What is resistance exercise? A review of current uses and potential ways forward.

The resistance exercise (RE) literature highlights the importance and impact of RE in sports performance, daily life, and clinical outcomes. While RE research dates back to the 19th century, current definitions of what constitutes RE are varied and give rise to questions about the requisites of RE. For example, some definitions refer to movements or muscle contractions against external resistance whereas others consider all repeated actions against one’s bodyweight. Taken to the limit, this could introduce confusion between RE and endurance exercise, for example. Without a clear definition, systematic reviews (with meta-analysis) discuss outcomes of studies examining the effects of RE in different settings, using heterogenous inclusion criteria (e.g., plyometrics may be included in some reviews but not in others). This may affect the direction and magnitude of effects, whereby it will be unclear if heterogeneous findings result from natural variation in response to RE or from different definitions of what constitutes RE. This challenges comparative analyses and may impair cohesive RE recommendations. Taken collectively, this obscures our understanding of RE effects. In an attempt to advance this understanding, the present review starts by mapping different types of definitions and illustrates their consequences. Secondly, this review provides a working definition of RE while discussing persisting challenges that require clarification before a consensus can be reached.