Introduction
Aging is associated with a reduction in cardiac and arterial function with a marked increase in arterial stiffness, resulting in isolated systolic hypertension [
1]. Pulse pressure is a surrogate pulsatile component of blood pressure made up of ventricular ejection, arterial stiffness and wave reflection [
2]. At rest, ventricular ejection does not change over the lifespan [
3] and following 12 months of endurance exercise ventricular ejection does not change at rest [
4]. Therefore, it is suggested that at rest pulse pressure represents either arterial stiffness or wave reflection in older adults [
2]. Furthermore, arterial stiffening is a predictor for a number of vascular diseases including heart failure, stroke and dementia [
5]. Arterial stiffening is a predictor of vascular disease, but is also strongly associated with the loss of physical function and onset of functional limitations of old age [
6].
The development of arterial stiffness has been linked to both abnormal lipid and glucose metabolism [
7]. However, with age there is a decrease in glucose tolerance, resulting in increased fasting and post-prandial blood glucose levels across the lifespan [
8]. In addition, circulating total cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides concentrations can be elevated with age [
9] and are strongly associated with cardiovascular disease risk [
10]. Higher total cholesterol: high density lipoprotein (HDL) cholesterol ratios have been reported in older adults with atherosclerotic alterations compared to those with no atherosclerotic alterations [
11]. The mechanisms linking lipid profile to arterial stiffness are multifactorial, including atherosclerosis, changes in the elastic elements of the arterial wall, endothelial dysfunction and inflammation [
12]. Following 12 weeks of an aerobic and resistance exercise programme there is an improvement in systolic blood pressure, pulse wave velocity and a reduction in lipid profile in obese women [
13]. Likewise, a 5-week aerobic exercise programme has been shown to decrease circulating triglycerides and glycosylated heamoglobin (HbA1c) in older men [
14]. Despite the benefits of aerobic and resistance exercise, the majority of older adults do not take part in traditional exercise with time, dislike of these exercise modes and risk of injury being barriers to exercise participation [
15].
Sprint interval training (SIT) can be a time-efficient exercise paradigm but duration of SIT protocols can vary between 10-min [
16] and 30-min [
17] depending on sprint duration and recovery. Longer SIT protocols have typically utilised 4–6 × 30-s sprints in a 1:8 work to rest interval on 3 days per week and produce similar adaptations to traditional endurance training [
18]. However, these protocols last close to 30 min. To overcome this number of recent studies have looked at utilising 10-min protocols using fewer sprints but still requiring a minimum of 3 training days per week. Metcalfe et al. [
19] demonstrated improved
VO
2 max (13%) and insulin sensitivity (28%) in young males when carrying out 2 × 20-s sprints. Gillen et al. [
20] demonstrate similar improvements in
VO
2 max (12%) in young adults when using 3 × 20-s sprints at a lower resistance and an 8% reduction in mean arterial pressure after 6 weeks of training. Despite this reduction in total time, the use of 20-s sprints may not be appropriate for older adults due to the extended cardiovascular load, which is similar to 30-s sprints in young adults [
21]. Further, these studies still require training to be carried out on 3 days of the week, which may limit people’s ability to follow these protocols. In a middle-aged population, twice weekly SIT sessions consisting of 6–10 × 6-s sprints, with a maximum training duration of 10-min, has been shown to increase
VO
2 peak (8%), decrease blood glucose area under the curve (6%) and improve physical function [
16]. Recently, it has been demonstrated that a progressive SIT protocol performed twice weekly over 6 weeks will also improve physical function and blood glucose control in older adults [
22]. However, the effectiveness of short sprints on blood pressure components has not been investigated.
Longer duration sprints have been shown to improve cardiovascular function and lower blood pressure in young adults [
18]. However, shorter duration sprints have been shown to improve physical function and glucose metabolism in older adults [
22]. Therefore, the aim of this study was to determine the effectiveness of a 10-week extremely short duration SIT protocol (6-s) on blood pressure and health in an older adult population. It was hypothesized that SIT group would have improvements in physical function and resting blood pressure.
Materials and methods
Participants
17 older adults (age range 60–71 years) were recruited for the study via local newspaper advertisement and were allocated using a stratified approach to ensure that baseline age was similar in the control group (CON: three males and four females; Table
1) or a twice per week SIT group (SIT: four females, six males; Table
1). More participants were recruited to the SIT group to allow for potential dropout, although dropout rate was zero. All participants were inactive and participants were excluded if they had any metabolic disease or cardiovascular disease. All participants had well-controlled hypertension (blood pressure ≤ 160/90 mmHg) and were taking oral hypertensive medication which remained unchanged for 6 months prior to and during the study. There was no significant difference in baseline characteristics of the two groups (Table
1), therefore, differences in the group sizes do not bias the result [
23]. Participants allocated to the control group were asked to maintain their normal lifestyle throughout the study period but took part in no structured training. Participants allocated to the SIT group took part in a twice weekly, 10-week SIT intervention, but no other exercise training. All participants were asked to report any changes in lifestyle or medication during the study. All participants provided verbal and written informed consent. The study had ethical approval from Abertay University Ethics Committee (SHS0701615) and conducted in accordance with the declaration of Helsinki.
Table 1
Participant characteristics, physical function and circulating lipids
Participant characteristics |
Age (years) | 66 ± 2 | 66 ± 2 | 66 ± 4 | 66 ± 4 |
Height (cm) | 164 ± 10 | 164 ± 10 | 169 ± 9 | 169 ± 9 |
Weight (kg) | 70 ± 13 | 71 ± 13 | 77 ± 13 | 75 ± 12a |
BMI (kg m−2) | 25.9 ± 3.3 | 26.2 ± 3.5 | 26.9 ± 3.5 | 26.3 ± 3.5 |
Blood measures |
Total cholesterol (mmol l−1) | 4.8 ± 1.4 | 4.8 ± 1.2 | 5.8 ± 1.5 | 4.6 ± 1.3 |
HDL cholesterol (mmol l−1) | 1.1 ± 0.4 | 1.2 ± 0.3 | 1.4 ± 0.4 | 1.5 ± 0.4 |
LDL cholesterol (mmol l−1) | 3.0 ± 0.9 | 2.9 ± 1.0 | 3.6 ± 1.1 | 2.6 ± 1.1 |
Total triglyceride (mmol l−1) | 1.2 ± 0.6 | 1.3 ± 0.8 | 1.7 ± 1.0 | 1.2 ± 0.7 |
TC:HDL-C | 4.2 ± 0.7 | 4.0 ± 0.7 | 4.4 ± 1.1 | 3.2 ± 0.7b |
LDL:HDL-C | 2.7 ± 0.6 | 2.4 ± 0.7 | 2.7 ± 0.9 | 1.7 ± 0.6a |
TG:HDL-C | 1.4 ± 1.0 | 0.9 ± 0.6 | 1.0 ± 0.3 | 1.1 ± 0.6 |
Physical function |
Get up and go (s) | 6.9 ± 1.1 | 6.9 ± 1.0 | 7.4 ± 1.2 | 6.6 ± 1.0b |
Loaded 50 m walk (s) | 37.3 ± 4.3 | 36.8 ± 4.0 | 38.3 ± 4.8 | 34.9 ± 5.1b |
Stair climb power (W) | 208 ± 86 | 200 ± 98 | 253 ± 46 | 285 ± 59a |
Baseline testing
Participant reported to the laboratory having fasted overnight and height was recorded using a SECA 217 Stadiometer (SECA United Kingdom, Birmingham, UK) and weight determined using a SECA Medical 780 weighing scales (SECA United Kingdom, Birmingham, UK).
Blood pressure
Prior to obtaining blood pressure measurements, all participants sat quietly for 5 min with both arms in a forward position, on a flat table surface. Blood pressure, pulse pressure and mean arterial pressure was measured using a WatchBP Office ABI Automatic Office Blood Pressure Measurement Device (Microlife WatchBP AG, Widnau, Switzerland). Triplicate blood pressure measurements were made, with a 1-min interval in-between, and the average value for blood pressure, pulse pressure (pulse pressure = systolic − diastolic pressure) and mean arterial pressure was recorded for both left and right arms. It has been suggested that differences in right and left arm blood pressure provides evidence of peripheral vascular disease and is of clinical importance [
24].
Lipid profile
A finger prick blood sample was taken to allow measurement of lipid profile. The initial blood droplet was discarded and the second blood droplet taken for analysis of fasting lipid levels (CardioChek PA, Polymer Technology Systems Inc, Indianapolis, USA, within run CV for total cholesterol 4.7%, HDL cholesterol 5.9% and triglyceride 4.3%). LDL cholesterol was calculated using the modified Friedewald calculation (LDL-C (mg dl
−1) = non-HDL-C × 90% − TG × 10%; where TG = triglyceride, non-HDL-C = total-C − HDL-C) [
25].
Physical function [26]
Get up and go test: Participants began seated with their arms folded across their chest. On the command go they rose from the chair, without using their arms, and walked 6 m, as fast as possible without running, before sitting down on a chair. This was repeated two times with the average time taken reported.
Loaded 50 m walk test: Participants were instructed to walk 50 m, as fast as possible without running, whilst carrying 20% of their bodyweight for males and 15% of their bodyweight for females. This was repeated two times with the average time taken reported.
Step test: Participants were instructed to ascend the nine stairs (each stair had a height of 16 cm) as quickly as they could. Power was calculated as the product of (total vertical height of the stairs/time) × (body weight × 9.81).
SIT intervention
All SIT sessions were fully supervised and took place at Abertay University. A bioharness 2 (Zephyr Technology, Annapolis, USA) was attached to participants prior to the training session to allow continuous recording of heart rate (bpm) and breathing frequency. Participants then completed 6 × 6-s all-out effort cycle sprints, against 7% bodyweight for males and 6% bodyweight for females, with a minimum of 60-s passive recovery or until heart rate was below 120 bpm. Passive recovery was chosen to allow the heart rate to recover. The cycle sprint began once the participant reached 100 rpm. Each week one extra sprint was added until the participants were completing ten sprints. No warm-up or cool down was performed before or after the session, with no adverse effects reported by any participant. All participants completed 100% of the training sessions. In week 1 training sessions averaged 8 ± 1.5 min and in week 10 training sessions averaged 11.6 ± 0.6 min.
Post-testing
All tests were repeated at the same time of day, with the same fast period and in the same order as baseline after 10 weeks. There was 5 ± 2 days between last training session and retesting of participants. This was to ensure that a training effect has being measured rather than a response to the last training session.
Data and statistical analysis
Heart rate area under the curve for the first 6 sprints in training session 1 and training session 20 was calculated using the trapezoidal rule. Statistical analysis was carried out using SPSS version 23. All data were checked for normal distribution using a Shapiro–Wilk test and was within normal values for skewness and kurtosis. Independent samples
t test was used to determine the differences in baseline characteristics between the groups. Effects of training on each variable were analysed using an ANCOVA to determine difference between groups. A one way repeated measures ANOVA was used to analyse the heart rate area under the curve and average power data from training session 1 and training session 20. Significance was accepted as
p < 0.05. Partial eta squared (
η2) was defined as 0.02 small, 0.13 medium and 0.26 large as proposed by Bakeman [
27]. A Pearson’s correlation was carried out between dependent variables.
Conclusion
In this study, we show for the first time the adaptation in blood pressure and physical function in older adults to a twice-weekly extremely short duration SIT. These results should be considered in context of the limitations of the study and future studies should look to record all medication being taken by participants and seek to record daily activity and nutritional intake across the intervention period. However, there are significant improvements in vascular and physical function and these improvements in physical function are strongly correlated to the improvements in pulse pressure (
R = 0.55), which may reflect greater arterial compliance following SIT. Given that one of time and dislike of traditional exercise are barriers to participation [
20] then there is a need to reappraise current exercise advice for older adults to do 150 min of moderate or 75 min of vigorous intensity exercise a week [
41]. The current study has a much lower time commitment but more research is required to determine minimum effective training load of SIT to promote optimal aging in older adults.