Polarized or threshold training: is there a superior training intensity distribution to improve V̇O₂max, endurance...

Conflicting evidence exists regarding the superiority of Polarized Training (POL) vs other training intensity distribution models. Compare POL vs threshold (THR) training on V̇O₂max, endurance capacity (EC) and mitochondrial function. Fifteen male Wistar rats (336.1 ± 30.4 g) were divided in: POL (n = 5), THR (n = 5) or control (CON; n = 5) groups. V̇O₂max (indirect calorimetry) and EC (treadmill exhaustion test) were determined at baseline four and eight-weeks of training. POL consisted of 80% running volume at 60%V̇O₂max and 20% at 90%V̇O₂max while THR trained only at 75%V̇O₂max. Both protocols were isocaloric and performed 5d/week. All animals were housed in cages with access to running wheel to allow ad libitum activity. After training, animals were sacrificed and left ventricle (LV) myocardium, diaphragm, tibialis anterior and soleus muscles were collected for high-resolution respirometry, biochemical and histological analysis. There were no baseline differences between groups. After training V̇O₂max and EC were similar between POL and THR even though THR V̇O₂max was higher compared to CON. After training, there were also no significant differences in OXPHOS or any of the other major mitochondrial function markers assessed between POL and THR in any of the tissues analyzed. The expression of MFN1, MFN2, PGC-1α, TFAM, DRP1, OPA1 and TOM20 as well as the activity of citrate synthase were also similar between POL and THR in all tissues. There were no significant differences in endurance performance or markers of bioenergetic function between POL and THR after eight-weeks of training.