Cross-education effect after unilateral eccentric-only isokinetic vs dynamic constant external resistance training

The aim of this study was to evaluate the effects of unilateral eccentric training using constant velocity or constant external load on untrained limb. Forty-nine participants were randomized in isokinetic (IK), dynamic constant external resistance (DCER) unilateral eccentric training or control groups. Knee-extension 1RM and isometric, eccentric and concentric knee extensors’ peak torques, as well as changes in vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass were measured. After training, both IK and DCER similarly increased over time 1RM (respectively, +3.6 kg, CI 95 % 0.6–6.5 and +4.3 kg, CI 95 % 1.6–6.9), concentric (respectively, +8.4 N/m, CI 95 % 0.0 to +16.4 and 9.8 CI 95 % 0.6–19.2), eccentric (respectively, +28.5 N/m, CI 95 % 11.0 to +46.0 and 21.1 CI 95 % 15.1–37.0), and isometric (respectively, +15.4 N/m, CI 95 % 0.7–30.0 and +13.9, CI 95 % 0.3–27.5) peak torques. No increase was found for vastus lateralis muscle thickness, fascicle length, pennation angle and quadriceps fat-free mass. Eccentric training was effective for inducing strength, but not structural, adaptations in untrained limb. Both in rehabilitation and training practice, use of easily available gym devices can be a good substitute for expensive and often unavailable isokinetic devices.