Acute effects of exercise and sauna as a single intervention on arterial compliance

According to the World Health Organization, one in four adults globally are not sufficiently active¹ and a substantial percentage of the current world population have at least one cardiovascular risk factor.^2,3 However, according to the latest physical activity advice,^4,5 physical activity accumulated in bouts of at least 10 minutes duration may mitigate these factors and improve a wide range of health-related outcomes. Aerobic exercise and sauna bathing have each been shown to provide health-related benefits through plausible pathways, including beneficial changes in arterial stiffness and haemodynamic indices.^6,7 Recent evidence has also shown that aerobic fitness is inversely associated with arterial stiffness⁸ and even repeated exposure to strenuous exercise does not appear to compromise vessel integrity.⁹ Although the cardiovascular health benefits of aerobic exercise and sauna exposure seem to be comparable in nature, the effects of using exercise and sauna exposure in a single session has yet to be elucidated. Using sauna bathing as an adjunct to a shortened length of aerobic physical activity has the potential to serve as a gateway towards habit change in populations who are inactive. As such, we investigated arterial stiffness and haemodynamic-related alterations associated with using aerobic exercise and sauna bathing as a single intervention in a population with at least one cardiovascular risk factor.

Participants (n = 77) were recruited from the city of Jyväskylä in central Finland through the local out-of-hospital health care centre. To be eligible for inclusion, participants had to be free of a prior diagnosis of cardiovascular disease (CVD) and show at least one of the following cardiovascular risk factors: a history of smoking, diabetes, hyperlipidaemia, hypertension, obesity or a family history of coronary heart disease. Participants were free from diagnosed and/or symptomatic CVD, musculoskeletal injury or any other physical or mental condition that could preclude participation in the experiment. Prior to participation in the study, all participants were informed about the purpose of the research and the measurement procedures and provided written informed consent before being screened by a cardiac specialist. The research protocol and study design were conducted in accordance with the ethical standards approved by the institutional review board of the Central Finland Hospital District ethical committee, Jyväskylä, Finland (Dnro 5U/2016) and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

The experimental design consisted of 15 minutes of aerobic exercise on a cycle ergometer (Ergoselect 200 K, Fysioline Oy, Tampere, Finland), followed immediately by 15 minutes of sauna exposure. Participants were asked to keep the cadence between 65 and 70 revolutions per minute (rpm) for the entire 15 minutes. The cycling cadence and its indicator lights were in full view of the participant at all times and flashed red when the cadence fell below 65 or surpassed 70 rpm. The cycling load in watts (W) was monitored and adjusted throughout the duration of the exercise to ensure that the heart rate for each participant was kept at 75% of their individual maximum exercise heart rate, pre-calculated using data obtained from a clinical exercise test conducted on a separate day. The transit time from the end of exercise to entering the sauna was <120 s and it was similar for all participants to ensure that the outcomes could be attributed to the combined intervention of exercise and sauna. Sauna exposure was based on a typical Finnish sauna characterized by low humidity and relatively high temperatures (73 ± 2℃).⁷ Fluid was consumed ad libitum throughout the entire experiment.

Systolic and diastolic blood pressure, mean arterial pressure (MAP), pulse pressure, pulse wave velocity (PWV) as a measure of arterial stiffness, the augmentation index (AIx), the left ventricular ejection time (LVET), the diastolic time and heart rate were taken at three different time points: before (PRE), immediately after (POST) and after a 30-minute recovery period (POST30). All measurements at the different time points were measured using the PulsePen device (DiaTecne s.r.l., Milan, Italy; www.pulsepen.com), which consists of one tonometer and an integrated ECG unit, by the same assessor to minimize ascertainment biases and adhered closely to published guidelines.¹⁰ The data are presented as mean ± SD values. The data were analysed for within-group (time) changes with a repeated measures analysis of variance (ANOVA). Within-group differences between POST to PRE and POST30 to PRE values were analysed using pairwise t-tests and the p-values were corrected for Bonferroni by dividing all pairwise p-values by the number of comparisons conducted for each variable. The level for significance was set at p ≤ 0.05. All statistical analyses were carried out using IBM SPSS Statistics v.22 software (IBM Corporation, Armonk, New York, USA).

Table 1 gives the descriptive characteristics of the population. Figure 1 shows the changes in outcome parameters from the experimental protocol of 15 minutes cycling followed by 15 minutes of sauna exposure. Compared with pre-intervention values, significant changes were observed post-intervention for PWV (9.4 versus 8.9 m/s, p < 0.001), AIx (6.8 versus 0.5, p = 0.002), MAP (101 versus 97 mmHg, p < 0.001), LVET (300 versus 269 m/s, p < 0.001) and diastolic time (608 versus 446 m/s, p < 0.001). The effects persisted after 30 minutes for MAP (101 versus 96 mmHg, p < 0.001), AIx (6.8 versus 1.7, p < 0.001), LVET (300 versus 292 m/s, p < 0.001) and diastolic time (608 versus 590 m/s, p = 0.016). Pulse pressure was significantly reduced compared with the pre-intervention values (41 versus 37 mmHg, p < 0.001).

Figure 1.

Changes in arterial stiffness and haemodynamic parameters. Error bars represent 95% confidence intervals. AIX: augmentation index; DBP: diastolic blood pressure; DT: diastolic time; LVET: left ventricular ejection time; MAP: mean arterial pressure; PP, pulse pressure; PWV: pulse wave velocity; SBP: systolic blood pressure.

Table 1.

Characteristics of participants (n = 77).

Patient characteristic
Age (years)	53.3 ± 9.8
Body mass (kg)	83.2 ± 14.8
Body mass index (kg/m2)	27.8 ± 4.2
Resting systolic blood pressure (mmHg)	137.1 ± 15.5
Resting diastolic blood pressure (mmHg)	83.3 ± 9.6
Resting heart rate (bpm)	68 ± 10
Maximum exercise heart rate (bpm)	174 ± 14
Aerobic exercise heart rate (bpm)a	131 ± 11
Sauna habits
Less than once a week	15 (19.5)
Once a week	14 (18.2)
Two to three times per week	30 (38.9)
Four or more times per week	18 (23.4)
Cardiovascular risk classification
Active smoker/history of smoking	12 (15.8)
Diabetes (type 1 or 2)	3 (4)
Dyslipidaemiab	51 (67.1)
Hypertensionc	15 (19.7)
Obesity (body mass index >30 kg/m2)	22 (28.6)
Respiratory diseased	10 (13.2)
Family history of coronary heart diseasee	31 (40.8)

Data are presented as mean ± SD values or n (%).

a

Exercise heart rate was defined as 75% of the individual maximum exercise heart rate.

b

Based on use of cholesterol drugs or serum low-density lipoprotein cholesterol >3.5 mmol/L.

c

Defined as systolic blood pressure >140 mmHg, diastolic blood pressure >90 mmHg or use of antihypertensive drugs.

d

Respiratory disease includes asthma and chronic obstructive pulmonary disease.

e

Positive family history of coronary heart disease if father (<55 years) or mother (<65 years) had premature coronary heart disease.

AIx decreased significantly after a combination of exercise and sauna and, although it may be associated with peripheral vascular changes such as vasodilation from sauna bathing, this decrease in AIx was not mediated by an increase in pulse pressure, as seen in sauna exposure alone, after 30 minutes of recovery.⁷

The similar and parallel changes seen in LVET and PWV were not expected because they have been shown to share an inverse relationship.¹¹ The decrease seen in LVET is indicative of the shortened time taken by the left ventricle to do mechanical work, which normally leads to an increase in PWV. However, our results showed that the PWV was also reduced, which could be attributed to our study protocol. The current study protocol of aerobic exercise followed by sauna exposure also led to significantly lowered pulse pressure during the recovery period. This is comparable with a recent study¹² in which changes to pulse pressure were retained 45 minutes after the end of an acute bout of aerobic exercise. However, our results also showed a reduction in MAP after a 30-minute recovery period. Our study was based on a single group intervention pre–post design, which is a limitation. However, given the pilot nature of the study and limited funding available, we considered this design to be appropriate to investigate the effects of exercise and sauna on cardiovascular function. This study was exploratory, based on the novel nature of the topic, and more advanced study designs will be needed in the future.

Our findings indicate that a combination of aerobic exercise and sauna led to positive alterations in MAP, pulse pressure and AIx, and these changes were retained after a 30-minute recovery period. Therefore the benefits of combining aerobic exercise with sauna use should not be discounted because it may be a gateway to encouraging a more optimum lifestyle. Long-term interventions involving the use of both aerobic exercise and sauna bathing should be investigated because beneficial cardiovascular adaptations may be a possibility.

Acknowledgements

We sincerely thank Timo Harvia and the staff of Harvia Oy for the sauna test facilities, Poikonen Sanna and Pihlajalinna Oy for assistance with recruitment and logistics, and all the participants for dedicating their time to this study.

Author contribution

EL, TL, SKK, PW and JAL contributed to the conception and design of the work. EL, TL, SKK, FZ and JAL contributed to the acquisition, analysis or interpretation of data for the work. EL, PW, SKK and JAL drafted the paper. EL, SKK, HK, PW, FZ and JAL critically revised the paper. All gave final approval and agree to be accountable for all aspects of work ensuring integrity and accuracy.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by Tekes, the Finnish Funding Agency for Technology and Innovation, Helsinki, Finland.