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Original Research
Three Week Hypergravity Training Intervention Decreases Ground
Contact Time During Repeated Jumping and Improves Sprinting
and Shuttle Running Performance
ERIC M. SCUDAMORE†1,2, JORDAN B. LOWE†1, VERONIKA
PŘIBYSLAVSKÁ†1,2, SAMANTHA L. JOHNSON†1,2, MARY C. STEVENSON†1,
TYLER W. LANGFORD†1, JAMES M. GREEN‡1, and ERIC K. O’NEAL‡1
1Department of Health Physical Education and Recreation, University of North
Alabama, Florence, AL, USA; 2Department of Health and Human Performance,
Middle Tennessee State University, Murfreesboro, TN, USA
†Denotes graduate student author, ‡Denotes professional author
ABSTRACT
International Journal of Exercise Science 9(2): 149-158, 2016. This study examined the
effects of a non-traditional training method, hypergravity training (HT), on anaerobic
performance. Highly active men (n = 9) completed a 3 week HT protocol in which weighted vests
were worn 8 h/day, 4+ days/week separate from training. Vest loads were 11.2 ± 0.6% of body
mass during week one, and increased to 13.2 ± 0.7% (week 2), and 16.1 ± 0.4% (week 3).
Performance testing included power clean 1-RM (PC), counter movement jumps, 4 continuous
jumps, 36.6 m sprints (SP), a 137.2 m short shuttle run (SSR), and a 274.3 m long shuttle run
(LSR). A 3 week non-hypergravity training period (NHT) proceeded HT. Baseline SP improved
from 4.69 ± 0.29 s to 4.58 ± 0.22 s post-treatment, and regressed after NHT (4.69 ± 0.24 s) (p =
0.006, ES = 1.80). Improvements in SSR (p = 0.012, ES = 1.71) occurred from baseline (26.7 ± 1.5 s)
to post-treatment (26.2 ± 1.4 s), followed by a return to near-baseline values (26.9 ± 1.8 s).
Jumping tasks displayed similar trends, but no statistical differences and modest effect sizes (0.51
- 0.62) were found except for improved ground contact time during repeated jumps post-HT (ES
= 2.26). PC and LSR performances did not improve. Three weeks of HT significantly enhanced
short running task performances and decreased ground contact time between 4 continuous
jumps. HT may be incorporated into training programs prior to key points in an athletic season
without hindering the quality of regular training session activities.
KEY WORDS: External load, load carriage, sprint, weighted vest, ground contact
time
INTRODUCTION
Hypergravity training (HT) consists of
wearing a weighted vest (WV) during daily
activities for a 3 - 4 week period. Bosco and
colleagues (3,4,5) proposed HT in addition
to wearing a WV during training could
result in anaerobic performance increases in
well-trained athletes through neural and
myogenic adaptations such as the number
and/or frequency of muscle fiber motor
unit activation and improved ATP
resynthesis. The investigators’ theory was
supported in their seminal study (5), as HT
coupled with wearing a WV during
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training improved explosive jumping
power characteristics in a small group (n =
6) of internationally competitive jumpers
and throwers. The HT period lasted 3
weeks and improved single vertical jump
(VJ) height, drop jump height, and mean
power output during a set of 5 continuous
jumps; while no change in performance
was exhibited for these tasks in a control
group (n = 5). Further strengthening the
effect of HT was noted as 4 weeks of
removal of the WV resulted in a return to
baseline performance for the treatment
group.
Bosco and colleagues completed two other
comparable HT studies in the early 1980’s
(3,4) and found similar results concerning
power improvement with small samples of
elite male and female national level
athletes. Only two additional
investigations have been published since.
Sands et al. (18) found similar improvement
trends in jumping tasks when 3 weeks of
HT was incorporated into a training
program for collegiate female track athletes.
A recently published study (2) found that
shorter HT intervention (8 days) did not
improve sprint performance but reduced
ground contact time during sprinting in
elite rugby players.
Wearing a WV during training is a popular
trend among individuals seeking
performance improvements, but the
efficacy of this practice remains somewhat
in question (15). In contrast, nearly all
studies to our knowledge that have
examined HT in trained populations (3, 4, 5,
17, 18) have found positive results
concerning anaerobic performance tasks.
However, the populations examined
(predominantly elite level athletes) and
performance tasks (mostly jumping task)
used in previous HT investigations have
been limited in scope and have often
incorporated a between subjects design
with small sample sizes. The effects of HT
are also somewhat unclear as every
published study has included wearing a
WV during both daily living and training
activities. Proper periodization allows
athletes to peak in performance during the
most important part of the competitive
season, and the addition of HT during daily
living activities only may optimize
competition performance without
interfering with the quality of individual
workouts. Therefore, the purpose of this
study was to determine the effects of a ~21
day HT protocol on multiple types of
anaerobic task performances in well-trained
young men.
METHODS
Participants
Investigators recruited highly active male
fitness athletes (n = 9) with a minimum of
12 months experience (4 sessions per week)
from local CrossFit gyms. All participants
competed in fitness competitions at levels
ranging from local to regional. Eleven
participants were initially recruited, but
two were unable to complete all testing
sessions due to injury unrelated to the
study or schedule conflicts. A priori power
analysis determined that a sample size of 8
would be needed if the change in
percentage of performance between
treatments was 3 ± 1.5%, with an alpha of
0.05 and power set at 0.80. Prior to data
collection, participants completed and
signed a written informed consent form
that outlined the requirements and risks of
the study. Age (21 ± 2 years), mass (91.1 ±
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4.4 kg) and height (181 ± 1 cm) were
recorded prior to testing. Height and mass
were measured using a digital scale (Tanita
EWB-800, Tokyo, Japan) and a standard
stadiometer respectively. Body fat
percentage (11.2 ± 3.9 %) was estimated
using Lange skinfold calipers (Cambridge,
MD, USA) and a 3-site method (men: chest,
abdomen, thigh) (16). All procedures were
approved by the local Human Subjects
Committee.
Protocol
Following anthropometric data collection,
all participants completed the first of two
familiarization session (protocol described
below). During the first familiarization trial
participants were instructed on how to
complete each performance tasks and then
allowed to practice the tasks as many times
as desired. Approximately one week later,
participants returned to complete a second
and final familiarization session. During
this session, the order of performance tests
and rest periods were identical to that used
during the experimental trials.
A week later, participants completed a pre-
experimental baseline test for the HT
intervention. Three weeks after HT
intervention, a post-HT trial was
completed. This trial also served as the
baseline performance testing for the three
week non-hypergravity training period
(NHT). During NHT participants
continued training as normal, but did not
wear a WV during daily living. Participants
were restricted from alcohol, excessive
caffeine consumption, and working out the
day before testing. Participants were not
allowed to complete exhausting workouts 2
days prior to testing. Differences in exercise
regimens were not accounted for, but
activity logs were implemented and
assessed to assure that drastic differences in
training type or volume did not occur
between treatments. Although participants
were recruited from multiple gyms, most
participants often completed the same
standardized workout of the day provided
by the CrossFit headquarters’ website.
Tests were divided into two phases. The
current manuscript reports the first half of
the tasks that were conducted without a
WV. The second sets of tasks were designed
to simulate tactical athlete specific tests (e.g.
stair climbing and casualty drag) and were
conducted while wearing a WV (Lowe et al.
In review). These tasks were performed last
and did not interfere with the tasks
discussed in the current manuscript.
Participants performed a 10 min self-
selected warm up prior to completing a
power clean 1-RM protocol. All participants
were familiar with the lift and were given 3
attempts to find their 1-RM. It was
assumed that the two familiarization
sessions would allow for an accurate
estimation of 1-RM during the baseline
session.
The next tests included two types of vertical
jumping tasks. The first was a standard
counter-movement jump test. Participants
completed a set of 3 single
countermovement jumps (CMJ1) with 60 s
rest between reps. Results were analyzed
based on cumulative average of all jumps.
The second vertical jump test consisted of 2
sets of 4 continuous jumps (CMJ4). The
CMJ4 sets were separated by 60 s rest
periods, and the average jump height and
ground contact time between jumps were
used for statistical analyses. A contact time
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mat (Just Jump, Probotics, Huntsville, AL)
was used to determine maximal jump
height during the CMJ1, and to report the
average jump height and contact time
between jumps for the CMJ4 test.
Following jump performance testing and a
4 min rest period, 3 sprints (SP) were
conducted on a rubber-padded concrete
gym floor. Participants started from a 2-
point stance and time was recorded from
4.57 - 41.15 m (5 – 45 yd) to reduce start
mechanics variability. Photogate timing
devices (Brower Timing Systems, Draper,
UT, USA) accurate to the nearest hundredth
of a second were used. After sprint testing,
participants completed 2 shuttle runs. The
first was 6 x 22.86 m (SSR) and the second
was 12 × 22.86 m (LSR). Both were
completed with all participants running
simultaneously in a competitive fashion
and were timed individually by assigned
investigators using stopwatches. A three
and a half minute rest period separated
each different task including rest time
between shuttle running bouts. Procedures
for all subsequent tests were performed in
identical fashion. Performance tests were
chosen to include high intensity tasks of
multiple durations ranging from single
maximal efforts (PC & CMJ1) to repeated
efforts lasting ~ 3-6 s (CMJ4 & SP), 25-30 s
(SSR), and 60 s (LSR).
Each participant was fitted with a WV (ZFO
Sports, San Jose, CA, USA) that was worn 4
or more days per week and for ≥8 h a day
on the days the vest was worn. To reach the
≥8 hour requirement, participants could
wear the WV in periods broken up
throughout the day, or for ≥8 hours
continuously. Participant’s weight vests
were loaded according to a predetermined
percentage of the individual’s body mass.
The mean initial load was 11.2 ± 0.6 % of
the participant’s body mass for the first
week. The load was increased to 13.2 ± 0.7%
the second week, and to 16.1 ± 0.4 % for the
third week. The HT phase lasted ~21 days
followed by 21 days of NHT. Each day the
WV was worn, participants reported the
hours worn, physical activities performed,
and discomforts from wearing the vest in a
daily activity log. Investigators
communicated with each athlete daily via
text message to ensure protocol compliance
and remind participants to record their
training activities.
Statistical Analysis
Changes in pre-post performance were
compared between HT and NHT phases for
each performance tasks using dependent
samples t-tests. All data are represented as
means and SD and displayed in absolute
values or ∆ pre-post percentage (∆% =
treatment - baseline / baseline). Cohen’s D
effect size data was also calculated by
dividing the raw difference of the change in
weight lifted, jump height, ground contact
time, or time to complete a running task
between treatments divided by pooled SD
of both training phases. One participant’s
data was excluded for PC because of a
minor wrist injury unrelated to the study,
and one participant’s CMJ4 data was
excluded because they had a difficult time
landing on the mat consistently resulting in
high inter-trial variability. Statistical
significance was considered when p ≤ 0.05.
RESULTS
All participants wore the WV for a
minimum of 32 h per week each week and
averaged 34 ± 4 h per week throughout the
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HT period. Participants trained heavily and
averaged very similar numbers of sessions
for resistance training (HT = 4.6 ± 1.2; NHT
= 4.4 ± 1.7 days per week), sprint and jump
training (HT = 0.9 ± 0.7; NHT = 0.7 ± 0.8
days per week), and endurance training
(HT = 1.8 ± 1.7; NHT = 1.3 ± 1.3 days per
week). Participants averaged completing
3.0 ± 1.0 and 2.5 ± 1.8 standardized
workouts per week during NHT and HT
respectively.
Raw data from baseline, post-HT, post-
NHT, and change in performance for each
treatment expressed in absolute values and
by percentage are displayed in Table 1.
Effect sizes for change in absolute values
for HT versus NHT are also displayed in
Table 1. Significant improvements in GCT,
SP, and SSR performance occurred after
the three week HT phase, followed by a
return to near baseline values after NHT
(Table 1). Figures 1 and 2 display
individual changes in performance for
mean SP and SSR across baseline, HT, and
NHT phases. Individual changes in mean
ground contact time during repetitive
jumping (CMJ4) from baseline, HT, and
NHT performance testing are displayed in
Figure 3.
Figure 1. Individual mean times for 3 sets of 36.6 m sprints
at baseline, HT, and NHT. Dashed lines represent
individuals that did not improve from baseline to HT.
Figure 2. Individual 137.2 m shuttle run times at baseline,
HT, and NHT. Dashed lines represent individuals that did
not improve from baseline to HT.
DISCUSSION
HT has been proposed as an
unconventional method to improve
anaerobic task performance. Prior
investigations have determined single and
multiple vertical jumping task performance
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Figure 3. Individual GCT during repetitive jumping
(CMJ4) at baseline, HT, and NHT. Dashed lines represent
individuals that did not improve from baseline to HT.
is vastly enhanced following HT coupled
with wearing a WV during training
sessions for collegiate and international
level sprinters and jumpers (3, 4, 5, 18), but
the only study assessing sprinting found a
single week of HT did not improve
performance (2). The current study was
unique in that it allowed for isolated
observation of HT without external loading
during training and provided additional
evaluation of changes in running task
performances after longer HT exposure in
well-trained but non-elite young men.
Most previous HT studies have noted
significant improvement in jumping task
ability with mean improvements in vertical
jump height reaching 10.6 cm after 3 weeks
of HT (3, 4, 5, 18). Despite modest
improvement in average peak jump height
for both CMJ1 and CMJ4 during HT phases
versus decreases in both tasks during NHT
(Table 1), no statistically significant
improvements were observed in jumping
height. However, ground contact time
between each jump during CMJ4 decreased
significantly after the HT period, and
returned to near baseline values after NHT.
The increased focus on jump training in the
populations previously studied possibly
explain why a lesser impact was noted in
our participants. Bosco (3) specifically
recruited participants who were competing
at the international level in track and field
and failed to increase jump height even
after a year of rigorous training with a large
emphasis devoted to jumping and
plyometric drills. Other HT study samples
included participants of similar skill level
and training protocols focused on
improving jump height and mechanics (5,
18). Although the participants in the
current study were highly fit and regularly
trained, their jump heights would not be
comparable to elite male sprinters or
jumpers and much of their jumping tasks
likely occurred under more of a
conditioning context than skill
improvement paradigm (e.g. large volumes
of repeated box jumps). Despite no
statistical improvement in CMJ1, the
significantly shorter CMJ4 ground contact
time and mean improvements of greater
than 2% for both CMJ1 and CMJ4 height
followed by a decline in performance after
cessation of HT support that the more
reasonable HT protocol incorporated in the
current study provided a sufficient
stimulus to induce physiological
adaptations and resulted in a practical real
world performance difference for many of
the athletes in regards to jumping
performance.
It must also be considered that with the
exception of Sands et al. (18), who stopped
using WV during training because of lower
leg injuries and Barr et al. (2), all other HT
and WV studies have required participants
to wear a WV during training. Data is
limited, but similar results supporting a
greater efficacy of WV training in elite
versus non-elite athletes are exhibited in
studies that have incorporated WV during
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training only. Professional basketball
players who wore WV during plyometric
training improved in multiple types of
jumping tasks versus controls, but studies
that have required wearing WV during
training only in recreationally trained
individuals have failed to show greater
improvement in jump performance versus
individuals who completed jump training
without an external load (14) or failed to
result in any improvements (20). More
research is needed, but results indicate such
training could benefit less elite athletes in
sports that require vertical jumping such as
basketball or volleyball.
Prior research has indicated a strong
correlation between power output
produced by male athletes during maximal
vertical jumping and Olympic lifting ability
(snatch, r = 0.93; clean and jerk, r = 0.90) in
experienced weightlifters (6). Supporting
this association, as with CMJ1 and CMJ4, no
statistical differences were noted in PC 1-
RM change between HT and NHT phases.
The consistency in means (Table 1) is
masked by high inter-individual variability
in performance. Four of the participants
had greater improvement during HT and 3
participants had greater performance
improvement during NHT. Although the
participants regularly incorporated
Olympic style lifting in their training (HT =
3.4 ± 0.9; NHT = 2.8 ± 1.3 days per week)
and displayed respectable 1-RMs, it is
plausible that the diversity of results is
attributable to less proficient technique
versus athletes who compete in Olympic
lifting or increments in which intensity was
increased (i.e. 2.28 kg after each successful
lift) was not sensitive enough to detect as
subtle performance improvement as noted
in other tasks. Past studies indicate that
highly skilled athletes near their maximum
potential at a particular task such as
jumping (3, 4, 5, 18) are more likely to
benefit from HT or wearing a weight vest
during the specific task during training
(11). Future HT studies with athletes who
compete in and have prolonged training
experience in Olympic lifting may find
different outcomes.
There is a popular anecdotal acceptance
that external load sprint training benefits
unloaded sprinting. Cronin et al. (9)
proposed that sprint training while wearing
a WV increases eccentric strength of the leg
extensor muscles and musculotendonous
stiffness, consequently improving the
acceleration phase of sprinting tasks;
however, we are unaware of any training
studies that support this concept. The
addition of external load during training
does not improve sprint and shuttle run
times compared to unresisted training
protocols, and running while wearing a WV
decreases step length, stride rate, and flight
time, while increasing ground contact time
at maximal velocity (8, 10, 19, 20). It is
plausible, that athletes may retain the
slower kinematic running pattern induced
by running with an external load over the
course of several weeks resulting in sprint
performance decrement (7).
While HT failed to yield statistically
significant increases in jumping task
performance, results indicate that HT was
an effective training aid for improving
sprint and shorter shuttle run performance.
Running performance displayed significant
improvement (P < 0.01) in both SP and SSR
during HT vs. NHT and produced large
effect sizes, but no significant changes were
noted in the LSR (Table 1). Figures 1 and 2
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display individual changes in percentage of
performance for SP and SSR, respectively.
All but 1 and 2 participants improved in SP
and SSR from baseline to HT, respectively.
Further strengthening this observation, all
individuals in SSR and all but 1 individual
in SP decreased in performance at the end
of NHT versus post-HT even though NHT
took place during weeks 3 through 6 weeks
resulting in 3 additional weeks of training
time.
Despite promising results in pilot tests and
reduced ground contact time, Barr et al. (2)
found no improvement in first 10 or last 10
m velocity during 40 m sprinting in elite
rugby players. The authors suggested the
short intervention period used and that the
rugby players’ pre-season high volume of
conditioning may have negated the
influence of HT. Lowe et al. (In review) (13)
reported immense changes (ES = 1.9 - 2.6)
in horizontal running tasks including a
short sprint that required participants to
change direction 3 times and kneel behind
objects of cover twice, backwards running
while dragging a 84.9 kg sled, and 182.9 m
shuttle run while wearing a 12 kg WV.
However, less dramatic improvement was
noted during stair ascension sprints by
Lowe et al. (In review) (13) (5 flight stair
climb: p = 0.03; ES = 1.05; split for first 3
flights: p = 0.13; ES = 0.68). The
discrepancies between improvements in
vertical vs. horizontal focused movement
tasks in both studies are intriguing.
In addition to negative alterations in
running kinematics, recent revelations have
determined that sprinting with a WV does
not result in increased vertical ground
reaction forces versus unweighted sprinting
due to the smaller rise in center of gravity
during sprinting flight phases conducted
while wearing a WV (8, 10). Perhaps, the
potential negative motor learning and
movement pattern residual effects that are
associated with WV sprint training are not
transferred during HT, but the
neuromuscular adaptations that have been
credited with the effectiveness of HT are
still incurred when the WV is worn during
daily living alone. The largest ES for any
measured variables was exhibited for
ground contact time during the CMJ4, but
total power (i.e. jump height) during both
jumping task did not differ to as great of an
extent as running performance improved in
SP and SSR. HT without wearing a WV
during training may have resulted in
decreased time for neural activation of
Type II muscle fibers but failed to increase
peak power output as significantly. This
theory may help explain why SP and SSR
improved but PC and jumping tasks did
not. Both running tasks required repetitive
ground contacts and/or change in
direction. Improvement in rate of muscular
recruitment could have resulted in multiple
steps in which foot-ground contact time
was decreased. Enhanced vertical vector
force production may require external
loaded jump training and explain why
Khlifa et al. (11) found significant
improvement for basketball players
completing plyometrics with WV, while
sprinting with a WV does not improve
sprinting (7, 19, 20). Regardless of the
mechanism, the immense improvements in
SP and SSR times in addition to findings by
Lowe et al. (unpublished data) (13) suggest
that HT may be a more effective training
aid in comparison to training while wearing
a WV for enhancement of sprint agility
tasks lasting 4 - 40 s.
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The major limitation of the current study
was that participants did not follow a
standardized training protocol and
nutritional factors such as diet and
supplements were not controlled.
Although physical activity was self-
selected, participants completed very
similar training routines during each
treatment phase and completed many of
the same CrossFit ‘workouts of the day’
which are standardized across gyms.
Additionally, direct evidence regarding
physiological mechanisms that resulted in
the enhancement of SP, SSR and ground
contact time during the CMJ4 is lacking.
Because of concerns for impairment during
space flight, the effects of extended
exposure to hypogravity have been
examined in depth. Chronic exposure to
microgravity or limb unloading results in
significant skeletal muscle atrophy (21) and
even greater decreases in maximal skeletal
muscle explosive power, particularly in the
lower limbs (1, 12). The effects of chronic
skeletal muscle loading has not been as
widely investigated and as with the current
investigation, most studies have focused
on performance outcomes versus
mechanistic explanations for alterations in
performance improvement. However, it
could be speculated through the
consistency of opposing outcomes within
hypogravity versus hypergravity studies
that HT results in reverse muscular and
neurological adaptation pathways from
reduced chronic skeletal muscle loading.
Future research is warranted to determine
if performance improvements from HT are
attributed to neurological, fiber typing, or
metabolic adaptations that have been
previously proposed (3, 4, 5). Additional
work needs to be completed to determine
optimal HT duration and loading schemes.
The application of HT appears to be an
effective training aid for the enhancement
of short distance sprinting and shuttle
running and decreases ground contact time
during repeated jumping. The addition of
external load during jumping activities
might be required if jump height
improvement is the primary training
objective. For optimal periodization,
athletes should consider incorporating HT
during the 3 weeks leading up to post-
season competition or key games as the
effects of HT are transient. Wearing the WV
for 32 h per week produced significant
improvements for the sample, but the
participant who accumulated the most
hours wearing the WV improved the most
in SP and SSR suggesting additional
exposure to HT may result in greater
change in performance. While HT was
successful in improving multiple anaerobic
performance tasks, physical discomfort was
experienced by several participants in the
erector spinae and trapezius muscles, and
on the shoulders at the points of contact
with the WV during HT. Almost all of the
reports of discomfort occurred during the
first days of wearing the vest and waned
within 2-3 days. This should be taken into
consideration and a progression beginning
with lighter loads and a “practice” HT
period should probably take place before
the competitive season commences.
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