Using the 6-minute walking test to evaluate the effect of high-intensity interval training on the functional capacity in heart failure patients: a systematic review and meta-analysis
Authors: Goberdhan C , Sairras S , Van Der Hilst K , Baldew S 
Published: October 2022

Abstract

Background
Determining the effect of training on exercise capacity in chronic heart failure (CHF) patients is mainly done by measuring peak oxygen uptake (VO2 peak) through cardiopulmonary exercise testing (CPET) [1,2]. However, CPET is not always available, especially in low-and middle-income countries. On the contrary, the 6-minute walk test (6MWT), a simpler and inexpensive alternative can be utilized, even in low resource settings [2,3].
Moderate continuous intensity training (MCIT) is commonly recommended in CHF patients [4], but growing evidence demonstrates the superior benefits of high-intensity interval training (HIIT) on the exercise capacity [5,6]. However, the benefits are predominantly measured with the CPET and expressed in VO2 peak [1,2]. Especially for low resource settings, there is a need for studies describing the effect of HIIT in CHF patients using the 6MWT as an outcome measure. To the best of our knowledge, there is no systematic review on the effect of HIIT in CHF patients, measured solely with the 6MWT.

Purpose
This study aims to synthesize the literature on the effect of HIIT on the exercise capacity using the 6MWT in CHF patients.

Methods
We systematically searched within the PubMed, EBSCOhost, Cochrane and PEDro electronic databases to identify randomized controlled trials published until August 2020 with no date of publication or language restrictions. We included studies that met the following criteria: 1) a randomized controlled trial; 2) performed in a CHF population; 3) the use of the 6MWT as an outcome measure with a pre-and post-exercise measurement of the distance; 4) HIIT without the combination of another type of exercise training. The funnel plot was used to estimate publication bias and the Tool for the assEssment of Study qualiTy and reporting in EXercise (TESTEX) was used for quality assessment [7].

Results
We found 169 studies, of which 164 were excluded for not meeting inclusion criteria, resulting in the inclusion of five studies (n=315, mean age = 61 years, 71.4% male). Three studies (n=163, mean age=58 years, 64.4% % male) used MCIT and two studies (n=152, mean age = 65 years, 78.5% male) usual care as the control group. The HIIT showed significant improvements on 6MWT distance (MD= 40.78 m; 95% CI 24.55–57.01; p value &lt;0.00001; I2=56%) compared to control groups (Figure 1).
The funnel plot (Figure 2) shows asymmetry upon visual examination and could indicate presence of publication bias. The quality assessment score was between 10–12 points with an overall median score of 11.2.

Conclusions
The distance on the 6MWT significantly improves with HIIT compared to sedentary controls and MCIT. However, our results are based on a small number of studies with heterogeneity across the control groups. Nevertheless, this study does provide information for physical therapist from low-resource settings about the expected effect on the 6MWT, when providing HIIT to CHF patients.

Funding Acknowledgement
Type of funding sources: None.