Nine apparently healthy females participated in a study examining the effects of 16 weeks of high-intensity functional training (HIFT) on markers of resting vagal tone. Participants underwent heart rate variability (HRV) testing before and after the 16-week intervention. HRV was analyzed in the time domain of root mean square of successive differences (RMSSD) and high frequency (HF) power. There were no significant differences found between pre and post intervention for lnRMSSD or lnHF, indicating that 16 weeks of HIFT did not significantly impact markers of resting vagal tone in this group of females.

1. E. Bechke, H. Mimms, W. Hoffstetter, P. Serafini, M. Smith,
Y. Feito Ph.D., FACSM, B. Kliszczewicz, Ph.D.
Kennesaw State University, Department of Exercise Science & Sport Management
RESTING VAGAL TONE FOLLOWING A 16-WEEK HIGH-INTENSITY
FUNCTIONAL TRAINING INTERVENTION
Nine apparently healthy females with at least three-weeks of CF training
experience were recruited from local CrossFit® affiliates near the Atlanta
Metropolitan area.
Protocol
 Prior to and following intervention, participants attended the Exercise
Physiology Laboratory at Kennesaw State University.
 Prior to each laboratory visit, participants were asked to avoid eating or
consuming any beverage other than water four-hours before testing.
Participants were also asked to avoid caffeine and alcohol for 12-hours
and 24-hours prior, respectively.
 Additionally, participants were asked to abstain from exercise 12-hours
before their laboratory visit.
 Descriptive data including age, sex, height (cm), and weight (kg) was
recorded before and after the 16-week intervention. Body composition
(BF%) was also analyzed using Dual-energy X-ray Absorptiometry
(DXA, iLunar; General Electric, CT).
 Training included participation in HIFT workouts with a focus on general
physical preparedness (GPP) a minimum of twice a week for 16-weeks.
HRV Analysis
 Participants underwent ten-minutes of non-stimulated rest in the supine
position to obtain beat-to-beat recording using a polar monitor strap and
Polar Team2 software (Lake Success, NY).
 Beat-to-beat recordings were transformed into a tachogram and analyzed
using online Kubios software (Version 2.2).
 The last five-minute segments of each ten-minute recording were
analyzed in the time domain of the Root Mean Square of Successive
Differences (RMSSD) and High-Frequency (HF) of the power spectrum
density.
 All recordings were visually inspected for multiple premature ventricular
complexes (PVC), any recording displaying three or more PVC’s were
discarded from the study.
Statistics
 A Shaprio-Wilks test was used to determine normality.
 A natural log (ln) transformation was used prior to statistical analysis due
to a violation of normality.
 A paired sample t-test was used to compare pre and post HRV measures.
 Alpha (α) was set at 0.05 and data is presented as means and standard
deviations (M ± SD).
METHODS
ABSTRACT
High-Intensity Functional Training (HIFT) has become popular among the
general fitness community over the last several years. A commonly known
form of HIFT is CrossFit® (CF) training, which can be described as a
functional training program of high-intensity and mixed modality. Although
popularity has increased, little empirical evidence exists in regards to the
autonomic nervous system’s (ANS) adaptation to HIFT. PURPOSE: The
purpose of this study was to examine alterations in resting vagal tone through
the measurement of heart rate variability (HRV) over a 16-week CF training
program. METHODS: Nine apparently healthy females (35.8 ± 9.25 years
old) participated in this study. On two separate occasions, pre and post 16-
weeks, participants attended the Exercise Physiology Laboratory at Kennesaw
State University in order to obtain a 10-minute resting HRV recording using
Polar Team2 monitors (Lake Success, NY). In order to quantify HRV, the last
five-minute segments of each 10-minute recording were analyzed using online
Kubios software (Version 2.2). The markers used to quantify HRV were the
time domain of the Root Mean Square of Successive Differences (RMSSD)
and the High-Frequency (HF) of the power spectrum density. RESULTS:
Data underwent a natural log transformation due to a violation of normality
and expressed as lnRMSSD and lnHF. Paired sample t-test showed no
significant differences between pre and post lnRMSSD (Pre: 3.69 ± 0.56 ms2,
Post: 3.78 ± 0.45 ms2; p = 0.501) and lnHF (Pre: 3.86 ± 0.41 ms2, Post: 3.91 ±
0.43 ms2; p = 0.760). CONCLUSION: 16-weeks of HIFT was not sufficient
enough to significantly influence markers of resting vagal tone.
INTRODUCTION
 High-Intensity Functional Training (HIFT) is an exercise method that
employs multiple energy pathways through resistance based aerobic
conditioning in relatively short duration bouts (1). Perhaps the most well
known form of HIFT is CrossFit® (CF) training, which is frequently
described as a functional training program of high-intensity and mixed
modality. The increasing prevalence of this type of programing raises
questions surrounding general physiological adaptations.
 A key system that adapts to exercise training is the autonomic nervous
system (ANS). The ANS function is believed to be directly related to
homeostatic control and recovery, predominantly through the
parasympathetic branch (vagal tone) (2). Cardiac autonomic control can be
non-invasively measured through the analysis of cardiac control (i.e., heart
rate variability). Heart rate variability (HRV) is the measurement and
analysis of the timing between consecutive beat-to-beat intervals (3). To
date, little empirical evidence exists regarding the ANS’s response to
HIFT.
 We believe that by measuring HRV prior to and following a 16-week
intervention, the effect of HIFT on vagal activity can be inferred.
Presented at the 63rd American College of Sports Medicine Annual Meeting
2 June 2016 – Boston, Massachusetts
RESULTS
 No recordings were discarded due to abnormalities.
 Participant characteristics can be seen in Table 1.
 Paired sample t-test showed no significant differences between pre and post
lnRMSSD and lnHF.
 lnRMSSD pre and post data is presented in Figure 1.
 lnHF pre and post data is presented in Figure 2.
 Based on our findings, participation in 16-weeks of HIFT was not sufficient
to significantly alter markers of vagal tone (lnRMSSD and lnHF) among this
group of females.
 Further investigation employing a larger sample size and supplemental time
points is encouraged.
CONCLUSIONS
PURPOSE
The purpose of this study was to examine alterations in resting vagal
tone through the measurement of heart rate variability (HRV) prior to
and following a 16-week HIFT program.
2.5
3
3.5
4
4.5
PRE POST
lnRMSSD
(ms)
2.5
3
3.5
4
4.5
PRE POST
lnHF
(ms2)
Figure 2
Figure 1
Intervention N Age
Height
(cm)
Weight
(kg)
BF%
PRE 9 35.8 ± 9.25 161.8 ± 9.27 61.1 ± 10.96 25.8 ± 5.51
POST 9 - - 59.9 ± 9.61 22.9 ± 4.64
Table 1
REFERENCES
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Adherence, and Intentions: An Intervention Study. BMC Public Health, 14(789).
2. Stanley, J, Peake, JM, and Buchheit, M. Cardiac parasympathetic reactivation following exercise: implications for training
prescription. Sports Med Auckl NZ 43: 1259-1277, 2013.
3. Malik, M. Heart Rate Variability Standards of Measurement, Physiological Interpretation, and Clinical Use. Circulation 93: 1043-
1065, 1996.