Long-term time-course of strength adaptation to minimal dose resistance training: Retrospective longitudinal growth modelling of a large cohort through training records https://www.researchgate.net/public...ng_of_a_large_cohort_through_training_records ABSTRACT Introduction: Public health guidelines for resistance training typically emphasize a minimal effective dose approach. The intention for such guidelines is that individuals engage in these behaviors over the long-term. However, relatively few studies have examined the longitudinal time-course of strength adaptations to resistance training and those which have typically utilize small samples and/or athletic populations. Further, no studies have employed approaches to incorporate participant level random factors into modelling. Thus, the aim of this study was to examine the time-course of strength development resulting from continued participation in minimal dose resistance training in a large sample through retrospective training records. Methods: Data was available for analysis from 14,690 participants who had undergone minimal dose resistance training (1x/week, single sets to momentary failure of six exercises) with records ranging up to 352 weeks (~6.8 years) in length. Linear-log growth models examining the development of strength over time were fit allowing random intercepts and slopes by participant. In addition, the interaction of sex and age were examined as fixed effects. Results: All models demonstrated a robust linear-log relationship which on the untransformed time scale clearly demonstrated the presence of a plateau in strength development around ~1 year into training after which strength was essentially maintained with minimal growth. Sex and age had minimal interaction effects. Conclusions: Substantial strength gains are possible with the use of a minimal dose resistance training approach. Though, these begin to plateau after ~1 year of training with little impact from sex or age on the emergence of this plateau. It is unclear if this plateau can be overcome through alternative approaches. Considering this, our results support public health recommendations for minimal dose resistance training to induce and maintain strength adaptations in adults. [Refer to the study in the link for full study details. Following is the excerpted discussion and conclusion of the study.] Discussion The results of this study demonstrate that, despite substantial initial gains in strength during the first year of participation in minimal dose resistance training, a plateau in growth occurs with gains slowing over continued participation. A linear-log model was a strong fit for this relationship. Unsurprisingly, both sex and age impacted model intercepts (i.e. baseline strength) with males and younger adults exhibiting greater strength than their female and older comparators. However, the interaction of sex and age with time was minimal, with largely similar slopes (i.e., shapes of growth curves over time) and plateaus. Using appropriate longitudinal growth modelling, this study supports previous suggestions of the plateau or ceiling phenomena for strength resulting from resistance training. Why a plateau in strength after ~1 year of participation in minimal dose resistance training occurs is worth considering; and, whether this represents a general phenomenon or one specific to this context. Some might consider the emergence of a plateau a result of unvaried stimuli in the standardised protocol employed, or that over time greater volumes of training are required to ensure continued adaptation. However, the hypothesis that variation in the specific variables that comprise a resistance training bout are required for continued strength adaptation in the long-term lacks a clear physiological rationale and empirical support (Fisher et al., 2018; Buckner et al., 2020). Meta-analyses on the effects of volume upon strength also suggest only trivially greater effects with moderate to higher volumes over the short term; further, they highlight that there is little data to enable identification of interaction effects with training experience (Ralston et al., 2017). More directly examining this, Hass et al. (2000) have shown that increasing volume after an initial year of minimal dose resistance training in previously resistance trained adults does not result in any greater adaptations than continuation of the minimal dose protocol. Indeed, both continuation of the minimal dose and increasing the dose resulted in relatively minimal adaptations. Of course, given the specificity of strength adaptation is dependent upon the way the variable is operationalised for measurement (Buckner et al., 2019), it may be possible to elicit continued improvement even after previous resistance training experience with specific training. By way of comparison to our existing results and to explore this, we applied the same longitudinal growth model to a random sample of 10,000 lifters (limited to exploring totals [kg] for squat/bench press/deadlift competition; (see https://osf.io/de3ws/ and https://osf.io/8jx3e/) from the Open Powerlifting dataset (https://openpowerlifting.gitlab.io/opl-csv/introduction.html). It seems a reasonable assumption that most who begin to engage in powerlifting competition have been previously exposed to resistance training. Yet, the choice to engage in powerlifting competition likely means training shifts specifically towards optimisation of strength as operationalised in that context (i.e., 1RM for squat, bench press, and deadlift). Further, powerlifters overwhelmingly employ periodisation in their training programs (Swinton et al., 2009; Shaw et al., 2020). In this exploratory powerlifting model relative gains were substantially smaller (~12.5%) compared with our present results (~50-60%) over the same ~6-year period. This of course would be expected given the assumption powerlifters were probably more experienced in resistance training upon beginning competition. Additionally, they were able to improve their total (kg) supporting the notion of some additional specific performance gains that might result from a shift towards specific training. However, despite this, we still observe a plateau after ~1 year of competition questioning whether the typical application of variation through periodisation by powerlifters can really enable continued strength adaptation with time. Thus, although some evidence suggests in the short-term (6 to 36 weeks) periodization might enhance strength gains (Williams et al., 2017), given sufficient time (>1 year) plateaus may be unavoidable irrespective of training approach. Collectively this evidence lends support to early plateaus in strength with resistance training as being a robust phenomenon. The observation that strength appears to plateau over roughly similar timeframes, even across different populations and training approaches, presents interesting practical implications. In support of recommendations from a public health perspective (Steele et al., 2017; Fisher et al., 2017; Bull et al., 2020), relatively simple minimal dose resistance training approaches can produce substantial strength gains which can be easily maintained over the long-term. Further, minimal dose approaches may offer utility to previously trained populations who may still produce small gains from their use (Androulakis-Korakakis, 2020), or at the least likely maintain strength already attained. Lastly, the present findings have particularly valuable implications for older populations considering the ~1% decline in strength per year that occurs with ageing (Rantanen et al., 1998; Frontera et al., 2000; Nahhas et al., 2010; Dodds et al., 2014; Kemmler et al., 2018). Over the ~6-year period of observation for this study, absent resistance training the older adults in the sample would have lost an expected ~6% of strength. However, we found that strength gains were still substantial, and maintained over this period even in these older participants. This lends support to the notion of ‘bending the aging curve’ as proposed by Signorile (2011). The strengths and limitations of the present study should be considered. Of course, a limitation is its observational nature limiting causal claims; however, considering the well evidenced time course of strength curves in adults with maturation and ageing absent resistance training, and the exclusion of survivorship bias explanations, we feel confident the growth curves presented are reflective of causal effects with time for minimal dose resistance training. A benefit to the utilization of observational data is that we were able to examine a larger sample than is feasible in experimental research. Indeed, to our knowledge this study is the largest thus far to investigate long term strength adaptations to resistance training. Further, we employed more appropriate statistical analysis for longitudinal growth modelling. Despite this, both a strength and limitation to this study is the examination of a very specific standardized minimal dose resistance training approach. Such standardization enabled operationalization of training loads as strength. However, the lack of variation in resistance training approaches means that we can only draw indirect comparisons to other approaches regarding the presence of a plateau in strength development (as we have done so with the Open Powerlifting dataset above). It is not directly clear whether changing the specific resistance training performed (i.e., loads, volumes, exercise selections etc.), or indeed other factors such as anthropometric or dietary changes, might enable further strength adaptation after this plateau occurs. Thus, future investigators should consider the availability of datasets where alternative resistance training approaches have been employed, or where anthropometric or dietary data over time have also been captured. Indeed, where within-bout training variables have been recorded this might enable their inclusion in modelling to explore their impact upon the shape of strength growth curves with time. Conclusion Substantial strength gains are possible with the use of a minimal dose resistance training approach. Though, these begin to plateau after ~1 year of training with little impact from sex or age on the emergence of this plateau. Considering this, our results support the use of minimal dose resistance training approaches, particularly from a public health perspective, to induce and maintain strength adaptations in adults.