Effects of High-Intensity Interval Training, Moderate-to-Vigorous Intensity Continuous Training, and Nordic Walking on Functional Fitness in Patients with Coronary Artery Disease

Patients with coronary artery disease (CAD) frequently experience diminished functional fitness (FF), such as aerobic endurance; muscular strength, endurance, and flexibility; and agility/dynamic balance. Limited FF reflects reduced physiological capacity to perform activities of daily living1 and predicts the risk of falls2 and loss of functional independence.3 Identifying functional limitations and prescribing an appropriate exercise intervention may mitigate the risk of disability in deconditioned patients with CAD. Our previous study showed that 12 wk of supervised high-intensity interval training (HIIT), moderate-to-vigorous intensity continuous training (MICT), and Nordic walking (NW) improve aerobic endurance assessed by the 6-min walk test (6MWT).4 The improvements were sustained for 14 wk following the completion of the supervised exercise programs (ie, at wk 26).5 Interestingly, while all exercise modalities increased 6MWT distance, NW showed superior effects at both wk 12 and 26. In NW, the use of walking poles engages core and upper body muscles6 and assists with dynamic stability and coordination of movement.7 To enhance strength, agility, and dynamic balance, NW may be a more effective exercise modality. Different exercise modalities, including HIIT, MICT, and NW, have been used in cardiovascular rehabilitation (CR). However, no study has directly compared their effects on FF. This study assessed: (1) the effects of a 12-wk HIIT, MICT, and NW program on FF and their sustained effects (ie, at wk 26) in patients with CAD; and (2) the proportion of patients with CAD living with limited FF. We hypothesized that NW would have superior effects on FF compared with HIIT or MICT. METHODS This was a substudy of a larger randomized controlled trial (Protocol #20160127-01H).4 Patients with documented CAD referred to a CR program were randomized 1:1:1 to a 12-wk HIIT (aerobic exercise equipment or dance/movement-based exercise), MICT (aerobic exercise equipment or walking), or NW (walking with Nordic poles) program followed by 14 wk of an observation phase.4,5 Both HIIT and MICT included cooldown with strength and stretching exercises, whereas NW included cooldown with stretching only. Detailed inclusion and exclusion criteria are provided in the Supplemental Digital Content (available at: https://links.lww.com/JCRP/A456). The Fullerton Functional Fitness Test, a valid and reliable measure of functional independence in older adults,1 was used to assess FF at baseline, wk 12, and wk 26. The test included the 6MWT to assess aerobic endurance; 30-sec chair stand/squat and arm curl to assess lower and upper body strength; back scratch and chair sit-and-reach for upper and lower body flexibility; and 8-ft up-and-go to assess agility/dynamic balance. Patients not meeting the age- and sex-specific fitness standards for 6MWT distance, 30-sec chair stand/squat and arm curl repetitions, and 8-ft up-and-go time3 were considered to have limited FF. Cut-off scores were not available for those <60 yr old (n = 58). Thus, scores for the age group of 60-64 yr were used, followed by sensitivity analysis excluding participants <60 yr old. Descriptive statistics were used to assess the proportion of patients with functional limitations. Linear mixed models for repeated measures with unstructured covariance were used to compare changes in FF between exercise interventions. Within each exercise intervention group, χ2 tests were used to assess changes in the proportion of patients with functional limitations over time. RESULTS A total of 130 patients with CAD (60.7 ± 7.5 yr old, 15.4% females) were randomized into HIIT (n = 43), MICT (n = 44), or NW (n = 43). At CR enrollment, 66% of patients had limited aerobic endurance, 69% had limited lower body strength, 72% had limited upper body strength, and 58% had limited agility/dynamic balance. The sensitivity analysis showed similar proportions of patients with limited aerobic endurance (61%), upper body strength (69%), lower body strength (71%), and agility/dynamic balance (58%). The proportion of patients with functional limitations did not differ between the intervention groups at CR enrolment. Changes in FF are summarized in the Table. At wk 12, there were improvements in 30-sec chair stands/squats (14.4 ± 4.7 vs 17.7 ± 4.7 repetitions) and arm curls (15.9 ± 4.2 vs 18.7 ± 4.1 repetitions), and 8-ft up-and-go time (5.5 ± 1.1 vs 4.9 ± .8 sec, main effect of time, all P < .001). The NW group increased arm curl repetitions (+3.5 repetitions) more than HIIT (+1.6 repetitions, interaction effect: P = .048) and MICT (+2.4 repetitions, interaction effects: P = .028). At wk 26, chair stands/squats (18.5 ± 5.4 repetitions), arm curls (19.1 ± 4.6 repetitions), and 8-ft up-and-go time (4.8 ± .8 sec) improved significantly when compared with baseline (main effect of time, all P < .001). The NW group increased arm curl repetitions more than MICT (interaction effect, P = .027). Chair sit-and-reach distance worsened at wk 12 and 26 (both P < .05). As previously reported,4,5 NW showed greater improvements in 6MWT distance at wk 12 and 26 compared with HIIT and MICT. Table - Functional Fitness and Proportion of Patients With Limited Functional Fitness at Baseline and Following Interventionsa Baseline wk 12 wk 26 Changes in functional fitness Number of chair stand/squat, repetitions Overall 14.4 ± 4.7 2.7 ± 3.2 b 3.5 ± 4.3 b HIIT 14.7 ± 4.7 2.8 ± 3.2 3.4 ± 4.6 MICT 14.6 ± 5.1 2.3 ± 2.9 3.1 ± 4.6 NW 13.9 ± 4.2 3.1 ±3.4 4.0 ± 3.6 Number of arm curls, repetitions Overall 15.9 ± 4.2 2.6 ± 3.7 b 3.1 ± 3.7 b HIIT 15.9 ± 3.9 1.6 ± 3.6 2.6 ± 3.3 MICT 16.8 ± 4.5 2.4 ± 4.1 2.7 ± 4.3 NW 15.0 ± 4.1 3.5 ± 3.2 c,d 3.9 ± 3.3 d Chair sit-and-reach, cm Overall 2.1 ± 13.9 −2.2 ± 10.4 e −3.6 ± 10.7 e HIIT 3.2 ± 11.0 −4.3 ± 8.9 −4.0 ± 10.2 MICT −1.0 ± 14.4 0.3 ± 1.1 −0.2 ± 9.8 NW 4.2 ± 15.6 −2.4 ± 11.8 −6.6 ± 11.3 Back scratch, cm Overall −9.0 ± 16.5 −1.4 ± 16.1 −0.7 ± 15.8 HIIT −8.9 ± 15.2 −3.4 ± 15.0 −1.5 ± 16.7 MICT −8.8 ± 18.9 −0.8 ± 18.6 −2.5 ± 18.8 NW −9.3 ± 15.6 −0.1 ± 14.7 1.9 ± 1.1 8-ft up and go time, sec Overall 5.5 ± 1.1 −0.5 ± 0.8 b −0.5 ± 0.8 b HIIT 5.5 ± 1.1 −0.4 ± 0.8 −0.6 ± 0.9 MICT 5.5 ± 1.0 −0.5 ± 0.6 −0.5 ± 0.8 NW 5.6 ± 1.3 −0.6 ± 0.9 −0.5 ± 0.8 Proportion of patients with limited functional fitness Aerobic endurance Overall 65.9 34.3 b 25.0 b HIIT 65.1 41.7 b 32.3 b MICT 72.1 38.2 b 33.3 b NW 60.5 22.9 b 9.7 b Lower body strength Overall 69.0 35.6 b 32.6 b HIIT 65.1 29.4 f 37.5 e MICT 67.4 44.1 e 30.0 f NW 74.4 33.3 b 30.0 b Upper body strength Overall 72.4 48.0 b 42.9 b HIIT 70.7 69.7 61.3 MICT 69.8 29.4 b 30.0 b NW 76.7 45.2 b 36.7 b Agility/dynamic balance Overall 57.7 40.6 e 34.4 b HIIT 55.8 47.2 42.9 MICT 52.3 37.1 36.7 NW 65.1 36.7 e 25.0 b Abbreviations: HIIT, high-intensity interval training; MICT, moderate-to-vigorous intensity continuous training; NW, Nordic walking.aData are presented as mean ± SD or %. Italicized values represent significant difference.bSignificantly different from baseline: P < .001.cSignificantly greater increase than HIIT: P < .05.dSignificantly greater increase than MICT: P < .05.eSignificantly different from baseline: P < .05.fSignificantly different from baseline: P < .01. Changes in the proportion of patients with limited FF are summarized in the Table. Overall, the proportions of patients with functional limitations were lower in all aspects of functional measures at wk 12 and 26. The proportion of patients with limited agility/dynamic balance significantly decreased following only NW. DISCUSSION Functional limitations mediate the causal pathway from disease to disability.8 A key factor in preserving mobility and physical independence is to maintain FF to perform activities of daily living, such as simple housework, lift and carry objects, get in and out of chairs, and walk enough to do errands.3 This study showed that approximately two-thirds of patients with CAD had functional limitations at CR entry, highlighting the need for interventions to target aerobic endurance, upper and lower body strength, and agility/dynamic balance. Enhanced assessment of functional limitations to tailor nutrition and exercise therapy,9 including the addition of resistance training,10 may play an important role to improve FF in patients with CAD. Exercise-based CR for 12 wk showed promising effects on improving FF and decreasing the proportion of patients with functional limitations. All exercise modalities (ie, HIIT, MICT, and NW) were efficacious in improving upper and lower body strength and agility/dynamic balance. Such improvements were sustained 14 wk after CR completion. Contrarily, the worsened lower body flexibility at wk 12 and 26 warrants additional strategies to target muscular flexibility. Our results demonstrated that NW confers additional benefits in increasing upper body strength and reducing the proportion of patients with limited agility/dynamic balance. These improvements were similar to those previously reported in patients with acute coronary syndrome undergoing the inpatient CR program including NW.11 Combined with our previous study showing greater improvements in 6MWT distance (ie, aerobic endurance) following NW when compared with HIIT and MICT,4,5 NW, a whole-body aerobic exercise with greater involvement of the upper body, confers additional benefits in improving FF following a cardiac event.

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