First-repetition accentuated eccentric loading (FR-AEL) is a relatively new approach to resistance
training. The first repetition performed using this method, in which a greater load is used during
the lowering phase than during the lifting phase and all subsequent repetitions, is expected to
improve the performance of subsequent repetitions within the same set. The purpose of this study
was to determine which type of muscle contraction (eccentric, concentric or isometric) has the
greatest effect on the mechanical variables of subsequent explosive concentric repetitions of
knee extension on a resistance training machine and on the mechanical variables of knee
extensor twitches. Seven explosive concentric repetitions were performed, or five twitches were
elicited at intervals ranging from 5 to 60 seconds after the potentiation protocols. Sixteen men
participated in the study. They completed four protocols (three experimental and one control) in
a randomised order. Measurements were performed unilaterally on a leg extension machine. The
effect on explosive concentric repetitions was evaluated on the basis of peak torque, maximal
rate of torque rise over a 100 ms interval, torque impulse during the first 100 ms, power index,
maximal rate of increase in EMG amplitude over a 100 ms interval and increase in EMG amplitude
during the first 100 ms. The effect on twitches was evaluated based on contraction time, twitch
amplitude, half-relaxation time, M-wave amplitude and maximal rate of twitch torque rise. The
results for the explosive concentric repetitions showed no differences between the types of
muscle contraction. The twitch results showed statistically significant differences between the
control and experimental protocols and among the experimental protocols. The greatest changes
compared with the control condition were observed following the isometric protocol, specifically
in twitch amplitude and maximal rate of torque rise. The changes in the twitch response are
consistent with the occurrence of post-activation potentiation (PAP). The results of the eccentric
and concentric protocols were similar. We believe that the isometric protocol was the most
effective because ofthe specificity of the movement pattern during the potentiating repetition and
the position in which the effects on the twitch response were measured (the potentiating
repetition and twitch measurements were performed isometrically at 60° of knee flexion). The
findings indicate that the type of prior muscle contraction influences the magnitude of PAP (based
on muscle twitch measurements). The effect on explosive concentric repetitions within a
resistance training set could not be reliably confirmed in this study.
|
