Postactivation Potentiation (PAP) is the phenomenon of increased, albeit transient, contractile properties of skeletal muscle resulting from non-fatiguing sub-maximal repetitions. Mechanisms underlying PAP are not clearly elucidated; however, it is suggested that alterations of calcium sensitivity and neural excitability are responsible. Relatively few studies have utilized variable resistance from elastic bands to elicit PAP. Even fewer studies have investigated changes in the rate of force development (RFD). PURPOSE: The purpose of this study was to determine the efficacy of variable-resistance conditioning stimulus for eliciting a potentiation effect in the biceps brachii. METHODS: A digital force transducer and sEMG interfaced with a computerized data acquisition system (1000 Hz sampling) were utilized to quantify the muscular contractile properties of peak force (N) and RFD (ΔN·sec‾¹). Thirteen resistance-trained men (age, 24.5 ± 9.3 yrs; stature, 178.4 ± 13.2 cm; mass, 91.6 ± 14.0 kg) performed pre- and post-test maximal voluntary isometric contractions (MVIC) of the biceps brachii, with a pre-determined number of conditioning sets (CS) between. CS consisted of six full-range concentric and eccentric arm curls with an elastic band providing resistance of 70 ± 10% of the pre-test MVIC. The independent variable consisted of five levels (CONTROL, 1CS, 2CS, 3CS, and 4CS). RFD was calculated as ΔN·sec‾¹ (slope representing 10–50% MVIC) when initiating a contraction. Data was analyzed as % change from pre- to post-test for each of the five levels. ANOVA compared pre-post % change of the five levels for each of the two dependent variables (MVIC, RFD). RESULTS: Repeated measures one-way ANOVA revealed no differences for force production (CON = -1.27 ± 5%, 1CS = +0.77 ± 5%, 2CS = -0.46 ± 4%, 3CS = +0.73 ± 5%, 4CS = -1.86 ± 7%, P>0.05). Similarly, the RFD pre-post % change was not different for any of the five levels (CON +1.22 ± 15%, 1CS +4.26 ± 28%, 2CS +5.08 ± 24%, 3CS +27.18 ± 54%, 4CS +8.11 ± 48%). When comparing pretest and posttest scores for each of the conditions, there were no differences observed except for one interesting comparison. When participants completed three conditioning sets (3CS), post-test RFD increased (Pre 1.42±0.89 ΔN·sec‾¹, Post 1.78±1.37 ΔN·sec‾¹, P = 0.04). CONCLUSION: As performed in this study, conditioning sets using variable resistance were not effective for eliciting PAP. None of the CS conditions increased MVIC as compared to either pretest values or CONTROL. However, three conditioning sets did evoke an increase in RFD as compared to pretest. More research is warranted to explore and confirm this interesting observation.

Supported by Pacific University Research Grant.

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