This is an excerpt from Strength Training for Soccer by NSCA -National Strength & Conditioning Association,Daniel Guzman & Megan Young.
BY ERNIE RIMER AND JO CLUBB
The countermovement jump (CMJ) is widely accepted by soccer strength and conditioning professionals as an assessment of lower extremity power (20, 64, 66). While CMJ height certainly depends on lower extremity power, CMJ height alone might not be a valid indicator of maximal power (see  for a review). Regression equations using CMJ height and BM can account for approximately 80% of the variance in peak power (61). Nevertheless, CMJ height remains the most widely used measure of lower extremity power. Interestingly, average CMJ height across teams in the same league has been associated with end-of-season standings (2).
A variety of equipment can be used to assess the CMJ, including force platforms, switch mats, and photocell technology. Force platforms can assess CMJ height using different principles, whereas other devices estimate CMJ height from flight time. Coaches should conduct a review of literature to determine the reliability and validity of their chosen device and should be aware of measurement differences between devices and the formulas used to determine jump height.
Coaches can refer to the manufacturer instructions for their specific measurement technologies.
The following protocol is for a CMJ without arm swing, but arm swing (i.e., Abalakov jump) can also be used.
- After adequate warm-up involving dynamic stretches, allow the athlete to perform three rehearsals using approximately 50%, 70%, and 90% efforts, respectively.
- During the rehearsal jumps, review proper CMJ technique with the athlete. Ask the athlete to stand motionless with feet hip- to shoulder-width apart and with hands on the hips. Next, ask the athlete to perform a rapid countermovement before jumping into the air.
- After rehearsal, follow manufacturer guidelines to prepare the testing device for measurement.
- Instruct the athlete to perform three maximal-effort CMJs, with about 1 minute of recovery between each attempt.
- Use consistent language and encouragement across all athletes and jumps.
- Premature foot motion (e.g., a small hop or stepping action) and an inadvertent arm swing can adversely affect reliability.
- Instructing athletes to squat after contact can reduce landing impact and increase safety.
- It might be possible to shorten recovery intervals if doing so does not cause systematic bias.
Normative data for CMJ height are shown in table 3.5. To the best of the authors’ knowledge, data provided is for the CMJ performed without arm swing. Coaches are also reminded of the variety in equipment and formula used to calculate CMJ height, which might be reflected in the data.