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Kliszczewicz, B., Snarr, RL., and Esco, M.. Metabolic and cardiovascular response to the
CrossFit workout ‘Cindy’: A pilot study. J Sport Human Perf 2014;2(2):1-9.
DOI: 10.12922/jshp.0038.2014
1
METABOLIC AND CARDIOVASCULAR RESPONSE TO
THE CROSSFIT WORKOUT ‘CINDY’: A PILOT STUDY
Kliszczewicz, B.1, Snarr, RL.2, and Esco, M.2
1Kennesaw State University, Kennesaw, GA 30144
2Auburn University at Montgomery, Montgomery, AL 36117
Keywords: CrossFit, High-Intensity Exercise, VO2, HR, Heart Rate
ORIGINAL RESEARCH OPEN ACCESS
ABSTRACT
Metabolic and Cardiovascular Response to the CrossFit workout ’Cindy’. CrossFit is a
fast growing sport of fitness that not only serves as a form of competition but as a form of
general exercise training. Little is known about this conditioning program and a better
understanding of the metabolic and cardiovascular demands is needed. PURPOSE: It is the
purpose of this pilot study is to examine the acute metabolic and cardiovascular demands of a
named CrossFit workout using semi- to well-trained subjects in order to establish a proper
control exercise. METHODS: 7 men and 2 women (mean age = 27.2 ± 9.6) who have trained in
CrossFit for at least 3 months participated in the study. Each subject performed a graded exercise
test on a treadmill to determine maximal oxygen consumption (VO2max). All subjects performed
the named CrossFit workout called ‘Cindy’, which consisted of as many rounds possible of 5
pull-ups, 10 push-ups, and 15 air squats in 20-minutes. A portable metabolic analyzer was used
to record volume of oxygen consumption (VO2) and rate of caloric expenditure (kcals.min-1).
The subjects also wore a portable heart rate (HR) monitor. Means SD were determined for the
following variables: VO2, %VO2max, HR, %HRmax, kcals.min-1, METs and total kcals.
RESULTS: The results demonstrated that ‘CINDY’ resulted in average VO2 of 33.3 ± 5.5 ml.kg-
1.min-1, which corresponded to 63.8 ± 12.3 % VO2max. In addition, the workout elicited a heart
rate of 170.8 ± 13.5 beats.min-1. Furthermore, the subjects expended 13 ± 2.9 kcals.min-1,
corresponding with a total caloric expenditure 260.6 59.3 kcals. The average MET level was
9.5 ± 1.5. CONCLUSION: The findings of this study suggest that ‘Cindy’ could be classified as
“vigorous intensity” based on established American College of Sports Medicine HRmax
guidelines i.e., between 76 - 96 % of HRmax, while VO2max parameters where classified as
“moderate intensity” i.e., between 46 to 64% of VO2max. Further investigation is needed to
compare the metabolic response of other popular CrossFit workouts.
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INTRODUCTION
In recent years professional and
governmental organizations have begun
emphasizing the importance of physical
activity and its role in preventative medicine,
health improvement, and maintenance
(Garber et al. 2011). Physical activity has
been shown to improve overall facets of
health such as improved skeletal muscle
strength, cardio-respiratory function, and
metabolic control (Garber et al. 2011). As the
understanding of adaption to exercise
evolves, so too does the application. In this
regard, there has been an increased interest in
short duration, high-intensity exercise bouts,
specifically the exercise programing of
CrossFit. This relatively new application of
exercise, has gained a strong following within
the active community. Much of this growth
can be attributed to purported reports of rapid
weight loss and increased cardiovascular
capacity (Smith et al. 2013), while also
offering varying, time-efficient workouts.
The underlying philosophy of
CrossFit training is to prepare an athlete to
successfully perform both randomized and
diverse tasks (Glassman 2002). According to
CrossFit, in order to train across a wide
spectrum of physical fitness components
(e.g., strength, power, endurance) within one
exercise scheme, programming must
incorporate both resistance (e.g., deadlift,
power clean, snatch, etc.) and endurance (e.g.,
running, rowing, cycling, etc.) modalities
within a single bout (Glassman 2002;
Glassman 2007). In lieu of this programming
philosophy, workouts of the day (WODs)
constantly vary and are rarely duplicated.
However, there are a few WODs that are
‘named’ and revisited in order to track
progress. Furthermore, the primary objective
of a traditional WOD is to attempt to
complete the prescribed tasks as fast as
possible, creating a short duration and high-
intensity session.
To date, very little empirical evidence
exists regarding any physiological response to
CrossFit, chronic or acute. Therefore, it is the
purpose of this pilot study to examine the
acute cardiovascular and metabolic demands
during a bout of a named WOD in order to
determine an appropriate intensity for an
exercise control groups in future studies. To
undertake this study, markers of chronotropic
(i.e., HR, %HRmax) and metabolic (i.e., VO2,
%VO2max, kcal) responses were measured
during the named WOD ‘Cindy’.
METHODS
Participants
Nine semi- to well-trained apparently
healthy participants (7 male, 2 female) age
27.2 yrs (± 9.6), weight 75.8 kg (± 13.9),
height 173.7 cm (± 9.4) participated in this
study. The pre-requisite for experience in the
current investigation was a three-month
minimum of CrossFit participation. In order
to be classified as “well-trained” participants
must be able to complete each movement of
the named WOD ‘Cindy’ without assistance
and have completed a minimum of 14-rounds
for men and 10-rounds for women in a prior
attempt. Prior to data collection, a signed
informed consent was obtained from each
participant. All participants were of low risk
for cardiovascular, metabolic, and/or
pulmonary diseases as determined by PAR-Q
and Health History Questionnaire. No
participants reported any prescribed or over
the counter medication during the time of the
study. Subjects were instructed to abstain
from exercise 24-hours prior to each trial, and
alcohol 12-hours prior. This study was
approved by the Auburn University at
Montgomery institutional review board.
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Experimental Design
Each participant arrived at the
laboratory on two separate occasions for data
collection between the hours of 7am and
11am. On the first visit participants were
familiarized with protocols and performed a
graded exercise test to determine maximal
oxygen consumption (VO2max). Participants
were instructed to return between 3-7 days
later in order to perform the second trial, a
high-intensity, short duration exercise bout
named ‘Cindy’.
Graded Exercise Test
Maximal oxygen consumption
(VO2max) and maximal heart rate (HRmax)
were assessed during the first session through
a graded exercise test (GXT) on a treadmill
(Trackmaster, Newton, KS). Using Bruce
Protocol, the workload during the GXT was
increased incrementally every 3-minutes until
a maximal value was reached. Expired gas
(i.e., oxygen and carbon dioxide) fractions
were sampled continuously using a
pneumotach, mixing chamber, and gas
analyzers through a portable analyzer (k4b2,
COSMED USA, inc., Concord, CA). During
the test, heart rate was assessed continuously
using a heart rate monitor (Polar Electro Oy,
Oulu, Finland). Test termination required
achievement of two of the following criteria:
a plateau in VO2 (± 2 ml.kg-1.min-1) despite an
increase in workload; respiratory exchange
ratio (RER) of ≥ 1.15; heart beat within 10
beats of age predicted maximum (220 – age),
or volitional fatigue.
Exercise Bout Protocol
Prior to the trial participants were
equipped with a portable gas analyzer K4b2
and a polar HR monitor to determine average
volume of oxygen consumed (VO2avg), heart
rate (HRavg), total energy expenditure
(EEtotal), and rate of caloric expenditure
(kcals.min-1). Once acclimated to the
equipment, participants began a 5-minute
warm up on the treadmill at a self-selected
intensity followed by a 1-minute rest.
Following the rest period participants began
the exercise bout. The CrossFit named
workout "Cindy” consists of as many rounds
possible of 5 pull-ups, 10 push-ups, and 15 air
squats in 20-minutes. The workout required
that the individual complete all prescribed
repetitions for the movement before moving
on to the next exercise and to do so as fast as
possible. For example, all 5 pull-ups must be
completed before moving on to the 10 push-
ups. Each movement was standardized to
ensure consistency between all participants.
Pull-up form standards required the
participant to start with arms fully extended,
pull their chin just above the bar, and then
return to the starting position and could be
accomplished through strict, kipping, or
butterfly variation. To perform the push-up,
participants started in a plank position with
the arms fully extended with the hands on the
ground directly beneath the shoulders.
Subjects then lowered the body until the chest
came in contact with the ground, then
returned to the starting position. Air-squat
standards required participants to perform a
traditional bodyweight squat until the hips
passed the knee, then returned to starting
position. Failure to achieve these standards
resulted in a repeat of the repetition of that
movement until successfully performed.
Statistical Analysis
Data was analyzed using SPSS/PASW
Statistics version 18.0 (Somers, NY). Mean
and standard deviations (SD) were calculated
for each of the following resting variables:
age (yr), height (cm), weight (kg). Mean and
standard deviations (SD) were calculated for
the following testing variables: HRmax (bpm),
%HRmax, HRave (bpm), VO2max (ml.kg-1.min-1),
%VO2max, VO2ave (ml.kg-1.min-1), EEtotal
(kcals), EEave (kcals.min-1), and average
metabolic equivalent (MET).
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RESULTS
All participants completed both
graded exercise testing and CrossFit bout
protocol. Mean anthropomorphic values and
maximal HR and VO2 obtained during the
first visit can be seen in Table 1. The average
rounds completed during the CrossFit trial
were 17.8 ± 3.7 rounds.
The VO2avg was 33.5 ± 5.5 ml.kg-
1.min-1 throughout the bouts, corresponding to
63.8 ± 12.3 % of the participants VO2max. As
expected, HR rapidly increased and was
sustained at an average of 170.8 ± 13.5
beats.min-1 throughout the trial. This sustained
HRavg corresponded to 91 4.2% of the mean
HRmax. The average EEtotal of the 20-minute
bout was 260.6 ± 59.3 kcals. The average rate
of energy expenditure throughout ‘Cindy’
was 13 ± 2.9 kcals.min-1. When factoring
body mass into energy expenditure over the
20-minute bout, the average value was 3.4 ±
0.48 kcal/kg. The average metabolic
equivalent sustained throughout the bout was
9.5 ± 1.5 METs.
Table 1. Participant Characteristics
Characteristic
Values ± SD
Age (yrs)
27.2 ± 9.6
Height (cm)
173.7 ± 9.4
Weight (kg)
75.8 ± 13.9
VO2max (ml∙kg-1∙min-1)
58.87 ± 6.8
HRmax (bpm)
186 ± 11
DISCUSSION
The purpose of this study was to
examine cardiovascular and metabolic
demands during an acute bout of the CrossFit
named workout, ‘Cindy’. The key findings
demonstrated that cardiovascular response
(HRavg) was greater than the metabolic
response (VO2avg) as represented by the %
maximal values. In terms of exercise
intensity, HRavg was elevated enough to be
categorized as vigorous intensity; while
VO2avg was only considered moderate (Garber
et al. 2011). Caloric expenditure was
relatively high, while the metabolic
equivalent was approximately three times
greater then that at rest.
Markers of Chronotropic and Metabolic
Response
While not measured directly in this
investigation, increased heart rate (HR) at the
onset of exercise is primarily caused by
parasympathetic withdrawal and followed by
sympathetic activation (Borresen & Lambert
2008). The magnitude of this HR response is
in accordance to oxygen demand of the
working tissue (Rowell 1974). In order to
meet the increase oxygen demands, the heart
must increase the rate of circulation. The
distribution of blood can increase up to five
times greater than resting values during a
maximal bout of exercise (e.g., 5L/min to
25L/min) (strand and Rodahl 1970).
Therefore, in order to meet the increasing
metabolic demands during exercise, a linear
increase of HR occurs with increasing
intensity.
Interestingly, the HR response of this
current study increased to 91% of mean
HRmax, which meets the American College of
Sports Medicine (ACSM) criteria for
vigorous exercising heart rate (76 -<96
%HRmax), while the oxygen consumption was
63.8 %VO2max, which falls under the criteria
of moderate activity (46 - ≤64 %VO2max)
(Garber et al. 2011). Although the observed
differences between intensity markers HR and
VO2 were unexpected, they are in agreement
with previous studies that portrayed this
similar effect (Burleson et al. 1998; A G
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Monteiro 2008; S. Beckham and Earnest
2000; Lagally et al. 2009).
Linear relationships are often seen
between exercising heart rate and VO2 during
an increase in workload. However, engaging
in a high-intensity exercise bout can result in
a rapid rise in HR, while VO2 levels struggle
to produce the same response (A G Monteiro
2008; Burleson et al. 1998; Lagally et al.
2009; S. Beckham and Earnest 2000). A
potential explanation for this is a greater
dependence on HR with increasing exercise
intensity to maintain cardiac output. As
exercise intensity increases beyond 40% of
VO2max, HR becomes the primary factor of
increased cardiac output (Rowell 1974). With
this rise in heart rate, the venous network is
unable to effectively return blood to the heart;
thereby, creating a plateau in stroke volume
(Allen, Byrd, and Smith 1976; Hurley et al.
1984). An additional explanation for the
discrepancy observed between HR and VO2 is
the continuous postural changes that occur
throughout the bout. Alterations in posture
and redistribution of blood to active muscle
groups likely present a challenge to
hemodynamics and consequently increase the
catecholamine response, which will lead to an
elevated HR (Borst et al. 1982).
While the current investigation only
elicited a moderate %VO2max, a previous
study on HIIT, performed by Tabata et al.,
1996, demonstrated conflicting results.
Subjects performed a workout with seven to
eight sets of cycling with a work-to-rest ratio
of 20 seconds on and 10 seconds rest (2:1).
Results showed linear responses of HR and
VO2, in which some subjects reached peaks
matching VO2max (vigorous intensity) during
the exercise bout (Tabata et al. 1996). These
conflicting results may perhaps be explained
by the differences in the exercise bouts
themselves. The current study used a
continuous high-intensity session with no
scheduled rest times, which may have
affected the cardiovascular and metabolic
responses. In addition, the modes of training
were different, as the previous study used a
strictly lower body workout; the bout of
‘Cindy’ combined upper and lower body
musculature. Likely differences in skeletal
muscle recruitment and metabolic responses
may have altered cardiovascular response due
to a phenomenon known as the exercise
pressor reflex. Generally, active or
contracting skeletal muscle influence
cardiovascular activity through alterations of
blood pressure, muscle afferents, and or
exercise metabolites, which subsequently
increase HR (Mitchell et al. 1983). The
exercise pressor reflex is believed to be a
possible explanation for elevated HR and a
lower oxygen consumption during low-
resistance exercise (Collins et al. 1991).
Dynamic low-resistance weight lifting and
upper body exercise cause a greater
recruitment of fast-twitch muscle fibers,
which results in a greater exercise pressor
reflex (Collins et al. 1991). Therefore, the
discrepancy between the Tabata et al. study
and the current findings may be in part due to
the pressor reflex.
A study performed by Lagally et al.,
2009, provided similar results to the current
study and supports the claims of Collins et al.,
1991. Participants underwent a 28.5-minute
continuous functional exercise workout
during which HR and VO2 were measured.
The exercise bout consisted of both upper and
lower body compound exercises. Thus,
increasing the amount of skeletal muscle
utilized during the session, as well as,
alternating between varying muscle groups,
which is similar to the current investigation.
The 28.5-minute workout elicited a vigorous
intensity exercising HR (i.e., 82.7 %HRmax)
and a moderate intensity %VO2max (i.e., 51.1),
which closely relates to the findings of the
current study.
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Markers of Energy Expenditure
In addition to an elevated HR and
moderate VO2, results also indicated a mean
MET level of 9.5 ± 1.6, which can be
categorized as vigorous intensity (Garber et
al. 2011). While typical high-intensity
resistance training or weight lifting elicits a
MET level of 6, the results of this study are
more consistent with HIIT, as well as
traditional aerobic modes of exercise.
Examples of these include vigorous intensity
calisthenics (8 MET’s), circuit resistance
training (8 MET’s), stair-treadmill ergometer
(9 MET’s), stationary cycling at 200 watts
(10.5 MET’s), running at 5.2-6 mph (9-10
MET’s), and competitive sports (8-12
MET’s), such as soccer and basketball
(Ainsworth et al. 2000).
In terms of energy expenditure
(EEtotal), participants elicited a mean of 260.6
± 59.3 kcals, which equated to 13 ± 2.9
kcals.min-1. While the length of time for the
current study was 20-minutes, Stanforth et al.,
2000, had participants complete a 50-minute
continuous circuit weight training exercise
session, incorporating both the upper and
lower body. Although the former study
utilized external resistance (i.e., free weights),
EEtotal was comparable to the current study
(i.e., 265 kcals compared to 260.6 kcals for
the current study). Thus, demonstrating that
the ‘Cindy’ bout may provide a greater
caloric expenditure versus an external
resistance program of greater session
duration. This may in part be due to the
differences in overall HR intensity of the
bouts. The current study resulted in a %HRmax
of approximately 91%, while the Stanforth et
al. study yielded only a 63%HRmax. While the
current study provides a caloric expenditure
response greater than multiple studies
examining traditional circuit weight training
(S. G. Beckham and Earnest 2000; Wilmore
et al. 1978; Bloomer 2005); it is also not the
only high-intensity, continual exercise study
to demonstrate this (Farrar, Mayhew, and
Koch 2010).
LIMIATIONS
Due to the nature of this pilot study
there are limitations that must be addressed.
The sample size of the current study can be
considered a limitation with only 9 subjects
(7-male, 2-female). Because “Cindy” is a
rigorous workout for females, it is difficult to
recruit enough subjects who were physically
capable of enduring the rigors of the 20-min
workout involving pull-ups and push-ups.
Furthermore, the goal of this pilot study was
to determine the average oxygen consumption
and HR response of the CrossFit workout
“Cindy”, and not to compare within or
outside the population, in that this was a
descriptive study.
CONCLUSION
CrossFit is a relatively new and
popular form of high-intensity exercise
training. To date, little empirical evidence
regarding metabolic or cardiovascular
responses during an acute bout of CrossFit
exists. Understanding the aforementioned
physiological responses to a bout of exercise
becomes important when considering the
application and prescription of exercise. In
this regard, the metabolic and cardiovascular
responses observed during the single bout
were of adequate duration and intensity to be
classified as moderate cardiorespiratory
training, according to ACSM guidelines
(Garber et al. 2011). The exercise bout was
also sufficient in expending an increased
amount of energy (i.e., kcals/min) for the
short duration of the workout.
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In summary, the examined CrossFit
workout ‘Cindy’ provides a moderate
stimulus to cardiovascular training, while
increasing HR to a vigorous high.
Furthermore, ‘Cindy’ provides a high rate of
caloric expenditure during a relatively short
duration bout. These findings provide
information necessary for creating an exercise
intensity based control bout for studies
examining a CrossFit workout of this type.
Further investigation is needed to examine the
anaerobic properties of CrossFit (i.e., Lactate)
as well as catecholamine responses in order to
better understand the physiological response
to this type of training. In addition, due to the
complex make up of CrossFit and its
programming, a deeper investigation is
needed to examine the different modalities
within a CrossFit WOD (i.e., Olympic lifting,
gymnastic movements, etc.).
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