Abstract
A detraining period after resistance training causes a significant decrease in trained-induced muscular adaptations. However, it is unclear how long muscle strength and hypertrophy gains last after different detraining periods. Thus, the present systematic review with meta-analysis aimed to evaluate the chronic effects of detraining on muscle strength and hypertrophy induced by resistance training. Searches were conducted on PubMed, Scopus, EBSCO, CINAHL, CENTRAL, and Web of Science. The difference in means and pooled standard deviations of outcomes were converted into Hedges’ g effect sizes (g). Twenty randomized and non-randomized trials (high and moderate risks of bias, respectively, and fair quality) were included for qualitative analysis of muscle strength and hypertrophy, while only two studies were included in the meta-analysis for maximum muscle strength. The resistance training group presented a significant increase in one-repetition maximum (1RM) chest press (g: 4.43 [3.65; 5.22], p < 0.001) and 1RM leg press strength (g: 4.47 [2.12; 6.82], p < 0.001) after training. The strength gains observed in the resistance training group were also maintained after 16–24 weeks of detraining (g: 1.99 [0.62; 3.36], p = 0.004; and g: 3.16 [0.82; 5.50], p = 0.008; respectively), when compared to the non-exercise control group. However, 1RM chest press and leg press strength level was similar between groups after 32 (g: 1.81 [−0.59; 4.21], p = 0.139; and g: 2.34 [−0.48; 5.16], p = 0.104; respectively) and 48 weeks of detraining (g: 1.01 [−0.76; 2.79], p = 0.263; and g: 1.16 [−1.09; 3.42], p = 0.311; respectively). There was not enough data to conduct a meta-analysis on muscular hypertrophy. In conclusion, the present systematic review and meta-analysis demonstrated that, when taking random error into account, there is no sufficient high-quality evidence to make any unbiased claim about how long changes in muscle strength induced by RT last after a DT period. Moreover, the effect of different DT periods on muscle hypertrophy induced by RT remains unknown since there was not enough data to conduct a meta-analysis with this variable.
Highlights
It is currently well understood that muscle strength and hypertrophy gains result from continuously performing resistance training (RT) [1]
A total of 3275 studies were excluded after analysis of title and/or abstract, resulting in 55 full-text copies of the remaining studies to be submitted for further evaluation
After reading full-text copies, 35 studies were excluded from this review due to the following reasons: (i) 20 studies used a within-group design and/or did not include a control group; (ii) 11 studies did not apply traditional RT and/or DT; (iii) two studies investigated clinical populations; (iv) one study performed an indirect assessment of 1RM strength; and (v) one study measured 10RM
Summary
It is currently well understood that muscle strength and hypertrophy gains result from continuously performing resistance training (RT) [1]. Current standard recommendations to Muscles 2022, 1, 1–15. Muscles 2022, 1 improve muscle function and size state that RT sessions should be performed continuously and in a non-interrupted fashion for at least 12 weeks [1]. Previous studies have shown various physiological effects of detraining (DT) periods after RT, such as reduced maximal function, decreased muscle size [5,8], and decreased neural drive to the muscle [9,10,11]. Some studies have reported the possibility of partially maintaining muscle strength after short-term or even prolonged DT periods. Häakkinen et al [12] reported that a short-term
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