Background: The countermovement jump (CMJ) has been one of the most used movements for monitoring neuromuscular fatigue in athletes. Usually the highest jump of three CMJs has been
used to monitor the responses to specific training load. However, researchers have found that using the highest jump to detect fatigue during the competition phase was not as sensitive as using the
average of multiple CMJs. There is minimal research investigating the benefits and limitations of reporting highest vs. average values when monitoring performance, a limitation of research in this
area being the failure to quantify the magnitude of the differences (e.g. the effect size synthesized by meta-analysis). Therefore, the purpose of this study was to validate via a meta-analysis,
whether best or average CMJ data were more sensitive in detecting fatigue.
Methods: The following keywords were used during the electronic search: “countermovement jump” or “vertical jump” (in PubMed, Scopus, and Web of Science). The main inclusion criteria
were as follows: i) studies tested CMJ at baseline and post-intervention and the results represented as mean and standard deviations; ii) used the highest and/or average jump height; iii) the duration
of the intervention was greater than or equal to three weeks. Heterogeneity of the included studies was evaluated by examining confidence intervals and I². I² values of 25, 50, and 75 indicate low,
moderate and high heterogeneity, respectively. Random effects were analysed using the DerSimonian and Laird approach. Data were analysed using CMA v3.
Results: Ten studies satisfied the inclusion criteria for the meta-analysis: a) seven studies utilized the best CMJ height (n=130 subjects; from 13±1 to 27±1 years old; ~7 w of
training in combat sports and soccer; and, b) three studies used the average of multiple jumps (n = 59 subjects; from 19±1 to 27±1 years old; ~7 w of training in athletics and soccer). The CMJ height
was sensitive to fatigue [Overall: ES=-0.27 (-0.48 – -0.05), p=0.01; I2=39.8, p=0.06], however the best performance data was not sensitive [Highest: ES=-0.04 (-0.33 – 0.24), p=0.76; I2=33.5, p=0.15].
On the other hand, the averaged jump height was sensitive [Average: ES=-0.56 (-0.89 – -0.24), p=0.00; I2=00.0, p=0.50].
Conclusions: From the meta-analysis it is evident that averaged CMJ height would seem the best variable to monitor neuromuscular fatigue. Furthermore, based on the normal distribution
of the Gauss curve, the researcher or practitioner has a much higher probability of finding the true score when the average value is used over the highest value. Finding the true score is essential
when monitoring an individual’s “real” performance change. In addition, the average CMJ height proving to be sensitive in detecting fatigue, means that relative cheap and easy to use equipment such as
a jump mat can be used to monitor performance, which is of great practical efficacy to the practitioner.