Abstract
The current randomized controlled study investigated whether or not the inclusion of the eccentric phase in resistance training favors the contralateral strength gains after different unilateral protocols, and whether such gains are retained after detraining. Sixty healthy women were randomly assigned to a unilateral concentric-only (CONC), eccentric-only (ECC), concentric–eccentric (TRAD) volume-equated knee extension training or control group (CON). The participants trained 2 days/week for 8 weeks and then did not train for further 8 weeks. Knee extensors isokinetic concentric, eccentric, and isometric peak torque and vastus lateralis muscle thickness were assessed in the contralateral limb at baseline, post-training, and post-detraining. At post-training, concentric peak torque increased in CONC [+9.2%, 95%CI (+6.2/+12.3), p < 0.001, ES: 0.70, 95%CI (0.01/1.39)], ECC [+11.0% (+7.7/+14.2), p < 0.001: ES: 0.66(0.09/1.23)] and TRAD [+8.5%(+5.7/+11.6), p < 0.001, ES: 0.50(0.02/0.98)]. Eccentric peak torque increased in ECC in ECC [+15.0%(+11.4/+20.7), p < 0.001, ES: 0.91(0.14/1.63)] and TRAD [+5.5%(+0.3/10.7), p = 0.013, ES: 0.50(0.05/0.95)]. Isometric peak torque increased in ECC [+11.3(+5.8/16.8), p < 0.001, ES: 0.52(0.10/0.94)] and TRAD [+8.6%(+3.4/+13.7), p < 0.001, ES: 0.55(0.14/0.96)]. No change in eccentric and isometric peak torque occurred in CONC (p > 0.05). Muscle thickness did not change in any group (p > 0.05). At post-detraining, all groups preserved the contralateral strength gains observed at post-training (p < 0.05). The findings showed that ECC and TRAD increased contralateral knee extensors strength in concentric, eccentric, and isometric modality, while CONC only increased concentric strength. The eccentric phase appears to amplify the cross-education effect, permitting a transfer in strength gaining toward multiple testing modalities. Both eccentric-based and traditional eccentric–concentric resistance protocols are recommended to increase the contralateral retention in strength gains after a detraining period.
Highlights
When resistance training is systematically performed unilaterally, the training effects are visible in the untrained limb, so that strength gains occur in the contralateral homologous muscles (Munn et al, 2004; Manca et al, 2017)
The findings showed that ECC and TRAD increased contralateral knee extensors strength in concentric, eccentric, and isometric modality, while CONC only increased concentric strength
The test–retest reliability was excellent for concentric (ICC = 0.932), eccentric (ICC = 0.910) and isometric (ICC = 0.928) peak torque and for vastus lateralis muscle thickness (ICC = 0.901)
Summary
When resistance training is systematically performed unilaterally, the training effects are visible in the untrained limb, so that strength gains occur in the contralateral homologous muscles (Munn et al, 2004; Manca et al, 2017). Unilateral dynamic traditional resistance training consists of the execution of both concentric and eccentric phase for a given exercise, and its effectiveness in promoting crosseducation was already reported (Shima et al, 2002; Munn et al, 2005; Fimland et al, 2009; Pearce et al, 2013; Green and Gabriel, 2018; Leung et al, 2018). When directly compared, eccentric-only vs concentric-only training appears as more effective in promoting contralateral strength gains (Hortobágyi et al, 1997; Kidgell et al, 2015). When performing a direct comparison, the training–testing specificity (e.g., concentriconly training and concentric strength test) and the capacity to promote contralateral strength in non-specific testing modalities should be accounted for. The effects of traditional concentric–eccentric training, the most used in practice, were not concurrently examined
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