Training & Testing 851

Autonomic Modulation in Resistance-Trained Individuals after Acute Resistance Exercise

Affiliations

Key words ▶ strength training ● ▶ spectral analysis ● ▶ sample entropy ●

J. D. Kingsley1, S. Hochgesang2, A. Brewer2, E. Buxton2, M. Martinson2, G. Heidner2 1 2

Exercise Physiology, Kent State University, Kent, United States Kinesiology, Recreation and Sport, Indiana State University, Terre Haute, United States

Abstract



The effects of different types of acute bouts of resistance exercise on autonomic modulation in individuals that are resistance-trained compared to untrained individuals are unknown. Seventeen untrained and 17 resistance-trained participants were assessed for autonomic modulation after various acute resistance exercise bouts. Electrocardiogram readings were collected at rest and 25 min after a control period, whole-, lower-, or upper-body acute bouts of resistance exercise. Heart rate variability and heart rate complexity were used to assess autonomic modulation. Participants were similar for age, height, weight and measures of body composition (p > 0.05) and

Introduction

▼ accepted after revision January 28, 2014 Bibliography DOI http://dx.doi.org/ 10.1055/s-0034-1371836 Published online: May 9, 2014 Int J Sports Med 2014; 35: 851–856 © Georg Thieme Verlag KG Stuttgart · New York ISSN 0172-4622 Correspondence Dr. James Derek Kingsley, PhD Exercise Physiology Kent State University 161 B MACC Annex Kent United States 44242 Tel.: + 1/330/672 0222 Fax: + 1/330/672 2250 [email protected]

Resistance-exercise training (RET) has been shown to assist with the management of a myriad of diseases, is often used as a rehabilitative modality and is currently recommended by professional medical organizations as part of a healthy lifestyle [1, 33]. It has been shown to improve muscle strength, prevent osteoporosis and have other benefits [25, 31, 34, 37, 38]. While the effects of RET on the cardiovasculature are emerging more frequently [8, 9, 17], the effects of acute bouts of resistance exercise are still relatively unknown [18]. Data have demonstrated that an acute bout of resistance exercise may reduce vagal modulation, as measured by decreases in high-frequency power using heart rate variability (HRV), or decreases in heart rate complexity (HRC) in moderately trained individuals [18, 19]. In a clinical setting, reductions in vagal modulation after exercise may be associated with ventricular arrhythmias and sudden cardiac death [32, 43, 44]. This increase in risk has been linked

were different for measures of maximal strength (p < 0.05). There were no differences (p > 0.05) in autonomic modulation at rest between groups. Significant decreases (p < 0.05) in parasympathetic modulation after the acute bouts of resistance exercise were noted. Sample entropy was not affected in the untrained group, but was significantly decreased after whole- ( − 17.5 %) and upper-body exercise ( − 13.5 %) in the resistance training group. The changes in sample entropy after lower-body resistance exercise were not significant ( − 15.7 %; p = 0.06). These data suggest that resistance exercise training further attenuates the parasympathetic responses to an acute bout of resistance training regardless of the modality compared to the untrained state.

to changes in autonomic modulation [7, 14, 21, 22]. More specifically, this risk may be associated with a reduction in vagal tone, due to the exercise stressor [18, 39]. Given this factor, the evaluation of autonomic modulation after an acute bout of resistance exercise may have significant clinical implications on cardiovascular health. To our knowledge, no study has examined the effects of various acute bouts of resistance exercise in resistance-trained individuals compared to untrained individuals. Studies that have utilized acute bouts of whole-body resistance exercise have reported large decreases in parasympathetic activity. According to the American College of Sports Medicine, intermediate and advanced lifters should utilize upper/lower-body split routines to maximize muscle hypertrophy [2]. However, to our knowledge no studies have examined the responses of autonomic modulation after acute bouts of lower- or upper-body resistance exercise in resistance-trained or untrained individuals. Therefore, the purpose of the present study was to evaluate autonomic modulation after various resistance exercise

Kingsley JD et al. Autonomic Modulation in Resistance-Trained … Int J Sports Med 2014; 35: 851–856

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Authors

852 Training & Testing

modalities in resistance-trained individuals. We hypothesized that resistance-trained individuals would have greater cardiac autonomic modulation compared to untrained individuals in response to different resistance exercise modalities.

Anthropometric measurement Body composition was assessed using whole-body air displacement plethysmography (BodPod; Life Measurement Inc., Concord, California, USA). Height was measured using a standard stadiometer (to the nearest 0.05 cm), and weight was assessed on a calibrated scale (to the nearest 0.1 kg).

Materials and Methods Participants Based on data from Heffernan et al. (2008) examining changes in Sample Entropy (SampEn) after an acute bout of resistance exercise, a large effect size (Cohen’s d; > 1.0) was calculated. For a power of 80 %, at least 8 participants per group would be needed. Based on these data, we recruited thirty-four individuals for this study. Participants that had been engaging in resistance training (RET group; 9 women, 8 men) reported that they had been participating in whole-body RET for 6 ± 2 years, more than 3 days a week, with less than 1.5 h of concomitant aerobic activity per week. The participants that were untrained (UT group; 7 women, 10 men) reported that they had not participated in RET for at least 1 year, and had engaged in less than 1.5 h of aerobic activity per week. Exclusion criteria included smoking, obesity, cardiovascular disease, metabolic disease, hypertension (resting blood pressure ≥ 140/90 mmHg), or taking any medications or supplements known to affect heart rate (HR) or blood pressure. These were assessed via a medical questionnaire. All participants gave their written informed consent prior to any data collection. This research was approved by the Indiana State University Institutional Review Board and meets the ethical standards of this journal [16].

Study design The study was a randomized cross-over design. The initial visit consisted of anthropometric measurements and assessment of muscular strength using the 10 repetition maximum (10RM). The second visit consisted of muscular strength verification. For the third and fourth visits participants reported to the Exercise and Cardiovascular Research Laboratory between the hours of 6 and 11 a.m. to control for diurnal variation. For testing, each of the participants were ≥ 3 h postprandial and had avoided caffeine, alcohol and strenuous exercise for at least 24 h prior to testing. The acute bouts of resistance exercise were separated by a minimum of 72 h, completed at the same time of day ( ± 1 h). The temperature of the room was constant at approximately 22 ºC. Once at the laboratory participants initially rested quietly in supine position for a period of 10 min. After the 10-min rest period, an electrocardiograph (ECG) was collected for a 5-min epoch to assess autonomic modulation. After resting data were collected, the participants were randomly assigned to one of four different conditions: (1) whole-body (WB; all 4 exercises), (2) upper-body (UB; seated row and chest press), (3) lower-body (LB; leg extension and leg curl), or (4) quiet control (CON). The acute bouts of resistance exercise consisted of three sets of 10 repetitions at each participant’s predetermined 10RM with 2 min of rest between sets and exercises. The CON had the participants rest in the supine position for 15 min. Within two minutes of completing the acute bout of resistance exercise, participants returned for assessment of recovery. The instrumentation was reapplied and the participants rested in the supine position for 25 min. At 25 min a second 5-min epoch was collected for assessment of autonomic modulation [18].

Muscle strength Muscle strength was assessed by the 10RM for 4 different exercises. The exercises included leg extension, leg curl, seated row and chest press (Hammer Strength; Life Fitness, Schiller Park, Illinois, USA). The highest resistance between the 2 days was used for the acute resistance exercise bout and data analysis.

Heart rate variability HRV was collected in a manner described by the Task Force of the European Society of Cardiology and North American Society of Pacing and Electrophysiology [39]. ECG signals were collected at a rate of 1 000 Hz using a modified CM5 configuration (Biopac Systems, Santa Barbara, California, USA). AcqKnowledge 4.2 (Biopac Systems) was used to extract beat-to-beat R-R intervals after visual inspection of noise, ectopics and artifacts. All participants breathed with a metronome set at 12 breaths per minute to control for the respiratory effects on autonomic modulation. Since small samples of beats were used, a duration of 5 min, fast Fourier transform was used to generate spectral power. HRV was calculated in both frequency and time domain. For the frequency domain, total power of HRV was used an index of total autonomic activity and vagal modulation. Low-frequency power (LF; 0.04–0.15 Hz) is comprised of both sympathetic and parasympathetic components. High-frequency power (HF; 0.15–0.4 Hz) is comprised of primarily parasympathetic modulation and was used an index of vagal modulation [28, 39]. The LF/HF ratio of HRV was used as an indicator of sympathovagal dominance [11]. Both power spectra were calculated in absolute (ms2) and normalized units (nu) to evaluate the power of each component in relation to total power. Normalized units (LF or HF) are derived by dividing the power of a component by the total power and then dividing by 100 [39]. The normalized values of LF (LFnu) and HF (HFnu) were used as measures of sympathetic and parasympathetic modulation, respectively [39]. Time domains included the square root of the mean squared differences of successive R-R intervals (RMSSD) and the proportion of successive normal-to-normal intervals greater than 50 ms (pNN50) quantified as the NN50 divided by the total number of beats, as well as the standard deviation of the NN interval (SDNN). The RMSSD and pNN50 were used as measures of HF oscillations and the SDNN was used as a measure of overall autonomic modulation [39]. Resting day-to-day repeatability as analyzed by intraclass correlation coefficients for HFnu and LFnu were 0.85 and 0.87, respectively. The coefficient of variation was also calculated at 12 % for HFnu and 14 % for LFnu at rest, which is similar to other published data [3].

Heart rate complexity SampEn was used to quantify the complexity of the R-R interval over the 5-min period of time after removal of the linear trend. In short, SampEn is defined as the probability of matches or sequences being similar over a short time series, which usually has a range of 0–2 [36]. If the signal is very predictive the value is close to 0 [36]. On the other hand, if the signal is quite variable it will have a value close to 2 [36]. SampEn relies on r, the filter

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Training & Testing 853

parameter (acceptable matches), m, the embedding dimension (duration of matches for comparison) and N, the number of data points [36]. It has been shown that the range for r can vary from 0.10 to 0.50 [41]. Furthermore, it has been suggested that r should be set at a particular percentage of the standard deviation of the time series, usually 20 % [24]. Previous reports using SampEn have set m at 2 due to the fact that the R-R intervals cannot be very large [24]. Kuusela et al. (2002) have suggested that despite the fact that SampEn is a robust measure, if researchers are using data sets with < 200 points it will produce large confidence intervals [24]. To compensate for this, Heffernan et al. (2007) recommend that 220–250 R-R intervals should be used for analysis and that this same number of intervals should be

used for all participants to maintain consistency [17]. Therefore, 250 points were used for resting and recovery analysis in all participants.

Participant characteristics between groups were assessed with a one-way analysis of variance (ANOVA). A Kolmogorov-Smirnov normality test demonstrated that absolute values of total power, LF and HF were not normally distributed. Accordingly, they were transferred to their natural log (Ln). A 2 × 2 × 4 repeated measures ANOVA was used to examine the effects of resistance training (RET group versus UT group) across time (rest and recovery) and across the 4 different conditions (WB, UB, LB, & CON) on heart rate (HR) and measures of autonomic modulation. If the interactions were significant using the ANOVA, Tukey’s HSD test was used for post hoc comparisons. Significance was set a priori at p ≤ 0.05. Values are presented as mean ± standard deviation. All statistical analyses were completed using SPSS version 21 (Chicago, Illinois, USA).

Table 1 Participant characteristics (N = 34). Variables

UT (n = 17)

RET (n = 17)

age (years) height (m) weight (kg) body fat ( %) fat-free mass (kg) fat mass (kg)

22 ± 2 1.69 ± 0.1 70.8 ± 17.1 22.6 ± 8.9 55.1 ± 15.3 16.5 ± 7.4

22 ± 1 1.73 ± 0.1 75.5 ± 16.3 17.5 ± 7.6 62.7 ± 14.8 13.3 ± 6.4

Results



Values are mean ± standard deviation

▶ Table 1. There were Participant characteristics are reported in ● no significant differences for the participants on age, height, ▶ Table 1, p > 0.05). The RET group weight or body composition (● was significantly stronger for all of the resistance exercises com▶ Table 2, p < 0.05). pared to the UT group (● There were no significant group × time × condition interactions for any of the HRV variables. There were also no differences in resting measures of autonomic modulation. There were also no differences in resting HR or HR in response to the acute bouts of resistance exercise. There were significant time × condition interactions for frequency domains of HRV such as LFnu, LnHF, ▶ Table 3, p < 0.05). Specifically, there HFnu and the LF/HF ratio (●

RET, resistance-trained; UT, untrained

Table 2 10-Repetition maximum (N = 34). Variables

UT (n = 17)

RET (n = 17)

chest press (kg) seated row (kg) leg curl (kg) leg extension (kg)

42 ± 18 37 ± 15 44 ± 15 45 ± 17

73 ± 34* 59 ± 27* 56 ± 14* 63 ± 18*

Values are mean ± standard deviation *p < 0.05, significantly different from untrained group RET, resistance trained; UT, untrained

Table 3 Heart rate and frequency domains of heart rate variability (N = 34). Variables

UT (n = 17) Control

Heart rate (bpm) rest recovery Ln total power rest recovery Ln low-frequency (ms2) rest recovery Low-frequency (nu) rest recovery Ln high-frequency (ms2) rest recovery High-frequency (nu) rest recovery LF/HF ratio rest recovery

RET (n = 17)

WB

UB

LB

Control

59 ± 11 54 ± 9

58 ± 10 77 ± 10†

54 ± 7 67 ± 12†

60 ± 10 72 ± 9†

62 ± 10 63 ± 11

8.5 ± 1.2 8.5 ± 1.0

8.2 ± 0.73 7.3 ± 0.78

8.4 ± 0.65 7.9 ± 1.4

8.5 ± 0.57 7.7 ± 0.84

8.3 ± 1.1 8.4 ± 0.98

6.12 ± 1.0 6.60 ± 1.1

6.07 ± 0.9 6.01 ± 0.66

6.31 ± 0.7 6.20 ± 1.3

6.47 ± 0.41 6.14 ± 0.8

18.8 ± 12.9 22.6 ± 12.1

18.7 ± 9.6 45 ± 14.1†

24.8 ± 20.0 33.2 ± 18.5

7.79 ± 1.0 7.95 ± 1.1

7.55 ± 1.2 6.22 ± 1.2†

81.1 ± 13.0 74.3 ± 13.0 0.27 ± 0.25 0.33 ± 0.25

WB

UB

LB

52 ± 6 68 ± 14†

56 ± 10 73 ± 14†

58 ± 8 73 ± 9†

8.5 ± 0.83 7.49 ± 1.0

8.9 ± 1.0 8.0 ± 1.5

8.5 ± 0.56 7.7 ± 0.91

6.74 ± 1.2 6.68 ± 1.4

6.55 ± 0.9 6.09 ± 0.9

7.02 ± 1.1 6.53 ± 1.1

6.70 ± 0.7 6.50 ± 1.1

27.8 ± 22.6 39.9 ± 22.7†

37.4 ± 25.5 38.9 ± 26.3

22.9 ± 12.9 44.2 ± 21.5†

27.7 ± 20.0 34.2 ± 26.9

27.6 ± 18.5 29.0 ± 20.2†

7.79 ± 1.0 7.05 ± 1.8†

7.78 ± 1.3 6.65 ± 1.6†

7.47 ± 1.4 7.25 ± 1.3

7.98 ± 0.9 6.46 ± 1.4†

8.06 ± 1.2 7.04 ± 2.1†

7.78 ± 0.8 6.40 ± 1.3†

81.1 ± 9.7 54.8 ± 14.2†

73.9 ± 19.1 66.3 ± 18.0

71.2 ± 22.0 60.0 ± 22.7†

61.9 ± 24.7 59.1 ± 24.5

77.0 ± 13.0 55.7 ± 21.5†

70.3 ± 20.6 65.2 ± 26.3

71.8 ± 18.0 50.5 ± 19.8†

0.25 ± 0.16 0.93 ± 0.49†

0.43 ± 0.45 0.61 ± 0.50

0.61 ± 0.84 1.07 ± 1.31†

0.96 ± 1.1 1.14 ± 1.48

0.33 ± 0.22 1.03 ± 0.72†

0.57 ± 0.58 0.95 ± 1.23

0.40 ± 0.19 1.56 ± 1.29†

Values are mean ± standard deviation †p < 0.05, significantly different from rest HF, high frequency; LF, low frequency; NU, normalized units; RET, resistance exercise trained; UT, untrained

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Statistics

854 Training & Testing

Table 4 Time domains of heart rate variability (N = 34). UT (n = 17) Variables SDNN rest recovery RMSSD rest recovery pNN50 rest recovery

RET (n = 17)

Control

WB

UB

LB

Control

WB

UB

LB

73.3 ± 26.1 83.0 ± 41.2

77.5 ± 24.9 43.7 ± 18.8†

85.2 ± 25.0 63.1 ± 40.6†

79.3 ± 22.3 52.0 ± 21.0†

74.3 ± 34.7 78.0 ± 33.3

82.2 ± 30.3 52.1 ± 24.4†

86.6 ± 29.3 59.5 ± 39.2†

76.8 ± 21.0 54.4 ± 18.3†

73.5 ± 31.9 81.9 ± 43.2

72.3 ± 35.1 33.9 ± 21.6†

79.6 ± 36.7 61.3 ± 52.4†

73.4 ± 35.3 43.3 ± 27.5†

71.8 ± 45.9 68.6 ± 43.2

85.4 ± 35.7 40.6 ± 31.2†

85.1 ± 37.8 52.7 ± 45.8†

79.0 ± 26.1 41.0 ± 26.6†

134 ± 72 130 ± 72

132 ± 72 55 ± 59†

139 ± 59 89 ± 92†

137 ± 65 77 ± 71†

105 ± 79 98 ± 73

141 ± 57 68 ± 88†

133 ± 61 100 ± 89†

124 ± 63 59 ± 67†

Values are mean ± standard deviation pNN50, proportion of successive normal-to-normal intervals greater than 50 ms; RMSSD, square root of the mean squared differences of successive R-R intervals; RET, resistance exercise trained; SDNN, standard deviation of the N-N interval; UT, untrained

Control

Upper Body

Whole Body

Lower Body

a

Untrained 2.0 1.8

Sample Entropy

were significant increases for LFnu and the LF/HF ratio after the acute bouts of WB and LB compared to control for both groups. The LnHF was significantly lower (p < 0.05) after each of the acute bouts of resistance exercise compared to the control in each of the groups. The HFnu was different than the LnHF such that it was only decreased (p < 0.05) after WB and LB. For HRV in the time domain there were significant time × condi▶ Table 4; tion interactions for SDNN, RMSSD, and pNN50 (● p < 0.05) such that they were lower after each of the acute bouts of resistance exercise compared to the control period. There was a significant group × time × condition interaction for SampEn (p < 0.05). After acute bouts of whole- ( − 17.5 %) and upper-body ( − 13.5 %) resistance exercise there were significant ▶ Fig. 1; p < 0.05) decreases in SampEn in the resistance-trained (● participants compared to the untrained participants. After the acute bout of lower-body resistance exercise there was also a decrease ( − 15.5 %) in SampEn in the resistance-trained participants, but it did not reach statistical significance (p = 0.06).

1.6 1.4 1.2 1.0 Rest

b

2.0

Recovery

Resistance Exercise Trained

Discussion



1.8 Sample Entropy

This is the first study to examine the responses of different resistance exercise modalities on autonomic modulation in resistance-trained individuals using both HRV and HRC. The primary findings of the present study were that, 1) reductions in vagal modulation after whole-, upper- or lower-body resistance exercises are similar in resistance-trained individuals compared to untrained individuals, 2) resistance-trained individuals may experience significant reductions in complexity after any acute bout of resistance exercise be it whole-body resistance exercise or a upper/lower-body split. In the present study, all of the HR and autonomic variables were similar between groups at rest. Our data are in agreement with Carter et al. (2003) and Cooke and Carter (2005), both of which reported that RET may not alter resting HR. The absence of change in autonomic modulation between the groups at rest is also in agreement with previous literature [6, 9]. The results of the present study further highlight that RET does not alter resting HR or autonomic tone as measured by HRV. However, the present study does not support the findings of Heffernan et al. (2007) that suggested increases in HRC with resistance-exercise training as our two groups were similar at rest.



*†

1.6

*†

1.4 1.2 1.0 Rest

Recovery

Fig. 1 Differences in sample entropy after a control period, and acute bouts of whole-, upper, and lower-body resistance exercise for a untrained participants (n = 17) and b resistance exercise trained participants (n = 17). *p < 0.05, significantly different from untrained group; †p < 0.05, significantly different from rest; ‡p = 0.06, different from rest.

The present study demonstrated significant reductions in vagal modulation after each of the different acute bouts of resistance exercise, which is analogous to previous research [18, 26]. Heffernan et al. (2006) reported similar findings such that total power and HFnu were significantly reduced after an acute bout

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†p < 0.05, significantly different from rest

of whole-body resistance exercise in active men consisting of 3 sets at the 10RM at 25 min post-exercise. Lima et al. (2011) reported that 70 % 1RM consisting of 3 sets for an acute bout of whole-body resistance exercise significantly increased sympathovagal dominance (LF/HF) and decreased parasympathetic activity (HF) at 20 min post-exercise. Collectively, these data suggest that an acute bout of resistance exercise may significantly reduce vagal modulation in young healthy individuals. Therefore, it is plausible that up to 25 min after an acute bout of resistance exercise, be it whole body or an upper-/lower-body split routine, the risk for a cardiovascular event is significantly increased in a resistance-trained or an untrained individual. To our knowledge there are only a small handful of studies that have examined SampEn after RET [17] or an acute bout of resistance exercise [19]. Heffernan et al. (2007) reported that 6-weeks of RET significantly increased SampEn in young, healthy men without any significant changes in spectral measures of HRV. In contrast, data from the present study suggest that RET does not alter SampEn as our data demonstrated no difference in SampEn between the groups. However, Heffernan et al. (2007) utilized an intra-group design as ours was an inter-group design, which might explain the difference. Without knowing the baseline measures of SampEn it is difficult for the present study to truly know if SampEn was affected by RET. In a separate article, Heffernan et al. (2008) reported that an acute bout of lower-body resistance exercise significantly reduced SampEn in young, active males. Even though we did not reach statistical significance after the acute bout of lower-body resistance exercise our data still suggest a movement toward a reduction in SampEn. A novel finding from the present study is that acute bouts of whole- and upper-body resistance exercise significantly decreased SampEn. Based on previous reports that have shown that cholinergic blockade with atropine reduces complexity while β-adrenergic blockade has no effect [5, 29], it is clear that an acute bout of resistance exercise suppresses vagal activity for at least 25 min after an acute bout of resistance exercise in resistance trained individuals. However, it is unclear if this finding is directly related to being resistance-trained. Therefore, it is important that future studies investigate the effects of acute bouts of resistance exercise in those individuals that are resistance-trained. Acute bouts of resistance exercise may also provide modifications on blood pressure [10, 35, 40]. De Souza et al. (2013) and Tibana et al. (2013) suggested that RET may be a useful modality to reduce blood pressure in women. Data from Queiroz et al. (2103) also suggest that this response is similar in men. While the reasons for this drop in blood pressure remain unclear, it has been postulated that they may occur due to increased levels of nitric oxide [15]. This, in turn, would allow for a decrease in vascular resistance which reducing afterload, thereby reducing any changes in left ventricular wall thickness. It is important to note that in the present study we did not directly measure autonomic modulation, but instead used HRV and HRC to measure it indirectly. Therefore, our data should be interpreted with some level of caution. While some studies support that the LF/HF ratio is a measure of sympathovagal balance [27], this is not universally accepted. While the Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology supports that normalized values of LF and HF are reciprocals, this is clearly not the case. It has been demonstrated that the sympathetic and parasympathetic systems can both be activated simultaneously as evidenced by

increases in sympathetic nerve activity [13] and bradycardia [12] in response to cold water facial immersion. We also did not measure muscle sympathetic nerve activity, and therefore our data reflect only parasympathetic activity. There are a few limitations of the present study that should be mentioned. For one, both males and females were used in the present study. While it has been reported that differences in linear [20] and non-linear [23] heart rate dynamics differ between genders, these findings are not conclusive when measured in the supine position [30]. We also did not control for the menstrual cycle in our female participants. Vellejo et al. (2005) suggested that the menstrual cycle does not affect HRV [42]. Bai et al. (2009) suggested that HRC may be altered by the menstrual cycle, but also stated that other hormones such as leptin, which also fluctuates during the menstrual cycle, may also play a significant role [4]. Another limitation may be that the findings were influenced by differences in exercise intensity. It is also important to note that these data apply to young, healthy individuals and may not necessarily be true for other populations. In conclusion, it appears that resistance training may significantly alter HRC after an acute bout of resistance exercise, but does not seem to affect HRV differently than an untrained individual. This is not necessarily surprising as it appears that HRC is a more sensitive measurement compared to HRV. It is clear that future research needs to further examine the effects of an acute bout of resistance exercise in resistance-trained individuals.

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856 Training & Testing

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Autonomic modulation in resistance-trained individuals after acute resistance exercise.

The effects of different types of acute bouts of resistance exercise on autonomic modulation in individuals that are resistance-trained compared to un...
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