The purpose of this study was to consider the effect of plyometric training and subsequentdetraining on changes in force-velocity relationship. Methods: Forty active students withaverage and standard deviation age of 24 ± 2.3 Year; weight 75± 5.6 Kg and height 176± 8.3Cm participated in this study. Subjects divided into control and experimental group. The Biodexand EMG were used to measure muscle contraction velocity and to assess muscle electricalactivity. The control group subjects asked to continue their daily activities and experimentalgroup subjects were asked to participate in a 6-week plyometric training program. Dataregistered in pre-test; post-training and post-detraining. The independent t-test and repeatedmeasures ANOVA and post hoc Tokay was used for data analysis. Results: The results showedsignificant increase in experimental group subject ׳s EMG in post-training period in all motionsand decrease EMG in post-detraining in slow and moderate motions (p <0.05). The controlgroup subject ׳s EMG not changed in all motions for all periods. Conclusions: it seems reductionof EMG activity of muscles was due to insufficient intensity of applied movements becauseapplying high intensity movements caused maintenance of physiological adaptation of training.