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The Effects of Weight Training on 1 RM Bench Press Strength Purpose The purpose of this experiment was to test the effect of six weeks of weight training on 1RM bench press strength Methods Subjects Thirty five subjects volunteered to participate in the study Their mean ± SD age, height and body mass was 25.3 ± 2.7 yr, 165.8 ± 12.7 cm and 69.6 ± 3.9 kg, respectively. Study Design The study was an independent groups design in which subjects were randomly assigned to the following training groups: 1 set of 10 reps 3 times per week, 2 sets of 10 reps 3 times per week, 3 sets of 10 reps 3 times per week, 4 sets of ten reps 3 times per week, and control group. The control group did not participate in strength training. The difference between pretraining and six week post-training 1 RM bench press strength was computed for each group. Reproducibility of 1RM bench press measurements were computed in a separate reliability study. Procedures The subjects reported to the weight room 3 times per week and completed their assigned number of sets. Each week the weights were adjusted so that the subjects could not complete the 10 repetition on their last set. Measurement of Reliability Eight subjects (not in the experiment) participated in a test-retest assessment of measurement reliability. One repetition maximum (1RM) squat was measured on each athlete on two different days(8). The between day reliability was determined using SPSS (ver 18) to compute the intraclass correlation coefficient (ICC) using a two factor mixed-effects model with type consistency. The average measures test-retest ICC for 1RM squat strength was 0.973 with a 95% confidence interval (CI) of 0.864 – 0.995. The mean change in 1RM squat strength between days was 2.8 ± 10.7 Kg. The sample size adjusted or unbiased standard error of measurement(4) was 7.83 Kg [95% CI 5.17 – 15.93 Kg]. The minimum detectable change (MDC), which is considered the minimal amount of change that is not likely to be due to chance variation in measurement was computed using the following formula: ππ·πΆ95% = 1.96 × √2 × ππΈπ ππ·πΆ95% = 1.96 × √2 × 7.83 ππ·πΆ95% = 21.70 πΎπ where MDC95% is the minimum detectable change at the 95% confidence level, and the SEM is the unbiased estimate of the standard error of measurement. Therefore, the MDC 95% in 1RM squat strength was 21.70 Kg. A Priori Statistical Power Analysis G*Power Version 3.0 was used to determine sample size using a meaningful significant difference in 1RM squat strength of 43.40 Kg (2 × MDC95), an SD of 32.85 Kg [this is the average sd of the day 1 and day 2 measures], a 2-tailed t- test and an alpha level of 0.05. To obtain an estimated power of 80%, 7 subjects per group would be required. Statistical Analysis The change (post-pre) in 1 RM bench press strength was computed for each group. Data were analyzed using SPSS version 18.0 for Windows. Values are expressed as means ± SD. The distribution of each variable was examined with the Kolomogorov-Smirnov and ShapiroWilk normality tests. A single factor ANOVA was performed to detect significant differences in the change in 1 RM bench press strength by levels of training group (1 set, 2 sets, 3 sets, 4 sets, control). Training group was a between subjects factor. Follow-up tests of significant ANOVA effects were compared using the Tukey post hoc test. The level of significance was set at P < 0.05. Results The means ± SDs for change in 1 RM bench press strength by training group (1 set, 2 sets, 3 sets, 4 sets, control) are shown in Figure 1. 10 Change in Strength (Kg) 9 8 7 6 * * 5 * 4 3 2 1 0 1 Set 2 Sets 3 Sets (* indicates significantly different from group 2, p < 0.05) 4 Sets Control The K-S and S-W tests of normality indicated that the variables were normally distributed. Levene’s test of homogeneity of variance indicated that the groups had equal variance. There was a significant difference between training groups [F(4,34) = 8.024, p = 0.000]. As shown in Figure 1, doing 2 sets per session (7.86 ± 1.67 Kg) was significantly different from: 1 set (5.29 ± 1.11 Kg), 3 sets (5.0 ± 0.87 Kg) and control (4.43 ± 0.98 Kg). No other pairwise comparisons were significant. References 1. 2. 3. 4. 5. 6. 7. 8. Faul F, Erdfelder E, Lang A-G, and Buchner A. G*Power 3: A flexible statistical power analysis program for the social, behavioral, and biomedical sciences. Behavior Research Methods. 39: 175-191, 2007. Haley SM, and Fragala-Pinkham MA. Interpreting Change Scores of Tests and Measures Used in Physical Therapy. Phys Ther 86: 735-743, 2006. Hopkins WG. Measures of reliability in sports medicine and science. Sports Med. 30: 1-15, 2000. Hopkins WG. Reliability from consecutive pairs of trials (Excel spreadsheet). In: A new view of statistics. sportsci.org: Internet Society for Sport Science, sportsci.org/resources/stats/xrely.xls, 2009. McGraw KO, and Wong SP. Forming inferences about some intraclass correlation coefficients. Psychological Methods. 1: 30-46, 1996. Schmitt JS, and Di Fabio RP. Reliable change and minimum important difference (MID) proportions facilitated group responsiveness comparisons using individual threshold criteria. Journal of Clinical Epidemiology. 57: 1008-1018, 2004. Shrout PE, and Fleiss JL. Intraclass correlations: Uses in assessing reliability. Psychol Bull. 86: 420-428, 1979. Weir JP. Quantifying test-retest reliability using the intraclass correlation coefficient and the SEM. J Strength Cond Res. 19: 231-240, 2005.