GoKawiilWe synthesized data from 137 systematic reviews (>30,000 participants). Compared with no exercise (control), RT significantly improved muscle strength, size (hypertrophy), power, endurance, contraction velocity, gait speed, balance, and multiple physical function outcomes. Few RT prescription (RTx) variables affected primary adaptations. However, voluntary strength was enhanced by lifting heavier loads (≥80% one-repetition maximum), through a complete range of motion, for 2–3 sets, at the beginning of training sessions, and ≥2 sessions/wk. Muscle hypertrophy was enhanced by higher volumes (≥10 sets/wk) and eccentric overload. Power was enhanced by moderate loads (30%–70% one-repetition maximum), low-to-moderate volume (≤24 repetitions⋅sets), Olympic-style weightlifting, and power RT (fast concentric phase). Power RT enhanced physical function. Training to momentary muscle fatigue, equipment type, exercise complexity, set structure, time under tension, blood flow restriction, and periodization did not consistently impact training outcomes.
Exercise is crucial for health throughout the human lifespan, and muscle strength and function are essential components of fitness. Resistance training (RT), also known as strength or weight training, is a specialized method of physical conditioning in which muscles are exercised by contracting against external resistance, such as free weights, machines, resistance bands, water, or body weight, through isometric, isotonic, or isokinetic actions, progressively increasing force output to improve muscular strength, power, endurance, and overall health and sports performance. The benefits of RT are being increasingly appreciated as health-promoting behavior (1,2), but were perhaps first documented to be beneficial beyond personal strength development by Captain Thomas DeLorme, who recognized the benefits of RT in wounded soldiers (3). Beyond the hallmark improvements in skeletal muscle mass and function, the benefits of engaging in RT include reduced mortality and risk for and management of cardiovascular disease, cancer, and diabetes (4–6), reduced depression (7,8), and improved sleep quality (9).
Most guidelines call for healthy adults to complete “muscle-strengthening activities at moderate or greater intensity that involve all major muscle groups on two or more days a week” (2). Exercise programs are generally constructed by manipulating six factors comprising the framework FITT-VP: Frequency, Intensity, Time, Type, Volume, Pattern, and Progression (10). Prescription of variably RT variable (RTx), however, involves several variables within each category that are inherent to any practice of RT. However, a barrier to engaging in RT is that people and practitioners often lack understanding of how to prescribe RT (5). Thus, RTx guidelines are required to support healthcare practitioners and exercise professionals when designing RT programs.
The American College of Sports Medicine (ACSM) 2009 Position Stand, “Progression Models in Resistance Training for Healthy Adults” (11), summarized, at the time, the available evidence for RTx variables, providing guidelines to enhance RT adaptations. Research on the topic of RT has expanded significantly since the publication of that Position Stand; in fact, a simple PubMed search for “resistance training” yields over 30,000 new results since 2009, indicating a need for an update. Evidence synthesis methods have also advanced considerably, and both the current (11) and prior (12) Position Stands were criticized (13,14) for lacking evidence-based rigor. Hence, to provide contemporary, evidence-based guidance to minimize bias, an updated RTx Position Stand was required, utilizing contemporary search and evidence grading methodologies.
Provided ample systematic reviews and meta-analyses, an overview of reviews can systematically summarize an abundance of information (13). An overview of reviews (i.e., umbrella review: a review of systematic reviews) is a systematic collection and assessment of available evidence that provides a comprehensive, user-friendly summary of a research topic, enabling practitioners and professionals to make evidence-based decisions without assimilating the results of numerous systematic reviews and meta-analyses (14,15).
The purpose of this overview of systematic reviews was to provide an updated, evidence-based summary of the impact of RTx variables on various outcomes relevant to RT in healthy adults. The outcomes of interest included muscle hypertrophy, strength, power, endurance, contraction velocity, and physical function (e.g., gait speed, balance, and stair climbing). The current document updates the ACSM 2009 Position Stand entitled “Progression Models in Resistance Training for Healthy Adults” (11).
An issue with overviews of reviews is the possibility of “double counting” (or more) papers that are included in more than one review ( 25 ). Such counting may unduly affect the results of the analysis, resulting in spurious levels of precision and confidence in the outcomes ( 26 ). We employed the corrected covered area (CCA) index to quantify the degree of overlap between systematic reviews to be pooled in an overview of reviews ( 27 ). To obtain an estimate of the degree of publication overlap, we calculated the CCA for strength using the ccaR package ( 28 ), arguably the most relevant outcome of our analysis.
The methodological quality of each included review was assessed independently by two reviewers using the AMSTAR (A Measurement Tool to Assess Systematic Reviews) tool, which yields a score ranging from 1 to 11 that incorporates assessment of publication bias (Supplemental Appendix 4, Supplemental Digital Content, https://links.lww.com/MSS/D323 ) ( 18 , 19 ). Outcome data were tabulated as collected, and no sensitivity analyses were conducted. Heterogeneity was reported as the I 2 statistic (meta-analyses) or the fraction of reviews showing a significant effect (systematic reviews). An outcome-level (bottom-line) statement and standardized effectiveness statement (Supplemental Appendix 5, Supplemental Digital Content, https://links.lww.com/MSS/D323 ) were produced by considering the methodological quality and extracted data ( 20 ). Outcome-level quality of evidence (QoE) was calculated using a method based on the Grading of Recommendations Assessment, Development and Evaluation approach for primary evidence ( 21 ). This method incorporates the design (meta-analysis: yes/no) and methodological quality (AMSTAR score) of each included review (Supplemental Appendix 6, Supplemental Digital Content, https://links.lww.com/MSS/D323 ). There remains no standardized method to evaluate the certainty of evidence in overviews of reviews ( 15 , 22 ), so a summary percentage scores were calculated to demonstrate the quality of evidence contributing to each conclusion. The summary percentage was calculated within each prescription variable for all three directions of evidence (impactful, not impactful, and cannot determine) by dividing the average QoE by four (the maximum QoE score) to yield a percentage score ranging from 0% (lowest possible QoE) to 100% (highest possible QoE). This method has been used in previous overviews of reviews ( 18 , 20 , 23 ). The effectiveness (impact) of RTx variables for each outcome was assessed based on standardized effectiveness statements and the quantity of evidence ( 24 ). The reviews, which contributed evidence for the impact of a prescription variable, were independently scrutinized to comment on favorable RTx parameters for improving each outcome.
Four reviewers (B. S. C., C. V. L., A. C. D., and J. P. S.) independently screened all records (title/abstract and full text) and extracted data from eligible reviews in duplicate, with discrepancies resolved by group consensus. Relevant data from eligible overlapping records were included and extracted. Authors of reviews with missing data were contacted via email with a request for the missing data, and WebPlotDigitizer (version 4; https://automeris.io/ ) was used if data needed to be extracted from figures. Record screening and data extraction were completed using the systematic review software Covidence ( https://www.covidence.org/ ). The complete list of data items sought is reported in Supplemental Appendix 3, Supplemental Digital Content, https://links.lww.com/MSS/D323 .
The systematic search strategy was executed in October 2024 in Ovid MEDLINE(R) ALL (1946 to current), Ovid Emcare (1995 to current), Ovid Embase (1974 to current), Cochrane Database of Systematic Reviews (2005 to current), EBSCOhost SPORTDiscus, and Web of Science Core Collection. Trained librarians developed the search strategies. Searches conducted on the Ovid platform were limited to English-language records, and no additional limits or filters were applied. The complete search strategy is reported in Supplemental Appendix 2, Supplemental Digital Content, https://links.lww.com/MSS/D323 .
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