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Comparison of Recovery Strategies on Muscle Performance After Fatiguing Exercise

Authors:
  • University School of Physical Education , Kraków, Poland

Abstract and Figures

The objective of this study was to assess the influence of different relaxation modes: stretching (ST), active recovery (AR), and passive recovery (PR) on muscle relaxation after dynamic exercise of the quadriceps femoris. Ten healthy male volunteers between 24 and 38 yrs of age participated in this study. After the warm-up, subjects performed three sets of dynamic leg extension and flexion (at an angle of 20-110 degrees) at 50% of previously determined maximal voluntary contraction (MVC), with 30 secs. of rest between sets. Immediately after completing the leg exercise, one of the relaxation methods was applied, in a randomized order (AR, PR, ST). Then, subjects performed isometric knee extension at 50% of MVC to the point of fatigue, and surface electromyogram (EMG) of the vastus lateralis muscle was measured. After AR, the mean MVC was significantly (P < 0.05) higher than after PR and ST. Moreover, there was no difference in MVC between AR and baseline (P > 0.05). Total time of the effort during EMG measurement was significantly lower for all three recovery modes than at baseline. During the effort after both PR and ST, there was no significant increase in motor unit activation, but a significant increase was noted after AR (P < 0.05). There was no difference in frequency between any of the recovery modes and baseline (P > 0.05). The results of this study suggest that the most appropriate and effective recovery mode after dynamic muscle fatigue involves light, active exercises, such as cycling with minimal resistance.
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Authors:
Anna Mika, PhD
Piotr Mika, PhD
Bo Fernhall, PhD
Viswanath B. Unnithan, PhD
Affiliations:
From the Department of
Rehabilitation, Academy of Physical
Education, Krako´w, Poland (AM, PM);
College of Applied Health Sciences,
University of Illinois at Urbana-
Champaign, Champaign, Illinois (BF);
and Sport Department, Liverpool
Hope University, Liverpool, United
Kingdom (VBU).
Correspondence:
All correspondence and requests for
reprints should be address to Anna
Mika, Katedra Rehabilitacji
Klinicznej, Wydzial Rehabilitacji
Ruchowej, Akademia Wychowania
Fizycznego, Al. Jana Pawla II 78,
31-571 Krako´w, Poland.
0894-9115/07/8606-0474/0
American Journal of Physical
Medicine & Rehabilitation
Copyright © 2007 by Lippincott
Williams & Wilkins
DOI: 10.1097/PHM.0b013e31805b7c79
Comparison of Recovery Strategies
on Muscle Performance After
Fatiguing Exercise
ABSTRACT
Mika A, Mika P, Fernhall B, Unnithan VB: Comparison of recovery strategies on
muscle performance after fatiguing exercise. Am J Phys Med Rehabil 2007;86:
474 481.
Objective: The objective of this study was to assess the influence of
different relaxation modes: stretching (ST), active recovery (AR), and
passive recovery (PR) on muscle relaxation after dynamic exercise of the
quadriceps femoris.
Design: Ten healthy male volunteers between 24 and 38 yrs of age
participated in this study. After the warm-up, subjects performed three sets
of dynamic leg extension and flexion (at an angle of 20–110 degrees) at
50% of previously determined maximal voluntary contraction (MVC), with
30 secs of rest between sets. Immediately after completing the leg
exercise, one of the relaxation methods was applied, in a randomized
order (AR, PR, ST). Then, subjects performed isometric knee extension at
50% of MVC to the point of fatigue, and surface electromyogram (EMG)
of the vastus lateralis muscle was measured.
Results: After AR, the mean MVC was significantly (
P
0.05) higher
than after PR and ST. Moreover, there was no difference in MVC between
AR and baseline (
P
0.05). Total time of the effort during EMG
measurement was significantly lower for all three recovery modes than at
baseline. During the effort after both PR and ST, there was no significant
increase in motor unit activation, but a significant increase was noted after
AR (
P
0.05). There was no difference in frequency between any of the
recovery modes and baseline (
P
0.05).
Conclusion: The results of this study suggest that the most appropriate
and effective recovery mode after dynamic muscle fatigue involves light,
active exercises, such as cycling with minimal resistance.
Key Words: Active, Passive, Stretching, Relaxation, EMG, Strength
474 Am. J. Phys. Med. Rehabil. Vol. 86, No. 6
RESEARCH ARTICLE
Strength
Muscle fatigue can be defined as any exercise-
induced reduction in the ability to exert muscle
force or power, regardless of whether the task can
be sustained or whether it has peripheral or central
causes.
1
Exercise-induced alterations in muscle ho-
meostasis, including hydrogen ion accumulation,
potassium loss, depletion of high-energy phos-
phates (ATP and creatine phosphate) and glycogen,
loss of calcium homeostasis, or local ischemia may
be some of the causative factors associated with
disruption of the muscle excitation– contraction
cycle during intense exercise and in postexercise
muscle fatigue.
2–5
Muscle recovery after physical activity is very
important, especially in the field of sport and re-
habilitation. In many events such as weight lifting
or the jumping and throwing events in track and
field, interbout rest periods are short, and fast
muscle recovery is an important factor leading to
better performance. In many of these activities,
repeated muscle performance is required after fa-
tiguing exercise with only a short rest period. A
similar situation occurs in rehabilitation, particu-
larly for rheumatologic and orthopedic problems,
where increased muscle tension causes faster mus-
cle fatigue, defined as a loss of ability to maintain
the expected force or power,
1
leading to joint in-
stability, which limits the rehabilitative process.
Moreover, better muscle recovery leads to reduced
risk of injury during sport activity and to lower
increases in muscle tension in pathologic joints.
The benefits of appropriate muscle recovery are
important in both sport and rehabilitation.
6,7
Therefore, there is a need to develop a suitable
method to enhance the rate of recovery after fa-
tiguing exercise. It has been suggested that various
forms of muscle relaxation may improve muscle
blood flow and enhance recovery by augmenting
removal of exercise metabolites—for instance,
ADP, free radicals, carbon dioxide, or hydrogen
ions
2–5,7
One of the methods commonly used for
muscle recovery augmentation is massage.
2
It is a
popular technique, purported to provide more ben-
efits, but the scientific literature does not support
the efficacy of manual massage after exercise as a
means to improve performance or to shorten the
time needed for muscle relaxation.
2
It seems that
light exercise is more effective than manual
massage in improving blood flow.
7–9
However,
Rodenburg et al.
10
have reported positive effects
from a combination of stretching and massage,
although they attributed those benefits more to
stretching than to massage. Therefore, it is possible
that postisometric relaxation, a modified form of
stretching (based on gentle, alternant isometric
contraction and muscle stretch) widely used in
rehabilitation,
11,12
may reduce elevated muscle
tension and may also be useful in muscle recovery
after dynamic exercise. Postisometric relaxation
may enhance muscle blood flow by lowering pe-
ripheral resistance. Increasing blood flow could
improve oxygen delivery and the efflux of noxious
substances, theoretically enhancing recovery.
Previous studies have indicated that light ex-
ercise (AR) increases blood velocity
7
and removal of
metabolites after exercise.
9
Limited evidence exists
to suggest that passive rest and massage are bene-
ficial for muscle relaxation.
9
To our knowledge, the
efficacy of postisometric relaxation on muscle re-
covery after dynamic exercise has not been deter-
mined. Information regarding other modes of re-
covery has been found to be inadequate.
The objective of this study was to assess the
influence of different relaxation modes (postiso-
metric relaxation, active recovery, and passive re-
covery) on muscle recovery after dynamic exercise
of the quadriceps femoris.
METHODS
Subjects
Ten healthy male volunteers (age 24 –38 yrs,
height 174.7 4.66 cm, body mass 77.5 11.16
kg) were recruited for this study. All were healthy,
recreationally active nonsmokers who were not en-
gaged in a systematic exercise program. Subjects
were asked to abstain from food and caffeine bev-
erages for 2 hrs before testing and to not perform
heavy exercise during the 8 hrs preceding the tests.
After being fully informed of the purpose of the
experiments, each subject signed a statement of
informed consent. Local ethical committee ap-
proval was obtained for the study.
Experimental Procedures
All subjects reported to the laboratory for five
visits. The experiments were all performed in the
morning to control for circadian variation in a
laboratory at an ambient temperature of 22–24°C.
Visit 1
During the first visit, all subjects were shown
the equipment to be used in the following visits,
and all of them were given an opportunity to be-
come familiar with the test protocol. During this
visit, after warm-up (5 mins of cycling at 30 W on
the stationary ergometer [Monark Exercise AB]),
subjects performed one isometric effort for a max-
imal voluntary contraction (MVC) measurement of
the quadriceps femoris (knee extension) (MedX
Knee Extension Dynamometer). After 2 mins of
rest, subjects performed one set (to the inability to
maintain defined workload) of dynamic leg exten-
sion and flexions at 50% of MVC. After 3 mins of
rest, an electromyogram of vastus lateralis was
June 2007 Muscle Recovery Strategies 475
measured during isometric knee extension at 50%
MVC, which was performed for 15 secs. The famil-
iarization with postisometric relaxation was per-
formed in a supine position for 2 mins.
Visit 2 (baseline)
There was a 1-wk gap between visits to avoid
the influence of muscle fatigue on the measure-
ments. At the beginning of the second visit, sub-
jects performed a standard warm-up of 5 mins of
cycling on the stationary ergometer at 30 W. After
the warm-up, MVC was determined. After 5 mins of
rest in a sitting position, subjects were required to
perform isometric knee extension at 50% of MVC
to inability to maintain defined workload, despite
verbal encouragement. During this effort, EMG of
the vastus lateralis muscle was measured (Fig. 1A).
Visits 3–5
At the beginning of each visit, subjects per-
formed a standard warm-up as described previ-
ously. After the warm-up, subjects performed three
sets (during each set, subjects performed as many
repetitions as possible, and the set was terminated
when the subjects could no longer complete the
full range of motion) of dynamic leg extension and
flexion (at an angle of 20 –110 degrees) at 50% of
previously determined MVC, with 30 secs of rest
between sets, using MedX equipment (MedX Knee
Extension Dynamometer). Immediately after com-
pleting the leg exercise, one of the following relax-
ation methods was applied, in a randomized order.
a. Postisometric relaxation (stretching, ST). To per-
form postisometric relaxation, the muscles of the
quadriceps femoris were passively stretched to a
point of onset of resistance, “soft end filling.”
10,12
From this position, the subject performed a pro-
longed, gentle, isometric contraction against re-
sistance (applied by certified physiotherapist) for
about 5 secs. Then subjects were told to relax, take
a deep breath and exhale completely. During ex-
halation, the muscle was gently stretched. From
this new position, the procedure was repeated
within 5 mins, according to the method of Levit
and Simons.
12
The procedure was performed in a
supine position.
b. Active recovery (AR): light pedaling on the cycle
ergometer (10 W) at 60 rpm for 5 mins.
c. Passive recovery (PR): subject was required to
lie down in a relaxed position as a passive rest
period for 5 mins.
After each of the relaxation techniques, MVC
was reassessed. After 5 mins of rest in a sitting
position, each subject was required to perform an
isometric knee extension at 50% of MVC, which
had been determined at the second visit. The in-
ability to maintain the defined workload was used
as the end point of the test. During this effort, EMG
was measured (Fig. 1B).
Measurements
MVC
The subjects performed a maximal isometric
right knee extension (static, at an angle of 78
degrees) in a sitting position with the trunk sup-
ported by the chair back, using the MedX leg-
extension dynamometer. The inferior third of the
leg was attached to the distal end of the movable
lever arm. The pelvic girdle of each individual was
stabilized by an immobilization strap. MVC was
determined as the highest torque of three trials.
Visual feedback and verbal encouragement were
provided throughout.
EMG
The skin was gently shaved, scratched, and
cleaned with ethyl alcohol. Bipolar surface elec-
FIGURE 1 Diagram of the experimental procedure, showing the time line of the various activities during visits 2–5. A, Diagram of
time line of activities during visit 2. B, Diagram of the order and time line of activities during visits 3, 4, and 5.
476 Mika et al. Am. J. Phys. Med. Rehabil. Vol. 86, No. 6
trodes (Ag/AgCl, 4-cm diameter, 25-mm interelec-
trode distance) were applied to the belly of the
vastus lateralis muscle. The electrodes’ placement
was marked for the following assessments. Sub-
jects were asked not to remove these marks until
the end of the program. EMG was measured during
an isometric knee extension at 50% MVC (at an
angle of 54 degrees) performed to the point of
inability to maintain the defined workload, despite
verbal encouragement on the MedX equipment.
The task was terminated when the subject could
not maintain the knee extension at the 54-degree
angle. All subjects were given the opportunity of
visual feedback to maintain a constant level of
isometric effort. During the EMG measurements,
changes in frequency (F) and root mean square
(RMS) of the power spectrum were calculated us-
ing the MP 150 equipment (Biopac Systems Inc.). F
(frequency domain) and RMS (time domain) are
considered parameters describing the motor unit–
activation pattern.
13–18
Total time of the effort dur-
ing EMG measurement was analyzed. To avoid
transient phenomena from rest to exertion, and
vice versa, the first and the last seconds were not
considered. The change in mean value of RMS
(change in muscle unit activation) from the first to
second half of the effort time after recovery mode
applied was evaluated.
Statistical Analysis
The data are expressed as means SD. Statis-
tical significance was tested and accepted at the
0.05 level of probability. Changes within
groups were examined by paired ttests or, when data
were not normally distributed, by the nonparametric
Wilcoxon signed rank test. Differences between
groups (recovery modes) were determined with a
repeated-measures ANOVA. The results were analyzed
using a statistical program (STATISTICA 95).
RESULTS
After AR, the mean MVC was significantly (P
0.05) higher (213.7 50.2) than after PR (206.8
28.4) and ST (205.5 40.5). Moreover, there was
no statistically significant difference in MVC be-
tween AR (213.7 50.2) and baseline (223.1
36.1) (measured during visit 2) (Fig. 2). Total time
for the effort during EMG measurement was sig-
nificantly lower for all three recovery modes (25.4
6.5, 23.6 5.3, and 25.0 5.1 for AR, PR, and ST,
respectively) than for baseline (31.5 7.4) (Fig. 3).
During the effort after both PR and ST, there was
no significant increase in the activation of motor
units, but a significant increase was noted after AR
(P0.05) (Table 1). There was no statistically
significant difference in F between any of the re-
covery modes and baseline (P0.05).
DISCUSSION
The results of this study suggest that the most
appropriate and effective recovery mode after dy-
namic muscle fatigue is light, active exercise, such
as cycling with minimal resistance. Only after AR
was the mean MVC value similar to baseline; this
mode of recovery also led to an increase in the
activation rate of motor units. The implications of
these findings are that the quadriceps muscle gen-
erated more force after AR than after PR or ST. The
findings from this study are in agreement with
previous research.
2,8,9
The accumulation of an excess amount of ex-
ercise metabolites in muscles under stress is a
FIGURE 2 Mean MVC value at baseline and after each of the recovery modes. The passive and stretching
recovery modes were significantly different from baseline. ††P0.001, recovery mode to baseline.
June 2007 Muscle Recovery Strategies 477
contributing factor to fatigue.
2–5,9
The removal
rate of these substances after heavy exercise is
higher during light aerobic exercise than during a
period of resting recovery.
19,20
If improved circu-
lation could enhance efflux of metabolites from
muscle, this also might speed recovery.
2
Continu-
ing light exercise immediately after intense activity
will have a positive effect on muscle blood flow.
7,8
For example, the study by Gupta et al.
9
confirms
that after supramaximal cycling exercise, blood lac-
tate was cleared more quickly by light exercise than
by passive rest, and that 20 mins of massage during
passive rest did not affect the lactate-clearance rate
at all.
It was also postulated that heavy exercise
might lead to exercise-induced injury, postexercise
degeneration, and subsequent muscle repair, all of
which may be prime factors in prolonged postex-
ercise loss of muscle-force production.
7
Improved
blood and lymph flow in injured muscle has been
suggested to enhance recovery by improving mi-
crocirculation,
21
helping reduce edema and accu-
mulation of exercise metabolites, and by enhancing
the regenerative process.
22,23
Hence, if enhanced
muscle blood flow does, in fact, improve the heal-
ing process, light muscle contractions may be the
most effective.
7
After heavy exercise, the benefits of light, ac-
tive exercise in comparison with those of passive
rest may be marginal, because the HR remains
above resting levels for some time, thus ensuring
good circulation in muscles that were exercised.
Also, the increased local muscle temperature helps
to maintain a higher rate of circulation.
24
Gupta et
al.
9
found the highest lactate value at 3 mins after
the end of exercise in all modes of recovery (active,
passive, and massage). The half-life of lactate in AR
was shortest because of better oxidation during
increased cardiac output, so the first detectable
difference in the removal of lactate was found in AR
at 10 mins after the end of exercise. Among the
three recovery modes, AR may be considered a
TABLE 1 Change in muscle unit activation (root mean square [RMS]) from first to second half of
effort time at baseline and after each of the recovery modes applied
Baseline Active Recovery Passive Recovery Stretching
First half of effort time, mV (mean SD) 0.22 0.06 0.30 0.09 0.29 0.09 0.31 0.09
Second half of effort time, mV (mean SD) 0.25 0.09 0.35 0.13 0.32 0.13 0.35 0.14
RMS (mV) 0.038 0.047 0.030 0.032
P0.05 0.05 NS NS
P0.05 comparing first with second half mean value of RMS.
NS, nonsignificant.
FIGURE 3 Total time of the effort during EMG measurement at baseline and after each of the recovery modes.
There was a significant decrease in the time of contraction at 50% of MVC during all of the recovery
modes, but there was no difference between modes. *P0.05, recovery mode to baseline; †P0.01,
recovery mode to baseline.
478 Mika et al. Am. J. Phys. Med. Rehabil. Vol. 86, No. 6
much better recovery process than massage and
passive rest, particularly when a faster rate of lactate
elimination is the main criterion.
9
The different cri-
teria used for the recovery process evaluation em-
ployed in our study (MVC and EMG analysis) support
those metabolic observations.
7,8,19,20,24
Stretching was recommended as a popular re-
covery strategy after muscle fatigue in the sporting
and rehabilitation domains.
25,26
But, there is a lack
of substantive information regarding the efficacy of
stretching, and the information supporting its ad-
visability in muscle recovery has been found to be
inadequate. Moreover, some authors have sug-
gested that intense, unaccustomed muscular exer-
cise, particularly that which involves eccentric
muscle contraction, will induce muscle damage
and may slow the speed of relaxation.
25–27
The
mechanisms associated with prolonged disruption
of maximum voluntary muscle-contraction force
generation after eccentric exercise may be associ-
ated with mechanical disruption of the sarcomeres
and sarcolemma.
28 –29
It has been suggested that
eccentric exercise results in the nonuniform over-
stretching of some sarcomeres, leading to injury,
possibly because of the inability of cross-bridge
cycling to keep pace with lengthening speed.
21,30
In the present study, the minor decrease in the
time of the effort after AR and ST than after PR in
comparison with the baseline value (Fig. 3) seems
to suggest that passive rest is not a recommended
option in muscle relaxation after fatiguing exer-
cise. The results from the present study are in
agreement with previous research
2,8,9
that has
demonstrated advantages of those two forms of
muscle relaxation. However, light aerobic exercise
was considered more effective
2,9
than stretching,
which has had demonstrable positive effects in
some studies
26
but not in others.
28,29
In sports per
se, warm-up and stretching exercise are often rou-
tinely performed and are accepted as preventing
muscle injury.
10
But, in the scientific literature,
stretching has yielded equivocal results.
10
A crucial question concerns the recovery time
between muscular efforts. In the present study, 5
mins of rest was applied. Only after AR was there a
lack of difference in the measured MVC compared
with the baseline value. Therefore, we may hypoth-
esize that only this kind of recovery allowed fa-
tigued muscle to recover sufficiently during this
time period. Moreover, the EMG data are in agree-
ment with the MVC data. RMS increased signifi-
cantly during the effort only after AR (Table 1); this
suggests that the muscle recovered sufficiently to
recruit more motor units. After ST and PR, RMS
was stable; this may suggest that the maximal
amount of motor units was recruited at the begin-
ning of the effort.
The lowering of the MVC in the present study
after fatiguing exercise is in agreement with previ-
ous reports.
31,32
Esposito et al.
13
have reported that
even after 10 mins of PR, exercise-induced muscle
fatigue led to only a 26% decrease in MVC. Similar
results have been reported by Persson et al.
33
in a
static endurance test, which consisted of a sub-
maximal unilateral activation of the right trapezius
and deltoid muscles for as long as possible. The
subjects developed significant signs of fatigue, as
defined by EMG criteria, in both muscles on the
right side during the test. The recovery from fa-
tigue was approximately half-complete 15 secs after
the end of the test and was complete or almost
complete 10 mins thereafter. Esposito et al.
13
also
evaluated, by EMG, the degree of alteration of elec-
trical activity of the motor units, suggesting that
they may still be present within a period of recov-
ery (10 mins) after a fatiguing exercise. Similarly,
Lariviere et al.
34
used EMG to evaluate passive rest
intervals of 10 or 15 mins after fatiguing back
exercise. Their results suggest that complete mus-
cle recovery was achieved with 10- to 15-min rest
periods. These results support the use of rest peri-
ods of 10 –15 mins between multiple fatigue tests.
In the present study, the subjects performed three
sets of flexion– extension exercise to the point of
fatigue, with 5 mins of rest between the three sets
and the MVC test. The shorter recovery time may
be the reason for the significant decrease in MVC.
This type of recovery duration is commonly used in
interval training programs that incorporate fatigu-
ing exercise. On the basis of these data, short rest
periods
35
seem insufficient to allow full MVC re-
covery; longer rest periods of 10 –15 mins would be
more appropriate.
34
Garland et al.
15
have demonstrated that the
discharge rate of most motor units (measured by
RMS) that were active from the beginning of a
contraction declined during a fatiguing contrac-
tion. The discharge rates of more recently re-
cruited units were either constant or increased
slightly. The mechanism of the alteration of motor
unit activation during muscle work is partly attrib-
utable to the linear increase in the RMS during the
first part of the exercise.
13,36
This has been found to
be mainly dependent on (1) changes in the muscle
fiber action potential, with a decrease in the con-
duction velocity and an enrichment in the low-
frequency content of the signal, and (2) recruit-
ment of additional motor units, coupled with an
increase in their average firing frequency to main-
tain a constant force and synchronization of active
motor units.
13,36
Several limitations of this study need to be
addressed. First, the study population was rela-
tively small, so future research should be con-
ducted with a bigger group. Further, the surface
June 2007 Muscle Recovery Strategies 479
EMG signals may vary depending on electrode
placement, so it is very important to mark the
electrodes’ location. Moreover, circadian variation
of the EMG signal is the reason that the EMG data
in the assessment of muscle unit activity should be
considered with caution.
A decrease of the EMG power spectrum to
lower frequencies during sustained isometric con-
traction has generally been accepted as a sign of
muscle fatigue.
2,7,16,17
A number of authors have
analyzed the EMG power spectrum during dynamic
exercise.
37– 42
In a few cases, decreases in frequency
during dynamic exercise have been found during
ergometer cycling,
37
in isokinetic dynamometer
exercise,
38,39
and in running.
40
Others have found
no change of frequency during ergometer cycling
41
and running.
42
As has been postulated by previous
research,
43
fatigue during dynamic exercise is ac-
companied by a decrease of electromyographic me-
dian power frequency; this might be attributable to
intramuscular factors. An insufficient muscle
blood supply under these circumstances might be
the decisive factor. These circumstances have been
found at extremely high exercise intensities.
43
In
the present study, no systematic decline of fre-
quency during exercise was found.
Considering that MVC decreased after PR and
ST but was unchanged after AR, AR seems to be the
best method of recovery after fatiguing, dynamic
exercise. ST and PR did not significantly increase
activation of muscle fibers (RMS) during the sec-
ond part of the effort, whereas RMS was signifi-
cantly increased during AR. The results of this
study suggest that the most appropriate and effec-
tive recovery mode after dynamic muscle fatigue
involves light, active exercises such as cycling with
minimal resistance.
Because this study has pertinence to athletes
as well as rehabilitation patient populations, future
research should address additional questions such
as the influence of sex, physical activity level, or
age on recovery.
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June 2007 Muscle Recovery Strategies 481
... Past research has a mixed and often contradicting set of results, with numerous studies indicating post-exercise stretching is not effective for improving recovery. Indeed, in one study with 10 healthy men (Mika et al., 2007), the participants performed three sets of leg extension and flexion at 50% of maximum voluntary contraction (MVC). Post-exercise recovery protocols were used, including light-intensity cycle ergometer and PNF stretching for 5 min. ...
... Therefore, nine studies fulfilled all inclusion criteria (Kokkinidis et al., 1998;Mika et al., 2007;Bonfim et al., 2010;Cè et al., 2013;Torres et al., 2013;McGrath et al., 2014;Muanjai and Namsawang, 2015;Cooke et al., 2018;César et al., 2021). As per protocol, in studies where the recovery methods were applied in multiple sessions (e.g., stretching after exercise and repeated at 24 and 48 h), only data before the second application was considered. ...
... Study characteristics are provided in Table 2. Three studies used a cross-over design (Mika et al., 2007;Cè et al., 2013;West et al., 2014), while the remaining used a parallel design. Sample size ranged from 9 (Cè et al., 2013) to 57 (McGrath et al., 2014), with ages ranging from 17 to 38 years-old, i.e., all studies were performed with adults or near-adulthood (i.e., the usual legal age of 18 years old). ...
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Background: Post-exercise (i.e., cool-down) stretching is commonly prescribed for improving recovery of strength and range of motion (ROM) and diminishing delayed onset muscular soreness (DOMS) after physical exertion. However, the question remains if post-exercise stretching is better for recovery than other post-exercise modalities. Objective: To provide a systematic review and meta-analysis of supervised randomized-controlled trials (RCTs) on the effects of post-exercise stretching on short-term (≤1 hour after exercise) and delayed (e.g., ≥24h) recovery makers (i.e., DOMS, strength, ROM) in comparison with passive recovery or alternative recovery methods (e.g., low-intensity cycling). Methods: This systematic review followed PRISMA guidelines (PROSPERO CRD42020222091). RCTs published in any language or date were eligible, according to P.I.C.O.S. criteria. Searches were performed in eight databases. Risk of bias was assessed using Cochrane RoB 2. Meta-analyses used the inverse variance random-effects model. GRADE was used to assess the methodological quality of the studies. Results: From 17,050 records retrieved, 11 RCTs were included for qualitative analyses and 10 for meta-analysis (n = 229 participants; 17-38 years, mostly males). The exercise protocols varied between studies (e.g., cycling, strength training). Post-exercise stretching included static stretching, passive stretching and proprioceptive neuromuscular facilitation. Passive recovery (i.e., rest) was used as comparator in eight studies, with additional recovery protocols including low intensity cycling or running, massage, and cold-water immersion. Risk of bias was high in ~70% of the studies. Between-group comparisons showed no effect of post-exercise stretching on strength recovery (ES = -0.08; 95% CI = -0.54 to 0.39; p = 0.750; I2 = 0.0%; Egger’s test p = 0.531) when compared to passive recovery. In addition, no effect of post-exercise stretching on 24-h, 48-h or 72-h post-exercise DOMS was noted when compared to passive recovery (ES = -0.09 to -0.24; 95% CI = -0.70 to 0.28; p = 0.187 - 629; I2 = 0.0%; Egger’s test p = 0.165 - 0.880). Conclusion: There wasn’t sufficient statistical evidence to reject the null hypothesis that stretching and passive recovery have equivalent influence on recovery. Data is scarce, heterogeneous and confidence in cumulative evidence is very low. Future research should address the limitations highlighted in our review, to allow for more informed recommendations. For now, evidence-based recommendations on whether post-exercise stretching should be applied for the purposes of recovery should be avoided, as the (insufficient) data that is available does not support related claims.
... There are scientific studies which stress that in the case of fatigue caused by physical exertion, the athlete should rest actively. Research [73,74] has shown that light exercises, applied after physical exercise, can accelerate the recovery from muscle fatigue and is more effective than passive rest. In a study [75], a higher rate of lactate decomposition was observed during active recovery compared to passive rest. ...
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Background: The aim of the study was to compare the effect of vibration massage and passive rest on accelerating the process of muscle recovery after short-term intense exercise. Methods: Eighty-four healthy men aged 20 to 25 years participated in the study. Study participants performed isometric (ISO-M Group) and auxotonic (AUX-M group) contraction exercise in the lower limbs. Vibration massage was administered after exercise in the first recovery period. In the same period, controls rested passively, without the support of vibration massage. To assess the effectiveness of the applied vibration, a 4-fold measurement of the maximum force of the muscles involved in the exercise was performed under conditions of isometric contractions on a leg press machine set at an angle of 45° degrees upwards. Results: Differences in maximum strength during isometric contraction were found compared to baseline in favor of the groups subjected to the experimental vibration massage. Differences were demonstrated in muscle strength between the study groups (p < 0.005). The second period of passive rest in all groups did not bring significant changes in the values of maximal lower limb strength. Conclusions: Properly selected characteristics of the vibration effect can be an effective method in accelerating recovery and regaining lost motor capabilities of muscle groups fatigued by exercise. This offers the potential to shorten rest periods between sets of repetitions in training or between training units.
... A number of physical interventions have been proposed to reduce muscle fatigue and lessen the decline in muscular performance caused by exercise, including massage (Arroyo-Morales et al., 2008), cooling (Anaya-Terroba et al., 2010;Pointon et al., 2011;Luomala et al., 2012;Eguchi et al., 2014;, stretching (Mika et al., 2007;Ghasemi et al., 2013;Padilha et al., 2019), electrical stimulation (ES) (Marqueste et al., 2003), AR (Zarrouk et al., 2011;Akagi et al., 2020), compression (Cavanaugh et al., 2015;Shimokochi et al., 2017), and light-emitting diode therapy (LEDT) (Kelencz et al., 2010;Yang et al., 2012;Toma et al., 2018). These physical interventions induce different physiological mechanisms to alleviate muscle fatigue. ...
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Introduction: Various interventions have been applied to improve recovery from muscle fatigue based on evidence from subjective outcomes, such as perceived fatigue and soreness, which may partly contribute to conflicting results of reducing muscle fatigue. There is a need to assess the effectiveness of various intervention on reducing neuromuscular fatigue assessed by a quantitative outcome, such as electromyography (EMG). The objective of this review and meta-analysis was to evaluate the effectiveness of different interventions and intervention timing for reducing fatigue rates during exercise. Methods: The literature was searched from the earliest record to March 2021. Eighteen studies with a total of 87 data points involving 281 participants and seven types of interventions [i.e., active recovery (AR), compression, cooling, electrical stimulation (ES), light-emitting diode therapy (LEDT), massage, and stretching] were included in this meta-analysis. Results: The results showed that compression (SMD = 0.28; 95% CI = −0.00 to 0.56; p = 0.05; I ² = 58%) and LEDT (SMD = 0.49; 95% CI = 0.11 to 0.88; p = 0.01; I ² = 52%) have a significant recovery effect on reducing muscle fatigue. Additionally, compression, AR, and cooling have a significant effect on reducing muscle fatigue when conducted during exercise, whereas a non-effective trend when applied after exercise. Discussion: This meta-analysis suggests that compression and LEDT have a significant effect on reducing muscle fatigue. The results also suggest that there is a significant effect or an effective trend on reducing muscle fatigue when compression, AR, cooling, and ES are applied during exercise, but not after exercise.
... As with the original meta-analyses, data from adults 18-55 years of age with no musculoskeletal impairments or morbidities performing single-joint isometric contractions were included. Since one of the primary goals was to estimate separate model parameters for the sexes, studies that did (Johnson, 1982) 15 0 100 100 1 1 (Karlsson et al., 1975) 3 0 15-85 100 1 8 (Kuroda et al., 1970) 6 0 25-100 100 1 4 (Larsson and Karlsson, 1978) 28 0 50 100 1 1 12 0 25 100 1 1 (Maïsetti et al., 2002a) 9 0 50 100 1 1 (Maïsetti et al., 2002b) 14 0 50 100 1 1 (Mathur et al., 2005) 11 11 20, 80 100 1 2 (Maughan et al., 1986) 25 25 20, 50, 80 100 1 6 (Maughan, 1988) 8 0 60 100 1 1 (Mika et al., 2007) 10 0 50 100 1 1 (Mulder et al., 2007) 5 0 45 60 2.5 5 (Nagle et al., 1988) 10 0 30 100 1 1 (Ng et al., 1994) 8 9 30, 50 100 1 2 (Ordway et al., 1977) 27 0 100 50 2 20 (Petrofsky and Laymon, 2002) 25 0 40 100 1 2 (Place et al., 2005) 11 0 20 100 1 1 (Place et al., 2006) 13 0 40 100 1 1 (Place et al., 2007) 13 0 40 100 1 1 (Ray and Mark, 1993) 7 1 30 100 1 1 (Ray et al., 1998) 7 0 30 100 1 1 (Rochette et al., 2003) 10 0 20 100 1 1 (Rodriquez and Agre, 1991) 21 20 40 100 1 1 (Rodriquez et al., 1993) 7 0 20, 40, 80 100 1 3 (Saugen et al., 1997) 8 0 40 60 10 4 (Smolander et al., 1998) 10 0 20, 40, 60 100 1 3 (Urbanski et al., 1999) 10 0 67 100 1 1 (Yamada et al., 2002) 14 0 20, 60 100 1 2 (Zech et al., 2008) 12 0 50 100 1 1 not specify the composition of their subject pool by sex were excluded. Also excluded were studies that specifically tested trained athletes or professionals requiring special physical training such as astronauts or long-distance runners. ...
Article
The three-compartment controller with enhanced recovery (3CC-r) model of muscle fatigue has previously been validated separately for both sustained (SIC) and intermittent isometric contractions (IIC) using different objective functions, but its performance has not yet been tested against both contraction types simultaneously using a common objective function. Additionally, prior validation has been performed using common parameters at the joint level, whereas applications to many real-world tasks will require the model to be applied to agonistic and synergistic muscle groups. Lastly, parameters for the model have previously been derived for a mixed sex cohort not considering the different fatigabilities between the sexes. In this work we validate the 3CC-r model using a comprehensive isometric contraction database drawn from 172 publications segregated by muscle group and sex. We find that prediction errors are reduced by 19% on average when segregating the dataset by functional muscle group (FMG) alone, and by 34% when segregating by both sex and FMG. However, minimum prediction errors are found to be higher when validated against both SIC and IIC data together using torque decline as the outcome variable than when validated sequentially against hypothesized SIC intensity-endurance time curves with endurance time as the outcome variable and against raw IIC data with torque decline as the outcome variable.
... The focus will exclusively be directed on active methods comprising movements or activities performed by the participants. Several studies have favored active over passive recoveries because of potential physiological benefits: better blood lactate removal and increased muscle performance (24), higher muscle voluntary isometric contraction (30), higher total quality recovery, and a decreased feeling of heavy legs (26). The last 2 findings support the use of active recovery not just for the physiological benefits already mentioned but also for positive perceptual and psychological considerations (26). ...
... In einer Studie vonRobey et al. (2009) hatte Stretching keinen Ein uss auf den empfundenen Muskelschmerz sowie die Wiederherstellung der Leistungsfähigkeit im Anschluss an eine intensive Belastung. Ähnliches dokumentiertenCheung et al. (2003);Connolly et al. (2003);Gulick et al. (1996) sowieMika et al. (2007). Sie zeigten, dass Stretching die Symptome mikroskopischer Muskelverletzungen nicht lindert. ...
Chapter
Ermüdung und Regeneration sind integrale Bestandteile des Trainingsprozesses. Dabei steht die kontinuierliche Leistungsentwicklung in ständiger Wechselwirkung mit den durch Trainings- und Wettkampfaktivitäten ausgelösten Ermüdungs- und Regenerationsvorgängen. Während die Steigerung der Trainingsqualität seit jeher im Fokus trainingswissenschaftlicher Bemühungen steht, richtet sich das Augenmerk zunehmend auch auf die Erholungsprozesse und deren Optimierung. Das Regenerationsmanagement lässt sich dabei im Wesentlichen in die Messung des Regenerationsbedarfs sowie in die individualisierte Planung und Anwendung von Regenerationsstrategien strukturieren. Hierbei ist die Bedeutung einer angemessenen Ernährung sowie von ausreichend Schlaf unbestritten. Zusätzlich kann in der (leistungs-)sportlichen Praxis aus einer Vielzahl an regenerationsfördernden Maßnahmen ausgewählt werden, deren Wirksamkeitsnachweis jedoch nur selten unter wissenschaftlich kontrollierten Bedingungen überzeugend erfolgt ist. Dies gilt sowohl für „traditionelle“ und bei den Athleten beliebte Maßnahmen wie beispielsweise die Massage als auch für neuartige Regenerationstrends wie Foam-Rolling oder für technologisch unterstützte Interventionsstrategien wie z. B. LED-Bestrahlung oder Kältekammern. Sowohl Ermüdungs- als auch Erholungsprozesse sind äußerst komplexe und multifaktorielle Phänomene, die in Abhängigkeit von den Belastungsmerkmalen sowie adressaten- und umweltspezifischen Besonderheiten auf verschiedenen Funktionsebenen des menschlichen Organismus (u. a. Muskulatur, Bindegewebe, zentrales Nervensystem, autonomes Nervensystem, endokrines System) in unterschiedlichen zeitlichen Dimensionen sowie in unterschiedlicher Geschwindigkeit und Ausprägung stattfinden. Basierend hierauf werden in diesem Kapitel sowohl die Wirkmechanismen und Effekte von Regenerationsinterventionen, die sich in der Sportpraxis großer Beliebtheit erfreuen, diskutiert als auch Grundlagen zum Ernährungsmanagement im Sport besprochen. Unter Berücksichtigung individueller und sportartspezifischer Rahmenbedingungen werden Praxistipps für die Regenerationssteuerung im (Leistungs-)Sport vorgestellt.
... Diversos programas de exercícios resistidos (ER), usualmente realizados nas academias de musculação, são amplamente utilizados para manter e/ ou melhorar a funcionalidade (KANG;KIM;LEE, 2018;KELLMANN et al., 2018), sendo empregados na reabilitação (HISLOP et al., 2019) e no treinamento físico (MOREL; HAUTIER, 2017). Quando, entretanto, realizados em alta intensidade e de forma aguda, a maior produção de espécies reativas de oxigênio e nitrogênio pode exceder a capacidade antioxidante, induzindo um estado transitório de estresse oxidativo (POWERS; JACKSON, 2008) e a maior concentração de marcadores inflamatórios (TEIXEIRA et al., 2014a), provocando dano muscular, o que diminui a funcionalidade e o desempenho musculoesquelético (DABBS; CHANDER, 2018;MIKA et al., 2007MIKA et al., , 2016. Por outro lado, a médio e a longo prazos, a inflamação, advinda desses exercícios, media o processo de reparo e promove a regeneração, o que faz parte do processo normal de remodelamento muscular advindo do treinamento (CALLE; FERNANDEZ, 2010). ...
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Os exercícios resistidos (ER) realizados de forma intensa resultam no surgimento de dor muscular de inicio tardio (DMIT) e na redução da funcionalidade. Diferentes formas de recuperação após os exercícios veem sendo estudadas para atenuar o desconforto e melhorar a funcionalidade. O objetivo do presente estudo foi avaliar os efeitos das recuperações passiva (RP) e ativa (RA) sobre a DMIT e a funcionalidade de voluntários fisicamente ativos após sessão de ER. A amostra foi composta por 15 voluntários, com idade média de 24,2 (± 2,2) anos e IMC de 24,7 (± 2,5) kg/m2, submetidos ao protocolo de ER e às formas de recuperação. As sessões de ER (agachamento, cadeira extensora e leg press) consistiram em 4 séries de 10 repetições, com 80% da carga máxima (intervalo de uma semana entre a avaliação e as sessões). A DMIT foi avaliada (Escala Visual Analógica) 24 h, 48 h e 72 h após sessão de ER. A funcionalidade (força muscular avaliada pelo pico de torque isométrico, flexibilidade, potência, agilidade, velocidade e resistência à fadiga) foi avaliada 30 min após as intervenções (RA e RP). A RA foi mais eficiente na redução da DMIT em relação à RP nos três momentos avaliados (24 h: -1,3, 48 h: -1.3 e 72 h: -1.5 pontos; p < 0.005). A RA melhorou em aproximadamente 9% a força muscular dos membros inferiores em relação à RP. As demais variáveis funcionais não apresentaram diferenças entre as recuperações. A RA diminui a DMIT e atenua a perda da força muscular após ER em voluntários fisicamente ativos.
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İçindekiler Giriş Kriz Yönetimi, Karar Verme ve Özgüven Kavramları.............91 2.1. Kriz Yönetimi.......................................................................91 2.1.1. Yönetim, Spor Yönetimi, Kriz ve Sporda Kriz Yönetimi Kavramları............................................................91 2.1.2. Krizin Evreleri.............................................................92 2.2. Karar Verme...................................................................94 2.2.1. Sporda Karar Verme...................................................95 2.2.2. Karar Verme Süreci Dönemleri................................96 2.3. Özgüven................................................................................97 2.3.1. Sporda Özgüven..........................................................98 3. Yöntem.........................................................................................100 3.1. Araştırma Modeli..............................................................100 3.2. Araştırmanın Evreni ve Örneklemi................................100 3.3. Veri Toplama Araçları.......................................................101 3.3.1. Kriz Yönetimi Ölçeği................................................102 3.3.2. Melbourne Karar Verme Ölçeği..............................103 3.3.3. Öz-güven Ölçeği.......................................................104 3.4. Verilerin Toplanması.........................................................105 3.5. Verilerin Analizi................................................................105 3.6. Bulgular...............................................................................105 4. Sonuç, Tartışma ve Öneriler.....................................................118
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DİRENÇ ANTRENMANLARININ TEMELİ, EGZERSİZ REÇETELENDİRİLMESİ ve SÜRECİ
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1. The relationship between intracellular metabolites and the generation of force during fatigue has been examined in the first dorsal interosseous muscle of the hand. With the arm made ischaemic, the muscle was fatigued by three bouts of maximal voluntary contraction, leaving approximately three minutes ischaemic rest between contractions. During one series of experiments intracellular phosphorus metabolites were measured by nuclear magnetic resonance during the intervals between the fatiguing contractions: in the second series contractile properties were tested with brief electrical stimulation during the rest intervals. 2. The relationships between loss of force and change in metabolite concentrations obtained with four normal subjects were compared with those from one subject with myophosphorylase deficiency (MPD) who could not utilize muscle glycogen and therefore produced no hydrogen ion from glycolysis during exercise. 3. For both the MPD and normal subjects the relationship between relative force loss and inorganic phosphate (Pi) concentration was curvilinear, force changing little in the early stages of the contraction when the intracellular Pi was accumulating rapidly but falling faster when the Pi was above 25 mM and increasing relatively slowly. 4. In the normal subjects intracellular pH fell from a mean of 7.03 +/- 0.01 (mean +/- S.E. of mean, n = 19) in the fresh muscle to 6.51 +/- 0.02 at the end of the fatiguing exercise; force, as a percentage of the initial value, fell in proportion to the increase in H+ concentration. In the MPD subject pH did not change and force loss was therefore independent of H+ accumulation. In the normal subjects the force of the fatiguing muscle showed an approximately linear relationship with the concentration of the monobasic form of inorganic phosphate. However, the MPD subject showed a quite different relationship, with force loss being much greater for a given concentration of monobasic phosphate. This result indicates that monobasic phosphate is not a unique determinant of force loss in fatigued muscle. 5. During the first 60 s of recovery in the normal subjects, pH remained low while force recovered, indicating a mechanism of force loss that was independent of H+ accumulation. However, the recovery of force was not complete, so that for comparable phosphocreatine contents the recovering, more acid, muscle generated less force than the muscle that was being fatigued. It was estimated that H(+)-dependent and independent mechanisms contributed roughly equally to the observed force loss. The relationship between force and the concentration of monobasic phosphate differed in fatiguing and recovering muscle.
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The effect of pre- versus postsynaptic mechanisms in the decrease in spinal reflex response during passive muscle stretching was studied. The change in the electromyographic (EMG) responses of two reflex pathways sharing a common pool of motoneurones, with (Hoffmann or H reflex) or without (exteroceptive or E reflex) a presynaptic inhibitory mechanism, was compared. The EMG activities were recorded in the soleus muscle in response to the electrical stimulation of the tibial nerve at the popliteal fossa (H reflex), and at the ankle (E reflex) for different dorsiflexion angles of the ankle. The compound muscle action potential (M wave) in the soleus and the abductor hallucis was recorded in order to control the stability of the electrical stimulation during stretching. The results indicate that in the case of small-amplitude muscle stretching (10 degrees of dorsiflexion), a significant reduction (-25%; P < 0.05) in the Hmax/Mmax ratio was present without any significant change in the Emax/Mmax ratio. At a greater stretching amplitude (20 degrees of dorsiflexion), the E reflex was found to be reduced (-54.6%; P < 0.001) to a similar extent as the H reflex (-54.2%). As soon as the ankle joint returned to the neutral position (ankle at 90 degrees), the two reflex responses recovered their initial values. In additional experiments, motor-evoked potential (MEP) induced by the magnetic stimulation of the motor cortex was recorded and showed a similar type of behaviour to that observed in the E reflex. These results indicate that reduced motoneurone excitation during stretching is caused by pre- and postsynaptic mechanisms. Whereas premotoneuronal mechanisms are mainly involved in the case of small stretching amplitude, postsynaptic ones play a dominant role in the reflex inhibition when larger stretching amplitude is performed.
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One hundred and twenty consecutive maximal leg extensions at a constant angular velocity of 1.5 radians. s-1 were performed by nine physical education students. Integrated electromyographic (IEMG) activity and power spectrum density function (PSDF) of the EMG were recorded from m. vastus lateralis, m. vastus medialis and m. rectus femoris using bipolar surface electrodes. Muscle biopsies were obtained from m. vastus lateralis before and after exercise. Tissue samples were analyzed for muscle fiber type distribution and lactate and glycogen concentration. Muscle force and IEMG decreased in parallel over the exercise period. Thus, the IEMG/force ratio was unchanged. Mean power frequency (MPF) of PSDF of the three muscles decreased by 10% (p<0.001) during the initial 25 contractions with no further decline during the latter part of exercise. The relative contribution of the highest bandwidth (130–500 Hz) of the PSDF decreased (p<0.001) between the first and final contractions. Muscle glycogen concentration decreased from 85 ± 23 to 68 ± 22 mmol ± kg-1 w. w.during the exercise. Muscle and blood lactate concentration averaged 12.1 ± 8.8 mmol ± kg-1 w. w.and 3.8 ± 0.8 mmol ± l-1, respectively. The relative changes in MPF and in the highest bandwidth were correlated with muscle lactate concentration and fiber type distribution: in individuals with a high proportion of fast twitch muscle fibers and/or the greatest lactate accumulation, MPF and high frequency components of EMG PSDF decreased most markedly. Reductions in muscle force and IEMG are suggested to be partly due to a decreased motor neuron firing rate. It is discussed whether lactate or associated metabolic changes are influencing the motor unit action potential through feedback processes
Article
EMG median power frequency of the calf muscles was investigated during an exhausting treadmill exercise. This exercise was an uphill run, the average endurance time was 1.5 min. Median power frequency of the calf muscles declined by more than 10% during this exercise. In addition EMG median power frequency of isometric contractions of the same muscles was measured before and in one minute intervals for 10 min after this run. Immediately after the run isometric median power frequency had declined by less than 5% for the soleus muscle, more than 10% for the gastrocnemius medialis and gastrocnemius lateralis muscles. In the 10 min following exercise the isometric median power frequency increased to pre-execise levels. Maybe the median power frequency shift to lower frequencies during dynamic exercise can be interpreted as a sign of local muscle fatigue.
During dynamic contractions performed on a cycle ergometer, we studied the influence of motor unit (MU) recruitment on the electromyographic (EMG) spectral content by exerting mechanical power of different intensities, which was chosen to remain below the maximal aerobic power (VO2max). The spectral parameters: EMG total power (PEMG), mean (MPF) and median (MED) power frequencies, which are the most representative of the EMG spectral content, were calculated according to the EMG activity of the vastus medialis muscle (VM) and soleus muscle (SOL) of the right leg. For VM and SOL, PEMG increased linearly with exerted power demonstrating an enhancement of MU recruitment. Moreover these relationships were less scattered when exerted power was expressed as a percentage of VO2max. Changes in MPF and MED with varying exercise intensities were different from one subject to another. For a set of subjects, MPF and MED were found to be independent of exerted power. Although VM and SOL muscles are different in fibre type composition, similar results were obtained for both EMG activities. We have concluded that for dynamic contractions performed at different intensities below VO2max, the recruitment of the MU has a poor effect on the EMG spectral content whatever the predominant type of fibre.
Models of the behaviour of the surface EMG signal during fatigue have assumed that there is a linear relationship between the mean power frequency of the EMG spectrum and muscle fibre conduction velocity. They attribute the fall in mean power frequency during fatigue to a proportionate fall in fibre velocity. Experiments have been performed on human vastus lateralis in which forces ranging from 10% to 90% of the maximum force were sustained for times such that the product of the target force and the time was constant. Muscle fibre conduction velocity was estimated using a cross-correlation technique to determine the lag between two EMG signals. The results confirmed the linearity between mean power frequency and fibre velocity. It is still possible, however, that other factors such as de- and recruitment of fibres and change in motor unit firing rates contribute to the fall in mean power frequency during fatigue. Even if these factors are important, the primary assumption of current EMG models relating mean power frequency and muscle fibre velocity has been confirmed.
Article
The passive tension resulting from dorsiflexion of the ankle was measured in relation to stretching in six handball players and six soccer players. Corresponding values of ankle angle and passive tension were meas ured by a strain gauge and a potentiometer connected to a pedal system. The passive tension versus ankle angle was meas ured before and 90 minutes after a single contract- relax stretching program of the plantar flexors. Stretch ing lowered the passive tension by up to 18%. Contract- relax stretching performed twice a day for 3 weeks lowered the passive tension in the plantar flexors by up to 36%. Before the last measurements, no stretching was performed for 20 hours or more. Stretching thus had both a short-term effect, matching the length of a training session, and a long-term effect, shown in a reduction of passive tension after 3 weeks. The relative decrease in passive tension after stretching exercises was constant from a neutral position of the ankle to maximal dorsiflexion. There was no correlation between 1) flexibility and the short-term effect of stretching, 2) flexibility and the long-term effect of stretching, or 3) the short-term and long-term effects of stretching. This indicates that pas sive tension was decreased in all subjects irrespective of their flexibility, and that subjects who had short-term effects after stretching did not necessarily demonstrate a long-term effect.
Article
The relationship between intramuscular pH and the frequency components of the surface electromyographic (EMG) power spectrum from the vastus lateralis muscle was studied in eight healthy male subjects during brief dynamic exercise. The studies were carried out in placebo control and metabolic alkalosis induced by oral administration of NaHCO3. At the onset of exercise, blood pH was 0.08 units higher in alkalosis compared with placebo. Muscle lactate accumulation during exercise was higher in alkalosis (32 +/- 5 mmol/kg wet wt) than in placebo (17 +/- 4 mmol/kg wet wt), but no difference in intramuscular pH was found between the two conditions. The EMG power spectrum was shifted toward lower frequencies during fatigue in the control condition (10.1 +/- 0.9%), and these spectral shifts, evaluated from changes in the mean power frequency (MPF) of the EMG power spectrum, were further accentuated in alkalosis (19 +/- 2%). Although the changes in frequency components of EMG correlated with muscle lactate accumulation (r = 0.68, P less than 0.01), no direct relationship with muscle pH was observed. We conclude that alkalosis results in a greater reduction in MPF associated with a higher muscle lactate accumulation. However, the good correlation observed between the two variables is not likely causative, and a dissociation between intramuscular pH and the increase in the low-frequency content of EMG power spectrum appears during muscle fatigue.