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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.
1. Aagaard P, Andersen JL, Dyhre-Poulsen P,
Leffers AM, Wagner A, Magnusson SP,
Halkjaer-Kristensen J, and Simonsen EB.
A mechanism for increased contractile
strength of human pennate muscle in
response to strength training: Ahanges
in muscle architecture. J Physiol 534:
613–623, 2001.
2. Adams G and Bamman MM. Characterization
and regulation of mechanical loading-
induced compensatory muscle
hypertrophy. C ompr Physiol 2: 2829–
2870, 2012.
3. Basco D, Blaauw B, Pisani F,
Sparaneo A, Nicchia GP, Mola MG,
AQP4-dependent water transport plays
a functional role in exercise-induced
skeletal muscle adaptations. PLoS One 8:
e58712, 2013.
4. Clarke MS and Feeback DL. Mechanical
load induces sarcoplasmic wounding and
FGF release in differentiated human
skeletal muscle cultures. FASEB J 10:
502–509, 1996.
5. Contreras B, Cronin J, Schoenfeld BJ,
Nates R, and Sonmez GT. Are all hip
extension exercises created equal?
Strength Cond J 35: 17–22, 2013.
6. Dangott B, Schultz E, and Mozdziak PE.
Dietary creatine monohydrate
supplementation increases satellite cell
mitotic activity during compensatory
hypertrophy. Int J Sports Med 21: 13–16,
7. Finkenzeller G, Newsome W, Lang F, and
Haussinger D. Increase of c-jun mRNA
upon hypo-osmotic cell swelling of rat
hepatoma cells. FEBS Lett 340: 163–166,
8. Frigeri A, Nicchia GP, Verbavatz JM,
Valenti G, and Svelto M. Expression of
aquaporin-4 in fast-twitch fibers of
mammalian skeletal muscle. J Clin Invest
102: 695–703, 1998.
9. Fry CS, Glynn EL, Drummond MJ,
Timmerman KL, Fujita S, Abe T, Dhanani S,
Volpi E, and Rasmussen BB. Blood flow
restriction exercise stimulates mT ORC1
signaling and muscle protein synthesis in
older men. J Appl Physiol (1985) 108:
1199–1209, 2010.
10. Goldberg AL, Etlinger JD, Goldspink DF,
and Jablecki C. Mechanism of work-
induced hypertrophy of skeletal muscle.
Med Sci Sports 7: 185–198, 1975.
11. Goto K, Ishii N, Kizuka T, and Takamatsu K.
The impact of metabolic stress on
hormonal responses and muscular
adaptations. Med Sci Sports Exerc 37:
955–963, 2005.
12. Goto K, Sato K, and Takamatsu K. A
single set of low intensity resistance
exercise immediately following high
intensity resistance ex ercise stimulates
growth hormone secret ion in men.
243–249, 2003.
13. Grant AC, Gow IF, Zammit VA, and
Shennan DB. Regulation of protein
synthesis in lactating rat mammary tissue
by cell volume. Biochim Biophys Acta
1475: 39–46, 2000.
14. Haussinger D. The role of cellular hydration
in the regulation of cell function. Biochem J
313: 697–710, 1996.
15. Haussinger D, Lang F, and Gerok W.
Regulation of cell function by the cellular
hydration state. Am J Physiol 267: E343–
E355, 1994.
16. Hornberger TA, Chu WK, Mak YW,
Hsiung JW, Huang SA, and Chien S. The
role of phospholipase D and
phosphatidic acid in the mechanical
activation of mTOR signaling in skeletal
muscle. Proc Natl Acad Sci U S A 103:
4741–4746, 2006.
17. Hornberger TA, Stuppard R, Conley KE,
Fedele MJ, Fiorotto ML, Chin ER, and
Esser KA. Mechanical stimuli regulate
rapamycin-sensitive signalling by
a phosphoinositide 3-kinase-, protein
kinase B- and growth factor-independent
mechanism. Biochem J 380: 795–804,
18. Kosek DJ, Kim JS, Petrella JK, Cross JM,
and Bamman MM. Efficacy of 3 days/wk
resistance training on myofiber hypertrophy
One on One
and myogenic mechanisms in young vs.
older adults. J Appl Physiol 101: 531–544,
19. Lambert IH, Hoffmann EK, and
Pedersen SF. Cell volume regulation:
Physiology and pathophysiology. Acta
Physiol (Oxf) 194: 255–282, 2008.
20. Lang F. Mechanisms and significance of
cell volume regulation. J Am Coll Nutr
26: 613S–623S, 2007.
21. Lang F, Busch GL, Ritter M, Volkl H,
Waldegger S, Gulbins E, and
Haussinger D. Functional significance of
cell volume regulatory mechanisms.
Physiol Rev 78: 247–306, 1998.
22. Lehman N, Ledford B, Di Fulvio M,
Frondorf K, McPhail LC, an d Gomez-
Cambronero J. Phospholipase D2-
derived phosphatidic acid binds to and
activates ribosomal p70 S6 kinase
independently of mTOR. FASEB J
21: 1075–1087, 2007.
23. Low SY, Rennie MJ, and Taylor PM.
Signaling elements involved in amino acid
transport responses to altered muscle cell
volume. FA SEB J 11: 1111–1117, 1997.
24. Meth S. Gender differences in muscle
morphology. In: Swedan NG, ed. Women’s
Sports Medicine and Rehabilitation.
Philadelphia, PA: Lippincott Williams &
Wilkins, 2001. pp. 5.
25. Mill ar ID, Barber MC, Lomax MA,
Travers MT, and Shennan DB. Mammary
protein synthesis is acutely regulated by
the cellular hydration state. Biochem
Biophys Res Commun 230: 351–355,
26. Miyazaki M, McCarthy JJ, Fedele MJ, and
Esser KA. Early activation of mTORC1
signalling in response to mechanical
overload is independent of phosphoinositide
3-kinase/Akt signalling. JPhysiol589:
1831–1846, 2011.
27. Monaghan L. Looking good, feeling good:
The embod ied pleasures of vibrant
physicality. Sociol Health Illness 23: 330–
356, 2001.
28. Nosaka K and Sakamoto K. Effect of elbow
joint angle on the magnitude of muscle
damage to the elbow flexors. Med Sci
Sports Exerc 33: 22–29, 2001.
29. Olsen S, Aagaard P, Kadi F, Tufekovic G,
Verney J, Olesen JL, Suetta C, and Kjaer M.
Creatine supplementation augments the
increase in satellite cell and myonuclei
number in human skeletal muscle induced
by strength training. J Physiol 573: 525–
534, 2006.
30. O’Neil TK, Duffy LR, Frey JW, and
Hornberger TA. The role of
phosphoinositide 3-kinase and
phosphatidic acid in the regulation of
mammalian target of rapamycin following
eccentric contractions. J Physiol 587:
3691–3701, 2009.
31. Philippou A, Halapas A, Maridaki M, and
Koutsilieris M. Type I insulin-like growth
factor receptor signaling in skeletal muscle
regeneration and hypertrophy.
J Musculoskelet Neuronal Interact 7: 208–
218, 2007.
32. Schliess F, Richter L, vom Dahl S, and
Haussinger D. Cell hydration and mTOR-
dependent signalling. Acta Physiol (Oxf)
187: 223–229, 2006.
33. Schliess F, Schreiber R, and Haussinger D.
Activation of extracellular signal-regulated
kinases Erk-1 and Erk-2 by cell swelling in
H4IIE hepatoma cells. Biochem J 309:
13–17, 1995.
34. Schoenfeld BJ. The mechanisms of muscle
hypertrophy and their application to
resistance training. J Strength Cond Res
24: 2857–2872 , 2010.
35. Schoenfeld BJ. Potential mechanisms for
a role of metabolic stress in hypertrophic
adaptations to resistance training. Sports
43: 179–194, 2013.
36. Sjogaard G. Water and electrolyte fluxes
during exercise and their relation to muscle
fatigue. Acta Physiol Scand Suppl 556:
129–136, 1986.
37. Sjogaard G, Adams RP, and Saltin B. Water
and ion shifts in skeletal muscle of humans
with intense dynamic knee extension. Am J
Physiol 248: R190–R196, 1985.
38. Spangenburg EE, Le Roith D, Ward CW,
and Bodine SC. A functional insulin-like
growth factor receptor is not necessary for
load-induced skeletal muscle hypertrophy.
J Physiol 586: 283–291, 2008.
39. Staron RS, Malicky ES, Leonardi MJ,
Falkel JE, Hagerman FC, and Dudley GA.
Muscle hypertrophy and fast fiber type
conversions in heavy resistance-trained
women. Eur J Appl Physiol Occup Physiol
60: 71–79, 1990.
40. Stoll BA and Secreto G. Prenatal
influences and breast cancer. Lancet 340:
1478, 1992.
41. Tanimoto M and Ishii N. Effects of low-
intensity resistance exercise with slow
movement and tonic force generation on
muscular function in young men. J Appl
Physiol (1985) 100: 1150–1157, 2006.
42. Tanimoto M, Sanada K, Yamamoto K,
Kawano H, Gando Y, Tabata I, Ishii N, and
Miyachi M. Effects of whole-body low-
intensity resistance training with slow
movement and tonic force generation on
muscular size and strength in young men.
J Strength Cond Res 22: 1926–1938,
43. Vandenburgh H and Kaufman S. In vitro
model for stretch-induced hypertrophy of
skeletal muscle. Science 203: 265–268,
44. Vierck JL, Icenoggle DL, Bucci L, and
Dodson MV. The effects of ergogenic
compounds on myogenic satellite cells.
Med Sci Sports Exerc 35: 769–776, 2003.
45. Willoughby DS and Rosene JM. Effects of
oral creatine and resistance training on
myogenic regulatory factor expression.
Med Sci Sports Exerc 35: 923–929, 2003.
46. Witkowski S, Lovering RM, and
Spangenburg EE. High-frequency
electrically stimulated skeletal muscle
contractions increase p70s6k
phosphorylation independent of known
IGF-I sensitive signaling pathways. FEBS
Lett 584: 2891–2895, 2010.
47. Zammit PS. All muscle satellite cells are
equal, but are some more equal than
others? J Cell Sci 121: 2975–2982,
48. Zou K, Meador BM, Johnson B,
Huntsman HD, Mahmassani Z, Valero MC,
Huey KA, and Boppart MD. The alpha(7)
beta(1)-integrin increases muscle
hypertrophy following multiple bouts of
eccentric exercise. J Appl Physiol (1985)
111: 1134–1141, 2011.
Strength and Conditioning Journal |
... The calculated means under resting and postexercise conditions were used for further analyses. Moreover, subjects had to rate their feeling of muscle pump perceived directly after exercising, also referred to as 'cellular swelling' together with hyperemia [46], on a visual analog scale from 0 to 10 (0 'no muscle pump at all' and 10 'maximum conceivable muscle pump'). ...
... Muscular microperfusion may represent only one factor among others to determine the degree of fluid shift [79], although it appears to play a relevant role as such. This assumption is additionally supported by our observation of a significant correlation between postexercise microperfusion and the specified muscle pump, which subjectively estimates the resulting pooling of fluid within the muscle and its cells, respectively [46]. Cell swelling, together with its favorable effects on protein accretion, is hypothesized to mediate some of the hypertrophic muscular response to training via involvement of osmosensors and subsequent activation of anabolic signaling pathways [38,46,80]. ...
... This assumption is additionally supported by our observation of a significant correlation between postexercise microperfusion and the specified muscle pump, which subjectively estimates the resulting pooling of fluid within the muscle and its cells, respectively [46]. Cell swelling, together with its favorable effects on protein accretion, is hypothesized to mediate some of the hypertrophic muscular response to training via involvement of osmosensors and subsequent activation of anabolic signaling pathways [38,46,80]. For hypertrophy-oriented resistance training as investigated in this study, methods investigating acute mechanisms related to cell swelling such as CEUS might be helpful to better understand the process of long-term anabolic adaptations in trained muscles. ...
Full-text available
Background: Various dietary supplements have been reported to enhance muscular perfusion in athletes practicing resistance training, especially through modulation of nitric oxide signaling. Objectives: The aim of this study was therefore to investigate selected 'NO-boosting' supplements in a real-life setting i) to generate novel hypotheses and perfusion estimates for power calculation in view of a definitive trial and ii) to assess the feasibility of the study design with particular focus on the use of contrast-enhanced ultrasound (CEUS) for perfusion quantification. Methods: Thirty young male athletes (24 ± 4 years) regularly practicing resistance training were enrolled in this three-arm, placebo(PL)-controlled crossover trial with ingestion of two commercially available supplements: an amino acid combination (AA) (containing 3 g of L-arginine-hydrochloride and 8 g of L-citrulline-malate) and 300 mg of a specific green tea extract (GTE). After intake, CEUS examinations of the dominant biceps brachii muscle were performed under resting conditions and following standardized resistance exercising. Quantitative parameters of biceps perfusion (peak enhancement, PE; wash-in perfusion index, WiPI) and caliber were derived from corresponding CEUS video files. Additionally, subjective muscle pump was determined after exercise. Results: For PE, WiPI, and biceps caliber, the standard deviation (SD) of the within-subject differences between PL, AA, and GTE was determined, thereby allowing future sample size calculations. No significant differences between PL, AA, and GTE were observed for biceps perfusion, caliber, or muscle pump. When comparing resting with post-exercise measurements, the increase in biceps perfusion significantly correlated with the caliber increase (PE: r = 0.266, p = 0.0113; WiPI: r = 0.269, p = 0.0105). Similarly, the biceps perfusion correlated with muscle pump in the post-exercise conditions (PE: r = 0.354, p = 0.0006; WiPI: r = 0.350, p = 0.0007). A high participant adherence was achieved, and the acquisition of good quality CEUS video files was feasible. No adverse events occurred. Conclusion: Based on our novel examination protocol, CEUS seems to be feasible following higher-load resistance exercising and may be used as a new method for high-resolution perfusion quantification to investigate the effects of pre-exercise dietary supplementation on muscle perfusion and related muscle size dynamics.
... The correct choice of the acute variables is another important component of a resistance training (RT) session (19,20). The combination of intensity and volume is fundamental to determine the dose-response in a RT session (19) and can induce specific metabolic and mechanical stress in the muscle (24,25). Schoenfeld et al., (26) described the duration as the total of the concentric, eccentric, and isometric components of repetition; and is predicated on the tempo at which the repetition is performed. ...
... Different physical conditions have been shown to induce acute cell swelling, the extent of which relies on the type of exercise, level of fatigue, volume, and intensity (24). RT exercises with momentary muscle failure reduce the intramuscular ATP and CP levels (and Pi, ADP, and AMP accumulation), a high glycolytic flux (production of H+ leads to metabolite accumulation), hypoxia (via muscle contraction), and venous pooling leading to cellular swelling (5,25,28,31). Acute cell swelling can be measured by ultrasound imaging. The ultrasound imaging measures the distance from the subcutaneous adipose tissue-muscle interface to the muscle-bone for a specific muscle (1). ...
... However, in this study, the increase in MT was partially observed as hypothesized. It is well-known that the duration of the exercise can produce higher metabolic and mechanical stress and consequently, might affect cell swelling (24,25). However, it is assumed that trained participants could be more efficient in removing the by-products from the metabolism with less effect on MT. ...
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International Journal of Exercise Science 15(6): 676-685, 2022. The primary purpose of this study was to evaluate the acute effects of different durations of the isometric forearm plank exercise (IFPE) on peak force, echo intensity, muscle thickness, and perception of effort in recreationally-trained participants. Fifteen resistance-trained participants (23±3years, 76.4±6.5kg, 173.3±6.5cm) performed the IFPE with bodyweight in one of three durations in a randomized order: a). 1-min, b). 2-min, and c). 3-min. Muscle thickness (MT), echo intensity (EI), peak force (PF), and rating of perceived exertion (RPE) were measured pre-test and post-test. Two-way repeated-measures ANOVAs (2x3) were used to test differences between tests (pre-test and post-test) and treatment (1-min, 2-min, and 3-min) for PF, MT, and EI. One-way ANOVA was used to compare RPE between treatments (1-min, 2-min, and 3-min). There was a significant increase between pre-and post-test only for 3-min IFPE (p=0.008). For EI, there was a significant increase between pre-and post-test only for 3-min IFPE (p<0.001). For PF, there were observed significant reductions on post-test between 1-min vs. 3-min (p<0.001) and 2-min vs. 3-min IFPE (p<0.001). For RPE, there were statistical differences between 1-min vs. 2-min (p<0.001), 1-min and 3-min (p<0.001), 2-min and 3-min (p=0.001). In conclusion, only 3-min IFPE induced an increase in MT and EI and a reduction in PF when compared to 1-min and 2-min (during the post-test). RPE increased with the increase in the duration of the IFPE.
... Are the muscle glycogen stores "full," and can the athlete get a pump? Glycolytic metabolites (e.g., lactate and inorganic phosphate) derived from glycogen use produce a post-exercise reactive hyperemia response known as a "pump" [203] that swells muscle tissue, increasing thickness as much as 10 % [204,205]. This poses an advantage for acutely increasing muscle size before stepping on stage and shifting fluid into specific muscle bellies (ideally even thereby reducing interstitial subcutaneous fluid volume to further enhance the appearance of muscularity), such than an athlete can preferentially "pump up" the musculature to improve the balance of the muscular development. ...
... The hyperemic "pump" requires adequate body fluid to move into the muscle belly; however, an athlete with high muscle glycogen levels but excessively reduced body water may experience "flatness," i.e., a lack of a muscle pump usually associated with a withered appearance due to excessive dehydration. On the other hand, lack of muscle glycogen to serve as the source for metabolic osmolytes for the pump effect [203] could also be to blame. ...
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Bodybuilding is a competitive endeavor where a combination of muscle size, symmetry, “conditioning” (low body fat levels), and stage presentation are judged. Success in bodybuilding requires that competitors achieve their peak physique during the day of competition. To this end, competitors have been reported to employ various peaking interventions during the final days leading to competition. Commonly reported peaking strategies include altering exercise and nutritional regimens, including manipulation of macronutrient, water, and electrolyte intake, as well as consumption of various dietary supplements. The primary goals for these interventions are to maximize muscle glycogen content, minimize subcutaneous water, and reduce the risk abdominal bloating to bring about a more aesthetically pleasing physique. Unfortunately, there is a dearth of evidence to support the commonly reported practices employed by bodybuilders during peak week. Hence, the purpose of this article is to critically review the current literature as to the scientific support for pre-contest peaking protocols most commonly employed by bodybuilders and provide evidence-based recommendations as safe and effective strategies on the topic.
... Exercise training causes changes between the intracellular and extracellular compartments of body fluids, and these changes depend on the type of exercise and the intensity of the training. Exercise that uses the glycolytic pathway as an energy source and leads to lactate accumulation contributes to osmotic changes in skeletal muscle cells (Schoenfeld, & Contreras, 2014). Increased internal muscle cell tone as a result of increased cell hydration acts as an internal mechanical stimulus for increased protein synthesis and decreased proteolysis (Grant, et al., 2000). ...
... This effect in MT might be explained as a result of a similar level of neuromuscular fatigue observed in both RT protocols. It is wellknown that RT protocols until muscle failure can produce higher metabolic and mechanical stress and consequently, affect cell swelling after a RT session (18,19). Based on the authors' knowledge, there are no studies that compared the acute responses of MT between RT protocols with different exercises, similar ROM, and recreationally-trained subjects. ...
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International Journal of Exercise Science 14(3): 1294-1304, 2021. The purpose of this study is to measure the acute effects of exercise variability on muscle thickness and physical performance after two resistance training (RT) protocols using the same or different exercises in recreationally-trained subjects. Fifteen resistance-trained men (23.1 ± 2.6 years, 83.4 ± 16.6 kg, 173.5 ± 8.3cm) performed one of two RT protocols: SINGLE: six sets of 10RM/two-minutes rest of the unilateral biceps curl exercise using cables or MIX: six sets of 10RM/two-minutes rest for the unilateral biceps curl exercises (cable: three sets and dumbbells: three sets, randomly). Muscle thickness (MT) and peak force (PF) were measured ten-minutes before (control), pre-RT session, and post-RT (immediately after and 15-minutes after). All acute RT variables were measured during both RT protocols: the maximal number of repetitions (MNR), the total number of repetitions (TNR), time under tension (TUT), and rating of perceived exertion (RPE). Two-way ANOVA (2 x 4) was used to test differences between RT protocol (SINGLE and MIX) and time (control, pre-test, post0, and post15) for MT and PF. Two-way ANOVAs (2 x 6) were used to test differences between RT protocol (SINGLE and MIX) and sets for MNR, RPEset, and TUT. For PF and MT, there were significant differences in time for both RT protocols (p < 0.05), however, there were not statistical differences between RT protocols. For MNR, RPEset, and TUT, there were significant differences in time (p < 0.05), however, there were not statistical differences between RT protocols. In conclusion, both RT protocols induced a similar increase in MT for elbow flexors and a reduction in peak force.
... In their Conclusion section, Schoenfeld and Contreras (64) claimed that heavy loads maximize motor unit activation, heavy multi-joint exercises should be the foundation of a hypertrophy training program, and that trainees should dedicate a component of their training (exercises with higher reps and shorter rest periods) to achieving the pump, which would provide an optimal hypertrophic stimulus. They failed to cite any evidence to support those recommendations. ...
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Researchers have expressed concern recently for standardization of resistance training protocols so that valid comparisons of different training variables such as muscular fatigue, time under tension, pre-exhaust exercise and exercise order, pyramid and drop sets, amount of resistance (load), range of repetitions, frequency and volume of exercise, interset rest intervals, etc. can be more closely studied and compared. This Critical Commentary addresses some recent review articles and training studies specifically focused on the stimulus for muscle hypertrophy in participants with several years of resistance training experience. It reveals that many of the recommended resistance training protocols have their foundation in some long-held, self-described bias. Blinding of assessors and statisticians, self-plagiarism, authorship responsibility, and conflicts of interest are briefly discussed as well. The conclusion is that most of the published peer-reviewed resistance training literature failed to provide any compelling evidence that the manipulation of any one or combination of the aforementioned variables can significantly affect the degree of muscle hypertrophy, especially in well-trained participants. Although the specific stimulus for optimal gains in muscle mass is unknown, many authors are desperately clinging to their unsupported belief that a greater volume of exercise will produce superior muscle hypertrophy.
... In another article, Schoenfeld and Contreras (64) wrote about the so-called muscle pump, presented a hypothetical (not theoretical) schematic effect of the muscle pump on chronic adaptations such as muscle hypertrophy (Figure, p. 22), and suggested different training manipulations such as drop-sets to maximize the pump. They claimed that a study by Goto and colleagues (65) showed that drop-set training resulted in a significant increase in muscle cross-sectional area compared with a traditional high intensity training protocol. ...
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Researchers have expressed concern recently for standardization of resistance training protocols so that valid comparisons of different training variables such as muscular fatigue, time under tension, pre-exhaust exercise and exercise order, pyramid and drop sets, amount of resistance (load), range of repetitions, frequency and volume of exercise, interset rest intervals, etc. can be more closely studied and compared. This Critical Commentary addresses some recent review articles and training studies specifically focused on the stimulus for muscle hypertrophy in participants with several years of resistance training experience. It reveals that many of the recommended resistance training protocols have their foundation in some long-held, self-described bias.
... In another article, Schoenfeld and Contreras (64) wrote about the so-called muscle pump, presented a hypothetical (not theoretical) schematic effect of the muscle pump on chronic adaptations such as muscle hypertrophy (Figure, p. 22), and suggested different training manipulations such as drop-sets to maximize the pump. They claimed that a study by Goto and colleagues (65) showed that drop-set training resulted in a significant increase in muscle cross-sectional area compared with a traditional high intensity training protocol. ...
Full-text available
Researchers have expressed concern recently for standardization of resistance training protocols so that valid comparisons of different training variables such as muscular fatigue, time under tension, pre-exhaust exercise and exercise order, pyramid and drop sets, amount of resistance (load), range of repetitions, frequency and volume of exercise, interset rest intervals, etc. can be more closely studied and compared. This Critical Commentary addresses some recent review articles and training studies specifically focused on the stimulus for muscle hypertrophy in participants with several years of resistance training experience. It reveals that many of the recommended resistance training protocols have their foundation in some long-held, self-described bias.
Kraft ist eine elementare Grundlage für jede Bewegung des Menschen und somit fundamentale Basis sportlicher Handlungskompetenzen. Das vorliegende Kapitel liefert einen Überblick über Bedeutung und Erscheinungsformen der Kraft, über biologische Grundlagen des Krafttrainings, über Anpassungsvorgänge, Trainingsmethoden und Belastungsdosierung sowie über konkrete Trainingsbeispiele. Krafttraining dient gleichermaßen zur Steigerung der Leistungsfähigkeit wie auch zur Verletzungsprophylaxe und schafft zugleich Selbstvertrauen und ästhetische Zufriedenheit. Die Kraft basiert auf verschiedenen Erscheinungsformen (z. B. Maximalkraft und Schnellkraft) und Kontraktionsformen der Muskulatur (z. B. statisch und dynamisch), die für die Sportpraxis je nach Disziplin von unterschiedlicher Bedeutung sind. Grundlegende biologische Kenntnisse zum Verständnis von Kraft und Krafttraining beziehen sich unter anderem auf den Aufbau der Muskulatur, die Muskelarchitektur, das Muskelfaserspektrum, die neuromuskuläre Signalübertragung und den Vorgang der Muskelkontraktion. Neben den klassischen Trainingsmethoden zur Verbesserung der Maximalkraft, wie dem Hypertrophietraining und dem IK-Training, existieren zahlreiche weitere ergänzende und innovative Interventionen. Exemplarisch sind das Vibrationskrafttraining, das exzentrische Overload-Training und das Okklusions- (bzw. besser Blutflussreduktionstraining) zu nennen. Alle Trainingsinterventionen bewirken Anpassungsmechanismen (Reaktionen und Adaptationen) auf teils verschiedenen physiologischen Funktionsebenen, einschließlich Veränderungen auf zellulär-molekularer Ebene. Aus der unendlichen Vielzahl an Trainingsformen werden konkrete Trainingsbeispiele strukturiert nach grundsätzlichen Trainingszielen vorgestellt (Abb. 4.1).
Background: The primary purpose of this study was to measure the acute effects on muscle thickness, arm circumference, and peak force between unilateral seated row and unilateral biceps curl exercises for elbow flexors after a RT session in recreationally-trained subjects. Methods: Fourteen resistance-trained men (25.3 ± 2.5years, 76.5± 6.4kg, 174.6 ± 7cm) performed 6 sets of 10RM and 2-min rest for one of two exercises (unilateral seated row exercise, USR or unilateral biceps curl, UBC). Muscle thickness (MT), arm circumference (AC), and peak force (PF) were measured before 10-min (control), pre-RT session and post- RT (immediately after, 15-min and 30-min). All acute RT variables were measured during both exercises: maximal number of repetitions (MNR), total number of repetitions (TNR), time under tension (TUT), rating of perceived exertion (RPE). Two-way ANOVAs were used to test differences between exercises and moments with an alpha of 5%. Results: For PF, there was a significant difference between pre- and post-0 for UBC and USR (p<0.001). For AC, there were significant differences between pre-test x post-0-min for both exercises (p<0.001). For MT, there were significant differences between pre-test x post 0-min (p<0.001), pre-test x post 15-min (p<0.001) for both exercises and pre-test x post 30- min only for UBC (p=0.006). Conclusions: Both exercises induced similar increases in AC and MT for elbow flexors and reduction in peak force.
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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.