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The Influence of Countermovement Jump Protocol on Reactive Strength Index Modified and Flight Time: Contraction Time in Collegiate Basketball Players

Authors:
  • Vegas Golden Knights

Abstract

The purpose of the present investigation was to evaluate differences in Reactive Strength Index Modified (RSIMod) and Flight Time to Contraction Time Ratio (FT:CT) during the countermovement jump (CMJ) performed without the arm swing (CMJNAS) compared to the CMJ with the arm swing (CMJAS), while exploring the relationship within each variable between jump protocols. A secondary purpose sought to explore the relationship between RSIMod and FT:CT during both jump protocols. Twenty-two collegiate basketball players performed both three CMJNAS and three CMJAS on a force plate, during two separate testing sessions. RSIMod was calculated by the flight-time (RSIModFT) and impulse-momentum methods (RSIModIMP). CMJ variables were significantly greater during the CMJAS compared to CMJNAS (p < 0.001). There were large to very large correlations within each variable between the CMJAS and CMJNAS. There were significant positive correlations among RSIModFT, RSIModIMP, and FT:CT during both the CMJAS (r ≥ 0.864, p < 0.001) and CMJNAS (r ≥ 0.960, p < 0.001). These findings identify an increase in RSIMod or FT:CT during the CMJAS, that may provide independent information from the CMJNAS. In addition, either RSIMod or FT:CT may be utilized to monitor changes in performance, but simultaneous inclusion may be unnecessary.
sports
Article
The Influence of Countermovement Jump Protocol on
Reactive Strength Index Modified and Flight Time:
Contraction Time in Collegiate Basketball Players
Aaron Heishman 1, 2, *, Brady Brown 1,2, Bryce Daub 2, Ryan Miller 1, Eduardo Freitas 1and
Michael Bemben 1
1Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019, USA;
brownbrady3@ou.edu (B.B.); ryanmiller1@ou.edu (R.M.); eduardofreitas@ou.edu (E.F.);
mgbemben@ou.edu (M.B.)
2
Department of Athletics, Basketball Strength and Performance, University of Oklahoma, Norman, OK 73019,
USA; bdaub34@gmail.com
*Correspondence: aaronheishman@ou.edu
Received: 23 January 2019; Accepted: 10 February 2019; Published: 12 February 2019


Abstract:
The purpose of the present investigation was to evaluate differences in Reactive
Strength Index Modified (RSI
Mod
) and Flight Time to Contraction Time Ratio (FT:CT) during the
countermovement jump (CMJ) performed without the arm swing (CMJNAS) compared to the CMJ
with the arm swing (CMJAS), while exploring the relationship within each variable between jump
protocols. A secondary purpose sought to explore the relationship between RSI
Mod
and FT:CT
during both jump protocols. Twenty-two collegiate basketball players performed both three CMJNAS
and three CMJAS on a force plate, during two separate testing sessions. RSI
Mod
was calculated
by the flight-time (RSI
ModFT
) and impulse-momentum methods (RSI
ModIMP
). CMJ variables were
significantly greater during the CMJAS compared to CMJNAS (p< 0.001). There were large to very
large correlations within each variable between the CMJAS and CMJNAS. There were significant
positive correlations among RSI
ModFT
, RSI
ModIMP
, and FT:CT during both the CMJAS (
r0.864
,
p< 0.001
) and CMJNAS (r
0.960, p< 0.001). These findings identify an increase in RSI
Mod
or FT:CT
during the CMJAS, that may provide independent information from the CMJNAS. In addition, either
RSI
Mod
or FT:CT may be utilized to monitor changes in performance, but simultaneous inclusion
may be unnecessary.
Keywords:
athlete monitoring; athlete performance; collegiate basketball; fatigue monitoring;
countermovement jump; CMJ arm swing; CMJ without arm swing
1. Introduction
The countermovement jump (CMJ) is routinely used by both practitioners and researchers to
monitor acute and long-term changes in athlete performance. The CMJ offers a non-invasive assessment
that can be performed in a time efficient manner, making it an attractive field measure to evaluate
neuromuscular performance [
1
]. In addition, the CMJ involves the dynamic muscle action known as the
stretch-shortening cycle (SSC), which is a key component in many sporting events [
2
]. More specifically,
the CMJ has been associated with slow-SSC (>250 ms in duration) performance, which has been related
to sprint acceleration, where ground contact time is longer [
3
,
4
]. This makes the CMJ assessment a
fundamental tool in appraising key performance indices among basketball athletes, which require
frequent acceleration and deceleration.
Two protocols are regularly employed when performing the CMJ. One protocol is performed
without an arm swing (CMJ NAS), which requires the athlete to maintain hand placement on their
Sports 2019,7, 37; doi:10.3390/sports7020037 www.mdpi.com/journal/sports
Sports 2019,7, 37 2 of 11
hips or grasping a practically-weightless implement (e.g., polyvinyl chloride pipe or wood dowel)
positioned on their shoulders during the CMJ [
5
9
]. The CMJ NAS method isolates lower extremity
force production by mitigating the influence of the arm swing. Alternatively, the second CMJ method
incorporates the use of the arm swing (CMJ AS), with previous literature advocating the inclusion
of the arm swing as it may reflect a greater degree of sport specificity and familiarity among skilled
jumpers [
10
13
]. Previous literature has supported the intra- and inter-session reliability of the majority
of CMJ variables during both CMJ protocols, especially in skilled jumpers [
5
,
7
,
10
,
14
,
15
]. However,
the arm swing appears to positively influence performance during the CMJ, such as increasing jump
height and velocity at take-off, when compared to the CMJ NAS [
16
19
]. These noted increases in
performance may allude to an athlete’s absolute maximal capacities, which could provide additionally
pertinent information during an athlete’s needs analysis useful in directing a training program.
Reactive Strength Index Modified (RSI
Mod
) and the Flight Time to Contraction Time Ratio (FT:CT)
are two common variables of interest during CMJ analysis. Adopted from the Reactive Strength Index
during the drop-jump, RSI
Mod
assesses an athlete’s ability to create maximal vertical impulse in a
minimal amount of time during the CMJ, while being credited as a valid measure of lower extremity
explosiveness as it includes factors of both force and speed [
3
,
20
,
21
]. RSI
Mod
is calculated by dividing
jump height (JH) by contraction time (CT) [
16
]. JH can be computed via the flight time method, where
the time the athlete is in flight is measured to determine jump height, and then used to generate
RSI
ModFT
, or by quantifying JH from the impulse-momentum method, which required the use of
force platforms and used to produce RSI
ModIMP
[
20
,
22
]. CT is defined as the duration (ms) from
jump initiation (start of movement) to take-off [
10
]. Similarly, FT:CT compares the ratio of an outcome
variable (FT) and a process variable (CT) in an effort to evaluate an athlete’s jumping strategy, ultimately
alluding to neuromuscular readiness [
20
]. Previous literature has utilized both RSI
Mod
and FT:CT to
evaluate athlete performance and monitor neuromuscular functional status [
23
25
]. In fact, RSI
Mod
and FT:CT are oftentimes utilized over traditional gross output measures (i.e., force, power, jump
height, etc.), as they may provide more relevant information reflecting changes in movement strategy
in an attempt to meet the gross output desired [
5
]. However, the similarities in computation between
the two metrics may make their simultaneous inclusion in analysis redundant for athlete monitoring
and performance testing. Nevertheless, previous literature has yet to compare performance differences
in RSI
Mod
and FT:CT between CMJ protocols, nor the relationship in performance within each variable
between the CMJ NAS the CMJ AS. Understanding the relationship within each variable between
protocols may aid coaches in determining which CMJ protocol to use for athlete assessment, while also
providing context for practitioners when comparing an athlete’s performance profile characteristics
with respect to normative data [26].
Recent work by McMohan et al. [
20
] demonstrated a strong correlation between the variables
of FT:CT and RSI
Mod
when performing the CMJ NAS in a cohort of sport science graduate students.
However, the maintenance of this relationship during the CMJ AS, where differences in mechanical
events of the CMJ are notably different, and among a cohort of skilled jumpers remains unknown.
In addition, previous literature has yet to explore differences in RSI
ModFT
, RSI
ModIMP
, and FT:CT
between the CMJ NAS and CMJ AS protocols. Therefore, the primary purpose of the present
investigation was to evaluate differences in RSI
ModFT
, RSI
ModIMP
, and FT:CT during the CMJ NAS
compared to the CMJ AS, while additionally exploring the relationship within each variable between
jump protocols. In addition, a secondary purpose sought to explore the relationship among RSI
ModFT
,
RSI
ModIMP
, and FT:CT during both the CMJ AS and the CMJ NAS. It was hypothesized RSI
ModFT
,
RSI
ModIMP
, and FT:CT would be significantly greater during the CMJ AS, while exhibiting moderate
to large correlations between CMJ protocols. Secondarily, it was hypothesized RSI
ModFT
, RSI
ModIMP
,
and FT:CT would demonstrate strong positive correlations during both CMJ NAS and CMJ AS, while
more specifically, the relationship between RSI
ModFT
and RSI
ModIMP
would produce enhanced limits
of agreement during the CMJ NAS compared to the CMJ AS.
Sports 2019,7, 37 3 of 11
2. Materials and Methods
2.1. Subjects
A convenience sample of twenty-two (Men: n = 14, age = 19.7
±
1.0 years, height = 1.98
±
0.71 m,
body mass = 94.7
±
6.2 kg; Women: n = 8, age = 20
±
1.6 years, height = 1.80
±
0.65 m, body
mass = 78.2 ±8.3 kg
) NCAA Division 1 collegiate basketball players were included in this study.
All subjects were active squad members of the University of Oklahoma’s Men’s and Women’s
Basketball teams. This research was approved by the Institutional Review Board of the University of
Oklahoma and all subjects provided written, informed consent before participating in the study.
2.2. Procedures
Data were collected using a randomized cross-over within subject study design. The dependent
variables of interests were RSI
ModFT
, RSI
ModIMP
, and FT:CT and have been defined previously [
10
].
All testing took place within a 2-week time frame during the off-season training period.
Subjects performed CMJ assessments during two different test sessions, with each test session,
including three CMJ NAS and three CMJ AS, for a total of six CMJ during Test Session 1 and six
CMJ during Test Session 2. The order of the jumps was randomly assigned, and subjects performed the
jump type in the reciprocal order during the second session of testing. A minimum of 2 min of rest was
allotted between jump trials. In addition, each subject performed both testing sessions in the afternoon
within the same time of day between 13:00 and 14:00, as previous literature has identified the influence
of time of day on jump performance [
27
]. In accordance with prior literature [
7
] and in an attempt to
control the impact of training loads on testing outcomes, CMJ testing was performed within the same
time-frame of the training week and training loads were strictly matched 72 h prior to both testing
sessions, with sport-specific practice duration matched in the days prior to both trial sessions. Further,
subjects were instructed to have no physical exertion prior to arriving on days of testing. In an effort
to maintain ecological validity, subjects wore their standard practice gear, including shoes of their
choosing, but each subject was required to wear the same pair of shoes during both testing sessions.
Furthermore, no dietary restrictions were implemented, however athletes were instructed to maintain
normal dietary intake, as outlined by the team’s sports nutritionist.
All testing was conducted at the basketball training facility prior to the start of strength
training sessions. The same standardized warm-up was performed before each testing session,
which included dynamic stretching and locomotion patterns (i.e., skipping, jogging and running),
similar to previous literature [
6
,
10
]. Movement intensities gradually increased over the warmup
duration to prepare participants for maximal performance during the jump testing. CMJs were
performed on the ForceDecks FD4000 Dual Force Platforms hardware (ForceDecks, London, UK), with
a sample rate of 1000 Hz. To limit the impact of instructions on the CMJ performance characteristics,
consistent instructions were provided to all participants during each CMJ trial [
28
]. In addition, verbal
encouragement was provided to support maximal effort during each jump attempt.
2.2.1. Countermovement Jump with No Arm Swing (CMJ NAS)
The subject started in the tall standing position, with feet placed hip width to shoulder width
apart and hands akimbo. The subject was then instructed to start with equal weight distribution on
both force platforms. A visual representation of weight distribution was displayed on a monitor in
front of the participant to provide synchronized and integrated feedback, allowing the participant to
adjust their positioning for equal quantities of body weight to be distributed on each force platforms
for the start of the jump. The subject then dropped into the countermovement position to a self-selected
depth, followed by a maximal effort vertical jump, and landed in an athletic position on the force
platforms. The subject reset to the starting position after each jump, and the procedure was completed
for a total of three jumps. If at any point the subject removed their hands from their hips or exhibited
excessive knee flexion once airborne, the jump was ruled invalid and repeated.
Sports 2019,7, 37 4 of 11
2.2.2. Countermovement Jump with an Arm Swing (CMJ AS)
In the same manner as the CMJ NAS, subjects started in the tall standing position, with feet
placed hip width to shoulder width apart, but with hands free for movement. The subject was then
instructed to start with equal weight distribution on both force platforms. A visual representation of
weight distribution was displayed on a monitor in front of the participant to provide synchronized
and integrated feedback, allowing the subject to adjust their positioning for equal quantities of body
weight to be distributed on each force platforms for the start of the jump. The subject then dropped
into the countermovement position to a self-selected depth, incorporating an arm swing in their most
natural, self-selected manner, followed by a maximal effort vertical jump and landing in an athletic
position on the force platforms. The subject reset to the starting position after each jump, and the
procedure was completed for a total of three jumps. If at any point the subject exhibited excessive knee
flexion once airborne, the jump was ruled invalid and repeated.
2.3. Data Analysis
The commercially available ForceDecks software (ForceDecks, London, UK) was used to analyze
all CMJs and generate the CMJ variables using conventional methods [
29
]. Before calculations are
made, the ForceDecks Software combines the data from the two force transducers (sum of the left
and right force data). The software uses a 20 N offset from the measured bodyweight obtained prior
to the jump, to define the start of the movement. The end of eccentric and the start of concentric
was defined as minimum displacement (absolute) which is equal to zero velocity, while take-off was
defined as the timepoint at which total vertical force fell below the threshold of 20 N below bodyweight.
Contraction time was calculated as the time interval between the onset of movement and take-off.
Flight time was calculated as the time interval between take-off and touch down. RSI
ModFT
was
calculated as jump height, determine by the conventional flight-time method (Jump Height
FT
= 1/2
g(t/2)
2
, where g = gravitational acceleration and ft = flight time) divided by contraction time, therefore
RSI
ModFT
= Jump Height
Flight Time
/Contraction Time [
10
,
22
,
29
,
30
]. RSI
ModIMP
was calculated as jump
height, determined by the conventional impulse-momentum method (Jump Height
IMP
= v
2
/2g, where
v = velocity at take-off and g = gravitational acceleration), divided by contraction time, therefore
RSI
ModIMP
= Jump Height
Impulse
/Contraction Time [
22
,
29
,
31
]. FT:CT was calculated as the flight time
divided by contraction time.
2.4. Statistical Analysis
Statistical measures are reported as mean
±
SD. Two-way (Condition (CMJ NAS vs. CMJ AS)
X Time (Test Session 1 vs. Test Session 2)) repeated measures analyses of variance (ANOVA) with
Bonferroni post hoc pairwise comparison used to determine significant condition and time main effects
and significant condition by time interactions within the variables of RSI
ModFT
, RSI
ModIMP
and FT:CT.
Effects sizes (Cohen’s d) were calculated and interpreted as trivial (0–0.19), small (0.20–0.49), medium
(0.50–0.79), and large (0.80 and greater) [
32
]. Pearson correlation coefficients were utilized to examine
the relationship between the CMJ NAS and CMJ AS protocols within the RSI
ModFT
, RSI
ModIMP
and
FT:CT variables, during Test Session 1 and Test Session 2. In addition, Pearson correlation coefficients
were used to examine relationships between the variables of RSI
ModFT
, RSI
ModIMP
and FT:CT within
each condition (CMJ NAS and CMJ AS), during Test Session 1 and Test Session 2. In accordance
with previous literature, correlation coefficients were interpreted as trivial (0–0.09), small (0.10–0.29),
moderate (0.30–0.49), large (0.50–0.69), very large (0.70–0.89), and almost perfect (0.90–1) [
20
,
32
,
33
].
Furthermore, a one-way repeated measures ANOVA was used to evaluate differences in RSI
ModFT
compared to RSI
ModIMP
during both the CMJ NAS and CMJ AS. A Bland-Altman Plot was utilized to
assess the Limits of Agreement between RSI
ModFT
and RSI
ModIMP
during both the CMJ NAS and CMJ
AS [
34
]. All statistical analyses were performed using SPSS software (Version 24; SPSS Inc., Chicago,
IL, USA), with the alpha level set at p0.05.
Sports 2019,7, 37 5 of 11
3. Results
The descriptive statistics are outlined in Table 1. Data normality was confirmed and is presented
as the mean of the three jumps performed during each condition from Test Session 1 and Test Session 2.
The inter- and intra-session reliability of the variables in the present study are reported elsewhere [
10
].
Table 1. Results for the RSIMod FT, RSIMod IMP, and FT:CT during both the CMJ AS and CMJ NAS.
Variable CMJ AS CMJ NAS
Test Session 1 Test Session 2 Test Session 1 Test Session 2
RSIModFT 0.577 ±0.20 0.567 ±0.17 0.458 ±0.13 0.451 ±0.12
RSIModIMP 0.607 ±0.25 0.573 ±0.18 0.451 ±0.14 0.442 ±0.12
FT:CT 0.773 ±0.19 0.766 ±0.19 0.672 ±0.13 0.667 ±0.13
CMJ = Countermovement Jump; AS = arm swing; NAS = no arm swing; RSI
ModFT
= Reactive Strength Index
Modified, computed via the flight time method; RSI
ModIMP
= Reactive Strength Index Modified, computed via the
impulse-momentum method; all data is reported as mean ±standard deviation.
There was a significant condition (CMJ AS vs. CMJ NAS) effect, with RSI
ModFT
(d= 0.67; p< 0.001),
RSI
ModIMP
(d= 0.66; p< 0.001), and FT:CT (d= 0.52; p< 0.001) all significantly greater during the CMJ
AS compared to the CMJ NAS. However, there were no significant differences revealed across time
(p> 0.05) and no significant condition ×time interactions (p> 0.05) for any variable.
When comparing the relationships between the CMJ AS and CMJ NAS within each variable,
during each test session, there was a very large significant positive correlation of RSI
ModFT
(Test Session 1: r = 0.803, p< 0.001; Test Session 2: r = 0.783, p< 0.001) and a very large significant
positive correlation of RSI
ModIMP
(Test Session 1: r = 0.789, p< 0.001; Test Session 2: r = 0.722, p< 0.001),
while there was a significantly large positive correlation of FT:CT (Test Session 1: r = 0.669, p< 0.001;
Test Session 2: r = 0.621, p< 0.001).
There was a significant positive correlation between RSI
ModFT
and RSI
ModIMP
during both the
CMJ AS (Test Session 1: r = 0.878, p< 0.001; Test Session 2: r = 0.925, p< 0.001) and CMJ NAS
(Test Session 1: r = 0.986, p< 0.001; Test Session 2: r = 0.980, p< 0.001). There was a significant positive
correlation between RSIModFT and FT:CT during both the CMJ AS (Test Session 1: r = 0.958, p< 0.001;
Test Session 2: r = 0.951, p< 0.001) and CMJ NAS (Test Session 1: r = 0.969, p< 0.001; Test Session 2:
r = 0.965, p< 0.001). There was also a significant positive correlation between RSI
ModIMP
and FT:CT
during both the CMJ AS (Test Session 1: r = 0.864, p< 0.001; Test Session 2: r = 0.910, p< 0.001) and
CMJ NAS (Test Session 1: r = 0.961, p< 0.001; Test Session 2: r = 0.960, p< 0.001).
There were no significant differences between RSI
ModFT
and RSI
ModIMP
during either the CMJ
NAS or the CMJ AS (p> 0.05). The Bland-Altman Plot in Figure 1outlines an average measurement bias
of 0.008
±
0.02 during the CMJ NAS. Measurements of RSI
Mod
by the flight time method (RSI
ModFT
)
ranged between
0.038 less and 0.054 greater than measurement by the impulse-momentum method
(RSIModIMP ) for 95% of individuals assessed during the CMJ NAS.
As illuminated by the Bland-Altman Plot in Figure 2, the average measure bias between RSI
ModFT
and RSI
ModIMP
during the CMJ AS was
0.028
±
0.12. In addition, measurements of RSI
Mod
by the
flight time method (RSI
ModFT
) varied between
0.265 less and 0.209 greater than measurement by the
impulse-momentum method (RSIModIMP ) for 95% of individuals assessed during the CMJ AS.
Sports 2019,7, 37 6 of 11
Sports 2019, 7, Firstpage-Lastpage FOR PEER REVIEW 6 of 11
Figure 1. Bland-Altman Plot comparing RSIModFT and RSIModIMP during the CMJ AS. CMJ =
Countermovement Jump; AS = arm swing; RSIModFT = Reactive Strength Index Modified, computed
via the flight time method; RSIModIMP = Reactive Strength Index Modified, computed via the impulse-
momentum method; SD = Standard deviation.
As illuminated by the Bland-Altman Plot in Figure 2, the average measure bias between RSIModFT
and RSIModIMP during the CMJ AS was 0.028 ± 0.12. In addition, measurements of RSIMod by the flight
time method (RSIModFT) varied between 0.265 less and 0.209 greater than measurement by the
impulse-momentum method (RSIModIMP) for 95% of individuals assessed during the CMJ AS.
Figure 2. Bland-Altman Plot comparing RSIModFT and RSIModIMP during the CMJ AS. CMJ =
Countermovement Jump; AS = arm swing; RSIModFT = Reactive Strength Index Modified, computed
via the flight time method; RSIModIMP = Reactive Strength Index Modified, computed via the impulse-
momentum method; SD = Standard deviation.
Figure 1.
Bland-Altman Plot comparing RSI
ModFT
and RSI
ModIMP
during the CMJ AS.
CMJ = Countermovement Jump; AS = arm swing; RSI
ModFT
= Reactive Strength Index Modified,
computed via the flight time method; RSI
ModIMP
= Reactive Strength Index Modified, computed via
the impulse-momentum method; SD = Standard deviation.
Sports 2019, 7, Firstpage-Lastpage FOR PEER REVIEW 6 of 11
Figure 1. Bland-Altman Plot comparing RSIModFT and RSIModIMP during the CMJ AS. CMJ =
Countermovement Jump; AS = arm swing; RSIModFT = Reactive Strength Index Modified, computed
via the flight time method; RSIModIMP = Reactive Strength Index Modified, computed via the impulse-
momentum method; SD = Standard deviation.
As illuminated by the Bland-Altman Plot in Figure 2, the average measure bias between RSIModFT
and RSIModIMP during the CMJ AS was 0.028 ± 0.12. In addition, measurements of RSIMod by the flight
time method (RSIModFT) varied between 0.265 less and 0.209 greater than measurement by the
impulse-momentum method (RSIModIMP) for 95% of individuals assessed during the CMJ AS.
Figure 2. Bland-Altman Plot comparing RSIModFT and RSIModIMP during the CMJ AS. CMJ =
Countermovement Jump; AS = arm swing; RSIModFT = Reactive Strength Index Modified, computed
via the flight time method; RSIModIMP = Reactive Strength Index Modified, computed via the impulse-
momentum method; SD = Standard deviation.
Figure 2.
Bland-Altman Plot comparing RSI
ModFT
and RSI
ModIMP
during the CMJ AS.
CMJ = Countermovement Jump; AS = arm swing; RSI
ModFT
= Reactive Strength Index Modified,
computed via the flight time method; RSI
ModIMP
= Reactive Strength Index Modified, computed via
the impulse-momentum method; SD = Standard deviation.
4. Discussion
The main findings of the present study were (a) a significant increase in RSI
ModFT
, RSI
ModIMP
,
and FT:CT during the CMJ AS compared to the CMJ NAS; (b) a large correlation within RSI
ModFT
,
RSI
ModIMP
, and FT:CT between jump protocols; (c) a large significant positive correlations among
RSI
ModFT
, RSI
ModIMP
, and FT:CT, during both the CMJ AS and the CMJ NAS; and (d) RSI
ModFT
and
RSI
ModIMP
demonstrated superior limits of agreement during the CMJ NAS compared to the CMJ AS.
Sports 2019,7, 37 7 of 11
The present study performed a novel comparison of RSI
ModFT
, RSI
ModIMP
, and FT:CT outcomes
during the CMJ NAS compared to the CMJ AS. As hypothesized, the present study illuminated
statistically significant increases, all of the medium effect sizes, in RSI
ModFT
, RSI
ModIMP
, and FT:CT
during the CMJ AS compared to the CMJ NAS. Improvements in performance during the CMJ AS
compared to the CMJ NAS is persistent throughout the literature [
15
19
], such as the increase in jump
height of 10–12% [
35
]. Likewise, the velocity at take-off has been shown to be 6–10% greater during the
CMJ AS [
16
,
18
,
36
]. Similarly to prior literature, the present investigation observed increases of 20%,
24%, and 11%, in RSI
ModFT
, RSI
ModIMP
, and FT:CT, respectively during the CMJ AS. While a variety of
theories have been postulated as responsible for the improvements in performance during the CMJ AS,
enhancements are likely the result of several mechanisms operating simultaneously. Early work by
Payne [
37
] proposed the ‘transmission of force’ theory in which the upward acceleration of the arm
swing increases reciprocal downward forces exerted through the body, increasing ground reaction
forces and ultimately leading to a greater vertical velocity of the center of mass. While intuitive,
this theory is likely an oversimplification, as newer work by Lees et al. [
18
] offers a more complex
explanation, involving a series of events that allows the arms to build energy early in the jump
and transfer that energy to the rest of the body in the later stages of the jump. Alternative theories
include the eccentric stretching phase perhaps leading to a potentiation effect, with an increase in
myoeletric activity during the subsequent concentric contraction [
16
], while others have speculated the
significant increase in tension during the onset of the concentric contraction may result in enhanced
chemical energy availability for force generation [
35
]. Regardless of the mechanisms at play, the
observed increase in performance during the CMJ AS in the present study offers novel insight into
maximal capacities that may be more directly related to performance during sport, beneficial to applied
practitioners and researcher.
Importantly, the present study identified only a large correlation, suggesting only about 38–64% of
the shared variance between the CMJ protocols. The increase in the performance variables of RSI
ModFT
,
RSI
ModIMP
, and FT:CT during the CMJ AS compared to the CMJ NAS, while lacking very large,
or nearly perfect, correlations between jump performances indicates different information may be
captured from the CMJ AS force-time signature not acquired from the CMJ NAS. Although much of the
previous literature has used the CMJ NAS protocol to assess RSI
ModFT
, RSI
ModIMP
, and FT:CT [
5
,
26
,
38
],
the present data suggests the inclusion of the CMJ AS protocol may identify alterations in maximal
performance capacities. In addition, the CMJ AS may provide information independent from that
obtained during the CMJ NAS and may relate more closely to the athlete’s expression of performance
capabilities during the actual sporting event tasks, especially in sports incorporating a large vertical
component. Furthermore, recognizing differences in performance between the CMJ NAS and CMJ
AS will be essential in developing and comparing reference RSI
Mod
and FT:CT values among various
athletic populations [26].
Ultimately, these data suggest it may be necessary for practitioners to perform both CMJ protocols
when assessing an athletes’ physical capacities. For example, practitioners may employ the CMJ NAS
to evaluate acute changes in neuromuscular readiness, as previous literature has established less error
of measurement. The CMJ AS may be more useful in to quantitating long-term changes in performance,
such as changes in performance after a training program or alterations in performance between training
phase, allowing coaches and practitioners to identify the changes in maximal performance capacities
and where differences in performance are likely to be greater than acute changes.
The present study illuminated significant and strong positive relationships among RSI
ModFT
,
RSI
ModIMP
, and FT:CT during the CMJ NAS, but uniquely identified a similar association among
the variables during the CMJ AS. The findings of the present study support recent work by
McMahon et al. [
20
] that also observed nearly identical Pearson’s correlation coefficients between
RSI
ModFT
and RSI
ModIMP
(r = 0.980, p< 0.001), between RSI
ModFT
and FT:CT (r = 0.947, p< 0.001), as
well as between RSI
ModIMP
and FT:CT (r = 0.944, p< 0.001) during the CMJ NAS. Moreover, these
shared findings further endorse a significant and almost perfect positive relationship among RSI
Mod
Sports 2019,7, 37 8 of 11
and FT:CT regardless of the computation method. Similarly, the relationship between RSI
ModFT
and FT:CT during the CMJ AS paralleled the results of the CMJ NAS, in an almost perfect fashion,
which was expected considering the extensive use of congruent parameters to compute the variable.
In contrast, the relationship between RSI
ModFT
and RSI
ModIMP
, as well as between RSI
ModIMP
and
FT:CT during the CMJ AS were still positively correlated and very large, however their relationship
did not parallel to the same degree as the aforementioned relationships. The small relational disparities
observed, especially during Test Session 1, coincide with observations of less reliability when using the
impulse-momentum method to calculate jump height during the CMJ AS [
10
], however the variables
remain strongly related.
The present study found no significant differences between RSI
ModFT
and RSI
ModIMP
during the
CMJ NAS or the CMJ AS. Important to note, these findings are in contrast to the recent findings by
McMahon et al. [
20
] which observed a significant difference between variables using the CMJ NAS
protocol, but only a trivial effect (d= 0.14). No differences between RSI
ModFT
and RSI
ModIMP
alone
would indicate that practitioners could select either variable for player assessment. Interestingly, the
CMJ NAS produced superior limits of agreement between RSI
ModFT
and RSI
ModIMP
compared to the
CMJ AS, as visualized by the Bland-Altman Plots in Figures 1and 2. The CMJ NAS demonstrated a
smaller average measurement bias and reduction in measurement difference variability. Differences in
the limits of agreement are likely due to exaggerated variability in the velocity at take-off during the
CMJ AS with the movement occurring at a greater velocity, leading to alterations in the reliability
of the impulse-momentum computation of jump height [
10
]. Previous literature has identified the
consequences of inaccurately pinpointing the instant of take-off by as little as 2–3 ms, which can
manipulate an increase in variability of both velocity and displacement by as much as 2% [
22
,
39
].
The flight time method assumes center of mass is the same during take-off as landing, therefore
differences in center of mass during take-off and landing can lead to an over estimation of the jump
height calculation. Its speculated that the flight time method overestimates jump height, as the
jumper’s center over mass is often higher at take-off than landing [
29
]. Previous literature has shown
the center of mass is located at a higher relative position at take-off during the CMJ AS compared to
the CMJ NAS [
17
], which may exacerbate differences in calculations in that the difference in center of
mass during take-off are not paralleled upon landing.
In addition, it is likely that the predetermined force thresholds used by the commercially available
software influence the discrepancies between RSI
ModFT
and RSI
ModIMP
, however collecting data at
higher sampling frequencies, such as 1000 Hz in the present study is thought to reduce measurement
error [
22
]. It should be mentioned that, it is also possible participants performed minute increases
in hip, knee, or ankle flexion once airborne, not visible to the eye in real-time during the CMJ AS
and which then did not occur during the CMJ NAS, resulting in a decreased association between
variables within jump protocols [
29
,
31
]. However, the research team ruled jumps invalid when such
characteristics were visible. In accordance with previous literature [
10
], these findings suggest the
use of the CMJ NAS may be the more suitable protocol for athlete assessments when RSI
Mod
is a key
variable of interest, especially when evaluating acute day-to-day changes in neuromuscular functional
performance. In addition, the enhanced limits of agreement during the CMJ NAS suggests the chosen
computational method of RSI
Mod
(RSI
ModFT
or RSI
ModIMP
) when utilizing the CMJ NAS will likely
exert a negligible influence on the RSIMod values.
Important to note, the present study found no differences between Test Session 1 and Test Session 2
and no significant condition by time interactions. These findings further support the inter-session
reliability of the variables in the present study, as reported elsewhere [10].
The present study is not without limitations. This investigation examined a relatively small,
homogenous sample of skilled jumpers. In addition, the levels of agreement among variables may be
influenced by the software used for analysis. Finally, training loads were not quantitively confirmed
with an athlete monitoring technique, such as internal or external training load measures [6].
Sports 2019,7, 37 9 of 11
In conclusion, the present study offers several key findings useful to applied practitioners using
the CMJ with increasingly available commercial force platform technology to evaluate changes in
performance and fatigue. The increases in RSI
ModFT
, RSI
ModIMP
, and FT:CT evident during the
CMJ AS illuminate the potential use of the CMJ AS to reveal changes in maximal performance that
may translate more closely to sport specific tasks, such as assessing performance changes after a
training block or between training phases. In addition, the observed relationship within RSI
ModFT
,
RSI
ModIMP
, and FT:CT between the CMJ AS compared to the CMJ NAS suggests each jump protocol
may provide novel insight valuable to assessing an athlete’s physical capacities. In addition, the
present investigation identified the strong relationship among RSI
ModFT
, RSI
ModIMP
, and FT:CT during
both the CMJ NAS and CMJ AS. Furthermore, it appears the RSI
ModFT
and RSI
ModIMP
exhibit greater
levels of agreement during the CMJ NAS compared to the CMJ AS. Practically, these findings indicate
that either RSI
Mod
or FT:CT may be utilized to monitor changes in neuromuscular function and
performance, but it is unnecessary to include both, as they may provide similar information about an
athlete’s force-time characteristics, conceivably making their simultaneous inclusion during a player
assessment redundant.
Author Contributions:
Conceived and designed the experiments, A.H. and B.D.; Performed the experiments,
A.H., B.B. and B.D.; Data Analysis, A.H., B.B. and R.M.; Original Draft Preparation, A.H.; Writing—Review and
Editing, B.B., B.D., E.F., R.M. and M.B.; Visualization, A.H., R.M. and E.F.; Supervised the project and project
administration, B.D. and M.B.
Funding: This research received no external funding.
Acknowledgments:
The authors thank all the student athletes who graciously took the time to participate in this
study. The authors would also like to express their appreciation to the Men’s and Women’s Basketball Programs
at the University of Oklahoma for their continued support of research aimed at not only improving athlete
performance but enhancing overall student athlete welfare.
Conflicts of Interest: The authors declare no conflict of interest.
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©
2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).
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Background As basketball match-play requires players to possess a wide range of physical characteristics, many tests have been introduced in the literature to identify talent and quantify fitness in various samples of players. However, a synthesis of the literature to identify the most frequently used tests, outcome variables, and normative values for basketball-related physical characteristics in adult male basketball players is yet to be conducted. Objective The primary objectives of this systematic review are to (1) identify tests and outcome variables used to assess physical characteristics in adult male basketball players across all competition levels, (2) report a summary of anthropometric, muscular power, linear speed, change-of-direction speed, agility, strength, anaerobic capacity, and aerobic capacity in adult male basketball players based on playing position and competition level, and (3) introduce a framework outlining recommended testing approaches to quantify physical characteristics in adult male basketball players. Methods A systematic review of MEDLINE, PubMed, SPORTDiscus, Scopus, and Web of Science was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to identify relevant studies. To be eligible for inclusion, studies were required to: (1) be original research articles; (2) be published in a peer-reviewed journal; (3) have full-text versions available in the English language; and (4) include the primary aim of reporting tests used and/or the physical characteristics of adult (i.e., ≥ 18 years of age) male basketball players. Additionally, data from the top 10 draft picks who participated in the National Basketball Association combined from 2011–12 to 2020–21 were extracted from the official league website to highlight the physical characteristics of elite 19- to 24-year-old basketball players. Results A total of 1684 studies were identified, with 375 being duplicates. Consequently, the titles and abstracts of 1309 studies were screened and 231 studies were eligible for full-text review. The reference list of each study was searched, with a further 59 studies identified as eligible for review. After full-text screening, 137 studies identified tests, while 114 studies reported physical characteristics in adult male basketball players. Conclusions Physical characteristics reported indicate a wide range of abilities are present across playing competitions. The tests and outcome variables reported in the literature highlight the multitude of tests currently being used. Because there are no accepted international standards for physical assessment of basketball players, establishing normative data is challenging. Therefore, future testing should involve repeatable protocols that are standardised and provide outcomes that can be monitored across time. Recommendations for testing batteries in adult male basketball players are provided so improved interpretation of data can occur.
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The purpose of this analysis was to construct a preliminary scale of reference values for reactive strength index-modified (RSImod). Countermovement jump data from 151 National Collegiate Athletic Association (NCAA) Division I collegiate athletes (male n = 76; female n = 75) were analyzed. Using percentiles, scales for both male and female samples were constructed. For further analysis, athletes were separated into four performance groups based on RSImod and comparisons of jump height (JH), and time to takeoff (TTT) were performed. RSImod values ranged from 0.208 to 0.704 and 0.135 to 0.553 in males and females, respectively. Males had greater RSImod (p < 0.001, d = 1.15) and JH (p < 0.001, d = 1.41) as compared to females. No statistically significant difference was observed for TTT between males and females (p = 0.909, d = 0.02). Only JH was found to be statistically different between all performance groups. For TTT no statistical differences were observed when comparing the top two and middle two groups for males and top two, bottom two, and middle two groups for females. Similarities in TTT between sexes and across performance groups suggests JH is a primary factor contributing to differences in RSImod. The results of this analysis provide practitioners with additional insight as well as a scale of reference values for evaluating RSImod scores in collegiate athletes.
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Heishman, AD, Daub, BD, Miller, RM, Freitas, EDS, Frantz, BA, and Bemben, MG. Countermovement jump reliability performed with and without an arm swing in NCAA Division 1 intercollegiate basketball players. J Strength Cond Res XX(X): 000-000, 2018-The countermovement jump (CMJ) is routinely used in athlete performance to quantify adaptions to training, as well as monitor neuromuscular readiness and fatigue. However, controversy remains in whether to incorporate an arm swing during the CMJ (CMJ AS) or keep the hands placed on the hips (CMJ NAS). Incorporating the arms provides a higher degree of sport-specificity that may yield improved reliability, especially in skilled jumpers. By contrast, the hands-on-hips approach isolates lower extremity force production and eliminates potential arm-swing variation. Therefore, the purpose of this study was to establish the reliability of CMJ typical (CMJ-TYP), CMJ concentric alternative (CMJ-Conc-ALT), and CMJ eccentric alternative (CMJ-Ecc-ALT) variables obtained during the CMJ AS and CMJ NAS. Twenty-two (men = 14, women = 8) NCAA Division 1 collegiate basketball players performed 3 CMJ AS and 3 CMJ NAS on a force plate, in a randomized order. To assess the test-retest reliability, participants returned 1 week later to perform 3 additional CMJ AS and 3 CMJ NAS. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were used to assess intersession and intrasession reliability for the various CMJ variables. A majority of CMJ-TYP and several CMJ-Conc-ALT and CMJ-Ecc-ALT variables exhibited adequate intersession and intrasession reliability (ICC > 0.700 and CV <10%) during both the CMJ AS and the CMJ NAS. Countermovement jump AS may provide more pertinent information about long-term changes in sport-specific performance, whereas the CMJ NAS may be more beneficial for detecting acute changes in neuromuscular fatigue and athlete readiness.
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The countermovement jump (CMJ) test is commonly conducted to assess neuromuscular function and is being increasingly performed using force platforms. Comprehensive insight into athletes’ neuromuscular function can be gained through detailed analyses of force-time curves throughout specific phases of the CMJ, beyond jump height alone. Confusingly, however, many different terms and methods have been used to describe the different phases of the CMJ. This article describes how six key phases of the CMJ (weighing, unweighting, braking, propulsion, flight, and landing) can be derived from force-time records to facilitate researchers’ and practitioners’ understanding and application to their own practice.
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Current research ideologies in sport science allow for the possibility of investigators producing statistically significant results to help fit the outcome into a predetermined theory. Additionally, under the current Neyman-Pearson statistical structure, some argue that null hypothesis significant testing (NHST) under the frequentist approach is flawed, regardless. For example, a p-value is unable to measure the probability that the studied hypothesis is true, unable to measure the size of an effect or the importance of a result, and unable to provide a good measure of evidence regarding a model or hypothesis. Many of these downfalls are key questions researchers strive to answer following an investigation. Therefore, a shift towards a magnitude-based inference model, and eventually a fully Bayesian framework, is thought to be a better fit from a statistical standpoint and may be an improved way to address biases within the literature. The goal of this article is to shed light on the current research and statistical shortcomings the field of sport science faces today, and offer potential solutions to help guide future research practices.
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Purpose: The reactive strength index modified (RSImod) has been recently identified and validated as a method of monitoring countermovement jump (CMJ) performance. The kinetic and kinematic mechanisms that optimize a higher RSImod score are, however, currently unknown. The purpose of this study, therefore, was to compare entire CMJ force-, power-, velocity- and displacement-time curves (termed temporal phase analysis) of athletes who achieve high versus low RSImod scores. Methods: Fifty-three professional male rugby league players performed three maximal effort CMJs on a force platform and variables of interest were calculated via forward dynamics. RSImod values of the top (high RSImod group) and bottom (low RSImod group) twenty athletes’ kinetic and kinematic-time curves were compared. Results: The high RSImod group (0.53±0.05 vs. 0.36±0.03) jumped higher (37.7±3.9 vs. 31.8±3.2 cm) with a shorter time to take-off (TTT) (0.707±0.043 vs. 0.881±0.122 s). This was achieved by a more rapid unweighting phase followed by greater eccentric and concentric force, velocity and power for large portions (including peak values) of the jump, but a similar countermovement displacement. The attainment of a high RSImod score therefore required a taller, but thinner, active impulse. Conclusion: Athletes who perform the CMJ with a high RSImod, as achieved by high jumps with a short TTT, demonstrate superior force, power, velocity and impulse during both the eccentric and concentric phases of the jump. Practitioners who include the RSImod calculation within their testing batteries may assume that greater RSImod values are attributed to an increase in these underpinning kinetic and kinematic parameters.
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Time of day is a key factor that influences the optimization of athletic performance. Intercollegiate coaches oftentimes hold early morning strength training sessions for a variety of factors including convenience. However, few studies have specifically investigated the effect of early morning vs. late afternoon strength training on performance indices of fatigue. This is athletically important because circadian/ultradian rhythms and alterations in sleep patterns can impact training ability. Therefore, the purpose of the present study was to examine the effects of morning vs. afternoon strength training on an acute performance index of fatigue (countermovement jump height, CMJ), player readiness (Omegawave), and self-reported sleep quantity. We hypothesized afternoon training sessions would be associated with increased levels of performance, readiness, and self-reported sleep. A retrospective analysis was performed on data collected over the course of the pre-season on 10 elite NCAA Division 1 male basketball players. All basketball related activities were performed in the afternoon with strength and conditioning activities performed either in the morning of afternoon. The average values for CMJ, Power output (Power), self-reported sleep quantity (sleep), and player readiness were examined. When player load and duration were matched CMJ (58.8±1.3 vs. 61.9±1.6cm, p = 0.009), power (6378.0±131.2 vs. 6622.1±172.0 W, p = 0.009) and self-reported sleep duration (6.6 + 0.4 vs 7.4 + 0.25 p = 0.016) were significantly higher with afternoon strength and conditioning training, with no differences observed in player readiness values. We conclude that performance is suppressed with morning training and is associated with a decrease in self-reported quantity of sleep.
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Background: A countermovement jump (CMJ) is routinely used in many sporting settings to provide a functional measure of neuromuscular fatigue. However, the variables that are most sensitive to fatigue remain somewhat unclear. The purpose of this study was to determine the acute changes in neuromuscular fatigue in rugby union players during a period of preseason training. Methods: Nine male (age: 19.0 ± 1.5 years) academy rugby union players performed five CMJ trials on three occasions, at baseline, 24 hours and 48 hours post-baseline. The fatiguing protocol consisted of multiple high-intensity training sessions commensurate with the period of preparation and the sport. A total of 14 CMJ variables were derived from the force-time curve. Meaningful differences in CMJ performance were examined using the magnitude of change (effect sizes; ES) compared to baseline. Results: Most variables, 9 of the 14, showed substantial decreases at 24 hours post- baseline. Mean concentric power, peak velocity, jump height and force at zero velocity were impaired by the greatest magnitude (ES = -0.98 to -1.57). At 48 hours post-baseline, substantial increases in eccentric duration, concentric duration and total duration were first observed (ES = 0.48 to 0.61). Concomitantly, peak power, peak velocity and jump height, recovered to baseline levels. Conclusions: During the late regeneration phase, neuromuscular fatigue can manifest itself as an altered movement strategy, rather than as a simple reduction in physical output such as jump height. Practitioners are therefore advised to incorporate a wide range of variables when trying to identify subtle changes in the bimodal recovery pattern associated with stretch-shortening cycle induced fatigue.