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DOES CORE STRENGTH TRAINING INFLUENCE
RUNNING KINETICS,LOWER-EXTREMITY STABILITY,
AND 5000-MPERFORMANCE IN RUNNERS?
KIMITAKE SATO AND MONIQUE MOKHA
Department of Sport and Exercise Sciences, Barry University, Miami Shores, Florida
ABSTRACT
Sato, K and Mokha, M. Does core strength training influence
running kinetics, lower-extremity stability, and 5000-m perfor-
mance in runners? J Strength Cond Res 23(1): 133–140,
2009—Although strong core muscles are believed to help
athletic performance, few scientific studies have been con-
ducted to identify the effectiveness of core strength training
(CST) on improving athletic performance. The aim of this study
was to determine the effects of 6 weeks of CST on ground
reaction forces (GRFs), stability of the lower extremity, and
overall running performance in recreational and competitive
runners. After a screening process, 28 healthy adults (age, 36.9
69.4 years; height, 168.4 69.6 cm; mass, 70.1 615.3 kg)
volunteered and were divided randomly into 2 groups (n=14in
each group). A test-retest design was used to assess the
differences between CST (experimental) and no CST (control)
on GRF measures, lower-extremity stability scores, and running
performance. The GRF variables were determined by calculat-
ing peak impact, active vertical GRFs (vGRFs), and duration of
the 2 horizontal GRFs (hGRFs), as measured while running
across a force plate. Lower-extremity stability was assessed
using the Star Excursion Balance Test. Running performance
was determined by 5000-m run time measured on outdoor
tracks. Six 2 (pre, post) 32 (CST, control) mixed-design
analyses of variance were used to determine the influence of
CST on each dependent variable, p,0.05. Twenty subjects
completed the study (n
exp
= 12 and n
con
= 8). A significant
interaction occurred, with the CST group showing faster times
in the 5000-m run after 6 weeks. However, CST did not
significantly influence GRF variables and lower-leg stability.
Core strength training may be an effective training method for
improving performance in runners.
KEY WORDS core exercise, running performance, stability
INTRODUCTION
Core strength training (CST) is widely used in the
strength and conditioning, health and fitness, and
rehabilitation industries with claims of improving
performance and reducing the risk of injuries
(12,14). It is believed among those professionals that to
improve athletic performance and prevent risk of injury, CST
is one of the vital components in the strength and
conditioning field. Despite the strong belief in these
purported positive effects, limited scientific studies have
shown no direct relationship between stronger core muscles
and better athletic performance (3,16,17). Significant im-
provement in core strength has been documented as a result
of CST, but the same research has failed to show significant
changes in the athletic performance from CST (3,16,17). This
type of research indicates that CST is a useful tool for
strengthening core muscles, but the carryover to mechanics
and performance needs further investigation. Core-related
exercises such as Swiss ball training, balance training, weight
training, and yoga have become popular physical activities
even among general populations in recent years. Even
though scientific studies have not shown any links to prove
performance enhancement, CST is becoming common for all
levels of athletes.
In a biomechanical analysis of running, abnormal ranges of
vertical ground reaction forces (vGRFs) and horizontal GRFs
(hGRFs) have been associated with overuse injuries
(2,7,10,13). Aging, lack of joint stability, muscle weakness,
harder running surfaces, and downhill running are found to
be indications of increasing impact vGRFs as well (2,5–7,18).
Stronger core muscles may help keep ground reaction forces
(GRFs) within an optimal range. In addition, because
previous lower-extremity injuries such as ankle sprain or
overuse injuries often contribute to create muscular imbal-
ance and poor proprioception, proper rehabilitation is
needed to regain stability (4). Thereby, CST would be an
option, and the CST may help improve dynamic stability of
the lower extremity. Adequate dynamic stability in the lower
extremity may have an important role in keeping vGRFs and
hGRFs within the normal range.
Core strength training may have an important role in
running performance, such as running within the normal
Address correspondence to Kimitake Sato, jpnsatok@hotmail.com.
23(1)/133–140
Journal of Strength and Conditioning Research
Ó2009 National Strength and Conditioning Association
VOLUME 23 | NUMBER 1 | JANUARY 2009 | 133
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range of GRFs at a given running velocity, and good dynamic
stability of the lower extremity. Therefore, the purpose of this
study was to determine the effects of 6 weeks of CST on
GRF, stability of the lower extremity, and overall running
performance in recreational and competitive runners. We
hypothesized that CST would have the following positive
influences: a) decrease peak impact vGRF (initial heel
contact), b) increase peak active vGRF (push-off force),
c) decrease the amount of time in breaking hGRF, d) increase
the amount of time in propulsive hGRF, e) increase Star
Excursion Balance Test (SEBT) scores, and f ) decrease 5000-m
run time.
METHODS
Experimental Approach to the Problem
This study was 6-week training study completed during
a marathon-training period. A test-retest design was used
to identify the effects of CST. The CST group performed
4 sessions of 5 core exercises per week for 6 weeks. Laboratory
testing lasted 0.5 hours on each subject in the control group
and 1.0 hours on each subject in the CSTgroup. The 5000-m
run was timed at outdoor tracks on different days because of
schedule restrictions.
Subjects
Twenty-eight recreational and competitive rear–foot-strike
runners (10 men, 18 women) initially qualified and volun-
teered for this study (age, 36.9 69.4 years; height, 168.4 69.6
cm; mass, 70.1 615.3 kg). They had no injuries at the time of
data collection. They answered specific questions regarding
their training strategies, pace, past injury history, and type of
footwear used to identify their running background. The
subjects were then randomly divided into 2 groups: control
(n= 14) and CST (n= 14). Twenty-eight runners performed
pretraining tests, and 20 participants completed the posttest
(n
con
=8,n
cst
= 12). Demographic information for the 20
participants is shown in Table 1. To detect any differences
in physical and performance characteristics between the
groups, an independent t-test was run. According to the test,
body mass (using the posttest result) and average running
pace (self-reported during the screening process) showed
significant differences between the groups (see Table 1).
During the screening process, the core stability of each
runner was assessed. The purpose of screening core stability
before accepting participants was to eliminate potential
participants who already possessed a high level of stability—a
level III or better score based on the Sahrmann core stability
test (scale = level I–V). Only 1 potential subject scored level III
and was omitted from the study. The procedure of this core
stability test follows that of Stanton et al. (17). Their pilot data
exhibited a reliability coefficient of 0.95 with an SEM of 7.7%
for this test. By assessing the core stability level, 28 qualified
subjects possessed level I or level II core muscle strength
before beginning the initial test. Each subject signed the
university-approved informed consent form after explanation
of the study procedures had been given.
Instrumentation
Force Plate. An AMTI force plate (Advanced Medical
Technologies, Inc., Watertown, Mass) was used (sampled at
600 Hz) to measure GRF variables. The Peak Motus software
(v. 8.2, ViconPeak, Centennial, Colo) was used to reduce the
data with fast Fourier analysis. The GRFs were normalized
mathematically to each participant’s body weight (BW) for
peak impact and active vGRFs: raw force (N) / 9.81 ms
22
/
BW. Duration of breaking hGRF and propulsive hGRF were
standardized by percentage from a foot contact time: total
foot contact time at 0.30 seconds = 0.15 seconds of breaking
hGRF and 0.15 seconds of propulsive hGRF; thus, 50%
and 50%.
Star Excursion Balance Test. The SEBT has been used in the
clinical field to measure the functionality of the lower
extremity (8,9,11,14). Olmsted et al. (14) describe the SEBT
as an economical, simple, and reliable instrument to measure
the dynamic stability of lower-body functionality. Kinzey and
Armstrong (11) report a reliability coefficient of 0.86 after
a practice session. Tapes were placed in 8 directions bisecting
each other at 45°angles on the floor of the laboratory. The
layout of the SEBT is shown in Figure 1.
TABLE 1. Demographic information (mean 6SD).
Experimental group, n= 12 Control group, n=8
Age (y) 37.75 610.63 39.25 610.81
Height (cm) 167.00 610.00 167.00 68.40
Body mass (kg)* 75.95 616.89 63.03 612.02
Average running pace (min:s)* 10:45 61:11 9:26 60:47
Average weekly mileage (miles) 20.75 66.66 23.75 66.41
Sahrmann core stability test (level) 1.54 60.40 1.75 60.38
*Significant difference between the groups, p,0.05.
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Core Strength Training in Runners
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According to the methods used by Gribble et al. (9), only
3 out of 8 directions were used in this study to reduce the
chances of fatigue during the test. The lengths of reaches in
all 3 directions (0, 90, and 180°directions) from both feet
were added and divided by each subjects’ leg lengths to be
comparable among them (e.g., if a subject scores 20 cm in
front, 30 cm on the side, and 30 cm in the back from both
feet, it is equal to a total of 160 cm; divided by the average leg
length of 80 cm = 200%).
Procedures
All qualified subjects reported to the laboratory and selected
outdoor tracks for testing on 2 occasions: a) pretraining and b)
6 weeks posttraining. Tests for GRF, lower-extremity stability,
and running performance were performed identically at both
sessions.
GRF Test
A reflective marker was placed
on the lateral part of the left
shoe to measure running veloc-
ity calculated by Peak Motus
software version 8.2 (Vicon-
Peak, Centennial, Colo). One
60-Hz camera (JVC Pro-
fessional Products Company,
Denver, Colo) was positioned
on the left side of the force
plate perpendicularly, to track
the reflective marker. Subjects
were instructed to contact the
force plate with their left foot.
Bennell et al. (1) have shown
that the GRFs from the left and
right feet during running were
strongly correlated (0.73–0.96);
thus, only left-foot kinetics were
measured. The subjects warmed up by running at a self-
selected pace outdoors, and then they returned to the
laboratory to run across the force plate. The layout of the
laboratory is shown in Figure 2.
This test simulated a real running situation; thus, if the
subject reached the force plate with abnormal steps such as
shuffling to achieve proper foot placement, the trial was
repeated.
Star Excursion Balance Test
Before the SEBT, the investigator measured all subjects’ leg
lengths to calculate a ratio of the total score of the SEBT and
leg length (total length / leg length = SEBT score) (8). Leg
length was measured from medial malleolus to anterior
superior iliac spine of each leg in centimeters by a tape
measure, and the measurements were averaged if there was
a minor leg length discrepancy. This ensured the accuracy of
performance among the subjects to analyze the level of
lower-extremity stability. The barefoot condition was re-
quired to eliminate extra balance and stability from the shoes
during the test (8). First, each subject placed his or her left
foot on the center of a 0–180°line. Then, each subject
reached out his or her toes as far as possible to the direction
of 0, 90, and 180°lines while maintaining balance. Next, each
subject switched to his or her right foot and followed the
same sequence. Kinzey and Armstrong (11) have indicated
that instruction and demonstration improve the reliability of
the test (from 0.67 to 0.87), along with practice sessions
before the test; thus, adequate amounts of practice time also
were provided. To maximize the reliability of the measure-
ment, the following detailed instructions were given
identically to all subjects: a) placing the foot on the line
with the medial part of the stable foot while reaching laterally
Figure 2. Layout of the laboratory.
Figure 1. Layout of the Star Excursion Balance Test.
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(90°) (see Figure 3), b) placing the toes of the stable foot
aligned on the line for the forward reach (0°) (see Figure 4),
and c) placing the heel of the stable foot on the line for the
backward reach (180°) (see Figure 5).
Subjects lightly touched the maximum reaching point
while in a static position for at least 3 seconds to ensure their
ability to stabilize their bodies (8). Each subject received 2
trials in each condition to reach his or her toes to the guided
directions. The length between the toes of the reaching foot
and the starting position of the stable foot were measured
manually with a tape measure (8).
5000-m Run Test
A 5000-m run was done at accurately measured outdoor
tracks. Because of the time availability of each subject,
the 5000-m run was done on a separate day from the
laboratory testing date (SEBT and GRF test). However, the
5000-m run was performed within 7 days of the laboratory
testing date.
After an adequate amount of warm-up including jogging
and stretching, the 5000-m run was timed. The accurately
measured track is 400 m per lap; thus, all participants ran 12.5
laps to complete a total distance of 5000 m. On completion of
this trial, the 5000-m run time was recorded in minutes and
seconds (e.g., 5000 m = 19 minutes 43 seconds). In addition,
temperature and humidity level were also recorded during all
subjects’ running trials.
Core Strength Training
The control group did not receive the CST protocol; they
were instructed to maintain their training routines and to
report any alterations to the investigator. The CST group
received the CST program that consists of 5 core-related
exercises performed 4 times per week for 6 weeks. The
following 5 exercises were visually demonstrated and verbally
instructed by the investigator after the pretraining test: a)
abdominal crunch on a stability ball to target abdominal
muscles, b) back extension on a stability ball to target back
extensor muscles, c) supine opposite 1-arm/1-leg raise to
target back/hip extensor muscles, d) hip raise on a stability
ball to target back/hip extensor muscles, and e) Russian twist
on a stability ball to target abdominal muscles. These exercises
have been used in previous studies to determine the effects of
CST (3,16,17). The exercises are relatively well balanced,
targeting core muscles (abdominal, hip flexor/extensor, and
back extensor muscles). Even though those exercises are
relatively novice level according to Stanton et al. (17), some of
them are considered a challenge for those who have no
experience in CST. All exercises were fully instructed and
demonstrated by a certified strength and conditioning
specialist to ensure the understanding of the proper
mechanics after the pretraining laboratory test. In addition,
the CST group received a hard copy of exercise instructions
Figure 3. Stable foot (left) position for lateral reach.
Figure 4. Stable foot (left) position for frontal reach.
Figure 5. Stable foot (left) position for back reach.
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including pictures and training logs. Stability balls were
provided to the experimental group because the treatment is
intended for home training. They were instructed to fill out
the training log after each session, and they also were
contacted by the investigator at the end of each week to
ensure adherence or to answer any concerns. Table 2 lists the
volume of the training for the 6 weeks. According to Cosio-
Lima et al. (3), the total session volume should increase to
challenge strength improvement rather than performing the
same volume throughout the treatment. Therefore, this study
was designed to increase the volume of exercise sessions
every 2 weeks.
Statistical Analyses
All dependent variables were entered into Statistical Package
for Social Sciences (SPSS Inc., Chicago, Ill). Six 2 32 (group
by time) mixed-design analyses of variance with repeated
measures were performed to determine any significant effects
of CST on the dependent variables. Significance was defined
as p#0.05.
RESULTS
Table 3 shows that CST had no significant influence on
lower-extremity stability scores measured by the SEBT or on
any aspects of the GRF variables. However, there was
a significant interaction in 5000-m run time, indicating that
CST significantly improved running times in the CST group
during 6 weeks.
Ground Reaction Force Test
As shown in Table 3, there are no significant effects on vGRF
measures. The peak impact and the peak active vGRF were
not influenced by the group or time, and there were no
significant effects for the hGRF measures (see Tables 4
and 5). The duration of the breaking hGRF was slightly
shorter, and the duration of the propulsive hGRF was slightly
longer, in the CST group, regardless of 6 weeks of training.
Star Excursion Balance Test Scores
Table 6 shows that the SEBT scores increased in both groups
during the 6 weeks. Although the SEBT score was shown to
be nonsignificant on the basis of the interaction effect, the
number did improve more (11.67-cm greater improvement)
in the CST group during the 6 weeks of training.
5000-m Run Time
A significant interaction was found, F(1,18) = 56.09, p,0.05.
Table 7 shows that the CST group improved their average
time compared with the control group.
DISCUSSION
The purpose of this study was to determine the influence of
CST on running kinetics, stability of the lower extremity, and
performance in runners. It was expected that CST would
positively influence running kinetics, stability of the lower
extremity, and 5000-m run time.
Peak impact vGRF is a commonly measured variable in the
biomechanics of running (5,7,10,13). If the impact of the
initial foot strike is too low (,1.5 BW), this could cause
a high loading rate relating to high active vGRF, but if it is
too high (.3.0 BW), it could lead to overuse injuries by
having a high force of heel impact (10,13,18). The normal
range is approximately 1.6–2.3 BW, according to previous
studies with similar running velocities (7,13). In this study,
both groups had averages in the relatively normal range for
peak impact vGRF (n
cst
= 1.65 and 1.74 BW; n
con
= 1.99 and
1.89 BW). Even though the CST group’s number increased
by 0.09 BW, it was not necessarily an excessive increase or
range. Therefore, the increase for the CST group should not
a concern for potential overuse injuries based on the impact
force.
Peak active vGRF is also a common variable that is
analyzed in running studies (5,7,10,13). High vGRFs were
thought to negatively affect runners by putting high pressure
on the mid- and forefoot, possibly leading to injury (10,13).
The suggested range is from 2 to 3 BW, based on previous
studies that have used relatively similar running velocities
(10,13,18). On the other hand, if this force is too low, the
runner may not be producing enough force to propel forward
(7,13). In this study, the peak active vGRF was within the
average range for all subjects, according to Novacheck (13).
The results show that the peak active vGRF did not change
significantly before and after the training period in the both
groups (see Table 4). It is questionable to state that CST may
have been the major role of this result for the experimental
group. The purpose of incorporating CST was to increase
core muscle strength to obtain better movement control,
especially in the lower extremity, to optimize running
kinetics. Although the results were the opposite of the
hypothesis, the result may be a good indication for the CST
group that their average 5000-m run time improved, whereas
peak active vGRF did not change.
When a foot lands in front of the body while running
(which often happens at downhill running and faster running
velocity), it leads to a longer duration and higher force of
breaking hGRF because the body becomes stiffer kinemat-
ically to accept greater foot impact (7). Reducing the duration
of breaking hGRF would help carry forward momentum.
Thus, increasing the duration of propulsive hGRF would
help runners to carry forward momentum, making their
TABLE 2. Training volume for the 6 weeks.
Sets Repetitions
First 2 weeks 2 10
Second 2 weeks 2 15
Third 2 weeks 3 12
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running more economical in biomechanics terms (7,13).
Gottschall and Kram (7) report that the ideal duration
of breaking hGRF is approximately 50% or slightly lower.
On the basis of the statistical analysis, there were no
significant effects of CST on either variable in the CST
group (see Table 3). Both groups slightly decreased
their duration of propulsive hGRF after 6 weeks (n
cst
=
23.45%; n
con
=21.37%).
The GRF data for both groups were potentially affected by
inconsistent running velocity between pre- and posttraining
GRF tests (n
cst
= pretest 2.64 ms
21
, posttest 2.81 ms
21
;n
con
= pretest 2.99 ms
21
, posttest, 3.08 ms
21
); this is one of the
limitations of this study. Faster running velocity correlates
with higher peak impact vGRF because of the harder initial
foot contact (7,13). Even though all subjects were instructed
to run across the force plate at the same speed and as
naturally as possible (both pre and post), many subjects,
especially in the CST group, ran faster during the posttraining
GRF test.
Even though there is no scientific evidence for the
effectiveness of having good balance and stability in athletic
performance, health and fitness professionals believe that
better stability of the lower
extremity is extremely impor-
tant to athletic performance,
and also for daily living, in
preventing potential injuries
(11). Therefore, it is necessary
to analyze whether CST would
improve stability levels in dy-
namic movement based on the
SEBT. The results show that
SEBT scores improved in both
groups because of possible test-
retest effects, which may be
why the interaction effects
were not significant. However,
the CST group improved their
SEBT scores better than the
control group (n
cst
= +21.92 cm; n
con
= +10.25 cm).
Regardless of the nonsignificant outcome, a better SEBT
score is a sign of improvement in dynamic stability for the
CST group. Even though it is not known whether this
improvement actually helps runners run faster or prevents
potential running-related injuries, a more stable lower
extremity should provide better and more consistent
movement control.
The 5000-m run was conducted for performance analysis
because the distance is one of the most popular distances for
participating in local races (18). The results show significant
improvement in the CST group after the training period
(faster times by an average of 47 seconds), and the control
group also improved their run times by an average of 17
seconds in the posttraining test. Even though minor
limitations including climate difference between pre and
post 5000-m runs and increasing weekly mileage during the
6-week period could have been factors for the faster time
results, both groups were equally affected by those
conditions. Core strength training may certainly be one of
the causes that improved running times, especially in the
CST group.
TABLE 3. Summary of the statistics on each variable.
Interaction
Main effect:
training
Main effect:
group
Peak impact vGRF NS NS NS
Peak active vGRF NS NS NS
Time in the breaking hGRF NS NS *
Time in the propulsive hGRF NS NS *
SEBT NS *NS
5000-m run time *
*Significant effect, p,0.05. NS = not significant (p.0.05); vGRF = vertical ground
reaction force; hGRF = horizontal ground reaction force; SEBT = Star Excursion Balance Test.
TABLE 4. Peak impact and peak active vertical ground reaction force (vGRF) for each group before and after training time
(mean 6SD).
Experimental group, n= 12 Control group, n=8
Peak impact vGRF (BW) Pretraining 1.65 60.38 1.99 60.38
Posttraining 1.74 60.46 1.89 60.24
Difference (pre-post) 60.09 20.10
Peak active vGRF (BW) Pretraining 2.30 60.36 2.49 60.26
Posttraining 2.31 60.42 2.52 60.24
Difference (pre-post) 10.01 10.03
BW = body weight.
138
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Core Strength Training in Runners
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This study’s design involved performing 4 training sessions
per week, which was higher than in previous studies (3,16,17).
Thus, the volume in the present study may have provided
a strong enough stimulus to show significant effects in
running performance. According to the qualitative feedback
from the subjects in the CST group, some were conscious of
using their core muscles to stabilize their running form. Thus,
the significant improvement in 5000-m run time for the CST
group may be a true effect of CST.
In summary, this study shows a significant effect on running
performance from performing CST. Because previous studies
using low training volumes (2 sessions per week for 6 weeks)
did not show significant effects, this study might prove that
a higher training volume is needed to show a significant effect.
However, CST did not significantly affect the GR F variables
or lower-extremity stability.
PRACTICAL APPLICATIONS
This study demonstrates that CST has an important role in
improving running performance from a physical perspective
by improving core muscle strength. Additionally, the CST
group became more conscious of body position once they
understood the importance of having good posture while
running. However, it also seemed that the CST did not
significantly influence running kinetics. Runners are in-
terested in every possible way of improving running
performance, such as purchasing lighter shoes and apparel,
trying famous training plans, changing running mechanics, or
taking endurance supplements. The CST is certainly one
possible way for any type of runner to use supplemental
strength training to optimize overall running efficiency. This
information is valuable to strength and conditioning coaches,
team coaches, and physical education teachers who are
implementing CST into their routine and who understand
the relationship between core strength levels and running
performance.
The CST is a great training tool for those professionals who
use it in the strength and conditioning field to improve
or maintain strength levels in the midsection of the body.
The CST also has been an effective training tool in the
rehabilitation field for recovering from previous musculo-
skeletal injuries to regain muscular strength. This study used
a relatively short training period (6 weeks), as have other
studies in thepast (3,16,17). A full year of continuous CSTand
TABLE 5. Duration of breaking and propulsive horizontal ground reaction force (hGRF) for each group before and after
training time (% as duration during a foot contact) (mean 6SD).
Experimental group, n= 12 Control group, n=8
Breaking hGRF (%) Pretraining 47.30 65.91 53.11 64.77
Posttraining 49.33 66.81 54.48 64.76
Difference (pre-post) +2.03 +1.37
Propulsive hGRF (%) Pretraining 52.70 65.92 46.89 64.77
Posttraining 49.25 66.70 45.52 64.57
Difference (pre-post) 23.45 21.37
TABLE 6. Star Excursion Balance Test scores for
each group before and after training time (% as
a ratio of total reaching length / leg length; mean
6SD).
Experimental
group,
n=12
Control
group,
n=8
Pretraining
(%)
198.75 626.70 199.13 626.34
Posttraining
(%)
220.67 626.90 209.38 626.89
Difference
(pre-post)
+21.92 +10.25
TABLE 7. Five-thousand-meter run time for each
group before and after training time (mean 6SD).
Experimental
group,
n=12
Control
group,
n=8
Pretraining
(min:s)
29:29 62:38 26:30 61:59
Posttraining
(min:s)
28:42 62:23 26:13 61:54
Difference
(pre-post)
20:47 20:17
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occasional tests may show changes in the biomechanical
characteristics of running performance.
ACKOWLEDGMENTS
The primary author would thanks the coauthor, Dr. Monique
Mokha, and the committee members for their mentorship
and extensive reviews during the study. Special thanks go to
local running clubs and marathon-training groups in south
Florida during the recruiting process.
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