title: Heterogeneity in resistance training-induced muscle strength and mass responses in men and women of different ages.
abstract: Physical activity recommendations for public health include typically muscle-strengthening activities for a minimum of 2 days a week. The range of inter-individual variation in responses to resistance training (RT) aiming to improve health and well-being requires to be investigated. The purpose of this study was to quantify high and low responders for RT-induced changes in muscle size and strength and to examine possible effects of age and sex on these responses. Previously collected data of untrained healthy men and women (age 19 to 78 years, n = 287 with 72 controls) were pooled for the present study. Muscle size and strength changed during RT are 4.8 ± 6.1 % (range from -11 to 30 %) and 21.1 ± 11.5 % (range from -8 to 60 %) compared to pre-RT, respectively. Age and sex did not affect to the RT responses. Fourteen percent and 12 % of the subjects were defined as high responders (>1 standard deviation (SD) from the group mean) for the RT-induced changes in muscle size and strength, respectively. When taking into account the results of non-training controls (upper 95 % CI), 29 and 7 % of the subjects were defined as low responders for the RT-induced changes in muscle size and strength, respectively. The muscle size and strength responses varied extensively between the subjects regardless of subject's age and sex. Whether these changes are associated with, e.g., functional capacity and metabolic health improvements due to RT requires further studies.
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland. juha.ahtiainen@jyu.fi.
authors.forename: Juha P
authors.initials: JP
authors.lastname: Ahtiainen
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Simon
authors.initials: S
authors.lastname: Walker
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Heikki
authors.initials: H
authors.lastname: Peltonen
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Jarkko
authors.initials: J
authors.lastname: Holviala
authors.affiliation: Gerontology Research Center, Department of Health Sciences, University of Jyväskylä, Jyvaskyla, Finland.
authors.forename: Elina
authors.initials: E
authors.lastname: Sillanpää
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Karavirta
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Janne
authors.initials: J
authors.lastname: Sallinen
authors.affiliation: Physiology, Research Institute for Olympic Sports, Jyväskylä, Finland.
authors.forename: Jussi
authors.initials: J
authors.lastname: Mikkola
authors.affiliation: Department of Welfare, National Institute for Health and Welfare (THL), Helsinki, Finland.
authors.forename: Heli
authors.initials: H
authors.lastname: Valkeinen
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Antti
authors.initials: A
authors.lastname: Mero
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Juha J
authors.initials: JJ
authors.lastname: Hulmi
authors.affiliation: Department of Biology of Physical Activity, University of Jyväskylä, P.O. Box 35, FI-40014, Jyvaskyla, Finland.
authors.forename: Keijo
authors.initials: K
authors.lastname: Häkkinen
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D005500:Follow-Up Studies; D064368:Healthy Volunteers; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055070:Resistance Training / Q000379:methods*; D012189:Retrospective Studies; D013997:Time Factors; D055815:Young Adult
keywords: Aging; Individual variation; Muscle hypertrophy; Responders