A. Ratkevicius et al., SUBMAXIMAL-EXERCISE-INDUCED IMPAIRMENT OF HUMAN MUSCLE TO DEVELOP ANDMAINTAIN FORCE AT LOW-FREQUENCIES OF ELECTRICAL-STIMULATION, European journal of applied physiology and occupational physiology, 70(4), 1995, pp. 294-300
The aim of this study was to test the hypothesis that low intensity ex
ercise-induced low frequency fatigue is caused by failure of excitatio
n-contraction coupling. Changes in knee extension torque at 5, 10, 15.
20 and 50 Hz electrical stimulation of quadriceps muscle in ten healt
hy, young, male subjects were recorded during 20-min voluntary exercis
e followed by 60-min recovery. In seven of the ten subjects, changes i
n torque during 3 min of 10-Hz stimulation were recorded 2 min and 20
min after 20 min voluntary exercise. Exercise was performed at 30% of
maximal voluntary contraction with a contraction plus relaxation perio
d of 6 plus 4 s. Torque at 5, 10, 15, 20 and 50-Hz stimulation at the
end of exercise was reduced to mean 91.0 (SEM 5.4)%, 68.7 (SEM 5.4)%,
67.2 (SEM 3.9)%, 66.5 (SEM 4.5)% and 74.7 (SEM 4.3)% of control values
, respectively. During the first 30 s of the 3 min 10-Hz stimulation,
torque was reduced in exercised muscle and increased in nonfatigued mu
scle. The reduction in torque was more marked 20 min after exercise th
an after 2 min. In conclusion, the pattern of depression and recovery
of muscle force observed was in agreement with the hypothesis that the
main cause of low intensity exercise-induced low frequency fatigue is
an impairment of excitation-contraction coupling.