Simon Brearley, Matt Buckthorpe, Jiaqing Xu and Chris Bishop
The Dynamic Strength Index (DSI) has been proposed as a practical tool to help strength and conditioning (S&C) coaches determine whether athletes should prioritise maximal strength or ballistic training to improve performance. This article critically evaluates the theoretical foundations and practical application of the DSI by examining the validity of its component measures - jump peak force and isometric peak force - and the interpretation of the resulting ratio. Drawing on biomechanical principles and contemporary research, the authors argue that jump peak force does not adequately represent fast dynamic strength or rate of force development (RFD), while the DSI ratio itself provides limited insight into force-velocity orientation or the most appropriate training intervention. Instead, the article recommends alternative diagnostic approaches, including load-velocity profiling and relative RFD assessment, alongside a task-specific understanding of the mechanical and temporal demands of sport. Practitioners are encouraged to interpret strength assessments within the context of sporting actions rather than relying on generalised DSI thresholds, enabling more informed, evidence-based programming decisions to enhance athletic performance.
A consultant in elite sport with expertise in both performance rehabilitation and the strength & conditioning - skill acquisition interface, Simon works with athletes looking to unlock higher performance levels. He has a specialism in golf but works with athletes from all sports to restore physical qualities following musculoskeletal health problems.
Matt is a Senior Lecturer who has published more than 35 peer-reviewed research papers. Matt joined St Marys in 2020, following his PhD and having spent nearly 10 years working in the industry.
Jiaqing (Jason) Xu is a researcher at the London Sport Institute, Middlesex University. He also provides application support for motion capture systems at Qualisys AB.
Chris is the current Head of Department at the London Sport Institute, Middlesex University and has published over 300 peer-reviewed journal articles, edited / co-edited 3 textbooks and serves as the Editor-in-Chief of the UKSCA’s Professional Strength and Conditioning Journal, as well as a Senior Editor/Associate Editor for NSCA’s 2 flagship journals. From an industry perspective, Chris has a keen interest in all things training and testing for athlete and clinical populations. More recently much of his time is dedicated to the world of Performance Science in Golf, where he is the Principle Investigator for Sports Academy – the health, medicine and performance arm of the PGA of America and also on the Science and Medical Advisory Board for The R&A, DP World Tour and Ladies European Tour.
Google Scholar: https://scholar.google.com/citations?user=jep0KcEAAAAJ&hl=en
