The influence of training characteristics on the effect of aerobic exercise training in patients with chronic heart failure: A meta-regression analysis

Highlights

• Exercise training improves exercise capacity in chronic heart failure patients.

• This effect is mainly determined by total energy expenditure of a program.

• Energy expenditure is the product of intensity, frequency, duration and length.

• Increase in frequency and duration elicits the greatest effect on exercise capacity.

Abstract

Although aerobic exercise training has shown to be an effective treatment for chronic heart failure patients, there has been a debate about the design of training programs and which training characteristics are the strongest determinants of improvement in exercise capacity. Therefore, we performed a meta-regression analysis to determine a ranking of the individual effect of the training characteristics on the improvement in exercise capacity of an aerobic exercise training program in chronic heart failure patients. We focused on four training characteristics; session frequency, session duration, training intensity and program length, and their product; total energy expenditure. A systematic literature search was performed for randomized controlled trials comparing continuous aerobic exercise training with usual care. Seventeen unique articles were included in our analysis. Total energy expenditure appeared the only training characteristic with a significant effect on improvement in exercise capacity. However, the results were strongly dominated by one trial (HF-action trial), accounting for 90% of the total patient population and showing controversial results compared to other studies. A repeated analysis excluding the HF-action trial confirmed that the increase in exercise capacity is primarily determined by total energy expenditure, followed by session frequency, session duration and session intensity. These results suggest that the design of a training program requires high total energy expenditure as a main goal. Increases in training frequency and session duration appear to yield the largest improvement in exercise capacity.

Introduction

The beneficial effects of aerobic exercise training (AET) programs for chronic heart failure (CHF) patients have been demonstrated throughout the last decades [1], [2]. However, training characteristics of exercise programs (i.e. training intensity, session duration, session frequency and program length) vary considerably between trials [3], [4], [5], [6]. Although it is generally conceived that all of these characteristics influence training results in CHF patients, it remains unclear to what extent they determine the effect of AET separately. In recent years, training intensity has been a point of debate. In the first decade of the 21st century, most AET-trials studied training programs with low to moderate training intensity, showing mainly beneficial effects on exercise capacity [6], [7]. Several smaller trials showed a greater improvement in exercise capacity, using a high training intensity [8], [9]. However, trials directly comparing moderate and high intensity training programs showed conflicting results [3], [10], [11]. Moreover, in most of the studies comparing different intensities, high intensity exercise was performed as interval training, while the low to moderate intensity exercise group underwent continuous training. The pure effect of training intensity therefore remains clouded by the use of different training modalities. Besides training intensity, data on the influence of other training characteristics on exercise capacity in CHF patients (i.e. session duration, session frequency and program length) are scarce and therefore remains largely unclear. Available data consist of a substudy of the HF-action trial which showed that high training volume (product of session duration, session frequency and program length) was positively correlated with improvement of peakVO₂, and Vanhees et al. showing that session frequency can be an important determinant of training effects in CHF patients [12]. A recent meta-analysis on this topic suggested that high training intensity and high training volume elicit the greatest improvement in exercise capacity in CHF patients [13]. However, analyses were performed without adjustment for total energy expenditure of the training program. A correction for total energy expenditure, the product of session duration, session frequency, training intensity and program length, is required to identify the effect of the individual training characteristics.

The objective of this meta-regression analysis was to explore which program characteristics determine improvement in exercise capacity after exercise training in CHF patients, taking two constraints into consideration: 1) To identify the effect of the individual training characteristics, an adjustment for total energy expenditure was made in the analyses of session duration, session frequency, program length and training intensity. 2) To isolate the effect of training intensity, the analyses was focused on aerobic continuous training as training modality.