Journal of Strength and Conditioning Research Publish Ahead of Print DOI: 10.1519/JSC.0000000000002279
D
Cardiac Autonomic and Blood Pressure Responses to an Acute Bout of Kettlebell Exercise
Alexei Wong1 –– Michael Nordvall1––Michelle Walters-Edwards1 –– Kevin Lastova1––
1
C EP
TE
Gwendolyn Francavillo1 –– Liane Summerfield1–– Marcos Sanchez- Gonzalez2
Department of Health and Human Performance, Marymount University, 2807 North Glebe
Road, Arlington, Virginia 22207, USA 2
Division of Clinical & Translational Research Larkin Community Hospital, 7000 SW 62nd Ave,
C
South Miami, FL 33143
A
Corresponding Author: Alexei Wong, PhD, Department of Health and Human Performance, Marymount University, 2807 North Glebe Road, Arlington, Virginia 22207. Telephone: 703-522-5600; E-mail: [email protected]
Running title: Autonomic and Blood Pressure responses to Kettlebell exercise
Copyright ª 2017 National Strength and Conditioning Association
1
Abstract: Kettlebell (KB) training has become an extremely popular exercise program for improving both muscle strength and aerobic fitness. However, the cardiac autonomic modulation and blood pressure (BP) responses induced by an acute KB exercise session are currently unknown. Understanding the impact of this exercise modality on the post-exercise autonomic modulation and BP would facilitate appropriate exercise prescription in susceptible populations. The present study evaluated the effects of an acute session of KB exercise on heart rate variability (HRV) and BP responses in healthy individuals. Seventeen (M=10, F=7) healthy subjects completed either a KB or non-exercise control trial in randomized order. HRV and BP measurements were collected at baseline, 3, 10 and 30 min after each trial. There were significant increases (P < 0.01) in heart rate, markers of sympathetic activity (nLF) and sympathovagal balance (nLF/nHF) for 30 min after the trial KB trial, while no changes from baseline were observed after the control trial. There were also significant decreases (P < 0.01) in markers of vagal tone (RMMSD, nHF) for 30 min as well as (P < 0.01) systolic BP and diastolic BP at 10 and 30 min after the trial KB trial while no changes from baseline were observed after the control trial. Our findings indicate that KB exercise increases sympathovagal balance for 30 min post-intervention which is concurrent with an important hypotensive effect. Further research is warranted to evaluate the potential clinical application of KB training in populations that might benefit from post-exercise hypotension, such as hypertensives.
21
Keywords: heart rate variability; high intensity interval training; post-exercise hypotension
22
C EP
TE
D
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
INTRODUCTION
24
Hypertension (HTN), characterized by increased blood pressure (BP), is a major risk factor for
25
cardiovascular disease (CVD) and end-organ damage (8). Autonomic dysfunction is recognized
26
as a primary pathophysiological mechanisms of HTN since it is related to both the development
27
and the complications of this condition (28). Heart rate variability (HRV) is acknowledged as a
28
A
C
23
29
parasympathetic (sympathovagal) balance (39). HRV is used in many research applications,
30
including the study of autonomic control during physical activity (16) and after (recovery phase)
31
acute exercise (16). The HRV and BP responses post-exercise appear to be related to the
32
intensity of the performed exercise, particularly in the first minutes of recovery (16,32).
measure of cardiac autonomic regulation, especially as a surrogate of the sympathetic–
Copyright ª 2017 National Strength and Conditioning Association
Moreover, a prolonged sympathetic predominance and concominant slow parasympathetic
34
reactivation contribute to a delayed BP recovery following exercise, which is thought to be
35
associated with increased risk of acute cardiac events (27,30). Therefore, understanding the
36
impact of various exercise modalities on autonomic regulation and BP would provide further
37
insight into the post-exercise relationship between these variables and may help in the
38
development of strategies to decrease exercise-related cardiovascular risk.
The kettlebell (KB), a cannonball shaped iron hand weight with a handle, dates back to
TE
39
D
33
the early 18th century in Russia where it gained popularity as an exercise implement (42). In the
41
last few years, resurgence in KB use has been due primarily to programs like CrossFit and Pavel
42
Tsatsouline’s workshops, where it is utilized as a training modality for improving both muscle
43
strength and aerobic fitness, thereby providing an alternative to established methods of exercise
44
(13). Owing to the design of the KB, its high-speed, ballistic and eccentric nature make it an
45
excellent form of exercise for loading of the hip extensor and posterior chain muscles (13,42).
46
The two hand-KB swing, a primary movement in KB training, is performed rhythmically
47
incorporating an explosive hip extension during the concentric phase, followed by dynamic hip
48
flexion during the eccentric phase of the swing (13,42). KB swings are usually used as a form of
49
high-intensity interval training, utilizing alternating bouts of exercise followed by short rest
50
periods (13). Despite the popularity of this form of exercise, research regarding the acute
52
A
C
C EP
40
53
hormone), which remain elevated for at least 15 min post-exercise (5). Additionally, Farrar et al.
54
(14) observed that KB swings caused a greater increase in oxygen consumption (VO2max) and HR
55
compared to traditional power or resistance exercise. While an increased VO2max and HR
51
cardiovascular responses to a KB swing routine is limited. It has been previously demonstrated that an acute session of KB swings causes elevations in heart rate (HR) and cortisol (a stress
Copyright ª 2017 National Strength and Conditioning Association
56
resulting from KB training are less than those induced by aerobic exercise (22), KB swings
57
present a metabolic challenge that may elicit unique cardiac autonomic and BP responses.
58
Therefore, the aim of the present study was to investigate the effects of a KB exercise session on
59
post-exercise cardiac autonomic function and BP responses.
D
60
METHODS
62
Experimental Approach to the Problem
63
Anthropometrics, health history and a familiarization session with the study tests, procedures and
64
the correct technique for the 2 hand-KB swing exercise were learned during an initial
65
familiarization visit. Using a crossover design, subjects were tested in the postprandial (≥4
66
hours) condition on two separate additional visits separated by at least 48 hours. Measurements
67
were performed during afternoon hours in a quiet, temperature-controlled room (23 ± 1 °C) and
68
at the same time of the day (± 2 h) to minimize potential diurnal variations in cardiac and
69
vascular reactivity. Subjects abstained from caffeine and alcohol consumption for at least 12
70
hours and avoided intense exercise 48 hours prior to testing. After HRV and BP instrumentation,
71
subjects rested in the supine position for at least 10 min before a 5 min baseline period.
72
Thereafter, subjects completed either the KB or the no-exercise control (CON) trial in a
73
randomized order. Immediately after the trials, subjects resumed the supine position for 30 min
75
C EP
C
A
74
TE
61
of recovery. Post-trial measurements of BP and HRV were collected between 3–6 min (Post-3), 10-13 min (Post- 10) and 30–33 min (Post-30).
76 77 78
Copyright ª 2017 National Strength and Conditioning Association
79
Subjects
81
A total of 17 (M=10, F=7) healthy (age=23 ± 1 years, height=1.71 ± 0.02m and weight=74.1 ±
82
4.9 kg) subjects between the ages of 18 and 27 years were recruited. Subjects were nonsmokers,
83
normotensive, free of cardiovascular and metabolic/endocrine diseases as evaluated by health
84
history, without musculoskeletal concerns that would limit exercise participation and were not
85
taking medication or nutritional supplements at the time of the study. All subjects reported being
86
active through individualized cardiovascular, strength and flexibility exercise programs
87
performed 2–4 times per week for at least 1 year prior to the study. However, subjects had
88
minimal experience with KB exercise. Female subjects were tested in the early follicular phase
89
of the menstrual cycle to avoid possible influence of endogenous estrogens on autonomic
90
function. All subjects were aware of the experimental procedures as approved by the institutional
91
review board and gave written consent before data collection.
C EP
TE
D
80
92
Procedures
94
Trials
95
During the KB trial, subjects completed 12 consecutive rounds of the 2 hand- kettlebell swing
96
exercise. The Russian style of the exercise was used, which is performed rhythmically
98
A
C
93
99
exercise (Figure 1). Each round consisted of 30 seconds of exercise followed by 30 seconds of
97
incorporating an explosive hip extension and swing ascension to eye-level during the concentric phase, followed by dynamic hip flexion and swing descension during the eccentric phase of the
100
rest. Males used a 16-kg KB, and females used an 8-kg KB (21). The KB swings were performed
101
at a rate of 1-s eccentric/1-s concentric phases (15 swings per round) and were controlled with
Copyright ª 2017 National Strength and Conditioning Association
the use of a metronome. Continuous feedback was given by an investigator in order to maintain
103
the correct form and the rhythmic timing of the swing. The 16 and 8-kg KB were used in this
104
study since it is the recommended weight for beginning males and females, respectively (21,42)
105
and appear to be standardized in previous KB research (5,21,22,26). The rationale for the
106
number and duration of rounds as well as the rest periods were based on literature focusing on
107
the acute responses and longitudinal adaptations to KB exercise. Such research reported acute
108
increases in HR (80-90% of predicted HRmax) (5,22), oxygen consumption (22) and hormones
109
involved in muscular adaptations (5) along with chronic improvements in maximal strength and
110
power (26) utilizing similar protocols. During CON trial, subjects remained in the supine
111
position for the same 12 min time duration as the KB trial.
112
C EP
TE
D
102
Heart rate variability
114
Baseline and post-trial R-R interval measurements were performed in the supine position. R-R
115
intervals were collected for 5 min at baseline and 3 min for Post-3, Post-10 and Post-30 using a
116
validated wireless monitor (Polar 800CX; Polar Electro OY, Kempele,Finland) via a chest strap
117
interfaced to a computer. HRV variables calculated from R-R interval series of 3 minutes have
118
been found to match well with those calculated from the typical 5-minutes R-R interval (2),
119
making 3 minute HRV analysis a surrogate method to assess HRV (2). All R–R intervals were
121
A
C
113
122
we calculated the root mean square of successive differences (RMSSD), which reflects
123
parasympathetic modulation(39). The autoregressive model was used to estimate the power
124
spectrum in the total power (TP, 0.00 - 0.40 Hz) and its main components: low-frequency (LF,
120
inspected for artifacts and premature beats. HRV was quantified from 5-min (baseline) and 3min (Post-3, Post-10 and Post-30) segments free of artifacts. As a time domain index of HRV,
Copyright ª 2017 National Strength and Conditioning Association
0.04 - 0.15 Hz) and high-frequency (HF, 0.15 - 0.40 Hz). TP of HRV is an estimation of the
126
global activity of the autonomic nervous system. The HF power is a marker of cardiac
127
parasympathetic activity (31,39) .The LF component of HRV in absolute units is mediated by
128
both sympathetic and parasympathetic activities(39). The HF and LF were normalized (nHF and
129
nLF) and expressed as a percentage of the TP, considered as HF+LF (39). The nHF and nLF are
130
defined as HF or LF / (LF + HF), expressing the spectral power as the relative (%) contribution
131
of the sympathetic (nLF) and parasympathetic (nHF) activities on the sinoatrial node.
132
Normalizing is appealing since it expresses the quantities on a more easily understood
133
percentage (0%–100%) scale. Additionally, normalizing considerably diminishes within and
134
across-subject variability in the total raw HRV spectral power (6). The ratio of nLF to nHF
135
(nLF/nHF) has been suggested as a mean to quantify the relationship between sympathetic and
136
parasympathetic nerve activities (sympathovagal balance) (31). Increased sympathovagal
137
balance is considered a reflection of sympathetic predominance (31).We followed the standards
138
for the measurement and interpretation of the HRV (39).
C EP
TE
D
125
139
Blood Pressure
141
Baseline and post-trial brachial BP was measured using an automatic oscillometric device
142
(HEM-705CP; Omron Healthcare, Vernon Hill, IL, USA). Two measurements at 1-min intervals
143
A
C
140
144
laboratory, the intraclass correlation coefficient for resting BP collected on two separate days is
145
0.95.
were collected and averaged at each time point (baseline, Post-3, Post-10 and Post-30). In our
146 147
Copyright ª 2017 National Strength and Conditioning Association
148
Anthropometrics
149
Height was measured using a stadiometer and recorded to the nearest 0.5cm, and body mass was
150
measured using a seca scale (Sunbeam Products Inc., Boca Raton, FL, USA), recorded to the
151
nearest 0.1 kg.
D
152
Statistical analysis
154
Data were examined for normality with the Shapiro–Wilk test. Differences in mean values for
155
each variable between conditions were compared by a 2x4 ANOVA with repeated measures
156
(trial [CON vs KB] by time [baseline, Post-3, Post-10 and Post-30]), followed by Bonferroni
157
alpha correction. Univariate associations were analyzed with Pearson’s correlation coefficients.
158
Data are shown as means ± SE. Statistical significance was defined a priori as P < 0.05.
159
Statistical analyses were performed using SPSS version 21.0 (IBM SPSS Analytics, Armonk,
160
NY). A power calculation done a priori determined that a population of 12 subjects would allow
161
the observation of a difference of 3%–5% between the groups (CON vs KB) with a power of
162
80% on the primary study outcome variables of LF/HF, SBP and DBP.
C EP
TE
153
C
163
RESULTS
165
BP, HR and autonomic function parameters at baseline and after 30 min of KB and control trials
167
A
164
168
nLF/nHF and RMSSD. There were significant increases (P
D
Cardiac Autonomic and Blood Pressure Responses to an Acute Bout of Kettlebell Exercise
Alexei Wong1 –– Michael Nordvall1––Michelle Walters-Edwards1 –– Kevin Lastova1––
1
C EP
TE
Gwendolyn Francavillo1 –– Liane Summerfield1–– Marcos Sanchez- Gonzalez2
Department of Health and Human Performance, Marymount University, 2807 North Glebe
Road, Arlington, Virginia 22207, USA 2
Division of Clinical & Translational Research Larkin Community Hospital, 7000 SW 62nd Ave,
C
South Miami, FL 33143
A
Corresponding Author: Alexei Wong, PhD, Department of Health and Human Performance, Marymount University, 2807 North Glebe Road, Arlington, Virginia 22207. Telephone: 703-522-5600; E-mail: [email protected]
Running title: Autonomic and Blood Pressure responses to Kettlebell exercise
Copyright ª 2017 National Strength and Conditioning Association
1
Abstract: Kettlebell (KB) training has become an extremely popular exercise program for improving both muscle strength and aerobic fitness. However, the cardiac autonomic modulation and blood pressure (BP) responses induced by an acute KB exercise session are currently unknown. Understanding the impact of this exercise modality on the post-exercise autonomic modulation and BP would facilitate appropriate exercise prescription in susceptible populations. The present study evaluated the effects of an acute session of KB exercise on heart rate variability (HRV) and BP responses in healthy individuals. Seventeen (M=10, F=7) healthy subjects completed either a KB or non-exercise control trial in randomized order. HRV and BP measurements were collected at baseline, 3, 10 and 30 min after each trial. There were significant increases (P < 0.01) in heart rate, markers of sympathetic activity (nLF) and sympathovagal balance (nLF/nHF) for 30 min after the trial KB trial, while no changes from baseline were observed after the control trial. There were also significant decreases (P < 0.01) in markers of vagal tone (RMMSD, nHF) for 30 min as well as (P < 0.01) systolic BP and diastolic BP at 10 and 30 min after the trial KB trial while no changes from baseline were observed after the control trial. Our findings indicate that KB exercise increases sympathovagal balance for 30 min post-intervention which is concurrent with an important hypotensive effect. Further research is warranted to evaluate the potential clinical application of KB training in populations that might benefit from post-exercise hypotension, such as hypertensives.
21
Keywords: heart rate variability; high intensity interval training; post-exercise hypotension
22
C EP
TE
D
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
INTRODUCTION
24
Hypertension (HTN), characterized by increased blood pressure (BP), is a major risk factor for
25
cardiovascular disease (CVD) and end-organ damage (8). Autonomic dysfunction is recognized
26
as a primary pathophysiological mechanisms of HTN since it is related to both the development
27
and the complications of this condition (28). Heart rate variability (HRV) is acknowledged as a
28
A
C
23
29
parasympathetic (sympathovagal) balance (39). HRV is used in many research applications,
30
including the study of autonomic control during physical activity (16) and after (recovery phase)
31
acute exercise (16). The HRV and BP responses post-exercise appear to be related to the
32
intensity of the performed exercise, particularly in the first minutes of recovery (16,32).
measure of cardiac autonomic regulation, especially as a surrogate of the sympathetic–
Copyright ª 2017 National Strength and Conditioning Association
Moreover, a prolonged sympathetic predominance and concominant slow parasympathetic
34
reactivation contribute to a delayed BP recovery following exercise, which is thought to be
35
associated with increased risk of acute cardiac events (27,30). Therefore, understanding the
36
impact of various exercise modalities on autonomic regulation and BP would provide further
37
insight into the post-exercise relationship between these variables and may help in the
38
development of strategies to decrease exercise-related cardiovascular risk.
The kettlebell (KB), a cannonball shaped iron hand weight with a handle, dates back to
TE
39
D
33
the early 18th century in Russia where it gained popularity as an exercise implement (42). In the
41
last few years, resurgence in KB use has been due primarily to programs like CrossFit and Pavel
42
Tsatsouline’s workshops, where it is utilized as a training modality for improving both muscle
43
strength and aerobic fitness, thereby providing an alternative to established methods of exercise
44
(13). Owing to the design of the KB, its high-speed, ballistic and eccentric nature make it an
45
excellent form of exercise for loading of the hip extensor and posterior chain muscles (13,42).
46
The two hand-KB swing, a primary movement in KB training, is performed rhythmically
47
incorporating an explosive hip extension during the concentric phase, followed by dynamic hip
48
flexion during the eccentric phase of the swing (13,42). KB swings are usually used as a form of
49
high-intensity interval training, utilizing alternating bouts of exercise followed by short rest
50
periods (13). Despite the popularity of this form of exercise, research regarding the acute
52
A
C
C EP
40
53
hormone), which remain elevated for at least 15 min post-exercise (5). Additionally, Farrar et al.
54
(14) observed that KB swings caused a greater increase in oxygen consumption (VO2max) and HR
55
compared to traditional power or resistance exercise. While an increased VO2max and HR
51
cardiovascular responses to a KB swing routine is limited. It has been previously demonstrated that an acute session of KB swings causes elevations in heart rate (HR) and cortisol (a stress
Copyright ª 2017 National Strength and Conditioning Association
56
resulting from KB training are less than those induced by aerobic exercise (22), KB swings
57
present a metabolic challenge that may elicit unique cardiac autonomic and BP responses.
58
Therefore, the aim of the present study was to investigate the effects of a KB exercise session on
59
post-exercise cardiac autonomic function and BP responses.
D
60
METHODS
62
Experimental Approach to the Problem
63
Anthropometrics, health history and a familiarization session with the study tests, procedures and
64
the correct technique for the 2 hand-KB swing exercise were learned during an initial
65
familiarization visit. Using a crossover design, subjects were tested in the postprandial (≥4
66
hours) condition on two separate additional visits separated by at least 48 hours. Measurements
67
were performed during afternoon hours in a quiet, temperature-controlled room (23 ± 1 °C) and
68
at the same time of the day (± 2 h) to minimize potential diurnal variations in cardiac and
69
vascular reactivity. Subjects abstained from caffeine and alcohol consumption for at least 12
70
hours and avoided intense exercise 48 hours prior to testing. After HRV and BP instrumentation,
71
subjects rested in the supine position for at least 10 min before a 5 min baseline period.
72
Thereafter, subjects completed either the KB or the no-exercise control (CON) trial in a
73
randomized order. Immediately after the trials, subjects resumed the supine position for 30 min
75
C EP
C
A
74
TE
61
of recovery. Post-trial measurements of BP and HRV were collected between 3–6 min (Post-3), 10-13 min (Post- 10) and 30–33 min (Post-30).
76 77 78
Copyright ª 2017 National Strength and Conditioning Association
79
Subjects
81
A total of 17 (M=10, F=7) healthy (age=23 ± 1 years, height=1.71 ± 0.02m and weight=74.1 ±
82
4.9 kg) subjects between the ages of 18 and 27 years were recruited. Subjects were nonsmokers,
83
normotensive, free of cardiovascular and metabolic/endocrine diseases as evaluated by health
84
history, without musculoskeletal concerns that would limit exercise participation and were not
85
taking medication or nutritional supplements at the time of the study. All subjects reported being
86
active through individualized cardiovascular, strength and flexibility exercise programs
87
performed 2–4 times per week for at least 1 year prior to the study. However, subjects had
88
minimal experience with KB exercise. Female subjects were tested in the early follicular phase
89
of the menstrual cycle to avoid possible influence of endogenous estrogens on autonomic
90
function. All subjects were aware of the experimental procedures as approved by the institutional
91
review board and gave written consent before data collection.
C EP
TE
D
80
92
Procedures
94
Trials
95
During the KB trial, subjects completed 12 consecutive rounds of the 2 hand- kettlebell swing
96
exercise. The Russian style of the exercise was used, which is performed rhythmically
98
A
C
93
99
exercise (Figure 1). Each round consisted of 30 seconds of exercise followed by 30 seconds of
97
incorporating an explosive hip extension and swing ascension to eye-level during the concentric phase, followed by dynamic hip flexion and swing descension during the eccentric phase of the
100
rest. Males used a 16-kg KB, and females used an 8-kg KB (21). The KB swings were performed
101
at a rate of 1-s eccentric/1-s concentric phases (15 swings per round) and were controlled with
Copyright ª 2017 National Strength and Conditioning Association
the use of a metronome. Continuous feedback was given by an investigator in order to maintain
103
the correct form and the rhythmic timing of the swing. The 16 and 8-kg KB were used in this
104
study since it is the recommended weight for beginning males and females, respectively (21,42)
105
and appear to be standardized in previous KB research (5,21,22,26). The rationale for the
106
number and duration of rounds as well as the rest periods were based on literature focusing on
107
the acute responses and longitudinal adaptations to KB exercise. Such research reported acute
108
increases in HR (80-90% of predicted HRmax) (5,22), oxygen consumption (22) and hormones
109
involved in muscular adaptations (5) along with chronic improvements in maximal strength and
110
power (26) utilizing similar protocols. During CON trial, subjects remained in the supine
111
position for the same 12 min time duration as the KB trial.
112
C EP
TE
D
102
Heart rate variability
114
Baseline and post-trial R-R interval measurements were performed in the supine position. R-R
115
intervals were collected for 5 min at baseline and 3 min for Post-3, Post-10 and Post-30 using a
116
validated wireless monitor (Polar 800CX; Polar Electro OY, Kempele,Finland) via a chest strap
117
interfaced to a computer. HRV variables calculated from R-R interval series of 3 minutes have
118
been found to match well with those calculated from the typical 5-minutes R-R interval (2),
119
making 3 minute HRV analysis a surrogate method to assess HRV (2). All R–R intervals were
121
A
C
113
122
we calculated the root mean square of successive differences (RMSSD), which reflects
123
parasympathetic modulation(39). The autoregressive model was used to estimate the power
124
spectrum in the total power (TP, 0.00 - 0.40 Hz) and its main components: low-frequency (LF,
120
inspected for artifacts and premature beats. HRV was quantified from 5-min (baseline) and 3min (Post-3, Post-10 and Post-30) segments free of artifacts. As a time domain index of HRV,
Copyright ª 2017 National Strength and Conditioning Association
0.04 - 0.15 Hz) and high-frequency (HF, 0.15 - 0.40 Hz). TP of HRV is an estimation of the
126
global activity of the autonomic nervous system. The HF power is a marker of cardiac
127
parasympathetic activity (31,39) .The LF component of HRV in absolute units is mediated by
128
both sympathetic and parasympathetic activities(39). The HF and LF were normalized (nHF and
129
nLF) and expressed as a percentage of the TP, considered as HF+LF (39). The nHF and nLF are
130
defined as HF or LF / (LF + HF), expressing the spectral power as the relative (%) contribution
131
of the sympathetic (nLF) and parasympathetic (nHF) activities on the sinoatrial node.
132
Normalizing is appealing since it expresses the quantities on a more easily understood
133
percentage (0%–100%) scale. Additionally, normalizing considerably diminishes within and
134
across-subject variability in the total raw HRV spectral power (6). The ratio of nLF to nHF
135
(nLF/nHF) has been suggested as a mean to quantify the relationship between sympathetic and
136
parasympathetic nerve activities (sympathovagal balance) (31). Increased sympathovagal
137
balance is considered a reflection of sympathetic predominance (31).We followed the standards
138
for the measurement and interpretation of the HRV (39).
C EP
TE
D
125
139
Blood Pressure
141
Baseline and post-trial brachial BP was measured using an automatic oscillometric device
142
(HEM-705CP; Omron Healthcare, Vernon Hill, IL, USA). Two measurements at 1-min intervals
143
A
C
140
144
laboratory, the intraclass correlation coefficient for resting BP collected on two separate days is
145
0.95.
were collected and averaged at each time point (baseline, Post-3, Post-10 and Post-30). In our
146 147
Copyright ª 2017 National Strength and Conditioning Association
148
Anthropometrics
149
Height was measured using a stadiometer and recorded to the nearest 0.5cm, and body mass was
150
measured using a seca scale (Sunbeam Products Inc., Boca Raton, FL, USA), recorded to the
151
nearest 0.1 kg.
D
152
Statistical analysis
154
Data were examined for normality with the Shapiro–Wilk test. Differences in mean values for
155
each variable between conditions were compared by a 2x4 ANOVA with repeated measures
156
(trial [CON vs KB] by time [baseline, Post-3, Post-10 and Post-30]), followed by Bonferroni
157
alpha correction. Univariate associations were analyzed with Pearson’s correlation coefficients.
158
Data are shown as means ± SE. Statistical significance was defined a priori as P < 0.05.
159
Statistical analyses were performed using SPSS version 21.0 (IBM SPSS Analytics, Armonk,
160
NY). A power calculation done a priori determined that a population of 12 subjects would allow
161
the observation of a difference of 3%–5% between the groups (CON vs KB) with a power of
162
80% on the primary study outcome variables of LF/HF, SBP and DBP.
C EP
TE
153
C
163
RESULTS
165
BP, HR and autonomic function parameters at baseline and after 30 min of KB and control trials
167
A
164
168
nLF/nHF and RMSSD. There were significant increases (P
