Effects of using high-intensity interval training and calorie restriction in different orders on metabolic syndrome: A randomized controlled trial

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Effects of using high-intensity interval training and calorie restriction in different orders on metabolic syndrome: A randomized controlled trial Rina So Ph.D. , Tomoaki Matsuo Ph.D. PII: DOI: Reference:

S0899-9007(19)30249-7 https://doi.org/10.1016/j.nut.2019.110666 NUT 110666

To appear in:

Nutrition

Received date: Revised date: Accepted date:

31 May 2019 11 November 2019 26 November 2019

Please cite this article as: Rina So Ph.D. , Tomoaki Matsuo Ph.D. , Effects of using high-intensity interval training and calorie restriction in different orders on metabolic syndrome: A randomized controlled trial, Nutrition (2019), doi: https://doi.org/10.1016/j.nut.2019.110666

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Highlights 

High-intensity interval training (HIIT) and calorie restriction (CR) improved cardiorespiratory fitness and metabolic syndrome risk factors.



Intervention order with HIIT and CR has no influence on risk factor improvement.



A single weekly HIIT can potentially help maintain an increase in CRF

1

Effects of using high-intensity interval training and calorie restriction in different orders on metabolic syndrome: A randomized controlled trial

Running head: Intervention order and metabolic syndrome

Rina So Ph.D.1,2, Tomoaki Matsuo Ph.D.1,2

1

Occupational Epidemiology Research Group, National Institute of Occupational Safety and Health, Japan

2

Research Center for Overwork-Related Disorders, National Institute of Occupational Safety and Health, Japan

Corresponding author: Rina So, Ph.D Nagao 6-21-1, Tama-ku, Kawasaki 214-8585, Japan Phone: +81-44-865-6111 (Ext. 8409); Fax: +81-44-865-6116 E-mail: [email protected]

2

Declarations of interest: none Author contributions: Substantial contributions to study conception and design: RS and TM; data acquisition: RS and TM; data analysis: RS; data interpretation: RS and TM; drafted the article: RS and TM.

Abbreviations: HIIT, high-intensity interval training; CR, calorie restriction; MetS, metabolic syndrome; VO2peak, peak oxygen consumption; MICT, moderate-intensity continuous training; CRF, cardiorespiratory fitness; WL, workload; FGs, food groups; WC, waist circumference; HR, heart rate; TG, triglyceride

3

Abstract Objective: Studies of the effectiveness of high-intensity interval training (HIIT) combined with calorie restriction (CR) are very limited, and the most effective order of intervention is unclear. Therefore, we investigated the impact of time-efficient HIIT with CR intervention on metabolic syndrome (MetS) and the impact of the intervention order on changes in MetS risk factors. Research Methods & Procedures: Thirty-two subjects with MetS underwent an 11-week intervention program comprising 8 weeks of HIIT and 3 weeks of CR. Subjects were randomly assigned to either the HIIT-then-CR or CR-then-HIIT groups. Thereafter, the CR-then-HIIT group performed a further 8 weeks of training once per week after the initial ． intervention period. Risk factors for MetS and VO2peak were assessed during the entire study period. Results: During the 11-week intervention period, body composition, MetS risk factors, and ． VO2peak significantly improved in both groups. No significant differences in these improvements were attributable to the intervention order; nonetheless, there was a tendency toward larger effect sizes in the CR-then-HIIT group. During the postintervention period (8 ． weeks), a single weekly HIIT session prevented VO2peak reduction in the CR-then-HIIT group (-2.0 ± 7.2%; P = 0.31). Conclusion: The time-efficient intervention program with HIIT and CR had a beneficial 1

effect on MetS; however, the intervention order had no influence on the changes in risk factors.

Clinical trial registration: #UMIN000029325 Keywords: intervention order, cardiorespiratory fitness, diet, weight-loss, HIIT

2

Introduction Lifestyle intervention with exercise and calorie restriction (CR) is a well-known clinical approach for treating metabolic syndrome (MetS) [1]. However, individuals with MetS are often not familiar with exercise training and dietary modification. A concurrent program comprising exercise and CR may generate synergistic effects [2]; however, it may be inconvenient to many due to time constraints and a sense of rebellion against drastic lifestyle changes [3]. This may be one of the reasons why MetS rates continue to increase. Therefore, time-consuming interventions involving traditional moderate-intensity continuous training (MICT) or a prolonged CR program may not be appropriate for our time-pressed society, and other evidence-based strategies should be considered as treatment for MetS. Recently, high-intensity interval training (HIIT) has been indicated as a highly effective, time-efficient exercise method, that promotes health benefits [4, 5]. In particular, HIIT has a positive impact not only on cardiac function of low-fitness individuals [4, 6] but also on blood values of individuals with MetS [7-10]. Despite HIIT having a substantially shorter duration and lower exercise volume than MICT, some studies [11, 12] have shown that HIIT results in similar or better improvements in MetS risk factors compared with MICT. In addition, clinical evidence supports HIIT as a safe therapy for the majority of individuals at high risk [4, 5]. These results suggest that combining HIIT with CR may be the most effective approach for improving MetS and achieving definitive weight loss. However, the best 3

approach to HIIT along with CR for MetS treatment remains unclear. Only two previous studies have reported that the benefits of HIIT combined with CR include improvements in weight loss and overall MetS components. Mora-Rodriguez et al. [13] demonstrated the positive effects of simultaneous (HIIT and CR) and sequential (HIIT first and then CR) applications on MetS and weight loss. Matsuo et al. [12] investigated the effects of a combined program with separate HIIT and CR intervention components (i.e., 4-week CR intervention following 8-week HIIT intervention) on MetS risk factors. Despite HIIT having a lower exercise volume than MICT, the two exercise training sessions had similar favorable effects on the risk factors, and adding CR intervention after exercise intervention had a strong influence on metabolic risk factors. Interestingly, these previous studies concluded that HIIT first followed by CR may have similar or better efficacy than conventional intervention methods (i.e., simultaneous or MICT). Mora-Rodriguez et al. [13] explained that as HIIT results in considerable depletion in muscle glycogen [14] requiring abundant carbohydrate ingestion [15] for its restoration, concurrent HIIT and CR does not provide necessary replenishment. This evidence showed that it is possible that the effects of HIIT first may have a continuous positive impact on the following non-exercise CR period. In addition, although CR induced weight loss reduces MetS complications, it does not reflect changes in body composition [14]; it cannot expect the additional effect of doing CR first. Conversely, reports suggest that increased mitochondrial density and capacity following HIIT 4

leads to increased fat oxidation [15], as well as enhancements in catecholamines, which have been shown to drive lipolysis [16]. Therefore, these possible mechanisms of HIIT-induced fat metabolism may contribute to the effectiveness of the program with HIIT first and then CR.

However, to our knowledge, the efficacy of the intervention order of the program comprising HIIT and CR for subjects with MetS has not been addressed. In contrast, one study [12] showed that cardiorespiratory fitness (CRF) was remarkably improved in the HIIT group during exercise training; however, it decreased after stopping HIIT (i.e., during the CR intervention without exercise period). It is important to determine the methods for maintaining improved CRF among subjects with MetS, as CRF is a powerful predictor of mortality in this population [17]. The present study aimed to investigate the effects of a time-efficient HIIT and CR intervention program on MetS risk factors. Moreover, we aimed to test the hypotheses that the intervention order influences MetS risk factors, i.e., the more positive effects cannot be expected with CR first and then HIIT.

Materials and Methods Study design and setting This study was 23-week single-center randomized controlled open-label and blinded outcome assessment study of two parallel groups. It was conducted at Kurosawa Hospital 5

(Takasaki, Gunma, Japan) between August 2016 and March 2017. The study protocol was reviewed and approved by Ethical Committee of the National Institute of Occupational Safety and Health, Japan. It was also registered in the UMIN Clinical Trials Registry (#UMIN000029325). Study procedures were performed according to the guidelines proposed by the Declaration of Helsinki.

Subjects Fig. 1 presents the schematic diagram of the study phases. Subjects were recruited from the Kurosawa Hospital (Takasaki, Gunma, Japan) via mail. The inclusion criteria were as follows: age 30–59 years and meeting the Japanese definition for MetS or pre-MetS [18] based on a medical examination performed within 1 year of the study at Kurosawa Hospital. Among the initial 33 entries, 32 were selected according to the following additional inclusion criteria: attending work at least three times per week, no participation in regular exercise activities (≤1 session per week, ≤30 minutes per session) during the past year; and no adverse medical problems based on the results of a resting electrocardiogram test administered by a physician. The study purpose and design were fully explained to all subjects before obtaining written informed consent.

6

Fig. 1. Schematic diagram This randomized controlled trial comprised an initial intervention program (11 weeks) followed by postintervention (8 weeks). Following inclusion and baseline measurements at week 0, the subjects were randomly assigned (1:1 ratio) to one of two groups using block ． randomization (age and VO2peak) after stratification by sex using a simple method (Excel 2010; Microsoft, Washington, DC, USA). Both groups participated in the intervention program for 11 weeks (i.e., 3 weeks of CR and 8 weeks of HIIT) in reverse order. The HIIT-then-CR group performed HIIT then CR, while the CR-then-HIIT group performed CR followed by HIIT. The HIIT-then-CR group participated in 8 weeks of non-intervention, and 7

the CR-then-HIIT group participated in an 8-week regimen of HIIT once weekly. Consequently, all subjects completed the 19-week study program; there were no dropouts.

Exercise training program All subjects participated in the main program that lasted 8 weeks, and were required to perform HIIT 3 days per week. The exercise training room was open from 17:00 to 21:00 every day. Subjects chose their own schedules and exercised under the supervision of trainers. Intensity and adaptation during HIIT were checked by trainers during every session. Detailed descriptions of the HIIT regimens have been reported previously[12, 19]. In summary, HIIT ． comprised three 3-minute cycling exercises at 80–85% peak oxygen uptake (VO2peak) with 2 ． minutes of active rest at 50% VO2peak between sets, resulting in a 15-minute session (including 1 minute of warm-up and 1 minute of cool-down)[12]. To determine each subject’s ． exercise intensity, the VO2peak measurement data were used, and a simple linear regression equation for each subject was calculated. The exercise intensity for each subject was ． recalculated and adjusted following the monthly recording of VO2peak measurements. During the 2 weeks after exercise intensity was adjusted, the workload (WL) gradually and progressively increased until the calculated WL was reached. Subjects were instructed to maintain their usual dietary intake for the duration of HIIT.

8

Calorie restriction program The 3-week, once weekly CR program (three 90-minute sessions) mainly comprised lectures, practical training sessions, and subject counselling. Subjects attended a group lecture led by a trained lecturer and three dieticians. The group lecture sessions occurred on Wednesday nights (19:00–20:30). Detailed descriptions of the dietary program have been reported previously [12]. In summary, the program was based on the four food groups (FGs) point method as follows: FG1 (dairy products and eggs), FG2 (meat, fish, and beans), FG3 (vegetables and fruits), and FG4 (grains, oil, and sugar). To simplify calculations for energy intake and nutrient balance, a cluster of foods equal to 80 kcal was equivalent to 1 point using this method. Each session included lectures and practical training regarding the methods of recording dietary intake, calculating daily intake (kcal to point), methods of incorporating meal replacements, and modifying meals. Only one subject in the HIIT-then-CR group was absent once, and we offered a supplementary lecture on another day. The subjects kept a daily log, in which they recorded in detail every food they ate during the 3-week CR period; however, we stopped any approach related to CR and subjects also stopped recording a diary when the CR period ended. Subjects were instructed to refrain from other exercise activities during the CR period.

Measurement procedures 9

All subjects underwent anthropometric measurements and evaluations of MetS risk factors and CRF at baseline (week 0), after the CR program, at the halfway point of the exercise program, after the exercise program ended (week 11), and at the end of postintervention (week 19). Total energy intake in kilocalories was assessed at baseline, during intervention (weeks 1- 11 weeks), and during postintervention (weeks 12-19) in each group. Total daily steps were measured during the entire study period. All tests were scheduled at least 2 days after the last exercise training session to examine the long-term effects of the exercise program. Blood samples were collected from the antecubital vein in the morning after a 12-h overnight fast. Subjects were instructed not to perform vigorous physical activity or consume alcohol within 24 h of these measurements. Moreover, they ． were instructed to complete the two test examinations (one at the laboratory for VO2peak and one at the hospital for measurements such as those for MetS risk factors) within the same week.

Anthropometric measurements Anthropometric measurements were performed for barefoot subjects dressed in underwear only. Body weight and fat mass were measured with an InBody device (InBody 270; Biospace, Seoul, Korea) that incorporated weight scales and measured both weight and bioimpedance. Height was measured once to the nearest 0.1 cm using a wall-mounted 10

stadiometer (YG-200; Yagami, Nagoya, Japan). The waist circumference (WC) was measured directly on the skin surface at the umbilicus while the subjects were in the standing position. The WC measurements were recorded in duplicate to the nearest 0.1 cm and averaged.

Cardiorespiratory fitness ． VO2peak was determined by a graded exercise test using a cycling ergometer (75XL III; Konami, Tokyo, Japan)[20]. After a 2-minute warm-up at 15 W, the exercise protocol was started at 30 W. The work load was increased by 15 W every minute until volitional ． exhaustion. VO2peak values were accepted only if the subjects met the following criteria: highest respiratory exchange ratio >1.10, heart rate (HR) near (<90%) the age-predicted maximum (220 - age beats/min), and inability to continue bicycle pedaling owing to ． ． exhaustion. During the test, VO2 and carbon dioxide production (VCO2) were measured using the mixing chamber method with an open-circuit computerized indirect calorimeter (AE-310S; Minato Medical Science, Osaka, Japan). The gas analyzer was calibrated before each trial. The HR at rest and during the exercise test were monitored using an electrocardiogram monitor (Dynascope; Fukuda Denshi, Tokyo, Japan).

11

Dietary assessments and total daily steps A method that involved recording weight and dietary data for 3 days was used to determine the total energy intake. During each 3-day period, subjects obtained photographs of their food and recorded the names and amounts of every food item they consumed. A skilled dietician performed an assessment using the recorded sheets and photographs and codified the food items and food weights. The dietary data were analyzed using a standard system software analysis tool (Eiyoukun version 6.0; Kenpakusya, Tokyo, Japan). The total daily steps were objectively measured using an accelerometer (HJA-750C; Omron Healthcare Co., Kyoto, Japan) during the entire study period.

MetS risk factors Systolic and diastolic blood pressures were measured using a mercury manometer after the subject rested for at least 20 minutes in a seated position. Serum concentrations of total cholesterol (TC) and triglycerides (TG) were determined using an enzymatic method (Kyowa Medex, Tokyo, Japan for both), and high-density lipoprotein cholesterol (HDLC) was measured using the heparin-manganese precipitation method with determiner HDLC (Kyowa Medex, Tokyo, Japan). Fasting plasma glucose (FPG) was assayed via the glucose oxidase method [21] using L-Type Glu 2 (Wako Pure Chemical Industries, Osaka, Japan), and hemoglobin A1c (HbA1c) was determined using the enzymatic method (Kyowa Medex, 12

Tokyo, Japan) [22]. Commercial ELISA kits were used to determine the serum levels of leptin (R&D Systems, Minneapolis, MN, USA) and adiponectin (Sekisui Medical, Tokyo, Japan). The ranges of inter-assay and intra-assay coefficients of variation were <3% for all blood parameters.

Statistical analyses The sample size was calculated based on data from our previous study [12]. The primary ． outcome variable of this study was the change in VO2peak throughout the intervention. A significant difference was assumed in the intervention effect with a standard deviation estimate of 10%, with an alpha error rate of 0.05, and statistical power of 80%. The minimum sample size per group was estimated to be 11 subjects. Assuming subject attrition such as dropout, 16 subjects were recruited for each group in this study. For statistical analyses, one subject in the CR-then-HIIT group was excluded owing to insufficient measurement data. Values have been expressed as means ± standard deviations. The Student’s unpaired t-test was used to compare the two groups at baseline. Categorical data have been represented as n (%) and were analyzed using the chi-square test. Paired Student’s t-tests were used to test the significance of changes in values within groups. An analysis of covariance with adjustments for respective baseline values was applied to compare changes during the initial intervention period (0-11 weeks) between groups. To compare any changes in measurement variables 13

between the groups, a two-way repeated-measures ANOVA (Time  group interactions) was applied. Tukey-Kramer’s post-hoc tests were applied when the difference was significant based on the results of the ANOVA. Cohen’s d effect sizes were also calculated to determine the magnitude of the group differences. An effect size scale with small (0.20-0.49), moderate (0.50-0.79), and large (≥ 0.8) groups was used. P ≤ 0.05 was considered statistically significant. Statistical analyses were conducted using SAS version 9.3 (SAS Institute Japan, Tokyo, Japan).

Results Characteristics of subjects and adherence to the intervention program There were no significant group differences in characteristics and medication use at baseline (Table 1). Attendance during the 11-week intervention program was 92.4 ± 5.9% during HIIT and 100% during CR for the HIIT-then-CR group, and 100% during CR and 87.8 ± 2.3% during HIIT for the CR-then-HIIT group. There were no significant group differences in attendance between HIIT (P = 0.20) and CR (P = 0.31). Table 1. Subject characteristics at baseline HIIT-then-CR

CR-then-HIIT

Group

(n = 16)

(n = 15)

differences

49.4 ± 6.3

51.1 ± 4.5

0.40

Female, n (%)

6 (19.4)

4 (12.9)

0.52

Hypertension, n (%)

2 (6.45)

5 (16.1)

0.17

Type 2 diabetes, n (%)

2 (6.45)

0 (0)

0.16

Age, year

14

Dyslipidemia, n (%)

2 (6.45)

1 (3.23)

0.58

Pre-MetS, n (%)

3 (9.7)

3 (9.7)

0.93

13 (41.9)

12 (38.7)

0.33

MetS, n (%)

Values are presented as n (%) or mean ± standard deviation. Abbreviations; HIIT, high-intensity interval training; CR, calorie-restriction; MetS, metabolic syndrome. The HIIT-then-CR group performed 8 weeks of HIIT followed by 3 weeks of CR. The CR-then-HIIT group performed 3 weeks of CR followed by 8 weeks of HIIT.

Changes during the intervention program (11 weeks) Table 2 demonstrates the changes in measurement values during the 11-week intervention period with the results of the ANCOVA analysis and the ES (Cohen’s d). Significant differences were only observed between groups at baseline for TG levels. During the 11-week intervention period, body composition (i.e., body weight, body mass index, WC, ． and fat mass) and physical fitness variables (i.e., VO2peak, HR at rest and total energy intake) were significantly changed within each group. Although there was significant group difference only in fat mass (P = 0.04), it showed a tendency toward larger effect sizes in the CR-then-HIIT group. Among the blood variables, the diastolic blood pressure and FPG significantly decreased only in the CR-then-HIIT group, with moderate-to-large effect sizes. Conversely, TG significantly decreased only in the HIIT-then-CR group, with a moderate effect size. Leptin significantly decreased in both groups, with moderate effect sizes. Significant group differences were not observed in all blood variables between groups. We ． also observed a large effect size for VO2peak in the CR-then-HIIT group, and a moderate effect 15

size in the HIIT-then-CR group. Compared to the baseline value, significant changes in the total energy intake during the 11-week intervention period were 535 ± 742 kcal/day in the CR-then-HIIT group and 727 ± 480 kcal/day in HIIT-then-CR group. However, there were no differences between groups. The measurement variables (i.e., body weight, WC, fat mass, TC, FPG and leptin) that showed significant group interaction (group x time, P < 0.001) during the 11-week intervention period are shown in Fig 2. Post-hoc analysis indicated that the changes in weeks 3 and 7 were significantly different between groups (P < 0.05); however, significant differences were not observed in week 11 (Fig. 2). The significant group interactions of ． ． VO2peak (ml/min) have been shown in Fig 3. Compared to baseline, the VO2peak (ml/min) percentage changes in the CR-then-HIIT and HIIT-then-CR groups were 9.7 ± 12.2% (P <0.01) and 5.8 ± 9.0% (P <0.05), respectively (Fig. 3); significant group interaction (P < 0.001) was observed during the 11-week intervention period.

Changes during the 8-week postintervention program (after 8 weeks) During the postintervention period, the HIIT-then-CR group with no intervention continued losing weight (1.5 ± 2.2 kg; P <0.01), whereas the CR-then-HIIT group maintained their body weight with HIIT once weekly (-0.7 ± 1.5 kg; P = 0.26). Moreover, the body mass index, WC, and fat mass only showed significant continuous reductions in the HIIT-then-CR 16

group. However, these changes were not observed for group interaction (group x time) during the 8-week postintervention period. Among the blood variables, no MetS components changed significantly during the 8-week postintervention period, and only adiponectin significantly increased in both groups; these changes did not differ between groups. The measurement variables showed significant group interaction during 19 weeks including the postintervention period (Fig 2); however, significant differences were not observed between groups during the 8-week postintervention period. ． The increased VO2peak during the intervention program in the CR-then-HIIT group was maintained during the postintervention period with HIIT once weekly. Conversely, 8 weeks ． without intervention resulted in significantly reduced VO2peak in the HIIT-then-CR group. The ． VO2peak (L/min) percentage changes during the postintervention period were -2.0 ± 7.2% (P = 0.31) and -6.9 ± 8.4% (P <0.01) in the CR-then-HIIT group and HIIT-then-CR group, ． respectively (Fig. 3). In addition, the changes in the VO2peak during the 8-week postintervention demonstrated significant group interaction (P < 0.05).

17

Table 2. Measurement values before and after of 11 weeks program HIIT-then-CR

Baseline

Changes during HIIT

Effe

(n = 16)

Changes during CR

Effe

CR-then-HIIT (n = 15)

ct

ct

size

size

Group

fro

fro

differe

Post (total

m

nce

11 week)

wee

(ANC

ks

ks

OVA)

0-1

0-1

1

1

Post (total

m

11 week)

wee

Baseline

Changes during CR

Changes during HIIT

Body composition Body weight, kg Body mass index, Waist circumference, cm Fat mass, kg

77. 6 28. 8 97. 1 26. 7

± 7.5 ± 2.8

± 5.6

± 5.5

-0. 44 -0. 18 -0. 69 -0. 63

± 1.2 ± 0.5

± 1.7

±

-3. 26 -1. 21 -3. 04

1.1

-1.

*

98

± ±

±

±

1.2 †

0.4 †

1.6 †

1.3 †

73. 9 27. 4 93. 4 24. 3

± ±

±

±

7.1

-0.

78.

ǂ

49

8

2.5

-0.

28.

ǂ

50

4

5.3

-0.

97.

ǂ

66

6

5.7

-0.

26.

ǂ

44

3

Blood variables

18

± 6.0 ± 2.6

± 5.0

± 6.7

-2. 98 -1. 07 -2. 95 -1. 66

± ±

±

±

1.7

-2.

*

57

0.6

-0.

*

91

2.2

-2.

*

46

1.6

-2.

*

87

± ±

±

±

2.2 †

0.7 †

2.4 †

2.1 †

73. 3 26. 5 92. 2 21. 8

± ±

±

±

5.9

-0.

ǂ

92

2.7

-0.

ǂ

80

5.1

-1.

ǂ

08

7.0

-0.

ǂ

67

0.07 0.10

0.13

0.04

SBP, mmHg DBP, mmHg TC, mg/dl HDLC, mg/dl TG, mg/dl§ FPG, mg/dl HbA1c, % Leptin Adiponectin

13 6 84. 7 21 4 45. 0 17 7 10 6 5.8 6 15 7 1.9 7

± ± ± ± ± ± ± ± ±

18.

-1.

1

38

11.

1.1

2 32.

3 -1.

4

19

14.

1.1

5 61. 0

3 -11 .5

24.

-2.

5

00

0.7

-0.

9

01

11

-35

1

.6

0.6 7

0.0 4

± ± ± ± ± ± ± ± ±

16.

-7.

2

75

8.4

-3.

1

13

17.

-9.

1

81

6.1

1.4

1 61. 9

4 -51 .2

12.

-7.

5

19

0.1

-0.

8

13

53.

-61

2*

.4

0.2

0.1

2

2

± ± ± ± ± ± ± ± ±

11.

12

5†

7

11. 5 31. 2 6.1 7

82. 7 20 3 47. 6

76.

11

3†

4

12. 9† 0.2 0 50. 3† 0.4 1

96. 6 5.7 74. 9 2.1

± ± ± ± ± ± ± ± ±

17.

-0.

12

8

51

9

10.

-0.

85.

2

18

6

48.

-0.

22

8

34

2

13.

0.1

51.

6

8

4

60.

-0.

11

2ǂ

64

3

13.

-0.

10

6

38

5

0.6

-0.

5.7

0

16

1

65.

-0.

14

8ǂ

73

6

0.8

0.1

2.1

4

8

4

± ± ± ± ± ± ± ± ±

19.

-4.

4

53

10.

-8.

4

07

32. 4

-29 .2

17.

-2.

0

00

48. 7 14. 4

-15 .5 -11 .0

0.5

-0.

4

03

11

-66

4

.4

0.6

-0.

9

19

4.2

0.4

± ± ± ± ± ± ± ± ±

15.

-4.

1

67

11.

-1.

1*

53

19.

16.

8* 6.7 2 38. 5 7.7 1* 0.1 1

0 4.6 7 0.7 3 1.0 7 0.0 2

70.

-4.

1*

63

0.2

0.2

6*

4

± ± ± ± ± ± ± ± ±

11. 6 9.9 6 20. 0† 6.2 8† 35. 3 8.3 4 0.2 0 20. 7 0.2 1†

12 0 76. 0 20 9 54. 1 98. 1 95. 5 5.7 74. 9 2.2

± ± ± ± ± ± ± ± ±

14.

-0.

2

46

9.0

-0.

3ǂ

92

27.

-0.

2ǂ

41

13.

0.1

9

6

60.

-0.

2

30

9.5

-0.

5ǂ

66

0.4

-0.

0

02

61.

-0.

0ǂ

62

0.6

0.0

6

6

0.99 0.06 0.81 0.96 0.02 0.91 0.23 0.65 0.51

Physical fitness variables VO2peak,

24.

ml/kg/min

5

VO2peak, ml/min HR at rest, bpm

19 18 71.

± ±

4.5

2.5

1

1

45

17

8

8

± 10.

-2.

± ±

3.3

0.1

8*

0

24

-76

2*

.2

± 7.7

-3.

± ±

2.6

27.

6

2

19

20

4

20

± 5.2

64.

± ±

4.8

0.6

8ǂ

0

4

47

0.2

19

1ǂ

2

33

-0.

66.

± 7.8

19

24.

± ±

6

0

40

-44

2

.1

± 11.

-0.

± ±

2.0

3.8

4

5

18

21

9

4

± 8.1

-4.

± ±

2.9

28.

0†

7

19

21

6†

04

± 5.4

61.

± ±

5.2

1.0

2ǂ

0

43

0.4

3ǂ

3

± 9.4

-0.

0.06 0.31 0.58

1

5

69

6

94

6

Total energy

20

33

-21

54

-51

intake, kcal/d

92

Total daily step,

73

steps/d

29

± ±

3

5

37

-45

47

7

± ±

3

1

14

17

93

8

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4

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2

3

47

7

47

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56

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48

-2.

20

54

-57

72

39.

49

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7

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18

54

3*

3

10

-43

12

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59

19

5

70

10

97

± ±

± ±

6 21 84

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± ±

12 68

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0

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-53

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98

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03

09

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0.33 0.87

Values are presented as n (%) or mean±standard deviation. Abbreviations: HIIT, high-intensity interval training; CR, calorie restriction; SBP, systolic blood pressure; DBP, diastolic blood pressure; TC, total cholesterol; HDLC, high-density lipoprotein cholesterol; TG, triglycerides; FPG, fasting plasma glucose; HbA1c, hemogrobin A1c; VO2peak, peak oxygen consumption; HR, heart rate. The HIIT-then-CR group performed 8 weeks of HIIT followed by 3 weeks of CR. The CR-then-HIIT group performed 3 weeks of CR followed by 8 weeks of HIIT. § Significant difference between the groups at baseline (P < 0.05) * Significantly different during HIIT within the same group (P < 0.05) † Significantly different during CR within the same group (P < 0.05) ǂ Significantly different during total program (11-weeks) within the same group (P < 0.05) ¶ Group difference (ANCOVA) showed that group difference of change with adjustments for respective baseline values during the initial intervention period (0-11 weeks).

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Fig. 2. Comparison of the percentage changes in the measurement variables with significant group interaction from baseline to intervention completion between the HIIT-then-CR group (black circles) and CR-then-HIIT group (white circles). Values are expressed as means ± SE. ###Significant group interaction (P< 0.001), #Significant group interaction (P< 0.05). *Significantly different than baseline within each group (P< 0.05). †Significantly different between groups (P< 0.05). 21

． Fig. 3. Comparison of the percentage changes in VO2peak from baseline to intervention completion between the HIIT-then-CR group (black circles) and CR-then-HIIT group (white circles). Values are expressed as means ± SE. ###Significant group interaction (P< 0.001), #Significant group interaction (P< 0.05). *Significantly different than baseline within each group (P< 0.05). †Significantly different between groups (P< 0.05).

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Discussion Based on the improvements of MetS risk factors and CRF, this study revealed that the time-efficient program with HIIT and CR had a significant impact. We hypothesized that the intervention order would have an influence on MetS risk factors; in particular, the CR-then-HIIT would not obtain any additional effects with improvements in MetS risk factors. However, this study showed no differences between the two programs; instead, larger ． effect trends were observed in body composition and VO2peak in the CR-then-HIIT group. This randomized study demonstrated that both of the intervention orders involving HIIT and CR are effective for improving MetS risk factors. In clinical practice, traditional approaches such as prolonged CR (i.e., >3 months)[23] and MICT sessions (i.e., >30 min/day) are usually adopted. These programs can successfully manage MetS; however, they are a burden to subjects as they find these programs difficult. This leads to decreased motivation and poor adherence, creating a barrier in the clinical field [24]. In this study, the focus was on a time-efficient approach to improving MetS. The program used in this study consisted of HIIT sessions performed three times per week, with each session lasting 15 minutes (45 minutes per week total), and one weekly 90-minute lecture regarding CR. Weight loss of 5–7%, moderate improvements in blood variables, and significantly ． increased VO2peak were obtained, with no dropouts and high attendance rates. These results 23

indicated that this type of lifestyle intervention is a feasible approach to MetS treatment. This study also suggested that less burdensome and time-efficient programs should be considered when developing future treatment guidelines for lifestyle-induced MetS. A previous study [12] investigated the impact of adding a short-term CR period following exercise intervention on MetS risk factors and compared the two exercise interventions (i.e., HIIT and MICT). In contrast to the MICT group, the effect sizes for some MetS risk factors in the HIIT group were relatively larger during the CR period. These findings suggest that positive effects from HIIT may continue during CR without HIIT. Based on these results, we examined whether the intervention order would influence changes in MetS risk factors, and we hypothesized that there are no additional effects on risk factor improvements in the CR-then-HIIT group. However, the results we obtained did not support this hypothesis. There are two possible reasons explaining why our hypothesis was disproved. One involves the effect of continued nutritional lifestyle changes [25]. Dolan et al.[26] indicated that performing a certain behavior potentially influences the subsequent behavior, and change in the perception of people may in turn influence the behavior spillover that occurs. In fact, the total energy intake of the CR-then-HIIT group did not increase during the HIIT period (39.3 ± 490 kcal/day; P = 0.81) despite stopping the CR intervention (i.e., record diary and lecture), which indicated that CR was continued. Additionally, the total energy 24

intake of the HIIT-then-CR group was not significant; however, it showed a trend for decrease during the HIIT period (-215 ± 543 kcal/day; P = 0.16). In this study, although no group difference was observed for changes in total energy intake during the 11-week intervention program (P = 0.33), behavior spillover effects may have had a positive impact on the improvement of MetS. It is important to interpret this phenomenon taking into account the factors involved in an intervention study that are affected by human behavior. Another possible reason why our hypothesis was incorrect could have been the different physiological mechanisms based on the program order. The present study showed that there was no group difference in MetS risk factors; however, the fat mass and body composition showed a tendency towards larger effects in the CR-then-HIIT group. HIIT under carbohydrate-restricted conditions caused molecular adaptations in muscle cells, leading to upregulation of the capacity for energy production via fat oxidation [27-29]; this may have led to larger effects on body composition in the CR-then-HIIT group. Although the effects of the intervention program on mitochondrial biogenesis have not been verified in this study, it was initially considered that CR first induced weight loss, this weight loss had a positive impact on improving mitochondrial biogenesis, and HIIT promoted this improvement synergistically. Furthermore, the results were consistent with those of previous studies that reported that weight loss due to a combination of CR and exercise interventions resulted in no changes in adiponectin levels [30, 31] and reductions in leptin 25

levels [32, 33] in obese individuals. Both, leptin and adiponectin have been posited to have a key role in mediating the effect of insulin, which is a determinant of inflammatory cytokines. Although our study showed a small, non-significant increase in adiponectin levels in both groups, a sufficient decrease in leptin showed that metabolic changes were occurring during these interventions; however, they did not result in statistical changes in adiponectin levels. However, this study could not provide enough data to explain the physiological mechanism. Therefore, further investigations are warranted to study the mechanisms involved. Another aim of our study was to determine whether once weekly HIIT could prevent a rapid decrease in CRF during postintervention. Matsuo et al.[12] showed that the ． improvement in VO2peak with 8 weeks of HIIT was promptly lost during a 4-week CR ． period; however, evidence of maintaining the improved VO2peak with HIIT is still lacking. Even if an exercise program comprising 15-minute HIIT sessions three times per week has benefits, continuing that program for a longer period may be burdensome for some subjects. Although a few systematic reviews [4, 34] have reported that HIIT performed at least three times per week for 12 weeks is required to improve body fat and CRF in obese subjects, there is no evidence that its health benefits will be maintained. Accordingly, we attempted ． to determine whether VO2peak could be maintained with HIIT once weekly. Our study ． revealed that HIIT once weekly for 8 weeks could maintain the improved VO2peak in the 26

CR-then-HIIT group (from 2104 ± 433 to 2073 ± 494 ml/min; P = 0.43); however, that ． VO2peak decreased when HIIT was discontinued (from 2020 ± 471 to 1891 ± 504 ml/min; P <0.05) in the HIIT-then-CR group. Wisløff et al.[35]

performed a study that indicated that

a single weekly session of high-intensity exercise could have a significant impact on maintaining CRF. Further studies are needed on this topic; however, our results showed the possibility of achieving health benefits such as improved CRF with once weekly HIIT. This study has limitations that need to be acknowledged. This randomized controlled trial was conducted at a single center with a small sample size, which limited the extrapolation of our findings. In the future, large multicenter trials should be performed to corroborate the results of this study. In conclusion, our study showed that an intervention involving HIIT and CR significantly improved MetS risk factors and CRF; however, the intervention order did not impact the risk factors. Our study also showed that HIIT can potentially help maintain an increase in CRF. Therefore, our results suggested that sequential application of HIIT and CR is effective for improving MetS. Additionally, less burdensome and time-efficient programs should be considered as successful intervention strategies for treating MetS.

27

Acknowledgments

We are grateful to Ms. Hana Jousei and the staff of Kurosawa Hospital for their support.

Funding This study was supported by JSPS KAKENHI (grant number 16H03251).

Data availability Raw data were generated at the National Institute of Occupational Safety and Health, Japan (JNIOSH). On reasonable request, derived data supporting the findings of this study are available from the corresponding author, RS, after approval from JNIOSH and the Research Ethics Committee. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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