5 research outputs found
Intracellular signaling in human skeletal muscle following different modes of exercise
Resistance and endurance exercise when performed regularly will cause specific
adaptations in human skeletal muscle. Resistance exercise is known to increase strength
and muscle mass while endurance training increases vascularisation and mitochondrial
density which results in enhanced oxidative capacity. To understand how these
adaptations occur, it is important to examine the molecular signaling events in muscle.
The Akt-mTOR pathway has been shown to have an important function in the
stimulation of protein synthesis.
This pathway is stimulated following resistance exercise in human muscle. During the
work included in this thesis it has become clear that endurance exercise also stimulates
Akt-mTOR signaling in human skeletal muscle. Study (I) revealed an increased
phosphorylation of mTOR, Akt and GSK3 and a marked decrease in eEF2
phosphorylation indicating a stimulatory response on elongation and initiation of
protein synthesis in the early recovery phase. Furthermore, as shown in study (II), this
stimulatory response is followed by an increase in the fractional synthetic rate (FSR),
which was progressively increased when measured up to 3 h following endurance
exercise.
It is usually recommended that resistance exercise is performed 2-3 times per week. In
study (III), markers for anabolic (Akt, mTOR, p70S6k, rpS6, eEF2 and GSK-3β) as
well as catabolic (MAFbx and MuRF-1) processes were investigated following two
sessions of resistance exercise separated by 48 hours. From this study it appears that
anabolic signaling is slightly enhanced following the second exercise session, and
furthermore, the changes in gene expression related to muscle protein degradation
(MAFbx and MuRF-1) is attenuated during the second exercise session.
Endurance exercise can compromise the adaptive response of strength training. On the
other hand, there is some evidence suggesting that combining endurance training with
resistance exercise may have beneficial effects on endurance exercise performance. The
final study was designed to evaluate whether resistance exercise can enhance the
muscle adaptive response to endurance exercise with respect to molecular signaling
related to increased protein synthesis and specific markers for mitochondrial
biogenesis. An enhanced signaling response was actually found in the combined
exercise protocol. Specifically, expression of genes related to increased mitochondrial
biogenesis and oxidative metabolism (PGC-1α, PRC and PDK-4 mRNA) as well
markers for anabolic signaling (mTOR, p70S6k), was enhanced when endurance
exercise was followed by a session of heavy resistance exercise. This data support the
notion that including resistance exercise in endurance training may be beneficial.
In summary, mixed muscle FSR is gradually increased following endurance exercise
when measured during the first 3 h of recovery and this increase is accompanied by
stimulation of mTOR signaling. Resistance exercise enhances effects on anabolic
signaling and attenuates expression of genes involved in muscle protein breakdown and
inhibition of muscle growth during a second exercise session performed two days after
the first. Finally, combining endurance and heavy resistance exercise can enhance acute
adaptive responses and indicates that combined exercise may be superior to endurance
exercise alone
Nya aspekter på aminosyrors roll i den muskulära anpassningen till träning
Sammanfattningsvis kan sägas att tillgängligheten av protein/aminosyror är nödvändig för den muskulära anpassningen till träning vid både styrke- och uthållighetsträning. Betydligt fler studier har undersökt effekterna på styrketräning, men vid båda typer av träning är dock kunskaperna om de bakomliggande mekanismerna ännu så länge små. Genom den omfattande forskning som pågår inom området kommer med all säkerhet de molekylära och cellulära förändringar som sker i samband med träning att kartläggas inom en relativt snar framtid. Därmed öppnas nya möjligheter att förbättra och optimera träningen, t.ex. genom kombination av olika typer av aktiviteter (uthållighet och styrketräning). Denna kunskap är också avgörande för att förstå och eventuellt kunna påverka träningseffekten genom förändringar i nutritionens sammansättning