Plyometric Training May Improve RSI More in Adults Than Youth

Explosive training does not belong exclusively to teenagers with fresh knees and a questionable relationship to gravity. A 2023 meta-analysis found that plyometric jump training improves reactive strength index (RSI) across the lifespan, and its adult subgroup improved more than its youth subgroup. The age-group moderator effect was 0.54 and statistically significant (p = 0.023).

That finding deserves attention, but it does not prove that a 55-year-old beginner should start bounding off boxes. The review did not provide dedicated controlled trials in adults over 40, nor did it establish injury rates for older trainees. What it does show is narrower and still useful: adults, as a broad subgroup, may have substantial room to improve a quality that supports fast, efficient jumping and acceleration.

What RSI measures—and why athletes care

RSI usually comes from a drop jump: jump height divided by ground-contact time. A higher score means the athlete produced more vertical displacement while spending less time on the ground. It is a practical measure of fast stretch-shortening cycle function—the rapid transition from absorbing force on landing to producing force for takeoff.

This is not a direct measure of health, longevity, fall prevention, or injury resistance. It is a performance metric. Still, the 2023 review reported that RSI correlated moderately to strongly with sprint performance (r = −0.43 to −0.33) and change-of-direction performance (r = −0.57). Faster sprint and change-of-direction times are lower numbers, which explains the negative correlations. These associations do not prove that raising RSI will automatically improve every athlete's sprinting or cutting, but they show that RSI tracks with abilities coaches actually train.

The strongest evidence: a lifespan meta-analysis

The main evidence comes from Ramirez-Campillo et al.'s 2023 systematic review and meta-analysis in Sports Medicine. It pooled 61 studies with 2,576 healthy participants across age groups and found that plyometric jump training improved RSI overall. Study heterogeneity was low, and the authors rated certainty of evidence as moderate using GRADE.

The most interesting result was the age moderator. Adults had larger RSI improvements than youth after plyometric jump training, with an effect size of 0.54 (p = 0.023). That is a statistically significant subgroup result, not a guarantee that every adult will outperform every young athlete or respond more strongly to the same program.

The authors proposed a plausible explanation: children and adolescent athletes may already accumulate reactive movement through sport and play, while adults without structured jump training may begin with more unused capacity for fast stretch-shortening cycle work. That explanation remains a hypothesis. The included evidence did not directly compare age groups using electromyography, tendon-stiffness measures, or age-stratified rate-of-force-development testing, so it cannot identify the mechanism behind the adult advantage.

The evidence supports an adult subgroup advantage in RSI response. It does not yet show that masters athletes respond the same way, or that plyometrics are safe for every older adult.

Dose matters, but the numbers are not a prescription carved in stone

Within the meta-analysis, programs lasting more than seven weeks outperformed programs lasting seven weeks or less. More than 14 total sessions outperformed 14 or fewer, and three weekly sessions outperformed lower frequencies. Those comparisons point toward a practical starting framework: an eight-week block, at least three sessions weekly, and more than 14 sessions total.

These are moderator findings, not controlled dose-titration trials. Longer or more frequent programs may also have had better coaching, more sensible progressions, or participants who adhered more consistently. Treat the figures as evidence-informed program parameters, not proof that 15 sessions work and 14 sessions fail.

A 2025 study of 34 subelite male adolescent soccer players gives the frequency question some practical context. In Trapletti et al., players completed nine weeks of volume-matched plyometric training either once or three times per week. The higher-frequency distribution produced better physical-performance outcomes and better muscle-soreness management than one weekly session. This was an adolescent soccer study, not an adult RSI trial, but it supports distributing plyometric work instead of cramming the weekly dose into one punishing session.

Youth are not one comparator group

The adult-versus-youth result should not be read as evidence that young athletes gain little from plyometrics. Youth studies repeatedly show meaningful adaptations. The complication is that biological maturation changes both reactive-jump mechanics and training response.

In Kumar et al.'s study of male youth athletes, maturity status influenced drop-jump kinetics. Athletes were grouped by distance from peak height velocity, and post-peak-height-velocity athletes showed different reactive-strength patterns from less mature peers. That matters because a chronological-age label can hide large developmental differences.

The same theme appears in girls' soccer. McGarrigal et al. followed youth female soccer players during an eight-week season. Adding once-weekly plyometric training to soccer improved slow and fast stretch-shortening cycle measures across maturity stages, with exceptions in the pre-peak-height-velocity group. Soccer training without the plyometric supplement improved only two fast stretch-shortening cycle markers, one in the mid-peak-height-velocity group and one in the post-peak-height-velocity group.

Likewise, a 2025 study by Kumar et al. found different response profiles in pre- and post-peak-height-velocity boys receiving combined resistance and plyometric training. These studies do not overturn the meta-analysis. They explain why its averaged youth subgroup is a blunt comparison: maturation affects both baseline reactive function and adaptation.

Transfer is plausible, but do not oversell it

Plyometrics can improve related athletic outcomes in specific populations. Cardiel-Sánchez et al. reported improved running biomechanics and jumping ability after plyometric training in U14 athletes. In adult hurling players, Byrne et al. found that seven weeks of composite training—bounce drop jumps paired with 20-meter sprints—improved strength, jump height, and sprint performance compared with sprint training.

Neither study proves that an RSI increase causes faster sprinting in adults. The U14 study involved youth, while the hurling intervention combined plyometric and sprint work rather than isolating jumps. They fit the broader case that reactive training can transfer to athletic performance, but the meta-analysis's RSI correlations remain correlations.

Testing RSI requires boring consistency

RSI can move with acute conditions, not just training adaptation. In a randomized comparison of 20 healthy, physically active adults, Rodrigues et al. found that 45 minutes of hot-water immersion at 40°C or 42°C acutely improved vertical-jump performance, lower-limb power, and stretch-shortening cycle measures compared with a 34°C control condition. The study examined an acute warm-up intervention, not training over weeks.

For RSI tracking, keep the drop height, surface, footwear, warm-up, time of day, fatigue level, and testing procedure as consistent as possible. Otherwise, a better score may reflect a hotter warm-up, fresher legs, or a different test setup rather than adaptation.

What adults can reasonably do with this evidence

For a healthy adult who already tolerates basic strength and impact work, a progressive plyometric block of more than seven weeks with three weekly exposures matches the pattern associated with better RSI outcomes in the meta-analysis. Start with lower-intensity contacts and conservative drop heights, then progress only when landing control and recovery hold up. A measured drop jump and a reliable method to record jump height and contact time can track RSI.

That advice is training guidance, not a safety clearance. The available evidence does not establish adverse-event rates for adults over 40, does not show whether adults over 50 respond like younger adults, and does not compare plyometrics head-to-head with heavy resistance training for adult RSI gains. Athletes returning from ACL reconstruction deserve particular caution: Maestroni et al. found that strength and jump-biomechanics relationships differed in amateur athletes after ACL reconstruction, so healthy-population assumptions may not travel cleanly into rehabilitation.

The defensible conclusion is encouraging but bounded. Plyometric jump training has moderate-certainty meta-analytic support for improving RSI, and adults improved more than youth in the review's subgroup analysis. The best next step is not to romanticize impact training. It is to test it progressively, measure it consistently, and recognize the gaps before asking older bodies to absorb more force.