The Repeated Bout Effect In Ipsilateral And Contralateral Limbs After Single Bouts Of Lengthening Contractions

A single bout of lengthening contractions can result in profound adaptations known as the repeated bout effect (RBE), which has been shown to protect skeletal muscle from subsequent insults of lengthening contractions. Chronic eccentric training has been shown to produce neuromuscular adaptations in the untrained homologous muscle, making the expectation tenable that acute bouts of eccentric contractions would evoke rapid adaptation in the contralateral limb. PURPOSE Firstly, to examine whether the RBE exists in the contralateral limb and secondly, to compare any protection to that manifested in the ipsilateral limb. METHODS Sixteen subjects, randomly assigned to an ipsilateral (IL) or contralateral (CL) group, performed maximal lengthening contractions of the elbow flexors, followed by an identical bout carried out on either the CL or IL limb 2 weeks later. Damage markers of creatine kinase (CK), muscle soreness (DOMS) and maximal isometric contraction (MVC) were measured before, 48 h and 96 h after the initial exercise and at the same time periods before and after the subsequent bout. [CK] data were log transformed and MVC was normalised and expressed as a percentage change from baseline. RESULTS: The CL group showed a diminished decrement in MVC and reduced DOMS in bout 2 (F = 9.0, P = 0.020; F = 7.6, P = 0.028, respectively). CK and DOMS showed significant group × bout × time interactions (F = 4.4, P = 0.022; F = 4.0, P = 0.030, respectively). Post-hoc pair-wise analysis revealed that in the second bout, compared to the CL group, the IL group demonstrated reduced CK at 96 h (P <0.001) and less soreness at 48 h (P = 0.006). MVC showed a group × time interaction (F = 5.6, P = 0.009); post-hoc pair-wise comparisons showed the IL group had a lower decrement in torque than the CL group at 48 h (P <0.001) and 96 h (P <0.045) in bout 2. CONCLUSIONS This is the first investigation to demonstrate evidence of a repeated bout effect in the contralateral limb from a single bout of lengthening contractions. However, the magnitude of protection is less in the CL limb than in the IL limb.