The Relationship Between Maximal Strength and Reactive Strength

Abstract

Maximum- and reactive-strength qualities both have important roles in athletic movements and sporting performance. Very little research has investigated the relationship between maximum-strength and reactive-strength. The aim of this study was to investigate the relationship between maximum-strength (isometric mid-thigh pull peak force; IMTP PF) and reactive-strength (drop-jump reactive-strength index; DJ-RSI) variables at 0.3 m, 0.4 m, 0.5 m and 0.6 m box heights. A secondary aim investigated the between- and within-group differences in reactive-strength characteristics between relatively ‘strong’ and ‘weak’ athletes. Forty-five collegiate athletes across various sports were recruited to participate in the study (age: 23.7 ± 4.0 years; mass: 87.5 ± 16.1 kg; height: 1.80 ± 0.08 m). Pearson’s correlation results showed that there was a moderate association (r = 0.302 - 0.431) between maximum-strength variables (absolute, relative & allometric scaled PF) and RSI at 0.3, 0.4, 0.5 and 0.6 m (p ≤ 0.05). In addition, two-tailed independent samples t tests showed that relatively stronger athletes (n = 11; 49.59 ± 2.57 N•kg-1) had significantly larger RSI than weaker athletes (n = 11; 33.06 ± 2.76 N•kg-1) at 0.4 m (Cohen’s d = 1.02), 0.5 m (d = 1.21) and 0.6 m (d = 1.39) (p ≤ 0.05). Weaker athletes also demonstrated significant decrements in RSI as eccentric stretch loads increased from 0.3 to 0.6 m box heights, whereas strong athletes were able to maintain their reactive-strength ability. This research highlights that in specific sporting scenarios, where there are high eccentric stretch-loads and fast stretch-shortening cycle (SSC) demands, an athlete’s reactive-strength ability may be dictated by their relative maximal-strength, specifically their eccentric strength.

Full text

548
ORIGINAL INVESTIGATION
International Journal of Sports Physiology and Performance, 2017, 12, 548 -553
http://dx.doi.org/10.1123/ijspp.2016-0216
© 2017 Human Kinetics, Inc.
The authors are with the Dept of Physical Education and Sport Sciences,
University of Limerick, Ireland. Address correspondence to Kris Beattie
at kris.beattie@ul.ie.
The Relationship Between Maximal Strength and Reactive Strength
Kris Beattie, Brian P. Carson, Mark Lyons, and Ian C. Kenny
Maximum- and reactive-strength qualities both have important roles in athletic movements and sporting performance. Very little
research has investigated the relationship between maximum strength and reactive strength. The aim of this study was to investigate
the relationship between maximum-strength (isometric midthigh-pull peak force [IMTP PF]) and reactive-strength (drop-jump
reactive-strength index [DJ-RSI]) variables at 0.3-m, 0.4-m, 0.5-m, and 0.6-m box heights. A secondary aim was to investigate
the between- and within-group differences in reactive-strength characteristics between relatively stronger athletes (n = 11) and
weaker athletes (n = 11). Forty-ve college athletes across various sports were recruited to participate in the study (age, 23.7 ±
4.0 y; mass, 87.5 ± 16.1 kg; height, 1.80 ± 0.08 m). Pearson correlation results showed that there was a moderate association
(r = .302–.431) between maximum-strength variables (absolute, relative, and allometric scaled PF) and RSI at 0.3, 0.4, 0.5 and
0.6 m (P ≤ .05). In addition, 2-tailed independent-samples t tests showed that the RSIs for relatively stronger athletes (49.59 ±
2.57 N/kg) were signicantly larger than those of weaker athletes (33.06 ± 2.76 N/kg) at 0.4 m (Cohen d = 1.02), 0.5 m (d =
1.21), and 0.6 m (d = 1.39) (P ≤ .05). Weaker athletes also demonstrated signicant decrements in RSI as eccentric stretch loads
increased at 0.3-m through 0.6-m box heights, whereas stronger athletes were able to maintain their reactive-strength ability. This
research highlights that in specic sporting scenarios, when there are high eccentric stretch loads and fast stretch-shortening-cycle
demands, athletes’ reactive-strength ability may be dictated by their relative maximal strength, specically eccentric strength.
Keywords: maximum strength, drop jump, isometric midthigh pull, eccentric
Maximal-, explosive-, and reactive-strength qualities differ
within and between sports, depending on an athlete’s anthropometry,
morphology, chronological age, and strength-training experience.1
Maximal strength is the ability to voluntarily generate maximum
force without a time constraint.2 Training the neuromuscular system
to increase maximal force capacity has been shown to improve
performance in athletic movements such as jumping,3 sprinting,4
and endurance activities5 (ie, economy and velocity at maximal
oxygen uptake [v<<Vdot1.eps>>O2max]). Maximal strength in the
leg musculature has traditionally been assessed via the 1-repetition
maximum back squat. However, since the early 2000s, research
groups have been reporting the effectiveness of maximal-strength
testing via the isometric midthigh pull (IMTP).6 Absolute peak
force (PF) measured using the IMTP has shown strong correlations
to athletic performance variables such as sprinting (5 m, r = .57;
20 m, r = .69),7 agility (modied 505, r = .57),7 countermovement-
jump (CMJ) peak power (r = .75–.95),8 shot-put (r = .67–.75),9 and
sprint-cycling peak power (r = .90).10
Reactive strength is the ability of the musculotendinous unit to
produce a powerful concentric contraction after a rapid eccentric
contraction.11 Reactive-strength training is commonly referred to
as “plyometrics.” Originally termed the “shock” method in Russia,
plyometrics is a method of jump training that involves an eccentric
shock stimulation to the musculotendinous unit (ie, depth jumps,
drop jumps).12 Most athletic movements in sport have plyometric
characteristics (ie, sprinting, jumping, changes of direction) and
are generally categorized by the characteristics of their sretch-
shortening cycle (SSC): fast (<250 milliseconds; sprinting, drop
jumps, bounding) or slow (>250 milliseconds; changes of direction,
depth jumps, CMJs).13 Plyometrics have been shown to effectively
improve sprint,14 agility,15 and change-of-direction16 performance.
Reactive-strength is commonly assessed through the drop-jump
reactive-strength index (RSI). Originally developed at the Australian
Institute of Sport in the early 1990s, the drop-jump RSI assessment
consists of an athlete stepping off a box, landing with minimum
ground contact time and jumping for maximum height.17 The drop-
jump RSI (calculated as jump height divided by contact time)17 is
usually assessed over a series of box heights (ie, 0.3 m, 0.4 m, 0.5
m, and 0.6 m) to ascertain the athlete’s reactive strength over dif-
ferent eccentric stretch loads.
Maximal- and reactive-strength qualities are dictated by specic
morphological characteristics (muscle-ber type, architecture, and
tendon properties) and neural characteristics (motor-unit recruit-
ment, synchronization, ring frequency, and intermuscular coordi-
nation).18 However, the exact neuromuscular mechanism(s) driving
each strength quality is still relatively unknown. The physiological
adaptations from strength training can produce either a positive
or negative transfer to sports performance.19 Positive transfer
throughout an athlete’s career requires the continual development
of training programs that target the appropriate strength quality
(ie, maximal-, explosive-, and/or reactive-strength exercises) and
intermuscular coordination (ie, specic strength exercises aimed at
increasing the output of the competition movement in a given sport
discipline12) needed to improve the desired sporting movement.12
In contrast, beginner or developmental athletes can display posi-
tive transfer across strength qualities from relatively nonspecic
and general strength programs.3 Previous work has found varied
correlations between slow SSC performance and dynamic and iso-
metric maximum-strength qualities (dynamic: CMJ vs. 1-repetition
maximum back squat, r = .54–.9420,21; isometric: CMJ vs IMTP PF,
r = .02–.0922). However, very little research has investigated the rela-
tionship between maximum-strength and fast SSC reactive-strength
performance (ie, drop-jump RSI). Dymond et al23 found a positive

IJSPP Vol. 12, No. 4, 2017
Maximal and Reactive Strength 549
relationship (r = .63) between maximum-strength and reactive-
strength performance in elite rugby players, where stronger athletes
(back squat ≥ 1.9 × body weight) showed a signicantly higher RSI
at higher box heights than their weaker counterparts (back squat ≤
1.9 × body weight). However, Dymond et al23 assessed maximum
strength from an estimated value (1-repetition maximum predicted
from 3- to 5-repetition-maximum loads). In addition, they did not
include analysis of the components of RSI—jump height (JH) and
ground-contact time (CT). Therefore, the aim of this study was
to investigate the relationship between maximum-strength IMTP
variables (absolute, relative, and allometric scaled PF) and reactive-
strength variables (RSI, JH, and CT) at 0.3-m, 0.4-m, 0.5-m, and
0.6-m box heights. A secondary aim was to investigate the between
and within-group differences in reactive-strength characteristics
between relatively stronger and weaker athletes.
Methods
Subjects
Forty-ve college athletes across various sports (rugby union, n =
20; weightlifting, n = 8; distance running, n = 8; powerlifting, n
= 4; recreational, n = 5) were recruited to participate in the study
(age, 23.70 ± 4.00 y; mass, 87.50 ± 16.10 kg; height, 1.80 ± 0.08
m). All individuals were familiarized with testing protocols before
assessment. After being informed of the benets and potential risks
of the investigation, each participant completed a health-screening
questionnaire and provided written informed consent before par-
ticipation in the study in compliance with the institution’s research
ethics committee and the Declaration of Helsinki.
Design
This study was designed to investigate the relationships between
maximal-strength performance (absolute, N; relative, N/kg; allome-
tric scaled PF, N/kg0.67) and reactive-strength performance (RSI, JH,
and CT) in athletes. Athletes were required to abstain from training
for 48 hours before testing and were asked to maintain a consistent
uid and dietary intake before testing.
Methodology
To assess maximal strength, we used the IMTP. For the IMTP,
participants maintained a clean “second-pull” position, which
consisted of a mean knee angle of 131° ± 9° and a near-vertical
trunk position. This position was selected for assessment because it
corresponds to the portion of the clean in which the highest forces
and velocities are generated.24 Each participant performed an
IMTP-specic warm-up, which consisted of pulling the IMTP bar
for 5 seconds at a self-directed 50% of maximal effort, 3 seconds
at 70 to 80% of maximal effort, and 3 seconds at 90% of maximal
effort. There was a 1-minute recovery period between warm-up
efforts. After this, each participant rested for 2 minutes before his
or her 2 maximal-effort trials, with 2 minutes of recovery between
trials. For each trial, the participant was instructed to “pull as hard
and as fast as you can” to ensure that maximal force was achieved.8
Each force–time curve was analyzed to make sure that there was
no countermovement or decrease in force before the initiation of
the pull. The maximum force generated during the 5-second IMTP
trial was reported as the absolute PF (N), relative PF (absolute PF
divided by participant’s body mass; N/kg), and allometric scaled PF
× (absolute PF ÷ [participant body mass0.67]; N/kg0.67). Allometric
scaling takes into consideration the fact that increases in body mass
do not translate to a linear increase in strength performance.22,25
All isometric testing was conducted on a custom-made isometric
rack (Odin, Ireland) that enabled the placement of a steel bar at
50-mm intervals to allow for the desired IMTP position in each
participant. The isometric rack was anchored to the oor and placed
over 2 AMTI force platforms (Advanced Mechanical Technology,
Watertown, MA) sampling at 1000 Hz.
Five minutes after the IMTP, participants started their reactive-
strength assessment. Reactive-strength ability was assessed through
drop jumps performed on a photoelectric-cell platform (Optojump;
Microgate, Mahopac, NY). Participants were instructed to step for-
ward off the box and on contact with the ground to jump “as high as
possible, as quickly as possible.” Participants were also instructed to
keep their hands on their hips throughout the drop jump to restrict
arm movement. Each jump was separated by 1 minute of recovery.
Each participant performed 2 trials at each box height (0.3, 0.4, 0.5,
and 0.6 m). The highest RSI at each box height was used for analy-
sis. In addition, the specic box height that produced the highest
RSI (optimal RSI box height) for each athlete was also analyzed.
Statistical Analysis
Relationships between maximum-strength variables (absolute,
relative, and scaled PF) and reactive-strength variables (JH, CT,
and RSI) were determined by Pearson product-moment correlation
using SPSS software (version 21.0, IBM Corp, Armonk, NY). Cor-
relations were evaluated as follows: small (.1–.3), moderate (.3–.5),
large (.5–.7), very large (.7–.9), nearly perfect (.9–1.0), and perfect
(1.0).26 Additional analyses included grouping participants into
quartiles with respect to relative PF (N/kg) to investigate RSI ability
of the strongest athletes (top quartile; n = 11) and weakest athletes
(bottom quartile; n = 11). Two-tailed independent-samples t tests
were used to assess differences between means of the stronger and
weaker groups. The criterion for statistical signicance was set at P
≤ .05. To determine the magnitude of differences between groups,
we calculated effect sizes (Cohen d). Effect sizes were categorized
as trivial (<0.2), small (0.2–0.6), moderate (0.6–1.2), large (1.2–2.0),
and very large (2.0–4.0).26 In-house coefcients of variation for
IMTP PF (3.6%) and drop-jump RSI at 0.3 m (5.7%), 0.4 m (5.3%),
0.5 m (5.7%) and 0.6 m (5.9%) were all deemed reliable.
Results
Relationship Between Maximal Strength
and Reactive Strength
Pearson correlation coefcients between IMTP and RSI variables
are presented in Table 1. Absolute PF (N) showed a small correlation
with RSI at 0.4 m (r = .286; P = .056) but moderate correlations at
0.3, 0.5, and 0.6 m (r = .302–.349; P ≤ .05). Relative PF (N/kg) and
PF scaled allometrically (N/kg0.67) showed a small correlation for
RSI at 0.3 m (r = .229–.289; P = .131) but moderate correlations
at 0.4, 0.5, and 0.6 m (r = .304–.431; P ≤ .05).
Strong and Weak Between-Groups Comparisons
Differences between relatively stronger athletes (top quartile) and
weaker athletes (bottom quartile) are presented in Figure 1 and
Table 2. Statistical differences (all P ≤ .01) and very large effect-
size magnitudes (d = 2.32 to 6.19) were found between groups for
absolute and scaled PF. There were no statistical differences between
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IJSPP Vol. 12, No. 4, 2017
550 Beattie et al
Table 1 Pearson Correlations Between Isometric Midthigh-Pull Peak Force (PF) and Reactive-Strength Index
Variables (n = 45)
Measure
0.3-m Drop-Jump
Height 0.4 m Drop-Jump
Height 0.5-m Drop-Jump
Height 0.6-m Drop-Jump
Height
JH (m) CT (s) RSI JH (m) CT (s) RSI JH (m) CT (s) RSI JH (m) CT (s) RSI
Absolute PF (N) .429** .125 .302* .364* .013 .286 .404** –.074 .327** .481** .025 .349*
Relative PF (N/kg) .220 –.001 .229 .290 –.073 .304* .338* –.150 .360* .443** –.055 .425**
Scaled PF
(N/kg0.67) .289 .058 .289 .357* –.039 .327* .406** –.129 .382** .506** –.023 .431**
Abbreviations: JH, jump height; CT, ground contact time; RSI, reactive-strength index; PF, peak force.
*Signicant at P ≤ .05. **Signicant at P ≤ .01.
Figure 1 — Reactive-strength-index (RSI) mean differences and magnitudes for relatively strong (n = 11; 49.59 ± 2.57 N/kg) and weak (n = 11; 33.06
± 2.76 N/kg) athletes. *Between-groups differences are signicant at the P ≤ .05 level. **Between-groups differences are signicant at the P ≤ .01 level.
†Within-group differences in the weaker-athlete group are signicant at P ≤ .01 level.
groups for RSI at 0.3 m (P = .062); however, there were moderate
differences at 0.4 m (1.22 vs 1.55; d = 1.02) and a large difference
at both 0.5 m (1.12 vs 1.51; d = 1.21) and 0.6 m (1.02 vs 1.45; d
= 1.39) (all P ≤ .05). There was also a moderate between-groups
difference (P = .014, d = 1.15) in the optimal RSI box height (0.35
vs. 0.46 m; ie, the specic box height that produced the athlete’s
highest RSI).
Within-Group Comparisons of Stronger
and Weaker Groups
Within-group differences in relatively stronger and weaker athletes
are presented in Figure 1. Compared with their 0.3-m RSI perfor-
mance, the weaker group showed signicant decrements in RSI
at 0.5-m (P = .008) and 0.6-m (P = .000) drop heights; however
there were no statistical decrements observed in RSI in the stronger
group (P ≥ .05).
Discussion
The primary aim of this study was to investigate the relationship
between maximum-strength (IMTP PF) and reactive-strength
ability (drop-jump RSI at 0.3, 0.4, 0.5, and 0.6 m). The main
nding of this study was that there was a moderate association
between maximum-strength variables (absolute, relative, and
allometric scaled PF) and RSI at 0.3, 0.4, 0.5, and 0.6 m (P ≤
.05). In addition, relatively stronger athletes (49.59 ± 2.57 N/kg)
had signicantly larger RSI than weaker athletes (33.06 ± 2.76 N/
kg) at 0.4 m (d = 1.02), 0.5 m (d = 1.21), and 0.6 m (d = 1.39). In
addition, the weaker athletes demonstrated statistical decrements
in RSI as eccentric stretch loads increased at 0.3-m through 0.6-m
box heights, whereas strong athletes were able to maintain their
reactive-strength ability.
Maximum-strength and reactive-strength qualities both have
important roles in athletic movements and therefore training these
neuromuscular qualities are crucial for elite sport performance.27
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IJSPP Vol. 12, No. 4, 2017
Maximal and Reactive Strength 551
However, very little research has investigated the relationship
between maximum-strength and reactive-strength performance. The
current study, which used the IMTP PF as a measure of maximum
strength, showed that there was a moderate relationship among all
maximum-strength variables (absolute, relative, and scaled PF) and
RSI at 0.5 m (r = .327–.382) and 0.6 m (r = .349 to .431) in athletes.
In addition, absolute PF at 0.3 m (r = .302), relative PF at 0.4 m (r
= .327), and scaled PF at 0.4 m (r = .304), showed a moderate cor-
relation with RSI. These ndings are similar to those of Dymond
et al23 in elite Rugby Union players. In the current study, Pearson
correlation between relative PF and RSI increased from .229 to
.425 as drop height increased (from 0.3 to 0.6 m), highlighting
the increased association between maximum strength and reactive
strength as eccentric stretch loads increased. Because there was
no relationship between maximal-strength variables and CTs, but
there were moderate correlations to JH (r = .364–.481), it could be
suggested that associations between maximal strength and RSI are
derived mainly from JH performance.
Between-Groups Analysis of Stronger
and Weaker Athletes
The secondary aim of this study was to investigate the between-
groups differences in reactive strength between relatively stronger
athletes (49.59 ± 2.57 N/kg) and weaker athletes (33.06 ± 2.76 N/
kg) over various eccentric stretch loads at 0.3-m through 0.6-m box
heights. The results showed that relatively strong athletes demon-
strated a signicantly larger RSI than weaker athletes at 0.4-m (1.55
vs 1.22; d = 1.02), 0.5-m (1.51 vs 1.12; d = 1.21) and 0.6-m (1.45
vs 1.02; d = 1.39) drop heights; however there were only moderate
statistically nonsignicant differences at 0.3 m (1.50 vs 1.26; d =
0.84). These results support the ndings of Dymond et al,23 who
found that stronger players demonstrated signicantly higher RSI
levels at higher drop heights (0.51 m) but not at lower drop heights
(0.12 and 0.36 m). Because the current study showed no signicant
differences in CT between relatively stronger and weaker athletes,
but there were large signicant differences in JH at 0.5 m (0.31 vs
Table 2 Comparison Between Relatively Stronger and Weaker Athletes in Isometric Midthigh-Pull Peak Force (PF)
and Reactive-Strength Index Variables
Measure Weaker athletes (n = 11) Stronger athletes (n = 11)
P
Cohen
d
Effect-size
magnitude
Isometric midthigh pull
relative PF (N/kg) 33.06 ± 2.76 (31.43–34.69) 49.59 ± 2.57 (48.07–51.11) .000** 6.19 Very large
absolute PF (N) 2913.85 ± 725.17 (2485.3–3342.4) 4360.85 ± 502.48 (4063.9–4657.8) .000** 2.32 Very large
scaled PF (N/kg0.67) 144.29 ± 17.62 (133.88–154.70) 216.94 ± 12.33 (209.65–224.23) .000** 4.78 Very large
0.3-m drop-jump height
jump height (m) 0.27 ± 0.06 (0.23–0.31) 0.31 ± 0.05 (0.28–0.34) .058 0.86 Moderate
ground-contact time (s) 0.21 ± 0.04 (0.19–0.23) 0.21 ± 0.03 (0.19–0.23) .905 0.05 Trivial
reactive-strength index 1.26 ± 0.24 (1.12–1.40) 1.50 ± 0.33 (1.30–1.70) .062 0.84 Moderate
0.4-m drop-jump height
jump height (m) 0.27 ± 0.06 (0.23–0.31) 0.32 ± 0.06 (0.28–0.36) .057 0.86 Moderate
ground-contact time (s) 0.22 ± 0.03 (0.20–0.24) 0.21 ± 0.03 (0.19–0.23) .354 0.40 Small
reactive-strength index 1.22 ± 0.25 (1.07–1.37) 1.55 ± 0.37 (1.33–1.77) .027* 1.02 Moderate
0.5-m drop-jump height
jump height (m) 0.25 ± 0.05 (0.22–0.28) 0.31 ± 0.04 (0.29–0.33) .011* 1.20 Large
ground-contact time (s) 0.23 ± 0.03 (0.21–0.25) 0.21 ± 0.03 (0.19–0.23) .158 0.63 Moderate
reactive-strength index 1.12 ± 0.28 (0.95–1.29) 1.51 ± 0.35 (1.30–1.72) .010* 1.21 Large
0.6-m drop-jump height
jump height (m) 0.24 ± 0.06 (0.20–0.28) 0.32 ± 0.05 (0.29–0.35) .006** 1.41 Large
ground-contact time (s) 0.24 ± 0.04 (0.22–0.26) 0.23 ± 0.04 (0.21–0.25) .387 0.38 Small
reactive-strength index 1.02 ± 0.28 (0.85–1.19) 1.45 ± 0.34 (1.25–1.65) .004** 1.39 Large
Optimal RSI box height (m) 0.35 ± 0.07 (0.31–0.39) 0.46 ± 0.13 (0.38–0.54) .014* 1.15 Moderate
Note: Values are reported as mean ± SD. Values in parentheses are 95% condence intervals.
Abbreviations: RSI, reactive-strength index.
*Between-groups differences signicant at P ≤ .05. ** Between-groups differences signicant at P ≤ .01.
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IJSPP Vol. 12, No. 4, 2017
552 Beattie et al
0.25 m; d = 1.2) and 0.6 m (0.32 vs 0.24 m; d = 1.41), it could be
suggested that differences in RSI performance between strong and
weak individuals is mainly derived from JH performance. Previous
research by Thomas et al22 found no differences between relatively
stronger and weaker athletes in CMJ height performance. As CMJ
is a slow SSC movement (>250 milliseconds) with a low eccentric
stretch load, it could be argued that stronger athletes have only
greater JH performance, and therefore a greater fast-SSC reactive-
strength ability (< 250 milliseconds), when high eccentric loads
are in place (ie, 0.4-m, 0.5-m, and 0.6-m drop jumps). In addition,
the current study also showed that stronger athletes produced their
best RSI performance at signicantly higher drop heights compared
with their weaker counterparts (d = 1.15), once again indicating that
stronger athletes need larger eccentric conditions to optimize their
JH and plyometric ability.
Within-Group Analysis of Stronger and Weaker
Athletes
Within-group analysis showed that the weaker group showed sta-
tistical decrements of RSI at 0.5-m (11%) and 0.6-m (19%) drop
heights relative to the 3.0-m drop height (ie, the lowest eccentric
stretch load); however there were no statistical changes in the stron-
ger group as drop height increased (P ≥ .05). This demonstrates that
stronger athletes can maintain their reactive-strength ability during
fast SSC movements (<250 milliseconds) under higher eccentric
loads, whereas weaker athletes cannot. Therefore, compared with
their stronger counterparts, the weaker athletes’ lower relative maxi-
mum strength may inhibit the utilization of SSC mechanism(s) under
high eccentric stretch loads (ie, at box heights of 0.5 and 0.6 m).
Neuromuscular Mechanisms
Reactive-strength performance is believed to be affected by several
musculotendinous SSC mechanisms.28 The results of the current
study showed that the differences in reactive-strength between
strong and weak athletes were dictated by JH performance. Research
has shown that JH performance has nearly perfect associations with
impulse during the concentric phase of a jump.29 However, it has
been suggested that the extent of concentric performance during
a SSC movement is largely dependent on the conditions of the
eccentric phase (ie, rate and magnitude of stretch).30 Even though
eccentric strength was not assessed in the current study, previous
research has shown a very large association (r = .90) between IMTP
PF and eccentric strength.31 Therefore, compared with their weaker
counterparts, the stronger athletes may have been able to perform a
faster downward phase during ground contact because they could
tolerate the high eccentric stretch loads at box heights of 0.4 m to 0.6
m due to their superior eccentric strength.32 This superior eccentric
strength may have allowed for increased negative acceleration and
momentum, allowing for utilization of SSC mechanisms (ie, series
elastic component and stretch-reex mechanisms), ultimately lead-
ing to improved concentric force, impulse, and JH.28
Practical Applications
If both maximal- and reactive-strength qualities are needed for
sporting performance, the moderate associations highlighted in the
current study stress the importance of training both in a physical
preparation program. The focus and proportion of programming
each strength quality depends on the individualized sporting
demands, strength-training history, and neuromuscular makeup of
the athlete.
However, in sporting scenarios where there are high eccentric, fast-
SSC demands (ie, cutting, stepping, jumps-to-acceleration), an ath-
lete’s reactive-strength ability may be dictated by his or her relative
maximal strength, specically eccentric strength. Because of their
poor eccentric strength, weaker athletes may not have the ability to
use their SSC mechanisms27 during athletic movements with high
eccentric stretch-loads. Athletes with an advanced strength-training
age may need to focus on further eccentric development from a the
perspective of force (ie, eccentric squats) and velocity (ie, altitude
landings) to further enhance reactive-strength ability. In addition,
strength and conditioning coaches and sport scientists should be
aware that during reactive-strength monitoring (ie, drop-jump RSI
assessment) or training (ie, plyometrics), relatively strong athletes
may need to use higher boxes or hurdles to produce the adequate
eccentric stretch load for optimal reactive-strength performance
and stress for adaptation.
Conclusions
The current study found a moderate association between maximum-
strength variables (absolute, relative, and allometric scaled PF) and
RSI at 0.3-, 0.4-, 0.5-, and 0.6-m box heights (P ≤ .05). However,
Pearson correlations between relative PF and RSI increased (r =
.229–.425) as drop height increased (from 0.3 to 0.6 m), highlight-
ing the increased association as eccentric stretch-loads got larger.
In addition, relatively stronger athletes had a signicantly higher
optimal RSI box height (0.46 vs 0.35 m; d = 1.15) and a signi-
cantly larger RSI than weaker athletes at 0.4, 0.5, and 0.6 m. In
addition, weaker athletes showed statistical decreases in RSI as
eccentric stretch loads increased, whereas stronger athletes were
able to maintain their reactive-strength ability in high-eccentric,
fast-SSC conditions. Future work in this area should focus on the
rate of reactive-strength adaptation from plyometric training in
relatively stronger and weaker athletes and the specic associated
musculotendinous adaptations.
Acknowledgments
The authors thank Robin Healy for his biomechanical and statistical advice,
as well as all the athletes who participated in this study (including players
from Munster Rugby and Connacht Rugby). The authors have no conicts of
interest that are directly relevant to the content of this article. This research
was supported by a University of Limerick Physical Education and Sport
Science (PESS) Scholarship awarded in 2012.
References
1. Suchomel TJ, Nimphius S, Stone MH. The importance of muscular
strength in athletic performance. Sports Med. 2016;46(10):1419–1449.
PubMed doi:10.1007/s40279-016-0486-0
2. Zatsiorsky VM, Kraemer WJ. Science and Practice of Strength Train-
ing. Champaign, IL: Human Kinetics; 2004.
3. Cormie P, McGuigan MR, Newton RU. Adaptations in athletic
performance after ballistic power versus strength training. Med
Sci Sports Exerc. 2010;42(8):1582–1598. PubMed doi:10.1249/
MSS.0b013e3181d2013a
4. Seitz LB, Reyes A, Tran TT, de Villarreal EZ, Haff GG. Increases
in lower-body strength transfer positively to sprint performance: a
Downloaded by robin.healy@ul.ie on 12/05/17, Volume 12, Article Number 4

IJSPP Vol. 12, No. 4, 2017
Maximal and Reactive Strength 553
systematic review with meta-analysis. Sports Med. 2014;44(12):1693–
1702. PubMed doi:10.1007/s40279-014-0227-1
5. Beattie K, Kenny IC, Lyons M, Carson BP. The effect of strength
training on performance in endurance athletes. Sports Med.
2014;44(6):845–865. PubMed doi:10.1007/s40279-014-0157-y
6. Stone MH, Sands WA, Pierce KC, Carlock J, Cardinale M, Newton
RU. Relationship of maximum strength to weightlifting performance.
Med Sci Sports Exerc. 2005;37(6):1037–1043. PubMed
7. Thomas C, Comfort P, Chiang CY, Jones PA. Relationship between
isometric mid-thigh pull variables and sprint and change of direc-
tion performance in collegiate athletes. J Trainology. 2015;4:6–10.
doi:10.17338/trainology.4.1_6
8. Kawamori N, Rossi SJ, Justice BD, et al. Peak force and rate of force
development during isometric and dynamic mid-thigh clean pulls
performed at various intensities. J Strength Cond Res. 2006;20(3):483–
491. PubMed
9. Stone MH, Sanborn K, O’Bryant HS, et al. Maximum strength-power-
performance relationships in collegiate throwers. J Strength Cond Res.
2003;17(4):739–745. PubMed
10. Stone MH, Sands WA, Carlock J, et al. The importance of isometric
maximum strength and peak rate-of-force development in sprint
cycling. J Strength Cond Res. 2004;18(4):878–884. PubMed
11. Newton RU, Laursen PB, Young W. Clinical exercise testing and
assessment of athletes. In: Schwellnus MP, ed. Olympic Text-
book of Medicine in Sport. Oxford, UK: Wiley-Blackwell; 2008.
doi:10.1002/9781444300635.ch4
12. Verkhoshanky Y, Verkhoshanky N. Special Strength Training Manual
for Coaches. Rome, Italy: Verkhoshansky SSTM; 2011:274.
13. Schmidtbleicher D. Training for power events. In: Komi PV, ed. The
Encyclopedia of Sports Medicine. Vol 3: Strength and Power in Sport.
Oxford, UK: Blackwell 1992:169–179.
14. Sáez de Villarreal E, Requena B, Cronin JB. The effects of plyometric
training on sprint performance: a meta-analysis. J Strength Cond Res.
2012;26(2):575–584. PubMed doi:10.1519/JSC.0b013e318220fd03
15. Miller MG, Herniman JJ, Ricard MD, Cheatham CC, Michael TJ. The
effects of a 6-week plyometric training program on agility. J Sports
Sci Med. 2006;5(3):459–465. PubMed
16. McCormick BT, Hannon JC, Newton M, Shultz B, Detling N, Young
WB. The effects of frontal- and sagittal-plane plyometrics on change
of direction speed and power in adolescent female basketball players.
Int J Sports Physiol Perform. 2016;11:102–107. PubMed doi:10.1123/
ijspp.2015-0058
17. Young WB. Laboratory assessment of athletes. IAAF. 1995;10(1):89–
96.
18. Cormie P, McGuigan MR, Newton RU. Developing maximal neuro-
muscular power. Part 1 – biological basis of maximal power produc-
tion. Sports Med. 2011;41(1):17–38. PubMed doi:10.2165/11537690-
000000000-00000
19. Young WB. Transfer of strength and power training to sports per-
formance. Int J Sports Physiol Perform. 2006;1:74–83. PubMed
doi:10.1123/ijspp.1.2.74
20. Stone MH, O’Byrant HS, McCoy L, Coglianese R, Lehmkuhl M,
Schilling B. Power and maximum strength relationships during
performance of dynamic and static weighted jumps. J Strength Cond
Res. 2003;17:140–147. PubMed
21. Wisløff U, Castagna C, Helgerud J, Jones R, Hoff J. Strong correlation
of maximal squat strength with sprint performance and vertical jump
height in elite soccer players. Br J Sports Med. 2004;38:285–288.
PubMed doi:10.1136/bjsm.2002.002071
22. Thomas C, Jones PA, Rothwell J, Chiang CY, Comfort P. An investiga-
tion into the relationship between maximum isometric strength and
vertical jump performance. J Strength Cond Res. 2015;29(8):2176–
2185. PubMed doi:10.1519/JSC.0000000000000866
23. Dymond C, Flanagan EP, Turner AP. The relationship between
maximal-strength and plyometric ability in Rugby players. Rev Port
Cein Desp. 2011;11(Suppl 2):77–80.
24. Enoka RM. The pull in Olympic weightlifting. Med Sci Sports.
1979;11(2):131–137. PubMed
25. Challis JH. Methodological report: the appropriate scaling of weight-
lifting performance. J Strength Cond Res. 1999;13(4):367–371.
26. Hopkins WG, Marshall SW, Batterham AM, Hanin J. Progres-
sive statistics for studies in sports medicine and exercise science.
Med Sci Sports Exerc. 2009;41:3–13. PubMed doi:10.1249/
MSS.0b013e31818cb278
27. Haff GG, Nimphius S. Training principles for power. Strength Condit
J. 2012;34(6):2–12. doi:10.1519/SSC.0b013e31826db467
28. Wilson JM, Flanagan EP. The role of elastic energy in activities with
high force and power requirements: a brief review. J Strength Cond Res.
2008;22(5):1705–1715. PubMed doi:10.1519/JSC.0b013e31817ae4a7
29. Ruddock AD, Winter EM. Jumping depends on impulse not power. J
Sports Sci. 2015;34(6):584–585. PubMed doi:10.1080/02640414.20
15.1064157
30. Cavagna GA, Dusman B, Margaria R. Positive work done by a previ-
ously stretched muscle. J Appl Physiol. 1968;24(1):21–32. PubMed
31. Spiteri T, Nimphius S, Hart NH, Specos C, Sheppard JM, Newton
RU. Contribution of strength characteristics to change of direc-
tion and agility performance in female basketball athletes. J
Strength Cond Res. 2014;28(9):2415–2423. PubMed doi:10.1519/
JSC.0000000000000547
32. Cormie P, McGuigan MR, Newton RU. Changes in the eccentric
phase contribute to improved SSC performance after training. Med
Sci Sports Exerc. 2010;42(9):1731–1744. PubMed doi:10.1249/
MSS.0b013e3181d392e8
Downloaded by robin.healy@ul.ie on 12/05/17, Volume 12, Article Number 4