The Effects of Ginseng on the Number of Bench Press Repetitions When Controlling for the Energy
Level of the Strength Coach
Purpose
The purpose of this experiment was to test the effects the dose of ginseng on the
number of bench press repetitions when controlling for the energy level of the strength coach.
Methods
Subjects
Fifteen 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 ginseng dose groups: placebo, low, high. It is well known that the enthusiasm
of the strength coach can affect the performance of athletes in the weight room. The
enthusiasm (energy level) of the strength coach was measured (0 – 7). The number of
repetitions on bench press (70% of 1 RM) was recorded one hour after consuming the ginseng
dose. Reproducibility of 1RM bench press repetitions was computed in a separate reliability
study.
Procedures
The subjects reported to the weight room after fasting for 12 hours. They were given
their assigned ginseng dose (placebo, low, high). One hour after consuming the ginseng they
performed as many repetitions of bench press with a 70% of 1RM weight load. The number of
repetitions performed and the energy level of the strength coach was measured.
Measurement of Reliability
Eight subjects (not in the experiment) participated in a test-retest assessment of
measurement reliability. Number of bench press repetitions (70% of 1RM) 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 number of repetitions
was 0.973 with a 95% confidence interval (CI) of 0.864 – 0.995. The mean change in number of
repetitions 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:
𝑀𝐷𝐶95% = 1.96 × √2 × 𝑆𝐸𝑀
𝑀𝐷𝐶95% = 1.96 × √2 × 7.83
𝑀𝐷𝐶95% = 21.70 𝐾𝑔
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% number
of repetitions 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 number of repetitions 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
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 Shapiro-Wilk normality tests. A single factor ANCOVA was used to determine the effect of
ginseng dose (placebo, low, high) on the number of bench press repetitions performed when
controlling for the energy level of the strength coach. Ginseng dose was a between subjects
factor and energy level of the strength coach was a covariate. Follow-up tests of significant
ANOVA effects were compared using the Sidak post hoc test. The level of significance was set at
P < 0.05.
Results
The means ± SDs for the number of bench press repetitions performed by dose of
ginseng (placebo, low, high) are shown in Figure 1.
8
Number of Bench Press
Repetitions
7
6
5
4
3
2
1
0
Placebo
(
Low
High
indicates significantly different from Placebo, p < 0.05)
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. The
strength coach energy level significantly affected the number of repetitions performed [F(1,26)
= 4.96, p = 0.035, power = .57, partial η2 = .16]. The dose of ginseng significantly affected
number of repetitions of bench press performed, after controlling for the energy level of the
strength coach [F(2,26) = 4.14, p = 0.027, power = .68, partial η2 = .24]. As shown in Figure 1,
subjects performed significantly more repetitions with the high ginseng dose (4.85 ± 2.12
repetitions) than the placebo dose (3.22 ± 1.79 repetitions. No other pairwise comparisons
were significant.
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