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There is a paucity of data on how manipulating joint angles during isolation exercises may impact overall session muscle activation and volume load in resistance-trained individuals. We investigated the acute effects of varying glenohumeral joint angle on the biceps brachii with a crossover repeated measure design with three di↵erent biceps curls. One session served as the positive control (CON), which subjects performed 9 sets of bicep curls with their shoulder in a neutral position. The experimental condition (VAR), varied the glenohumeral joint angle by performing 3 sets in shoulder extension (30), 3 sets neutral (0), and 3 sets in flexion (90). Volume load and muscle activation (EMG) were recorded during the training sessions. Muscle swelling and strain were assessed via muscle thickness and echo-intensity responses at pre, post, 24 h, 48 h, and 72 h. There were no significant di↵erences between conditions for most dependent variables. However, the overall session EMG amplitude was significantly higher (p = 0.0001) in VAR compared to CON condition (95%-CI: 8.4% to 23.3%). Our findings suggest that varying joint angles during resistance training (RT) may enhance total muscle activation without negatively affecting volume load within a training session in resistance-trained individuals.
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sports
Article
The Eects of Varying Glenohumeral Joint Angle on
Acute Volume Load, Muscle Activation, Swelling,
and Echo-Intensity on the Biceps Brachii in
Resistance-Trained Individuals
Christopher Barakat 1, Renato Barroso 2, Michael Alvarez 1, Jacob Rauch 1, Nicholas Miller 1,
Anton Bou-Sliman 1and Eduardo O. De Souza 1,*
1Department of Health Science and Human Performance, University of Tampa, Tampa, FL 33606, USA
2School of Physical Education, University of Campinas, Campinas 13083-851, Brazil
*Correspondence: edesouza@ut.edu
Received: 2 August 2019; Accepted: 2 September 2019; Published: 4 September 2019
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Abstract:
There is a paucity of data on how manipulating joint angles during isolation exercises
may impact overall session muscle activation and volume load in resistance-trained individuals.
We investigated the acute eects of varying glenohumeral joint angle on the biceps brachii with
a crossover repeated measure design with three dierent biceps curls. One session served as the
positive control (CON), which subjects performed 9 sets of bicep curls with their shoulder in a neutral
position. The experimental condition (VAR), varied the glenohumeral joint angle by performing
3 sets in shoulder extension (30
), 3 sets neutral (0
), and 3 sets in flexion (90
). Volume load and
muscle activation (EMG) were recorded during the training sessions. Muscle swelling and strain
were assessed via muscle thickness and echo-intensity responses at pre, post, 24 h, 48 h, and 72 h.
There were no significant dierences between conditions for most dependent variables. However,
the overall session EMG amplitude was significantly higher (p =0.0001) in VAR compared to CON
condition (95%-CI: 8.4% to 23.3%). Our findings suggest that varying joint angles during resistance
training (RT) may enhance total muscle activation without negatively aecting volume load within a
training session in resistance-trained individuals.
Keywords:
muscle length-tension relationship; bodybuilding; exercise selection; echo-intensity;
muscle strain
1. Introduction
Physique athletes such as bodybuilders are primarily focused on maximizing muscle hypertrophy
for their sport [
1
]. The literature implies that resistance training is the most eective method to increase
muscle hypertrophy [
2
5
]. In addition, many RT variables (i.e. intensity, volume, exercise selection,
joint angle, tempo) influence the acute responses [
6
,
7
]. Thus, coaches and athletes intentionally
manipulate RT-variables within a session in order to optimize the session stimulus as well as training
adaptations [1,8].
In this regard, recent evidence suggests that mechanical tension plays the greatest mechanistic role
for muscle hypertrophy [
3
]. One objective variable that indirectly quantifies mechanical tension within
a session is the volume load (sets
reps
load kg). While there is some controversy [
9
,
10
], it has
been suggested that producing greater training volumes per session would optimize muscle mass
accrual [
5
,
11
]. Additionally, the literature also suggests that other factors associated with metabolic
stress (i.e. swelling, lactic acid accumulation) might impact skeletal muscle growth [
2
,
3
]. Furthermore,
muscle activation is another key factor suggested to promote skeletal muscle adaptations [
2
,
8
,
12
14
].
Sports 2019,7, 204; doi:10.3390/sports7090204 www.mdpi.com/journal/sports
Sports 2019,7, 204 2 of 11
Muscle activation is often analyzed by surface electromyography (EMG) and the data proposes the
greater EMG amplitudes, the greater the motor unit recruitment [
15
]. Additionally, several acute
variables may impact how muscle is activated during a RT session [
15
17
]. For example, relative
intensity (% of one-repetition maximum (1RM)), total volume, rest intervals, and even joint angle aect
muscle activation [15,16,18,19].
Interestingly, manipulating joint angle and RT at dierent muscle lengths has been shown to
impact the acute responses associated with EMG and metabolic responses [
7
,
19
21
]. Altering joint
angles influences the muscle length-tension relationship, thus aecting its ability to actively produce
force [
13
,
19
,
22
,
23
]. Furthermore, overloading a muscle in its lengthened position will lead to an
inecient actin–myosin coupling (decreasing force output) while increasing the amount of strain and
damage produced [
7
,
21
,
23
,
24
]. Nosaka et al. [
7
] reported significant increases in muscle damage and
subjective soreness levels when training the elbow flexors at long muscle lengths compared to short
muscle lengths in untrained individuals. While previous studies have investigated how the elbow
joint angle and muscle length changes impact muscle activation [
19
,
22
,
25
,
26
], these studies had the
shoulder joint in a fixed position (i.e., often flexed to 45 or 90 degrees using an isokinetic dynamometer),
with minimal data on how glenohumeral angle would aect muscle activation of the biceps.
Only one study has investigated the eects of varying glenohumeral angles on muscle activation of
the biceps. Oliveira et al. [
18
] reported dierences in muscle activation of the biceps brachii in three RT
exercises (e.g., incline dumbbell curl, standing dumbbell curl, dumbbell preacher curl). However, the
use of dierent dumbbell exercises may have limited our understating on how varying glenohumeral
joint angles would impact biceps brachii activation. For example, they reported the least amount of
muscle activation when the elbow is fully flexed during the dumbbell preacher curl. This was likely due
to the vertical force of the dumbbell and its inability to produce torque in that position of that particular
exercise, not because of the glenohumeral joint angle. Therefore, the muscle activation dierences
reported would be explained by the variation in the resistance profile between those free-weight
exercises rather than the variation in shoulder angle per se. While the aforementioned study provided
insight on dierences in muscle activation with dierent exercises, the eects of varying joint angles
are not fully understood.
More recently, Marcolin et al. [
27
] examined dierences in muscle activation of the biceps
brachii and brachioradialis while performing three forearm variants of curl (dumbbell, EZ bar, and
straight bar) in resistance-trained individuals. They found dierences in activation between all three
exercises, with the EZ bar producing the greatest muscle activation on the biceps brachii even though
glenohumeral joint angle was unchanged (0 degrees) between the three forearm variants. So, although
dierences in muscle activation are clearly multifactorial, it has not been investigated how varying joint
angles throughout a training session would impact total muscle activation compared to an exercise
utilizing a single joint angle. Yet, there is a paucity of data that examines how manipulating the joint
angle through greater exercise variation aects session volume load, and metabolic stress factors in
resistance-trained individuals.
Therefore, the purpose of our study was to investigate how altering glenohumeral joint angle
would aect session volume load, muscle activation, swelling and strain of the biceps brachii in
resistance-trained individuals. We hypothesized that varying glenohumeral positions would enhance
the acute training response by increasing total muscle activation and inducing more strain on the biceps.
2. Materials and Methods
2.1. Experimental Design
This was a randomized crossover repeated measures design, which investigated the eects of
altering glenohumeral joint angle with three dierent cable bicep curls (Free Motion, Logan, UT, USA)
on session volume load, muscle activation, acute muscle swelling, and echo-intensity. One session
served as a positive control (CON) in which all nine working sets of elbow flexion were performed with
Sports 2019,7, 204 3 of 11
the shoulder in the neutral position (0
). In the experimental session (VAR), participants performed
three sets of elbow flexion in three dierent glenohumeral joint positions (-30
,0
, 90
), (Figure 1). The
order in which the subjects performed each biceps curl variation was randomized. Each experimental
session started with a 10 RM load that was predetermined and assessed during the familiarization
sessions. Rest intervals between sets (60 s) and repetition tempo (2:2) were held constant amongst
both conditions. Volume load (i.e., sets
reps
load (kg)) was assessed for each session to examine if
altering glenohumeral joint angle would impact total work output. Muscle activation was measured
through surface electromyography (EMG). Acute muscle thickness and echo-intensity were measured
via ultrasound at rest/pre, immediately post, 24 h, 48 h, and 72 h after the training. Measurements
were performed on the dominant arm and sessions were interspersed by one week and the subjects
performed the remaining condition (e.g., CON or VAR).
Figure 1.
Glenohumeral joint angles—(
A
) -30
extension, lengthened; (
B
)0
, neutral; (
C
) 90
flexion,
shortened. Please confirm which form of degree you want to use: degree or the unit “
” and please use
the same form for unification in the main text.
2.2. Subjects
Eleven subjects (5 males, 6 females) college students volunteered for this study (age:
21 ±1.47 years
,
height: 166.8
±
7.1 cm, body mass: 66.6
±
10.4 kg, resistance training experience: 4.7
±
1.91 years,
10 RM: 9.3
±
3.1 kg). Inclusion criteria consisted of having at least 1 year of RT experience (defined as a
minimum of three RT sessions per week) for males and females between the ages of 18–30. Subjects were
excluded from participation if they were currently taking any medications, anti-inflammatory drugs,
or had a history of drug abuse. All subjects reported no previous history of neck or upper extremity
injury, and no surgical history. This study was approved by the university research ethics committee.
All subjects read and willingly signed informed consent form by the Institutional Review Board.
2.3. Familiarization
Prior to data collection, each subject’s dominant arm was identified. All subjects performed
three familiarization sessions interspersed by 72 h prior to the commencement of the study. During
familiarization sessions, subjects underwent 10-repetition maximum (10 RM) testing bilaterally on the
cable bicep curl exercise in three dierent glenohumeral angles. The three-glenohumeral joint angles
were shortened (flexion to 90
), neutral (0
), and lengthened (
30
). Each position was measured with
a goniometer (Baseline
®
Evaluation Instruments, White Plains, NY, USA) by a certified athletic trainer
and glenohumeral joint angle was maintained throughout the entire set without artificial stabilization.
Subjects exercise execution was strictly enforced and visually monitored by the researchers throughout
the training session to avoid possible cheating. Testing consisted of three separate 10-RM strength
assessments, one for each glenohumeral angle as described above.
Sports 2019,7, 204 4 of 11
2.4. Experimental Sessions
Subjects underwent two dierent training sessions interspersed by one week. Each session
consisted of 9 working sets of cable biceps curls with one session serving as the positive control (CON)
and one serving as the experimental session (VAR). During the CON session, subjects were instructed
to maintain a neutral shoulder position (0 degrees) for the entire session. With the shoulder at 0 degree
and the elbow at 90 degrees, subjects started the session with a 5-s maximum voluntary isometric
contraction (MVIC) for elbow flexion and then rested for 60 seconds before performing one warm-up
set of 10 repetitions with 50% of their 10 RM load which was determined during their familiarization
sessions. This MVIC and submaximal set was performed as a means to normalize the EMG data.
From there, subjects performed their first working set with their 10 RM. Repetition cadence was held
constant throughout the session with a 2-s concentric and 2-s eccentric controlled by a metronome
(EUMLab, Xanin Tech, Hangzhou, China). Subjects rested for 60-s in between sets. As fatigue set in and
subjects could no longer complete 10-repetitions their load was reduced on the subsequent set to keep
them within an 8–10 repetition range while performing each set at maximum intensity (e.g., 8–10 RM).
During the VAR session, subjects started oeach position with an MVIC and submaximal set (50% of
their 10 RM). Thereafter, they performed three working sets in each angle at maximum intensity with
the same repetition cadence and rest interval (60-s) as the positive control (CON). A certified strength
and conditioning specialist and a certified athletic trainer were providing verbal encouragement and
ensuring proper exercise execution throughout the duration of the study.
2.5. Overall Session EMG
Muscle activation (EMG) was recorded using a 16-channel electromyography system (Trigno,
Delsys, Boston, MA, USA) with an acquisition frequency of 2000 Hz and a hardware band-pass filter of
20–450 Hz. The skin area was shaved, abraded, and cleaned with an isopropyl alcohol pad to reduce
skin impedance before electrode placement. One active bar wireless electrode (10 mm center to center,
size: 27
37
13 mm, weight: 14 g, Trigno, Delsys, Boston, MA, USA) was placed on each subject’s
dominant arm at the mid-belly mark (37.5%) of the biceps (Figure 2). The electrode was positioned
parallel to the presumed orientation of the muscle fibers. The position of each electrode during the
first session was marked on the skin with a henna tattoo. EMG signals were acquired in bipolar
mode. In order to normalize the EMG data, a maximum voluntary isometric contraction (MVIC) was
performed at each shoulder position followed by a submaximal set (50% 10 RM) before starting the
experimental working sets in that position. We determined maximal muscle activation during the
MVIC selecting a 500 ms window in which EMG values were maximal. In addition, as there is high
between day variations in EMG, this procedure was performed on each session, therefore our EMG
was expressed as the percentage of the maximal activation on each experimental session. The raw
electromyography signals were digitally filtered (4th order Butterworth, band pass 20–500 Hz) and
converted to root mean square (RMS). For the dynamic contractions, RMS was calculated for the entire
set and normalized by the highest values obtained during the isometric contraction in 500 ms windows.
Average EMG data was calculated for the entire session (i.e., overall session EMG).
Sports 2019,7, 204 5 of 11
Figure 2.
Mid-belly (37.5%) location site utilized for electrode placement, muscle thickness, and
echo-intensity assessments.
2.6. Muscle Thickness
Ultrasonography (GE LOGIQ, General Electric Company, Fairfield, CT, USA) was used to assess
muscle thickness (MT) of the elbow flexors of each subject’s dominant arm using a linear array probe
(GE LOGIQ, General Electric Company, Fairfield, CT, USA) with a frequency of 8.0 MHz. To obtain
b-mode images, subject laid supine in anatomical position, with their shoulder in external rotation and
forearm supinated. The ultrasound probe was applied perpendicularly to the skin for measurement.
A water-soluble gel (AQUASONIC
®
100, Parker Laboratories, Inc., Fairfield, NJ, USA) was used on
the transducer to aid acoustic coupling and remove the need for excess contact pressure on the skin.
MT was defined as the distance between the interface of the muscle tissue and subcutaneous fat to the
humerus. Two dierent areas were measured at 25% (distal) and 37.5% (mid-belly) of distance from the
olecranon to the acromioclavicular joint. MT was assessed at rest/pre, immediately post, 24 h, 48 h, and
72 h post after exercise in order to assess changes in muscle swelling. To increase test-retest consistency,
each site was marked with henna. To further ensure accuracy of the MT assessments, at least 3 images
were obtained for each site. The median of the 3 assessments was used for statistical analysis. The
coecient of variation (CV) was determined prior to the start of the study using five dierent subjects
with similar characteristics to those in the study. The CV for muscle thickness assessments was 1.3%.
The same-blinded researchers performed sonography an all assessments.
2.7. Echo Intensity
The echo intensity was measured using the same ultrasound device, probe, and standardizations
already described. The echo intensity was determined by gray-scale analysis using the standard
histogram function in Image-J (National Institute of Health, Laboratory for Optical and Computational
Instrumentation, Madison, WI, USA, version 1.37). A region of interest (ROI) was chosen in each
scan to include as much muscle as possible without any bone or fascia. The echo intensity in the
region of interest was expressed in values between 0 and 256 (0: black; 256: white). Similar to the MT
assessments, echo intensity analysis was performed at rest/pre, immediately post, 24 h, 48 h, and 72 h
post session. For the echo intensity, the same-blinded experienced researcher analyzed all ultrasound
images. Echo intensity of the biceps brachii was assessed to examine potential regional dierences in
fluid accumulation, strain, and potential muscle damage across conditions.
Sports 2019,7, 204 6 of 11
2.8. Statistical Analysis
Shapiro–Wilk testing confirmed that dependent variables were normally distributed. An analysis
of variance (ANOVA) with repeated-measures was used to scrutinize the eects of varying glenohumeral
joint angle on acute muscle thickness and echo intensity assuming condition (i.e., control and varying)
and time (i.e., pre, post, 24 h, 48 h, and 72 h) as fixed factors. Whenever, a significant F-ratio
was obtained, a post-hoc test with a Tukey
´
s adjustment was performed for multiple comparisons
purposes. A paired T-test was used to compare the eects of conditions on volume load and overall
session EMG. The significance level was previously set at p <0.05. The 95% confidence intervals
(95%-CI) were presented for the significant comparisons. The GraphPad Prism 8
®
was used to perform
statistical analyses.
3. Results
3.1. Volume Load and Overall Session EMG
There were no significant dierences in volume load between VAR and CON conditions (VAR:
596 kg
±
170 kg vs. CON 606 kg
±
175 kg, p =0.59), Figure 3A. On the other hand, the overall session
EMG amplitude was significantly higher (p =0.0001) in VAR compared to CON condition (95%-CI:
8.4% to 23.3%), Figure 3B.
Figure 3.
Total session volume load (
A
) and overall session surface electromyography (root mean
square % of maximum isometric voluntary contraction) (B).
3.2. Muscle Swelling and Echo Intensity
For mid-belly muscle swelling, there was a main time eect (p =0.0001) indicating that muscle
swelling was greater at post compared to baseline (95%-CI: 0.35 to 0.56 cm). In addition, ES analysis
revealed moderate acute eects for both VAR and CON conditions (ES: 0.54 and 0.43), respectively.
The muscle swelling returned to baseline 24 h post similarly across conditions. For distal muscle
swelling, there was a significant main time eect (p =0.0001) indicating that muscle swelling was
greater at post compared to baseline (95%-CI: 0.33 to 0.52 cm). In addition, ES analysis revealed
moderate acute eects for both VAR and CON conditions (ES: 0.41 and 0.61), respectively. The muscle
swelling returned to baseline 24 h post similarly across conditions. The individual responses for
changes at the 25% (distal) and 37.5% (mid-belly) landmarks from pre to post, 24, 48, and 72 h workout
are presented in Figure 4.
For mid-belly echo intensity (MBEI), there was a significant main time eect (p =0.0001) indicating
that EI was greater at post compared to baseline (95%-CI: 5.67 to 26.05 A.U). In addition, ES analysis
revealed larger eects for both VAR and CON conditions (ES; 1.49 and 1.24), respectively. The MBEI
returned to baseline 24 h post similarly across conditions. For distal echo-intensity (DEI), there was a
significant main time eect (p =0.0001) indicating that EI was greater at post compared to baseline
(95%-CI: 4.69 to 22.29 A.U). However, ES analysis suggests that magnitude of eect was larger in the
Sports 2019,7, 204 7 of 11
VAR when compared to CON condition (ES; 1.04 vs. 0.60), respectively. The EI returned to baseline
24 h post similarly across conditions. The individual responses for changes at the 25% (distal) and
37.5% (mid-belly) landmarks from pre to post, 24, 48, and 72 h workout are presented in Figure 5.
Figure 4.
Muscle thickness (i.e., swelling) individual responses for changes at the 25% (distal) and
37.5% (mid-belly) landmarks from pre to post, 24, 48, and 72 h workout.
Figure 5.
Echo-intensity individual responses for changes at the 25% (distal) and 37.5% (mid-belly)
landmarks from pre to post, 24, 48, and 72 h workout.
Sports 2019,7, 204 8 of 11
4. Discussion
The purpose of our study was to investigate how altering glenohumeral joint angle would aect
session volume load, muscle activation, acute swelling, and echo-intensity of the biceps brachii in
resistance-trained individuals. We partially confirmed our hypothesis as our main findings indicate
that varying glenohumeral joint angles increased muscle activation without impacting total volume
load compared to the control condition. Additionally, the magnitude of eect for echo-intensity at
the 25% (distal) biceps suggests a greater response immediately post-workout in the VAR condition.
However, both conditions responded similarly and returned to baseline levels 24 h post. Furthermore,
there was a similar response between conditions regarding acute muscle swelling.
4.1. Volume Load and Overall Session EMG
Research has suggested a dose response relationship between training volume load and increases
in muscle mass [
10
,
11
,
28
,
29
]. However, it is noteworthy to mention that there is no study comparing
the eects of altering joint angles on session volume load. Therefore, it is dicult to compare our
study to current literature. In this acute study, both conditions demonstrated similar volume load (e.g.,
VAR: 596 kg
±
170 kg, CON 606 kg
±
175 kg, p =0.59) working at the same intensity. Although it is
understood that altering the muscle lengths can impact its ability to produce force [
13
,
23
], our data
suggest that trained individuals can maintain volume loads across greater joint angle variety with
isolation movements (e.g. elbow flexion) within a training session.
Interestingly, despite similar volume load, overall session EMG was dierent between conditions.
Our results demonstrated that VAR condition produced greater total muscle activation compared to
CON (e.g., 95%-CI: 8.4% to 23.3%, p =0.0001). This data highlights potential dierences between
internal work demands (muscle activation) and external work (volume load). Although it is well
established in the literature that dierences in muscle length influences motor unit recruitment and
muscle activity [
30
,
31
], the findings are contradictory [
19
,
25
,
32
,
33
]. Thus, making our findings quite
dicult to reconcile. However, our data suggest there is an acute benefit to varying glenohumeral joint
angle when performing biceps curls. Therefore, further research is required to determine whether or
not these dierences in acute muscle activation would enhance chronic adaptations (i.e., muscular
hypertrophy and strength).
4.2. Muscle Swelling and Echo Intensity
Acute muscle swelling and echo intensity were used as markers of metabolic stress and muscle
strain [
6
]. Regarding acute muscle swelling we reported an average (~12.2%) which corroborates
with previous research that demonstrated ~13.5–15.0% increase in muscle swelling in strength-trained
individuals [
16
,
34
]. However, the acute muscle swelling returned to the baseline 24 h post the training
session. Our findings partially agree with Nosaka et al. [
7
] findings regarding muscle swelling and
damage. Utilizing both circumference measurements and muscle thickness (i.e., swelling) assessments,
they reported a significant main time eect from pre to post in both regions (mid-belly and distally).
However, they reported larger increases distally, whereas we observed similar changes at both regions
between conditions. Contrary to our findings, their muscle swelling did not return to baseline 24 h
post and remained elevated. They reported the greatest increase in swelling 72 h post exercise in
the distal region for their lengthened condition. Our conflicting results are due to the dierences in
subject population. Their subjects were described as nonathletes and not involved in regular RT (i.e.,
untrained). Whereas we investigated resistance-trained individuals with an average of 4.7 years of
RT experience. It is well understood that well-trained individuals have significantly greater recovery
capabilities compared to untrained [
35
]. For example, Newton et al. [
35
] observed significantly greater
recovery on makers of muscle damage in trained subjects compared to untrained undergoing RT of the
elbow flexors.
Sports 2019,7, 204 9 of 11
In regards to echo-intensity, while we found a main time eect for both conditions from pre/rest
to immediately post workout at both sites of the biceps (MBEI, DEI), echo-intensity was back to
baseline 24 h post. Distally (DEI) the eect size analyses suggested that VAR condition produced
more strain compared to CON (ES; 1.04 vs. 0.60). Previously, Nosaka et al. [
7
] reported significantly
greater echo-intensity and plasma creatine kinase in their lengthened condition. Perhaps, their data
shines light as to why this present study VAR condition demonstrated a larger magnitude of eect
for DEI, as this condition performed three working sets in a lengthened position for the long head
of the biceps (
30 degrees glenohumeral extension) that CON did not. However, it is noteworthy to
mention that while previous studies have demonstrated that training in a lengthened position produced
greater muscle damage, these investigations were in untrained individuals [
21
,
35
,
36
]. Our findings
only suggest that exercising in a lengthened position places more strain during exercise leading
to increases in echo-intensity immediately after the training session. However, more research is
warranted to determine if exercising in a lengthened position would translate to better adaptations
in resistance-trained-individuals.
4.3. Limitations
Our study has several limitations that need to be addressed. 1) EMG data can be influenced
by multiple factors (i.e., subcutaneous tissue, spatial filter transfer function, innervation zone (IZ),
electrode placement, etc.) and must be taken with caution [
37
]. 2) In particular, dynamic contractions
in fusiform muscles (i.e., biceps brachii) are very dicult to study as any observed changes may be due
to either muscle activation or the geometry of the electrode-muscle system (i.e., muscle lengthening
or shortening, fiber overlap) [
38
] Additionally, during the concentric contraction of the biceps, the IZ
shifts upwards, moving underneath the electrode, thus impacting amplitude values. 3) Our electrode
placement may not have been optimal [
38
] as our mid-belly (37.5%) anatomical landmark frame (ALF)
was determined based on the distance from the acromion to the olecranon and not the distance between
the acromion and distal insertion of the biceps brachii. Moreover, the optimal electrode site for the
short head and the long head of the biceps brachii has been identified as 61% and 62% of the ALF,
respectively, where ours was placed on the muscle belly at 62.5% of our ALF for consistency sake
between multiple assessments (EMG, muscle swelling, and echo-intensity). 4) We did not assess
perceptual measures (i.e. RPE) between conditions to monitor potential exertion dierences. 5) We
did not evaluate the subject’s perceived soreness throughout the recovery period. 6) We had a small
sample size (n =11). 7) Lastly, this was an acute study. Further research is needed to examine the
chronic eects of varying joint angles and its eects on RT-induced adaptations.
5. Conclusions
In conclusion, our findings suggest that varying joint angles during RT may enhance total
muscle activation and can potentially induce more strain without negatively aecting volume load
within a training session in resistance-trained individuals. From a practical application standpoint,
resistance-trained subjects or bodybuilders trying to maximize the training stimulus of each session
should utilize multiple exercises that vary joint angles. This may lead to a greater internal stimulus
(muscle activation) while performing the same amount of total work (volume). However, we cannot
draw conclusions on how this may influence chronic adaptations, as this was an acute study.
Author Contributions:
Conceptualization, C.B., M.A., and E.O.D.S.; methodology, C.B., M.A., and E.O.D.S.;
validation, E.O.D.S.; formal analysis, R.B., E.O.D.S.; investigation, C.B., M.A., J.R., N.M., A.B.-S.; data curation,
C.B., M.A., J.R., N.M., R.B.; writing—original draft preparation, C.B., M.A., J.R., E.O.D.S.; writing—review and
editing, C.B., M.A., J.R., N.M., A.B.-S., R.B., E.O.D.S.; visualization, C.B., M.A.; supervision, M.A., J.R., N.M.,
A.B.-S.; project administration, C.B., E.O.D.S.
Funding: This research received no external funding.
Conflicts of Interest: The authors declare no conflict of interest.
Sports 2019,7, 204 10 of 11
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©
2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
... From a theoretical point of view, three possible reasons are proposed for explaining the non-homogeneous hypertrophy of a muscle: a) a difference in muscular activation the across muscle length [12], b) a variation in relative intensity on the muscle tissue during dynamic movement due to change in velocity and mechanical advantage [13], and c) a passive tension and active insufficiency of biarticular muscles [14]. Besides, given that different exercises lead to distinct stimuli along the muscle length [7][8][9][10], alternating or varying the choice of the exercises seems a good alternative to stimulate various muscle sites. ...
... Unlike the N-VAR group, the VAR group showed significant MT increases of the proximal elbow flexors and the middle lateral thigh sites. These findings may be explained by the sum of some factors, including muscle morphology, the position of the joints involved in performing the exercises, and range of motion [8,14,22]. ...
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The study aimed to compare the effect of performing the same or different exercises for a muscle group on resistance training (RT) sessions on muscle hypertrophy at different sites along muscle length. Twenty-two detrained men (23.3 ± 4.1 years) were randomly allocated to the following groups: a group that performed the same exercises in all training sessions (N-VAR = 11) or one that varied the exercises for the same muscle groups (VAR = 11). All were submitted to 3 weekly sessions for nine weeks. Muscle thickness was assessed at the proximal, middle, and distal sites of the lateral and anterior thigh, elbow flexors, and extensors by B-mode ultrasound. The VAR group significantly increased all the sites analyzed (P < 0.05). Furthermore, the proximal site of the lateral thigh showed a larger relative increase when compared to the middle site (P < 0.05). In contrast, the N-VAR group were not revealed significant improvements only for the middle site of the lateral thigh and the proximal site of the elbow flexors (P > 0.05). Our results suggest that to perform different resistance exercises can induce hypertrophy of all sites assessed in detrained young men.
... Optimization method has been a concern of many researchers to investigate the musculoskeletal system and estimate muscle forces [1][2][3][4][5] which is usually used to statically or dynamically minimize specific objective function using particular design variables. Static optimization method has much lower computational cost than dynamic optimization method, maybe for this reason, many researches use static optimization method [5][6][7][8][9][10][11][12] Hence, optimization technique is required to estimate muscle forces because of musculoskeletal system redundancy [1][2][3][4]. Many studies have been done utilizing static optimization criteria where they used muscle forces as design variables spanning different joints [1,10,[13][14][15][16]. ...
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Purpose: To compare the effects of different resistance training volumes on muscle performance and hypertrophy in trained men. Methods: 37 volunteers performed resistance training for 24 weeks, divided into groups that performed five (G5), 10 (G10), 15 (G15) and 20 (G20) sets per muscle group per week. Ten repetition maximum (10RM) tests were performed for the bench press, lat pull down, 45º leg press, and stiff legged deadlift. Muscle thickness (MT) was measured using ultrasound at biceps brachii, triceps brachii, pectoralis major, quadriceps femoris and gluteus maximus. All measurements were performed at the beginning (pre) and after 12 (mid) and 24 weeks (post). Results: All groups showed significant increases in all 10RM tests and MT measures after 12 and 24 weeks when compared to pre (p <0.05). There were no significant differences in any 10RM test or changes between G5 and G10 after 12 and 24 weeks. G5 and G10 showed significantly greater increases for 10RM than G15 and G20 for most exercises at 12 and 24 weeks. There were no group by time interaction for any MT measure. Conclusions: The results bring evidence of an inverted "U shaped" curve for the dose response curve for muscle strength. Whilst the same trend was noted for muscle hypertrophy, the results did not reach significance. Five to 10 sets per week might be sufficient for bringing about optimal gains in muscle size and strength in trained men over a 24-week period.