The mitogen-activated protein (MAP) kinase pathways have been highlighted a
s a possible link between exercise and adaptive changes in skeletal muscle
In this study, the effect of exercise intensity on the activation of the ER
K/MAP kinase pathway was investigated in human skeletal muscle. One-leg exe
rcise at low (40%, maximal oxygen consumption, VO2max, for 30 min) and high
(75% VO2max for 30 min) intensity resulted in 11.5+/-8. 1-fold and 39.7+/-
6.3-fold (mean +/-SEM) increases in ERK1/2 phosphorylation (P<0.001), respe
ctively. The phosphorylation of MEK1/2, the upstream kinase of ERK1/2, incr
eased with exercise intensity (P<0.05) to 2.5+/-0.9 and 4.8+/-1.1 times the
basal level at the low and high intensity, respectively. The statistical a
nalysis revealed a systematic difference between basal, low and high intens
ity exercise levels for both kinases. There was no change in the phosphoryl
ation of either kinase in the non-exercised leg. The phosphorylation of the
transcription factor cyclic AMP response clement binding protein (CREB), a
possible downstream target of the ERK/MAP kinase signalling pathway, was u
naffected by exercise. The phosphorylation of ERK1/2 was significantly high
er in purified freeze-dried compared to crude wet muscle after exercise, wh
ereas the opposite pattern was observed for CREB. In conclusion, phosphoryl
ation of ERK1/2 and MEK1/2 increases in an exercise intensity-dependent man
ner in human skeletal muscle and this seems to originate in the muscle fibr
es themselves.