What You Need to Know

In this study, the researchers sought to quantify the acute metabolic response to reduced-exertion high-intensity interval training (REHIT) performed on the CAROL bike, as well as the excess post-exercise oxygen consumption (EPOC) following those workouts. This study compared the metabolic response and EPOC to steady-state treadmill exercise at both a moderate and vigorous intensity. While the CAROL rides, which were of a shorter duration than the treadmill workouts, burned fewer calories during the exercise bout, the EPOC was much more significant in terms of both intensity and duration. Why is this important? This study reveals one of the reasons why REHIT elicits comparable benefits to traditional moderate-intensity exercise of a longer duration: The benefits of REHIT continue to accumulate as you go about your day, which means that you’ll burn more calories and see further training adaptations over time.

There is a dose-response relationship between energy expenditure and multiple health outcomes, including cardiorespiratory fitness, risk of coronary artery disease and all-cause mortality, type 2 diabetes and obesity. Importantly, the overall energy expenditure of a bout of exercise consists of the calories burned during the exercise itself as well as any increased caloric expenditure above the resting metabolic rate that occurs during the recovery period. This post-exercise energy expenditure is known as excess post-exercise oxygen consumption, or EPOC.

Because EPOC contributes approximately 6 to 15% to a person’s overall exercise energy expenditure, it can be an important—but often overlooked—consideration when designing exercise programs for clients.

Lance Dalleck, PhD, and his team of researchers in the High Altitude Exercise Physiology Program at Western Colorado University set out to quantify EPOC following reduced-exertion high-intensity interval training (REHIT)—which is a modified, shorter-duration form of high-intensity interval training (HIIT). The research team used the CAROL bike, a stationary bike that incorporates REHIT, which shortens the traditional HIIT workout by using fewer and shorter sprints, though those sprints are performed at a supra-maximal intensity. According to the manufacturer’s website, the bike uses a form of artificial intelligence that controls the resistance and timing on the rides and adjusts the resistance to each individual’s level of both power and fatigue, helping them get progressively fitter and stronger.

ACE sponsored two previous studies exploring REHIT on the CAROL bike. The first quantified the acute and chronic responses and found that the workouts elicited more potent and time-efficient improvements in cardiorespiratory fitness and cardiometabolic health when compared to traditional moderate-intensity continuous training. The second investigated whether this form of exercise can combat the harmful effects of a sedentary lifestyle and found that REHIT elicits improvements in measures of cardiometabolic health and can be an important, time-efficient strategy to incorporate into a client’s workout regimen.

The current study sought to build on those earlier studies by quantifying both the acute metabolic responses to the CAROL bike’s “fat burn” and “intense” rides (see descriptions below) and the excess post-exercise oxygen consumption (EPOC) following these two rides.  

The Study

The researchers recruited 20 participants between 25 and 76 years of age, none of whom had any evidence of cardiovascular, pulmonary and/or metabolic disease (Table 1). The participants initially completed a trial to quantify resting metabolic rate and performed graded exercise testing to determine their maximal oxygen uptake (VO2max). They then completed a total of five rides to familiarize themselves with the CAROL bike prior to the initiation of the study. 

Table 1

Participant Characteristics

 

Participant

Age

(years)

 

Sex

Height

(cm)

Weight

(kg)

VO2max

(mL/kg/min)

1

30

F

170

73

52.4

2

25

M

188

69

59

3

33

F

175

58

45.8

4

29

M

170

72

61.3

5*

37

F

163

64

47.5

7

44

F

163

50

33.2

8

39

M

175

94

54.7

9

52

F

165

62

36.6

10

49

M

191

98

50.4

11

47

F

173

71

41.9

12

50

M

185

64

44.5

13

55

F

158

58

29.1

14

57

M

191

87

34.8

15

61

F

177

72

25.3

16

63

M

180

81

30.1

17

66

F

165

67

34.1

18

69

M

178

75

28.5

19

72

F

167

79

29.2

20

76

M

187

95

28

Mean

49.8

---

175.3

73.7

41.2

SD

15.1

---

10.1

13.1

11.7

Range

25–76

---

158–191

50–98

25.3–61.3

*Participant 6 withdrew from the study before pilot testing was completed.

The participants then performed, in random order, four separate trials—two rides on the CAROL bike and two bouts of treadmill exercise—during which were collected to quantify the acute metabolic responses and EPOC. Energy expenditure was calculated from the gas exchange data and then quantified using the VO2 data. After each trial, the participants sat until their post-exercise VO2 had returned to their resting metabolic rate levels.

CAROL rides

  • Intense ride: Two-minute warm-up, a 20-second sprint, a three-minute recovery, a second 20-second sprint, and a three-minute cool-down (total workout time – 8:40)
  • Fat burn ride: Two-minute warm-up, 30 eight-second sprints with 12 seconds of rest in between, and a three-minute cool-down (total workout time – 15:00)

Treadmill exercise

  • Moderate-intensity workout: 55–59% of heart-rate reserve (HRR) (total workout time – 30:00)
  • Vigorous-intensity workout: 75–80% HRR (total workout time – 20:00)

The Results

Individual power output and physiological responses to the CAROL intense and fat burn rides are presented in Table 2. Individual resting oxygen uptake and metabolic responses to the two rides are presented in Table 3.

Table 2

Power Output and Physiological Responses to CAROL Intense and Fat Burn Rides

 

 

 

Participant

 

 

Target HR

(bpm)

CAROL

Intense Ride

CAROL

Fat Burn Ride

Peak Power

(Watts)

Total Power

(Watt-seconds)

Max HR

(bpm)

Peak Power

(Watts)

Total Power

(Watt-seconds)

Max HR

(bpm)

1

152–171

635

22,946

152

286

53,794

151

2

157–176

646

20,791

148

365

56,437

155

3

150–168

480

18,386

141

176

40,511

141

4

153–172

655

19,890

144

362

62,699

154

5*

146–165

414

17,460

143

203

46,543

136

7

141–158

396

17,151

138

136

33,603

122

8

145–163

814

21,223

151

557

75,889

162

9

134–151

469

20,206

153

164

39,217

137

10

137–154

757

21,463

144

568

72,884

168

11

138–156

309

15,679

147

191

42,801

133

12

136–153

511

18,444

145

238

45,634

140

13

124–140

291

17,951

133

137

34,501

127

14

130–147

583

18,611

147

263

50,466

140

15

127–143

338

16,001

138

167

39,462

136

16

127–143

597

21,635

151

198

40,136

144

17

123–139

305

16,082

120

180

31,737

122

18

121–136

439

17,088

139

183

38,065

133

19

118–133

353

18,088

135

145

33,285

132

20

115–130

354

16,568

129

194

36,851

128

Mean

---

492

18,719

142

248

46,027

140.1

SD

---

159

2,162

8.5

129

13,009

12.9

Range

115–176

291–814

15,67922,946

120–153

136–568

31,737–75,889

122–168

*Participant 6 withdrew from the study before pilot testing was completed.

Note: HR = Heart rate; bpm = Beats per minute; Max HR = Maximal heart rate; SD = Standard deviation 

Table 3

Resting Oxygen Consumption and Metabolic Responses to CAROL Intense and Fat Burn Rides

 

 

 

Participant

 

 

Resting VO2

(mL/kg/min)

CAROL

Intense Ride

CAROL

Fat Burn Ride

Exercise

(kcal)

EPOC

(kcal)

EPOC duration

(min)

Exercise

(kcal)

EPOC

(kcal)

EPOC duration

(min)

1

3.45

38

98

95

84

204

210

2

3.82

52

104

90

105

212

185

3

3.34

42

87

70

88

183

160

4

3.86

55

96

100

116

201

235

5*

3.36

43

82

60

89

167

115

7

3.38

37

69

65

79

161

145

8

4.13

59

137

110

133

295

225

9

3.55

40

78

70

92

163

155

10

3.87

61

121

95

146

262

220

11

3.48

36

83

85

83

171

185

12

3.69

46

86

75

98

183

170

13

3.39

30

77

105

69

161

220

14

3.63

51

90

80

111

195

165

15

3.35

32

70

50

73

153

105

16

3.81

47

98

70

101

211

145

17

3.75

29

61

55

67

144

135

18

4.13

43

79

60

95

164

120

19

3.71

34

67

65

75

139

145

20

4.37

49

84

70

103

167

140

Mean

3.69

43.4

87.7

77.4

95.1

186.1

167.4

SD

0.3

9.5

18.6

17.6

21.0

39.4

39.6

Range

3.34–4.37

29–61

61–137

50–110

67–146

139–295

105–235

*Participant 6 withdrew from the study before pilot testing was completed.

Note: VO2 = Oxygen uptake; EPOC = Excess post-exercise oxygen consumption; SD = Standard deviation

The overall energy expenditure (i.e., caloric expenditure during exercise + calories burned via EPOC) of the two CAROL rides and the two bouts of treadmill exercise are presented in Figure 1.

Figure 1
Energy expenditure of traditional moderate-intensity and vigorous-intensity treadmill (TM) exercise compared to CAROL intense and fat burn rides

Figure 2 illustrates the EPOC following each of the four bouts of exercise. As you can see, there was a statistically significant increase (p<0.05) in post-exercise metabolism, as evidenced by a greater EPOC, when individuals performed either of the CAROL rides when compared to the treadmill exercise. In fact, that magnitude of EPOC following the fat burn ride was more than 2.5 times greater than following vigorous-intensity treadmill exercise, while EPOC following the intense ride was two times greater than following moderate-intensity treadmill exercise.

Figure 2
The EPOC following moderate-intensity treadmill exercise, vigorous-intensity treadmill exercise, CAROL intense ride and CAROL fat burn ride

In addition to quantifying the intensity of EPOC, the researchers looked at the duration of EPOC after each of the four exercise bouts (see Table 3). They found that the duration of EPOC following the CAROL fat burn ride was statistically significantly (p<0.05) longer—actually more than twice as long—when compared to the CAROL intense ride (Figure 3).

Figure 3
Duration of EPOC following intense CAROL rides (upper panel – gold) and fat burn CAROL rides (lower panel – orange)

The Bottom Line

According to the research team, the most important findings of this project are twofold. First, it provides gold-standard measures of the exercise energy expenditure to be expected during both the fat burn and intense rides on the CAROL bike. And second, it provides scientific evidence to support the notion that personalized, true REHIT performed on the CAROL bike contributes to a significantly greater increased post-exercise metabolism (i.e., EPOC) when compared to more traditional moderate-intensity or vigorous-intensity exercise.

So, what is the benefit of the extended and elevated EPOC?

Exercise guidelines often talk about the benefits of exercise being tied to energy expenditure, but it’s important to understand that energy is expended both during and after a bout of exercise. This study reveals one of the mechanisms by which REHIT can elicit comparable benefits to traditional moderate-intensity exercise of a longer duration. As Dr. Dalleck explains, “The benefits of this type of training continue to accumulate as you go about your day, which will drive further training adaptations.”

Dr. Dalleck also highlights the fact that, in addition to enhancing training adaptations, “Meaningful EPOC, over the long term, can have an important impact on the overweight and obesity epidemic.” Daily occupation-related energy expenditure has decreased by approximately 140 calories over the past several decades, and this reduction in energy expenditure accounts for a significant portion of the increase in mean U.S. body weights for both women and men. Therefore, it’s vital that we find other ways to increase calorie burn to counter the negative effects of an increasingly common sedentary lifestyle. HIIT and REHIT are often talked about in terms of their performance and fitness benefits, but this research shows that ramping up EPOC over the long haul can also help people achieve weight-loss and weight-maintenance goals.

This study was first published in the peer-reviewed International Journal of Research in Exercise Physiology.