The hypothesis was tested that the magnitude of cross education is greater following training with muscle lengthening than shortening. Changes in contralateral concentric, eccentric, and isometric strength and vastus lateralis and biceps femoris surface electromyographic (EMG) activity were analyzed in groups of young men who exercised the ipsilateral quadriceps with either eccentric (N= 7) or concentric (N= 8) contractions for 36 sessions over 12 wk. Control subjects (N= 6) did not train. Concentric training increased concentric strength 30% and isometric strength 22%, and eccentric training increased eccentric strength 77% and isometric strength 39% (allP< 0.05). Eccentric training improved eccentric strength three times more than the concentric training improved concentric strength (P< 0.05), and eccentric compared with concentric training improved isometric strength about 2 times more(P< 0.05). The eccentric group improved significantly from pre- to mid-training in eccentric and isometric strength (P< 0.05). The control group showed no significant changes (P< 0.05). Surface EMG activity of the vastus lateralis increased 2.2 times (pre- to mid-training), 2.8 (mid- to post-training) and 2.6 more (pre- to post-training) (P< 0.05) in the eccentric than concentric group. No significant changes in EMG activity occrred in the control group(P> 0.05). It was concluded that the greater cross education following training with muscle lengthening is most likely being mediated by both afferent and efferent mechanisms that allow previously sedentary subjects to achieve a greater activation of the untrained limb musculature.