How HIIT Can Improve Cardiovascular Function

Contributed by Sarah L West, PhD, Assistant Professor of Kinesiology, Trent University

As we have learned through the research pieces highlighted on Fast Twitch Grandma, aging is associated with many physiological changes. One such example is the cardiovascular system, which undergoes many alterations with aging. Vascular function (i.e., how well your blood vessels are working), and the structure of the vascular system transform in way that increases one’s chance of heart attack or other negative cardiovascular events (i.e., the blood vessels get stiffer and don’t function as well).

Exercise can improve many aspects of health in the aging population. Our team has highlighted this in research discussions that demonstrate that exercise improves psychological well-being, preserves brain function, and reduces the risk of dementia. Exercise also has a positive impact on the cardiovascular system. Despite these (and numerous more) advantages, many older adults remain inactive (an issue we are trying to address by disseminating information through Fast Twitch Grandma!).

High intensity interval training (HIIT) has been a large focus of our research article reviews, and for good reason. HIIT is an effective exercise method to improve health through shorter bouts of highly intensive exercise. A large advantage of HIIT is you receive the beneficial effectiveness of exercise but with less time commitment. This may then lead to increased compliance. Typical HIIT training protocols suggest that exercise sessions should occur at least twice per week. However, older adults can take longer to recover from exercise or physical stress, and therefore traditional HIIT protocols may be too difficult for the aging population.

With this in mind, Grace and colleagues developed a research study to look at the effects of low-frequency HIIT training (defined in their study as one session of HIIT every 5 days) on vascular function in older males. They had 2 different groups; aging males who were largely sedentary all their life, and compared them to aging males who had been life-long exercisers. The authors hypothesized that the life-long sedentary group would have worse vascular function compared to the life-long exercisers. They also guessed that a low-frequency HIIT program would improve vascular function.

Overall, 22 life-long sedentary men and 17 life-long active men were evaluated in the study. The average age of the men was ~62 years of age. The life-long sedentary men weighed more, and had a higher body mass index compared to the life-long exercisers. Prior to engaging in the HIIT program, the sedentary group underwent a 6-week progressive and supervised exercise conditioning phase (for safety and familiarization reasons). In this 6-week phase, the sedentary men increased their activity levels to meet the suggested activity guidelines (150 minutes per week). After the conditioning phase, both the life-long sedentary and exercising men underwent the low-frequency HIIT program for 6 weeks (which consisted of 30 seconds of cycling sprints, 6 times, with 3 minutes of recovery, once every five days). Flow mediated dilation (which assesses vascular function) was measured before and after each training phase. Lower flow mediated dilation indicates worse vascular function. Before any intervention, the life-time sedentary men had a lower flow mediated dilation (i.e., worse vascular function) compared to the life-time exercisers.

Following the 6-week conditioning phase, the life-time sedentary group’s flow mediated dilation increased (i.e., improved), and was no longer lower then the life-time exercisers. Following the 2nd 6-week phase (the low frequency HIIT program), flow mediated dilation did not improve in either of the life-time sedentary or exercising groups. Therefore, this study demonstrated that structured, progressive conditioning improves vascular function in previously sedentary men, but that a low frequency HIIT program does not further improve vascular function in men who were previously sedentary, or active. Although it appears that the findings of this study are negative, it should be noted that even though the low frequency HIIT program did not further improve vascular function, it was enough to maintain vascular function in both groups.

So what can we take away from this article? The main message may be that exercise in general is a potent intervention to improve vascular function, but that a very low-frequency HIIT program may not be enough to further improve vascular function.   Engaging in low-frequency HIIT can maintain vascular function, but perhaps to see improvements an increased frequency HIIT program is necessary. More studies are needed in this area to determine the number of times per week that HIIT should be done for the best vascular benefits (but it appears that once per week is not enough). So get out there and exercise… more than once per week!

Sources:

Grace FM, Herber P, Ratcliffe JW, New KJ, Baker JS, Sculthorpe NF. Age related vascular endothelial function following lifelong sedentariness: positive impact of cardiovascular conditioning without further improvement following low frequency high intensity interval training. Physiological Reports, 3(1), 2015.