Lower Limb Stiffness Testing in Athletic Performance: A 1 Critical Review 2 Sean J. Maloney, Iain M Fletcher 3 Department of Sports Science and Physical Activity, University of Bedfordshire, 4 Bedford, United Kingdom 5 CORRESPONDING AUTHOR 6 Sean Maloney, Research Graduate School, University of Bedfordshire, Polhill 7 Avenue, Bedford, MK41 9EA 8 Sean.Maloney@beds.ac.uk 9 44 (0)1234 400 400 10 ORCID ID: 0000-0002-6637-5310 11 12 Keywords: Reactive Strength, Plyometrics, Assessment, Spring Mass Model, 13 Torsional Spring Model 14