively affects joint proprioception (Allen and Proske, 2006; Walsh et al., 2006; Winter
et al., 2005). Indeed, immediately after the concentric exercise task,
subjects of the present study made significant position matching
errors (2.6 degrees) by adopting a more extended position with
the indicator arm (Fig. 4). According to Brockett et al. (1997) and
Gandevia et al. (2002), sense of limb position is provided by signals
from skin, joint and muscle receptors. The level of resting activity
from muscle spindles would, therefore, signal the length of the
muscle and, accordingly, the position of elbow. The present results
could suggest that the signal from muscle spindles had decreased as
a result of the concentric exercise task. To match the level of proprioceptive signal (i.e., spindle discharge rates), the exercised muscle
would have been stretched more than the control muscle by adopting a more extended arm position. Hence, it could be argued that
Table 5
Mean values (±SE) of constant error (CE) in degrees for the three angles in all experimental conditions.
70°
Pre-exercise
Isometric
Concentric
Eccentric
Total mean
*
Trend at p 6 0.09.
110°
Mean value
±SE
[95% CI]
0.02
0.58
0.78
0.35
0.03
±1.1
±1.5
±1.1
±1.2
±1.1
[2.4
[2.9
[3.3
[2.4
[2.3
to
to
to
to
to
2.4]
4.0]
1.7]
3.1]
2.4]
150°
Mean value
±SE
[95% CI]
1.63
3.32
4.92
3.62
3.37*
±0.9
±1.1
±1.4
±1.7
±1.1
[3.6
[5.8
[8.1
[7.5
[5.8
to
to
to
to
to
0.3]
0.8]
1.7]
0.3]
0.9]
Mean value
±SE
[95% CI]
0.04
0.23
2.25
2.18
1.04
±1.2
±1.1
±1.2
±1.1
±0.8
[2.7
[2.2
[5.0
[4.8
[2.8
to
to
to
to
to
2.8]
2.6]
0.5]
0.4]
0.8]
S. Fortier et al. / Journal of Electromyography and Kinesiology 20 (2010) 298–304
the pattern of positional errors observed in this study is the result of
exercise-related changes in the response of muscle spindles. Others
studies have also indicated that the activity of muscle spindles declines during sustained voluntary contractions (Macefield et al.,
1991; Vallbo, 1970). Bongiovanni et al. (1990) presented evidence
that the fusimotor mediated spindle discharge would progressively
decline during iMVC, and this decline was attributed to a progressive withdrawal of spindle-mediated fusimotor support to a-motoneurons. It has also been stated that the spindle afferents’ role
would be different with concentric contractions because fusimotor
drive may be insufficient to overcome muscle shortening. Consequently, spindle afferents in the contracting muscle may fall silent
(Gandevia, 1998). This reduced stretch sensibility of spindles after
voluntary concentric contractions could be one explanation for
the increased threshold for muscle spindle discharge. This would
be matched by the indicator arm adopting a more extended position, where the muscle and its spindles were subjected to a greater
degree of stretch, and thus leading to a decline in position sense
after concentric contractions, as seen by the main finding in the
present study. On the other hand, disturbance in position sense
was not significant in the eccentric experimental condition probably because, as mentioned by Gregory et al. (2004), intrafusal fibres
of muscle spindles are not prone to damage of the kind seen in
extrafusal fibres after a series of eccentric contractions. The difference in our exercise protocols compared to other studies could be
one of the explanations for the dissimilarity in results. In the present study, high-intensity exercise protocols were used. These protocols led to a lower drop in iMVC than seen in the other studies using
lower-intensity exercise protocols with higher number of muscle
contractions. Different mechanisms may be involved when using
a high-intensity exercise protocol which could be associated with
different outcomes on position sense.
Another explanation of the present results could be that our
subjects adopted a more extended forearm position because the
latter could have been subject to a smaller moment of the force
of gravity. In fact, the most recent hypothesis in the literature is
that accurate placement of forearms would be achieved by a combination of muscle spindle signals and effort-related signals. For instance, results from Walsh et al. (2004), Winter et al. (2005), and
Allen and Proske (2006) have been interpreted as evidence in favour of an effort-related signal contributing to position sense during limb placement. They proposed that the effort required
maintaining position of the arm against the force of gravity would
provide us with information about its location in space. If subjects
match efforts to align their arms they would place the fatigued arm
more nearly vertically where less force is required to support it and
where the same effort would be required to maintain its position.
Further to their procedure, they concluded that subjects adopted of
a more vertical arm position for two reasons. First, the moment of
the force of gravity on the arm was less. Second, a more vertical position was closer to the elbow flexors’ optimum length for active
tension (Walsh et al., 2004). Similarly to the aforementioned studies, after the concentric exercise our subjects placed their fatigued
arm closer to the vertical, that is, a more flexed indicator arm position with the angle 70° (CE = 0.03° ± 1.04) and a more extended
indicator arm position with the angles 110° (CE = 3.37° ± 1.09)
and 150° (CE = 1.04° ± 0.79). These patterns could be explained
by the smaller moment of the force of gravity acting on the fatigued arm. In addition, although not significant, it is worth noticing
that CE tends to be larger at 110° than at 70° and 150° of elbow
flexion (p < 0.09) which further supports the force of gravity effect
(see Table 5). Therefore, results of the present study agree with
those of Winter et al. (2005), that is, muscle spindles as well as
sense of effort are responsible for the sense of position.
Potential limitations to the study warrant considerations. First,
the calculation of MF based on the assumption of non-stationary
303
signal may have had an impact on our EMG interpretation. However, the spectral EMG signal was analysed along with other
parameters (i.e., post-iMVC and blood lactate) to confirm the
occurrence of muscle fatigue during exercise tasks. Second, the
use of iMVC to predict maximal concentric and eccentric muscle
contractions may have led to over/underestimation of the true
muscle contraction performances. Notwithstanding slight possible
inaccuracies in force determinations, post-exercise tasks iMVCs
were altered indicating that fatigue occurred with all types of muscle contraction.
5. Conclusion
The hypothesis of this experiment was that eccentric exercise
would result to a greater decrement in force leading to a larger
impairment of position sense. The present results showed that a
high-intensity concentric exercise protocol impaired position
sense to a greater extent compared to the other types of muscle
contractions despite a greater drop in iMVC after eccentric exercise
task, which partly refute our assumptions. It is concluded that
muscle spindle afferents and the effort required to support the
limb against the force of gravity can provide information about
forearm position. The nature of repetitive muscle contractions
inducing fatigue should be taken into consideration to minimize
a loss in movement accuracy in contexts such as research, sport
performance and clinical rehabilitation. However, further research
is needed to understand better muscle spindle and effort-related
signal mechanisms related to muscle fatigue.
Acknowledgments
We thank all of the volunteers who participated in the project.
We also thank Dr. Nicolas Forestier for his comments on the final
version of the manuscript. The technical assistance of Lise Petrie
is gracefully acknowledged and the School of Human Kinetics
and Recreation for the use of laboratory facilities.
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Sylvie Fortier is a M.Sc. degree holder and currently
working as a Research Assistant in School of Human
Kinetics and Recreation at Memorial University of
Newfoundland, Canada. Her main research interests
are Sports Performance and Motor Learning.
Fabien A. Basset is a Ph.D. Degree holder and currently employed as an Assistant Professor in School
of Human Kinetics and Recreation at Memorial University of Newfoundland, Canada. His main research
interests are on Exercise Physiology and Sports
Performance.
François Billaut is a Ph.D. Degree holder and currently employed as an Assistant Professor in the
Department of Kinesiology and Physical Education at
University of Lethbridge, Canada. His main research
interests are Muscle Fatigue, Sport Performance, and
Sex Differences.
David Behm is a Ph.D. Degree holder and currently
employed as a Professor in School of Human Kinetics
and Recreation at Memorial University of
Newfoundland, Canada. His main research interests
are Exercise Physiology, Muscle Fatigue, and Sports
Performance.
Normand Teasdale is a Ph.D. Degree holder and
currently employed as a Professor in Groupe de
Recherche en Analyse du Mouvement et Ergonomie
at Université Laval, Canada. His research focus is on
Motor Control.