Science
Periodization
The reason you do not just add weight every session forever is that the body adapts. Periodization is the framework for managing that adaptation intentionally.
What the evidence says
Periodization describes how training stress, volume, and intensity are organized over time to produce ongoing adaptation. The basic problem it solves: a fixed training stimulus stops producing a training response after the body adapts to it. Varying the stimulus — in a structured, progressive way — keeps adaptation happening.
Linear periodization is the simplest model. Load increases over time while volume stays roughly fixed. Beginners using 5×5 at progressively heavier weights are doing linear periodization. The limitation is that you are always at the same place in the intensity/volume curve — when you are lifting heavy, you are not accumulating volume, and vice versa.
Block periodization (also called conjugate or sequential block) separates training into phases (blocks) with distinct focuses: accumulation (high volume, lower intensity), transmutation (moderate volume and intensity), and realization (low volume, peak intensity). The idea is that you build fitness attributes in sequence and peak them simultaneously before a competition or test. Sheiko and most professional powerlifting coaches use block-based approaches.
Daily undulating periodization (DUP) varies the training stimulus within a week rather than across months. Strength day (heavy, low reps), hypertrophy day (moderate), power day (lighter, fast) might all happen in the same training week. Research suggests DUP may produce slightly better outcomes than linear periodization at equivalent volumes — likely because the frequent variation prevents accommodation. Most modern intermediate programs implement some version of DUP even if they do not call it that.
Evidence base
Sources
Source 01
Rhea et al. 2002 — A comparison of linear and daily undulating periodized programs(opens in a new tab)One of the foundational studies comparing linear vs. DUP for strength gains.
Source 02
Issurin 2010 — New horizons for the methodology and physiology of training periodization(opens in a new tab)Review of block periodization theory and application.
Source 03
Greg Nuckols — The History of Periodization(opens in a new tab)Practical overview of periodization models for strength training.
LiftProof defaults draw from the published strength literature.