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Plyometric exercise training is thought to
be essential for the development of the
stretch-shortening cycle1and can therefore
be used to improve performance measures
such as vertical jump height2.
Reactive Strength Index-modified
(RSImod) is a reliable method of measuring
an athlete’s explosiveness during
plyometric exercises such as depth jumps
and countermovement jumps1.
The purpose of the research was to
measure the between-limb differences in
RSImod across three plyometric tasks.
The research also investigated differences
in RSImod between the three tasks for both
limbs, whilst concurrently making
comparisons with peak ground reaction
force (GRF).
Reactive Strength Index-modified in different plyometric tasks
Josh Walker1, Sarah B. Clarke1, Emma V. Waller1, Aaron Robey-
Broome1, and Randall L. Jensen2
1Institute for Sport, Physical Activity & Leisure, Leeds Beckett University
2School of Health and Human Performance, Northern Michigan University
Purpose Method
Results
Conclusion References
Author
Josh is a Level 6 Sport & Exercise Science student at Leeds Beckett
University.
@joshwalker456
j.walker3695@student.leedsbeckett.ac.uk
1. Ebben, E. P. & Petushek, E. J. (2010). Using Reactive Strength Index Modified to Evaluate Plyometric Performance.
Journal of Strength & Conditioning Research, 27, 2700-2707.
2. Lloyd, R. S., Oliver, J. L., Hughes, M. G., & Williams, C. A. (2012). The Effects of 4-Weeks of Plyometric Training on
Reactive Strength Index and Leg Stiffness in Male Youths. Journal of Strength & Conditioning Research, 26, 2812-
2819.
3. Hopkins, W.G. (2000). A new view of statistics Internet Society for Sport Science:
http://www.sportsci.org/resource/stats/.
Scan here
for e-poster
Acknowledgements
Participants: n=11, Recreationally-active, Age = 20.4±1.5 years,
Height = 1.74±0.07 m, Body mass = 80.1±12.9 kg.
Countermovement
Jump (CMJ)
Hands placed
on hips
Limbs on
separate force
platforms
Stop Jump (SJ)
Three steps
before jump
Land on both
limbs
Limbs on
separate force
platforms
Dominant Leg
Jump (DLJ)
Unilateral stop
jump
Three steps
before jump
Land on
dominant limb
Non-dominant Leg
Jump (NLJ)
Unilateral stop
jump
Three steps
before jump
Land on non-
dominant limb
Standardised warm-up on a cycle ergometer with jumping video-
assisted protocol familiarisation.
All jumps performed in a randomised order. Each jump repeated three
times, and an average of each jump was used.
•No significant difference in RSImod or peak GRF between limbs in any of the jumps (p>0.05).
•For the dominant limb, RSImod was significantly greater in SJ than CMJ (p=0.002, d=1.75) and the DLJ (p<0.001, d=1.74).
•For the non-dominant limb, RSImod was significantly greater in SJ than CMJ (p<0.001, d=1.66) and the NLJ (p<0.001, d=1.67).
•RSImod significantly correlated with peak GRF for both single leg jumps (DLJ: r= 0.70, p= 0.018; NLJ: r= 0.80, p= 0.003), and
for the CMJ in the dominant limb only (r=0.69, p=0.020).
CMJ
Stop Jump
DLJ vs.
NLJ
Dominant
0
.52±0.10b
0
.83±0.23ac
0
.52±0.12b
Non
-Dominant
0
.52±0.11b
0
.84±0.25ac
0
.49±0.16b
Between
-limb
Cohen’s d
0
.02
0
.02
0
.14
Cohen’s d
Interpretation
3
Trivial
Trivial
Small
aSignificantly different (p<0.05) from CMJ
bSignificantly different (p<0.05) from SJ
cSignificantly different (p<0.05) from matched Single leg Jump
•SJ is a more explosive type of movement, and coaches may want
to make use of this form of plyometric task when looking to
enhance performance variables such as speed and power.
•As no between-limb differences were found, coaches and
researchers probably should not use RSImod or peak GRF as a
measure of limb asymmetry.
•Lower RSImod in single-limb tasks shows participants were less able
to produce similar forces over similar contact times.
•Future studies should measure RSImod in athletes of different
sporting activities, such as team sports vs. individual sports, as well
as to establish whether RSImod limb asymmetries exist in males and
females separately.
•This study was supported in part by the Northern Michigan University College of Health Sciences and
Professional Studies.
•Thank you to Dr Catherine Tucker and the Learning Support Officers at Leeds Beckett University for
assisting with equipment setup and data collection.
