Long-Term Time-Course of Strength Adaptation to Minimal Dose Resistance Training Through Retrospective Longitudinal Growth Modeling

ABSTRACT

Public health guidelines for resistance training emphasize a minimal effective dose intending for individuals to engage in these behaviors long term. However, few studies have adequately examined the longitudinal time-course of strength adaptations to resistance training. Purpose: The aim of this study was to examine the time-course of strength development from minimal-dose resistance training in a large sample through retrospective training records from a private international exercise company. Methods: Data were available for analysis from 14,690 participants (60% female; aged 48 ± 11 years) having undergone minimal-dose resistance training (1x/week, single sets to momentary failure of six exercises) up to 352 weeks (~6.8 years) in length. Linear-log growth models examined strength development over time allowing random intercepts and slopes by participant. Results: All models demonstrated a robust linear-log relationship with the first derivatives (i.e., changes in strength with time) trending asymptotically such that by ~1-2 years strength had practically reached a “plateau.” Sex, bodyweight, and age had minimal interaction effects. However, substantial strength gains were apparent; approximately ~30–50% gains over the first year reaching ~50–60% of baseline 6 years later. Conclusion: It is unclear if the “plateau” can be overcome through alternative approaches, or whether over the long-term strength gains differ. Considering this, our results support public health recommendations for minimal-dose resistance training for strength adaptations in adults.

KEYWORDS:

• Age
• growth
• longitudinal
• sex
• strength training

Acknowledgments

The authors would like to thank Andrew Vigotsky for his insights regarding the statistical modelling approach taken in this study.

Authors contributions

JS, BK, and RR conceived of the study; BK and RR contributed data to the study; JS conducted the statistical analysis; all authors interpreted the findings; JS wrote the first manuscript draft; all authors contributed to revising and approving the final manuscript draft and agree with the order of presentation of authors.

Disclosure statement

Bram Kroeske and Rob Reuters acknowledge their employment by fit20 International BV whose data this study is based upon. James Steele also reports having received honoraria from fit20 International BV in the form of travel and accomodation. The authors claim no other relevant conflicts of interest.

Data availability statement

Data associated with this article is available online at https://osf.io/jn6ay/.

Notes

¹ Calculated from Table 3 in Baker and Newton (2006) as the mean change in bench press strength from the first two years (1998 to 2000) relative to the mean change from the second two years (2000 to 2002) i.e., (141–129.6)/(148.1–141) = 1.6

² Which Miller et al. (2018) considered changes exceeding a value of d = 0.3, where d = (Δ / SD_pooled)

³ The year 2009 was the first year that facilities opened and began collecting data in the cloud and as such some retrospectively entered data from paper records prior to this may have errors and so was removed. Further, from 2017 onwards the facilities introduced new sensors technology to their exercise devices to provide additional metrics on workout performance. This resulted in some changes to protocols including loads used by trainees. As such we filtered to this date to ensure that the data set was comparable across time with respect to the protocol employed. We intend at some point in the future to separately analyze the dataset from 2017 onwards using the sensor captured data.

⁴ Where exercises were missed in any given session this was usually due to injury preventing a particular exercise being completed.

⁵ When exceeding the upper range of the target time under load by ≤10 seconds the load was increased by the smallest increment on the resistance machine which was 2.5 kg, and if >10 seconds it was increased by 5 kg.

⁶ The two additional datasets included the Open Powerlifting dataset (available from https://openpowerlifting.gitlab.io/opl-csv/introduction.html) and a survey of users of the Reddit forum r/weightroom (available from https://docs.google.com/spreadsheets/u/0/d/1w8Fnx0tDissaB89AsdqXrVvydv-fF2mhha3vDtxWVCY/htmlview). Both datasets used have also been uploaded to the project page on the Open Science Framework (see https://osf.io/jn6ay/).

⁷ These were modeled separately as we did not have complete case-wise data for all covariates.

⁸ Due to the computational time required to fit the models a reasonably large, yet manageable random sample was used.

⁹ Note, a full analysis of this dataset is currently underway and will be presented in a separate forthcoming manuscript.

Additional information

Funding

The author(s) reported that there is no funding associated with the work featured in this article.