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The evidence-based pyramid

This is an excerpt from Science and Development of Muscle Hypertrophy 3rd Edition by Brad Schoenfeld.

A cornerstone of EBP involves synthesizing the best available evidence to optimize decision making. Because evidence differs in quality, researchers have proposed an evidence hierarchy, often depicted as a pyramid (figure 1.1). In this model, evidence positioned higher on the pyramid is considered more trustworthy.

Anecdote—information gleaned from personal experience—resides at the bottom rung of the evidence-based hierarchy. From a hypertrophy standpoint, bodybuilders represent a primary source of anecdotal evidence. These athletes have developed exceptional muscularity largely through training and nutritional experimentation, and thus, their insights constitute a form of expert opinion. Similarly, personal trainers, strength and conditioning professionals, and fitness influencers contribute to the body of anecdotal evidence surrounding muscular development.

Some people are quick to discount the opinions of bodybuilders and other fitness practitioners as “bro-science”—an informal term used to describe unsubstantiated claims common in gym culture and social media. However, it is misguided to dismiss knowledge gained from expert opinion. In the case of bodybuilders, each competitor effectively serves as his or her own “laboratory” for experimentation, customizing their practices through trial and error. Over successive generations, effective strategies tend to be retained while less successful ones are discarded, gradually improving the collective body of experiential knowledge. Thus, while an anecdote lacks the rigor of controlled experimentation, it can nevertheless provide utility for decision making.

Despite its value, an anecdote has several important drawbacks. For one, it is highly susceptible to bias, as individuals may unconsciously notice outcomes that confirm existing beliefs while overlooking contradictory evidence. For instance, a trainee who believes that consuming branched-chain amino acids (BCAAs) enhances hypertrophy may perceive superior muscular gains even in the absence of objective improvement. Moreover, anecdotal accounts lack a comparator condition; the absence of a control group precludes the determination of whether a different strategy might have yielded better results. Finally, an anecdote offers limited generalizability—the ability to extrapolate results to the larger population. Individual hypertrophic responses to exercise and nutrition vary widely (12, 17), and outcomes achieved by one person may not extend to others due to differences in genetics, anabolic pharmacological use, lifestyle factors, or a combination of these variables.

To overcome these shortcomings, higher forms of evidence apply the scientific method—a systematic, controlled process designed to answer questions objectively. The scientific method involves empirical assessment, whereby information is collected and interpreted through direct observation, measurement, experimentation, or a combination of these factors. When properly implemented, the process provides the basis for drawing more informed opinions on a topic than can be achieved from relying on anecdote or logic alone.

A hierarchy exists within the different forms of empirical evidence. Randomized controlled trials (RCTs) represent the gold standard of empirical research designs as reflected by their position in the upper tier of the evidence-based pyramid. In an RCT, participants are randomly assigned to either experimental or control groups to isolate the effect of a specific variable while minimizing confounding influences as much as possible. Assuming a sufficient sample size, the design helps to ensure that participants in both groups are relatively equal in all ways except for the specific imposed intervention. In this regard, any differences observed from the intervention can reasonably be attributed to the variable of interest, providing the ability to draw causality. For example, to evaluate whether intra-workout BCAA supplementation enhances hypertrophy, researchers might assign trained individuals to a BCAA or placebo condition over a 10-week training period, ensuring that total protein and energy intake are equal across groups. If both groups gain similar muscle mass, one can reasonably conclude that BCAAs did not contribute additional benefit.

An issue with RCTs in the applied sciences is that they often have relatively small sample sizes. This is particularly true in longitudinal hypertrophy studies, which are extremely time consuming and often involve thousands of person-hours to conduct testing and supervise participant training. The upshot is a high degree of sampling variance—the amount of statistical variation that occurs from taking repeated random samples of a given population—increasing the likelihood of inconsistency between interventions. To account for this issue, researchers can conduct systematic reviews—a structured method used to synthesize all available evidence on a given topic and critically appraise the individual studies to draw stronger conclusions. Systematic reviews can be combined with a meta-analysis—a statistical technique that pools data from each of the included studies and essentially creates one large study with greater statistical power (6). This enhances the ability to detect true effects that individual studies may miss due to their small sample sizes and the associated random variance (i.e., statistical “noise”) between interventions. Accordingly, systematic reviews or meta-analyses reside at the top of the evidence-based pyramid.

Other empirical designs provide useful, although comparatively weaker, forms of evidence. For example, case studies evaluate a single subject (or a small number of subjects) for different outcomes within a real-world context, offering detailed descriptive insights but limited generalizability. Cross-sectional and cohort studies can provide somewhat higher levels of evidence by assessing participants retrospectively or prospectively, respectively, when experimental manipulation is impractical or unethical. Although informative, these designs lack the experimental control necessary to infer causation.

Other forms of empirical evidence can also have utility in EBP. In vitro (outside the living) studies involve assessing data in a petri dish, test tube, or culture flask, which facilitates the study of biological processes under highly specified conditions. In vivo (in the living) animal studies allow for very high levels of control—far more than is possible in humans—and the ability to employ procedures that would be considered unethical in humans. While such studies have greatly advanced understanding of hypertrophy mechanisms, their ecological validity is limited. Rodent overload models, for example, often involve extreme interventions (e.g., synergist ablation, chronic stretch) that elicit hypertrophic responses far exceeding those observed in humans, both in temporal aspects as well as the magnitude of adaptations. Moreover, species differences in muscle fiber composition (20), satellite cell dynamics (2), and hormonal regulation (3, 21), constrain direct extrapolation to human physiology. Consequently, these findings should be regarded as preliminary evidence pending confirmation in human trials.

Finally, it is worth emphasizing that field observations remain invaluable in generating hypotheses. Anecdotal accounts, such as those from bodybuilders, often inspire empirical investigation. Descriptive research—such as surveys of athlete practices—helps to identify patterns warranting experimental study. For example, Hackett and colleagues (11) surveyed a cohort of competitive bodybuilders to document their training practices. The findings provide valuable information for developing research that systematically tests the validity of these practices, thereby generating more objective evidence regarding their practical implementation. In this way, anecdotal and empirical approaches are complementary, with personal observation guiding hypothesis formation and scientific inquiry refining practical understanding.

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