An HIIT approach for special populations
Gibala and colleagues2 found consider- able evidence that HIIT is a “potent” and time-efficient training method for cardiovascular and musculoskeletal adaptations that lead to better health. More large-scale and long-term stud- ies are needed, they say, to determine HIIT’s effects in reducing disease risk or improving health in people with chronic disease. Preliminary evidence from some studies shows improved cardiorespira- tory fitness for some populations:
• people with coronary artery disease
• individuals with congestive heart failure
• adults in middle age with metabolic syndrome
• obese individuals
In many cases, cardiovascular fitness after HIIT was better when compared to moderate-intensity training.
Other studies found that HIIT led to improvements in the endothelium (the lining of the blood vessels). The brachial artery in the upper arm also dilated to a greater extent during HIIT compared to continuous aerobic training. In ad- dition, while more studies are needed, investigations have shown that as few as 6 sessions of HIIT over a 2-week period improves estimated insulin sensitivity in previously sedentary, overweight adults. What is unclear is the exact intensity and minimal volume that results in healthy outcomes, achieved in a shorter time frame.
Whitehurst3 examined HIIT studies and implications for older adults and people with heart disease. The data revealed that compared to endurance training, HIIT was associated with improved stroke volume and left-ventricular heart health; HIIT participants also had greater cardiorespiratory benefits. Stud- ies that included coronary heart disease patients measured HIIT workouts per- formed over periods ranging from 4 to 16 weeks, designed as follows:
Work: 4 minutes at 85–95% heart rate maximal (HRmax)
Recovery: 3 minutes
Work/recovery cycle: repeated 4–6 times (28–42 minutes)
Three studies with healthy older adults performed from only one bout of exer- cise to 6 weeks of HIIT with the follow- ing workout:
Work: 30 seconds at “all out” effort
Recovery: 4–5 minutes
Work/recovery cycle: repeated 4–7 times (~20–35 minutes)
In addition to mitochondria improve- ments, these studies reported increases in the muscles’ maximal capacity for oxygen use and fat loss beneath the skin. During one 52-week study, patients with coronary heart disease exercised 60 min- utes, without using a structured work/ recovery cycle, at an intensity that varied between 70 and 90% of maximum oxy- gen consumption (VO2max). Investiga- tors reported improved insulin sensitiv- ity, possibly providing exercise strategies for those with type 2 diabetes.
Even older adults with limited capaci- ty appear to tolerate HIIT, the author concluded. For high-risk older adults, a preprogram moderate-to-aggressive cycle ramp test was recommended to identify a participant’s exercise capaci- ty and help individualize the program. High-effort, “all out” intervals of less than one minute may be beyond the car- diovascular or musculoskeletal capacity of unconditioned older adults or those with diseases, the author acknowledged, but older individuals should consider HIIT a viable alternative to continuous aerobic training.