Comparison of Unilateral, Asymmetric and Traditional Bilateral Resistance Training in Untrained Women: A Pilot and Proof-of-Concept Study

Background: Both unilateral and asymmetric loading have been used to increase training specificity and create over-load in a target limb to reduce inter-limb asymmetries. The aim of the study was to compare the effects of conducting either unilateral- or asymmetric-loaded resistance training with traditional bilateral resistance training on maximal dynamic and isometric strength in untrained women. Methods: Thirty-four women not conducting regular resistance training were randomized into unilateral (UNI), bilateral (BIL) or asymmetric (ASY) upper-body resistance training (2–3·wk−1, 10 wk, 24 sessions in total). UNI conducted all exercises unilaterally (one arm at a time), BIL conducted all exercises bilaterally (both arms), and ASY added 10% of the total load to the non-dominant side. Maximal strength was tested in chest press, seated row (1-RM and MVC in both), and pallof press (only MVC). Results: At post-test, BIL demonstrated greater bilateral 1 RM strength than ASY (p = 0.017, d = 1.25) in chest press, while UNI demonstrated greater 1 RM strength in the dominant side than ASY (p = 0.006, d = 1.45). For the other strength tests, no differences were found between groups in chest press (p = 0.068–0.481), seated row (p = 0.091–0.591) or MVC peak force for both chest press and seated row (p > 0.05). All groups demonstrated pre–post improvements for all measurements in chest press (p < 0.05) and seated row (p < 0.05), but only ASY demonstrated improvements in pallof press on the non-dominant side. Conclusions: Compared to traditional bilateral training, unilateral resistance training did not result in similar effects on dynamic or isometric strength. Asymmetric resistance training demonstrated a lower change in chest press strength on the bilateral and dominant sides compared to the other groups.