Effects of Variable Resistance Training on Maximal Strength: A Meta-analysis : The Journal of Strength & Conditioning Research

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Manuscript Clarification

Effects of Variable Resistance Training on Maximal Strength: A Meta-analysis

Nilo dos Santos, Wanderson Divino1; Gentil, Paulo1; Lima de Araújo Ribeiro, Alexandre2; Vieira, Carlos Alexandre1; Martins, Wagner Rodrigues2,3

Author Information
Journal of Strength and Conditioning Research 32(11):p e52-e55, November 2018. | DOI: 10.1519/JSC.0000000000002836
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Request for Clarification:

Our research group has been using the study by Soria-Gila et al. (8) entitled “Effects of variable resistance training on maximal strength: a meta-analysis” to provide rationale for our randomized clinical trials performed using elastic resistance. However, we noted some problems with the article (statistical analysis and overall results) that we think need to be clarified.

Analysis Performed

All procedures were performed using the same Review Manager software and the original articles (1–7). However, our analyses provided different results from those reported by Soria-Gila et al. (8). There were mainly 2 divergences.

First Divergence

The authors reported significantly greater upper strength gains using variable resistance training (VRT) in comparison with the conventional resistance program (CRT). For trained individuals, the VRT was superior in 1 repetition maximum (1RM) gain to the CRT (Soria-Gila et al. (8), Figure 2, p. 3264).

Contrary to this, our analyses did not show differences between VRT and CRT for strength gain (Figure 1). For trained and untrained individuals, the subgroup analyses indicated no difference between VRT and CRT (Figure 1).

Figure 1.:
Forest plot performed in our analyses for trained and untrained subgroups. IV = intravenous; CI = confidence interval; RT = resistance training.

Second Divergence

The authors reported that the VRT revealed superior improvements in 1RM gain to upper and lower limbs to the CRT (Soria-Gila et al. (8), Figure 3, p. 3264).

Our analyses did not show greater strength gain for long-term VRT compared with CRT, both for upper limbs and lower limbs (Figure 2).

Figure 2.:
Forest plot performed in our analyses for upper- and lower-body strength subgroups. IV = intravenous; CI = confidence interval; RT = resistance training.

This is where we find the mistakes in the insertion of the data by Soria-Gila et al. (8):

  • Cronin et al. (3): They used data from the control group (no intervention) instead of the CRT data;
  • Shoepe et al. (7): The data were inverted from VRT to CRT;
  • McCurdy et al. (5): They used data from a chain-loaded test (1RM) instead of the plate-loaded test (1RM) for the VRT group.


Based on the aforementioned mistakes, corrections should be made in the subgroup analyses, which would change the overall results. The resulting analyses reveal that the differences between CRT and VRT do not reach statistical significance. Considering the importance of a systematic review with meta-analysis to the literature, we believe it is important to send this manuscript clarification to the authors of the original article.


1. Anderson CE, Sforzo GA, Sigg JA. The effects of combining elastic and free weight resistance on strength and power in athletes. J Strength Cond Res 22: 567–574, 2008.
2. Bellar DM, Muller MD, Barkley JE, Kim CH, Ida K, Ryan EJ, et al. The effects of combined elastic- and free-weight tension vs. free-weight tension on one-repetition maximum strength in the bench press. J Strength Cond Res 25: 459–463, 2011.
3. Cronin J, McNair PJ, Marshall RN. The effects of bungy weight training on muscle function and functional performance. J Sports Sci 21: 59–71, 2003.
4. Ghigiarelli JJ, Nagle EF, Gross FL, Robertson RJ, Irrgang JJ, Myslinski T. The effects of a 7-week heavy elastic band and weight chain program on upper-body strength and upper-body power in a sample of Division 1-AA football players. J Strength Cond Res 23: 756–764, 2009.
5. McCurdy K, Langford G, Ernest J, Jenkerson D, Doscher M. Comparison of chain- and plate-loaded bench press training on strength, joint pain, and muscle soreness in Division ii baseball players. J Strength Cond Res 23: 187–195, 2009.
6. Rhea MR, Kenn JG, Dermody BM. Alterations in speed of squat movement and the use of accommodated resistance among college athletes training for power. J Strength Cond Res 23: 2645–2650, 2009.
7. Shoepe TC, Ramirez DA, Rovetti RJ, Kohler DR, Almstedt HC. The effects of 24 weeks of resistance training with simultaneous elastic and free weight loading on muscular performance of novice lifters. J Hum Kinet 29: 93–106, 2011.
8. Soria-Gila MA, Chirosa IJ, Bautista IJ, Baena S, Chirosa LJ. Effects of variable resistance training on maximal strength: A meta-analysis. J Strength Cond Res 29: 3260–3270, 2015.

Authors' Response:

After analyzing the objections made by Santos et al., we recognize and accept the errors to which they refer. We have always acted with the utmost honesty, thoroughness and rigor in our work to obtain valid and reliable results, with the highest possible scientific quality. The errors discovered in this case are due to the transcription of the data between the spreadsheets.

We have now entered the correct data into our analysis, obtaining the following results:

  • No significant differences were observed in the Comparison of trained and untrained subjects both groups (Figure 1). When considering only the trained group, there is no difference between both types of training, although it is close to being significant (p = 0.10). It is important to highlight the need for a greater number of articles comparing both types of training in the future (especially with trained subjects) as it will truly demonstrate differences, and reduce the heterogeneity of the analysis.
  • Comparison between the upper and lower body: there are no significant differences in the strength gain in either subgroups (Figure 2).

Figure 1.:
Forest plot for trained and untrained subgroups.
Figure 2.:
Forest plot for upper and lower body strength subgroups.
© 2018 National Strength and Conditioning Association