The aim of the present series of studies was to investigate acute neuromuscular responses to (1)
different strength training loadings and using (2) different external resistances. In addition,
chronic adaptations and dynamic performances were compared to (3) the changes in isometric
force-time parameters at the group level, and to (4) the individual timing of the improvement in
the rate of force development (RFD) due to hypertrophic or maximum strength followed by
power strength training periods. The latter one was achieved by systematic, repeated monitoring.
Sixty-nine physically active men (20-35 yrs), but not experienced in resistance training, took part
in the present series of studies. Cross-sectional study designs included hypertrophic (5 sets of 10
repetition maximum), power (5 sets of 5 repetitions at 40% of one repetition maximum) and
maximum strength (15 sets of one repetition maximum) loadings using pneumatic and weight-
stack devices with and without add
itional elastic resistances for the knee extensor muscles.
During single explosive contractions, pneumatic resistance allowed greater power production at
lower resistance levels due to higher velocities compared to weight-stack resistance. Conversely,
weight-stack with additional elastic resistance increased power production due to greater torque
towards the end of the movement compared to “pure” weight-stack resistance. However, during
power strength loadings with explosive contractions, weight-stack resistance targeted the initial
force production and, consequently, induced greater neuromuscular fatigue indicated by changes
in muscle activity (EMG) during the first 100ms compared to pneumatic and weight-stack with
elastic resistances. Nevertheless, greater resistance during weight-stack with elastic resistance
induced greater central fatigue compared to “pure” weight-stack. Weight-stack resistance
followed more closely maximal force production of muscles inducing greater peripheral fatigue
during hypertrophic and maximum strength loadings compared to pneumatic resistance.
Repeated maximal repetitions during maximum strength loadings also led to central fatigue
during weight-stack resistance.
During the longitudinal study, time to reach peak RFD was identified as a potential
parameter to differentiate adaptation between “peripheral and central focused” strength training,
while the steepest phase of RFD may identify adaptations particularly during maximal
strength/power training. Monitored isometric RFD parameters seemed to more sensitively and
systematically reflect short-term responses from different training stimuli compared to peak
isometric MVC. Nevertheless, MVC correlated strongly with the long-term changes in 1RM due
to strength training. From the individual trainee’s perspective, the timing of the improvement in
monitored RFD was related to baseline CSA and training-induced changes in anabolic and
catabolic hormonal regulation. Based on these individual differences, RFD improved in one-third
of the trainees following the maximum strength training period, one-third following the power
strength training period, and the remaining one-third did not respond to either of the
aforementioned training periods. Regularly repeated isometric monitoring during strength
training could assist in tailoring training programs and selecting durations of the periodization
cycles for each athlete, individually.
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