Beyond FITT: addressing density in understanding the dose-response relationships of physical activity with health-an example based on brain health

Fabian Herold; Liye Zou; Paula Theobald; Patrick Manser; Ryan S Falck; Qian Yu; Teresa Liu-Ambrose; Arthur F Kramer; Kirk I Erickson; Boris Cheval; Yanxia Chen; Matthew Heath; Zhihao Zhang; Toru Ishihara; Keita Kamijo; Soichi Ando; Joseph T Costello; Mats Hallgren; David Moreau; Vahid Farrahi; David A Raichlen; Emmanuel Stamatakis; Michael J Wheeler; Neville Owen; Sebastian Ludyga; Henning Budde; Thomas Gronwald

doi:10.1007/s00421-025-05858-3

Beyond FITT: addressing density in understanding the dose-response relationships of physical activity with health-an example based on brain health

Eur J Appl Physiol. 2025 Jun 26. doi: 10.1007/s00421-025-05858-3. Online ahead of print.

Authors

Fabian Herold^{1

2

3}, Liye Zou⁴, Paula Theobald³, Patrick Manser^{5

6}, Ryan S Falck^{7

8

9

10}, Qian Yu⁴, Teresa Liu-Ambrose^{8

9

10}, Arthur F Kramer^{11

12

13}, Kirk I Erickson^{14

15

16}, Boris Cheval^{17

18}, Yanxia Chen⁴, Matthew Heath^{19

20

21}, Zhihao Zhang⁴, Toru Ishihara²², Keita Kamijo²³, Soichi Ando²⁴, Joseph T Costello²⁵, Mats Hallgren^{26

27}, David Moreau²⁸, Vahid Farrahi²⁹, David A Raichlen^{30

31}, Emmanuel Stamatakis^{32

33}, Michael J Wheeler^{27

34}, Neville Owen^{34

35}, Sebastian Ludyga³⁶, Henning Budde³⁷, Thomas Gronwald^{38

39}

Affiliations

¹ Department of Physiology, Faculty of Medicine, HMU Health and Medical University Erfurt, Erfurt, Germany.
² Institute of Interdisciplinary Exercise Science and Sports Medicine, MSH Medical School Hamburg, Am Kaiserkai 1, 20457, Hamburg, Germany.
³ Research Group Degenerative and Chronic Diseases, Movement, Faculty of Health Sciences Brandenburg, University of Potsdam, Potsdam, Germany.
⁴ Body-Brain-Mind Laboratory, Shenzhen University, Shenzhen, China.
⁵ Motor Control and Learning Group, Department of Health Sciences and Technology, Institute of Human Movement Sciences and Sport, ETH Zurich, Zurich, Switzerland.
⁶ Division of Physiotherapy, Department of Neurobiology, Care Sciences and Society, Karolinska Institute, Stockholm, Sweden.
⁷ School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada.
⁸ Aging, Mobility, and Cognitive Health Laboratory, Department of Physical Therapy, The University of British Columbia, Vancouver, BC, Canada.
⁹ Djavad Mowafaghian Centre for Brain Health, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.
¹⁰ Centre for Aging Solutions for Mobility, Activity, Rehabilitation and Technology (SMART) at Vancouver Coastal Health, Vancouver Coastal Health Research Institute, Vancouver, BC, Canada.
¹¹ Center for Cognitive and Brain Health, Northeastern University, Boston, MA, USA.
¹² Department of Psychology, Northeastern University, Boston, MA, USA.
¹³ Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, IL, USA.
¹⁴ Department of Neuroscience, AdventHealth Research Institute, AdventHealth, Orlando, FL, USA.
¹⁵ Department of Psychology, University of Pittsburgh, Pittsburgh, PA, USA.
¹⁶ Center for the Neural Basis of Cognition, University of Pittsburgh, Pittsburgh, PA, USA.
¹⁷ Department of Sport Sciences and Physical Education, Ecole Normale Supérieure Rennes, Bruz, France.
¹⁸ Laboratory VIPS2, University of Rennes, Rennes, France.
¹⁹ School of Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, ON, N6A 3K7, Canada.
²⁰ Canadian Centre for Activity and Aging, University of Western Ontario, London, ON, N6A 3K7, Canada.
²¹ Graduate Program in Neuroscience, University of Western Ontario, London, ON, N6A 3K7, Canada.
²² Graduate School of Human Development and Environment, Kobe University, Kobe, Japan.
²³ Faculty of Liberal Arts and Sciences, Chukyo University, Nagoya, Japan.
²⁴ Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo, Japan.
²⁵ Extreme Environments Laboratory, School of Psychology, Sport and Health Sciences, University of Portsmouth, Portsmouth, UK.
²⁶ Epidemiology of Psychiatric Conditions, Substance Use and Social Environment (EPiCSS), Department of Public Health Sciences, Karolinska Institute, Solna, Sweden.
²⁷ Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, Australia.
²⁸ School of Psychology and Centre for Brain Research, University of Auckland, Auckland, New Zealand.
²⁹ Institute for Sport and Sport Science, TU Dortmund University, Dortmund, Germany.
³⁰ Human and Evolutionary Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
³¹ Department of Anthropology, University of Southern California, Los Angeles, CA, 90089, USA.
³² Mackenzie Wearables Research Hub, Charles Perkins Centre, University of Sydney, Sydney, NSW, Australia.
³³ Faculty of Medicine and Health, School of Health Sciences, University of Sydney, Sydney, NSW, Australia.
³⁴ Physical Activity Laboratory, Baker Heart & Diabetes Institute, Melbourne, VIC, Australia.
³⁵ School of Health Sciences, Swinburne University of Technology, Melbourne, VIC, Australia.
³⁶ Department of Sport, Exercise and Health, University of Basel, Basel, Switzerland.
³⁷ Institute for Systems Medicine (ISM), MSH Medical School Hamburg, Hamburg, Germany.
³⁸ Institute of Interdisciplinary Exercise Science and Sports Medicine, MSH Medical School Hamburg, Am Kaiserkai 1, 20457, Hamburg, Germany. Thomas.Gronwald@medicalschool-hamburg.de.
³⁹ G-Lab, Faculty of Applied Sport Sciences and Personality, BSP Business and Law School, Berlin, Germany. Thomas.Gronwald@medicalschool-hamburg.de.

PMID: 40569418
DOI: 10.1007/s00421-025-05858-3

Abstract

Research on physical activity (PA) and health has a fundamental concern with dose-response relationships. The variables of (1) Frequency, (2) Intensity, (3) Time, and (4) Type (i.e., the FITT principle) have traditionally been used to operationalize the dosage of PA. We consider some limitations of FITT and propose that it can be complemented by the additional variable density (from the German exercise and training variable Belastungsdichte), which can be defined as the timing of successive work bouts within a single PA bout as well as the timing between successive PA bouts within a specific time period; it does so by quantifying the temporal intervals between successive work or PA bouts (i.e., time spent at a lower PA intensity or resting such as in napping/sleeping or sedentary behaviors). Using the field of PA and brain health as an example, we discuss the opportunities and challenges for further research employing the variable density and consider its potential to improve the understanding of dose-response relationships between PA and health outcomes.

Keywords: Brain; Cognition; Dose; Physical exercise; Sedentary behavior.

Publication types

Review