Comparing Polarized Vs Threshold Training For Improving Diaphragm And Myocardium Mitochondrial Function In Wistar Rats

Cardiac and respiratory muscles mitochondrial function is determinant for endurance performance. Polarized training (POL) has been suggested to be superior to threshold training (THR) in improving endurance performance, but there is no evidence on its effects on cardiac and respiratory muscles mitochondrial function. PURPOSE: Compare an 8-week POL vs THR training protocol on mitochondrial respiration, function, and dynamics in the left ventricle (LV) and diaphragm. METHODS: 15 male Wistar rats (336.1 ± 30.4 g) were divided in three groups: POL (n = 5), THR (n = 5) and controls (CON, n = 5). VO2max was determined by indirect calorimetry at baseline. POL performed 12 min@90%V̇O2max + 48 min@60%V̇O2max while THR performed 5 min@50%V̇O2max + 48 min@75%V̇O2max treadmill running 5d/w during 8-weeks. O2 uptake during training was similar between POL (3128 L/d O2) and THR (3277 L/d O2; p = .261) groups. CON performed treadmill running 10 min/d, 10 m/min, 5d/w to equalize treadmill stress. All animals were housed in cages with access to running wheel to allow ad libitum physical activity. At the end of the protocol all animals were sacrificed, and LV and diaphragm samples were collected for mitochondrial respiration assessment by high-resolution respirometry, western blotting and citrate synthase (CS) activity determination by spectrophotometry. RESULTS: POL and THR training increased non-phosphorylating resting state (leak) with electron provision through complex I. Although values were higher in the POL group for both the LV and diaphragm, differences were not significant. No significant variations in OXPHOS respiration were observed across groups for LV (p = 0.219) and diaphragm (p = 0.707) as well as regarding the expression of MFN1 in the LV (p = 0.557) and diaphragm (p = 0.621), MFN2 in the LV (p = 0.518) and diaphragm (p = 0.373), PGC1-alpha expression in the LV (p = 0.423) and diaphragm (p = 0.363) and TFAM expression in the LV (p = 0.353) and diaphragm (p = 0.515). There were also no differences between groups in LV (p = 0.348) and diaphragm (p = 0.753) CS activity. CONCLUSION: POL and THR groups displayed similar bioenergetic adaptations regarding mitochondrial oxidative phosphorylation capacity, mitochondrial biogenesis markers and CS activity in the LV and diaphragm. FCT grants UID/DTP/00617/2020, LA/P/0064/2020, PTDC/SAU-DES/4113/2020 and 2022.10037.BD.