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The Muscle Pump: Potential Mechanisms and Applications for Enhancing Hypertrophic Adaptations


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Cellular swelling, often referred to as "the pump," has been shown to mediate increases in muscle protein synthesis and decreased protein degradation. This paper will explore the potential hypertrophic benefits associated with the pump and discuss practical implications for resistance training program design.
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One on One
The One-On-One Column provides scientifically
supported, practical information for pers onal trainers
who work with apparently healthy individuals or
medically-cleared special populations.
The Muscle Pump:
Potential Mechanisms
and Applications for
Enhancing Hypertrophic
Brad J. Schoenfeld, MSc, CSCS, CSPS, NSCA-CPT
and Bret Contreras, MA
Department of Health Sciences, Program of Exercise Science, City University of New York, Lehman College, New
York, New York; and
Department of Sport Performance, Auckland University of Technology, Auckland, New Zealand
esistance exercise has been
shown to induce acute altera-
tions of intra- and extracellular
water balance (36), the extent of which
is dependent on the type of exercise
and intensity of training. The model
for these changes in fluid balance has
been described as such: During intense
muscular contractions, the veins taking
blood out of working muscles are com-
pressed, whereas arteries continue to
deliver blood into the working muscles,
thereby creating an increased concen-
tration of intramuscular blood plasma.
This causes plasma to seep out of the
capillaries and into the interstitial
spaces. The buildup of fluid in the
interstitial spaces brings about an extra-
cellular pressure gradient, which trig-
gers a flow of plasma back into the
muscle (i.e., reactive hyperemia) (34).
This enhanced reperfusion results in
a phenomenon commonly referred to
by sports scientists as “cellular swell-
ing” and by bodybuilders as “the
pump,” whereby muscles become en-
gorged with blood. The pump is mag-
nified by resistance exercise that relies
heavily on anaerobic glycolysis, partic-
ularly “bodybuilding-style training”
that involves moderate to higher repe-
titions with limited rest intervals (35).
Such exercise results in a substantial
accumulation of metabolic byproducts
including lactate and inorganic phos-
phate, which in turn function as osmo-
lytes and thereby draw additional fluid
into the cell (8,37).
T he pump is generally thought to be
a temporary phenomenon. Bodybuilders
“pump up” by performing high repetition
sets immediately before a competition in
an effort to make their muscles appear
full and dense while on stage (24). More-
over, there is a heightened sensation of
Copyright Ó National Strength and Conditioning Association Strength and Conditioning Journal |
pleasure associated with the pump,
which has been popularly described by
Arnold Schwarzenegger as a “tight feel- somebody is blowing air into
your feels fantastic.” (27).
Lifters therefore often will “chase the
pump” in their training regimens, struc-
turing workouts to maximize intracellu-
lar fluid accumulation. Although these
short-term effects of the pump are well
documented, recent research suggests
that the pump may, in fact, mediate
long-term adaptive responses. T his
paper will explore the potential hyper-
trophic benefits associated with the
pump and discuss practical implications
for resistance training program design.
Muscle hypertrophy represents the
dynamic balance between protein syn-
thesis and breakdown. Three primary
factors have been postulated to mediate
hypertrophic adaptations pursuant to
resistance training: mechanical tension,
metabolic stress, and muscle damage
(34). There is compelling evidence that
mechanical tension is the primary impe-
tus for this adaptive response. Goldberg
et al. (10) was the first to report that
heightened force development is the
critical factor governing increases in
muscle hypertrophy. This finding has
since been corroborated in numerous
studies (17,26,38,43,46).
Tension on muscles initiates a phen-
omenon called mechanotransduction
whereby sarcolemmal-bound mecha-
nosensors, such as integrins and focal
adhesions, convert mechanical energy
into chemical signals that mediate var-
ious intracellular anabolic and cata-
bolic pathways in a manner that
shifts muscle protein balance to favor
synthesis over degradation (48). Stud-
ies show that mechanical tension
directly stimulates mammalian target
of rapamycin (mTOR) (16), possibly
through activation of the extracellular
regulated kinase/tuberous sclerosis
complex 2 pathway (26). These actions
are believed to be carried out via syn-
thesis of the lipid second messenger
phosphatidic acid (PA) by phospholi-
pase D (16,30). Research also indicates
that PA can phosphorylate the down-
stream anabolic translational regulator
p70S6 kinase in an mTOR-indepen-
dent fashion (22), presenting yet
another path whereby mechanical
stimuli may directly drive anabolic
Given the importance of mechanical
tension in promoting anabolism, it is
logical to conclude that training with
heavy loads is an effective means for
increasing muscle growth. The use of
higher intensities places greater tension
on muscles, thus stimulating greater
mechanotransduction. As noted, how-
ever, other factors are purported to play
a role in postexercise muscle protein
accretion. In particular, there is compel-
ling evidence that exercise-induced
metabolic stress can mediate a hypertro-
phic response, and cell swelling is
believed to be an important component
to this process (35).
In simple terms, the pump represents
an increase in intracellular hydration
that causes the muscle fiber to swell.
Research shows that cell swelling acts
as a physiological regulator of cell
function (14,15), stimulating protein
accretion by both increasing protein
synthesis and decreasing protein break-
down (13,25,40). These effects have
been demonstrated in a variety of dif-
ferent cell types including hepatocytes,
osteocytes, breast cells, and muscle
fibers (21). In muscle, fast-twitch (FT)
fibers have been found to be particu-
larly sensitive to osmotic changes,
presumably related to their high con-
centration of water transport channels
called aquaporin-4 (AQP4). AQP4 is
strongly expressed in the sarcolemma
of mammalian FT glycolytic and FT
oxidative-glycolytic fibers, facilitating
the entry of plasma into the cell (8).
Numerous studies show that FT fibers
display a superior potential for growth
as compared with slow-twitch fibers
(1,2,18,39), suggesting that cell swelling
may promote hypertrophy by favor-
ably impacting net protein balance in
these fibers. Indeed, ablation of AQP4
was found to correlate with muscular
atrophy in mice (3), although it is not
clear whether this finding is related to
an inhibition of cell swelling or simply
a reduction in spontaneous physical
Although the underlying mechanisms
remain to be fully elucidated, it has
been hypothesized that cell swelling-
induced anabolism is a means of cell
survival (Figure). According to theory,
an increased pressure against the cyto-
skeleton and/or cell membrane is per-
ceived as a threat to cellular integrity,
thereby initiating an intracellular sig-
naling response that promotes rein-
forcement of its ultrastructure (20,34).
The signaling response is believed to be
facilitated by integrin-associated vol-
ume osmosensors within muscle fibers
(23). When the membrane is subjected
to swelling-induced stretch, these
sensors initiate activation of anabolic
protein-kinase transduction pathways,
potentially regulated at least in part by
growth factors that exert their influ-
ence in an autocrine/paracrine fashion
Figure. Theoretical schematic for cellular
swelling mechanisms of
action on muscle hypertrophy .
One on One
(4,19). Research suggests that these
functions are carried out in an
mTOR-dependent (9) and/o r inde-
pendent (32) manner, a nd there is evi-
dence that mitoge n-activated protein
kinase pathways may play a role in
associated anabolic signaling (7,3 3).
Hyperhydration also may have a direct
effect on amino acid tran sport sys-
tems. Phosphatidylinositide 3-kinase
appears to be an important signaling
component in modulating glutamine
and methylaminoisobutyric acid trans-
port in muscle because of increased cel-
lular hydration (23).
It has been hypothesized that cellular
swelling may enhance hypertrophic
adaptations through increased satellite
cell activity (6). Satellite cells are muscle
stem cells that reside between the basal
lamina and sarcolemma. While resting,
these precursor cells remain quiescent.
When muscle is subjected to mechani-
cal overload, however, satellite cells
enter the cell cycle and initiate muscular
repair by first undergoing proliferation
and then differentiating into myoblast-
like cells (31). Once differentiated,
myoblasts are then able to fuse to trau-
matized myofibers and donate their
nuclei to increase the cell’s ability to
synthesize new contractile proteins
(47). Studies investigating the myogenic
properties of creatine monohydrate
(CM), an osmolyte, show a positive
impact on satellite cell accretion (29)
and differentiation (44), as well as myo-
genic regulatory factor expression (45).
Dangott et al. (6) proposed that the os-
molytic properties of CM may instigate
proliferation of satellite cells and facili-
tate their fusion to hypertrophying my-
ofibers. At this time, the satellite cell
hypothesis remains speculative, how-
ever, because it is not clear whether
myogenic effects are, in fact, mediated
by cell swelling or simply resultant to
external overload.
To date, there is a paucity of resistance
training studies directly investigating
the effects of acute cell swelling (i.e.,
the pump) on muscle hypertrophy.
However, basic research provides
a compelling reason to believe that
exercise-induced cell swelling enhances
hypertrophic gains. To achieve a pump,
local muscle activation must be high
enough to occlude venous output;
however, the contractions must be
repeated for sufficient repetitions to
allow for the pooling of blood. Further-
more, muscle tension must remain per-
sistent to prevent blood from escaping
the musculature. For these reasons,
exercise selection and manner of execu-
tion must be chosen wisely to provide
a maximal cell swelling stimulus.
Bodybuilders seeking the pump gener-
ally employ 2 different sets, repetitions,
and timing schemes. The first is the
use of several high repetition sets com-
bined with short rest periods. An
example would be 2–3 sets of ;20 rep-
etitions with 60 seconds of rest in
between sets. The second is the use
of repeated medium repetition sets
combined with short rest periods. An
example would be 5–10 sets of 8–12
repetitions with 30 seconds of rest in
between sets. Both of these strategies
are viable approaches and conceivably
can be used interchangeably to maxi-
mize the pump.
Another option for enhancing the
pump is to perform a drop set, whereby
a high intensity set is immediately fol-
lowed by a lower intensity bout with
the load decreased by ;25–50%. This
training strategy results in significant
metabolite accumulation (12), thereby
enhancing cellular hydration. Goto
et al. (11) showed that a drop set pro-
tocol resulted in a significant increase
in muscle cross sectional area, opposed
to a traditional high-intensity strength
training protocol alone. However, the
study did not control for total training
volume, leaving open the possibility
that the increased muscle protein
accretion was the result of an increased
volume rather than from the effects of
cell swelling.
Exercise selection is an important
aspect of pump training. Some exer-
cises place more constant loading on
the musculature because of their tor-
que-angle curves, whereas others load
up a particular range of motion but
diminish drastically in other ranges.
Because cellular swelling is predicated
on a prolonged venous occlusion,
those exercises that maintain constant
tension would necessarily maximize
the pump. For example, the good
morning requires the greatest muscle
force in the hip extensors at long mus-
cle lengths; the 458 hyperextension at
medium muscle lengths and the hori-
zontal back extension at short muscle
lengths (5). Although the good morn-
ing, therefore, would have the greatest
impact on inducing muscle damage
(28), the lack of tension in the upper
range of movement would diminish
cellular swelling. On the other hand,
the constant muscular tension (i.e.,
mean torque loading throughout the
repetition) associated with the 458
hyperextension heightens vascular
occlusion, thereby resulting in a greater
pump. Traditional single-joint machine
exercises such as the “pec deck,”
“reverse pec deck,” leg extension, and
seated leg curl exercises are generally
good choices for pump training
because of the constant tension they
place on the musculature.
Exercises can also be modified for
a greater pump effect. Exercises that
have diminished loading on a particular
muscle throughout the range of
motion can be altered so that perfor-
mance focuses only on the portion of
the movement that maximally stresses
the muscle is performed. For example,
bottom-half push-ups or dips are a bet-
ter strategy for achieving a pump in
the pectorals than full range push-ups
or dips. Resistance bands and chains
can also be used in concert with the
barbell to accommodate the strength
curve and place more tension that is
constant on the muscle.
Finally, when training for the pump, it
is important to perform exercises in
a continuous manner so that the target
muscles are not allowed to relax. Tani-
moto and Ishii (41) showed a significant
decrease in local muscle oxygenation—
consistent with vascular occlusion—in
the performance of low-intensity knee
extension exercise (50% 1RM) without
Strength and Conditioning Journal |
a relaxation phase as compared with
high-intensity (80% 1RM) exercise per-
formed with a 1-second relaxation
between repetitions. The authors
attributed this decrease in muscle oxy-
genation level to the continuous con-
tractions of the knee extensor muscles
in exercise without relaxation. Similar
results were reported in follow-up dur-
ing multijoint lower-body exercise (42),
emphasizing the importance of main-
taining continuous tension on the
working muscles if the goal is to max-
imize cellular swelling.
In summary, progressive resistance
training in low-to-medium repetition
ranges has earned its keep in the train-
ing programs of bodybuilders and
other athletes seeking to maximize
hypertrophy, for good reason. Heavy
loads maximize muscle activation,
and progressive overload ensures that
muscles receive increased mechanical
tension over time. Therefore, increas-
ing strength on heavy multijoint
movements should be the foundation
of long-term hypertrophy training.
However, it is likely that exercise cen-
tered on achieving a “pump” through
higher repetition sets combined with
shorter rest periods also provides a
potent hypertrophic stimulus that is
synergistic to heavy compound lifting.
Therefore, individuals seeking maximal
hypertrophy should consider dedicat-
ing a component of their training ses-
sions toward “pump” training, ideally
after heavier strength work, to take
advantage of the multiple pathways
involved in muscle hypertrophy.
Future research should be undertaken
to investigate whether cell swelling,
in fact, leads to increased hypertro-
phy over that of heavy strength train-
ing alone (i.e., whethe r its inclusion
is additive or redundant). Moreover,
future research should determine the
precise mechanisms through which
“pump” training increases hypertrophy
and determine which exercises and
training methods are best suited for
eliciting a pump in the various muscles
of the body. Finally, future research
should dictate the optimal manner in
which heavier strength training and
lighter pump training can be integrated
together to maximize hypertrophic
Conflicts of Interest and Source of Funding:
The authors report no conflicts of interest
and no source of funding.
Brad J. Schoenfeld is a lecturer in the
exercise science program at CUNY’s
Lehman College and director of their
human performance laboratory.
Bret Contreras is currently pursuing
his PhD in Sports Science at the Auck-
land University of Technology in Auck-
land, New Zealand.
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Strength and Conditioning Journal |
... To the author's knowledge, no study has been conducted to assess the effective number of sets per RT session on mechanical and metabolic stress. Understanding the limits of the number of sets is essential to increase efficiency in prescribing and controlling each RT session, optimizing the time for each RT session, and inducing favorable levels of metabolic stress and mechanical tension (Lim et al., 2022;Marchetti, 2022;Medicine, 2021;Schoenfeld, 2013;Schoenfeld & Contreras, 2014). ...
... The first hypothesis was that more sets per RT protocol will induce a greater reduction in the average number of repetitions and increase the time under tension and the total number of repetitions; however, sRPE will remain constant for all RT protocols. The second hypothesis considers that more sets per RT protocol will induce a greater reduction in peak force and increase muscle thickness (Damas et al., 2018;Schoenfeld, 2010Schoenfeld, , 2013Schoenfeld & Contreras, 2014;Schoenfeld et al., 2016). The results of this study will help coaches and trainers understand and prescribe better acute RT sessions based on the number of sets, avoiding excessive volume. ...
... It is well known that different RT protocols have been shown to induce different acute cell swelling, the extent of which relies on the type of exercise, level of fatigue, volume, and intensity (Schoenfeld, 2013). RT exercises with momentary muscle failure reduce the intramuscular ATP and CP levels (and Pi, ADP, and AMP accumulation) and increase the glycolytic flux (production of H+ leads to metabolite accumulation), hypoxia (via muscle contraction), and venous pooling leading to cell swelling (Chen et al., 1996;Schoenfeld & Contreras, 2014;Sjøgaard et al., 1985;Usher-Smith et al., 2009). In this study, both neuromuscular fatigue and cell swelling were assessed via PF and MT, respectively. ...
Full-text available
This study aimed to measure the acute effects of resistance training (RT) protocols with a different number of sets and non-equalized volume on muscle thickness, peak force, and physical performance in recreationally trained participants. Fifteen participants performed the unilateral biceps curl exercise in four different RT protocols (G 4 : 4 sets of 10RM, G 8 : 8 sets of 10RM, G 12 : 12 sets of 10RM, and G 16 : 16 sets of 10RM). The average number of repetitions (ANR), the total number of repetitions (TNR), time under tension (TUT), muscle thickness (MT), peak force (PF), and rating of perceived exertion (sRPE) were measured pre-test and post-test. ANOVAs were used to test differences between all dependent variables. For ANR, there were differences between G 4 xG 8 , G 4 xG 12 , and G 4 xG 16. For TNR, there were differences between all RT protocols. For TUT, there were differences between the first and last set for all RT protocols and between RT protocols for the last set. For PF, there were differences between the pre-and post-test for all RT protocols and between RT protocols for Post-0.
... Therefore, in addition to the choice of exercise, the correct manipulation of the acute variables of intensity and volume is essential to induce adequate levels of metabolic stress and mechanical tension in an RT session (20,21,26,31,32). Metabolic stress can be indirectly characterized by the level of cell swelling after an RT exercise or workout. ...
... It is known that EI is related to edema and changes in EI were recently used as a non-invasive way to determine whether the acute change in MT was due to an intracellular shift or rather due to the fluid accumulation around the muscle fibers (42,43). In combination with imaging techniques, the peak force (PF) produced after an RT session and TUT during each set complement the metabolic analysis as it indicates an increase in the production of lactate and hydrogen ions (neuromuscular fatigue) and may influence water uptake into muscle cells according to cell permeability (3,5,16,32,37,40). Additionally, TUT may have an even greater impact than cell swelling as a marker of hypertrophy as mechanical signals appear to be a primary hypertrophy stimulus (41). ...
... Different RT protocols have been shown to induce different acute cell swelling, the extent of which relies on the type of exercise, level of fatigue, volume, and intensity (31). RT exercises with momentary muscle failure reduce the intramuscular ATP and CP levels (and Pi, ADP, and AMP accumulation) and increase the glycolytic flux (production of H+ leads to metabolite accumulation), hypoxia (via muscle contraction), and venous pooling leading to cell swelling (5,32,37,40). In the present study, MT and EI were obtained to measure the acute cell swelling at three-time points (pre-, post-0, and post-15) in both RT protocols (RT4x10RM and RT1x40RM). ...
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The primary purpose of this study was to evaluate acute dose response of different intensities with total volume equalized during the abdominal crunch exercise on muscle thickness, echo-intensity, peak force, time under tension, total load lifted, and perception of effort in recreationally-trained participants. Fifteen resistance-trained participants (23 ± 3 years) performed the abdominal crunch exercise in one of two different resistance training (RT) protocols in a randomized order: RT4x10RM (4 sets of 10RM / 1-min rest) or RT1x40RM (1 set of 40RM). Muscle thickness (MT), echo- intensity (EI), peak force (PF), time under tension (TUT), total load lifted (TLL), and session rating of perceived exertion (sRPE) were measured pre-test and post-test (0-min and 15-min). Two-way repeated-measures ANOVAs (2 x 3) were used to test differences between RT protocols (RT4x10RM and RT1x40RM) and time (pre-test, post-0, and post-15) for MT, EI, and PF. Paired t-test was used to compare RT protocols for sRPE, TLL, and TUT. For MT, there were significant differences for RT4x10RM between pre- x post-0 (p = 0.011), pre- x post-15 (p < 0.001), and post-0 x post-15 (p = 0.02); and for RT1x40RM between pre- x post-0 (p < 0.001) and pre- x post-15 (p = 0.003). For EI, there was a significant difference for RT4x10RM between pre- x post-0 (p = 0.002). For sRPE, there was no significant difference between RT protocols. For TLL and TUT, there were significant differences between RT protocols (p < 0.05). In conclusion, both RT protocols (RT4x10RM and RT1x40RM) induced similar increases in MT but not for EI. TLL and TUT were higher for RT4x10RM. PF and sRPE were similar between RT protocols.
... However, evidence indicates that low-load (LL) training can promote similar hypertrophic adaptations to the use of heavier loads (29), which may be at least in part mediated by metabolite accumulation (24). From a mechanistic standpoint, it has been hypothesized that acute cell swelling associated with metabolic stress (i.e., "the pump") may be a contributing factor in the hypertrophic response to LL training (5,28). ...
... The cell swelling induced by RT promotes alterations in intra-and extracellular water balance, the extent of which is dependent on the type of exercise and intensity of training (26,28). In vitro evidence indicates that cell swelling results in an increase in protein synthesis and a decrease in proteolysis in a variety of tissues (17,26). ...
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International Journal of Exercise Science 16(3): 513-524, 2023. Cell swelling caused by resistance training is proposed to provide an anabolic stimulus for muscle growth and it is believed that these effects are heightened with the use of low loads. The purpose of this study was to compare the acute effects of two volume-equated resistance training (RT) protocols, low-load (LL) versus high-load (HL), on elbow flexor muscles thickness, arm circumference, and blood lactate concentration in well-trained individuals. Eight resistance-trained males performed the following two RT protocols involving unilateral elbow flexion of the dominant arm: i) LL, four sets with 50% 1 repetition-maximum [1 RM] and ii) HL, ten sets with 85% 1 RM until failure, and equated volume. Pre-and post-session measurements included muscle thickness of the elbow flexors (biceps brachii and brachialis), upper arm circumference, and blood lactate concentration. Significant pre-to post-session increases were found in both protocols for muscle thickness (F (1, 28) = 11.74, p = 0.0019), and blood lactate (F (1, 28) = 35.55, p < 0.0001); no statistically significant differences were observed between conditions, however, the magnitude of increases favored LL. Significant between-condition differences favoring LL were observed for total repetitions (p = 0.007), time under tension (p = 0.007), and training density (p = 0.007). These results suggest that LL training promotes superior post-session increases in muscle thickness, indicating that RT protocols with longer times under tension and densities are beneficial when the goal is to promote acute cell swelling.
... Mišićna hipertrofija izazvana vežbanjem je omogučena putem nekoliko miogeničnih puteva u kojima mehanički stimulus (vežbanje sa opterećenjem) preko aktivacije niya molekula izaziva povećanu sintezu mišićnih proteina. Nekoliko primarnih anabolnih puteva ukljućuju Akt/ Mammalian target of rapamycin (mTOR), mitogen-aktiviranu proteinsku kinazu (MAPK) i kalcium (Ca2+) zavisne signalne puteve (Schoenfeld, 2014). ...
... Trening sa opterećenjem izaziva promene izmedju intracelularnog i ekstracelularnog kompartmana telesnih tečnosti, a ove promene zavise od tipa vežbi i intenziteta treninga. Vežbanje koje kao izvor energije koristi glikolitički put i dovodi do nakupljanja laktata je doprinosi osmotskim promenama u ćelijama skeletnih mišića (Schoenfeld, . & Contreras, 2014). Povećani unutrašnji tonus mišićne ćelije kao rezultat povećane hidriranosti ćelije deluje kao unutrašnji mehanički stimulus za povećanu sintezu proteina i smanjenje proteolize ( Millar, et a., 1997;Grant, et al., 2000). Jedan od pretpostavljenih mehanizama za anabolni stimulus je rastezanje membrane i olakšani transport aminokiselina u ...
Conference Paper
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The aim of this paper is to determine the state of the football player before starting preparations for the upcoming half-season. The sample consisted of 18 players of the third federal rank. The subjects were first measured body height (anthropometer) and then the body composition using the Inbody 770 instrument. Subsequently, tests were performed to assess the explosive leg power (CMJ, CMJa, SJ) using an instrument Optojump, agility (9-6-3- 6-9, sprint 20m) and endurance (Yo-Yo endurance). Correlations have shown that there is a correlation between BMI and agility tests. The percentage of body fat and body fat in kilograms correlated with CMJ and sprint in all three stages. After the research, the level of readiness of athletes was determined and an adequate plan and program of the training process will be developed in order to achieve the best possible results in the upcoming period.
... This growth is primarily achieved via hypertrophy, the thickening of muscle fibers. It is proposed that such hypertrophic adaptations occur in response to mechanical tension, metabolic stress, and/or muscle damage 5 . Provided an adequate stimulus, skeletal muscle regeneration composes three phases: (1) an initial inflammatory phase, followed by (2) satellite cell activation and differentiation, and finally (3) a maturation phase where newly formed myofibers are remodeled 6 . ...
... As such, increased blood flow during exercise aids in transporting growth factors and nutrients to downstream effectors. Moreover, spatial priming and adaptive responses to cellular swelling corresponding sarcoplasmic hypertrophy further exemplify the muscle pump as an anabolic primer 5,26,27 . At the cell's surface, an acute bout of resistance exercise has shown to upregulate IGF-1 receptor expression in type I muscle fibers, but not in type II muscle fibers 83 . ...
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A complex network of biochemical pathways carries out the process of muscle regeneration/growth following resistance exercise. The initial inflammatory response following muscle damage is primarily mediated by the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB), cyclooxygenase enzymes, and prostaglandins. Muscle damage also stimulates the activation, proliferation, differentiation, migration, and fusion of satellite cells onto damaged myofibers, resulting in myofibrillar hypertrophy. The progression of the myogenic lineage is predominantly coordinated by the wingless/integrated family of glycoproteins which engages in crosstalk with NF-κB and the mitogen-activated protein kinase (MAPK)/extracellular signaling-regulated kinase network. The MAPK cascade is essential for mechanotransduction, the process of converting mechanical stimuli into biochemical responses such as accelerated protein synthesis and satellite cell activation. Muscle protein synthesis is primarily governed by the insulin-like growth factor 1/phosphoinositide 3-kinase/protein kinase B/mammalian target of rapamycin pathway. Several calcium-dependent pathways are also integrated into the process of myogenesis and influence skeletal muscle plasticity. These dynamic interactions are part of the anabolic priming by resistance exercise effect, which defines resistance exercise as an acute catabolic event that potentiates multiple downstream anabolic pathways. Plateaus in muscle growth are attributed to deteriorating inflammatory signaling with repeated bouts of muscle damage as well as increasing thresholds for continuous adaptations, which ultimately become unreachable beyond a certain point. The physiological ceiling of skeletal muscle mass is also credited to myostatin. However, recent discoveries suggest the role of myostatin is not limited to preventing excessive skeletal muscle hypertrophy.
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The biophysical response of the human body to electric current is widely appreciated as a barometer of fluid distribution and cell function. From distinct raw bioelectrical impedance (BIA) variables assessed in the field of body composition, phase angle (PhA) has been repeatedly indicated as a functional marker of the cell's health and mass. Although resistance training (RT) programs have demonstrated to be effective to improve PhA, with varying degrees of change depending on other raw BIA variables, there is still limited research explaining the biological mechanisms behind these changes. Here, we aim to provide the rationale for the responsiveness of PhA determinants to RT, as well as to summarize all available evidence addressing the effect of varied RT programs on PhA of different age groups. Available data led us to conclude that RT modulates the cell volume by increasing the levels of intracellular glycogen and water, thus triggering structural and functional changes in different cell organelles. These alterations lead, respectively, to shifts in the resistive path of the electric current (resistance, R) and capacitive properties of the human body (reactance, Xc), which ultimately impact PhA, considering that it is the angular transformation of the ratio between Xc and R. Evidence drawn from experimental research suggests that RT is highly effective for enhancing PhA, especially when adopting high-intensity, volume, and duration RT programs combining other types of exercise. Still, additional research exploring the effects of RT on whole-body and regional BIA variables of alternative population groups is recommended for further knowledge development.
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Nitric-oxide-stimulating dietary supplements are widely available and marketed to strength athletes and weightlifters seeking to increase muscle performance and augment training adaptations. These supplements contain ingredients classified as nitric oxide (NO) precursors (i.e., “NO boosters”). Endogenous NO is generated via a nitric oxide synthase (NOS)-dependent pathway and a NOS-independent pathway that rely on precursors including L-arginine and nitrates, with L-citrulline serving as an effective precursor of L-arginine. Nitric oxide plays a critical role in endothelial function, promoting relaxation of vascular smooth muscle and subsequent dilation which may favorably impact blood flow and augment mechanisms contributing to skeletal muscle performance, hypertrophy, and strength adaptations. The aim of this review is to describe the NO production pathways and summarize the current literature on the effects of supplementation with NO precursors for strength and power performance. The information will allow for an informed decision when considering the use of L-arginine, L-citrulline, and nitrates to improve muscular function by increasing NO bioavailability.
BACKGROUND: Intrinsic foot muscle (IFM) dysfunction and poor foot arch are associated with various foot conditions. Toe flexor exercise (TFE) has been used to improve it; however, the immediate effects of TFE on each IFM and how it relates to changes in navicular bone height (NH) are unclear. OBJECTIVE: This study aimed to investigate acute muscle swelling in the IFM after TFE and the association between changes in NH and IFM size. METHODS: Fourteen adults participated in this study. NH and cross-sectional area (CSA) of the IFM were acquired pre and post- TFE. The CSA of the IFM, including the abductor hallucis (AbH), flexor hallucis brevis, flexor digitorum brevis, and quadratus plantae, was acquired with ultrasonography. In the TFE, each participant completed five sets of eight repetitions with maximum strength. RESULTS: The NH and CSA of all IFM significantly increased significantly post-TFE (p< 0.01). Only the increase in AbH was moderately and positively correlated with the change in NH (r= 0.54, p< 0.01). CONCLUSION: This study suggests that the acute swelling of AbH after TFE is associated with an immediate increase in NH, supporting the important role of AbH in the formation of foot arch.
This study aimed to investigate the motor unit firing property immediately after concentric or eccentric contraction exercise. Eighteen healthy men performed repetitive maximal isokinetic knee extension exercises with only concentric or eccentric contraction until they exerted less than 80% of the baseline strength. Before and after the fatiguing exercise, high-density surface electromyography of the vastus lateralis was recorded during submaximal ramp-up isometric contraction and individual motor units were identified. Only motor units that could be tracked before and after exercise were analyzed. Muscle cross-sectional area of the vastus lateralis was measured using ultrasound, and electrically evoked torque was recorded before and after the exercise. Sixty-five and fifty-three motor units were analyzed before and after the concentric and eccentric contractions, respectively. The results showed that motor units with moderate to high recruitment thresholds significantly decreased recruitment thresholds under both conditions, and the motor unit discharge rates significantly increased after concentric contraction compared to eccentric contraction. A greater muscle cross-sectional area was observed with concentric contraction. The evoked torque was significantly decreased under both conditions, but no difference between the conditions. These results suggest that fatiguing exercise with concentric contraction contributes to greater neural input to muscles and metabolic responses than eccentric contraction.
Enzymes have played crucial role in the production, fortification and preservation of food and beverages; one that is economical and eco-friendly. Most modern-day nutritional supplements used by athletes focus primarily on, enhancing physical endurance, maximizing nutrient absorption, and mitigating injuries induced in sports. Inclusion of bioactive compounds, such as enzymes, has dramatically improved the aforesaid attributes in supplements. Whey supplements fortified with proteolytic enzymes have been shown to enhance the bio-absorption of proteins by hydrolyzing into its basal amino acids. These supplements also contain Lactases for breaking down sugars for consumers who are lactose intolerant. Energy drinks used by athletes contain blends of ornithine alpha-ketoglutarate and aminotransferases that help in replenishing lost arginine pools during intense physical activity. Conversion of arginine to nitrous oxide in the cells has been directly related to increased blood flow to the muscles for enhanced workout and functioning. Amylases in energy drinks have been shown to restock the lost muscle glycogen by helping the conversion of complex carbohydrates to simple sugars, such as glucose. However, most of these enzymes are present in proprietary blends, with very less information on the ingredients. This chapter therefore discusses elaborately on numerous other enzymes, and their potential applications in sports supplementation.
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In this study we assess the functional role of Aquaporin-4 (AQP4) in the skeletal muscle by analyzing whether physical activity modulates AQP4 expression and whether the absence of AQP4 has an effect on osmotic behavior, muscle contractile properties, and physical activity. To this purpose, rats and mice were trained on the treadmill for 10 (D10) and 30 (D30) days and tested with exercise to exhaustion, and muscles were used for immunoblotting, RT-PCR, and fiber-type distribution analysis. Taking advantage of the AQP4 KO murine model, functional analysis of AQP4 was performed on dissected muscle fibers and sarcolemma vesicles. Moreover, WT and AQP4 KO mice were subjected to both voluntary and forced activity. Rat fast-twitch muscles showed a twofold increase in AQP4 protein in D10 and D30 rats compared to sedentary rats. Such increase positively correlated with the animal performance, since highest level of AQP4 protein was found in high runner rats. Interestingly, no shift in muscle fiber composition nor an increase in AQP4-positive fibers was found. Furthermore, no changes in AQP4 mRNA after exercise were detected, suggesting that post-translational events are likely to be responsible for AQP4 modulation. Experiments performed on AQP4 KO mice revealed a strong impairment in osmotic responses as well as in forced and voluntary activities compared to WT mice, even though force development amplitude and contractile properties were unvaried. Our findings definitively demonstrate the physiological role of AQP4 in supporting muscle contractile activity and metabolic changes that occur in fast-twitch skeletal muscle during prolonged exercise.
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It is well established that regimented resistance training can promote increases in muscle hypertrophy. The prevailing body of research indicates that mechanical stress is the primary impetus for this adaptive response and studies show that mechanical stress alone can initiate anabolic signalling. Given the dominant role of mechanical stress in muscle growth, the question arises as to whether other factors may enhance the post-exercise hypertrophic response. Several researchers have proposed that exercise-induced metabolic stress may in fact confer such an anabolic effect and some have even suggested that metabolite accumulation may be more important than high force development in optimizing muscle growth. Metabolic stress pursuant to traditional resistance training manifests as a result of exercise that relies on anaerobic glycolysis for adenosine triphosphate production. This, in turn, causes the subsequent accumulation of metabolites, particularly lactate and H(+). Acute muscle hypoxia associated with such training methods may further heighten metabolic buildup. Therefore, the purpose of this paper will be to review the emerging body of research suggesting a role for exercise-induced metabolic stress in maximizing muscle development and present insights as to the potential mechanisms by which these hypertrophic adaptations may occur. These mechanisms include increased fibre recruitment, elevated systemic hormonal production, alterations in local myokines, heightened production of reactive oxygen species and cell swelling. Recommendations are provided for potential areas of future research on the subject.
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Social scientists of medicine have largely, although by no means exclusively, focused their research on illness and sickness thus obscuring social scientific investigations of positive health and wellbeing. Undoubtedly, important reasons exist for this but the relevance of studying ‘healthy’ bodies requires emphasis and wider acknowledgement within the newer (embodied, non-dualistic) sociology of health and illness. This is necessary because the concrete corporeal manifestations of ‘health’ in everyday life – components of and preconditions for embodied social practice – may, paradoxically, erode bodily capital while simultaneously contributing to it. Using qualitative data generated during an ethnography of bodybuilding subculture, this paper contributes to the sociology of ‘healthy’ (transgressive) bodies. It describes the somatic representation of health and youth, the so-called erotics of the gym and the perceived benefits of anaerobic exercise for everyday pragmatic embodiment. Contra critical feminist studies, it furthers an appreciative understanding of ‘risky’ bodywork in post- or late modernity and underscores the value of bringing healthy lived bodies into medical sociology.
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Mechanical stimuli increase skeletal muscle growth in a mammalian target of rapamycin (mTOR)- and p70(S6K)-dependent manner. It has been proposed that costameric proteins at Z bands may sense and transfer tension to these initiators of protein translation, but few candidates have been identified. The purpose of this study was to determine whether a role exists for the α(7)-integrin in the activation of hypertrophic signaling and growth following eccentric exercise training. Five-week-old, wild-type (WT) and α(7)BX2-integrin transgenic (α(7)Tg) mice were randomly assigned to one of two groups: 1) sedentary (SED), or 2) exercise training (EX). Exercise training consisted of downhill running 3 sessions/wk for 4 wk (-20°, 17 m/min, 30 min). Downhill running was used to induce physiological mechanical strain. Twenty-four hours following the final training session, maximal isometric hindlimb plantar flexor force was measured. Gastrocnemius-soleus complexes were collected for further analysis of signaling changes, which included AKT, mTOR and p70(S6K), and muscle growth. Despite increased p70(S6K) activity in WT/EX, no significant changes in cross-sectional area or force were observed in WT/EX compared with WT/SED. AKT, mTOR, and p70(S6K) activation was higher, and whole muscle hypertrophy, relative muscle weight, myofibrillar protein, and force were significantly elevated in α(7)Tg/EX compared with α(7)Tg/SED. A marked increase in average myofiber cross-sectional area was observed in α(7)Tg/EX compared with all groups. Our findings demonstrate that the α(7)β(1)-integrin sensitizes skeletal muscle to mechanical strain and subsequent growth. Thus the α(7)β(1)-integrin may represent a novel molecular therapy for the treatment of disuse muscle atrophy.
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The mammalian target of rapamycin complex 1 (mTORC1) functions as a central integrator of a wide range of signals that modulate protein metabolism and cell growth. However, the contributions of individual pathways regulating mTORC1 activity in skeletal muscle are poorly defined. The purpose of this study was to determine the regulatory mechanisms that contribute to mTORC1 activation during mechanical overload-induced skeletal muscle hypertrophy. Consistent with previous studies, mechanical overload induced progressive hypertrophy of the plantaris muscle which was associated with significant increases in total RNA content and protein metabolism. mTORC1 was activated after a single day of overload as indicated by a significant increase in S6K1 phosphorylation at T389 and T421/S424. In contrast, Akt activity, as assessed by Akt phosphorylation status (T308 and S473), phosphorylation of direct downstream targets (glycogen synthase kinase 3 β, proline-rich Akt substrate 40 kDa and tuberous sclerosis 2 (TSC2)) and a kinase assay, was not significantly increased until 2–3 days of overload. Inhibition of phosphoinositide 3-kinase (PI3K) activity by wortmannin was sufficient to block insulin-dependent signalling but did not prevent the early activation of mTORC1 in response to overload. We identified that the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK)-dependent pathway was activated at day 1 after overload. In addition, a target of MEK/ERK signalling, phosphorylation of TSC2 at S664, was also increased at this early time point. These observations demonstrate that in vivo, mTORC1 activation at the early phase of mechanical overload in skeletal muscle occurs independently of PI3K/Akt signalling and provide evidence that the MEK/ERK pathway may contribute to mTORC1 activation through phosphorylation of TSC2.
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The quest to increase lean body mass is widely pursued by those who lift weights. Research is lacking, however, as to the best approach for maximizing exercise-induced muscle growth. Bodybuilders generally train with moderate loads and fairly short rest intervals that induce high amounts of metabolic stress. Powerlifters, on the other hand, routinely train with high-intensity loads and lengthy rest periods between sets. Although both groups are known to display impressive muscularity, it is not clear which method is superior for hypertrophic gains. It has been shown that many factors mediate the hypertrophic process and that mechanical tension, muscle damage, and metabolic stress all can play a role in exercise-induced muscle growth. Therefore, the purpose of this paper is twofold: (a) to extensively review the literature as to the mechanisms of muscle hypertrophy and their application to exercise training and (b) to draw conclusions from the research as to the optimal protocol for maximizing muscle growth.
In mammalian systems, skeletal muscle exists in a dynamic state that monitors and regulates the physiological investment in muscle size to meet the current level of functional demand. This review attempts to consolidate current knowledge concerning development of the compensatory hypertrophy that occurs in response to a sustained increase in the mechanical loading of skeletal muscle. Topics covered include: defining and measuring compensatory hypertrophy, experimental models, loading stimulus parameters, acute responses to increased loading, hyperplasia, myofiber-type adaptations, the involvement of satellite cells, mRNA translational control, mechanotransduction, and endocrinology. The authors conclude with their impressions of current knowledge gaps in the field that are ripe for future study. © 2012 American Physiological Society. Compr Physiol 2:2829-2870, 2012.
Load on the human body can be influenced by shoes and surfaces which is important both in sports and rehabilitation. The loading which can primarily be influenced are impact situations and friction as well as the stability of the foot. This stability is of main interest in the prevention of pain and injury. However, a certain amount of loading is necessary to improve strength and structure of biological materials. In the past, the development of shoe and surface materials has hardly been perceived under this aspect, but may be increasingly important in the future. Die in Sport und Rehabilitation auftretenden Belastungen des Bewegungsapparats sind durch Böden und Schuhe beeinflußbar. Beeinflußt werden können vor allem die Aufprall- und Reibungskräfte sowie die Stabilität des Fußes, wobei letztere insbesondere in der Beschwerdeprophylaxe eine wichtige Rolle spielt. Ein gewisses Maß an Beanspruchung ist jedoch nötig, um biologischen Materialien Stärke und Struktur zu verleihen. Die materialtechnische Entwicklung von Böden und Schuhen ist aber kaum auf dieses wesentliche Ziel hin verfolgt worden. Hier liegen noch entscheidende Entwicklungsmöglichkeiten offen.
Insulin-like growth factor (IGF-I) is hypothesized to be a critical upstream regulator of mammalian target of rapamycin (mTOR)-regulated protein synthesis with muscle contraction. We utilized a mouse model that expresses a skeletal muscle specific dominant-negative IGF-I receptor to investigate the role of IGF-I signaling of protein synthesis in response to unilateral lengthening contractions (10 sets, 6 repetitions, 100 Hz) at 0 and 3 h following the stimulus. Our results indicate that one session of high frequency muscle contractions can activate mTOR signaling independent of signaling components directly downstream of the receptor.