High or Low Intensity Running - What's Better for the Heart of Untrained Men, When the Energy Exp. is Identical?

It takes some effort to avoid making the transition from the sofa to the ICU.

What's better for heart disease protection - high or medium intensity exercise as it is still prescribed by the majority of doctors? A recent study from the University of Erlangen-Nürnberg (Germany) probed the effects of high vs. moderate intensity training on cardiovascular risk markers of 81 untrained, healthy not exactly lean (BMI 27.2kg/m²) men aged 30-50 years.

The subjects were randomized to either a high intensity interval training or a moderate intensity steady state training group who burnt the exact same amount of energy during their workouts.
In contrast to other studies, the groups did not train at the same time. The study started in September. From September to December, the HIIT group performed high intensity interval training

• at 80-100% of their maximal heart rate during 90s-120min intervals,
• with 1-3 min pauses at 70-75% of the maximal heart rate

so that 40% of the total training volume were performed at high heart rates, 35% at maximal heart rates, and 25% of the total volume at 25% of medium heart rates.

Figure 1: Overview of the study protocol (translated from Kemmler. 2015).

During the first three months, the medium intensity steady state group (MIST) group served as sedentary control (see Figure 1). A control group in which the markers of cardiovascular health rather deteriorated than improved.

Figure 2: Changes in left ventricular myocardial mass (LVMI), cardiovascular fitness (CV), intima-media thickness (IMT, associated with increased CVD risk), body fat, and lean mass (Kemmler. 2015).

What is of interest is thus not really the difference between the control and the HIIT group, but the difference between the HIIT and MIST group. A difference of which the data in Figure 2 indicates that there was a significant advantage of doing HIIT vs MIST training - at least as far as the cardiovascular disease markers are concerned.

What may come as a surprise is that despite the significant improvements in fitness and metabolic disease scores (-2.06 pts vs. -1.6 pts with HIIT vs. MIST, respectively), the amount of fat lost was more pronounced in the MIST group; and that in spite of the fact that they performed only 5% of their training at the maximal heart frequency, 10% at high intensities and the vast majority of exercise, i.e. 85%, at a moderate exercise intensity. In view of the fact that the design of the study required that all participants expended the same amount of energy, it's quite interesting that the subjects in the MIST study burned more body fat than the subjects in the HIIT study. In the absence of a strictly controlled energy intake, it's yet no reliable evidence that would disprove the rule that HIIT is - specifically for leaner folks - the more effective fat burner. The result of the study at hand should thus not be overrated.

Figure 2: Endothelial function measured as FMD (left); maximal oxygen uptake (right) before and after 12-week high intensity interval or moderate intensity steady state exercise in patients with heart failure (Wisløff . 2007)

Before I get to the conclusions, I would like to point out that having a exisiting heart condition is not necessarily a reason to refrain from high intensity exercise. On the contrary, a 2007 study by Ulrik Wisløff et al. clearly indicates that aerobic interval training is superior to moderate continuous training even in heart failure patients. More specifically, the scientists from the Norwegian University of Science and Technology in Trondheim found that "[e]xercise intensity was an important factor for reversing LV remodeling and improving aerobic capacity, endothelial function, and quality of life in patients with postinfarction heart failure" (Wisløff. 2007).

Yet in spite of the fact that the researchers  highlight that their results would have "important implications for exercise training in rehabilitation programs" - the impact on the real world prescriptions in such programs is negligible.,
References:

• Beniamini, Yael, et al. "High-intensity strength training of patients enrolled in an outpatient cardiac rehabilitation program." Journal of Cardiopulmonary Rehabilitation and Prevention 19.1 (1999): 8-17.
• Kemmler, Wolfgang, et al. "Hoch-versus moderat-intensive Laufbelastung–Einfluss auf kardio-metabolische Risikogrößen bei untrainierten Männern." DMW-Deutsche Medizinische Wochenschrift 140.01 (2015): e7-e13.
• Tanasescu, Mihaela, et al. "Exercise type and intensity in relation to coronary heart disease in men." Jama 288.16 (2002): 1994-2000.
• Tinkham, Michelle. "Health Promotion in Cardiac Rehabilitation Patients through the Use of a High-Intensity Interval Training Protocol." World Journal of Cardiovascular Diseases 4.10 (2014): 493.
• Warburton, Darren ER, et al. "Effectiveness of high-intensity interval training for the rehabilitation of patients with coronary artery disease." The American journal of cardiology 95.9 (2005): 1080-1084.
• Wisløff, Ulrik, et al. "Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients a randomized study." Circulation 115.24 (2007): 3086-3094.