Muscle ischemic preconditioning reduces feedback from group iii and iv muscle afferents.

INTRODUCTION The primary aim of this study was to test the hypothesis that muscle ischemic preconditioning (MIP) reduces feedback from group III and IV muscle afferents measured indirectly by muscle metaboreflex. The second aim was to investigate whether the hypothesized reduction in afferent feedback (Crisafulli et al, 2011) causes a reduction of rating of perceived exertion (RPE) as predicted by the afferent feedback model of PE (Marcora, 2009) MATERIAL AND METHODS Nine healthy subjects visited the laboratory three times in a single-blind, randomized and counterbalanced experimental design. In a preliminary day they underwent a one leg incremental test up to exhaustion to detect Wmax then an experimental (EXP) and control (SHAM) session in separated days. To test muscle afferent activity, two post-exercise muscle ischemia (PEMI) were executed. PEMI involved: 3 min of baseline, 3 min of exercise at 70% of Wmax, 3 min of thigh occlusion followed by 3 min of recovery. MIP treatment during EXP or SHAM was executed between the two PEMI sessions. MIP involved 3 cycles of occlusion of 5 min at 220 mmHg separated by 5 min of reperfusion. During the SHAM session, occlusion was 20 mmHg. Cardiac output (CO), mean arterial pressure (MAP) and RPE during exercise were monitored during both PEMI sessions. RESULTS CO and MAP responses were significantly reduced after MIP (CO = 6.92 ± 1.81 vs 5.79 ± 1.39 l•min-1 and MAP= 109.25 ± 9.85 vs 103.70 ±10.43 mmHg). RPE was not affected by MIP (15.67 ± 1.87 vs 15.56 ± 2.07). None of the parameters reported any statistical changes in the SHAM condition. DISCUSSION This study shows for the first time that MIP reduces feedback from group III and IV muscle afferents as indicated by a significant reduction in muscle metabo-reflex. Despite this reduced afferent feedback, RPE was unchanged. This finding provides further experimental evidence that feedback from III and IV muscle afferents is not a sensory signal for PE. REFERENCES Crisafulli A. et al J Appl Physiol. 2011 Aug;111(2):530-6. Marcora S. J Appl Physiol. 2009 Jun;106(6):2060-2.