Resistance training (RT) bout promotes exercise-induced muscle damage (EIMD), but repetition of exercise stimulus lead to attenuation of EIMD termed the repeated bout effect. However, EIMD can be measured directly or estimated using indirect markers, and their responses have never been followed nor compared throughout an RT period.
PURPOSE: Analyze EIMD directly (Z-band streaming) and indirectly (maximal isometric voluntary contraction (MVC), muscle soreness (SOR) and creatine kinase (CK) activity) throughout a RT program.
METHODS: 10 healthy untrained young men (27 ± 1 years; body mass index 23.6 ± 1.0 kg·m-2) performed isoinertial RT twice a week, for 10 weeks and were evaluated for: a) Z-band streaming magnitude from muscle biopsies at pre- and 48h post-RT bout at the first (T1), third (T2) and last (T3) RT week; and b) MVC in an isokinetic dynamometer, SOR using a visual analog scale and CK activity on plasma were assessed at pre-, 24h (except CK) and 48h post-RT bout at T1, T2 and T3.
RESULTS: Z-band streaming area increased at 48h at T1 (10.3 ± 3.6%) and at T2 (10.8 ± 2.5%) compared with pre at the respective week (T1: 0.1 ± 0.1%; T2: 4.9 ± 1.0%). Z-band streaming was lower at 48h at T3 (2.4 ± 0.9%) when compared to 48h values at T1 and T2. MVC decreased and SOR increased significantly at 24h (MVC: 78 ± 5%, SOR: 40 ± 6 mm) and 48h (MVC: 78 ± 5%, SOR: 61 ± 8 cm) at T1. In addition, CK increased at 48h (416 ± 81 UI·l-1) at T1. There were no significant changes from baseline for the indirect markers at T2 and T3.
CONCLUSION: The repeated bout effect induced by 4 previous RT bouts (at T2) measured directly by Z-band streaming was small or even negligible, as compared with attenuations of MVC, SOR or CK. Therefore, the early attenuation of EIMD extensively reported in the literature is seen only when examining indirect markers than by direct measurement of muscle remodelling (Z-band streaming) at least when using a continuous isoinertial RT. Clearly indirect markers of EIMD do not reflect the direct measures of EIMD and protein remodelling seen as Z-band streaming. Indirect markers are poor reflections of actual damage to the muscle per se and should be used with caution.
Supported by FAPESP (grants #2012/24499-1, #2014/19594-0 and #2013/21218-4), CNPq (grants #304205/2011-7 and #307023/2014-1) and NSERC.