There is a perception that medium intensity continuous training (MICT) must be part of an exercise program to make training complete, to burn more calories, to lose more weight, or to be completely fit. With more high intensity interval training (HIIT) research studies being done and showing reduced skin folds, total body mass, fat mass, trunk fat, and fasting plasma insulin levels, it is time to ask the question: Which type of exercise is better for fat loss – continuous or interval training?
- Understand the research that compares MICT to HIIT.
- Understand how fitness and metabolic health are influenced by MICT and HIIT.
- Explain the research showing why some participants get little, or no benefit, from doing MICT.
Do We Need to Do MICT?
Testimony to re-thinking the use of MICT with all clients is compelling research indicating that some people do not respond to MICT. Bouchard, et al., (1999) investigated the differences in improvement of V02max with subjects who participated in an identical training program. 481 sedentary adult Caucasians from 98 two-generation families rode cycle ergometers for 20 weeks. They were tested for their V02max on cycle ergometers twice before, and twice after, the training program. The training consisted of exercising at a heart rate of 55% of V02max for 30 minutes/day for 14 weeks. They increased training heart rate to 75% of V02max for 50 minutes/day for 6 weeks. The subjects trained 3 days/week through the entire study.
The results show the average change in V02max was 400 ml/minute. Some subjects increased their V02max by more than 1000 ml/minute. But, many subjects did not improve V02max, or had little improvement. Roth (2007) indicates there is no normal response to exercise. Moreover, trainers can expect clients not to respond to MICT or respond very little, while other clients will have a dramatic response. This is a first clue that some clients need a different type of exercise than MICT in order to get their desired benefits.
Research Comparing MICT to HIIT
Tremblay, Simoneau, and Bouchard (1994), investigated the impact of exercise Intensity on skinfolds and muscle metabolism by comparing moderate-intensity aerobic exercise (MIAE) and HIIT. There were two groups: 1) performed 20-weeks of MIAE by cycling 4 or 5 x/week, 30 to 45 minutes at 60% - 85% of heart rate reserve and 2) a 15-week HIIT group who performed 10 – 15/15 – 30 second intervals then 4 - 5/60 - 90 second intervals at 60% - 70% of their maximum with a recovery heart rate being down to 120-130 beats per minute.
The total energy cost of the two programs was MIAE = 28,757.04 kcals and HIIT = 13,829.17 kcals, a difference of 14,927.87 kcals. The results show the HIIT group decreased sum of 6 skinfolds nine times less than MIAE program. The MIAE group decreased sum of 6 Skinfolds 79.2 to 74.7 mm (4.5 mm) and HIIT decreased sum of 6 Skinfolds 94.2 to 80.3 mm (13.9 mm). There was also significant increase in enzymes promoting fat being used as energy for muscle contraction in the HIIT group.
Trapp, et al., (2008) investigated the effect of high-intensity intermittent exercise training (HIIE) and steady state exercise (SSE) on fat loss and fasting insulin levels of young women. Forty-five women with a mean BMI of 23.2 (20.2 years) were put into one of three training protocols: HIIE, SSE, or a control group. HIIE and SSE groups did 15 weeks of exercise on Monark cycle ergometers.
The HIIE protocol was: 8-seconds all out sprinting and 12- seconds pedaling slowly (20 - 30 rpm’s) for a maximum of 60 repeats per session. The subjects started with a resistance of 0.5 kg and worked as hard as they could during the sprinting phase. Subjects started with as little as 5 minutes in the conditioning phase and gradually increased work time to a maximum of 20 minutes. Once an individual could complete 20 minutes of HIIE at 0.5 kg, resistance was increased by increments of 0.5 kg. The women adapted to the training stimulus rapidly so that by the end of 2 weeks (six exercise sessions), all women were able to complete the full 20 minutes of exercise. Steady state training consisted of a 5minute warm-up then exercised at 60% V02peak starting for 10–20minutes and gradually increasing to a maximum of 40minutes per session.
The results show both groups significantly improved cardiovascular fitness. Only HIIE had a significant reduction in total body mass, fat mass, trunk fat and fasting plasma insulin levels. There was significant fat loss in legs compared to arms in the HIIE group only.
Zhang, et al., (2017) compared the effects of HIIT to prolonged continuous exercise training (PCET) on abdominal visceral fat reduction in obese young women. Forty-three subjects were divided into a HIIT, PCET, or no training control group for 12 weeks.
The HIIT protocol consisted of repeated 4minute cycling bouts at 90% of V̇O2max, followed by 3minute passive recovery until 300 kJ of work was achieved. The HIIT exercise times were as follows: weeks 1-4 = 29.4minutes, weeks 5 – 8 = 37.8minutes, weeks 9 – 12 = 34.4minutes. PCET performed continuous exercise on a cycle ergometer at an intensity of 60% V̇O2max until the targeted 300 kJ of work was achieved. The PCET exercise times were as follows: weeks 1-4 = 51.2minutes, weeks 5 – 8 = 74.4minutes, weeks 9 – 12 = 62.6minutes.
The results showed the HIIT and PCET groups had the same reductions in abdominal visceral fat area (−9.1 cm), abdominal subcutaneous fat area (−35 cm), and combined abdominal visceral fat area and abdominal subcutaneous fat area (−44.7 cm). The HIIT and PCET groups had the same reductions in fat percentage (−2.5%), total fat mass (−2.8 kg), and fat mass of the android (trunk & upper body) (−0.3 kg), gynoid (hips, buttocks, thighs) (−0.5 kg), and trunk (−1.6 kg).
Of interest is the PCET average training time was 62.73minutes compared to the HIIT training time of 33.86 minutes, a difference of 28.87minutes. The authors conclude that PCET had no quantitative advantage compared with HIIT in the reduction of abdominal visceral fat reduction, and that HIIT appears to be the predominant strategy for controlling obesity because of its time efficiency.
Ross, de Lannoy, and Stotz (2015) wanted to investigate the effect of different intensity and duration on improvements in V02max on a treadmill. They wanted to see if it is possible to eliminate “non-responders.” There were 121 middle-aged (53.2 yrs) subjects, 75 females and 46 males, all of whom were abdominally obese. All subjects completed 90% of the 5weekly workouts over 24 weeks.
Subjects performed one of three training protocols: 1) low-amount, low-intensity, 30 minutes at 50% of peak V02 designed to burn 180 – 300 kcals/session, 2) high-amount, low-intensity, 60 minutes at 50% of peak V02, designed to burn 360 – 600 kcals/session 3) high-amount, high-intensity, 40 minutes at 75% of peak V02, designed to burn 360 – 600 kcals/session.
The results show that the number of non-responders at end of study was as follows: 38.5% (15 of 39) in low-amount/low-intensity group, 17.6% (9 of 51) in high-amount/low-intensity group, 0% in high-amount/high-intensity group. The authors show that low-intensity exercise amounting to 150 minutes/week was insufficient to improve cardiovascular fitness for 38.5% of subjects. This is what most physical activity guidelines recommend for all adults to do.
Medium intensity continuous training has its’ place in the training program for many clients. Many clients, and trainers, like it because it is easy to do, it can be done almost anywhere, it is easy to monitor the intensity and duration, and many clients see and feel results that make them happy. However, showing a small cross-section of HIIT studies comparing interval training to MICT, it appears there may be benefit to consider HIIT in the training program for clients who are not getting results from MICT or who want to lose more fat.
Bouchard. C., et al., (1999). Familial aggregation of VO(2max) response to exercise training: Results from the HERITAGE Family Study. Journal of Applied Physiology, 87(3),1003-1008.
Ross, R., de Lannoy, L. & Stotz, P.J. (2015). Separate effects of intensity and amount of exercise on interindividual cardiorespiratory fitness response. Mayo Clinic Proceedings, 90(11),1506-1514.
Roth, S. M. (2007). Genetics primer for exercise science & health. Champaign, IL: Human Kinetics.
Trapp, et al., (2008). The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. International Journal of Obesity, 32(2), 684–691.
Tremblay, Simoneau, & Bouchard. (1994). Impact of exercise intensity on body fatness and skeletal muscle metabolism. Metabolism 43(7), 814–818.
Zhang, et al., (2017) Comparable effects of high-intensity interval training and prolonged continuous exercise training on abdominal visceral fat reduction in obese young women. Journal of Diabetes Research, 2017:5071740. doi: 10.1155/2017/5071740.