Biological Background of Block Periodized Endurance Training: A Review.

Block periodized (BP) training is an innovative and prospective approach that is drawing increasing attention from coaching scientists and practitioners. However, its further dissemination and implementation demands serious scientific biological underpinnings. More specifically, the fundamental scientific concepts of homeostatic regulation, stress adaptation and the law of supercompensation determine the biological essence and content of appropriate block mesocycles, i.e., the accumulation, transmutation and realization cycles, respectively. Such a separation is intended to prevent conflicting physiological responses and provide a favorable interaction for training effects. Several studies have evaluated the metabolic effects of various training programs, and the superiority of the BP model has been confirmed in terms of significant gains of maximal oxygen uptake, maximal power output and positive trends in athletic performance. It was found that the endocrine status of athletes is strictly dependent on appropriate blocks such as voluminous extensive workloads combined with resistance training (accumulation), lower-volume intense training (transmutation), and event-specific precompetitive training (realization). Evidence from molecular biology indicates the major regulators that determine meaningful adaptive events within specific block mesocycles. Specifically, voluminous extensive accumulation blocks stimulate mitochondrial biogenesis and protein synthesis in slow-twitch muscle fibres, whereas lower-volume intense workloads of the transmutation blocks evoke adaptive modifications in fast-twitch glycolytic and oxidative-glycolytic muscle fibers. Furthermore, such a training program causes a remarkable elevation of myonuclear content in muscle fibers that enables athletes to regain previously acquired abilities. The precompetitive realization block produces accentuated expression of stress-related and myogenic genes that affect protein synthesis and increase muscle glycogen. In addition, such a program stimulates and increases the size, force and power of fast-twitch fibers.