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TIME COURSE OF STRENGTH AND ECHO INTENSITY
RECOVERY AFTER RESISTANCE EXERCISE IN WOMEN
REGIS RADAELLI,
1
MARTIM BOTTARO,
2
EURICO N. WILHELM,
1
DALE R. WAGNER,
3
AND RONEI S. PINTO
1
1
Exercise Laboratory Research, Physical Education School, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil;
2
Strength Training Laboratory, College of Physical Education and Exercise Science, University of Brası´
lia, Brası´
lia, Brazil; and
3
Health, Physical Education, and Recreation Department, Utah State University, Logan, Utah
ABSTRACT
Radaelli,R,Bottaro,M,Wilhelm,EN,Wagner,DR,andPinto,
RS. Time course of strength and echo intensity recovery after
resistance exercise in women. J Strength Cond Res 26(9):
2577–2584, 2012—The purpose of this study was to
evaluatethetimecourseresponses of strength, delayed-
onset muscle soreness (DOMS), muscle thickness (MT),
circumference (CIRC), and ultrasonography echo intensity
(EI) after a traditional hypertrophic isoinertial resistance
training session in young women. Ten (22.0 63.2 years)
healthy, untrained volunteers participated in the study. The
resistance exercise session consisted of 4 sets of 10
repetitions at 80% of 1 repetition maximum (1RM) of the
dominant arm elbow flexors. Maximum isometric elbow
flexion peak torque (PT) at 90°, MT, and EI were recorded
for both arms at baseline (PRE), immediately after exercise
(0 hours) and at 24, 48, and 72 hours after exercise. Com-
parisons were made using a 2 35 mixed factor analysis of
variance. There was a significant (p,0.05) loss in PT and
increase in MT at 0, 24, 48, and 72 hours. In contrast, EI
increased only after 24, 48, and 72 hours, not at 0 hours.
There were no significant changes in PT, DOMS, MT, and EI
in the nondominant (control) arm after the exercise protocol.
Our data suggest that after 4 sets of 80% of 1RM of
unilateral elbow flexion resistance exercise, nonresistance
trained women need .72 hours to fully recover muscle
strength,MT,CIRC,andEI.Furthermore,theEIappearsto
be a sensitive and reliable method to assess MD.
KEY WORDS resistance exercise, muscle damage, muscle
thickness
INTRODUCTION
One of the acute variables that determine the
adaptations to strength training is the training
frequency, and this is related to muscular recovery
between training sessions (23,25). Despite the
importance of this variable, the optimal amount of time after
a resistance training session for adequate recovery has not
been well established. Muscular performance recovery
between sessions is directly related to different factors, and
one of these factors is the muscle damage (MD) induced by
the training session (28). Strength training promotes a decrease
in force production immediately after the training session
mainly because of neural and metabolic factors (3,15,20,35).
However, the decrease in strength induced by MD because of
high-volume or high-intensity strength training remains longer
(13,16). This MD leads to important changes, such as (a)
disorganization of sarcomeres occurring mainly in Z lines, (b)
damage to the sarcolemma, (c) damage to the T tubules and
myofibrils (1,2,19,34), (d) increase in muscle soreness, and (d)
increases in levels of blood creatine kinase and potassium
(11,22). Associated with these changes, there is an increase in
muscle thickness (MT) and in the echo intensity (EI) obtained
by ultrasonography (5,15). The EI can be measured from
different intensities of the ultrasound image grayscale.
The EI is a relative new and interesting method and has been
reported in the literature as an indirect marker of MD. The EI
changes related to MD are not usually observed until 24 hours
after the exercise session (21,29–31). On the other hand,
increases in MT and decreases in force production, which are
not because of muscle edema, can be seen immediately after an
exercise session. The increase in MT is mainly because of active
hyperemia, and the decrease in strength is because of neural
and metabolic factors such as a reduction in creatine phosphate
concentration and an increase in inorganic phosphate and
hydrogen ion concentrations (35,41). Thus, EI may be a better
index of MD than the observed changes in MT or strength
during the first 24 hours after an exercise session.
Previous studies used the changes in EI to monitor the
recovery time of strength training sessions (6,14,19). Nosaka
and Newton (28) and Chen et al. (8) observed that even after
96 and 120 hours, respectively, their subjects’ EI had not
Address correspondence to Re
´gis Radaelli, regis.radaelli@hotmail.com.
26(9)/2577–2584
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Ó2012 National Strength and Conditioning Association
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returned to preexercise levels. However, these authors used
maximal eccentric contractions and high volumes in their
protocols, and during a session of conventional isoinertial
strength training, it is more common to perform submaximal
eccentric contractions (26). Furthermore, MD is significantly
dependent on the intensity of the eccentric phase of each
exercise repetition (33). Therefore, these studies may have
overestimated the duration of time that EI is elevated after
a typical strength training session.
Recently, Flores et al. (14) reported that following 8 sets of
10RM resistance exercise, women and men experienced similar
immediate strength loss, but over 4 days, women still had not
recovered the strength and MT to baseline level. These authors
used high-volume strength training for women, and there is
a lack of research on the strength recovery in women using
lower volume conventional isoinertial weight training. Fur-
thermore, the EI technique warrants additional investigation,
especially when applied to strength training sessions that
induce less MD (e.g., submaximal eccentric contractions),
before firmly establishing its sensitivity. Thus, the purpose of
this study was to evaluate the time course responses of strength,
delayed-onset muscle soreness (DOMS), MT, circumference
(CIRC), and analyze the EI responses, after 4 sets of traditional
hypertrophic isoinertial resistance exercise in young women
inexperienced in strength training.
METHODS
Experimental Approach to the Problem
The participants visited the laboratory 6 times. On the first
day of the experiment, the subjects performed a baseline
elbow flexion 1 repetition maximum (1RM) test. For
reliability, the 1RM test was repeated 72 hours later on visit
2. On visit 3, 1 week after the second 1RM test, baseline
measures of peak torque (PT), DOMS, MT, and EI were
taken from the dominant and nondominant elbow flexors. On
the same day (visit 3), the subjects performed a resistance
training session consisting of 4 sets of 10 concentric-eccentric
repetitions at 80% of 1RM of elbow flexion exercise only with
the dominant arm. The dependent variables were assessed at
preexercise (PRE), immediately post (0 hours), 24, 48, and 72
hours after the resistance training protocol. All the measures
were taken on both arms.
Subjects
Ten women (22.7 63.2 years) with no resistance training
experience and no systematic training in the last year were
recruited for the study. The subjects were tested from July
to September. Their weight and height were 52.4 63.2 kg
and 165.5 65.6 cm, respectively. Before participation, each
volunteer read and signed a detailed informed consent form
approved by the University Institutional Review Board
describing the study and its potential risks and benefits.
The subjects were not allowed to perform any vigorous
physical activities or unaccustomed exercises during the
experiment period. The participants were free from any
musculoskeletal disorders and were not taking any medica-
tion or dietary supplements.
Resistance Training Protocol
The resistance training protocol consisted of 4 sets of 10
repetitions of unilateral elbow flexion on a Scott bench
(preacher curl, Sculptor, Porto Alegre, Brazil) with a dumbbell
resistance equal to 80% of each subject’s 1RM and a 3-minute
rest interval between sets (25). To determine each subject’s
concentric after eccentric 1RM, the participants visited the
laboratory 2 times. First, the subjects were familiarized with
the procedures of the study, and the 1RM load was
determined. The subjects returned to the laboratory 72
hours later to repeat their 1RM test. The elbow flexion 1RM
load was determined as the heaviest weight the subject was
able to lift at either test session, using proper technique with
cadence (2 seconds for the concentric phase and 2 seconds
for the eccentric phase) controlled by a metronome (Quartz,
Torrance, CA, USA). The range of motion of the 1RM test
was 10–110°(0°= full elbow extension) and was determined
before the test by a goniometer. The range of motion was
visually controlled by the researchers. Three minutes of rest
was given before each attempt at a higher weight. The 1RM
value was determined within 3–5 trials. The baseline test-
retest intraclass correlation coefficient (ICC) and SEM for the
1RM were 0.93 and 4.5%, respectively.
One week after the second 1RM test, the subjects returned
to the laboratory to perform the resistance training protocol.
The elbow flexion exercises were done with only the
dominant arm while the nondominant arm served as the
control. All the subjects performed the resistance training
protocol with the same cadence and range of motion
described for the 1RM test (6,30).
Peak Torque
Unilateral elbow flexion was assessed on a Cybex NORM
dynamometer (Ronkonkoma, NY, USA). The equipment was
calibrated before the tests according the manufacturer’s
instructions. The subjects were placed in a supine position
with the shoulder of the tested arm abducted 45°, and a velcro
strap was across their arm and chest to minimize compen-
satory movements. Furthermore, the center of rotation of the
dynamometer was aligned with the center of rotation of the
elbow, and the forearm was supinated. The elbow adapter
length was adjusted for each subject, and the participants
were instructed to keep their nontested arm at their side. The
test consisted of three 5-second maximal isometric voluntary
contractions with the elbow flexed at 90°and 3 minutes of
recovery between each effort. The greatest PT among 3
isometric voluntary contractions, provided by Humac 2009
software version 12.17.0 (Humac, Stoughton, MA, USA), was
used for future analyses.
Circumference
To measure the arm CIR, the subjects remained supine with
their arms relaxed at their sides. The CIR was measured with
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a tape measure, 8 cm above the elbow joint (9). The CIR
measurement site was marked with a dermographic pen and
remained visible till the end of the study.
Delayed-Onset Muscle Soreness
Muscle soreness was quantified using the methodology
described by Chen et al. (7,9). The subjects were asked to
indicate their level of muscle soreness on a 100-mm visual
analog scale (0 mm ‘‘no pain’’ and 100 mm ‘‘extreme
pain’’) after full range of flexion and extension at the
elbow. The specific location being assessed for DOMS
was the mark 8 cm above the elbow joint described
previously.
Muscle Thickness and Echo Intensity
The MT and EI were assessed by ultrasonography
according to the same methodology used by other authors
(5,6,28). The images were obtained by B-mode ultraso-
nography (Ultravision Flip plus, Philips, Belo Horizonte,
Brazil). Both images (MT and EI) were obtained at 8 cm
above the elbow joint (8). During the image acquisition, the
subjects remained supine with the tested arm relaxed. The
high resolution with a linear probe of 7.5 MHz was
positioned perpendicular to the evaluated muscles. A
water-based gel was used to promote acoustic contact
without causing excessive probe pressure on the skin
during imaging acquisition. In each image, both biceps
brachii and brachialis MT were identified. The coefficient
of variation was 4.2%, and the baseline test-retest ICC was
0.94. The same image used to assess MT was used to
measure the EI. The EI in each of the elbow flexor muscles
was determined using a 1-cm
2
region, based on a histogram
of gray scale (0: black, 256: white). The EI was quantified
using the Image-J software (version1.37, National Institutes
of Health, Washington, D.C., USA). The test-retest
reliability presented ICC for EI was 0.91, and the coefficient
of variation was 2.2%.
Statistical Analyses
All the values are reported as mean 6SD. Normality of
the distribution for outcome measures was tested using the
Kolmogorov-Smirnov test. After assuming that the sample
was normally distributed (p.0.05), comparisons were
made using a 2 35 (arm [dominant and nondominant] 3
time [Pre, 0, 24, 48, 72 hours]) mixed factor analysis of
variance (ANOVA). When the ANOVA showed a signifi-
cant main effect, Bonferroni post hoc tests were used to
detect differences in the value between bouts. A 2 35
(muscle [biceps brachii and brachialis] 3time [Pre, 0, 24,
48,72hours])wasusedtoanalyzeMTandEIdifferences
between muscles. Dependent variables were PT, DOMS,
CIR, MT, and EI. The ICC for the 1RM test-retest
reliability was also performed. Significance was set at p,
0.05. All analyses were performed with the software SPSS
17.0(IBM,Somers,NY,USA).
Figure 1. Peak torque across time for both arms; #significant difference
(p,0.05) of Pre; †significant difference (p,0.05) between arms.
Figure 2. Circumference across time for both arms; #significant difference
(p,0.05) of Pre; †significant difference (p,0.05) between arms.
Figure 3. Muscle soreness across time for both arms; *significant
difference (p,0.05) of 24 and 48 hours; #significant difference of Pre,
0, 48, and 72 hours; $significant difference of Pre, 0, 24, and 72 hours;
†significant difference (p,0.05) between arms.
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RESULTS
Peak Torque
The PT was significantly lower in the dominant arm at all time
points postresistance exercise when compared with that in the
nondominant arm (Figure 1). In the dominant arm, PT
significantly (p,0.05) decreased between 12 and 16% after the
resistance training protocol (0 hours = 16%; 24 hours = 12%; 48
hours = 14%; 72 hours = 15%). There were no significant (p.
0.05) differences across time in PT for the nondominant arm.
Circumference
The CIR was significantly higher in the dominant arm at all
time points postresistance exercise when compared with that in
the nondominant arm (Figure 2). In the dominant arm, CIR
significantly (p,0.05) increased between 2 and 3% (0 and 24
hours = 2%; 48 and 72 hours = 3%) after the resistance training
protocol. There were no significant (p.0.05) differences
across time in CIR for the nondominant arm.
Muscle Soreness
The DOMS was significantly higher in the dominant arm at 24
and 48 hours when compared with that in the nondominant
arm (Figure 3). In the dominant arm, DOMS significantly (p,
0.05) increased between 31 and 49% (0 hours = 0%; 24 hours =
49%; 48 hours = 31%; 72 hours = 0%) after the resistance
training protocol. There were no significant (p.0.05)
differences across time in DOMS for the nondominant arm.
Figure 4. Change in muscle thickness across time for biceps brachii (A) and brachialis (B); *significant difference (p,0.05) of Pre, 24, 48, 72 hours; #significant
difference of Pre and 0 hours; †significant difference (p,0.05) between arms.
Figure 5. Change in echo intensity across time for biceps brachii (A) and brachialis (B); *significant difference (p,0.05) of 24, 48, 72 hours; #significant
difference of Pre and 0 hours; †significant difference (p,0.05) between arms.
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Muscle Thickness
The biceps brachii MT was significantly higher in the
dominant arm from 0 to 72 hours when compared with that in
the nondominant arm (Figure 4A). In the dominant arm,
biceps brachii MT significantly (p,0.05) increased between
3.6 and 9.9% (0 hours = 9.9%; 24 hours = 5.6%; 48 hours =
5.4%; 72 hours = 3.6%) after the resistance training protocol.
There were no significant (p.0.05) differences across time
in biceps brachii MT for the nondominant arm.
At 0 to 72 hours, the brachialis MT in the dominant arm
was significantly higher (p,0.05) than that in the
nondominant arm (Figure 4B). The increase in the dominant
brachialis MT was between 2.9 and 9.7% (0 hours = 9.7%; 24
hours = 5.6%; 48 hours = 3.8%; 72 hours = 2.9%). There were
no significant (p.0.05) differences across time in brachialis
MT for the nondominant arm. Also, there were no significant
differences (p.0.05) in the MT between biceps brachii and
brachialis after the resistance training protocol.
Echo Intensity
The EI was assessed from both elbow flexor muscles (biceps
brachii and brachialis). The biceps brachii EI was significantly
higher in the dominant arm at 24, 48, and 72 hours when
compared with that in the nondominant arm (Figure 5A). In
the dominant arm, EI significantly (p,0.05) increased
between 6 and 14% (0 hours = 0%; 24 hours = 6%; 48 hours =
11%; 72 hours = 14%) after the resistance training protocol.
There were no significant (p.0.05) differences across time
in EI for the nondominant arm.
At 24, 48, and 72 hours, the brachialis EI was significantly
higher in the dominant arm when compared with that in the
nondominant arm (Figure 5B). In the dominant arm, EI
significantly (p,0.05) increased between 2 and 5% (0 hours =
0%; 24 hours = 2%; 48 hours = 4%; 72 hours = 5%) after the
resistance training protocol. There were no significant (p.
0.05) differences across time in EI for the nondominant arm.
However, a significant difference (p,0.05) in EI was observed
at 24, 48, and 72 hours between biceps brachii and brachialis.
DISCUSSION
The main finding of this study was that the recovery period of
72 hours was not enough time to promote the recovery of
muscle strength, CIR, MT, and EI induced by a protocol of 4
sets of 10 repetitions of elbow flexion at 80% of 1RM in
untrained young women. Also, an important finding was that,
unlike the other dependent variables (PT, CIR, and MT), the
EI from the biceps brachii and brachialis did not change
immediately after the exercise protocol. These findings
showed that EI is a useful tool to indirectly assess MD.
The major consequence of MD is the prolonged reduction
in strength production capacity, and this is one of the most
reproducible indicators of MD (1,3). The decrease in strength
production observed immediately after exercise is not
because of MD but to peripheral (within the muscle) and
central (reduced motor drive) neuromuscular fatigue (13).
For example, Raastad and Halle
´n (33) observed a decline of
22% in electrically evoked force after 50-Hz stimulation, after
high- and moderate-intensity strength exercises of the knee
extensors, indicating that the reduction in performance was
of peripheral origin; however, the authors did not exclude
a central fatigue theory. The reduction in creatine phosphate
concentration and increases in inorganic phosphate and
hydrogen ion concentrations (35,41) are also possible causes
of force reduction immediately after exercise. However, the
prolonged decline in the capacity to produce strength seems
to be a consequence of MD and an impaired excitation-
contraction relationship, in which less Ca
2+
is released from
the sarcoplasmic reticulum by the action potential (21,32,33).
Ingalls et al. (21) noted that an impaired excitation-
contraction relationship was the primary mechanism
associated with prolonged force loss. The 15% reduction in
the ability to produce strength 72 hours after the exercise
protocol observed in our study was lower than that reported
by others (14,27,28,31), probably because of the differences in
the volume and intensity between the exercise protocols.
Because MD is associated with eccentric intensity, the lower
intensity of eccentric contractions and exercise volume of this
study compared with the others better mimic traditional
strength training programs.
The recovery in force production in our results was lower
than in other studies (12,18). Also, this study and others
(17,24) suggest that muscle strength does not recover after 72
hours. Ha
¨kkinen et al. (18) showed that women of various
ages unaccustomed to resistance training experienced an
18.8–30.9% decrease in strength immediately after a lower-
body workout consisting of 5 sets of 10 repetitions with
a 10RM load. They recovered only 94% of their strength 2
days after the workout. Similarly, Logan and Abernethy (24)
observed that 3 days of rest is required to recover strength in
experienced lifters. Therefore, the recovery in strength,
among our and other studies, may be dependent on the
intensity of eccentric contractions, volume, and muscle
groups involved.
Other studies found decreases in force production and
increases in EI (7,29); however, the relationship between
them was not discussed previously in the literature. The
highest increase in EI generally is observed 3–4 days after
exercise (27,29). This study observed the highest value of
biceps brachii and brachialis EI at 72 hours postresistance
exercise. Thus, the increase of EI, which is related to edema
formation (15), might be more predictive of prolonged (e.g.,
72 hours postworkout) rather than immediate performance
decrement, because at 0-hour, muscle fatigue is primarily
responsible for strength loss (35,41).
The increase in CIR, and MT, reinforced that a period of 72
hours was insufficient for the complete MD recovery from the
exercise bout. The increases in C IR and MT are the result of
MD, the inflammatory process, and protein synthesis (9,37).
Thus, for young women untrained in strength, 72 hours was
not a sufficient amount of time to observe a full recovery from
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inflammation induced by the exercise protocol. Muscle
soreness is also widely used as an indirect indicator of MD
(7,10). The soreness peak is generally observed 24–48 hours
after exercise (10) as seen in our results. Also, Nosaka and
Clarkson (27) observed that DOMS was developed 1 to 3
days after exercise, whereas CIR was largest at 4–5 days after
exercise. One cause of this phenomenon might be that the
stimuli for the sensation of muscle soreness may be the
pressure inside the muscle, but swelling itself does not
necessarily cause soreness (4,20). The significant reduction in
DOMS 72 hours postexercise in our study, despite the other
indirect markers of MD remaining elevated, supports other
research studies suggesting that muscle soreness does not
reflect the magnitude of the MD induced by exercise (30,40).
However, at 24 and 48 hours postexercise DOMS peaked
and force production was at its lowest; thus, these data
suggest that DOMS may be a good indirect marker between
24 and 48 hours after exercise.
An increase in EI values has been used as an indicator of
MD after an exercise bout (15,27,31). However, to our
knowledge, this is the first study to use the EI to analyze the
MD induced by a traditional isoinertial resistance training
session. The results showed that the EI was a sensitivity
method to measure MD induced by resistance training. The
increase in EI may be associated with an increase in the
interstitial space between fibers, which results from muscle
swelling or increase in plasma enzyme levels (15). Although it
was not the main objective of the study, it is important to
note that the increase in the EI of the biceps brachii muscle
was greater than the brachialis at 24, 48, and 72 hours
(Figures 5A and B). However, there were no differences in
MT between biceps brachii and brachialis across time after
the exercise protocol. It is important to observe that MT
increased 14% in biceps brachii and only 5% in brachialis.
However, the EI difference between biceps brachii and
brachialis was only 0.2% (9.9 vs. 9.7%). These findings draw
attention to the sensitivity of the EI measurement.
Furthermore, the differences between these 2 muscles in
muscle architecture and activation may have caused this
difference in the magnitude of EI increases. Allen et al. (2)
observed that the biceps brachii has a greater activation in
relation to the brachialis during elbow flexion, a fact that may
have contributed to this difference in this indirect marker of
MD. However, further studies are needed to better clarify
these differences in MD between the biceps brachii and
brachialis muscles after bouts of elbow flexion. Also, an
important finding from this study is that EI at 0 hours does
not change, and MT and CIR significantly changed at
0 hours. The increase in MT and CIR at 0 hours is mainly
related to the active hyperemia and not to the MD. Active
hyperemia is the increase in organ blood flow (hyperemia)
that is associated with increased metabolic activity of
a muscle contraction. However, the increase in EI is not
related to hyperemia, rather it is likely associated with
inflammatory responses. Fujikake et al. (15) noted that the
increase in EI was not caused by infiltration of inflammatory
cells; however, in this same study, the authors demonstrated
that the inflammation responses such as edema might be
associated with increases in the EI at 24 and 48 hours. The
increase at 72 hours after the exercise might be associated
with the production of new connective tissue (27). Thus,
these results showed that EI may be a better index of MD
than MTor CIR because active hyperemia does not influence
the EI measurements (36).
Regarding the period of recovery between exercise bouts,
the results of our study confirm the information that sessions
that include eccentric contractions may require a period of at
least 72 hours for muscle recovery (23). The fact that
impairments in neuromuscular function were still observed
72 hours after a protocol of conventional strength training
may have important implications in the next session of
training. Because of the temporary decrease in the ability to
produce strength, the subject may not be able to accomplish
the total volume estimated for the session, and this variable
has an important influence on neuromuscular adaptations
(23,39,40). In a longitudinal study, Ha
¨kkinen et al. (18) found
that women who underwent training sessions 3 times a week
showed smaller increases in muscle strength than those
subjected to it twice per week. These authors explained that
the results were obtained possibly because of incomplete
muscle recovery between training sessions in the high-
frequency group. Thus, based on the findings of Ha
¨kkinen
et al. (18) and the results of this study, women unaccustomed
to resistance training should wait at least 72 hours before
starting the next training session for the same muscle group.
A limitation of this study is that we did not control for the
subjects’ menstrual cycle. The literature suggests that estro-
gen has a protective function in the muscle cell membrane to
the damage induced by exercise (38). Thus, different stages in
the menstrual cycle may have influenced the magnitude of
damage and recovery.
In conclusion, 72 hours of recovery after a protocol of
conventional strength training was not sufficient to promote
a complete recovery of elbow flexor muscles of young women
unaccustomed to strength training. The results highlight the
need for adequate control of the recovery period between
sessions, especially during initial training. Also, we found that
EI, assessed by ultrasonography, is a sensitivity and reliable
measurement of MD induced by a traditional resistance
exercise protocol.
PRACTICAL APPLICATIONS
The recovery time between resistance training sessions is one
important variable that should be controlled in periodized
training programs, and a well-planned training program
should consider complete muscular recovery before begin-
ning the next training session for the same muscle group.
Therefore, according to our results, the exercise technicians
or strength coaches should wait at least 3 days before starting
the next training session of the same muscle group during the
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first weeks of training to ensure adequate recovery in novice
lifters. Furthermore, because portable ultrasound is gaining
popularity and becoming more accessible, and the EI
measurement technique is relatively easy, EI assessments
can help strength and conditioning coaches to better monitor
recovery among training sessions.
ACKNOWLEDGMENTS
The authors thank the anonymous reviewers for their
insightful comments in the formulation of this article.
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