Comparing Polarized Vs Threshold Training For Improving Mitochondrial Function In Skeletal Muscle Of Wistar Rats

Recently, Polarized Training (POL) was suggested to be superior to other training intensity distributions (TIDs) for improving endurance, however, there is no evidence comparing the superiority of POL vs Threshold Training (THR) in mitochondrial function. PURPOSE: Compare an 8-week POL vs THR training protocol on mitochondrial respiration, function, and dynamics in tibialis anterior and soleus muscles. 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 (80% low intensity/20% high intensity) while THR performed 5 min@50%V̇O2max + 48 min@75%V̇O2max (moderate intensity) 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 (isocaloric exercise protocol). 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 tibialis anterior and soleus muscles 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 in both soleus and tibialis anterior muscles (p < .005). No significant differences across groups were observed in OXPHOS respiration for soleus (p = .297) or tibialis anterior (p = .622), or regarding the expression of MFN1 in soleus (p = 0.313) and tibialis anterior (p = 0.613), MFN2 in soleus (p = 0.929) and tibialis anterior (p = 0.789), PGC1-alpha in soleus (p = 0.858) and tibialis anterior (p = 0.595), and TFAM in soleus (p = 0.757) and tibialis anterior (p = 0.950). There were also no differences in CS activity between groups in soleus (p = 0.121) and tibialis anterior (p = 0.558). CONCLUSIONS: POL and THR groups displayed similar bioenergetic adaptations regarding mitochondrial oxidative phosphorylation capacity, mitochondrial biogenesis markers and CS activity in tibialis anterior and soleus muscles. This work was funded by FCT grants UID/DTP/00617/2020, LA/P/0064/2020, PTDC/SAU-DES/4113/2020 and 2022.10037.BD.