Changes in eccentric utilization ratio [EUR], reactive strength index[RSI] and leg stiffness in highly trained sprinters between training phases [Article Review]
- Whistle Performance
- Mar 23
- 3 min read
The training and development of elite sprinters require precise monitoring to ensure athletes are peaking at the right time. While practitioners use a variety of jump tests to assess power and stretch-shortening cycle (SSC) performance, there has been a notable lack of research tracking how these specific jump parameters change across different phases of an annual training cycle in highly trained sprinters.
The researchers conducted this study to determine if variables like the eccentric utilization ratio (EUR), reactive strength index (RSI), squat jump (SJ), and countermovement jump (CMJ) actually change as elite sprinters transition from the general preparation phase into the highly specific indoor competition phase. Ultimately, the goal was to identify which metrics are the most sensitive markers of training status and competition readiness.
Results
The researchers tracked 10 elite sprinters over a 3-month period and found a clear divide in how different jump metrics responded to the training phases:
What Improved: Both SJ and CMJ parameters showed significant increases from the preparation to the competition phase. SJ height increased from an average of 43.10 cm to 46.30 cm, while CMJ height jumped from 46.78 cm to 49.18 cm. The relative peak power for both jumps also increased significantly.
What Stayed the Same: Interestingly, parameters measured by the 10/5 rebound jump—specifically reactive strength index (RSI) and leg stiffness (LS)—showed no significant changes. Furthermore, the eccentric utilization ratio (EUR) remained relatively stable, with only a non-significant 2.4% decrease.
4 Key Takeaways
SJ and CMJ are Your Best Phase Markers: Because preparation phase training emphasizes building maximal strength and power, SJ and CMJ are highly sensitive to these adaptations. Improvements in these jumps correlate well with sprint acceleration, making them highly effective markers for tracking competition readiness.
Reactive Strength and Stiffness are Year-Round Staples: You might expect reactive strength to spike during competition season, but elite sprinters actually maintain incredibly high levels of reactive strength and leg stiffness year-round. Because their baseline is already so elite, significant phase-to-phase fluctuations are hard to detect.
Use EUR Cautiously in Sprinters: EUR (the ratio of CMJ height divided by SJ height) is often used to gauge stretch-shortening cycle performance. However, because sprinters consistently perform plyometric and reactive strength training all year, EUR is not a sensitive indicator of training phase changes for this specific population.
More Stiffness Isn't Always Better: While high leg stiffness is absolutely necessary for maximum velocity sprinting, research suggests that once an athlete reaches an elite threshold, higher stiffness values do not automatically equal faster sprint times. Optimal stiffness is highly individualized.
Conclusion: Valuable Takeaways for Sport Performance Practitioners
For strength and conditioning coaches working with track athletes or speed-based field sports, this study is a great reminder to select the right testing battery to measure seasonal progress.
Practitioners should heavily rely on SJ and CMJ parameters (specifically jump height and power output per body mass) as the primary indicators that your off-season training is successfully translating into competition readiness. Conversely, do not panic if your athletes' RSI or EUR metrics don't skyrocket during the season; elite speed athletes maintain high reactive baseline levels year-round, rendering these specific metrics less sensitive to seasonal changes. Finally, avoid comparing your athletes' leg stiffness or reactive strength to generalized normative data. Instead, profile these metrics individually to find the unique optimal stiffness level that corresponds with each athlete's best sprint times on the track
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