Cardiac determinants of heterogeneity in fitness change in response to moderate intensity aerobic exercise training: the DREW study

Frailty Status Modifies the Efficacy of Exercise Training Among Patients With Chronic Heart Failure and Reduced Ejection Fraction: An Analysis From the HF-ACTION Trial

BACKGROUND

Supervised aerobic exercise training (ET) is recommended for stable outpatients with heart failure (HF) with reduced ejection fraction (HFrEF). Frailty, a syndrome characterized by increased vulnerability and decreased physiologic reserve, is common in patients with HFrEF and associated with a higher risk of adverse outcomes. The effect modification of baseline frailty on the efficacy of aerobic ET in HFrEF is not known.

METHODS

Stable outpatients with HFrEF randomized to aerobic ET versus usual care in the HF-ACTION (Heart Failure: A Controlled Trial Investigating Outcomes of Exercise Training) trial were included. Baseline frailty was estimated using the Rockwood frailty index (FI), a deficit accumulation-based model of frailty assessment; participants with FI scores >0.21 were identified as frail. Multivariable Cox proportional hazard models with multiplicative interaction terms (frailty treatment arm) were constructed to evaluate whether frailty modified the treatment effect of aerobic ET on the primary composite end point (all-cause hospitalization and mortality), secondary end points (composite of cardiovascular death or cardiovascular hospitalization, and cardiovascular death or HF hospitalization), and Kansas City Cardiomyopathy Questionnaire score. Separate models were constructed for continuous (FI) and categorical (frail versus not frail) measures of frailty.

RESULTS

Among 2130 study participants (age, 59±13 years; 28% women), 1266 (59%) were characterized as frail (FI>0.21). Baseline frailty burden significantly modified the treatment effect of aerobic ET (P interaction: FI × treatment arm=0.02; frail status [frail versus nonfrail] × treatment arm=0.04) with a lower risk of primary end point in frail (hazard ratio [HR], 0.83 [95% CI, 0.72-0.95]) but not nonfrail (HR, 1.04 [95% CI, 0.87-1.25]) participants. The favorable effect of aerobic ET among frail participants was driven by a significant reduction in the risk of all-cause hospitalization (HR, 0.84 [95% CI, 0.72-0.99]). The treatment effect of aerobic ET on all-cause mortality and other secondary endpoints was not different between frail and nonfrail patients (P interaction>0.1 for each). Aerobic ET was associated with a nominally greater improvement in Kansas City Cardiomyopathy Questionnaire scores at 3 months among frail versus nonfrail participants without a significant treatment interaction by frailty status (P interaction>0.2).

CONCLUSION

Among patients with chronic stable HFrEF, baseline frailty modified the treatment effect of aerobic ET with a greater reduction in the risk of all-cause hospitalization but not mortality.

Mechanistic Effects of Aerobic Exercise in Alzheimer's Disease: Imaging Findings From the Pilot FIT-AD Trial

Despite strong evidence from animal models of Alzheimer's disease (AD) supporting aerobic exercise as a disease-modifying treatment for AD, human mechanistic studies are limited with mixed findings. The objective of this pilot randomized controlled trial was to examine the effects of 6-month aerobic exercise on hippocampal volume, temporal meta-regions of interest (ROI) cortical thickness, white matter hyperintensity (WMH) volume, and network failure quotient (NFQ), measured with MRI, in community-dwelling older adults with AD dementia. Additionally, the relationships between 6- and 12-month changes in MRI biomarkers and the AD Assessment Scale-Cognition (ADAS-Cog) were examined. Sixty participants were randomized, but one was excluded because baseline MRI failed quality control: 38 randomized to cycling and 21 to stretching. The intervention was moderate-intensity cycling for 20–50 mins, three times a week for 6 months. Control was low-intensity stretching. The study outcomes include hippocampal volume, temporal meta-ROI cortical thickness, WMH volume, and NFQ. Outcomes were measured at baseline, 6 months, and 12 months. The sample averaged 77.3 ± 6.3 years old with 15.6 ± 2.9 years of education and 53% men. Both groups experienced significant declines over 6 months in hippocampal volume (2.64% in cycling vs. 2.89% in stretching) and temporal meta-ROI cortical thickness (0.94 vs. 1.54%), and over 12 months in hippocampal volume (4.47 vs. 3.84%) and temporal meta-ROI cortical thickness (2.27 vs. 1.79%). These declines did not differ between groups. WMH volume increased significantly with the cycling group increasing less (10.9%) than stretching (24.5%) over 6 months (f = 4.47, p = 0.04) and over 12 months (12.1 vs. 27.6%, f = 5.88, p = 0.02). NFQ did not change significantly over time. Pairwise correlational analyses showed a significant negative correlation between 6-month changes in hippocampal volume and ADAS-Cog (r = −0.34, p < 0.05). To conclude, aerobic exercise may reduce the decline in hippocampal volume and temporal meta-ROI cortical thickness during the intervention period, but the effect sizes are likely to be very small and dose-dependent and reverse once the intervention stops. Aerobic exercise is effective on slowing down WMH progression but has no effect on NFQ. Hippocampal atrophy was associated with cognitive decline during the intervention period.

Clinical Trial Registration:www.ClinicalTrials.gov, identifier: NCT01954550.

Biological and methodological factors affecting V ̇ O 2 max response variability to endurance training and the influence of exercise intensity prescription

NEW FINDINGS

What is the topic of this review? Biological and methodological factors associated with the variable changes in cardiorespiratory fitness in response to endurance training. What advances does it highlight? Several biological and methodological factors exist that each contribute, to a given extent, to response variability. Notably, prescribing exercise intensity relative to physiological thresholds reportedly increases cardiorespiratory fitness response rates compared to when prescribed relative to maximum physiological values. As threshold-based approaches elicit more homogeneous acute physiological responses among individuals, when repeated over time, these uniform responses may manifest as more homogeneous chronic adaptations thereby reducing response variability.

ABSTRACT

Changes in cardiorespiratory fitness (CRF) in response to endurance training (ET) exhibit large variations, possibly due to a multitude of biological and methodological factors. It is acknowledged that ∼20% of individuals may not achieve meaningful increases in CRF in response to ET. Genetics, the most potent biological contributor, has been shown to explain ∼50% of response variability, whilst age, sex and baseline CRF appear to explain a smaller proportion. Methodological factors represent the characteristics of the ET itself, including the type, volume and intensity of exercise, as well as the method used to prescribe and control exercise intensity. Notably, methodological factors are modifiable and, upon manipulation, alter response rates to ET, eliciting increases in CRF regardless of an individual's biological predisposition. Particularly, prescribing exercise intensity relative to a physiological threshold (e.g., ventilatory threshold) is shown to increase CRF response rates compared to when intensity is anchored relative to a maximum physiological value (e.g., maximum heart rate). It is, however, uncertain whether the increased response rates are primarily attributable to reduced response variability, greater mean changes in CRF or both. Future research is warranted to elucidate whether more homogeneous chronic adaptations manifest over time among individuals, as a result of exposure to more homogeneous exercise stimuli elicited by threshold-based practices.

Short-Term Changes in Cardiorespiratory Fitness in Response to Exercise Training and the Association with Long-Term Cardiorespiratory Fitness Decline: The STRRIDE Reunion Study

Background

Substantial heterogeneity exists in the cardiorespiratory fitness (CRF) change in response to exercise training, and its long‐term prognostic implication is not well understood. We evaluated the association between the short‐term supervised training‐related changes in CRF and CRF levels 10 years later.

Methods and Results

STRRIDE (Studies of a Targeted Risk Reduction Intervention Through Defined Exercise) trial participants who were originally randomized to exercise training for 8 months and participated in the 10‐year follow‐up visit were included. CRF levels were measured at baseline, after training (8 months), and at 10‐year follow‐up as peak oxygen uptake (vo₂, mL/kg per min) using the maximal treadmill test. Participants were stratified into low, moderate, and high CRF response groups according to the training regimen–specific tertiles of CRF change. The study included 80 participants (age: 52 years; 35% female). At 10‐year follow‐up, the high‐response CRF group had the least decline in CRF compared with the moderate‐ and low‐response CRF groups (−0.35 versus −2.20 and −4.25 mL/kg per minute, respectively; P=0.02). This result was largely related to the differential age‐related changes in peak oxygen pulse across the 3 groups (0.58, −0.23, and −0.86 mL/beat, respectively; P=0.03) with no difference in the peak heart rate change. In adjusted linear regression analysis, high response was significantly associated with greater CRF at follow‐up independent of other baseline characteristics (high versus low [reference] CRF response: standard β=0.25; P=0.004).

Conclusions

Greater CRF improvement in response to short‐term training is associated with higher CRF levels 10 years later. Lack of CRF improvements in response to short‐term training may identify individuals at risk for exaggerated CRF decline with aging.

Absence of Fitness Improvement Is Associated with Outcomes in Heart Failure Patients

PURPOSE

This study aimed to examine the clinical effect of cardiorespiratory fitness (CRF) and improvements in CRF after cardiac rehabilitation (CR) in heart failure (HF) patients for their risk for all-cause mortality and unplanned hospitalization and to investigate possible factors associated with the absence of improvement in CRF after rehabilitation.

METHODS

We included 155 HF patients receiving CR between October 2009 and January 2015. Patients performed an incremental bicycle test to assess CRF through peak oxygen uptake (V˙O2-peak) before and after CR-based supervised exercise training. Patients were classified as responders or nonresponders on the basis of pre-to-post CR changes in V˙O2-peak (≥6% and <6%, respectively). Cox proportional hazards models evaluated all-cause mortality and unplanned hospitalization during 5 yr of follow-up. Patient characteristics, HF features, and comorbidities were used to predict changes in V˙O2-peak using logistic regression analysis.

RESULTS

Seventy HF patients (45%) were classified as responder. Nonresponders had a significantly higher risk for all-cause mortality or hospitalization (hazard ratio, 2.15; 95% confidence interval (CI), 1.17-3.94) compared with responders. This was even higher in nonresponders with low CRF at baseline (hazard ratio, 4.88; 95% CI, 1.71-13.93). Factors associated with nonresponse to CR were age (odds ratio (OR), 1.07/yr; 95% CI, 1.03-1.11), baseline V˙O2-peak (OR, 1.16 mL·min·kg; 95% CI, 1.06-1.26), and adherence to CR (OR, 0.98/percentage; 95% CI, 0.96-0.998).

CONCLUSIONS

Independent from baseline CRF, the inability to improve V˙O2-peak by CR doubled the risk for death or unplanned hospitalization. The combination of lower baseline CRF and nonresponse was associated with even poorer clinical outcomes. Especially older HF patients with higher baseline V˙O2-peak and lower adherence have a higher probability of becoming a nonresponder.

Inter-Individual Responses of Maximal Oxygen Uptake to Exercise Training: A Critical Review

It has recently been reported how to quantify inter-individual differences in the response to an exercise intervention using the standard deviation of the change scores, as well as how to appraise these differences for clinical relevance. In a parallel-group randomised controlled trial, the key trigger for further investigation into inter-individual responses is when the standard deviation of change in the intervention sample is substantially larger than the same standard deviation derived from a suitable comparator sample. 'True' and clinically relevant inter-individual differences in response can then be plausibly expected, and potential moderators and mediators of the inter-individual differences can be explored. We now aim to critically review the research on the inter-individual differences in response to exercise training, focusing on maximal oxygen uptake (VO₂max). A literature search through the relevant bibliographic databases resulted in the identification of six relevant studies that were published prior to the influential HEalth, RIsk factors, exercise Training And GEnetics (HERITAGE) Family Study. Only one of these studies was found to include a comparator arm. Re-analysis of the data from this study, accounting for random within-subjects variation, revealed an absence of clinically important inter-individual differences in the response of VO₂max to exercise training. The standard deviation of change was, in fact, larger (±5.6 mL/kg/min) for the comparator than the intervention group (±3.7 mL/kg/min). We located over 180 publications that resulted from the HERITAGE Family Study, but we could not find a comparator arm in any of these studies. Some authors did not explain this absence, while others reasoned that only inter-individual differences in exercise response were of interest, thus the intervention sample was investigated solely. We also found this absence of a comparator sample in on-going studies. A perceived high test-retest reliability is offered as a justification for the absence of a comparator arm, but the test-retest reliability analysis for the HERITAGE Family Study was over a much shorter term than the length of the actual training period between baseline and follow-up measurements of VO₂max. We also scrutinised the studies in which twins have been investigated, resulting in concerns about how genetic influences on the magnitude of general within-subjects variability has been partitioned out (again in the absence of a comparator no-training group), as well as with the intra-class correlation coefficient approach to data analysis. Twin pairs were found to be sometimes heterogeneous for the obviously influential factors of sex, age and fitness, thereby inflating an unadjusted coefficient. We conclude that most studies on inter-individual differences in VO₂max response to exercise training have no comparator sample. Therefore, true inter-individual differences in response cannot be quantified, let alone appraised for clinical relevance. For those studies with a comparator sample, we found that the inter-individual differences in training response were not larger than random within-subjects variation in VO₂max over the same time period as the training intervention.

Response to Endurance Exercise Training in Older Adults with Heart Failure with Preserved or Reduced Ejection Fraction

OBJECTIVES

To systematically examine the relative magnitude and predictors of responses to exercise training in older adult with heart failure (HF) with reduced ejection fraction (HFrEF), and preserved EF (HFpEF).

DESIGN

Secondary analysis of a randomized controlled trial.

SETTING

Outpatient cardiac rehabilitation program.

PARTICIPANTS

Individuals with HF (24 HFrEF, 24 HFpEF) who underwent supervised exercise training.

MEASUREMENTS

The study included individual-level data from the exercise training arms of a randomized controlled trial that evaluated the effect of 16 weeks of supervised moderate-intensity endurance exercise training in older adults with chronic, stable HFpEF and HFrEF. Changes in peak oxygen uptake (VO_2peak ) in response to supervised training in individuals with HFpEF were compared with that of individuals with HFrEF. The significant clinical predictors of changes in VO_2peak with exercise training were assessed using univariate and multivariate regression models.

RESULTS

Training-related improvement in VO_2peak was higher in participants with HFpEF than in those with HFrEF (change: 18.7 ± 17.6% vs -0.3 ± 15.4%, P < .001). In univariate analysis, echocardiographic abnormalities in left ventricular structure and function and lower body mass index were associated with blunted response of VO_2peak with exercise training. In multivariate regression analysis using stepwise selection, submaximal exercise systolic blood pressure, and resting early deceleration time were independent predictors of change in VO_2peak .

CONCLUSION

The change in VO_2peak in response to endurance exercise training in older adults with HF differs significantly according to HF subtype, with greater VO_2peak improvement in HFpEF than HFrEF. These results suggest that the current Centers for Medicare and Medicaid Services policy excluding individuals with HFpEF from reimbursement from cardiac rehabilitation may need to be revisited.

Metabolic Effects of Exercise Training Among Fitness-Nonresponsive Patients With Type 2 Diabetes: The HART-D Study

OBJECTIVE

To evaluate the impact of exercise training (ET) on metabolic parameters among participants with type 2 diabetes mellitus (T2DM) who do not improve their cardiorespiratory fitness (CRF) with training.

RESEARCH DESIGN AND METHODS

We studied participants with T2DM participating in the Health Benefits of Aerobic and Resistance Training in Individuals With Type 2 Diabetes (HART-D) trial who were randomized to a control group or one of three supervised ET groups for 9 months. Fitness response to ET was defined as a change in measured peak absolute oxygen uptake (ΔVO(2peak), in liters per minute) from baseline to follow-up. ET participants were classified based on ΔVO(2peak) into fitness responders (ΔVO(2peak) ≥5%) and nonresponders (ΔVO(2peak) <5%), and changes in metabolic profiles were compared across control, fitness responder, and fitness nonresponder groups.

RESULTS

A total of 202 participants (mean age 57.1 ± 7.9 years, 63% women) were included. Among the exercise groups (n = 161), there was substantial heterogeneity in ΔVO(2peak); 57% had some improvement in CRF (ΔVO(2peak) >0), with only 36.6% having a ≥5% increase in VO(2peak). Both fitness responders and nonresponders (respectively) had significant improvements in hemoglobin A1c and measures of adiposity (ΔHbA(1c): -0.26% [95% CI -0.5 to -0.01] and -0.26% [-0.45 to -0.08]; Δwaist circumference: -2.6 cm [-3.7 to -1.5] and -1.8 cm [-2.6 to -1.0]; Δbody fat: -1.07% [-1.5 to -0.62] and -0.75% [-1.09 to -0.41]). No significant differences were observed in the degree of change of these metabolic parameters between fitness responders and nonresponders. Control group participants had no significant changes in any of these metabolic parameters.

CONCLUSIONS

ET is associated with significant improvements in metabolic parameters irrespective of improvement in cardiorespiratory fitness.